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Post by lollygagger on Mar 25, 2017 15:16:10 GMT
My panel says it provides 22v open circuit and 17v at peak power.
So I size the cables for 150w at 17v yes?
This comes out at 2.4mm dia with 3% losses.
If I do same calc for 12v I find I need 4mm dia.
Which is right?
I'll go for 4mm anyway, just wondered if solar sites that provide calculators are "accidentally" encouraging us punters to use "system" voltage. Most people would put 12v in the box for that I think, but is that right?
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Post by peterboat on Mar 25, 2017 15:32:07 GMT
Use4mm it's what fits the connectors I have always used the supplied cable it's less hassle if anything goes wrong
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Post by Gone on Mar 25, 2017 16:17:39 GMT
Ignoring cable length, the cable between the panels and the controller can usually be a bit thinner as the panel voltage will be in your case 17V so at (for example) at 150W the current will be about 8.8 amps in full sun. The cable between the controller and the battery will be running at say 14V so at 150W would have a current of 10.7 amps. In your case the voltage and current differences between in and out are quite small, so I would use the same size cable.
If using an mppt controller with commercial panels which are typically 37V and you have two or three in series the the voltage difference and hence current between in and out will be much bigger.
So for a 200W system with 2 panels the input volts will be 74V and a current of less than 3 amps, whereas the output of your mppt controller will be 14.4 volts and nearly 14 amps. So the output side will need a much bigger cable to minimise volt loss.
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Post by bodger on Mar 25, 2017 17:12:01 GMT
Use4mm it's what fits the connectors I have always used the supplied cable it's less hassle if anything goes wrong +1 |
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Post by JohnV on Mar 25, 2017 17:12:25 GMT
one thing to remember is that the proper 4mm and 6mm solar cable is double insulated with a UV resistant outer case
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Post by lollygagger on Mar 25, 2017 18:35:50 GMT
Thanks all 4mm it is then.
I also do the trick of buying panels with cable ready attached normally.
I'm tripping over a panel with no cables in the boat, the sun came out and fitting it jumped up the job queue.
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Post by lollygagger on Apr 9, 2017 11:41:13 GMT
Update time.
I got myself a 15a mppt charge controller identical to the one I fitted on my camper, some cable, connectors, fuses, some mini trunking and a double cable gland, bolted the panel I've been lugging about to the roof, installed the rest and it's up and running.
I switched off the mains charger to see if a 150w panel can keep up with the fridge and a few LED lights. A couple of days in, including one overcast and yes it can.
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