Offgrid living

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Backup Generator Charger (slrpnk.net)

submitted 1 week ago by oeuf@slrpnk.net to c/offgrid@slrpnk.net

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Can anyone recommend a charger (or type of charger) to use for recharging a 24v lead acid leisure battery bank from a backup generator? Currently we have a cheap charger bought online but it only puts out about 130 watts, which means running it for quite a long time to significantly recharge the batteries and is much less than gets fed to them when the sun shines. TIA

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[–] perestroika@slrpnk.net 2 points 6 days ago* (last edited 6 days ago) (1 children)

Then take one that can take about 80% of the generator power and feed that into the battery bank. Size the charger to the lower of both numbers.

80% feels like too much.

My electric car has a 1600 W charging mode. My emergency gasoline generator supplies 2100 W theoretically if the power factor is 1 (totally resistive load). When I connect my charger in 1600 W mode, the generator trips and drops the load, however. It manages to work at 1200 W or below. And this happens despite the charger having a slow ramp-up behaviour (it doesn't go to full load in a second, but during 5 seconds).

So based on experience, I would advise to pick a charger that can take 50..60% of the generator's power.

For a 24V lead acid battery, look for chargers designed for warehouse equipment (forklifts), wheelchairs, truck batteries and such.

[–] Nomad 2 points 5 days ago (1 children)

Your car has a charge controller and a temperature sensor in the battery pack. A dumb charger with too much capacity could in theory overload the battery and get it too hot.

[–] perestroika@slrpnk.net 2 points 5 days ago* (last edited 5 days ago)

It definitely has. But in my case, I'm not bypassing it - the external part of the charger is communicating to the car using the Type 1 interface and telling "charge at X amps". (But I know that's not applicable to DIY situations.)

...and since the tripping occurs within the ramp-up period or very soon after (e.g. on second 7), I'm fairly certain nothing has managed to overheat yet. I think that some generators have poor steering regulators, mine included.