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Old 28-01-2015, 18:24   #1
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Mixed AWG Solar Install

Currently upgrading solar to about 25 amps. The run from the equipment arch thru the transom is about 10' and currently wired with 8 AWG and will be a real PITA to rewire with larger gauge. I show 8 AWG over 10' to still be within 3% loss for 25 amps. So, I'm considering leaving the 8 AWG in the arch and installing 4 AWG from just inside the transom to the controller (about 25').

Reasonable idea or not?
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Old 29-01-2015, 07:03   #2
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Re: Mixed AWG Solar Install

When calculating voltage drop/wire size, Circuit Length is equal to Positive wire length + Negative wire length; so a 10' run will be about 20' of wire (Cct Length).
Number 8 AWG wire is good for 450 Amp/Feet (at 3% Vd - 12V nominal), so about 22.5 Amps over 20' Circuit Lenth, or 6.4 Amps at 70' Cct Length.

See ➥ Wire Size Chart.1 - Read /w "Ohm's Law & You" Cruisers & Sailing Photo Gallery

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Old 29-01-2015, 07:15   #3
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Re: Mixed AWG Solar Install

Thanks Gord, I understand basic circuit clacs, but wondering if there are any potential issues with a mixed AWG circuit. I've always just run the necessary AWG for the entire circuit. Which is what I would normally do in this case, but not rewiring the arch will sure save me some pain & agony.
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Old 29-01-2015, 07:17   #4
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Re: Mixed AWG Solar Install

Yes, that is a reasonable idea - no problem at all. Another idea if you have an MPPT controller and the mounting/shading works is to wire the panels in series for a higher voltage and let the MPPT worry about the higher current.

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Old 29-01-2015, 07:20   #5
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Re: Mixed AWG Solar Install

Mixed AWG wiring is actually pretty common if you think about it. Your main panel is probably fed by larger wire than the circuits feeding off it. Higher current things like HF radios, windlasses, etc often have 3-4' of smaller gauge pigtails that are meant to be connected to larger gauge feed wires. Sub-panels and bus bars are mixed-gauge.

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Old 29-01-2015, 09:09   #6
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Originally Posted by colemj View Post
Mixed AWG wiring is actually pretty common if you think about it. Your main panel is probably fed by larger wire than the circuits feeding off it. Higher current things like HF radios, windlasses, etc often have 3-4' of smaller gauge pigtails that are meant to be connected to larger gauge feed wires. Sub-panels and bus bars are mixed-gauge.

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Good examples I think. Im going mixed AWG.
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Old 29-01-2015, 09:40   #7
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Re: Mixed AWG Solar Install

Consider the MPPT.

Putting the panels in series increases the voltage, but the current stays the same. Up to the insulation rating of the wire (usually 600V) and the maximum input of the MPPT (typically 150V) the loss is only related to current (I^2R).

So, you may be able to keep your existing wiring and have less loss in the wire than at 12v nominal.

Plus you should see some advantage from the MPPT (most claim 10%).

Cheers,
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Old 29-01-2015, 11:03   #8
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Re: Mixed AWG Solar Install

I'm not sure I like the idea. You are still running more amps through that 8 and as a result of the V drop heating it up. Will the drop in voltage be significant once you get the end ?
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Old 29-01-2015, 11:31   #9
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Re: Mixed AWG Solar Install

My panels are configured in a similar way, 10 awg till under the deck. Works fine.
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Old 29-01-2015, 12:25   #10
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Re: Mixed AWG Solar Install

Quote:
Originally Posted by NahanniV View Post
Consider the MPPT.

Putting the panels in series increases the voltage, but the current stays the same. Up to the insulation rating of the wire (usually 600V) and the maximum input of the MPPT (typically 150V) the loss is only related to current (I^2R).

So, you may be able to keep your existing wiring and have less loss in the wire than at 12v nominal.

Plus you should see some advantage from the MPPT (most claim 10%).

Cheers,
JM.
Thats a thought, but Im in the tropics (hot panels = less advantage), shading issues on most boats (not bad on mine though), and the controller is rated for 50V max which is less than the total if in series.
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Old 29-01-2015, 12:26   #11
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Re: Mixed AWG Solar Install

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My panels are configured in a similar way, 10 awg till under the deck. Works fine.
Panel configuration (watts,volts, amps)?
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Old 29-01-2015, 12:28   #12
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Re: Mixed AWG Solar Install

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Originally Posted by Cadence View Post
I'm not sure I like the idea. You are still running more amps through that 8 and as a result of the V drop heating it up. Will the drop in voltage be significant once you get the end ?
Per calcs no, but will test and report back.

And, looking at it today, I can easily shorten up the run a bit to more like 7' which will help.
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Old 29-01-2015, 13:43   #13
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Re: Mixed AWG Solar Install

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Originally Posted by belizesailor View Post
Per calcs no, but will test and report back.

And, looking at it today, I can easily shorten up the run a bit to more like 7' which will help.
Every little bit helps. For what I know after reading your posts, it doesn't seem the voltage drop would effect you, being in the tropics with a high ambient temp, just watch the insulation on the 8s. I doubt it will really be a problem.
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Old 29-01-2015, 13:49   #14
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Re: Mixed AWG Solar Install

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Originally Posted by belizesailor View Post
Panel configuration (watts,volts, amps)?
2x 158 watt nominal 19v(?) to one Bluesky MPPT controller
2x 100 watt nominal 20v(?) to a separate Bluesky MPPT controller

100 watt panels are cheap Chinese flex panels.
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Old 29-01-2015, 13:54   #15
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Re: Mixed AWG Solar Install

Actually, putting two equal panels in series increases voltage times two BUT LOWERS TOTAL CURRENT back to the rated current of a single panel. Panels work just like batteries. For example, two 12v 8a panels in parallel gives you 12v at 16a. Putting them in series gives you 24v but total current will be back to the original 8a of the panels. So putting panels in series lowers the current on your 8ga AND there lowers the path loss along your 8ga wiring segment of the circuit. (Thats why power companies use 13k, 128k volts on their distribution wires... lower lost.)

But the issue with putting solar panels in series is that with panels in series, depending on the design of your panels, if a shadow cross either panel the total voltage out may drop to zero and you may not have any voltage output/ charging. When the two panels are in parallel and one has a shadow, that panel voltage drops/ doesn't contribute anything to the charging... but the other non-shadowed panel still operates with its 12v at 8a and you continue to have charging, although at half the possible rate if both had full Sun.




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