[NLRS] Battery charge regulator

Wed Sep 7 13:56:48 EDT 2011

I would drop kick the gel cell batteries, ok but don't hurt your foot that 
was an expression only, and get a couple deep cycle batteries.  If your 
worried about spillage and safety get a couple Optima Yellowtop deep cycle 
batteries, these are 55Ah each and can handle being charged by an automotive 
alternator without any dropping resistor or additional regulation.  I run a 
single one in the shack as a backup to keep everything running during an 
outage, or until I start the generator if it’s a long outage, so essentially 
its my UPS for the DC powered equipment.  I have been running this setup for 
six years now using an Iota DLS-55 55A continuous duty power supply with IQ4 
battery charging addon, allows you to direct connect the battery and cycles 
between quick charge at 14.2 and float at 13.8 by adjusting the power supply 
output.  Also cycles once weekly to check the battery health, etc.

You could run a pair of them for 24v, I did this for field day once to run 
an amp, voltage select you could do it simple enough with a relay setup to 
latch the batteries together for 24v and split them for 12v and ease of 
charging while going down the road.  I did this with a pair of 40a DPDT 
relays, you could get by with a few SPDT relays if you needed more current 
capacity, such as continuous duty rated contactors, I just used what I had 
on hand.  The first relay gets the positive from one battery to the common 
of one of the relays poles, the NC contact for that common goes to the 
positive of the second battery, the NO contact goes to the negative of the 
second battery.  The second pole of the relay has its common to the negative 
of the second battery and the NC contact to the negative on the first 
battery and the combined ground terminal on the bus strip for both 12v and 
24v negative.  The 12v positive comes off the first battery, so the 12v 
devices are always powered off the first battery even when the 24v selection 
is made.  The 24 positive comes off the second batterie positive which goes 
to the common of the second relay, the NO contact becomes the 24v output.  I 
wired this all up with a simple toggle switch to energize the relays and a 
terminal strip with connections for both voltages making a bus strip.  I can 
draw this up if someone wanted to see a picture.

The way this works is you connect your 12v charging input from the vehicle 
to the 12v terminal on the bus strip and the combined ground terminal, with 
the relays off both batteries are charged by the vehicle and all 12v devices 
have power from both batteries being in parallel, when you flip the switch 
and turn on the relays the 12v devices and charging input is still connected 
to the first battery but now you also have a 24v output with both batteries 
in series.

73,
Scott KBØNLY

-----Original Message----- 
From: Dr. Gerald N. Johnson
Sent: Wednesday, September 07, 2011 12:10 PM
To: nlrs at mailman.qth.net
Subject: Re: [NLRS] Battery charge regulator

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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