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Wire gauge questions

flinkpoyd01

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Jun 24, 2022
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Hi all, first post. Thanks for having me :)

I'm building a system on my travel trailer with 3x 200watt Newpowa panels mounted permanently to the roof in parallel, a 60a Renogy Rover controller, and a 200ah Ampere Time LiFePo4 battery. My question relates to wire gauge. The Current at Pmax (Imp) of the panels is 10.75a. Given the parallel arrangement, at 100% efficiency (won't happen) I'd theoretically have 32.25a traversing the wiring to the controller. If I need to make a run of say, 20', what gauge wire would you recommend? The trailer is already prewired for roof solar but I'm guessing it's small gauge and I'll need to use it to pull new wiring. Based on amperage charts online it looks like 6 -8 awg is recommended for this. Is that correct?

Second (related) question: I purchased a 3 into 1 Y connector to connect the panels on the roof. After purchasing it, I found that the "1" lead combining the 3 leads from the panels is 10 awg. Being that this would be the "start" of combined amperage run to the controller, shouldn't I have 6-8 awg coming off of the 3 combined leads? I'm not seeing any Y connectors on the market with a higher gauge than 10.

Thanks!
 
teach a man to fish... :)


use the "Estimated Resistance" Tab

I appreciate the link and the approach :). Calculating voltage drop is certainly helpful in terms of understanding the "waste" of collected energy.

That being said, am I correct in assuming that with a y connector that terminates in a 10awg, 1 foot length (or slightly less) wire, the bottleneck of the smaller gauge wire makes it unnecessary to run larger than 10awg wire from that point to the controller 20 feet away? Or is the loss accumulated differently (based on the calc, .035% loss across the 10 awg, 1 foot length connector wire and then if running 8awg for the rest of the run, a ~4% drop across the rest of the run resulting in around a 4% total loss)?

Followup question- at what level of resistance due to loss across the wire by being undersized does the wire become warm and/or hazardous?

Thanks!
 
I appreciate the link and the approach :). Calculating voltage drop is certainly helpful in terms of understanding the "waste" of collected energy.

That being said, am I correct in assuming that with a y connector that terminates in a 10awg, 1 foot length (or slightly less) wire, the bottleneck of the smaller gauge wire makes it unnecessary to run larger than 10awg wire from that point to the controller 20 feet away? Or is the loss accumulated differently (based on the calc, .035% loss across the 10 awg, 1 foot length connector wire and then if running 8awg for the rest of the run, a ~4% drop across the rest of the run resulting in around a 4% total loss)?


Loss is a function of:

gauge, current, voltage and length.

Just because you have 10awg in the system somewhere doesn't mean you can't use thicker elsewhere in the string for votlage drop considerations. Using 10awg DOES limit the total current to what that 10awg segment of cable can handle.

Followup question- at what level of resistance due to loss across the wire by being undersized does the wire become warm and/or hazardous?

Wire ratings are based on where the insulation would fail. If a wire is rated for 30A @ 60°C, that means at 30A, the wire will be hot to the touch. it won't be 60°C because it's also shedding heat to ambient, but it will still be pretty toasty.

If you limit voltage drop to <3%, you meet code. Others have expressed that 1-2% is best for optimal MPPT operation.

If you size wire for the needed ampacity and limit voltage drop to < 3%, you win.
 
Hi all, first post. Thanks for having me :)

I'm building a system on my travel trailer with 3x 200watt Newpowa panels mounted permanently to the roof in parallel, a 60a Renogy Rover controller, and a 200ah Ampere Time LiFePo4 battery. My question relates to wire gauge. The Current at Pmax (Imp) of the panels is 10.75a. Given the parallel arrangement, at 100% efficiency (won't happen) I'd theoretically have 32.25a traversing the wiring to the controller. If I need to make a run of say, 20', what gauge wire would you recommend? The trailer is already prewired for roof solar but I'm guessing it's small gauge and I'll need to use it to pull new wiring. Based on amperage charts online it looks like 6 -8 awg is recommended for this. Is that correct?

Second (related) question: I purchased a 3 into 1 Y connector to connect the panels on the roof. After purchasing it, I found that the "1" lead combining the 3 leads from the panels is 10 awg. Being that this would be the "start" of combined amperage run to the controller, shouldn't I have 6-8 awg coming off of the 3 combined leads? I'm not seeing any Y connectors on the market with a higher gauge than 10.

Thanks!
use a 6mm^2 solar cable as sold on Ali.
 
That being said, am I correct in assuming that with a y connector that terminates in a 10awg, 1 foot length (or slightly less) wire, the bottleneck of the smaller gauge wire makes it unnecessary to run larger than 10awg wire from that point to the controller 20 feet away
Personally IF I were going to stay parallel I would probably homerun from each panel to inside and use a terminal block with fuses. That’s half the cost of a combiner box with fuses which is another option.

I probably would not stay parallel, however. I would buy one more panel, return the Renog River, get an mppt (epever? ampinvt? powrMR?) and run 2 series, 2 parallel panels with a Y branch connector.

You may not need 800W; a 200Ah battery suggests low usage. But I think 400Ah of storage is the start of real power storage for a camper.
I can tell you for free that you will have refrigerator freedom at 400Ah with a cloudy day or maybe two- LiFePo will help because partially charged lead acid batteries get harmed, while LiFePo can deal. A gas fridge negates that, but if replaced with a < $200 120V fridge your propane usage at today’s cost will be nice (although payback on that ain’t going to be immediate regardless- just nice to spend and not spend for years.)

Just some thoughts. Use them or not at whatever works for you.
 
O/k so very conservative estimate of max current 32 amps (from first post).

Start by looking at the current ratings of commercial wire. These will vary quite a lot from brand to brand, because the safe current depends on temperature rise, which in turn depends on the type and quality of the insulation.

But if Brand "X" say their cable can safely carry 32 amps it probably can, without melting or bursting into flames.

Next step is to work out if the voltage drop is acceptable using one of the online cable calculators.
Here lies a trap ! If it says 40 metres of length. that means 20 metres of distance, because there will be two wires involved.
Some cable calculators make this distinction very clear, others do not, so beware.

What voltage drop is acceptable ?
That is entirely up to you, but 3% would be very conservative and 6% is starting to become significant.
The jumps between wire gauges are fairly large, so something should fall fairly readily within that range.
 
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