Charging batteries with generator?

I have a OEM WFCO converter in my camper. It will not go into boost charging mode no mater how discharged my battery. Therefore it can take a VERY long time to recharge a battery because the charger a!ways operates in adsorption mode. As others have said using the 12 VDC output from your genset is not very efficient either. What works best for me is to power the camper with the genset and use an inexpensive 10 amp manual charger plugged into 120 vac and connected directly to the battery. I only need to use it for about an hour every other day to keep the battery 50 to 90% charged.

Assuming you have an on board smart charger. Some RV's have quality converter/chargers, and some do not. Mine, a Jayco 23RB does not. It's a WFCO 8955 model. I am going to fix that however. Have a Progressive Dynamics 55A unit with Charge Wizard on the way as I type.

Mandalay Parr wrote:
Probably let the onboard smart charger do it.

rbpru wrote:
If your generator is designed to charge batteries it should be faster than charging through the 120 volt line and the internal charger. But how much faster is hard to say.

My home generator has a twelve volt line but I am not sure if it is for battery charging or just a 12 volt line.

Your typical onboard charger is on the order of 30-60amps @ 12v

The 12V outlet on our Yamaha 2400i is 8amps unregulated.

At the low end, the onboard charger will be 4 times as fast and even the cheap ones are probably better controlled.

Another key aspect is the size and state of charge of the battery bank. Don't try and charge the battery bank to 100%. As a leadacid battery reaches 80-90% of full charge, the amps it can take in drops off rapidly, so the last 10-20% takes a very long time to charge but you get very little energy into the battery.

Better to charge more often but stop around 80-90% full. (Do plug in when you get home as it's good for the batteries to reach 100% periodically).

the battery charger outlet on generators is a very low current charger most are no more than 8 amp output. its going to take many hours to charge a low battery at that rate. not a very efficient way to charge your battery. look at the size of the wires that come with the 12 charging cord very thin made for a low current charge.

iota charger or inteli power charger.
Get it as close to battery as possible.
For size use 15 to 20% of your battery capacity.
Make sure it does not trip the generator breaker.

I chose Iota 55.

POLORBR wrote:
What is the most efficient way to charge batteries with a generator? Is using the 12 volt DC charging cord connected directly to the batteries any more efficient than plugging the camper power cord into the generator. Why? Just curious. Thanks in advance.

what year is your RV?

the newer RV's usually have a decent onboard converter/charger, and it is usually the ONLY way to charge the batteries...

so no matter if you are plugged into shore power, or running off the generator, the 120vac power coming in goes into the converter and comes out as 12vdc, and on to the battery.

the only way to get your batteries to charge quicker is to get a higher amp multiple stage smart charger... and depending on the size of your battery bank, it may be charging to its full potential on the charger you have.
1 or 2 G27 batteries can only use about 45amps of charge, so a bigger charger is not beneficial, but if you have 3 or more G27 batts, or larger/more batts, a 60-80 amp charger could help you..

pianotuna wrote:
my generator specifically states to NOT use the 12 volt outlet and at the same time draw 120 volt AC from it.

The Honda 2k manual says to turn eco throttle off when using the 12v socket. Yuck..I don't think so. IMHO it's a poor choice for charging anything but the smallest battery.

Hi,

My generator specifically states to NOT use the 12 volt outlet and at the same time draw 120 volt AC from it.

It is far faster to use the converter in the RV for battery charging. Some folks even add additional chargers in addition to the converter. That can be useful when generator hours are limited by park regulations.

POLORBR wrote:
What is the most efficient way to charge batteries with a generator? Is using the 12 volt DC charging cord connected directly to the batteries any more efficient than plugging the camper power cord into the generator.

The 12VDC outlet of most generator has very limited power (it main purpose is to power the field windings). It also has not "charge controller".

Either a separate battery charger or use the one built in to your converter.

Agree on just plugging in the trailer and letting the onboard charger handle it, 12v DC output from the genny is unregulated.

If you are going to be doing a lot of dry camping it pays to upgrade your converter/charger to something more efficient. Most OEMs use cheapo converters and only use a #8 wire back to the batteries. I upgraded to the Progressive Dynamics PD 4260 with charge wizard and also upgraded the wire to the batteries to a #4. The PD charger lets me put it in boost mode at 14.4v (instead of 13.6v) and the fatter wire minimized the voltage drop to the batteries. The PD is a 3-stage charger and will automatically drop the voltage back as needed so you don't boil the batteries.

I can get my pair of 6v deep cycle batteries from 50-60% back to nearly a full charge in 2 hrs of gen time. Before I was running the genny all day trying to get enough power bqck to last through the night.