This is an example of where some code requirements bump up against logic. I believe the AC voltage will be quite usable at the site, just not for code requirements of the AHJ, and it may get pretty low during high usage times. They make the electrician size it for 100A minimum for an ADU, even though the loads are pretty minimal, and then require <5% VD from the main service entrance. That is the requirement for the certificate of occupancy.
Luckily, off-grid buildings don't have these requirements at all. I'm going to size it as an off-grid and probably tie it in at some point in the future. Thanks for the input. On Sun, Apr 19, 2020 at 10:20 AM <drake.chamber...@redwoodalliance.org> wrote: > We had a similar situation, and are now feeding a battery bank with a pair > of 48 V Iota chargers. Iota can run on very low voltages. We have one Iota > on each leg of the the 120/240 split phase to balance the load. It works. > --- > > > > On 2020-04-18 21:25, Ray wrote: > > 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 <maclew...@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 > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & > settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette:www.re-wrenches.org/etiquette.htm > > Check out or update participant bios:www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > -- Mac Lewis *"Yo solo sé que no sé nada." -Sócrates*
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