Cable size ? (1 Viewer)

[Vikdikdok]

Would it be overkill to use jumpstart cable from solar panel via MPPT to batteries ?

 

[DBK]

Yes, completely. The current at most will be in tens of amps not the hundreds jump start cables are sized for.

They will work of course but thinner cables will do the job and fit the MPPT terminals, which thick cables won't.

 

[Raul]

What’s the max A rating of the mppt, and distance from the mppt to the battery?

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[pappajohn]

A hint....
Cable tails at solar panel will probably be 4mm².
Jump leads are usually 35mm².
Jump leads won't fit the controller terminals.
Biggest you should need to avoid excessive volt drop over length will be 6mm² or 10mm².

 

[autorouter]

Cable tails at solar panel will probably be 4mm².
Jump leads are usually 35mm².
Jump leads won't fit the controller terminals.
Biggest you should need to avoid excessive volt drop over length will be 6mm² or 10mm².

Agreed, any jump leads I buy will be 35mm2 minimum. But Halfords Essentials jump leads are 8mm2 and cost £10. A good way to get thick wire, especially if you are in a hurry or have problems with online shopping.

 

[Leakylunar]

So can I assume 4mm cable will be fine from controller to battery if only 3-4 feet?

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[Lenny HB]

4 mm sq cable is fine unless you have a very long cable run then use 6 mm sq. Easy way of cabling is to buy a male to female solar cable with MC4 plugs already fitted. Buy twice the length you need then cut it in half. You can then plug into the solar panel cables and run the tails down to the regulator.

 

[Leakylunar]

 

[Lenny HB]

So can I assume 4mm cable will be fine from controller to battery if only 3-4 feet?

Yes, people often go overboard with solar cabling as the biggest loss with be when the panels are producing their max output, the loss will be small in the winter when the panels are only producing a 2 or 3 amps.
Although the recommendation is to aim for a 3% volt drop, in practice 5% is fine.
Be careful if you buy auto cable as sizing often includes the insulation which means a 4mm auto cable is realy only 2.5mm sq.

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[Servo]

This may help

 

[Lenny HB]

This may helpView attachment 355480

That chart is very poor it does not give voltage loss and is very missleading.

e.g. for 10 amps with a cable run of 6 m it states 4.5 mm sq but states the same size cable 4.5 for 10m.

For a loss of 5% over 6m, 4 mm sq is OK but for 10m you need 6 mm sq sq cable.

 

[Pausim]

I find the voltage drop calculator half way down this link very useful https://www.12voltplanet.co.uk/cable-sizing-selection.html

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[Servo]

That chart is very poor it does not give voltage loss and is very missleading.

e.g. for 10 amps with a cable run of 6 m it states 4.5 mm sq but states the same size cable 4.5 for 10m.

For a loss of 5% over 6m, 4 mm sq is OK but for 10m you need 6 mm sq sq cable.

Feel free to complain to Aqafax .

 

[Lenny HB]

Feel free to complain to Aqafax .

Better not to post something that is misleading.
Unfortunatly there is a lot of missinformation on the web.

 

[Servo]

Aqafax is a major disputer of cable to the marine industry, as I say fell free to complain .

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[walburga]

I've often thought about this...I've got a 15 amp fuse in the solar circuit (can't remember if it's on the battery side or the solar panel side of the regulator), but..do I get a voltage drop over the length of the fuse wire, approx 10mm long, or does the fuse somehow 'throttle' the leccy?
My system has always worked well, 2 x110 amh LB's, 100 watt roof panel, 60 watt stand alone panel, so the answer may be theoretical, but in practical terms all appears ok.

regards
Allen

 

[Raul]

From PV panel to controller it’s ok to have some voltage drop. But, from controller to battery it isn’t. You aim to keep looses as min as practical, and definitely under 3%. At 14.4v a 3% loos is massive. Is 0.43v drop. The battery will see a lower voltage than one is set in the controller.
On circuits with 24v and up, a 3% is affordable. But on a 12v the operating voltage is small as it is.

I did ask, what’s the amp rating of controller, and distance to the battery? I can calculate you the cross section needed for various losses.

 

[autorouter]

do I get a voltage drop over the length of the fuse wire, approx 10mm long, or does the fuse somehow 'throttle' the leccy?

In theory, there will always be a voltage drop along a fuse or indeed any length of wire, however thick (assuming you are not using superconducting wires, which are not as far as I know generally available). In addition, a fuse will have a very small resistance because it is designed to heat up and melt if the current exceeds the nominal value of the fuse.

However the resistance value is usually very small, and if you are having voltage drop problems it's much more likely it's loose or corroded contacts on the fuse or wiring than anything the fuse itself will cause.

Fuses should not normally carry more than 75% of their rated value, and in those conditions will last indefinitely. If they are constantly run at or just below their rated value they will get hot, and loose or corroded contacts are more likely.

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[pappajohn]

Fuses should not normally carry more than 75% of their rated value, and in those conditions will last indefinitely. If they are constantly run at or just below their rated value they will get hot, and loose or corroded contacts are more likely.

Except for cheap Chinese shite off ebay which may carry 75% MORE than its rated value before blowing getting so hot the plastic melts

 

[Vikdikdok]

Apologies for my late update, the MPPT is a Victron 75/15. The distance from panel on roof to controller is (approx) 18" ( size i'm not sure, but it does throw out 2.5 / 3A in good sunshine) , distance from controller to leisure batteries (2 x 110Ah sealed lead acid) is approx 7ft. I hope to fit another solar panel of 200 / 250w and 'assume' the Victron controller will safely handle the combined output. I'll have a look at Halfords jump leads & those male to female solar cable with MC4 plugs

 

[Raul]

You won’t need jump leads. Solar cable 4mm2 , will be plenty from controller to battery.
From panel to controller, look at ebay for a solar extension cable, crimped on both ends with mc4’s.

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[Vikdikdok]

Once again many thanks for coming to the aid of a numpty

 

[DBK]

Apologies for my late update, the MPPT is a Victron 75/15. The distance from panel on roof to controller is (approx) 18" ( size i'm not sure, but it does throw out 2.5 / 3A in good sunshine) , distance from controller to leisure batteries (2 x 110Ah sealed lead acid) is approx 7ft. I hope to fit another solar panel of 200 / 250w and 'assume' the Victron controller will safely handle the combined output. I'll have a look at Halfords jump leads & those male to female solar cable with MC4 plugs

The Victron 75/15 has a maximum power rating of 220W so if you want to add a second panel of around 200W you need another controller. Nothing wrong in doing that and it even has advantages.

 

[Vikdikdok]

DBK, thanks for the info, I'll 're-adjust' the extra panel to 150w as I can't afford to replace this Victron 75/15

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