Thread: Alternator Current & Electrical System Draw

on a 97 disco it should be a 100 amp alternator from factory


simple maths doesn't allow for the battery to be incapable of absorbing the charge rate to pump it up in an hour from flat.
something called heat is a big factor in trying to charge the battery that quickly.

try looking at 'traxide tronics' website,
tim has a lot of good information there, and will assist you if you cannot find the answers you want.

tim is one of our approved vendors on this site and supplies dual battery charging systems, among other things.

Thanks Harry.

Hi Sam, as harry posted, you have a 100 amp alternator and your Disco uses anything from around 10 amps to 40 amps for the vehicles electrics, depending on what you have switched on. ( headlights, sound system, A/C )

As to your battery, available amperage is only part of the equation.

The charging voltage ( the Disco’s operating voltage ) is the main controlling factor.

With the Disco 1 your are looking at anything from 13.6 to 14.4v.

Next is the type of battery, a standard flooded wet cell battery will take up to 6 hours of driving to fully charge a low battery with an operating voltage of 13.6v and it doesn't matter how small or big the battery is, it's the same charging time.

But if you have something like an Optima battery, 30 minutes driving could fully charge it.

Now you have more questions then answers!

But if you have something like an Optima battery, 30 minutes driving could fully charge it.

My experience does not bear this out fully.
I have a dedicated 85amp alternator for my second battery.
The battery is an AGM 90AH or now 95AH. Any Optima that fits in a RRC is MUCH smaller in capacity (usually 55AH) so may charge quicker.

I find when it is down to say 11volts, the voltage input from my alternator is about 13.7 volts. This slowly rises to 13.9 over about 1 hour, then stays at 13.9 for about another 2-3 hours when it goes to 14.1 volts and stays there.

My conclusion from this is that the battery quickly achieves about 90-95% charge but that the remaining 5-10% takes quite a while to achieve.

So I find even with a dedicated alternator , it takes at least 4 hours of driving to fully recharge a 90AH AGM battery which have much less internal resistance than a starting battery..

The regulator on my primary alternator failed in Kakadu and I rewired the second alternator to feed the two batteries, and the voltage was down to 13.7 or so even after driving to Darwin, so the one alternator was not fully charging the second battery even after 6-8 hours. The starting battery was fully charged at the start.
Regards Philip A