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Home-made Battery Pack
After tripping many times on the power cord between my scope setup and my car as well as dragging out a power supply and extension cord in my backyard, I decided that I needed a compact self-contained  power supply.  The supply needed to provide enough power for at least 8 hours of use. The setup has the following power requirements:


Losmandy G11 mount: 500 mA
SBIG ST-4 CCD autoguider: 1 A
Kendricks Dew controller + one 5" and one 3" dew heater: 1 A at 50% setting
Total power = 2.5A
In addition, I sometimes bring a friend that has a Meade LX6 scope and he uses my power as well. For 8 hours of use,  I would need about 24 Amp hours.  This  rules out all of the car emergency starters that are around 17 AH and leaves the Kendricks 34 AH packs.  One look at the price and I was sure I could make one much cheaper. Here's what you need:
Battery Pak
I wanted a battery that did not leak, need any maintenance and was reasonable in price.  This ruled out standard lead acid batteries for cars.  I finally settled on a 32 AH GelCell battery that I bought at a local automotive parts supply store.  WalMart also sells these batteries at around $100 CDN. 

You will also need the following parts:
3 automotive style 12V cigarette sockets, panel mount
3 10A inline fuses
6 Crimp connectors
I bought all of the these parts at WalMart for a cost of around $70 CDN  for a total of $170 CDN.  Compare this to the price of the Kendricks system which costs around $400 CDN.  Sure it doesn't have a voltmeter and uses circuit breakers instead of fuses, but its easy enough to bring a VTM with you.  The voltage on a Gel Cell will range between 13V fully charged and 12 V discharged.
Here is the finished product
Charging the battery
Do not use a standard automotive battery charger for charging Gel Cells!  It will lead to a damaged battery.  You will need to buy a "Float Charger" that has a lower voltage.  Kendricks sells a 6A unit that will charge the battery in about 8 hours.  Alternatively, you can buy this charger from Schumacher
All images and contents are Copyright 2000 by Tom Blahovici. All rights reserved. The images and contents may not be reproduced, published, copied or transmitted in any form without written permission of the author.