[NLRS] Battery charge regulator

[Dr. Gerald N. Johnson]

Gel cells are extremely picky about the maximum charge and probably load 
currents. Both charging and high discharge currents cause dissociation 
of the water of the electrolyte.

At the same time, charging is best controlled by voltage regulation.

A simple series resistor will not limit the current if the battery is 
really low or the charging voltage drifts high.

Modern voltage regulator ICs have provisions for current limiting as 
well as voltage regulation and need to be part of the charging 
regulator. Can be linear or switching. But the current has to be sampled 
and limited or the gel cell objects.

If the battery label doesn't show the maximum charging current the 
maker's specifications should.

73, Jerry, K0CQ

On 9/7/2011 11:30 AM, tosca005 at umn.edu wrote:
>
>
> Well, I managed to "cook" one of my 31 AH gel cell batteries while trying
> to recharge it. It didn't explode or rupture spilling acid all over the
> place, but the case sure looks funny as it pushed outward from internal gas
> liberation. Fortunately, it held together without cracking open, but...
>
> Anyway, not wanting to repeat that experience, I am looking for a battery
> charge regulator. I realize that a 1.4 ohm 150 watt resistor in the
> positive lead of the (replacement) battery would limit the charge current
> to about 10 amps, but it would also limit the drain current to the same 10
> amps or so, which is not enough when roving when some of the "low
> microwave" amps kick into high gear. I would like a device or circuit that
> would limit the charging current into the battery to whatever is optimal
> for a gel cell battery, but not limit how much current is drawn out of the
> battery under severe load.
>
> An even tougher need is a way to put two 12v gel cells in series to provide
> 24 volts at high current for a few of the amplifiers that need 18-26 volts,
> and still be able to safely charge the pair of batteries from the vehicle's
> 12 volt electrical system. I have a 12V to 24V inverter that can deliver
> about 30 amps at 24 V, but some of the amplifiers want even more than 30
> amps when driven to the max. I figure that a pair of healthy gel cells in
> series could provide all the current I need for short periods of time, as
> long as I can keep them properly charged. Using the 12-to-24V inverter
> output across the series-connected 12V batteries would potentially work, if
> not for the problem of lack of charging current regulation leading to
> another catastrophic battery failure, which would not be nice on the road.
>
> Ideas, anyone?
>
> 73 de W0JT
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