Wires get hot?

[pda1]

Today my panels produced a consistent 1600 watts.
The array is 2S-4P (250 watt panels 40 volts for a 24 volt battery system)

The amperage from the Combiner box to the MPPT (Victron 150/60) was around 30 amps and the Cerbo/VRM showed a peak of 33 amps. I checked the wires from the combiner to the MPPT and they were warm to the touch. The wires are 10 awg.

Now, the wires from the MPPT to the batteries were slightly warm too. They are 2 awg. The amperage from the MPPT to the batteries was about 45 amps (also used a clamp-on ammeter). I'm not so concerned about the wires from the MPPT to the batteries- they can handle it.

I am concerned about the wires from the combiner box to the MPPT. What gauge should I increase them to, if at all?

Thanks.

 

[zanydroid]

For raw solar DC on #10 you need to keep ISC under 35/1.56 amps or 30/1.56 amps depending on how you read NEC. This is how DC strings are designed to code

(Raw in contrast to DC that goes through an intervening power component like an optimizer that guarantees a current cap. A raw solar panel does not guarantee a current cap)

For continuous observed current it should be under 35/1.25 or 30/1.25 again depending on reading.

30 is the widely accepted starting point for these calculations.

4P is probably rarely going to be code compliant for #30 on modern solar panels, but with 250W it might be fine

Did not do this homework before assembling?

 

[CoolWill]

30 amps on a #10 will make it warm. It's fine.

 

[zanydroid]

30 amps on a #10 will make it warm. It's fine.

If the 30A was measured on a low or standard production day then a over STC day will cook that wire.

 

[pda1]

For raw solar DC on #10 you need to keep ISC under 35/1.56 amps or 30/1.56 amps depending on how you read NEC. This is how DC strings are designed to code

(Raw in contrast to DC that goes through an intervening power component like an optimizer that guarantees a current cap. A raw solar panel does not guarantee a current cap)

For continuous observed current it should be under 35/1.25 or 30/1.25 again depending on reading.

30 is the widely accepted starting point for these calculations.

4P is probably rarely going to be code compliant for #30 on modern solar panels, but with 250W it might be fine

Did not do this homework before assembling?

Of course I did. However, today I cut down some trees that consistently blocked the array so the increased power resulted. Also, I'm referring to the wires FROM the combiner box to the MPPT. The wires between panels are fine and produce around 7 amps

 

[pda1]

The run is about 30 feet.

So, the question is- what size wire to should it be increased to? 8 awg?

 

[zanydroid]

Of course I did. However, today I cut down some trees that consistently blocked the array so the increased power resulted. Also, I'm referring to the wires FROM the combiner box to the MPPT. The wires between panels are fine and produce around 7 amps

NEC math is written to be agnostic to local conditions like that…..

It’s still raw DC from solar panels after the combiner so same rules apply except you multiply by 4 for the 4P.

#8 is definitely fine for that current.

 

[pda1]

Of course I did. However, today I cut down some trees that consistently blocked the array so the increased power resulted. Also, I'm referring to the wires FROM the combiner box to the MPPT. The wires between panels are fine and produce around 7 amps

NEC math is written to be agnostic to local conditions like that…..

It’s still raw DC from solar panels so same rules apply except you multiply by 4 for the 4P.

#8 is definitely fine for that current.

Ok....thanks.

Nuts....now I'll have to fish the new wires. Better safe than sorry.

In the mean time I'm going to isolate two of the panels....or pray for cloudy days. The major power production was caused by recharging to the LiFePo4 batteries and not the loads.

 

[timselectric]

Definitely increase to #8.

 

[pda1]

Will do. Thanks.

 

[zanydroid]

You might be able to get things safer by limiting the battery charge current in the SCC settings.

Not allowed by code because it doesn’t protect against a short on the #10 not being able to tolerate a high production day.

 

[pda1]

'Had considered that as well but the 8 awg is a better option.

I have 2 extra panels so the system would be 2S-5P for a possible 2.5kW (9 amps per string). But, I think the Victron 150/60 limits the input to the MPPT to something like 1700 watts. I'm not sure about that.

 

[CoolWill]

If the 30A was measured on a low or standard production day then a over STC day will cook that wire.

It would have to be way more than 30 amps. #10 has a 75 degree ampacity of 35 amps and 40 amps in the 90 degree column. Now, I'm not saying that everything is A-OK here. But if the concern is a warm wire with 30 amps on it, then it's no concern at all.

 

[pda1]

It would have to be way more than 30 amps. #10 has a 75 degree ampacity of 35 amps and 40 amps in the 90 degree column. Now, I'm not saying that everything is A-OK here. But if the concern is a warm wire with 30 amps on it, then it's no concern at all.

You're probably right.

They were noticeably warm...not hot....just warmer than was to my liking. Also, I've got to put a fan on the MPPT to cool it a bit.

Gentlemen, at my age I have little tolerance for "risk". (That's why I'm not gambling in the stock market).

 

[zanydroid]

'Had considered that as well but the 8 awg is a better option.

It was a temporary suggestion if desperate for power because it does not protect against a short before the MPPT cooking the wire (maybe I’m trolling Timelectric to yell at me lol).

I have 2 extra panels so the system would be 2S-5P for a possible 2.5kW (9 amps per string). But, I think the Victron 150/60 limits the input to the MPPT to something like 1700 watts. I'm not sure about that.

Does 3S exceed on VOC in your climate? You can consider 3S3P.

 

[Hedges]

The array is 2S-4P (250 watt panels 40 volts for a 24 volt battery system)

Can you tilt 2S2P towards morning sun, the other 2S2P toward afternoon?
That will reduce peak current (by about 30% if 90 degree angle between them) and extend hours of production.

 

[pda1]

It was a temporary suggestion if desperate for power because it does not protect against a short before the MPPT cooking the wire (maybe I’m trolling Timelectric to yell at me lol).

Does 3S exceed on VOC in your climate? You can consider 3S3P.

3S doesn't exceed the MPPT. Only once in the past 2 years has the 2S reach 79 volts. The MPPT is rated up to 150v. 3S would give 120 volts and that's safe for my 150v 60A MPPT.

But....I had have to buy a 2 more panels (which would be a total of 12 in the array) or reduce the size down, as you suggested.

I'd buy the panels off Ebay from San tan solar. They're a good seller. The problem is they ship via R&L Carriers who have proven themselves to be clods (hit my truck with their forklift) and have ZERO customer service, and, you'd better pickup your shipment when they say or R&L will charge you something like $300 a day storage fee.

 

[timselectric]

I don't like warm wires.
Putting aside the safety issues. The wasted energy that is being converted to heat. Isn't going where you want it to.

 

[pda1]

Can you tilt 2S2P towards morning sun, the other 2S2P toward afternoon?
That will reduce peak current (by about 30% if 90 degree angle between them) and extend hours of production.

Well, no, I can't. The array is in a fixed position.

I don't like warm wires.
Putting aside the safety issues. The wasted energy that is being converted to heat. Isn't going where you want it to.

Frankly, I'm glad I'm having this problem as I had anticipated purchasing another 2kW of panels.
Will just leave things as they are and get 8 awg wires until I get frustrated by the reduced output on cloudy days.

 

[Dave911]

I don't know if you are trying to be NEC compliant or not, but in many parts of the world and in many installations I have seen in the US, if you need 40 amps of capacity and you have rolls of 10 gauge THHN wire, you run two wires for each phase. Then crimp a lug on both of the wires and terminate the lugs together. The two wires should be as close to the same length as possible. The NEC doesn't like this unless the wire is larger, but I have seen it done many times with no ill effects. On larger power runs, this is the norm since huge conductors, even if stranded, don't like to be pulled around conduit bends even with lubricant (wire lube).