Battery charger/maintainer

I know this is sort of reviving the dead horse post about the battery maintainers and float chargers that probably everyone has stomped on or at least passed their opinion on. I have a question and I would like an answer to it. I have installed a 20 Kw Onan natural gas stand by generator and am using a 200 ampere manual transfer switch with it. Here is my question: The battery float charger set up for the generator was in the automatic transfer switch which I can't use because it is only a 125 amp setup. So I have a 1 amp Battery Minder brand float charger/ desulfator that is connected to the generator battery to keep it charged and conditioned. The generator also has an automotive type alternator for charging the battery when the set is running. Here is where I would like to know if there will be a problem. What will happen to the trickle charger setup when the alternator is running? Will there need to be something like a diode installed into the output line of the Battery Maintainer to prevent the alternator from burning it up? Or is this not a problem? I have not ran the set with the Maintainer hooked to it in case there needs to be something to prevent letting the magic smoke out of the Battery maintainer and will wait for a qualified answer. Thanks for everyone's help and advice. Gene Davis Tennille, Ga.

You can't put a diode in series with the float charger because that would introduce a 0.6 Volt voltage drop and confuse the float charger.

You mention it being a float charger/desulfator. If a float charger only, I would say you'd be OK and the float charger just simply wouldn't kick in with the engine charging system functioning.

With a desulfator, I'm not so sure.

It would be easy enough to power the desulfator through a 120 Volt NC relay that opens when the generator "comes on line", disconnecting power to the desulfator while the machine is running.

I have a half dozen of those little BatteryMINDER 12117 and have on occasion, run the machine while the maintainer was still connected and plugged in. It did not seem to harm them, atleast short term. I suspect when the maintainer sees the higher voltage of the alternator, it just goes to float mode. I don't remember reading in the BatteryMINDER owners sheet, any warning about not starting the engine with the maintainer connected.

Definitely a diode won't work. I have no clue if the alternator will let the smoke out of charger. If you want to find out, connect charger to your car and turn car on. If you see smoke, you just got your answer.

If I wanted to isolate charger without seeing it it smokes, i would use a current sensor and a relay to turn the power off to charger when there is current coming out of the generator.

GeneralAire Current Sensing Relays come in 120v or 24v models. It would be simple to use the 120v model and a 120v relay NC contact to power up charger when no current is coming from generator. When sensor detects current in generator wires, it will pull in the relay and turn off charger.

http://www.ebay.com/itm/GA51-120-Volt-GeneralAire-Current-Sensing-Relay-for-Apriliaire-Duct-Fans-51-/161880725009?hash=item25b0d7d611:g:93UAAOxyF19SE3ys

the GA50 GeneralAire is the 24vac model which you will need a 24vac relay and 24v transformer.

I've use both sensors, they work well for detecting AC current.
geo.

No problem. 14 volts of charge voltage is not going to hurt the maintainer. In fact, I have several tractors and a motorhome with 1.5 amp or 2 amp maintainers hardwired into the system and are exposed to alternator charge voltage whenever the engine is running. Two of them are el-cheapos from Harbor Freight, 8 years old, and still fine.

I do not think the alternator charging at the same time as the trickle charger will be a problem, but most maintainers instructions say (unplug the ac power before starting engine). I have had a couple of the older maintainers fail when I forgot to unplug them, and the ones with inline fuses I have blown the fuse 3 or 4 times. Many transfer switches had relays that shut the trickle chargers off when they went to start mode. Your 200 amp may have that if it also controls generator start and run.