Alternators, Amps and Batteries

[Royalratch]

I've upped the options in my cars over the years as most of us have, Heated Seats, iPhone Charger, amps etc etc.

But my alternator has stayed the same since build (318iS / 65amp?).

I think it's causing issues with charging my battery which was a 50amp from factory (just upgraded to 70amp) and don't think it can take the new loads being placed on it.

What I need to know is:

1) How do I know what Alternator I have?

2) What is the correct E30 Alternator to run a 70amp battery powering lots of extras? 65 or 80? 90? 120?

[Royalratch]

Come on lads... coughBrianmoooeeere... cough... ahem.

[Kos]

ratch

i had a standard alternator on my 316i, original never replaced with a bosch silver battery. whilst i didnt have heated seats and i phone charger i was running 2 JL audio amps, 1300rms 2 X10 subs and components up front and never had an issue. the same rig in my e36 derv with similar battery and again no issues

so you should be fine with a normal alternator, if a decent alternator place can overhaul yours and make it crank out a bit more power

[Royalratch]

Hmmm.

I could well be wrong - it's just my guess that it's a case of an overloaded alternator because the 6-Cylinder cars have upto 120amp alternators and usually a higher spec.

So I just threw in a bigger (longer) 70amp battery and the original alternator will still charge it and any extra load even if it's rated at less than 70amps?

[spook]

If your alternators a little bit tired, renew the regulator

I have a big Bosch silver running my 316.

[Royalratch]

But that's just it Spook, it may not be tired, it may be pushing a load it wasn't designed for even if it's 100% healthy.

I'm trying to figure out if I need a bigger alternator not one that works better but is the same amps.

[Kos]

what issues are you having ?

[Brianmoooore]

Alternator output doesn't have to match the battery capacity in any way.
Think of the battery as a water tank, with a bigger battery equalling a bigger water tank.
The electrical load you are using is the flow through a pipe leading from the bottom of the tank, and the alternator is the pipe filling the tank (with a ball valve, to prevent over filling). Bigger alternator equals a bigger pipe.
All the time the engine's running, the pipe is filling the tank, and you are drawing water from the tank. You can draw water from the tank faster than it's going in. but only for so long, but that time will be longer for a bigger tank. If you now reduce the flow from the tank, to below the rate at which it's filling, eventually it will recover and be full again, but a larger tank will take longer than a smaller one.
If you want to draw large quantities of water from the tank for longer, you will have to increase the size of the pipe filling it (equals bigger alternator.)

[Raj_p]

So what your saying is, he needs to replace the battery with s water tank?

But seriously if the extras you have you wont need to fit a higher ampage alt.

[Royalratch]

Cheers lads.

@willnz - great idea. Calculating the current draw of your average load or full load would be very useful actually.

By 'Ammeter' do you mean a normal multimeter set to read Amps / DC?

And place it after the battery - what did you man 'with?'

[Brianmoooore]

'Normal' multimeter is only rated at about 10A max. You'd need something capable of measuring 5 - 10 times that, with leads to suit.

[Royalratch]

Aaah.

I love the way willnz casually throws some monster piece of kit in there like we'll have it in out back pockets!

Thanks again guys - !