8 vs 10 AWG cable for solar install

[sailingunity]

I just placed on order 3 - 200 watt solar panels. Max voltage is 21, max amps 11 (230 watts). The extra 30 watts is because they are bifacial. Plan to run each panel to individual charge controllers.

I have about 35 plus or minus feet of cable to run to my charge controllers - according to the online calculators I *should* be running 8 gauge cable. I have no problem doing that, but finding 8 gauge tinned wire with the MC4 connectors pre-spliced on has proven difficult. The ones I have found are "solar cable" and possibly only 7 strand. Also thought about DIY, but the tool that will crimp 8 gauge MC4 connection is over $300.

What do you think, just go with 10 gauge? Voltage drop would only really be an issue at full sun, assuming they even reach the full 11 amps output from both sides of the panel. Or should I buy 8 gauge and just cut the MC4 connector off and butt splice / heat shrink.

[Sailmonkey]

Why not just buy 8 awg and put mc4 connectors on it?

You don’t really need any special tools to assemble an mc4, I give a squeeze with staking pliers, then solder the wire in for good measure. I know someone’s going to say how solder is the devil, or how I’m risking my life by doing this......whatever.

[rbk]

If you do really want 8 awg these guys have been awesome to deal with:
https://tinnedmarinewire.com/wire/
They may be able to help source the MC4 for you

[transmitterdan]

AWG 10 is large enough in my opinion. That opinion would change if the total length of wire used was long. Voltage drop is about 11mV per foot at 11A.

[sailingunity]

Originally Posted by Sailmonkey

Why not just buy 8 awg and put mc4 connectors on it?

You don’t really need any special tools to assemble an mc4, I give a squeeze with staking pliers, then solder the wire in for good measure. I know someone’s going to say how solder is the devil, or how I’m risking my life by doing this......whatever.

You mean not use the fancy crimper tool? Guess I could do that - I have this detail oriented side of me that might always think about how I didn't crimp that connection the "right" way.

[sailorboy1]

I just used the 10 awg to a junction box in the boat the first 8 feet or so the then 8 Awg from there to the panels

It isnt as big a deal as it sounds anyway. By the afternoon the current supplied drops because the charge is getting up there and the losses become small

[Bill O]

[QUOTE=sailorboy1;2895212]I just used the 10 awg to a junction box in the boat the first 8 feet or so the then 8 Awg from there to the panels
QUOTE]


We similarly used a junction box after a few feet of 10 awg to make the transition to 8 awg wire.


Bill O.

[smac999]

or mount the 3 controllers near where the panel wire enters boat. run 3x 10awg to panels. and then like 25' of 4awg to battery for all 3 controllers.

[FlyingScot]

Are you calculating distance both ways when using the calculators? Less drop is always better, the only question is how much so. IMO, solar is all about the details.

[Paul L]

Originally Posted by sailorboy1

I just used the 10 awg to a junction box in the boat the first 8 feet or so the then 8 Awg from there to the panels

It isnt as big a deal as it sounds anyway. By the afternoon the current supplied drops because the charge is getting up there and the losses become small

Did similar, works fine.

[oleman]

A hydraulic crimper from China is fine for all nominal size cables. The total crimp is accomplished a few MM at a time and under operator control. Lugs are just as important. Mine come from Mouser and are molex brand, a great product.

[kas_1611]

You crimp MC4 connectors? Wow.

I just squeeze them tight with a pair of bent needle nosed pliers, wrap the excess wire tightly around the neck then a drop of solder to secure. No issues and no power loss. Only problem I have with them is they don't always tighten onto the cables properly but a dollop of silicone soom fixes that problem and stops water ingress while remaining easy to remove should you need to undo the connector.

[roland stockham]

8awg gives you 2% voltage drop, 10awg is 3.3% both at full power. if you are using a PWM controller this will make no difference. If you have a MPPT you will loose a few percent but only at full power, at 7A you are back down to 2%. Alternatively can you re-rout the cable, 35ft sounds quite a lot and if you can get it down to 22ft you are back under the 2%. From the electrical point of view there is no magic in the 2% goal it is simply a measure of transmission losses. Cables are not normally going to heat up unless you are running massive current such as powering starters of inverters. The reason it is critical in charging circuits is that even a very small voltage drop at the battery terminals will significantly reduce charging current. Dropping from 14.8v to 14.4 will halve the charge current. But solar panels don't bulk charge anyway (unless you have lots of amps) so the battery will absorb anything they produce anyway. The critical link for this is the one in any case is from the controller to the battery which should be as short as possible. The link from the panel to the controller will probably make little difference.

[CaptainJohn49]

In normal household wiring 10ga. is rated for 30 amps, 12ga. is rated for 20 amps and 14ga. is rated for 15 amps. I don't know why multi-strand tinned marine wire would be any different. When running long runs go to the next heaver gauge. If you expect 11 amps from your panel you are an optimist. You can expect 60-70% output for most hours during mid-day. That should put the output at 6 to 8 amps. 10ga. should be plenty for the individual run from the panel to the controller.



CaptainJohn49

[GordMay]

Originally Posted by CaptainJohn49

In normal household wiring 10ga. is rated for 30 amps, 12ga. is rated for 20 amps and 14ga. is rated for 15 amps. I don't know why multi-strand tinned marine wire would be any different...

In conventional home electrical systems (120/240 volts ac), wire is sized primarily for safe amperage carrying capacity (ampacity). The overriding concern is fire safety.
In low voltage systems (12, 24, 48VDC) the overriding concern is power loss. Wire must not be sized merely for the ampacity, because there is less tolerance for voltage drop (except for very short runs).
For example, a 1V drop from 12V causes 10 times the power loss of 1V drop from 120V.


Photo Voltaic (Solar) battery charging circuits are critical, because voltage drop can cause a disproportionate loss of charge current. To charge a battery, a generating device must apply a higher voltage than already exists within the battery. That's why most PV modules are made for 16-18V peak power point. A voltage drop greater than 5% will reduce this necessary voltage difference, and can reduce charge current to the battery by a much greater percentage.
The general recommendation is to size for a 2-3% voltage drop.


If you think that the PV array may be expanded in the future, size the wire for future expansion. You’ll will appreciate that, when it comes time to add to the array.
In some cases of long distance, the increased module cost of using higher voltage modules (18+ volts peak power point) may be lower than the cost of larger wire.