Ex-mil S3 Lwt FFR battery cable size

[tracer.smart]

I fitted two new Lucas 069 batteries in my 24v Lwt FFR to replace some Halford units, but found out the +ve cable is now too short as it has been cut to the old battery size and runs to an isolator switch.

Looking at the cold start rating on the new Lucas units, it is hefty at 550CCA, with operating current of 68Ah.

The cable I can source to cover this is 20mm thick, and rated to 600A. Or I can go with a 500A rating at 10mm thick, closer to what’s already fitted.

Question is can I go with the lower rated one, or would this be a problem waiting to happen?

Edited by tracer.smart on Tuesday 20th April 14:22

[100SRV]

The CCA (Cold Cranking Amps) is a transient value related to how long you run the starter motor for. 50mm CSA cable should be more than adequate but if you up-rate the positive cable be sure to do the same for the negative. Is the battery negative connected directly to the engine or to the chassis with a braid strap connecting the engine to the chassis?

Automarine have a good chart showing cable type, CSA (Cross-sectional Area) and current / power ratings.

[tracer.smart]

100SRV said:

The CCA (Cold Cranking Amps) is a transient value related to how long you run the starter motor for. 50mm CSA cable should be more than adequate but if you up-rate the positive cable be sure to do the same for the negative. Is the battery negative connected directly to the engine or to the chassis with a braid strap connecting the engine to the chassis?

Automarine have a good chart showing cable type, CSA (Cross-sectional Area) and current / power ratings.

Thanks 100SRV, very helpful. The battery negative is connected to the chassis with a braid strap, and difficult to get to. Current positive and negative cables look about 12mm diameter, so I’m guessing more than the 50mm CSA you’re suggesting. Batteries that came out were 360CCA and 41Ah.

If there was a mismatch between positive and negative cables gauge, is the risk a voltage drop?