[RE-wrenches] Portable power station for surge loads

[Ray Walters]

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> 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 <http://www.millersolar.com/>
>>
>> CA License C-10 77398
>>
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