Proposed System....what do you think?

HRTKD

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The Victron BMV-712 is a shunt with display. It will communicate with the SmartSolar devices, creating a network. Supposedly, it allows the solar charge controllers to coordinate between themselves. I have two Victron SmartSolar devices and the BMV-712. There does seem to be some coordination, but I haven't dug into it.
 

pda1

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Looks good to me :)

I'd be tempted to get two identical MPPT units in case you want to add a couple of panels to the smaller group later or if one of them fails you could swap to get the maximum output whilst waiting for a replacement.

Make sure your battery settings are the same on both units and they should play nicely together.
Thanks for the reply. OK, maybe will use identical mppts as your idea makes sense.

The problem next to solve is wire size to use from the panels to the controllers. The run will be about 100 feet.

Peter
 

crossy

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OK, max power current 16.54A (2 x 8.27A in parallel), max power voltage of the 3 panel strings about 91V. 100 ft run.

The usual 6mm2 (10AWG) cable would drop around 4V (4%) swallowing 63W of your valuable power.
Going to 10mm2 (8AWG) you'd drop about 2.3V (2.5%) swallowing 38W of your solar.

It might be better to run 2 x 6mm2 pairs from the roof (1 pair per string) and do the parallel connection at the MPPT but of course you double your cable costs :(

Unfortunately the standard MC4 connectors won't handle anything over 6mm2.
 
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pda1

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OK, max power current 16.54A (2 x 8.27A in parallel), max power voltage of the 3 panel strings about 91V. 100 ft run.

The usual 6mm2 (10AWG) cable would drop around 4V (4%) swallowing 63W of your valuable power.
Going to 10mm2 (8AWG) you'd drop about 2.3V (2.5%) swallowing 38W of your solar.

It might be better to run 2 x 6mm2 pairs from the roof (1 pair per string) and do the parallel connection at the MPPT but of course you double your cable costs :(

Unfortunately the standard MC4 connectors won't handle anything over 6mm2.
8awg is somewhat agreeable in price. Ebay has it for about $75 for 100 feet of single conductor.

Maybe it would be a good idea to run the wires in conduit out from the combiner box?

Thanks again,

Peter
 

crossy

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Do check your local regulations/codes as to what you can/can't do on the roof, the rooftop cables are in a very hostile environment (we don't want your insurance to find a reason not to pay even if the solar wasn't involved in any claim).

We have 6mm2 "solar" cable but we have relatively high voltage strings (400V ish) and short runs, no combiner box needed.

Here in Thailand we are in a very liberal environment, pretty much "do whatever you like on your own property".
 
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pda1

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I've considered relocating the panels and all electronics and batteries to the yard and then run a 10/2 awg with ground to a panel in the basement. The batteries will most likely not want to be exposed to cold temperatures below 50 degrees F. Oh well.

Yes, know full well insurance would use any reason not to pay.

400v? How do you feed an mppt with that?
 

anadiner

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Er, what?

AFAIK the only place that happens is on Venus. Or maybe after Superman lost his shit when Lois died.
I know LOL its whacko. I argued with a friend yrs back then he showed up with a compass to prove it.
 

wattmatters

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400v? How do you feed an mppt with that?
It's just a matter of buying a device with an MPPT with a higher voltage rating.

All in one off grid units are available with MPPT inputs in the range of 400-500V.

MPPT inputs in domestic grid tie inverters are often rated up to 1000V DC.
 

anadiner

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I've considered relocating the panels and all electronics and batteries to the yard and then run a 10/2 awg with ground to a panel in the basement. The batteries will most likely not want to be exposed to cold temperatures below 50 degrees F. Oh well.

Yes, know full well insurance would use any reason not to pay.

400v? How do you feed an mppt with that?
Seriously. Lately (I guess its called progress) has voltage getting to crazy numbers. I havent caught up technologically yet.
 

wattmatters

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I argued with a friend yrs back then he showed up with a compass to prove it.
Compasses don't point north. They align with the Earth's magnetic field, save for any local magnetic fields which may overwhelm that. Depending where you are magnetic north can be quite some azimuth angle away from true north.
 

HRTKD

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Compasses don't point north. They align with the Earth's magnetic field, save for any local magnetic fields which may overwhelm that. Depending where you are magnetic north can be quite some azimuth angle away from true north.

And that magnetic field is in flux all the time. There's some talk that the north and south pole could switch. Beats me how.

I used to teach orienteering so I understand what you're saying about north and magnetic north.

But I digress.
 

DerpsyDoodler

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And that magnetic field is in flux all the time. There's some talk that the north and south pole could switch. Beats me how.

I used to teach orienteering so I understand what you're saying about north and magnetic north.

But I digress.
It's happened before. I forget the details. It will happen again, but i think it will be out of our lifetime when it does happen again.
 

pda1

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Regrettably I called the local building inspector to ask if a permit is required for installing an off-grid system. I wish I never called. On the other hand....as mentioned before....if a fire occurred it's a certain fact the insurance company wouldn't pay.

It will mostly likely cost me more for the wretched permits, the electrician and associated increase in property taxes than the project is worth. My guess is an electrician wouldn't even know what constitutes an off grid pv system and the necessary equipment. 'Even have to get a structural engineer to determine if our roof is strong enough to support the panels.

But, what they can't "see" they can't tax or inspect.

'Will see what it'll cost to satisfy the local requirements.
 

crossy

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Yeah, I thought the UK regulated the **** out of DIY electrical and building stuff but the US just takes the biscuit. Here in Thailand nobody really cares what you do.

Any mileage in putting the panels on a car port or even (maybe portable?) ground stands or are you still regulated to heck?

As you say, "what the eye can't see the heart won't grieve over" but a lot of UK local authorities are using drones to look for illegal structures, you can absolutely guarantee they got that idea from across the pond :(
 

HRTKD

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Lean some tires up against the wall and call it a trailer. Nobody cares what you do to a trailer.
campervan.gif
 

pda1

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The building code enforcers over here use satellite photos even though they are a few years old.

A good expression comes to mind, "don't ask permission from someone who can't say yes".

I'll figure something out. I sure did learn a whole lot from you fellas.
 
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