A visual observer can operate all night long without worrying whether power will run out since visual astronomy needs little if any power at all. Not so for astrophotographers or those doing camera assisted viewing (EAA). Tracking mounts, cameras, dew heaters, computers, etc. all demand a continuous supply of power. How this demand is satisfied mostly depends upon whether we set up at home or in the field. At home we usually have access to a plentiful supply of AC power and AC transformer can supply the dc power needed for many but not all of our equipment. At a distant dark site or star party we most likely need to bring our own dc power with us.
There are three key questions to address when thinking about power. First, how much power is needed for a nights activities? Second, how will we distribute the power to each device? And, third, which among the many power sources is best for our particular case?
Before we consider how much power we need, let's first determine the proper metric. When assessing power needs most discussions focus on the number of amps a mount, camera, etc. uses. This is not surprising since battery capacities are given in amp-hours (Ahs). This leads to an assessment of the total number of amps used by our equipment times the number of hours we plan to use it, leading to an Ah capacity determination. But since most batteries are not voltage regulated their voltage will drop during use and the current drawn will increase to keep the power constant. So it is better to work in terms of the total power consumed since that, not the current, is constant (unless of course we change the power settings on a dew heater, camera cooler, etc.).
Another point to consider is whether or not to use AC adapters which may come with our equipment. At home it is a simple matter to plug the AC transformer into a nearby outlet but in the field without access to an AC outlet an AC transformer is an inefficient way to produce the dc power needed. Most AC transformers and inverters waste 10% or more of our precious power. It is generally much better to stick with dc when in the field. This is especially true of power hungry laptops if you can find a dc power source which works with you laptop.
There are two way to determine our power needs, measure it or estimate it. If possible it is better to measure the actual power consumed with our own particular setup and under our typical use conditions. It is fairly easy to measure the AC power during an actual session using a Kilowatt meter in line between the power supply and the AC transformer. To measure DC power requires splicing a dc power meter in line between your dc power source and your devices. I attached Anderson PowerPoles to the wires of an inexpensive watt meter placed in between the battery and the equipment being powered. This is how I was able to check the power consumption for my complete astrophotography setup turning on one item at a time and running for 20 to 30min to get a good average of the power requirement for each. An alternative is to use a volt meter to measure the current and voltage separately and calculate the power used. I was able to measure the current used by each of my mounts while tracking and during high speed slews with my digital volt meter. Because I was using a regulated voltage source at 13.8V, I simply needed to measure the current to determine the power used.
It might be surprising to many but mounts do not draw as much power as one thinks. As the table shows , most mounts generally use less than 0.5 amps at 12V during tracking. Even when performing a slew in both axes at once, less than 1amp or 6-12W is typical of all but the largest mounts. When estimating power for a mount use the tracking power since slews will be infrequent during a session. However, when sizing the maximum current required use the High Speed (HS) slew current with a 25% margin to avoid mount stalls. The maximum current measurement is also needed to properly size any fuses in line and to calculate the wire gauge needed between the power source and the equipment.
In addition to the mount, we need to determine the power requirements for all the other equipment we use. Once again, most would be surprised at how little power cameras, guiders, focusers and filter wheels require. In fact, focusers and filter wheels draw so little power and are active for so tiny a fraction of the observing session that they can be ignored as background noise. Computers, camera coolers and dew heaters are the biggest consumers of power. And, since coolers and heaters have variable settings the power they consume can span a wide range. The table below shows measurements for my astrophotography setup using the power meter built into my Jackery solar generator. The same measurements were also verified using the above mentioned method of an in line dc power meter. By far the 15.4" laptop is the biggest consumer of power and is typical of many similarly sized laptops. To minimize my power needs I have moved to using a mini-pc, Beelink U57, to run the software controling my equipment. I use my laptop to monitor the imaging session while wirelessly connected to the Beelink. That way my laptop's internal battery will last through most of my session before needing to plug it into my power supply greatly reducing its power needs. In contrast, the Beelink consumes less than a third the power of the laptop. If you have a tablet and can wirelessly connect to a mini-pc like the Beelink you can likely run for 10 hours on the tablet's internal battery.
If you cannot or do not want to measure the power yourself, you can use the table above to make an estimate of your own power needs. While everyone's equipment is different, the difference in power consumption for similar equipment will not be dramatic. The items most likely in need of adjustment for each individual case are the dew heat and the laptop. Kendrik has a nice table showing the power and current for different sizes of dew straps which can be used to estimate different actual use cases.
A typical astrophotography setup with a cooled camera and dew heater can be expected to consume somewhere between 30 and 50 watts not counting the computer. Computers are the big wild card and adding as little as 20w for a mini-pc up to 65w or more for a laptop depending upon the size and type.
Once you have an estimate of your power needs you will need to determine how to distribute that power to your equipment. There are two basic ways. The first is to run individual power cables from the power supply directly to each device. This is the method that I used for 10 years with a 12V lead acid battery inside a plastic battery box equipped with a cigarette socket connection. To connect the individual dc power cables from the battery to the device I used a cigarette plug splitter. This is simple, inexpensive and easily adapted to varying numbers of connections but results in many power cables running from the supply to the mount and telescope.
A more elegant option is to use a central power distribution hub at the mount from which to supply power to all the devices. Power is routed to the hub from the battery with a single cable and from there out to each individual device. Each output of the hub can be fused to protect the equipment from damage and can even be computer controlled. The hub can be attached to the telescope so that only a single power cable hangs from the mount. Alternatively the hub can be attached to the tripod underneath the mount to avoid adding additional weight to the mount. If the mount is equipped with through the mount cabling like my MyT, dangling power cables are easily avoided. One of the least expensive power hubs is a Powerwerx Power Distribution Block. This comes in 4 and 8 position configurations. It has multiple Anderson PowerPole connector pairs tied to a common buss bar. Simply connect a battery to one pair with a heavy duty 18AWG cable with a cigarette plug on the battery side and Anderson PowerPole connectors on the other side to provide power to the distribution block. From there power can be supplied to each device using individual cables with Anderson PowerPole connectors on one end and 5.5mm x 2.1mm dc connectors on the other end. DC extension cables can be used wherever longer connections are needed. I have made my own cables to specific lengths for each piece of equipment by using genuine Anderson PowerPole connectors and a simple crimping tool. One tip is to use the 30amp connectors even though none of our equipment will draw that much current because the 15amp connectors are too small to attach 18AWG or thicker wires. Also, I highly recommend the genuine Anderson PowerPoles rather than the more cheaply made copies which I have found to be lacking. Alternatively there are Chinese versions of the power hubs which have the advantage of including fuses on the distribution block for each power position.
Even more sophisticated solutions are the power distribution hubs made specifically for astronomy with even more functionality than the Powerwerx type hubs. An example is the Pegaus Astro Pocket Powerbox Advance which I use. This has 4 12VDC outputs along with 2 variable dew heater outputs, 1 regulated adjustable dc output port and 4 powered USB3.0 ports. It has built in current and volt meters, can supply up to a total of 12A, has short circuit and reverse polarity protection, and functions as a stand alone device or with computer control. The Powerbox can be mounted on the OTA or at the base of the mount as pictured below. I use a heavy duty 18 gauge cable with a cigarette connector on one end and a 5.5mm x 2.1mm connector on the other end to supply power from the battery to the Powerbox. From there, power is routed to each device with the power cables included with the Powerbox.
The ASIAir Pro and the PrimaLuceLab Eagle Core are other examples of astronomy specific devices which provide power and USB hubs. However, these also include a Raspberry Pi computer to also serve as a mini-pc at the telescope. These all-in-one solutions are designed to provide seamless integrated control of all the equipment and software needed for astrophotography.
When designing the power distribution layout it is best practice to keep the power distribution cables as short as possible with the proper gauge wire to avoid voltage drops across them which just wastes power. Here is a voltage drop calculator which will help in selecting the right gauge and length of wire to minimize voltage drops. For instance a 22AWG wire 4 ft long expected to carry 3A of current will experience a voltage drop of 0.39V which will reduce the voltage at the equipment from 12V to 11.61V. Using an 18AWG wire instead will cut the voltage drop by more than half to 0.15V. The challenge becomes making cables with the tiny 5.5mm x 2.1mm dc connectors with wire gauges of 16AWG.
Once the amount of power needed has been determined and a power distribution plan is chosen, the next step is to decide which of the many power sources is best for ones own situation. Let's first consider the case where AC power is readily available but an AC transformer is not available for every piece of equipment. In this case a regulated AC to DC power supply is a good choice. An excellent example which I use in my home observatory is a Pyramid AC to DC regulated power supply. These come in different current capacities from 5 amps on up along with screw terminal connections and/or a cigarette lighter socket connection. The Pyramid supplies are voltage regulated to supply a constant 13.8V which works with all of my mounts and equipment without issue. I prefer to use the Pyramid instead of the AC power adapters that come with some of my equipment as it allows me to simplify my power distribution with less power bricks running all over the place.
When in the field or at a star party we usually do not have access to AC power. In these cases a battery is the usual alternative. For many years flooded lead acid batteries were the only power option available. They have the advantage that they are cheap with a deep cycle flooded 100Ahr battery available for ~$100. But they are heavy, weighing ~60lbs, can only be discharged to 50% of rated capacity without damage, must be kept upright to avoid acid spills and need monthly upkeep. These days AGM batteries are more popular as they are sealed to prevent spillage and offer additional capacity with a depth of discharge (DOD) of 80% without damage to the battery. At a cost of $170 to $215 for a 100Ah battery they cost twice as much as lead acid batteries, also weigh ~60lbs and still need monthly upkeep. The 100Ah Renogy Deep Cycle AGM battery is just one example of these types of batteries.
Recently lithium ion batteries have become more readily available. Be aware that there are competing lithium chemistries used with each having its particular advantages and disadvantages. The two most applicable to astronomy are the LiFePO4 and NMC. LiFePO4 is the less expensive of the two and is commonly found in RV and boating applications which can require daily charge and discharge cycles. Examples of these types of batteries include the highly rated BattleBorn and Lithionics 100Ahr batteries which have capacities of 1200Wh of energy. They weigh less than 30lbs and include an onboard battery management system (BMS) which protects the battery from overcharging, short circuits, overheating, etc. LiFePO4 can be fully discharged without damaging the battery and most manufacturers spec their LiFePO4 batteries at >2500 full discharge cycles before the battery begins to lose some of its original capacity. A full discharge cycle means the battery is taken down to 0% capacity and then fully recharged. Even after the ~2500 full discharge cycles the batteries will still have ~80% of their original capacity. Celestron has two PowerTank Lithium battery models which use LiFePO4 technology and come with capacities of 84 and 159Wh. These have a cigarette socket and 5.5mm x 2.1mm dc outputs, two USB charging ports and a power level display.
There is a lot of confusion as to whether or not Lithium batteries can be fully discharged without damaging them. The confusion seems to stem from the fact that a battery can be a single cell, like a AA battery, or a multi-cell like a standard 6 cell lead acid battery. It is true that single cell batteries, whether LIthium or other chemistries, will be damaged if they are fully discharged. However, what we are talking about is not a single Lithium cell battery but instead a collection of cells designed to provide 12V and higher current capacity than a single cell can provide. Lithium batteries like those mentioned above and the ones to be discussed below are all collections of cells with a BMS designed to make certain that no cell is fully discharged even when the battery capacity level indicates that it is fully discharged or the battery shuts off. This is why the manufacturer's can rate them for 100% DOD without any damage. Of course, the life of any battery can be increased by using a lower DOD but the tradeoff is less useable power from that battery.
The other popular Li chemistry is Lithium Nickel Magenese Cobalt Oxide or NMC for short. The advantage of NMC over LiFePO4 is its higher energy density, hence lighter weight for the same capacity. These batteries are commonly found in power tools, ebikes, electric vehicles and solar generators. Solar generators have become very popular for outdoor adventurers because of their light weight and high energy capacities which makes them a good choice for astronomy applications. Examples are the line of solar generators by Jackery and Maxoak's Bluetti. These highly rated generators come in models from 160Wh to 2400Wh and can supply 10 to 12A of current. Jackery and Bluetti also sell portable solar panels for recharging in the field. The solar generators are more than just bare batteries as they include a regulated 12Vdc output, a BMS, a pure sine waver inverter for AC power, multiple USB charging ports, a built-in MPPT solar charge controller, an AC charger, a display to monitor battery capacity, On/Off switches and an integrated carrying handle among other nice features. These all-in-one portable power stations are light weight as well with the 1000Wh model from Jackery weighing only 20lbs and the 500Wh model from Bluetti weighing under 14lbs. Celestron has an NMC battery with 73Wh capacity called the PowerTank Lithium LT. It has a regulated voltage output and USB charging capability as well but can only support a maximum of 3A while the all-in-one power stations can supply 9 -10A.
If power needs are very low such as my setup with a Celestron 6SE and ASI224MC camera, a fairly small lithium battery like those from TalentCell work just fine. These can provide power for a full night. TalentCell offers a range of small and lightweight NMC batteries with capacities ranging from 36Wh to 142Wh with prices from $26 to $88. They recently came out with an 83Wh LiFePO4 battery rated for 1500 cycles to full discharge for $52. All of their batteries come with a wall charger and a 5V/2A USB port as well. The smaller capacity batteries can supply a maximum of 3A at 12V while the larger ones max out at 6A and also have a 9V outlet as well. I have the 100Wh model which which has worked well for my simple EAA setup as described above. I do not believe that the TalentCell batteries are voltage regulated.
All battery types should not be left in storage fully discharged to avoid damage to the cells. On the other hand, while lead acid batteries should be stored fully charged, Lithium batteries should not be stored with a charge of more than 80 or 90% of capacity to prolong their useable life. Just top them off to their full capacity before taking them into the field for use.
As we have seen the options for portable power sources run the gambit in terms of capacity, price, weight, size and features. What is important to one person may not be important to another. For someone with a limited budget the lowest cost option may be the best choice. For someone else the cost spread over the useable life of the battery might be the most important factor. And for still others an abundance of features might dictate the optimum choice. Table 1 below shows the different battery options available from different vendors, their base cost, and rated Ah and Wh capacities. Obviously not all options can be summarized in a single table. For instance, flooded lead acid and AGM batteries with smaller capacities and base costs are also available, however, the ones listed here are representative of the overall cost analysis which follows.
One simple metric for comparison is cost per Useable Wh. This is simply the capacity times the maximum DOD allowed to avoid damage. Table 2 shows the maximum DOD for lead acid batteries is 50% which means that a 100Ah lead acid battery can only supply 50Ah or 600Wh of power to avoid damage to the cells. AFMs have a maximum DOD of 80% while LiFePO4 and NMC batteries have a maximum DOD of 100%. With this the Useable Wh for each battery can be calculated and is provided in the table which shows that a 100Ah LiFePO4 battery has twice the useable power of a flooded lead acid battery. One would have to buy and carry 2 lead acid batteries to a dark site to supply the same power as a single LiFePO4 battery with the same Ah rating. On the other hand, lead acid batteries are the cheapest on a cost per Wh basis.
Another metric is the cost averaged over the total number of cycles during the expected lifetime of the battery. Table 2 shows the number of discharge cycles expected for each battery type. We can immediately see that traditional lead acid batteries are at a big disadvantage to all other battery types and that LiFePO4 batteries have the highest number of lifetime cycles. Of course the lifetime cycles can be increased for any battery chemistry if the battery is not discharged to the maximum DOD shown in the table. But that means that capacity is sacrificed for a longer battery life. The last column in Table 2 shows the cost averaged over the power one can expect from the battery over its lifetime. With this metric, lead acid batteries are no longer the cheapest option as LiFePO4 batteries with their much longer number of cycles are as much as 1/3 the cost per lifetime power of lead acid batteries.
So what is the best battery choice. If the up front cost is the dominate factor, AGMs are the best choice since their cost per Wh is only slightly higher than flooded lead acid batteries while a 34% smaller AGM battery will supply the same total power of flooded lead acid battery. If longevity, weight and safety are the prime factors then the LiFePO4 batteries are the obvious choice by far but the upfront cost is significant. In this category, the Lithionics or Battleborn batteries provide the largest capacities while Talentcell is the best cost option for under 100Wh capacity. On the other hand, if the added features of the all-in-one power supplies are important, then one of the models from Jackery or Bluetti with capacities of 167 to 2400Wh are good options. Keep in mind that the all-in-one models include a BMS, a pure sine wave AC inverter, USB charging ports, an MPPT solar charging controller, a charger, a power meter and display, convenient power ports and more. They are also voltage regulated and hold their voltage all the way down to zero capacity. These additional features would add upwards of $300 to the total cost if bought along with one of the other battery options. And the all-in-one models come in a fully integrated, compact and rugged package.
Personally I have made the switch to Lithium based solutions for field power. I like the light weight, voltage regulation, high capacity and added features of the Jackery 1000Wh model that I currently use. There are models both from Jackery and Maxoak Bluetti which will fit any budget and capacity requirement. For my lightweight and portable EAA setup which requires much less power I rely on my Talentcell 100Wh battery.
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I posted a review of the Jackery 1000Wh solar generator earlier this month with my overall impression being that it is a very well designed and built power supply which can power even the hungriest astronomy setup for 8-10hrs without needing a recharge. While the Jackery can be recharged fastest with an AC outlet using the supplied charging cable, it can also be recharged quickly during the day using Jackery's Solar Saga 100w solar panels. Here I review the results of over a month's testing of a pair of 100w solar panels along with the generator both at my home observatory and during a 3 night trip to a dark site.
Jackery makes two versions of their solar panels, a 60w and a 100w model. While I tested a pair of the 100w models, they share design features with the 60w model as described here with the differences being size, weight and power output. Both panels use Monocrystalline solar cells with up to 23% efficiency and a voltage output of 18V and a current of 5.55A. The panels have over voltage, short circuit and surge protection built in. They have an operating temperature range of 14 deg F to 149 deg F. They come with a 24 month warranty but an included registration card will extend that to 36 months. The 100w panel is 48in x 21in x 0.2in when fully extended to capture the sun's rays. For transport and storage it conveniently folds in half. A pair of magnets cleverly embedded in plastic at two corners of the panel help to keep the panel folded when not in use or during transport. It also has a built in rubber carrying handle and weighs only 9.1lbs. All of these smart design features make it very easy to transport and set up in the field.
Each half of the full panel has a kickstand which stays put with velcro for travel and can be extended to support the panel when charging. The panels have a protective laminate layer for dust and weather resistance. A zippered pouch on the backside holds the 3m charging cable which is hard wired to the panel. The 8mm connector on the other end plugs into the charging port on the Jackery when charging the generator. Each panel also has a 5V 2.4A USB-A and a 5V 3A USB-C charging port on the backside so that a cell phone or tablet can be charged directly from the panel with the proper charging cable. Overall, I am impressed with the quality of the build and cleverness of the design making it easy to use. I give Jackery an A+ for design smarts and convenience.
I ran a series of tests with the 1000Wh solar generator using my typical astrophotography imaging setup over 4 weeks at my home observatory and in a three night field test at a dark site location. In between tests I had multiple occasions to recharge the generator with the pair of 100w solar panels under varying sky conditions including best (full sun) and worst (overcast) case skies along with the in between cases of partial sun and clouds. To use two solar panels a Y adapter cable which is supplied with the 1000Wh generator is used to combine the outputs of both solar panels which are then fed into the generator's input port. It is not absolutely necessary to use both solar panels but the recharging time will be significantly reduced with two panels instead of one. I should point out that all of these took place in late September and early October as we moved into fall and the sun is lower in the sky and the days are roughly 11hrs long.
The first thing I checked was the output of each solar panel. Keep in mind the output power of a solar panel varies with sun intensity and angle of the panel relative to the suns rays. Maximum output is seldom achieved, and when it is it is not sustained over long periods unless you re-align the panel due to changing solar intensity and angle. The meter on the Jackery 1000Wh generator showed that panel #1 was charging at a rate of 87/88w on a sunny day which is well within what other reviews have shown. Next I tested the second panel but its output was only 42/43w. Clearly the second panel was not performing up to spec. I contacted Jackery and they made arrangements for the second panel to be returned to them and a new one sent in its place, but since I was headed to a dark site for new moon in a week I asked them to wait until after my excursion to replace the second panel and forged ahead with the panels I had on hand. On a very sunny day the input to the generator with the pair of panels connected in parallel with the Y adapter cable varied from 118w to 125w over the course of the day as it charged from 20% to 100% in just 7 hrs. This rate of charge says that it should take ~ 8.75hrs to fully recharge the battery from 0% to 100%, which is in line with the advertised time of 8hrs.
Not all days will be sunny so I checked how well the panels worked during several days with very little direct sunlight. The second solar recharge took place during the massive CA wildfires including three of the largest in the state's history very close to my home. With smoke filled hazy skies the entire day, the panels were able to recharge from a SOC of 23% to 100% in approximately 9.5hrs. The input to the solar generator typically read between 80w and 90w for much of the day. Apparently, enough UV light made it through the smoke particles in the sky. I was quite surprised.
For the third solar recharge I picked a day with periods of partial sun, high thin clouds, but mostly a steady overcast condition. The output power of the panels fluctuated from 0w to 122w but hovered mostly around 22-48w throughout the day. In this case the two 100w panels could only provide enough power to recharge the generator from 18% SOC to 67% SOC in 9 hours. The Jackery panels are not unique in this regards as no solar panel can provide much output if the sun doesn't shine. But I was impressed that even under these gloomy skies I was able to recharge the generator by almost 50%. Odds are that if the day is that overcast we would not expect a clear night for astronomy so this would not be a problem.
The charging rate was very linear with the SOC increasing just over 9% per hour of solar exposure up until the final 1% percent. This is nice in that, if the sky conditions are expected to remain fixed throughout the day, one can make a fairly accurate estimate of how long it will take to recharge under different sky conditions.
During my 3 night field trip to do astrophotography during the new moon I had the opportunity to recharge the panels after the first two nights. The first night I spent 8 hours imaging resulting in the generator dropping to 28% SOC. With full sun the next day I was able to fully recharge the generator as well as top off my laptop battery with Jackery's pass through charging option in a bit over 6 hours. Pass through charging allows the generator to be recharged at the same time it is supplying power to a load. The second night I imaged for only 6 hours and was easily able to recharge the generator in less than 6 hours in full sun. With this setup I could have easily imaged 8 hours a night indefinitely, fully recharging the generator, laptop and my cell phone during the day with the solar panels so long as I had ~7 hours of sunshine.
Once I returned from my field trip I returned the under performing panel to Jackery with a prepaid voucher and quickly received a replacement. The first thing I did was to test it against the first panel under fully sunny skies. This time both panels consistently output 96/97w of power in tests on two different sunny days. This is exceptionally high compared to what I have read for any 100w solar panels on the market. Obviously the sun's intensity and angle or both are extremely important to obtaining maximum power output. I could easily improve the output by ~10w carefully adjusting the azimuth and angle of the panels.
Next I checked the output with the pair of panels connected in parallel with the Y adapter. The configuration produced 129w of input power to the generator which remained steady over time. Why not 192W you might ask yourself. If you read my review of the solar generator you will see that with the supplied AC adapter the input power was 164w. Then why the difference with the two 100w panels? Well, I read in one review that the Jackery limits the total input current and since the AC adapter supplies current at 24V that would mean that the current limit is 164w/24V = ~7A. Considering that the solar panels supply current at 18V, and assuming the same current limit of 7A that would set the maximum input power at 18V x 7A = 126W which is very close to what I measured. The net result is that one does not get the full advantage of the two 100w solar panels due to this current limitation which is disappointing.
The input power limit of ~126w led me to the next test measuring the total recharge time with a single 100w panel. I monitored the panel output hourly and used that opportunity to adjust the position of the panel to maximize its output, thereby keeping above 90w for most of the time. Since the days are shorter now and the sun is lower in the sky I had to run the test over two days to fully recharge the generator from 1% to 99% SOC. It took a total of 10.5hrs to recharge completely, which is a rate of 9.3% per hour and the rate was very steady all the way up until 99%. 9.3% of 1000w is 93w which is consistent with my observation of the fact that the output remained above 90w for most of the charging period. Also, 93w x 10.5hr = 977Wh which is also consistent with the fact that the SOC went from 1% to 99%, or 98% of 1000Wh = 980Wh. So, I suspect that during the typical star party season with the sun rising earlier and setting later than it does in Nov, one could fully recharge the 1000Wh generator with a single panel in one day.
Overall, I was suitably impressed with the build quality, design smarts and obvious capabilities of the Jackery Solar Saga 100. My truly on complaint is the price. At a price of $299.99 the Jackery 100w solar panels are more expensive than other folding panels. However, none of the other folding panels I have reviewed on line appear to have as durable, compact and ergonomic design as the Jackery. Nonetheless, it is best to keep an eye out for one of Jackery's sales to get the best possible price.
High efficiency solar cells
Lightweight with handles
Sturdy, durable design
Embedded USB charging ports
No protective case
Hard wired charging cable
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I have been powering my astronomy rig in the field using either two 100Ah lead acid deep cycle batteries or my Yamaha EF2000is generator for a dozen years. While relatively cheap, batteries are heavy (50-60lbs), can only be discharged to 50% of capacity, are not voltage regulated, need to be maintained monthly, and do not have built in meters, USB charging, AC output, etc. At $1000 a generator is expensive, heavy (~50lbs), does not have either DC or USB outputs and is not permitted at most star parties. So I decided it was time to look at Li based power with solar recharging. Why Li? Because the power to weight ratio is much, much better than lead acid batteries, Li batteries have a higher depth of discharge (DoD) than lead acid batteries without damage and they maintain their voltage through most of the discharge cycle. The obvious downside to Li based power is the higher initial cost.
At first I considered 100Ahr LiFePO4 batteries like the well regarded Battleborn batteries marketed primarily to the RV and boating industries since I am planning to use these to add solar to my new RV in the coming year. But after much research I decided that a "solar generator" rather than a standalone Li battery is a much better match for astronomy applications. What is a solar generator? It is a Li battery with a battery management system (BMS), DC, AC and USB outputs, power input/output/SOC meter, an LCD display, power charging ports and a solar charge controller all built into a single lightweight, rugged and portable unit. There are many different suppliers of solar generators available today which are primarily marketed to the outdoor adventurer. Many solar generators use Lithium Nickel Manganese Cobalt Oxide (NMC) chemistry instead of LiFePO4
because of its nearly 2 to 1 advantage in energy density to weight ratio. I zeroed in on the solar generators from Jackery after reading many positive reviews about their design, features and performance. Their line of solar generators includes 160Whr (13.9Ah @ 12V), 240Whr (20Ah @ 12V), 300Whr(25Ah @ 12V), 500Whr (41.7Ah @ 12V) and 1000Whr(83.5Ah @ 12V) models with prices ranging from $139.99 to $999.99 with frequent sale pricing. These provide plenty of options for different astronomy needs. I contacted Jackery and suggested that amateur astronomers might be a market for them and they were kind enough one of their 1000Whr generators with a pair of their 100w solar panels for me to put to the test with my astronomy rig. Below are the results of more than a month of extensive testing in my backyard observatory and on a 3 night star gazing adventure in the field.
The Jackery comes well packaged with the generator shipped triple boxed. The PS1000 generator includes an AC charger in a soft carrying case, a car charger cable, an adapter to connect two solar panels in parallel for faster charging and a user manual. It enjoys free shipping, a 30 day free return and a 2 year warranty. Inside the box I found a registration card which enables a warranty extension to 3 years. The generator is solidly built using rigid ABS plastic casing and sports a smart functional design. With dimensions of 13.1 x 9.2 x 11.1 in. (L x W x D) it is only slightly larger than my lead acid batteries and fits nicely between the tripod legs of my mount. It's molded handle and weight of only 22lbs makes it a breeze to transport. Everything one needs to access is conveniently located on the front of the generator including:
1) a 10A DC cigarette adapter socket with dust cap;
2) a 5V 2.4A USB-A output ;
3) two 3A USB-C outputs;
4) a USB-A Quick Charge 3.0 output;
5) three 110V AC outputs from the internal 1000w pure sine wave inverter;
6) 8mm and Anderson Power Pole inputs to recharge the generator;
7) an LCD display which shows power output, input and battery % SOC and is low enough intensity as to not disturb fellow astronomers.
8) On/Off buttons for the power outputs and the display.
A small LED light is mounted on the side. The Jackery can be recharged with the included AC charger, with optional solar panels or by car.
I conducted a series of tests of the Jackery using my Software Bisque MyT mount, Celestron C11 OTA, Celestron focuser, ASI1600MC camera, Orion SSAG guide camera (not shown in the accompanying photo), Astrozap dew heat strap, TEMP-est cooling fans, and a Pegasus Power Box Advanced (PPBA). I used a cigarette adapter to 5.5mm x 2.1mm cable to supply power from the Jackery to the PPBA which in turn distributed power to the MyT, dew heater and focuser. The cameras and fans drew their power from the MyT. Since the MyT requires 48V I used a DC-DC up converter on the output of the PPBA to transform 12V to 48V rather than using the less efficient AC adapter. I use The Sky X (TSX) to control everything except the PPBA which is controlled by its own application. I did run one test using the Jackery's AC outlet to power the MyT without any problems but that method unnecessarily wastes power in the conversion process.
Since the first month of testing occurred during the massive wildfires here in CA I could not actually image. Instead, I ran everything exactly as I would during a regular imaging session with the ASI capturing dark frames to the laptop, the fans running, the guider taking dark frames and the heater powered at 50%. Since a laptop is typically the most power hungry device used and not everyone uses the same laptop, if they use one at all, I decided to run 3 different test setups:
1. Everything but the 15.4" laptop powered by the Jackery through the PPBA.
2. As in 1 but with the laptop powered through the Jackery's AC inverter.
3 As in 1 including a BeeLink mini-pc powered by the Jackery through the PPBA. The Beelink ran TSX and I used my laptop on its internal battery linked to the Beelink via Team Viewer as a monitor only to minimize power consumption.
For these tests I tried not to discharge the generator batteries below 20% SOC to be very conservative in terms of long term battery lifetime. The manufacturer specs the batteries to > 500 full discharges to 0% SOC so you could increase all of my total times below by 25% if you are comfortable using the full capacity of the Jackery. Here are the test results:
Test #1: I was able to achieve a total run time of 27hrs over 3 successive sessions before reaching a SOC of 20%. That is enough power for 3 nights of 9 hour imaging sessions without the need for a recharge in between, although a recharge is always possible. I noted that the ouput voltage of the Jackery remained steady at 12.9-13.1V all the way down to 20% SOC.
Test # 2: To extend the session as long as possible, I disconnected the laptop from the Jackery when it reached a SOC of 25% and let the laptop run on its own internal battery until it reached ~5% and the Jackery reached 20%. This powered everything for 9hrs, sufficient for a long overnight imaging session powering everything with the Jackery. Considering that the Jackery was able to be fully recharged with 2 solar panels in 7.5hr , one could run indefinitely this way so long as a reasonable degree of sunshine is available during the day. Alternatively, the Jackery could be recharged in 6-7hrs with an AC outlet.
Test#3: For this test I only used my laptop on its internal battery to check in on the BeeLink via Team Viewer occasionally. As I show below, the BeeLink which has no monitor consumes much less power than a 15.4" laptop so I was able to run for 8hrs and only draw the Jackery's SOC down to 59%. At that rate of power consumption I should be able to run for 15.6hrs without dropping the Jackery below a 20% SOC. That is nearly enough power for 2 nights of 8hr imaging without the need to recharge in between. Or I could use the extra power of the Jackery to keep my laptop powered using it as a monitor to check on imaging progress from time to time.
Actual Field Tests
While the tests at my home observatory are telling, there is nothing like an actual test in the field. So, just after the October new moon and with clear skies at last I headed to a dark sky site along the central CA coast. I did not use the SSAG since I wasn't guiding and I also did not need the heater. However, for all three nights I powered my laptop with the Jackery as in Test #2 above for a completely self contained test of the Jackery. The first night I powered everything up at 6:17PM, just before dark and rough aligned on the crescent moon. As it turns out, my first night would be one of frustration as I learned after running a 120 point TPoint model that my PA was way off. It took a second TPoint run for me to realize that my daytime mechanical alignment was so far off that I had to rotate the entire mount and tripod and adjust the gross altitude pin on the mount to have any hope of an accurate PA. After 2 more TPoint runs I finally got a good PA and was able to begin imaging the M74 galaxy in Pisces at f/10. I typically dislike first nights in the field given my history of such self-inflicted wounds. My frustration actually provided a good power test since the mount spent a great deal of the first 4 hrs slewing back and forth across the sky more than 500 times. I powered down at 2:15 for a total run time of 8hrs with the laptop still fully charged and the Jackery at a SOC of 28%. In other words, I could have run for another 2 hours if I had been able to stay awake. During the next day I fully recharged the Jackery with the solar panels in about 6hrs so it was ready for the following night.
I ran for 6hrs on the 2nd night completing my image collection of M74 and finishing with 50% SOC, easily recharging once again with the solar panels during the next day. The final night I ran for another 6 hrs finishing with 47% SOC as I imaged the edge on spiral galaxy NGC891 in Andromeda. Overall, the Jackery performed as I had expected allowing me to image for as long as 8-10hrs had I been able to stay awake, fully recharging each day with two 100w solar panels to be ready for the next evening. I was also able to use the Jackery during the day using its pass through charging feature to keep my cell phone recharged. Pass through charging allows the Jackery to simultaneously charge a device like the cell phone or laptop, while it is itself being recharged by solar or AC power. It will take correspondingly longer to recharge the generator depending upon the power used to recharge the connected device.
Power Use Case Analysis
Since everyone uses different equipment for their setups, I used the PPBA to measure the power requirements for each individual device and built the power consumption table shown below. Since my camera does not have cooling, I borrowed an ASI294MC Pro with cooing from a friend and measured the power requirements for three different degrees of cooling. Not surprisingly, the biggest power draw by far is my laptop and that is with the display turned down, Bluetooth and WiFi turned off. The camera cooler and dew heater on full are the next biggest power hogs. I find that I can usually run my heater at 50% with a dew shield and not have any dew problems, but others may find they need to run full power. Also, smaller OTAs will require smaller heater straps and correspondingly less power. The MyT mount power increases during slews but as I found when running TPoint in my field tests, 15w is a good average power consumption to estimate the total power needs for this mount if running by DC. In the past I measured the current requirements for a number of different mounts (CGE, CG5, Nexstar 6", ETX80 and IOptron Cube) and found that they use significantly less power than the MyT ranging from 2w to 6w during tracking. The ASI1600 is typical of cameras, including guiders, which operate on 0.5w or less without cooling. I do not have a powered filter wheel or camera rotator but I suspect that the power draw from those is negligible since they are used sparingly through the course of the night.
Taking these numbers into account, the following table summarizes the power required for each of my test cases and the corresponding maximum capable run time for discharges to 20% and 0% SOC of the Jackery. I added an additional case called "Hypothetical" which is identical to my Field test with the laptop powered by the Jackery up until the last 2 hours, but I added the additional power requirements of the dew heater at 50% power (10w) and a camera cooler at 100% power (20.5w) to get a total power requirement of 112w. One can see that for a setup that draws between 40 and 60w, fairly typical of an imaging rig using a mini-pc or a separately powered laptop, the Jackery 1000 can supply multiple nights of power without a need to recharge in between. Even in the most power hungry 'Hypothetical" case the Jackery 1000 can supply power for a long night of imaging.
As noted above, the Jackery has a regulated power output. In my tests, the output voltage remained between 12.9 and 13.1V all the way down to 15% SOC showing excellent power stability. Another thing to note is that the drop in SOC was very linear with time, falling by the same % each hour all the way down to 15%.
Like all other solar generators that I have investigated, Jackery specs the battery life to >500 full cycles after which the full capacity of the batteries will drop to 80%, or 800Wh for this particular model. At that point it will still supply 80% of its original capacity so one would still be able to get continued use out of it but the total run time would be shorter than during the first ~500 or more cycles.
The Jackery can be used to power devices over the temperature range of 14deg F to 104deg F which will cover the typical star party season but might be a problem for hardy soles who like to observe away from home during frigid nights. Recharging of the Jackery requires a temperature above freezing, 32deg F, but I read of a clever trick where the generator is placed inside a cooler so that it stays warm enough under its own heat while recharging at temperatures below 32deg F. These are limitations typical of Li-chemistry batteries and it should be noted that the BMS will prevent the battery from being used outside these conditions so it cannot be accidentally damaged. Maintenance of the generator is simple requiring a discharge to 50% SOC and recharge once every 3 months.
I am thoroughly impressed with the build quality, performance and ease of use of the Jackery PS1000 as a source to power a typical astro-imaging session through a long night under dark skies. With the option to recharge within 7hrs by AC outlet and 8hrs by twin solar panels, if not less, I can look forward to eliminating those heavy lead acid batteries and avoid annoying my friends with my generator running through the night. The biggest downside to the PS1000 is its price. However, when I look at the cost of two 75Ah AGM batteries needed to match the Jackery's power, plus a quality pure sine wave inverter, MPPT charge controller for solar charging, power meters, USB charging sockets, cases, etc. I believe the cost of a DIY system easily exceeds $600 not counting the assembly effort. And one still has to carry two 50lb home built power supplies and connect them in series. Another consideration is that the Jackery can double as a backup generator in case of a power outage. The PS1000 will keep my refrigerator running for 9hrs before needing a recharge and, unlike my Yamaha generator, I can use it inside my house. For those with lesser power needs, say 40-60w the $499.99 Jackery 500 would be a lower cost option to achieve a 7-8hr imaging session. And for visual observers, the much less expensive 160 and 240w models would be more than sufficient for their power needs.
I gave the folks at Jackery feedback on how they might make their generators more user friendly to the astronomy community. First, they might consider a 5.5mm x 2.1mm or an Anderson Power Pole DC output in addition to the cigarette adapter output. Or they could supply a cigarette adapter to 5.5mm x 2.1mm or Anderson Power Pole extension cable to make it easier to for us to connect the Jackery to our equipment. However, it was easy to find a cigarette to 5.5mm x 2.1mm power cord on Amazon that serves the purpose.
The Jackery generator can be recharged with one or two of the Jackery Solar Saga panels in parallel or, with an MPPT to 8mm adapter with any solar panel under 30V and 10A. I plan to do a separate review of their solar panels in another blog soon so look for that soon.
High capacity and DoD
Extremely light weight
Well designed and simple to use
Simple to add solar recharging
Single 12V output
No 5.5mm x 2.1mm or Anderson Power Pole output
500 cycles to 80% remaining capacity
If you want to find out more about and shop for Jackery products, you can find them here Amazon.com. Links are Amazon Associate links.
Last year I purchased a SB MyT telescope mount to use when I travel to dark sites. The one annoyance to me with SB mounts (MyT, MX+, ME) is the fact that they are designed to work with 48V instead of 12V like almost every other mount along with cameras, focusers, filter wheels, heaters, coolers, etc. This is not a problem when one has AC power available as the mount comes with a very good 110VAC to 48VDC transformer. However, one seldom has access to AC power in the field. While using an DC to AC inverter is an option, inverters are an inefficient way to power a mount especially considering that power out in the field can be a precious commodity.
Software Bisque recommends the 56VDC EGO battery for use with their mounts in the field because their mounts can operate at voltages between 48v and 60V. But again, since almost every other piece of equipment we typically use for astronomy works on 12VDC, I prefer not to add another battery type, to the list of equipment I need to carry with me in the field. And the EGO battery, charger and SB adapter are fairly expensive.
The solution for me and many others is to use a DC-DC voltage boost converter which will take a 12VDC input (actually many take a range of input voltages) and convert this to 48VDC output. This allows me to stick 12VDC power for all of my power needs in the field. There are quite a few different converters available on Amazon for ~$15 to $30. I initially purchased the SMAKN for under $30. The MyT AC transformer supplies a maximum of 1.6A at 48V or 77W so this converter is more than sufficient for the application.
The manufacturer lists the following features for this unit:
1. Embeded Smart Chips provide protection from (1) Over current; (2) Over heating; (3) Short Circuit; (4) High voltage
2. High conversion efficiency and stability with synchronization rectification technology. Up to 95% efficiency.
3. SMT technology
4. Aluminum casing with silicone seal for waterproof, dust proof and anti-shock performance.
The input wires, red + and black -, are 14 AWG while the output wires, yellow + and black -, are 16 AWG as the input current will be 4X the output current in proportion to the voltage boost of 12V to 48V.
I first tested this on the bench with a dummy load to measure the voltage output of the converter and to make sure it was a steady 48V and that the unit did not overheat under extended use. The output of the converter is 48.5V which compares well with the no load output of the SB AC transformer of 47.9V. The converter does not get hot, but does get slightly warm to the touch under extended use. The voltage remained steady within +/-0.3V during extended testing. I was also able to measure the efficiency of this unit to be 95-96% in line with the manufacturer's specs.
Since the converter comes with 2 pairs of pigtail wires I had to decide how to connect the input of the converter to my power supply and the output to my mount. I considered hard wiring the pigtails to the appropriate cables on either side, but then decided to use Anderson Power Pole connectors instead. You will need the 30A version connectors because of the larger gauge of the power input wires. I ordered a 14AWG cable with Anderson Power Pole connectors on one end and a 2.5mm x 2.1mm connector on the other end for the connection between the power supply and the DC-DC converter. For the output, I made my own cable with 16AWG wire and 30A Anderson connectors on one end and a locking 5.5mm x 2.1mm DC connector on the other end. I attach the DC-DC converter to the leg of my tripod and run the wires from there to the power supply and up to the mount.
Since I like to have spares when it comes to any critical component that can fail in the field, I purchased a slightly different converter, the 3A, 144W version from Aweking for ~$25, as the backup. At 144W this is still more than sufficient for use with the MyT. Looking at the two side by side it is apparent that these are built in the same factory, but to slightly different specs, and sold by different distributors on Amazon. The only observable difference is the writing on the backsides identifying the current/power rating and the name of the company distributing
them. The Aweking unit performed identically to the SMAKN unit on the bench.
Next I tested each converter separately to power the mount over several different days. I supplied power to the voltage converters through my Pegasus Power Box Advanced which provides a constant view of the current and voltage drawn as well as a time log of the same and watt-hours. I could find no discernible issues running the mount with the DC/DC converter instead of the AC transformer. I am sold on this approach as a viable field power option.
While I was at it, I was able to log the power draw of the mount under different conditions. I share that here for those trying to figure out what size battery they need to power the MyT. I am using a Celestron C11 Edge with a Stellarview 50mm guide scope mounted with an ADM rail along with an ASI1600MC camera, a SSAG guide camera and Celestron motorized focuser. Total weight should be around 40lbs and is well balanced. Tracking draws 12-16w of power (0.9 to 1.25amps at 13.25V) depending upon the orientation of the OTA. Slews in one axis consume 25-35w (1.9 to 2.6 amps at 13.25V) and high speed slews in both axes take as much as 62w (4.9 amps at 12.7V). Hopefully this is helpful data for others wanting to use their MyT in the field with a 12V battery.
You can find the products listed in this blog in the links provided below. I only list products which I use myself or know to work well. Links are Amazon Associate links.