How do I uprate alternator wire for 90Amp?

[theserb]

Hello all.

I have 1989 1.9 DG camper

Just finished wiring up a full liesure system with heavy duty (100Amp+) split charge relay, wires and fuses. I recently fitted 2x110AH marine leisure batteries and uprated my alternator from 45amp to 90amp.

Now I am an electrical engineer but not very good with cars. The internal wiring from the main battery to liesure system is all safe and fused corectly.

However I havent uprated the wire from the alternator itself. The one that was originally fitted for the 45Amp alternator doesnt look man enough to handle 90 Amps and Im worried about it melting when my liesure batteries are discharged and demand lots of current.

I have some spare 100Amp+ wire and want to replace it. There are two wires coming from the alternator and one looks like it goes to the starter motor. Is it the one to the starter motor that I need to replace? Does the charging current get sent up the fat starter cranking wire? Any advice would be appreciated and I want to make sure Im uprating the correct wire.

Regards

Stefan Stojanovic

[California Dreamin]

No it's the long positive lead that goes all the way back to the starter battery that will need uprating IF any do.
You could ADD an extra wire rather than replace it...so the cxurrent is being shared.
Martin

[kevtherev]

Just wondering why you think it was necessary to double the Alternator rating?

Have you added something that draws excessive power from the Alternator..like a powerful music system?

[California Dreamin]

I know what Kev is getting at....you don't necessarily need to upgrade the alternator when fitting larger leisure batteries..
However the one benefit would be quicker re-charging so I suppose it all depends on how much driving there would be between discharging.

Alternators work on a downward curve (initial high charge rate decreasing to only a few amps) so this related from going from 10% to 100% charged.
The bulk of the charge occurs early on but the last 20% of charge can take several hours to achieve.

There is another theory here....as the petrol starter motor on a WBX can draw upto 160amps on a cold start, the original wiring (in theory) should easily be able to manage the percieved maximum charge of just 90amps going back the other way.

However....in reality this very long cable suffers from lots of voltage drop so any additional help from a second wire will benefit both starting and charging.

Martin