Battery bank cable

[seaangler23]

Speccing for a leasure bank of 3 110ah battery's what size cable would be suitable? The run to the isolator switch is only about 1.5m and the max load I think would be if the engine battery was to drain and using the leasures to start the engine/charge the battery, obviously the bigger the better but at what point is it just throwing money away on cable, anything else to take into concideration?

 

[PaulRainbow]

Will also depend on what the engine is and how far from the isolators to the engine.

 

[yoda]

Handy calculator here:

https://www.12voltplanet.co.uk/cable-sizing-selection.html

If you work on the worst case being full output from the alternator to the battery (70amp?) you come out with 4 or 5 AWG cable depending on length of run and the amount of voltage loss you are prepared to suffer. Link has a handy chart to convert AWG to cross sectional area.

Yoda

Yoda

 

[simonfraser]

you're not exactly going to waste a lot of money on 1.5m of cable, would def overspec that one.

 

[PaulRainbow]

Handy calculator here:

https://www.12voltplanet.co.uk/cable-sizing-selection.html

If you work on the worst case being full output from the alternator to the battery (70amp?) you come out with 4 or 5 AWG cable depending on length of run and the amount of voltage loss you are prepared to suffer. Link has a handy chart to convert AWG to cross sectional area.

Yoda

Yoda

How did you manage to work that out without knowing how long his cables are or what engine he has ?

 

[VicS]

Handy calculator here:

https://www.12voltplanet.co.uk/cable-sizing-selection.html

If you work on the worst case being full output from the alternator to the battery (70amp?) you come out with 4 or 5 AWG cable depending on length of run and the amount of voltage loss you are prepared to suffer. Link has a handy chart to convert AWG to cross sectional area.

Yoda

Yoda

But the OP wants the installation to be capable of engine starting from the leisure battery bank. That will require cable capable of carrying the full starter motor current and is, no doubt, why PR was asking about the engine.

ITYWF that the OP has a Bukh 48 engine (with a 1 kW starter motor). and for which the exiting/ original battery wiring is spec'd as 50mm² (0 AWG)

50mm² seems fairly generous as 50mm² battery cable is rated at 345 amps and has a resistance of 0.0004 ohms per metre

I would therefore use the same size cable ( 50mm²) for wiring the leisure bank to the isolator and for the negative earth, retaining the existing cable between the engine and the isolator unless of course the exiting cables are unexpectedly long in which case they would be better up rated, together with the new cabling, to something heavier based on the total lengths involved

 

[Hoolie]

I rewired our similar installation with 50mm² tinned cable, but kept the 35mm² connections to the engine as I wasn't sure the new cable insulation had a high enough temperature rating.

 

[Norman_E]

Similar distances and all mine are 50mm.

 

[VicS]

I rewired our similar installation with 50mm² tinned cable, but kept the 35mm² connections to the engine as I wasn't sure the new cable insulation had a high enough temperature rating.

The working temperature range of the cable from 12volt Planet is -30 to + 70 C

 

[Hoolie]

The working temperature range of the cable from 12volt Planet is -30 to + 70 C

The flexible cable I bought from Furneax-Riddell has the same rating AFAIK. But the existing cables to the engine have much harder and tougher insulation. Only a short link <1 metre so no problem keeping them.

 

[seaangler23]

Thanks all.
Yes a buhk 48, I've taken the starter load is the most it should have to handle and should be built for that.
I've used the calculator before but was making sure I hadn't missed anything, all the cable runs are short 1 to 2m

 

[PaulRainbow]

But the OP wants the installation to be capable of engine starting from the leisure battery bank. That will require cable capable of carrying the full starter motor current and is, no doubt, why PR was asking about the engine.

Yes, that's right.

ITYWF that the OP has a Bukh 48 engine (with a 1 kW starter motor). and for which the exiting/ original battery wiring is spec'd as 50mm² (0 AWG)

50mm² seems fairly generous as 50mm² battery cable is rated at 345 amps and has a resistance of 0.0004 ohms per metre

I would therefore use the same size cable ( 50mm²) for wiring the leisure bank to the isolator and for the negative earth, retaining the existing cable between the engine and the isolator unless of course the exiting cables are unexpectedly long in which case they would be better up rated, together with the new cabling, to something heavier based on the total lengths involved

I agree that 50mm is generous, but i'd also use it if the original cable is 500mm, makes sense to keep it all the same.