Recharging batteries from a Generator - RV-Dreams Community Forum

BiggarView · RV-Dreams Family Member

Recharging batteries from a Generator

bjoyce · RV-Dreams Family Member

Tell us about your battery charger first, since the generator is just a power source for it. Converter, inverter/charger, model, charging amps, etc. I have an inverter/charger with a 125 amp charger, which would run at 125 amps of bulk charging for around 2 hours just to start working on the 400 AH deficit. At some point, a gut estimate says a deficit of 150 to 200 AH , the charger would start tapering and take 2 to 3 hours more to finish the job. I am sure there are charts out there that will help get the numbers better. Once you get to taper charge, it doesn't matter as much how large the battery bank is, it will take about the same time to finish.

Lithium's will charge faster since the taper charge happens later in the process and thus takes less time.

BiggarView · RV-Dreams Family Member

Can you tell I'm still learning this stuff? Ok, I guess we will be looking at something like the Magnum pure sine wave hybrid invertor/charger(seems highly reccomended here) MSH4024RE.

bjoyce · RV-Dreams Family Member

You don't want the 4024 since it is 24 volts. I have the MSH3012M 12 volt Hybrid and it works well. I am not seeing a 4000 watt 12-volt hybrid from Magnum, just the 3000 watt we have, at my favorite place to look - http://www.donrowe.com/magnum-energy-s/1821.htm.

BiggarView · RV-Dreams Family Member

Does that mean that if had your 125amp number for a charger and I was using say 100 amps a day I could run 3 days or so before recharging the battery bank(800ah AGMs) and then it would be roughly 4-5 hours of run time? 5-6 days with a 1200aH battery bank and 6-7 hours run time to recharge? Ball park numbers(my guess), just getting a feel for the process and capabilities of such a system.

BiggarView · RV-Dreams Family Member

sorry, i typo'd that wrong. That was the one I meant to base it on.

bjoyce · RV-Dreams Family Member

Your numbers sounds reasonable. Most with limited charging only try to fully charge their batteries once a week, but get the batteries at least into taper charge more often.

Jack Mayer · RV-Dreams Family Member

I agree with Bill - your estimates sound in the ballpark. Just be aware that you will not be FULLY charging the bank because the absorption cycle tapers the charge and it will take too long to complete fully. It is always a tradeoff on how long you run the genset vs SOC (state of charge) on the bank. Same thing applies to solar, really....you often do not get a "full" charge back in - your instrumentation resets itself to "full" at some percent of the full charge. That can be set, of course, but the point is that most of these boondocking techniques do not actually "fully" charge the battery in practice. And that is why many people go onto grid power at some point to "fully" charge the bank. There are circumstances where you can get a true full charge boondocking, but most people do not see that.

As a point of general interest, our new coach will have the 3000 hybrid inverter that Bill has, 6xL16 AGMs for 1200 Ah storage, 1200 watts of high voltage panels, MidNite Solar Classic 150 solar controller. Even with our "piggish" use of power I expect to have no issues boondocking as long as I want to.

-- Edited by Jack Mayer on Thursday 19th of June 2014 09:51:16 AM

BiggarView · RV-Dreams Family Member

Thanks Bill & Jack. Always good to know that I'm getting the right handle on the info being put out there. It was my thought that we would have to hook up to shore power at some kind of interval to, as Jack put it, "fully" charge the bank. We plan on doing some serious boondocking, what exactly that will entail is still up for discussion, at this stage we are looking at what Howard and Linda did with a phased approach to be a more or less self contained set-up by adding solar later, if needed for the style of boondocking we envision. Still to evaluate is the size of the battery bank to fulfill our needs. All things in good time.

Jack Mayer · RV-Dreams Family Member

I'll give you the advice I gave Howard when I designed and installed his system in a "phased" approach....

You will want solar if you are at all serious about boondocking. You should plan on it now, at least in your budgeting. You can wait to put it in, but you WILL want it. :)

Bill and Linda · RV-Dreams Family Member

Brian:

Jack is putting the point on the whole discussion. For longer than a couple of days boondocking is really hard to accomplish without solar unless you run the generator a lot or are not using much power at all. As outlined, it has to do with the charge time required for that last 15-20 % that batteries take to fully recharge even if you are using a generator. At least recharge properly and not kill them.

Because we traveled almost every day on a trip up to the Arctic Ocean the truck alternator substituted for the solar panels and did a fine job. But if we had not been traveling the generator time would have just been excessive (expensive!) even though we were not using TV at night and we had all LED lighting. (Satellites are too low to receive that far north.)

Just perspective from our experience.

Bill

-- Edited by Bill and Linda on Thursday 19th of June 2014 05:59:26 PM

BiggarView · RV-Dreams Family Member

We have room in our outfitting budget plan to put upto 800 watts of solar into the mix. We know we want to do some boondocking, the question is how much. The question was an attempt to get a feel for the amount of time needed to run the genny if it was our only source of OTG/boondocking power to keep the batteries up to the demand, what limitations that might have and how to mitigate them, help put a framework on any potential fuel consumption and finally to assist in determining at what approximate point we should consider the solar part of the equation. The feedback has been very helpful in that regard. Hadn't considered the truck alternator as source of trailer battery recharging, so that something else I will take into the mix of options.

B-R-I-A-N (don't worry Bill, I get that all the time) wink

-- Edited by biggaRView on Friday 20th of June 2014 08:19:56 AM

Bill and Linda · RV-Dreams Family Member

biggaRView wrote:

B-R-I-A-N (don't worry Bill, I get that all the time)

Sorry, just a typo from my poor old eyes.

Correction made.

Bill

BiggarView · RV-Dreams Family Member

When I get to be as knowlegeable/experienced as you, Bill Joyce, Jack, Cherie & Chris, Sherry & Jesse, Howard & Linda, Terry & Jo and countless others (no intent to diminish any of them) who have already added to our knowledge base, I will be flattered to be called Brain. Fortunately for me, I will always be able to learn from all of you "Brains".

I tip my hat to all.

Brian

jimindenver · RV-Dreams Family Member

Most people I know that run a generator for recharging have a way of getting that full charge once a week or so. Usually by hitting a campground with electric for a day to dump tanks, take on water, do laundry, etc. We used a generator for a season and the first thing I noticed is a fully charged battery would drop to 12.5v after the first day of use. After that the battery would drop to 12.4v after being charged with the generator the day before. Had I gone too long like that, my battery would have lost capacity from being under charged.

800w of solar is nice, I wish I had that kind of roof space. I would think that even a quarter of that now would make a huge difference. It may not keep up with your needs but it will help cover them, extending your time between run of the generator. When you do run the generator the solar will take over after and continue to charge the bank, getting it much closer to full.