Second Alternator mount and wiring.

I've just taken delivery of a Gwyn Lewis 2nd Alternator mount and 100 amp alternator. Happy Days.

My plan is to fit the 2nd alternator where the air con pump used to be but that will leave each alternator on the opposite side to the battery it is charging. So, I want the original 65a alternator to charge the Aux NS battery and the new 100a alternator to charge the original battery.

Step 1. Reroute the original wiring through to the new alt and upgrade the main cable to 25mm2 from this alt to the battery. The new alt has B+, D+ and W. Will I find three wires on the back of the old alt? I know there is a main cable and W cable. The instructions say to earth the alt through a wire but there doesn't appear to be a connection. The alt is earthed to the engine which in turn has a new lead to the battery - is this okay?

Step 2. Wire the old alt to the Aux battery. I'll need a new main cable - how do I earth this? Motor to aux battery as before? Do I need any other connections?

Any thoughts and comments welcomed.

Earth it in the same way, earth bond to the block or chassis - there are plenty of cables on fleebay.

Good luck with it - something i want to do one day!

Sorry if this is a bit of a dumb question, but what is the advantage of doing this over installing a split charge system?

:search: there is another currently active thread on this subject

redhand said:

:search: there is another currently active thread on this subject

Click to expand...

No there isn't - don't you think I seached first

There's a thread about second battery location - I've had a second battery for years.

twice_nightly said:

Sorry if this is a bit of a dumb question, but what is the advantage of doing this over installing a split charge system?

Click to expand...

If I am not careful I get two batteries at half charge. This way I want to ensure that both batteries are full.

Bump said:

Earth it in the same way, earth bond to the block or chassis - there are plenty of cables on fleebay.

Good luck with it - something i want to do one day!

Click to expand...

Cheers Bump.

Please excuse the daft questions...

Is "earth bond" the same as earth, ie, run an earth cable?
Isn't the alternator earthed because it's bolted to the block?

I added extra earths to the main battery, after advice from the AA man who came out when a dodgy earth meant it was a non starter. I used a set of fat (£56 quids worth) jump cables, cut to length with soldered terminals. Battery to chassis and battery to motor.

I'll do a write up when it's done.

Will you not lose a few mpg with this mod?

s3ndy said:

Will you not lose a few mpg with this mod?

Click to expand...

It can't get lower than it is already.

It's replacing the aircon pump so I guess it's swings and roundabouts.