How much amperage can an alternator support? no really...

Huw Powell audi at
Wed Feb 6 17:37:35 PST 2008

LL - NY wrote:

> At those current levels, you'd want to consider an inductive current meter.

Yeah, one of them.  We once measured my starter current that way next 
door when I was having hot start problems.  It was about 200A, so I got 
a new one.

I think I even own one of those meters, but I don't think I've ever used 
it. Hmmmmm...

> You don't need to break the lines to measure the current, just clamp the
> coil around the lead in question (the ground line to the battery would be
> best) and determine the current draw.
> LL - NY
> On 2/6/08, Huw Powell <audi at> wrote:
>>>So - as far as I can tell - based on the what I have from the list so
>>>Fuel Pump = 10a (always on)
>>>CIS = 10a (always on)
>>>Ignition = 10a (always on)
>>>Rad Fan = 20a (always on - at least for now)
>>>Heater Fan = 15a (always on in the winter ;)
>>>Brake Lights = 5a (on a lot)
>>>Computer, gauges, etc = 5a (always on)
>>>Head lights low = 55w x 2 = 110 w = 10a
>>>So given this set - looks like I need 85amps (in the winter). Do the
>>>numbers look right?
>>Yes, and no.  They all look like good "estimates" - but I suspect they
>>are all overestimates.
>>The car in stock trim would be using 85 amps (when the rad fan is on)
>>without turning on the defroster or radio?  I doubt that.
>>Access to a decent high-current ammeter would answer your questions in a
>>  matter of minutes with "real" numbers.  Hmmm, wait, more than a couple
>>of minutes, you'd have to disconnect the alt and run on only the battery
>>to have good numbers.
>>Oh, here's one for you - replace your brake and parking lights with the
>>LED versions. A bit pricey, but lower current.
>>Huw Powell
>>quattro mailing list
>>quattro at
>>Watch this space for ads :)

Huw Powell

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