Correct Voltage Alternator for 318is?

[Pal318is]

I currently have a 65A Alternator in my iS, however have always noticed the battery being low, since I had this one in.
I've noticed on Realoem that it should actually 90A..

What have iS owners running in their own cars?

Thanks

[TouringTash]

Shouldn't it be 80 Amps for the 4 pots and 90 for the 6's?

[Pal318is]

It says 80A on Realoem too. However this is for cars upto 89'. Cars up too 92' are 90A or so it says

[TouringTash]

Hmmm

Could this be down to manufacturing ie. making them all 90Amps to cut costs in having to produce two?

The less current an alternator has to generate the less mass of either magnet or copper wire needs turning hence it should weigh a bit less.
I've never weighed the two but the logic sounds err sound.


Edit are the coil packs different on the later iS cars? Trying to think of a reason for needing upto 90amps if 80 will suffice. It's not as if BMW added weight to an E30 for the sake of it, right?

[Pal318is]

Hmmm

Could this be down to manufacturing ie. making them all 90Amps to cut costs in having to produce two?

The less current an alternator has to generate the less mass of either magnet or copper wire needs turning hence it should weigh a bit less.
I've never weighed the two but the logic sounds err sound.


Edit are the coil packs different on the later iS cars? Trying to think of a reason for needing upto 90amps if 80 will suffice. It's not as if BMW added weight to an E30 for the sake of it, right?

I see your logic bud, but tbh i'm unsure of the reasons why
As far as i'm aware, the coil packs are the same for the m42..

[TouringTash]

Do BMW still supply 80Amp alternators, if they only stock the 90Amp ones...
though

The M40 uses an 80amp one up to the last in '94 so my logic of only one being made back then goes up in smoke.

Time to get the paper, pencil and manual out and have an add up fella to see what the book says it'll be drawing.
I wouldn't suggest trying it out with a meter and measuring the total current draw in one go as the leads will hopefully survive long enough for the fuse inside the meter to blow.
remember that you need a greater current (amps) than what is being 'drawn' to run all the electrics due to extra needed to top up the battery.

I would check the weights on realoem of the two or ask a fragger if they have a couple to put on the scales. If the 80Amp one is lighter and it'll supply enough current for your needs then happy days.
Though if you have any amps, uprated bulbs, natsat, flashing lights under car etc. etc. the 90amp would be a better bet.

[Pal318is]

All of the units i've seen for sale so far, have been 80A units. Not seen a 90A at all..

I've seen this one for sale, but i'm not sure of fitment? looks okay tbh, but just want to make sure..

http://www.ebay.co.uk/itm/320945497247? ... 500wt_1414

[TouringTash]

Ask the guy for the part number as it isn't too clear just to confirm.
Worth asking him if he has the bracket the 'toothy' nut uses to adjust the belt easily.

[Pal318is]

Ask the guy for the part number as it isn't too clear just to confirm.
Worth asking him if he has the bracket the 'toothy' nut uses to adjust the belt easily.

Bracket is attached and bolt included in the sale. Think I will get this one, as it looks almost identical to my current one, except its 80A's

Thanks for the input mate

[Brianmoooore]

The handbook that came with your iS states the alternator should be 65A or 80A.
Either should be sufficient to keep the battery fully charged, unless you have a 10,000W sound system.
If your battery isn't being fully charged, check the voltage output from the alternator, assuming the battery itself is good.

[Pal318is]

No 10,000W sound system here
I had the battery checked from Halfrauds about a week ago and they said its low, but could do with a charge. It's the 2nd battery i've had from them, since this problem started.. Just thinking the alternator is the culprit, unless i have a bad earth somewhere..

[Brianmoooore]

Check the voltage across the battery with the engine running and the headlamps on.

[Pal318is]

Check the voltage across the battery with the engine running and the headlamps on.

Thanks Brain