Alternator amp rating

[Chris Hebden]

Hi, i was wondering what the 5 GT alternator is rated to (in amps)?

I have 100 watt headlamp bulbs in and if i turn on any other electronic device (with these switched on) the idle really drops off and the batt light starts to flicker.

I reckon on the lamps drawing roughly 9amps is this too much or is my alt on its way?

Cheers Chris

[Shane P]

60 amp, uprated units are 10 amp more apparently

From what i have seen, R9's and 11's and other trims of Mk2 R5 use 50 amp units, which are a hell of a lot cheaper ! :)

[Chris Hebden]

60 amp, uprated units are 10 amp more apparently

From what i have seen, R9's and 11's and other trims of Mk2 R5 use 50 amp units, which are a hell of a lot cheaper ! :)

60amp! Why is mine struggling with 9!!!?

Cheers for the info mate, stupid question, do the other stated above fit the 5 ok?

[Scoff]

Hi Chris, it's not the alt's fault. thats 9A per bulb, so 18A, plus the side lights front and rear, plus a few amps to run the ignition and anything else you have switched on. Lets say you have 25A draw on the alternator at idle. Thats a lot, but it isn't the alternator that's struggling, it's the engine that can't cope.

If the lights get bright and the volts come back up the moment you rev the engine, then the alternator is working fine. Imagine that your asking the alternator for 25A at only 900rpm engine speed. the alternator needs sufficient torque from the engine to keep it turning. If the engine speed drops off, it is because the alternator is asking for more torque than the engine can provide at that point. as a result, the alternator can't do it's job. modern cars get around this with a combination of closed loop idle control and electrical load monitoring, meaning that rpm's will rise to keep the alternator happy when electrical load increases. Ofcourse, the GT has non of that so you either have to re fit 70w bulbs or raise the idle speed.

A bigger alternator will make no odds, it'll still need the same torque from the engine at idle to make the desired current.

[Spooky]

Chris, I'm pretty sure there's an article about how to stabilize the voltage when the car is running or under electrical load.

[Chris Hebden]

Exactly that Chris, raise the revs the brightness increases, thanks for the explanation (forgot about both bulbs :scared:)! Shame, as the bulbs make a lot of difference on the road but i can loose upto 300rpm when turning them on! I'll have a shop around for some different bulbs! Cheers

[Spooky]

So, increasing the idle speed is the answer...

That's why when you switch the air con, headlights etc on in newer cars you can hear/see the idle speed increase by itself :)

[Chris Hebden]

So, increasing the idle speed is the answer...

That's why when you switch the air con, headlights etc on in newer cars you can hear/see the idle speed increase by itself :)

But to get reasonable idle speed with the headlights on i'd have to turn the idle upto 1100+ rpm (without lights on) which to me is a bit much! At the min i have it idling at 950rpm without lights and roughly 700rpm with lights on

[Chris Hebden]

Chris, I'm pretty sure there's an article about how to stabilize the voltage when the car is running or under electrical load.

Canne find it cappen!