Before jumping into which power source is best, we should first make an estimate of the total power requirements of our equipment. Most calculate this in terms of amp-hours, Ah, but watt-hours, Wh, is a better measure since as the battery voltage drops over time the current must increase to maintain the constant power which the equipment needs. A Wh or Ah indicates how many hours the battery could supply 1 watt or 1 amp of current at 12volts. If 2 watts or 2 amps are used, then the number of hours is half that, 3 watts or amps is one-third that and so on. I have used an inexpensive power meter to measure the current, voltage, watts, amp-hour, watt-hour used by some of my equipment.
Mounts In the table below are measurements of the current and power used by a number of different mounts during tracking and also during high speed slews in both axes. Simple tracking uses very little current for most mounts with the exception of the MyT. While all the other mounts operate at ~12.7V the MyT works at 48V. The data in the table below for the MyT was taken at 13.2V which is the input voltage to my DC-DC converter used to convert a 12V battery to 48V for the MyT. High speed slews obviously require more power than the slow movement during tracking. For power planning I would use the tracking data and add 5 to 10% if you plan to view a lot of objects over the night.
Astrophotography Setup I measured the current and power draw for each piece of equipment in my astrophotography setup. This includes the mount, cameras, camera cooler, dew heater, powered USB hub, focuser, fans, mini-pc, laptop. I used my voltage regulated Jackery solar generator as input to my Pegasus PowerBox Advanced power distribution hub. The PowerBox measures the power, voltage and current output. By turning on one piece of equipment at a time and letting it run for 20min or longer I was able to get an accurate measure of the power consumed by each item. While your equipment may not be exactly the same, it is safe to assume that the power required for similar items is not much different. If I run everything with the mini pc instead of the laptop, use the ASI294 camera instead of the ASI1600, run the cooler at 100%, run my dew heater at 50% the total power needed is ~67watts or 5.2amps. If I want to run for 4 hours I need a power supply that can supply ~300 watt-hours or ~20 amp-hours without discharging below the recommended state of charge (SOC). If I want to run for 10 hours I would need a power supply capable of supplying ~700 watt-hours or ~50 amp-hours, also without discharging below the recommended SOC.
Video Cameras The table below shows the currents required for several different analog cameras. Since the LnTech 300, Revolution Imager 1 and the Mallincam Micro are all the same camera other than branding, they all use the same current. In addition, I would believe that the Mallincam Jr, Jr Pro and Xterminator all draw similar currents. Notice that all cameras use less than 500mA without accesories and without TEC cooling turned on. Accessories like the Mallincam cooling fans and the Revolution Imager 2 LCD monitor significantly increase the current drawn, but all are still well below 1amp. I was unable to get the TEC cooler to function on my Xtreme and therefore do not have a measurement of the current, but would expect it would add 1-2 amps to the total current used.
Battery Options for Astronomy
There are several options when it comes to powering your astronomy equipment. If at home with access to AC power transformers can be used to power mounts, video cameras, camera coolers and laptops. Often these come with the astronomy gear or can be purchased separately from the astronomy manufacturer. A regulated DC power supply like those from Pyramid along with a 5.5 x 2.1mm adapter cable which I use in my backyard observatory also works very well. Just make sure to match the supply's constant current rating to the demands of your equipment. A powersplitter cable comes in handy if one does not use a separate power distribution box like the Pegasus Powerbox.
In the field a battery is the most common option when AC power is not available. For many years I have used two 100Ah Deep Cycle Marine lead-acid batteries which have sufficient capacity to power my cameras, accessories, mount, dew heater and even my laptop (with a voltage inverter) for multiple evenings before needing to be re-charged. However, lead-acid batteries are extremely heavy and should only be discharged to 50% of the stated capacity in order to maintain their usable life which is why I always carried 2 and even 3 of these large batteries with me. Lead-acid batteries require monthly maintenance to maintain a charged state. They also require something like a battery to cigarette lighter socket adapter to connect to astronomy gear, some type of charger (AC or MPPT if using solar), and an inverter to power most computers. While many people continue to use lead-acid batteries sealed, maintenance free versions like the AGM batteries are becoming more common. They still should not be discharged below 50%, need power adapters and cost ~ 2X as much as standard lead-acid batteries.
I have also used a Yamaha generator in the field where it is allowed and will not disturb my astronomy neighbors. It will supply power all night long for all of my equipment. Because it supplies AC power I still need to bring one of my Pyramid DC supplies and extension cords, but I do not have to worry about re-charging batteries the next day as one 5 gal can of gasoline will supply 4-5 nights of power.
Recently, Lithium-Ion rechargeable batteries have become widely available in capacities from 3 to 1000Ah. Lithium batteries are much lighter than lead-acid batteries. Unlike lead-acid batteries, lithium batteries maintain their output voltage over most of their capacity range. A highly rated 100Ah LiFePO4 battery from Battle Born, manufactured in the U.S., weighs 31lbs, nearly half that of the equivalent lead-acid battery. Since lithium batteries can be safely discharged to 20% of their stated capacity, the Battle Born will supply 60% more power than the lead-acid battery. The larger lithium batteries like the Battle Born also come with a battery management system (BMS) which regulates the output voltage and protects the battery from damage by unsafe operating conditions.
For low total power demands I use an 8.3Ah lithium battery from TalentCell to power a small mount like my IOptron Cube, Celestron SLT or Meade ETX80, video camera and 9" LCD display all night long. They have models from 6 to 11Ah ranging in price from ~$34 to $90. Since these weigh 1-2lbs and are small they can be mounted right on top of the telescope. In addition to 12VDC these usually have 5V USB outputs to charge cell phones and some even have a 9V output. All of these batteries come with 2.1mm x 5.5mm dc connectors and are supplied with AC chargers.
Celestron and Meade Lithium power solutions - TBD
For more serious power needs of an astrophotography setup a larger lithium battery like the Battle Bornor Ampere Time may be necessary. These batteries are marketed to the RV and Marine industries and use LiFePO4 cells which rated for >2000 charge and discharge cycles. There is another option which I now use for power in the field marketed as a solar generator. These are all-in-one solutions which include the battery, BMS, MPPT charge controller, AC charger, a 12V/10A cigarette port, multiple USB charging/quick charging ports, a pure sine wave AC inverter with multiple outputs, power On/Off switches, a power and capacity meter and an LCD display in one compact and lightweight package. These solar generators us LiNMC cells which are much lighter than the LiFePO4 cells since the target market is the outdoor adventurer. There are many different manufacturers but the one I now use is the 1002Wh model from Jackery which also makes models with 160Wh, 240Wh, 300Wh, 500Wh capacities. At 12V the 1002Wh Jackery has a capacity of 83.5Ah. You can read my complete review of the 1002Wh model here. I also use the Jackery 100W solar panel to recharge the unit during the day. Jackery products are available from Amazon. If you decide to purchase one, be patient and look for the frequent sales of $20 to $100 off depending upon which model you buy.
The one downside to lithium batteries is their high cost. The LiFePO4 batteries cost ~$9.25 per useable Ah compared to ~$3.6 per useable Ah for a lead-acid AGM battery. Solar generators are the most expensive at ~$13.5 per useable Ah but that is because they are all-in-one units which provide much more in a single package than a bare battery.
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