Suggestion for 24 volt charger run off generator for back up

Dailypix · September 2016

I recently changed over to a 24 volt system. Sometimes in winter (my off grid solar is in Northern Ontario) my panels do not generate enough power to keep the batteries charged. I get about 5 feet of snow sometimes in the snow belt and it is often cloudy. When I was on 12 volts I used a charger attached to a generator. That was good for only 12 volts. Now that I converted to 24 volt I need to purchase another charger I think. Can anyone suggest a good solution? I have 10 12 volt batteries wired to make 5 24 volt batteries all are rated the same 1000 / 200 hrs.

Vic · September 2016

Hello Dailypix,

The Iota brand Chargers are popular for this use:
https://www.solar-electric.com/catalogsearch/result/index/?p=1&q=iota+charger

Scroll down. There are many to choose from.

If your batteries are 100 Ah each, your battery Capacity could be about 500 Ah, in a perfect world. 10 percent of 20 Hour Capacity is the common charge rate target.

With parallel strings, equal current between individual strings of batteries is not certain, so some strings may draw more current that other strings ...

Many of the Iota chargers have a high AC Inrush current, which can cause issues with smaller gensets.

Just to try to get the discussion going.

FWIW, Vic

BB. · September 2016

Iota has been a good basic charger--Except that it had very high input surge current and a relatively poor power factor. Would require a larger genset to reliably run the Iotas. There is a new version of Iota with a "power factor corrected" input--I don't know anything about them otherwise--But should be worth a look (just checked, only available in 12 volt output--Never mind).

https://www.solar-electric.com/residential/batteries-battery-storage/battery-chargers.html

Another product that had some happy folks here was the Xantrex TC2 chargers. But they were very hard to get for a long time (our host even dropped them because of this--As recall from years ago).

http://www.xantrex.com/power-products/battery-chargers/truecharge-2-24v.aspx

What are your batteries (1000/200???)? Is each 12 volt battery rated 200 Amp*Hours (at 20 Hour Rate)?

The recommended rate of charge is 5% to 13% (for solar panels) and 5% to 20-25% for genset/AC utility chargers--Although, it is easier to overheat batteries with >13% rate of charge--So I would suggest that you monitor temperatures and have limited charging times (such as with a genset) when >13% rate of charge.

5% rate of charge is pretty low--And I would suggest 10% or so as a good compromise. If, you have 5 parallel strings of 12 volt @ 200 AH batteries, that would be a 24 volt @ 1,000 AH battery bank. That is a large bank and you would be looking at a ~100 Amp*Hour battery charger. There are not a lot of "generator friendly" 100 Amp 24 volt chargers out there--The inverter-chargers from major off grid system manufacturers do look like a good option (100 Amp charger is not rare)--And they are pretty programmable (charging set points, maximum AC input current control, etc.). I am not a fan of dual use devices (such as combined AC Inverter+AC battery charger)--But given the few large genset friendly battery chargers and some of the neat features of integrated AC inverter-chargers--They are difficult to ignore.

-Bill

Dailypix · September 2016

Thank you for your comments. I believe one of my problems (among many as I got into this process knowing nothing and paying for my mistakes) is that I have too many batteries for my solar panels to support. I will begin by removing about half of the batteries because I am not getting a full charge with the solar panels even after several days without load except for a small energy efficient fridge.
By removing the batteries I should be able to top up the remainder with the solar panels alone.
It would be easier for the generator to charge the smaller bank in case of a heavy week of snow or two weeks of clouds.

I could charge up the disconnected batteries and give them four hours of trickle charging once in awhile when I have the generator on to run power equipment or the space heater when I first get up to the cabin in winter. Then if I have to I can swap out the depleted batteries for the spares.

mike95490 · September 2016

A "small efficient fridge" is, in fact, a pretty heavy load, and will suck batteries down pretty quick.
You may, if the chargers are transformer isolated, be able to use a pair of 12v chargers, one on each battery, but don't let
any wires touch, There is a chance the batteries can short through the chargers AC power cord so be careful,

Suggestion for 24 volt charger run off generator for back up

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