[RE-wrenches] Portable power station for surge loads

Sat Mar 21 20:36:18 PDT 2026

Thanks everyone for the input.  Here are answers to some of the questions:

I have a heat gun that runs right at 1300 watts (10.8 amps).  I made before
and after voltage measurements and got 6.5% voltage drop.  (124 VAC versus
116 VAC).

My spreadsheet predicts 3.4% VD.  There are some Polaris splices that might
contribute to the overall resistance.

My plan would to power only the cooktop with the integrated
inerter/battery/charger unit, if this becomes the decision.

I like the all in one unit because I don’t want the complexity and
foot-print of separate inverter and battery array.  This ADU is a rental
and the owners are elderly and need plug and play simplicity.

We could bump the circuit to 240 VAC, or higher, for that matter.  However
there is an off-grid home in the middle of this feeder that taps off 120
VAC very occasionally to get through cloudy/low hydro days.  Then we would
need three transformers.

I did recall that there are induction cooktops with batteries built in .  I
need to research that more thoroughly.

Still pondering.

William

William Miller

Miller Solar

www.millersolar.com

CA License C-10 77398

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
Behalf Of *Ray Walters via RE-wrenches
*Sent:* Saturday, March 21, 2026 6:20 PM
*To:* re-wrenches at lists.re-wrenches.org
*Cc:* Ray Walters
*Subject:* Re: [RE-wrenches] Portable power station for surge loads

I remember doing some measurements on a long wire run, and being surprised
that the actual voltage drop was much less than the calculations.  That's
when I found a small note at the bottom of the NEC Table 8 conductor
properties used for official VD calculations.   The resistance is listed at
167 F (75C), so if you use the adjustment equation in Note 2, it is much
less VD, and corresponds to reality.  For underground conductors, I might
use 25C.  Use common sense.

The formula is R2=R1 (1+ a(T2-75))

I made a spread sheet about 15 years ago, that uses that formula for doing
wire sizing.  Happy to share, if anyone is interested.

Ray Walters
Remote Solar

On 3/21/2026 3:21 PM, Jay via RE-wrenches wrote:

Are you trying to run the whole house or just the burner?

I’m also curious about how you calculated the VD. I ran it on a few
programs and it came up much less VD. I’d go direct or try the load and
measure the VD. It won’t use the full power for long. Or at least when I
use my induction top it takes so short to bring anything to a boil, after
that it’s turned down.

Lots of options.

On Mar 20, 2026, at 11:23 PM, William Miller via RE-wrenches
<re-wrenches at lists.re-wrenches.org> <re-wrenches at lists.re-wrenches.org>
wrote:

Friends:

A long-time client has an ADU 755 conduit feet from the main house.  They
started off-grid but they are now grid connected.

In 1999 we pulled a 120 volt feeder of #1 aluminum to the ADU.  This
provides about 10 amps at 5% voltage drop.

This client wants to abandon a propane cook-top in the ADU in favor of an
induction cook-top (indoor air pollution as a consideration).  A sample two
burner induction cook-top is 1800 watts--too much power draw for this
feeder.

I was wondering if a portable power station rated at enough power to run
the induction cook-top might solve this problem.  The 10 amp power feed can
charge the power station at (hopefully) an acceptable amperage over an
extended time period and the power station can provide enough surge power
to run the cook-top intermittently.

I see the Bluetti AC500, for example, can be adjusted to draw no more than
10 amps when plugged into AC.  Unfortunately this charge rate, when running
at the full 10 amps, allows little overhead for other loads.  I presume
this 10 amps draw is only 10 amps when the internal battery is fully
discharged.  Maybe other units can charge at a lower rate.

Have any of you tried this?  Any input is appreciated.

William

William Miller

Miller Solar

www.millersolar.com

CA License C-10 77398

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