How long do I need to run generator to charge house batteries-Onan 4.0

Started by cosmic, February 21, 2015, 04:33 PM

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Went to check on the winnie today, and found my battery bank at 11.9 volts. I need to charge the 2 deep cycle batteries up before damage occurs to the batteries.

Now I could un hook the batteries and bring them home and charge them. (big pain in the  $@!#@! )
OR.... I was hoping to  start the onan 4.0 for a few hours or all day. I know my rear tank is full. So my question is. HOW LONG TO RUN THE GENNY. ??? I thought the onan sends like 1 or 2 amps back to the battery??
Hoping someone has done this before. I have 2 120 amp hour deep cycles...
Thanks... Vic


 :)rotflmao you should be doing that today. I'm just finishing up watching NASCAR and then going to pull my two 6 volt Titan T-105's and charge them. I think to charge them properly it takes a fare bit of time. I'm going to stick my neck out and say about 24 hours to a full charge. Now that's depending on how low they are. D:oH!

Mr. T

The generator gets its electrical power from one of the house batteries.  In time, the generator will drain your house batteries, because it uses more amps than the converter is replacing.  I plug my 10 amp charger from the auto store into the house circuit while the gen is running.  Two to three hours will usually get the batteries up to snuff.  Four or more if the batteries really low.

Don T.



Just to let someone down the road know. I ran the genny for 3 hours. I came back and the onan 4.0 fully charged both batteries. On its own with no external charger. from 11.9 (40 percent left) to full charge. I should be good for the rest of this crazy cold winter. Really didn't want to see 2 new batteries go to hell. It was my fault I didn't take them out and bring them in the house, but like all of us I get lazy some times.
We have been in a real cold spell here in Ontario for the last month. -40 Celsius.  for my American friends that's. -40 F as well.
Just lucky they didn't turn to 12 x8 blocks of ice..
I must say I was just shocked that the old onan did this in the time I left it run. I just bought 2 solar panels (2 40 watt units) 3 days ago and thought how I could prolong my boondocking. I'm thinking now I am going to return the solar panels and buy 2 more big deep cycles for the bank. shoot this will leave me with 250 bucks extra to spend on something more worth while. and with 4 big 12 volt deep cycles im good for 4 to5 days before I need to run the genny or plug in for a day. which will probably never happen.


It is good to run your Genny, under load, every week or two, for 15-30 minutes, to exercise the innards of the engine.
It will do several things, keep the oil on the engine surfaces, and keep the fuel from lacquering up in the carb. keep the batteries charged
I am turning on stuff in the mototrhome to put the engine under load,
Jerry P
89 Winnebago Chieftain 23RC
A work in progress


Don and Mary
2000 TC1000 Bluebird bus conv.


Something wrong here Don. your chart says 1 to 1.5 amp charging rate. which is a trickle charge at best. So how could that be possible to bring my bank back to full? Perhaps I checked the level to soon after I shut everything down...
I will go check the bank again this morning and see what my meter reads.


The batteries are being charged by the converter in your motorhome at a much higher rate then that.


Like any normal engine the gen charges it starting batteries (Battery bank) when running,
but when off, and plugged in, it charges at a lower rate.

Jerry P
89 Winnebago Chieftain 23RC
A work in progress


There may be a little confusion here of how the DC electrical system works in the motorhome.  First off, I don't think all power centers incorporate a battery charger.  But here is how mine is set up with the 6300 series Parallax power control center.

The unit has a switching relay to either put the battery online or take it offline.  When either the gen or the cable is providing AC to the power center, the switching relay takes the battery off line.  The converter is now providing 12vdc to the power distribution panel.  If your power control center has the battery charge option (indicated by "C" in the model number) the battery will be placed on the charge circuit of the power control center.  If you don't have the charge option, the battery is not charged but is not being consumed by the motorhome either.  It's sitting there waiting to either be used when AC power is removed from the motorhome by turning off the gen or unplugging from the wall.  Most MHs include an option to charge the coach battery from the alternator up front while the unit is being driven down the road.

On my unit, with the Microlite gen, the set produces a 1 amp charge current back to the battery while the gen is running.  So the gen should not consume the battery.  I don't know if this is how other gens are set up but I would think so.


Don and Mary
2000 TC1000 Bluebird bus conv.


When you start your generator and power the motor home up from the generator it is the same as plugging it into shore power and your onboard converter or charger will charge the batteries at whatever rate it is rated for. I have a 45 amp Boondocker so when I am running my generator and have the coach powered up on the generator then the Boondocker is running on AC and charging my batteries at 45 amps. It is a four stage charger so the charge will taper of according to what is needed. There is no DC charging circuit in a lot of the RV generators, some do and some do not.


4.0 BGE is limited to a 1 amp charge current used to restore the energy used to start the generator.
Most original converters used on 70 era Winny's limited their battery charging circuit to 4 to 6 amps.
If converter has been upgraded, battery charge will depend on what you upgraded to and how it was installed.



So it took me a couple days to get back to the rig, because it just to damn cold here in southern Ontario.  $@!#@!
I went and checked the battery level this morning. 12.4 volts which is 80% charge. this might have to do with the -40 temperature.  i??
My onan is a 1976 and my converter is the original 1975 as far as I know.. So if 6 amps is the best I could have got from the converter. It was enough to take my batteries back to a level that is quite ok for long term storage... Again I ran the genny for 3 hours under no load. (at idle)

Thanks all of you for your help and hope you all keep worn. :'(


Generators should never be run at idle do to the fact that the regulator will be trying to compensate for low voltage and can burn up. You only get 110 volts at 1800 or 3600 rpm depending on the generator.


Motorpro hit it, I think.  Your coach must have a converter/charger, powered by 110vAC, that charges the coach batteries.  I don't see the 3 hour run putting back that many amps into the batteries if it weren't.
See if this sounds right: The 120vAC power is coming from either the shore line (when plugged in), or the generator (when it's running), and goes into your distribution panel, then circuit breakers, to send throughout your MH.  The converter is plugged in to an outlet (power in), converts this 120 vAC power to to 12vDC power, and then sends this power (out) to your 12 vDC power panel - and also has separate cables/lines to charge your coach batteries with up to 45 amps (or whatever your converter/charger is rated at).
Walt & Tina