I need 7m of both red and black 25mm cable - any recommendations please?

[StillGoing]

Are you sure 25mm2 is big enough?

 

[MisterB]

i have managed to source some 25mm2 cable at a local welding supplier. he only has 10m in stock though so i would need to go direct to the chassis as suggested .... i am assuming thats a standard installation method ..?

 

[bigtwin]

Are you sure 25mm2 is big enough?

View attachment 824795

Because it’s feeding a dc to dc charger the increased volt drop, arguably, doesn’t matter (the dc to dc will compensate for it).

Ian

 

[bigtwin]

i am assuming thats a standard installation method ..?

Not if you have a shunt fitted.

Ian

 

[MisterB]

Are you sure 25mm2 is big enough?

View attachment 824795

i thought that as its the DC to DC charger that does the work and kicks out the 60A, then 25mm2 to the DC to DC should be sufficient?

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[StillGoing]

i thought that as its the DC to DC charger that does the work and kicks out the 60A, then 25mm2 to the DC to DC should be sufficient?

It’s not just the amps. The voltages will be wrong. The B2B will think the battery is at a lower state of charge (voltage) than it is because of the voltage loss on the cable and the battery will never get fully charged because it won’t receive the right voltage from the B2B.

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

I think you need to find a shorter route or install bigger cables.

autorouter is probably the best person to advise.

 

[autorouter]

Which DC-DC charger is it? And where are you mounting it? If you mount it near the battery, so that the output wires are as short as possible, then the DC-DC charger will put out the correct voltage for charging the battery. And there will be a minimal voltage drop between the DC-DC charger and the battery.

If you mount it near the alternator, then there will be a voltage drop between the DC-DC charger and the leisure battery. However, maybe the DC-DC charger has 'voltage sensor' wires. These are thin wires that run directly from the leisure battery to the DC-DC charger, and are used to tell the DC-DC charger exactly what voltage the battery has. It can then compensate for the voltage drop on the power cables by boosting the voltage until the battery is at the correct voltage.

You could run a couple of thin wires at the same time as you are installing the big power cables. If you are only installing one power cable, and using the chassis as the return, you still need to run two sensor wires, pos and neg, directly to the battery terminals.

 

[bigtwin]

It’s not just the amps. The voltages will be wrong. The B2B will think the battery is at a lower state of charge (voltage) than it is because of the voltage loss on the cable and the battery will never get fully charged because it won’t receive the right voltage from the B2B.

He is discussing the cables from the engine battery to the dc to dc and not the cables from the dc to dc to leisure batteries. He has already started that the latter run is 0.5m.

Ian

 

[Raul]

Guys, the Op explained that DC to DC is near the batteries 0.7 ish meters. So the 25mm2 its perfectly fine, the voltage drop only counts AFTER converter on the output.

MisterB, Take the negative of the chassis near your leisure battery, and to the b2b input.

 

[bigtwin]

MisterB, Take the negative of the chassis near your leisure battery, and to the b2b input.

Of course! My point about the shunt applies to the output side - doh!

Ian

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[JockandRita]

MisterB, Take the negative of the chassis near your leisure battery, and to the b2b input.

With my leisure batteries in the rear garage, that's how I did mine, with a positive feed running all the way along the chassis, from the starter battery to the B2B input, (fused at each end) then a short positive feed to the batteries, again fused.

Cheers,

Jock.

 

[MisterB]

Almost finished, just waiting for some more terminal crimps to arrive.

i have noted all the comments and managed to get the cable run from the B2B to the leisure battery down to around 200mm including in line fuse, so im sure i have limited the voltage drop to as little as possible. i am also taking the negative right back to the starter battery - as it happens i only need 10m of cable in total, so the cable i bought from the local welding supplies is more than enough in terms of length.

thanks for all the comments, help etc

best wishes