[RE-wrenches] Rectifier

[Ray]

When doing the volt drop calculation, be sure to correct for 
temperature, per the note after table 8, chapter 9 of the NEC. The table 
values default at 167 deg F (75 C).  An underground cable will be 
operating closer to earth temperature.   When I run volt drop for a 4/0 
copper cable at 60 deg F, I'm seeing that you could go over 60 amps and 
maintain a volt drop of 3%.

Not sure what the requirements for the building are, but that exceeds 
most of my off grid systems.  60+ amps at a final voltage of 232 v is 
almost 14kW. Is there air conditioning?  What are the calculated loads 
for this building?  Is the inspector actually calling this a problem?

I would do a proof of concept: turn every light on in the place, along 
with some typical appliances (hair dryer, microwave) hit a circular saw 
to really make the point, with a DMM plugged in.  I found long ago that 
actual measured volt drop was not as bad as Chapter 9 first predicts.


Ray Walters
Remote Solar
303 505-8760

On 4/18/20 3:41 PM, Darryl Thayer wrote:
> Hi Mac, There are a few questions like is it Al or Cu wire, What makes 
> it unusable?
> for Voltage drop, I use Vd=2KIL/CMA for your case the unknown is the 
> current.  The installation of an inverter with grid support.  Many 
> inverters have this,  you want a multimode inverter such as a 
> Schneider, Outback, SolArk and I could name at least 4 more.  A normal 
> house will run on 30 amps.  So assume 30 amps, 
> Vd=2x21.6x30x1100/211600 =6.7 volts
> So if the main house is at 240 Volts the remote house is at 233 
> Volts.  The multimode inverter could be set at grid support beyond 30 
> Amps.  For higher house loads the inverter can support up to 30 to 50 
> amps additional.  (SolArk is 50 amp) I would add a balancing 
> transformer at the end of the line to make the 120 loads balance.  (an 
> Autotransformer) such that  120 volts loads are balanced and the load 
> is shared between 240-Volt conductors. Based on my customers' 
> experiences I would use AGM LA batteries, as I expect low usage of the 
> battery and quick recharge, but that is the customer's choice.  I had 
> one customer that had 10 years on the float-AGM battery set.
>
> On Fri, Apr 17, 2020 at 8:15 AM Mac Lewis <maclewis1 at gmail.com 
> <mailto:maclewis1 at gmail.com>> wrote:
>
>     Hi wrenches,
>
>     I've got a architect client with a sub-optimal power situation on
>     one of the projects he is working on.  I'm running through a
>     couple of scenarios that may work.  Its a ADU (accessory dwelling
>     unit) that is about 1100' from power.  The farmer had taken it
>     upon himself to bury some 4/0 a few years ago to run power out
>     there.  Voltage drop is the big issue and its not going to pass
>     the AHJ inspection.  We could just ditch the grid and go off-grid,
>     but it seems like a shame to not tap into the grid resource. 
>     Instead of dealing with the voltage drop, I was thinking it may
>     make sense to rectify that low AC voltage input and parallel a
>     smallish battery bank (size is yet to be determined), then use an
>     off-grid inverter to serve the loads at good voltage.
>
>     I am looking for feedback on this concept.  What do you think?
>
>     Also, are there any recommendations for good quality rectifiers
>     with wide input voltage window?
>
>     Thanks in advance for your help
>
>     -- 
>
>
>
>     Mac Lewis
>
>     *
>
>     "Yo solo sé que no sé nada." -Sócrates
>
>     *
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