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rrsutherland · 12-13-2020, 01:49 PM

Hey all! Going to be picking up a "new to us" toy hauler soon. Never had an onboard generator before and wondering about the battery pack. If we decide to switch from flooded to AGM batteries do we need to do anything to our generator to switch charging modes? On the onboard charger on my boat there is a switch from flooded to AGM. Is there such on the commonly found Onan 4000 in our 2008 toy hauler?

DavidEM · 12-13-2020, 06:01 PM

An Onan 4000 is a gasoline AC generator, right? It produces 120V AC power and is used when shore power is not available. It has nothing to do witch charging other than supplying power to the charger.

David

rrsutherland · 12-13-2020, 10:37 PM

Sure enough David. I reckon I should re-word the question. Here goes!
If I want to switch my house batteries to AGM from flooded lead acid is there any change I have to make to the charger that is powered by my onboard Onan generator?
How's that?

Persistent · 12-14-2020, 07:07 AM

You probably won't need to change anything. AGM batteries have a slightly different voltage charge profile requirement from flooded cell batteries. Newer converter/chargers often manage to work for both. On the other hand there may be a programmable setting in the new charger that will optimize. Check the new converter/charger operator's manual for instructions.

Charging lead/acid batteries consumes water by breaking water down into hydrogen and oxygen. AGM batteries are sealed so, water cannot be added like flooded cells. The chemistry in AGM batteries reabsorbs hydrogen and oxygen gas to replace the lost water. If high voltage is applied to AGM batteries to charge them, too much gas may be produced. Gas will vent. Once vented, there is no way to replace the water.

Many AGM batteries allow use of 14.4 volts when batteries are deeply discharged. The voltage must be decreased to 13.6 as the charge progresses and then to 13.3 for long term storage. Excess voltage may produce venting.

Flooded cell batteries benefit from the same charging profile, but it is not so critical. Water can be replaced if higher voltages are used. Some chargers apply higher voltages for various conditioning reasons. The higher voltages may cause venting in AGM's and so should be avoided.

Change setting to "AGM" if the charger allows. Follow recommendations in operators manual.

My low end WFCO charger does not have a setting for different battery chemistries. It's charging profile works very well for both AGM and flooded cell batteries. It does not apply any "conditioning" charge voltages.

Use a volt meter on the battery terminals while charging to see what the charger actually does. If voltages stays above about 13.6 for long late stage periods or performs bursts of high voltage during idle times, you may wish to investigate further.

I wish you good luck and happy trails ahead!

DavidEM · 12-14-2020, 07:09 AM

Good, makes sense now.

Most converters have a selector for FLA, AGM and Gel batteries and some also have a lithium setting. So switch it to AGM. If it does not have a battery type selection capability then it probably is old, and may not even charge properly. So replace it.

AGMs can charge at higher rates than FLA batteries, about 25% of their amp hour rating or a bit more. So you may also want to go with a bigger converter to minimize generator run time. You will probably have to upgrade the wiring size if you do this.

David

rrsutherland · 12-14-2020, 08:16 AM

: thumb:Many thanks all!!! You guys are great! Much good info here. I haven't picked up this camper up yet but will the 18th. Hope the weather holds for a little bit. Right now the owner is running the double golf cart battery parallel set up and I may not want to even change it for now. With my present camper I usually spend a couple of weeks ice fishing in the winter and dry camp at the lakes I go to. Temps as low as -20F. I use the vault toilet at the campground and a Buddy Heater for the majority of my heat reducing the need to run the huge construction generator I bring. Looking forward to an onboard generator and bringing the 4whlr inside at night!

Oregon RR · 12-16-2020, 11:14 PM

FYI.

I've got the Onan 400 in my toyhauler. Been very happy. Loud, but works as promised.

Based on experience, I recommend you plumb in a fuel cutoff valve right in front of the carb. This way, you can run the unit dry before you put the TH in storage.

The Onan carburetor is very prone to gumming up and then either refusing to start or start, but with awful engine surging up and down. The Cummins techs will just replace the carb - they don't even attempt to repair.

I don't run the unit periodically while in storage like some folks recommend. I've gone 3 or 4 months between uses several years ago and no problems.

Hope you really enjoy the new toyhauler! The ice fishing sounds like a blast!

rrsutherland · 12-17-2020, 07:50 AM

Very good advice Oregon RR and I plan on following it. I did the same with the construction type gen I have and it helped a bunch. My most significant trouble I had with that one though was of my own making. I put in an in-line fuel filter thinking I'd do some good because it would sometimes sit for a month without use. Darned thing would start right up with one or two pulls and run great 'til I got back in the camper then just die! Go back outside, one pull, run great, go back inside, quit!! Fought with that for a week ice fishing and when I got back down to Casper I took it to the shop. Seems I put the wrong filter in-line. Instead of a paper element it needed a bronze one. The paper would collapse and starve the engine. Well, lessons learned I guess. Thanks all and stay safe out there!!

Roadglide54 · 12-17-2020, 07:24 PM

A little story about a comment on the onan generator. I have a 5500 started flooding. I remove the carburetor cleaned it and it flooded again after removing the second time I found the float Is full of gas. Onan dealer said there’s no part number for the float and nowhere in America to be found because of Dam Sam. New carburetor $350 I replaced it with an aftermarket $60 carburetor started right up and runs fine as the OP mentioned about draining the gas from the carburetor Is a good idea . Dealers blame the crack float On the gas . My 5500 has 400 hours and five years old .