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Old 11-28-2015, 09:56 PM   #1
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House batteries charge faster when idling than on gennie?

I'm boondocking out in the middle of nowhere with a group of friends. We have a newborn, so my wife needs to pump and feed the young'n in the middle of the night. This means we need somewhat charged house batteries. We got back a little late, so I decided to idle the rig instead of running the gennie because the rig is quieter (gas rig).

It turns out the house batteries were much more charged in 30 minutes than running the gennie for a couple of hours! Is this normal? I've heard many people say it takes several hours to fully charge the house batteries. If this is normal, I think I'll just idle my rig to charge the house batteries if I don't need the gennie for any other reasons. If it's not normal, I guess I'll have to check my charger to see if something is wrong. (Note that the batteries still charge on the gennie, just not as quickly).
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Old 11-28-2015, 10:57 PM   #2
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Yes and No.....A lot depends on your coach. Some gas coaches may put out more amps via the engine than the coach battery charger. A lot depends on the quality of the charger and it's ability to charge at different levels.

For many years, when we camped with our Class C at Yosemite during Thanksgiving, three house batteries sometimes didn't get us through the night. The onboard Onan was loud. I found it better to start the 460 Ford and let it idle. I had a huge exhaust on it and it was very quiet. Not only did it charge faster, but in cold weather, I turned on the dash heat and really warmed up the coach.
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Old 11-29-2015, 03:04 AM   #3
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Ditto re Dutch Star Don's post.

I have run the house batteries down in cold weather in my gas B+ and I found it better to run the engine when noise was a concern. It not only charged the batteries but the furnace did not need to come on when the engine was pumping out heat. The result is the batteries charged faster partly because there was no current drain from the furnace fans at the same time the batteries were being charged. Never did that in my much larger DPs. The liquid cooled Generators on the DP's were much quieter than the huge engine and the 4 batteries in my DP's lasted longer than 2 in my B+. I have a gen auto start on my current B+ but I don't enable it at night when the gen coming on could disturb my neighbors. With no neighbors close by, I set it on and it has started. Have 2 very good AGM batteries and seldom need a boost at night but have had to start the vehicle on occasion or the auto start turned on the gen. Have remote start for the engine so can start it without getting out of bed.

I suspect there is nothing wrong with your charger, likely your alternater has greater charge current than the converter/charger and no need for the furnace to come on with the engine heating up the coach.

Of course a gas vehicle engine is very quiet compared to an air cooled gen and I try to be a good neighbor and keep the noise level down so I use whatever option seems right at the time.
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Old 11-29-2015, 08:08 AM   #4
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On my Daybreak, the alternator was capable of charging at about 200 amps. The voltage regulator would keep it under that. My convertor/ invertor was 55 amps. The alternator will not charge at maximum at idle, but still more than 55 amps. So in my opinion, the house batteries will recharge faster on the engine than on A/C wheather from shore power or generator.
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Old 11-29-2015, 08:18 AM   #5
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On our unit the alternator will be able to charge the batteries faster but I do not think you are doing your batteries any favours but putting 100 amps into a 200 amp battery bank.
Some sites suggest a maximum charging rate of 1/5th the battery bank size.
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Old 11-29-2015, 09:42 AM   #6
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Quote:
Originally Posted by harris155 View Post
On our unit the alternator will be able to charge the batteries faster but I do not think you are doing your batteries any favours but putting 100 amps into a 200 amp battery bank.
Some sites suggest a maximum charging rate of 1/5th the battery bank size.
While slow charge is better indeed for battery longevity, it is quite normal to have the alternator charge batteries at higher rates as required based on voltage levels, (which of course controls current flow) we all do this while driving for hours and hours, so why not a idle when the circumstance requires noise abatment measures? Makes sense to me anyway & how often does one "slow charge" a car battery?
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Old 11-29-2015, 09:44 AM   #7
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Thanks everyone, at least that confirms I'm not going crazy! It gives me another option when I don't need additional power for AC or the microwave, or don't want to bug neighbors. It also confirms that there's nothing wrong with the charger.

I agree Harris155 - a slow charge is better for the batteries.
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