MY HOME BREWED POWER SUPPLY

Ever find a nice observing site only to learn that it's not even close to any conventional power sources? 
I'm sure you have.

And I'm sure you are aware that most other observers frown on
petroleum guzzling (and fume emitting) generators, which
leaves us with a dilemma.

I tried running on dry cell batteries, but they have a rather short life, especially in the cold. 
And especially when you have a lot of items that require battery usage.


Next I tried a car battery. It worked great but was very heavy to lug around.
And it only solved half my problem. It allowed me to run my DC powered accessories,

but not the AC powered ones.

Next, I bought one of those "power station" batteries you see nowdays in the auto parts stores.
They usually have some worthless gadgets attached like an air pump (Which DOESN'T work)
or million candlepower spotlights, or emergency strobes, or other such silliness.
Mine lasted about a year and quit working. 


Finally I decided to do something proactive. I'd figure out just what I needed and then build it.
This page is the result.
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The first step was to determine exactly what I needed in the way of power.

I need 12v DC to run the telescope RA & Dec motors, focuser, illuminated reticle eyepieces, map lights, etc.
Surprisingly this all takes very little energy to run, even when we're talking all night long.

Things start getting hairy, though, when we look at the AC power spectrum. Let's see, there's the laptop.
(Sure, it's got a battery, but it only last about 1 1/2 hours.) For an all nighter I need an AC source.
Then there's the hair dryer. It's small and I only use it sparingly, but when you need to dry your optics off
it's a neccessity. Then there's the TV moitor I use when shooting with the video eyepiece or webcam.
These accessories require quite a bit of power.

So, in conclusion I decided that a deep cycle marine battery would be needed to supply the power I would need
for an all nighter. I chose a marine battery because they are condusive to long term low voltage draws unlike
conventional auto batteries. Typically, marine batteries have a higher reserve capacity, which is what I need,
versus a car battery which is designed for high bursts of energy for very short periods of time.

Next, I would need a power inverter. One that was strong enough to power my accessories yet not so demanding that
it would drain my battery in a few hours. I chose a 400 watt unit. It's powerful enough to run my hair dryer for
short periods of time without doing too much damage to the battery voltage level.

Next, while not absolutely neccessary, I wanted a meter of some sort, so I could watch the system status while in use.
I chose a small plug in digital meter I found at a truck stop. It only monitors voltage, but that is sufficient as long as
you realize that voltage drops according to wattage used, and keeping track of the voltage drop over time gives you
a pretty good idea of what's going on.

Last, I would need a charging system for the battery. Something small, that would provide a good trickle charge
over  a good length of time. (Usually 12 to 24 hours.) Marine batteries (actually all batteries) work best when trickle charged,
versus a short burst of large amperage charging. I selected a 1.5 amp charger/conditioner, which would charge the battery to
capacity very slowly. It can also remain attached to the battery and will poll the battery periodically and shut itself off when
it has determined that  the battery is fully charged. The nice thing about a charger/conditioner is that you can leave it plugged in
for days and weeks with full confidence that it will be ready when you are.
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Well, I thought that was all I would need.....

Once I bought all the stuff I realized that I would never be able to carry it all. I need something to put it all in. Something compact.
My wife suggested a dolly or luggage carrier, so off we went to Super-K. A luggage pull behind was just the ticket. On the way home I
was thinking of how I was going to attach all this gear to the luggage carrier. So, we stopped back at the Auto Parts store and I purchased
a  plastic battery carrier. I could attach the carrier to the luggage rack and hopefully attach the other components to the batter carrier.
Now to put it all together......
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Powercell folded up for
charging & storage
Powercell ready to
Roll !
Powercell ready
to power up

Powercell Charging Unit
All the power outputs are kept inside
the case for storage and transportation
Here's the AC inverter
ready for use


Here's the DC plugs.
The Powercell Meter
(Shows 12.7 Volts)
The proud new owner of a
AC/DC Powercell !

The cost of this project was ~ $175.oo.
It can be made cheaper, of course, using a smaller battery, inverter, minus the meter, etc.
The largest expenditure of time was shopping for all the parts.
It actually only took about 1 1/2 hours to assemble the unit.

!   A WORD OF CAUTION   !

When selecting a power inverter read the specs carefully. Don't buy one unless it has undervoltage protection.
We can compare electricity to water in a hose. When we turn on the water valve, water pressure pushes the
water through the hose. Likewise, electromotive force pushes electrons through a wire when we turn on the switch.

When we turn off the water valve, the pressure ceases and the flow stops. The same with electricity. When a power inverter
input voltage drops below a certain level, usually about 11.7 volts, there is not enough force to continue pushing the electrons.
Unless the unit has undervoltage protection circuitry, the voltage can "back up" just like water in a hose, allowing voltage
from the ac side of the inverter to escape backward through  the DC side of the inverter and possibly causing damage
to any dc devices attached to the inverter.

I'd recommend that if you build a powercell, find a meter of some sort  and watch it!
If/when the battery level drops below 11.9 volts shut off the inverter.
Even with undervoltage protection!
The undervoltage circuitry should protect you, but why take that chance?