12 res load sanity check

jtdiesel65

 

It's a 24 volt system.  Two xw 4024 set at 66% charge capacity which gives 100 amps on each XW for 200 amps total. The generator is a 12 res on propane with 50amp rating so 50a*120v=6000VA each leg or 12000VA total. When charging, a clamp on reads ~26amps /leg. Strangely the XWs show ~15 amps /leg at 120 v...like half what the clamp on reads. Not sure why.

I'm trying to figure out if I should knock back the charge capacity for the sake of the gen set. 200amps at 25v is 5000 va, but a 12RES is a 12000 VA genset.  5000/12000 is 42% load. There are some losses but even add another 20% for losses and that's 62% load. Seems like I'd be more in the 50-55% generator load with losses and only at bulk.

how's that math sound?

thx

Estragon

What size (Amp-hours) and type (eg flooded L.A.) is the battery bank?

jtdiesel65

It's a 1576 AH battery, but I'm more looking with regard to best load conditions on generator in order to make it last as long as it can.

BB.

More or less, for a gasoline/propane type genset (not industrial), 50%+ is probably best loading for fuel economy (as you unload a gas/propane genset below 50% loading, the fuel flow does not drop that much).

Unless it is a commercially rated genset, I would suggest not running battery charging >80% of rated load). Note that Power Factor can come into play... Most residential gensets (and inverters) are rated for (in reality) VA (or kVA) max loading (wiring, generator windings, etc.).

If PF=1.0 (pure resistive loading such as heaters, filament bulbs, etc.)... Then VA = Watts ...

Watts = Power Factor (typically around 0.50 to 0.80 for non-PF corrected loads, and around 0.95 PF for PF corrected loads, like modern computer power supplies, etc.).

Electrical max Ratings should use Volt*Amp measurements (i.e., use an AC current clamp DMM). So, this is the 0.80 * kVA rating of the genset... (to keep wiring and generator/alternator wiring from running hot).

Motor loading (and fuel flow) is, more or less, based on Watts (Volts * Amps * Power Factor). Many of the modern Inverter-Chargers seem to run Power Factor ~ 0.90 or better when loaded (drawing lots of charging current, other AC loads, etc.).

Lightly loaded chargers and inverter-chargers (and lightly loaded motors) tend to have much poorer power factor (something in the range of ~0.65 to 0.50 --- Or could be worse, but not typically an issue at low current/power draws--Like a few Watts or 10's of Watts).

-Bill

Estragon

With ~1600ah bank, 200adc charging in bulk should be fine.  Depending on other loads, you could increase that a bit if you want.  20% loss seems high.  With PFC charger, 10% strikes me as a reasonable guess.  Like Bill, I think ~50-75% of rated capacity is ideal for gas/propane.  Diesels like to work, so a bit higher for them.

I tend to only use my (diesel, at ~75% of rated capacity) generator to bulk charge to 85-90%.  If sun permits, solar finishes with reduced current absorb.  If absorb is needed but no sun, I use a little honda in eco mode to finish.

For genny longevity, I run it unloaded for a few minutes after charging to let it cool down properly.