Hi Mike,
I donât have a battery powered astronomy rig (yet) but I am an electronics
tech with some experience with batteries. A deep cycle battery is what you are
looking for because you can safely discharge it and recharge it over and over
again. You can recharge a deep cycle lead acid battery with an inexpensive 12V
battery charger. We have a computerized cart at the office that runs off a 12V
35Ah battery powering a small computer, monitor, and a small printer that all
runs off 12V. Drawing between 1.5 and 3 amps depending on usage I am getting a
12 hour use period between charges on this setup. We charge it overnight on a
10A charger with no issues. Iâve also built several battery packs in Pelican
cases for use powering cameras on film sets.
You can calculate the amp hour capacity you need by multiplying the current
draw by the time you want it to run. If you have the ability, measuring the
current draw with a multimeter would give you an accurate picture of the
current being used. The specified amperage of the power supply may be much
higher than the actual current drawn. You may be surprised at how little you
may really be using.
Another option is to add another small battery to your car along with a battery
isolator, maybe in the trunk or a spare tire area. The battery isolator
basically allows current to flow one way and allows you to use the secondary
battery without discharging your main one. When the car is running, the aux
battery is charged from the car.
If you decide to DIY, always always always protect the battery with an inline
fuse and always be very diligent protect the terminals from shorting out. You
can find plastic Pelican style cases to mount the battery in and add DC jacks
on the outside. If you want something more robust for power connectors, check
out the Neutrik PowerCon connectors for a locking solution. You could also put
a connector on the charger because most of them come with alligator clips on
them. I just cut those off and put a PowerCon on the charger too. Also look
for a meter that can be mounted to the case to monitor power usage, preferably
a red LED display that is easy on the eyes.
Hereâs a photo of a case with the connectors and a display like I am
describing. It looks like this has a small power inverter in it for providing
120V AC as well, which it sounds like you do not need.
https://i.ytimg.com/vi/m04CXhoQ2jU/maxresdefault.jpg
Tim Stoel
tim@xxxxxxxxxxxxxxxx <mailto:tim@xxxxxxxxxxxxxxxx>
On Sep 5, 2018, at 12:26 PM, Michael McDonald <mikemac@xxxxxxxxxxx> wrote:
Iâm considering venturing farther afield than my backyard with my
telescope. Iâm even considering attending next monthâs All Arizona Star
Party. Besides trying to figure out how to pack up and carry all of this
âstuffâ, I need to figure out how to power the whole mess. Right now, all
of my major components (Advanced VX mount, ZWO cooled imager, and Gigabyte
Brix) all take 12 volts DC as input. If I add up the output amperage on all
three AC power supplies, they supply a combined 10A.
Iâve heard that people have used car batteries in the past for
âportableâ power. My understanding is that car batteries are designed
for short (less than 30 seconds), high current (300A) use. What Iâve been
reading suggests you shouldnât âdeep cycleâ these batteries because
doing so significantly shortens their lifespan. Iâm having a hard time
finding what kind of continuous current they can supply and for how long.
Iâve heard that wheelchair batteries are designed for long, deep cycle
applications. But I have no first hand experience with them so I donât know
whatâs involved in using them, including recharging.
Lithium-Ion batteries store a lot of power but if you drain them too fast,
they have a tendency towards pyrotechnics, destroying my fellow
astronomersâ night vision. (And getting you into trouble with the Forest
Rangers!) I know some of the big names in astro equipment make specialized
batteries for running some of your equipment. But they donât seem to have
the capacity for all of my equipment.
So what do all of you experienced observers use to power your astro equipment
when youâre out in the field?
Mike McDonald
mikemac@xxxxxxxxxxx
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