Overdumping

[(unknown)]

I have a pair of SW5548s. Charging sources are solar on a MX60 and a 10KW Genset on the SW5548 AC2 inputs. And soon to have DC Hydro on a C40.

My question is how best to keep from overloading my C40 dump if the Genset auto-starts, or the sun is shining.

--Doug

[DanB]

I suppose the C40 keeps up pretty well 'most' of the time.

If that's the case then maybe use the aux relays in one of your inverters to turn on an additional heater.  If it's only an issue when the generator is on, you could probably use 1 aux relay to drive a bigger relay that turns on a big 120VAC baseboard heater or something.

Seems kind of a waste to be dumping power when you generator is on so hopefully it's not the sort of thing you need to do very often.

[Flux]

I  assume that the generator charges the battery via the charging section of an inverter ( I assume a SW5548 is an inverter)

The Mx60 can be set to a lowish float voltage, assuming that the inverter chargers are also regulated then they can be set slightly higher. The C40 should have the highest setting and it should only dump the hydro.

If your engine driven battery charger can not be regulated then you will have to watch the volts don't rise excessively with the engine running ( bit of equalising)

As Dan said, you would normally not want to run the generator with fully charged batteries. If you have to do so then either switch a decent load on or use a voltage sensing relay to do it automatically as Dan suggests.

As long as the load resistor fitted to the C40 can't take more than 40A you will not hurt it.

Flux

[Ungrounded Lightning Rod]

IMHO running a backup genny into a battery which has its dump load on is dumping money/fuel into a fire and fiddling while the smoke and heat blow away.

I'd be inclined to use a relay/contactor to disconnect the battery charging by the backup genny when the (final stage of) dump-load comes on.  The genny can keep running at idle and its fuel consumption will drop dramatically.

If you have other loads on the backup genny you should be sure they aren't something that would be bothered by transients from switching the charger function on and off.

If the genny has a reliable remote auto start / auto shutdown feature and no other loads I'd set it up so it starts when battery voltage sensing detects low-limit on discharge, and stop it with a timeout triggering when the "dump charge" disconnect has been on for long enough that you have confidence that the solar is keeping ahead of the main loads.  (And of course with a manual start/stay-on override when you want to run a power tool or something directly from the genny.)

[(unknown)]

If the C40 works like the SW5548s, it can be stuck in float with the batteries in a state where the Genset will eventually autostart, e.g. <49.2VDC, the default 24hr voltage.

Dumping the Genset power is exactly what I want to avoid, so I'm not too crazy about the baseboard heater idea. Also the Genset puts out more power than the C40 can possibly handle anyway.

I was thinking more along the lines of either disconnecting the C40 during the time the Genset is running, or else setting the float on the C40 to a value higher than bulk.

[Flux]

Simplest thing would be to disconnect the C40, but if you set it high enough it shouldn't bother you. If you set for equalising voltage it should be ok, if your hydro is a small percentage of your total input then a bit more equalising will not hurt.

If the batteries are AGM then you will have fun with that system.

If you have the correct dump resistor on the C40 that will decide the maximum current it can dump, not the gen set.

If the gen set is just charging batteries then you could use a relay powered from it to disconnect the C40 when it is running. If you use it to power other larger loads when the batteries are well up then you may just have to let the C40 dump.

Flux

[(unknown)]

"Simplest thing would be to disconnect the C40"

There's a note inside that says "Do Not Disconnect Under Load"

"If you have the correct dump resistor on the C40 that will decide the maximum current it can dump, not the gen set."

AFAIK the C40 will shutdown at that point, to avoid internal damage.