Recommend a battery charger for backup generator use?

doctorZeus

Since context can help so much, let me start with a quick summary. The rig I'm working on is off grid, mostly hobby/project but also for backup/emergency power. I'm thinking if grid power is out for days and I'm using more battery power than I expected and/or hit low sun, I'd like to be able to supplement solar power with a generator running a battery charger to re-charge my battery bank. I also plan to run the genset periodically at least for a few days to keep a chest freezer going along with a couple of window unit air conditioners, so since my generator (3,500 running watts, 4,500 starting) should have some spare watts I'd like to make sure I'm keeping the batteries topped off or certainly have the capability to do that if/when necessary.

Right now my requirements appear to be able to recharge between four and six 6V golf car batteries running 430ah or 645ah @ 12V. Something fancy with 3 or 4 stages with dedicated flooded cell deep cycle "settings" would be a bonus to maybe help me condition and/or maintenance/float charge the batteries under normal grid power and/or under genset (may as well if I'm running it anyways for the appliances), but my main requirement would be to bring the batteries up from 40/50% (or lower) to 80/90% as quickly as possible without hitting them so hard I'm doing damage. Since I'm still considering a 24V bank, tackling both 12V and 24V scenarios or even better suggesting a charger that can handle both would be a major bonus for me. I'm thinking since I don't plan to do this very often I should be able to hit them pretty hard..a tiny bit of "damage" I suppose is OK to get me back in the game as quickly as possible, I just want to make sure I'm within the parameters of "reasonable" and not doing long term damage that will be instantly noticeable.

To rephrase and (maybe) further simplify the question, for the 430 to 645 ah @ 12V battery bank how many amps would you recommend I use to "bulk" charge from 40/50% up to 80/90%? Is it reasonable to expect to charge the entire bank at once, or do I need to charge them in 12v pairs (two 6V in series) or even one at a time @ 6V?

You guys have been great..thank you in advance for any guidance/suggestions!

doctorZeus

Re: Recommend a battery charger for backup generator use?

I was having trouble finding this information doing general google searches but I think I at least found some footing from Northern Arizona Wind & Sun's site after clicking on the deep cycle battery charger home page. It says:

"We recommend that your battery charger be rated for about 15% to 30% of your battery amp-hour capacity - That is, if you are charging a 100 amp-hour battery that you use a 15 to 30 amp charger. For a typical RV setup with a pair of the 220 amp-hour golf car batteries, we recommend no larger than a 60 amp charger."

So for a 430ah or a 645ah bank, I would need a roughly 60amp to 90amp charger, respectively? Any concerns with charging the entire bank? Since 90 amp appears to be as high as the site sells, does that mean after 90amp you would need to start charging components of the battery bank separately?

Edited to add .. looks like I need a bigger generator!!

Cariboocoot

Re: Recommend a battery charger for backup generator use?

As far as charger choice goes the best thing to get is an inverter with a built-in charger. The good ones can be programmed to meet battery needs just like the solar charge controller. In fact that's what you do: set the parameters the same on both. Problem: they cost around $2,000.

Outside of those no one makes an "ideal" stand-alone battery charger. Iota has some that are close to the same sort of charging profile you get with solar, but they are fixed output not programmable. Since they usually are only used on occasion to make sure the batteries don't get too low, perfect performance is not really vital.

Charging demands are the same as with solar: if you can provide 10% of the battery bank's Amp hour rating as peak charge current it should work fine. So for 430 Amp hours @ 12 Volts you need a charger around 43 Amps, or as close as you can come. Since the gen will also be running loads it is possible to go lower (no need to compensate peak charge rate for load draw).

So you could pick something like this 45 Amp unit: http://www.solar-electric.com/dls-45.html
Or you could save a few dollars and go for the 30 Amp: http://www.solar-electric.com/dls-30.html

As long as that current potential is above 5% of the batteries' Amp hour rating it should work fine.

If you look at the whole selection http://www.solar-electric.com/bach1.html you see they go up to 75 Amps in 12 Volt. But they don't make 12/24 Volt switchable units (at least Iota doesn't).

It's amazing what you can get away with for occasional "Bulk only" charging. Even a standard auto charger with enough current potential will do. As long as they are regulated they will bring the batteries up high enough to keep sulphation at bay.

niel

Re: Recommend a battery charger for backup generator use?

take a look at some of these inverters to see what you could be looking for. (going for examples and not telling you to buy these even though these would be good)
http://www.magnumenergy.com/Literature/Data%20Sheets/Inverters/64-0200%20Rev%20I%20%28MS%20Series%20Data%20Sheet%29.pdf
the current is adjustable with the remote (recommended it be purchased for the magnum inverters) and they do carry remotes that enable generator starting for some generators.
http://www.magnumenergy.com/Products/productsRemotes.htm

do not think these are able to sell to the grid as they do not. they allow the ac from the grid to pass through the inverter and automatically switch to the inverter when utility power goes out. the ac from the utility or the generator can be used to charge your batteries through the inverter, but don't forget that you would have charging power coming from solar as well and you don't want to pump too much into the batteries. many batteries do not handle 30% and we often recommend here on the forum about 13% as the top end, but i suspect you could safely go to 20% with more maintenance on the batteries. the higher maintenance is due to the higher charge rates and can make for more of a mess on the tops of the batteries as well as deplete the electrolyte faster. always monitor the levels as going below the plates will destroy your batteries. a good hydrometer will help you as well to keep the condition of the batteries monitored.

mike95490

Re: Recommend a battery charger for backup generator use?

2 different issues:
a) battery charge rate
&
b) generator capacity, and the PF (power factor) rating of the charger(s).

Since many have addressed the charge rate issue, the batteries don't care where the amps come from, the sun, a inverter with a high power charge circuit, or an automotive style charger. I've got a auto style charger, manual connection and button selection for starting the charge, and it can go to 40a for charging.

So - on to power factor. That's a fancy AC measurement of how efficient the charger uses the AC powerline, cheapies manage about .60 PF, and the fancy one in my inverter is about .95, so there is a wide variation. A good charger with a PF closer to 1.0 (perfect) costs more than a cheapie, but you can use a smaller generator and save fuel.

I think there was a stickie here about choosing a genset and charger, and it went into great detail about all this.

vtmaps

Re: Recommend a battery charger for backup generator use?

doctorZeus wrote: »

Is it reasonable to expect to charge the entire bank at once, or do I need to charge them in 12v pairs (two 6V in series) or even one at a time @ 6V?

Actually, the ideal situation would be to charge the batteries individually. Each battery would be charged exactly to its needs.

When you have batteries in series, each battery gets the same charging current. No two batteries are identical, so when you charge multiple batteries in series, by the time the last cell is fully charged the other cells have been overcharged.

When you charge batteries in parallel the problems are much worse, and are discussed here:
http://forum.solar-electric.com/showthread.php?14674

Of course, you should know that very few of us charge our batteries individually. Its not practical to disassemble your battery bank every day to charge it up, and even if it were practical (with switches and relays) to reconfigure multiple batteries and chargers, it would not work for those of us off grid who are using our battery bank even as we charge it.

--vtMaps

westbranch

Re: Recommend a battery charger for backup generator use?

for example, along wit Mikes comment of using both charger and PV to bulk charge, here is a mid price range charger from Holland with 4 stage charging.

http://www.tbs-electronics.nl/products_omnicharge_specifications.htm#table

@ 12 v you would get 60A output

PNjunction

Re: Recommend a battery charger for backup generator use?

Xantrex Truecharge 2 chargers also come to mind with various settings for your specific battery chemistry and so forth...