Re: Battery ratings

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From: James Bennett (james@research.nj.nec.com)
Date: Thu Nov 30 1995 - 19:15:29 EST


Since I have recently been reading about the care and feeding of
gel cell batteries, I will share what I have learned so far.
First I highly recomment the book "Handbook of Batteries" by
David Linden, published by Mcgraw Hill. It has almost everything
you would ever want to know about all types of batteries.
As for gell cells, it seems that most of them are rated at a 20 hour
rate for the current capacity. However, according to the discharge
curves for gell cells, they do not do too badly at higher discharge
rates. For example a 5AH cell could deliver 5A/20H or 250mA for 20
hours. At 5A/1H = 5AH it would last approximately 40 minutes.
In the case of pulsed current draw (such as cw transmitting)
the cell has rest periods in which it can regain chemical
equilibrium. Thus in pulsed service it will approach its
full AH capacity. So a rig drawing 3A intermittently should run
for several hours on a 7.5AH cell.
So much for the lecture, now to practical experience. I have
approximately a dozen gell cells in 6 and 12V and capacity
of 1.2- 7AH which I use for powering various radio and lighting
equipment. For the new 12V 7Ah cells, I have powered my
Yaesu FT301S for 4 or 5 hours of receiving(~600mA) and
transmitting (2A) and the batteries were still at ~12V.
I have also used them to power a 55W spotlight for >1 hour.
One trick with the 12V cells is to float them across the
13.8V output of a DC supply to your rig. The cell will remain
charged and can supply extra current if your power supply is
of insufficient capacity. If you do this I recommend fuses in
the battery and power supply leads( just in case).

James Bennett
Amateur Radio: KA5DVS/2 (yes I am in NJ)
email james@research.nj.nec.com
NEC Research Institute
Princeton, NJ


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