Running the battery charger and alt at the same time

[Seangie]

Clifford asked a few weeks ago about installing something to prevent the battery charger and alternator from running at the same time. 

Is this a bad idea to have them both on at the same time? 

My start batts and house batts are tied together with a manual switch and I often leave them tied together.  Once in a great while we run the genny while running down the road and more often than not I dont stop to get out of the bus to go in the back to manually disconnect the batts but rather just start the genny when its getting warm in the bus.

I know it doesnt hurt my battery charger at all but was wondering the implications on the alternator.

Thanks.

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[eagle19952]

My house bank and starts are one and the same, and have been for over 15 years, the generator runs my inverter charger, and my over the road AC is my AC, I have basement air 220v. My batteries average 7-8 years, I have replaced one alternator in 2009-2010.
I had a Trace 2012 that I replaced in 2008 with a Xantrex Freedom Marine 3kw in 2008.
Once I ran my generator non stop from Anchorage Alaska, to Bellingham Washington in October/November because it was my only source of heat...again 220v central electric heat.
I recently replaced my wet cells with AGM's, not sure how they will react to a "dual" charge, but assuming that all of the voltage regulators are working as they should, I see no problems.

[gus]

I think inverters/converters automatically sense when the alt is trying to charge the house batts and shuts down, never had a problem with mine.

If the alt were affected you would see the VM doing weird things. Happened to me once with an Onan genset that had a small alt built into the flywheel and I didn't know it.

[TomC]

I had to disconnect the alternator from the generator (I have the generator attached to the starting batteries-but also have a solenoid jumper to the deep cycle batteries). Believe it or not, that little alternator on the generator would over power the huge Delco 50DN and cause the alternator light to flash on the dash. Once I disconnected it, all problems stopped. Good Luck, TomC

[gus]

My 4107 has the genset connected to the house batts with a solenoid switch via a converter to the start batts, works better that way.

[bobofthenorth]

If you have multiple charge sources and your tach takes its signal off the alternator then you may lose your tach if one of the other charge sources has a setpoint that is higher than the alternator.  This can be alarming until you figure out what is happening.  And even after you figure out what is happening it can be really inconvenient.

[gumpy]

The higher charge voltage on the battery charger / inverter charger will cause the regulator to shut off the alternator output. It then announces itself with a "Not Charging" light on the
dash, if properly equipped. Yeah, the first time that happens accidentally, it's a scary thing, especially when the last time you saw that light it cost $1400 to replace the alternator
that had just eaten itself.

I don't think it will cause harm to the alternator or the charger, though. They both operate on sensed battery voltage and either will shut down as the voltage climbs above
their setpoint. Typically, the charger will be higher than the alternator, so it is the one that will be charging, while the alternator will be spinning freely.