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Hi sounds an idea swo but you would need some form of charge and load controller for the trailer batteries, to protect the wiring when the alternator was charging the batteries or when they were suppling the motorhome. Thats if you used the existing towbar socket, don't know the rating of the wires but doubt its much over 20amps.
Olley
______________________________________________________________ If you have a problem you canīt fix its because your hammerīs not big enough
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Hi Eddie, Dick (Moandick) has already taken me to task over that, but in my defence you should have seen it before I cleaned it.
Hi teenyob yes you will get 17v but as the amperage increases the voltage drop will increase more, the smaller the wire.
According to the documentation I got with my controller you should aim for no more than 5% voltage drop at the max. amperage the panels can produce.
I suspect if you took a reading at the panels on a sunny day when your batteries needed charging, and another at the controller (Assuming its close to the batteries) you would notice a fair difference.
Hi Dave OK I guess 16mm2 is over the top for John, maybe 8-10mm2 would be more appropriate.
Where's Frank (sallytrafic) for the full SP on this? I can do the practical side as easy as wink, but when it comes to the theory my head hurts.
Olley
Hello there Olley and all,
The cables from my 2 x 80w Panels to the Secca Solar Controler are run in 2 x 2mm2, the cable from panel 1 is about 1meter an d from panel 2 around 1.5m The cable from the controller to the batteries is 6mm2 and is about 2m long.
I thought this was sufficient?
Trev.
______________________________________________________________ OH! if your going away, donīt forget your motorhome!
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It was a good day for solar panels today! The first in a while in which our batteries attained 100% and Float stage. Not sure what tomorrow and the coming days will bring, though.
Happy camping for those out-and-about this weekend!
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Hi Eddie, Dick (Moandick) has already taken me to task over that, but in my defence you should have seen it before I cleaned it.
Hi teenyob yes you will get 17v but as the amperage increases the voltage drop will increase more, the smaller the wire.
According to the documentation I got with my controller you should aim for no more than 5% voltage drop at the max. amperage the panels can produce.
I suspect if you took a reading at the panels on a sunny day when your batteries needed charging, and another at the controller (Assuming its close to the batteries) you would notice a fair difference.
Hi Dave OK I guess 16mm2 is over the top for John, maybe 8-10mm2 would be more appropriate.
Where's Frank (sallytrafic) for the full SP on this? I can do the practical side as easy as wink, but when it comes to the theory my head hurts.
Olley
Hello there Olley and all,
The cables from my 2 x 80w Panels to the Secca Solar Controler are run in 2 x 2mm2, the cable from panel 1 is about 1meter an d from panel 2 around 1.5m The cable from the controller to the batteries is 6mm2 and is about 2m long.
I thought this was sufficient?
Trev.
Yes trev I thought you had used 6mmē but its not what you implied in the earlier post.
______________________________________________________________ Regards Frank
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Hi Trev have a look at this calculator, its for SWA (single wire armoured) but the results I believe are right.
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On my set up using 16mm2 at 15amps over 10metres I lose nearly half a volt. If I had used 25mm2 it would be reduced to a quarter of a volt, and if I had used 2.5mm its nearly three volts which is getting on for 20% of my power down the drain. (or more correctly lost in heat )
So correct wiring sizing on solar panels is very important.
Olley
______________________________________________________________ If you have a problem you canīt fix its because your hammerīs not big enough
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So I'm dropping 0.22 V due to the inadequacies of the 6mm cable I've used. I think this justifies my original comments. In a van the size of John's where the cable runs will be shorter & the voltage drop less 16 mm cable is probably too big.
I'll temper that by saying, obviously no losses are good & this will obviously be assisted by having bigger less resistive wiring.
Dave.
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I'll temper that by saying, obviously no losses are good & this will obviously be assisted by having bigger less resistive wiring.
Dave.
Hi Dave, can't argue with that I agree 16mm2 is a bit over the top for John, but I wish now I had used 25mm2 didn't realise at the time how far my panels would be from the batteries.
Olley
______________________________________________________________ If you have a problem you canīt fix its because your hammerīs not big enough
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Your point about the cables is'nt lost on me. Like you I did the whole installation myself & the cabling was something I gave a lot of thought to. There's no point building a high specification solar array & then crippling it with undersized conductors. I'd be interested to know what the installers at shows are using ?
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which is getting on for 20% of my power down the drain. (or more correctly lost in heat 
