25mm2 cable

[blackrose]

I'm looking to buy some cable for my solar installation and happened to find a 2m length of black BS 6195 Type 4 cable (1993) left over from another job. I never throw anything like that away and try to use stuff that's left over if I can rather than just buying more.

 

The distance from my controller to batteries is about 6ft, so would this cable suitable be as one of the connections and just buy an equivalent length of 25mm2 battery cable in red? The only thing is that the multi-strands of the black cable don't look like they're copper?

Edited September 11, 2022 by blackrose

[Chewbacka]

A quick Google shows it is probably tinned copper which is better than plain copper as it is resistant to oxidation.  It was also stated as multi strand 196/0.04 which is required by BSS.  So assuming your cable matches the above I would use it.  Let’s see what others think.

[Tracy D'arth]

Tinned flex cable is better on a boat than plain copper.  Use it with impunity.

[jonathanA]

I'd have thought 25mm might be a bit large for the terminals on your controller ? 

 

If not happy days...

[ditchcrawler]

Don't forget the fuse at the battery end

[blackrose]

11 minutes ago, jonathanA said:

I'd have thought 25mm might be a bit large for the terminals on your controller ? 

 

If not happy days...

 

It might be I'm not sure. I've bought the Epever 60amp mppt. I'll give it a go.

10 minutes ago, ditchcrawler said:

Don't forget the fuse at the battery end

 

Yes will do.. I need to understand the fuse rating I need. Just in the positive side?

 

[jonathanA]

13 minutes ago, blackrose said:

 

It might be I'm not sure. I've bought the Epever 60amp mppt. I'll give it a go.

 

Yes will do.. I need to understand the fuse rating I need. Just in the positive side?

 

60A controller would have thought 60A fuse.  And yes in +ve.

Edited September 11, 2022 by jonathanA

[blackrose]

For cable sizing from panels to the controller which is the correct calculation based on 2 x 455w panels connected in series. 12v system. Panel specs are Vmpp (V) 41.3, lmpp (A) 11.02. Cable run is approx 5m one way.

 

Which one of these is correct, or neither?

 

[David Mack]

Neither. For the panel to controller cables you should use the panel voltage - 82.6V for your panels in series, current 11.02 A and total (out and back) distance of 10m.

[blackrose]

Ok thanks David. So I only need 4mm2 cable? It seems very thin but easier and cheaper to install I suppose.

 

Edited September 12, 2022 by blackrose

[Jen-in-Wellies]

17 minutes ago, blackrose said:

Ok thanks David. So I only need 4mm2 cable? It seems very thin but easier and cheaper to install I suppose.

That's the advantage of series wiring and high voltage for transmission. Much thinner wire needed for the same power going through.

[Alan de Enfield]

24 minutes ago, blackrose said:

Ok thanks David. So I only need 4mm2 cable? It seems very thin but easier and cheaper to install I suppose.

 

 

6 minutes ago, Jen-in-Wellies said:

That's the advantage of series wiring and high voltage for transmission. Much thinner wire needed for the same power going through.

 

 

Thats why on 'mains' voltage you can have a 25 metre (50 mt return length) extension lead that is only 1.5mm2.

 

(I get even less losses on my 120v panel using 6mm2 which fits nicely into the MC4 connectors)

[GUMPY]

It's worth thinking about what size the cable would need to be for the lower voltage parallel operation. Then size your cables to whichever is the greater just in case.

 

[blackrose]

32 minutes ago, Loddon said:

It's worth thinking about what size the cable would need to be for the lower voltage parallel operation. Then size your cables to whichever is the greater just in case.

 

 

Yes I was thinking that too, then there's no retrofitting.

 

I'm still a bit unclear on parallel or series panel connection. You and Alan de Enfield recommended parallel but everyone else including Bimble are saying series. I've looked at the advantages and disadvantages of both online but the website I looked at was written from the perspective of someone who recommend series.

 

https://www.explorist.life/solar-panels-series-vs-parallel/

[blackrose]

57 minutes ago, Loddon said:

It's worth thinking about what size the cable would need to be for the lower voltage parallel operation. Then size your cables to whichever is the greater just in case.

 

 

So just halve the voltage for the parallel calculation?

 

 

[Jen-in-Wellies]

You only have two panels. If you place them close together and remember not to moor in shade, then there are no advantages to parallel. Perhaps easier for you to arrange, with a wide beam. Depends on the roof width and panel sizes. More of a problem when there are a lot of panels strung out along the length of a narrowboat roof and one getting shaded is more likely. Then the series advantage of fewer joints and fuses and thinner cable makes total sense.

Jen

[GUMPY]

1 hour ago, blackrose said:

 

Yes I was thinking that too, then there's no retrofitting.

 

I'm still a bit unclear on parallel or series panel connection. You and Alan de Enfield recommended parallel but everyone else including Bimble are saying series. I've looked at the advantages and disadvantages of both online but the website I looked at was written from the perspective of someone who recommend series.

 

https://www.explorist.life/solar-panels-series-vs-parallel/

Series is good if you have "low voltage" panels i.e. about 20v then you need to be concerned about volt drop and shading. With 43v panels parallel is fine less concern about volt drop and less concern about shading 

[cuthound]

2 hours ago, Jen-in-Wellies said:

That's the advantage of series wiring and high voltage for transmission. Much thinner wire needed for the same power going through.

 

Indeed, it is why the National Grid operates between 400,000 and 275,000 volts and distribution to the local substation down to 11,000 volts.

 

The cable cross sectional area would be massive if all electricity was distributed at 230 volts.

 

[David Mack]

1 hour ago, blackrose said:

 

So just halve the voltage for the parallel calculation?

 

 

Halve the voltage and double the current for parallel installation.

[Alan de Enfield]

1 hour ago, Loddon said:

Series is good if you have "low voltage" panels i.e. about 20v then you need to be concerned about volt drop and shading. With 43v panels parallel is fine less concern about volt drop and less concern about shading 

 

My panels are 120v EACH, if I wired them in series I'd soon be up in 'dangerous DC voltage' country. 120v is bad enough.

[GUMPY]

The roof panels here sit at about 200v and the battery is at 118v.

All quite low voltage compared to the 2500vDC at 1/2 amp I used to play with. That could be dangerous

 

[blackrose]

3 hours ago, Jen-in-Wellies said:

You only have two panels. If you place them close together and remember not to moor in shade, then there are no advantages to parallel. Perhaps easier for you to arrange, with a wide beam. 

 

I'm going to have 2 x 2m long panels arranged end to end down the centre of the roof. They're just over a metre wide which gives me enough room to walk down either side. 

 

So that's 4m length of panels to be kept out of the shade. To be honest during that recent heatwave I went out onto the river to search for shade and it wasn't easy to find. If I wire the panels in series I assume the combined voltage isn't a safety issue?

https://www.bimblesolar.com/455w-canadian-solar-panel

 

Parallel installation would require 16mm2 cables and it looks like a more complex installation so I think I'll connect in series.

 

I'm sure I can do a decent installation once I know exactly what I'm doing, but my technical electrical knowledge is crap so I'm having to check and recheck everything. 

Edited September 12, 2022 by blackrose

[Jen-in-Wellies]

25 minutes ago, blackrose said:

If I wire the panels in series I assume the combined voltage isn't a safety issue?

Anything over 48V is potentially a safety issue. Cover the panels with blankets when working on the wiring and ensure there isn't exposed circuitry where inquisitive fingers can get to when finished. Ensure that any fuses, holders, etc that are used on the solar side are rated for the voltage. MC4 connectors are good in this respect. Even when disconnected the live terminals are recessed.

Jen

Edited September 12, 2022 by Jen-in-Wellies

[blackrose]

Why do the panels have to be covered when you're working on the system? Why can't they just be disconnected/isolated? Does the voltage have to go somewhere if they're left uncovered?

[GUMPY]

2 minutes ago, blackrose said:

Why do the panels have to be covered when you're working on the system? Why can't they just be disconnected/isolated? Does the voltage have to go somewhere if they're left uncovered?

If they are producing power then its not good to disconnect under load as it causes arcing and connectors are  not rated for disconnect current, covering them prevents this.

View it as turning off the switch on the wall