Typical last mile battery runtime (protecting against power cuts)

William Herrin bill at herrin.us
Sun Feb 5 09:12:36 UTC 2023

On Sat, Feb 4, 2023 at 10:56 PM Roy <r.engehausen at gmail.com> wrote:
> > On 2/5/23 07:02, Roy wrote:
> >> My all electric house is in a rural area.  The generator that came
> >> with the place is a 20KW Onan,  The bad news is in can't handle the
> >> house.  I think it is the Aux Heat on the heat pump that is the
> >> problem.  I have to also power the well pump and the septic pump.
> Single phase.  The house is 200A service and the barn is another 200A
> service

Hi Roy,

My guess is that your 20kw Onan isn't up to stably producing 20kw any
more. Or perhaps the older transfer switch with its mechanical timer
relays has gotten dodgy. The modern consumer gear is very reliable but
the pre-2010s commercial/industrial gear (such as Onan) takes a lot of
TLC to keep it working right.

Another thing that can happen is uneven load. The utility won't care
that 80% of your draw is on one side of the circuit but that'll stop a
generator in its tracks.

If you want to know for sure, get yourself an inductive clamp meter
and start checking the amperages at the breakers. You can get a cheap
one under 50 bucks. You just set it for AC amps, take the cover off
your breaker panel and clamp the jaws around the "hot" wires coming
from each breaker, one at a time.

As John mentioned, unless you have a really large house or a tankless
electric water heater, it's really odd to overwhelm a 20kw generator.
Even with the auxiliary resistive heat.

Bill Herrin

For hire. https://bill.herrin.us/resume/

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