Home Forums Hunting & Shooting Hunter's Campfire Question: Generator charging RV battery

New to travel trailers after 40 yrs of tent camping. Have a recently acquired travel trailer equipped with two 12-volt lead acid batteries that are not carrying their load. We mostly boondock and are getting by with a 3,000-watt Honda generator and/or three 100-watt solar panels. Extremely rare for us to hook up at a commercial campground with maybe 5 days-worth out of perhaps 80 days of use over the last two years. When using the generator, we've just been connecting it to the heavy utility plug on the trailer with the assumption that we are running our whatever AC current demands and simultaneously charging our batteries. We're now switching to a single 200-amp hour lithium battery, and I'll finally get to the question.

When generator charging, would it be more efficient (i.e. less generator run time) to connect directly to the battery poles (12-volt) than plugging into the trailer's electrical system?

Thanks, and have a good one,

I would let the built in inverter do the charging. It should be more efficient and better for the batteries than either directly DC charging or plugging in a battery charger. That’s my take, assuming your inverter is functioning properly. An added benefit is you can use all the electronic stuff on your trailer when charging.

I'd agree with what K1500 said but ask what you have onboard for a battery monitor?

A good would have already answered the questions you have asked.



LINK

Pretty rare my solar system doesn't keep my batteries sufficiently charged when boondocking which is 3 to 4 months a year.

If your new battery if a lithium iron battery you may need a special charger. I say may, because some chargers have a lithium setting. Mine required I move jumper.
My boat has lithium's also and the on board charger has a lithium setting.
Lead acid chargers will not completely charge a lithium.
The lithium can take massive charges and you may want to look for a system that uses you truck alternator to charge it while traveling, do not hook it directly to your car battery the lithium will draw so much power it will fry your alternator.

A 3500 watt generator is not a lot, but let the converter charge the batteries (make sure it's putting out voltage).

Whenever these batteries fail - I assume they're deep cell - look into buying identical 6 volt golf cart batteries next time and hook them up in series. Same voltage but more amps. Good luck.

He's 50 years ahead of you.

I spent 28 days on my generator last year. I ran it for about 2 hours a day. I ran a 20amp charger in addition to the inverter built into the trailer.

It worked flawlessly.

Lots of good advice already.

3500 watts is plenty. I suspect your batteries are dying, sounds like you have that covered with the new 200 amper.

How much power are you using? An onboard propane furnace draws a LOT of juice if left on overnight!

Really? I only have a 17ft'er but I set the thermostat to 65 and go to bed. The battery keeps the blower motor running all night, and usually only goes down about 50-75%. Then my solar panel charges it back up by usually noon.

Coldest Temps I've been in was about 6 degrees.

The answer is it depends. I have had several rvs, generators, solar panels and chargers all DIY.

If using the AC plug into your trailer running a generator then the trailer has a convertor to take AC to DC and then usually a limit as to how much charge your batteries get. These take into account alot of RVers are in parks on shore power. One of my old motorhomes limited that charge to 3 amps! The furnace burned 5 so in cold weather I was loosing charge when the furnace ran. I by passed that and added a separate charger. Good chargers can push a lot of amps and taper to not cook the batteries when topping them off. Replacing all incandescent bulbs with LEDs make a difference as well.

As mentioned by going lithium you are spending some coin so get a purpose built charger and wire it into your new batteries.

Impressive!
I'm assuming lithium? Dropping lead-acid batteries down to 50% will kill 'em quick.

I have a 35' 5R toyhauler and when camping in the cold i have a small Honda 800 watt generator on the other end of 200' of extension cord. Fuel it up before bed and run it all night to keep the batteries up. If the 2 RV batteries are full charged running the furnace, in the morning i will be lucky to have 10% remaining charge. I think the size and height of the rig you try and heat has the most influence on how often the furnace kicks on. Mine is a fugging cavern. It takes mucho run time to get it "wife" comfortable.

Solar to harvest electricity and plenty of lithium batteries to store it. Our alternator will also charge the lithium batteries in about 30 minutes when engine on in cloudy/snowy weather.

Presently the trailer does not support a battery monitoring system. Just the push button idiot lights that show full, 2/3, 1/3, empty. Plans are to install a battery monitoring system in the near future to allow viewing of voltage, draw, life expectancy of the present charge, and the number of cycles the battery has endured. As to lights, the unit is already LED throughout.

Full time power draws include the clock/radio, some power to the gas fridge that's probably needed to ignite a pilot, a CO warning system, and a smoke detector. The latter two are hard wired in and even the battery disconnect will not cut them out. From purchase to present the lead acids have always been reading full at bedtime, and then about 50% of the time they're weak and a bit short to run the furnace in the morning. There's no way the present system could handle an overnight furnace run. We were initially considering the series 6-volt batteries but decided lithium would be a bit more cost effective in the long run.

To date, the solar panels have kept up with the lead acid needs, and everything is of course charged and functional when plugged into the rig for towing. Near all consults suggest the lithium unit will put out about 4 times the capacity of the lead acids and probably endure 10 times more charging cycles. I was simply wondering if hooking up the generator's 12-volt charging plug directly to the battery was more efficient than routing generated AC into the system and having the trailer inverter switch it back to DC. Given the Honda generator already supports a 12-volt charging plug I thought it's use might be a bit more efficient by facilitating a shorter run time. Not a physicists or electrician though and was hoping someone might know. Have generally considered myself well off but seeing fuels above $4/gal has me counting shekels.

Hitandmiss: The "wife" comfortable is indeed the issue. If it was solely my trailer, there'd be no air conditioner, microwave, furnace, tv, phone/camera charging stations, slide outs, etc. Preparation, setup, persistent cleaning needs, etc are almost like being at home. I can spill coffee, toss peanut shells, and track in with muddy boots if I forget something with the wall tent then simply tear down and come home.

Happy trails,

It depends on the charger in your camper, and the one on your genny.
LiFePO can ingest lots of amps vs. the lead acid, so having the proper charger is really important.
How are your solar panels charging your batteries currently?
My system uses a solar charger that is set specifically to battery type, and I can charge the LiFePO in about half of the time that the old agm took.

Some of this has been posted but here is my take.

Edit- I just read your other post. The charger that plugs in to the front of my Honda and directly to the battery is sloooowwww. Much better off with the right charger.

First, I think lithium is the future. Prices are coming down. Renogy is selling their 12 volt 200 amp hour lithium for $999. I currently have a Renogy hybrid gel 12 volt 200 AH battery and it is good so far. The next one will be Lithium. It seems cold can effect lithium. Renogy’s will shutdown charging at 32F and will not discharge below -4F. Not sure if that is a concern for you.

You never said what type of charger you have. I assume you have a converter/charger in the camper. Make sure it works with a lithium battery. If not, get the proper charger. Lithium batteries can take up to a 100 amp charge. A proper charger will charge it quickly and maintain it properly.

My setup is a inverter charger from Renogy. It will charge the gel cell at around 50 amps and taper off to maintain it as long as the generator is running. It has a setting for lithium. I can also charge off 3-100 watt solar panels.

As a note if you hook up two 6 volt 200AH batteries in a series you will have 12 volts and 200AH. Hook them up parallel and you will have 6 volt and 400 AH. You can take four 6 volt 200 AH batteries, wire two separate pairs in series and wire those pairs in parallel and have 12 volt 400AH.

Troops:

Thanks for the comments. Looks as though I'll have to determine what the capacities might be for the charging systems presently in the trailer. It's a Winnebago Minnie purchased two years ago. Sounds like one needs a charging unit capable of 14+ volts to fully appreciate Lithium potentials. Will get with the dealer and see if he knows.

Yeah, can't really guess at your generators 12v output vs what the RVs charging system is doing.

A monitor will take all the guess work out of it.
It'll give you details of what's drawing what as well which can be quite helpful.

The 120v inverter that came with my current RV was on fulltime powering what the manufacturer decided was essential.
Their idea was to keep both TVs powered 24/7, killing that helped alot. Not only does the inverter burn power when not in use, the TVs have transformers that stay hot when plugged in too.

I've done a ton of researching this for my Montana 3120 2021 unit I ordered with the 300W solar panel, which came with a 30w Victron smart solar MPPT charge controller. It does a good job keeping my 400Ah bank of Battleborn Lifpo4's charged during my learning tests, which is made easier with a Victron smart shunt basic unit that came with the rv to give me remote access to monitor the bank, and determine when to use my combined 2000and 2200 Honda generators for topping off the bank. One key need is if your RV have a lithium switch to get the full recharging done? You can drain the batteries down to around 20% storage before needing to recharge them, and your solar MAY do a decent job for a day or 2 before needing to run the generator, depending on your load and sun. Lots of folks park in wooded area's, and if you don't have an MPPT charger, you won't get optimum recharging. The shunt I have will bluetooth to your phone, or you can get the $200 readout I believe V-712 unit. Mine came with just the shunt, and I'm happy with using my phone or the tablet controller of the Montana.

Another issue I had was our 75A Factory recharging system was only delivering 48A at max on shore power, after doing a few draw down tests before camping while maximizing my setup. I had to increase the charge wire from the main panel/ charger to the batteries, vs buying a new charger and locate it near the batteries.

BTW the recharging done while towing, if using the standard plug, is like 5 amps. Most run a positive wire, around 2-4# to the back of the truck and make a connection through the hitch to a recharging device in the trailer, like a DC to DC charger. Look ate recharging suggestions here
https://battlebornbatteries.com/charging-battleborn-lifepo4-batteries/

Hope this helps.


Allen

What year is the camper? Most likely will need to change out the converter to a new style that is able to be switched to charge lithium or lead batteries. Most chargers from 2020 back will not charge lithium and can potentially damage them