Lazy man's battery charger

My military (MEP-017A) (circa 1969)10HP 5KW genset has a 24 volt starting system. I'm using two 12 volt garden tractor batteries wired in series. I do not have a 24 volt battery charger although I have several 12 volt chargers. Currently when a charge is needed, I am disconnecting and putting the batteries in parallel, charging, then putting them back in series again which is a real hassle. My question is, can I charge the batteries with one (or two, if need be) 12 volt chargers while still in series and still connected to the genset. I would like to leave the charger(s)permanently connected to the batteries so that I can easily give them a maintenance charge with the ease of simply plugging in the chargers (or even leaving them on a timer). I notice that even when connected in series, I'm still getting a 12-14 volt reading across each battery. I'm hoping that I can just treat them as two separate 12 volt batteries for the purpose of charging without damaging either the charging/starting system, the batteries, or the charger(s). Will it work?

It is posible with two separate chargers and blocking diodes.

You could do it with one charger, bu the cost of the contactor relay that would make it work makes it cheaper to just buy a 24 volt charger.

But when you factor in the cost of constructing such a setup too, you can build an inexpensive 24 volt battery charger.

If you have a basis in electronics, find an old transformer from a furnace control or find an old stereo, something middle of the road that is no longer of use, and pull the transformer out of it. A number of late sixties to early seventies M Wards and Sears units still abound, and they used 24 volts in the circuit. Add 1 diode if a 24 volt transformer or make a bridge with 2 diodes, add a voltage regulator circuit (LM317) should be adequate, and the circuit for 28 volts.

You can charge both batteries in the setup using two chargers. Hooking both batteries together in a 12 volt configuration and using one charger is not good. The reason is the internal resistance may be different and both batteries may not get fully charged. As always remove the charger when starting/running the genset to prevent damage to the charger(s).

Joe

I maintain surplus generators which the goverment has given our local vol. fire deparment.

You can hook two 12 volt battery chargers in series to charger two 12 volt batteries in series.

With two chargers in series, there is a small but real potential for a fire if there is a component failure in one of the chargers. Moreso than usual with a single charger.

I don't see any reason why you can't just attach a separate 12 volt charger to each battery while they are connected together in the starting circuit. Would someone please explain?

Larry,

I have some 24 Volt equipment, and routinely charge the two 12 Volt batteries while in-circuit with a 12 Volt charger connected to each battery. There is absolutely no reason to expect a problem with this. I always disconnect the chargers when running the equipment.

Fully charge your two 12 volt batteries (sp's are equal) then use the internal 24 volt alternator (on the mep017 behind the starting pulley) to keep them charged as they are routinely used, being drained and charged equally during normal use cycles. If the batteries are same age and size and so forth then the twelve cells don,t care which battery they are in, they look like a 24 volt battery. Rich

Yes, Steve - There's no problem in using your one charger to charge each battery separately, even while they are still connected in series and in the genset. I have several old military gensets, and this works just fine. Watch the polarity carefully, and keep in mind that you musn't connect the charger to the chassis ground when charging the 'upper' battery, as it's negative terminal isn't at ground potential.

This is certainly the preferred method. However it does require periodic running the generator (which really is not that bad of an idea for many reasons.) and some people do not want to go to that much work.

One thing that I have found to be very useful for battery maintanence is to wash down the exterior of the case with baking soda and water keeping it away from the vents or covers so none gets into the battery. But also making sure that everything is clean and dry between cels and especially posts. Then spraying the battery down with a water dispersal agent like WD40. The dirt and acid that can accumulate on top of the battery will discharge the battery, and shorten the life expectancy somewhat.

Cleanliness alone may reduce the number of times the set must be started and run to charge the batteries to a point where it can be a monthly routine rather than a weekly routine.