Hi all,

Looks like loading my battery with electrics like heated rear window etc is making my RPM dip quite dramatically again.

2007 STI Hawk.
The battery seems to hold charge overnight and shows 12.6 volts. Yesterday I loaded it up with everything electric, and my PSI 3 showed at one point 12v charging from the alternator, so I'm pretty sure my alternator needs replacing. After a good battery charge with my C-tek charger, all seems well, but then I think it's not getting enough juice from the alternator and I get the RPM dip at idle after a day or so, and that's showing the alternator struggling I think.
That said, I've never seen the battery light flickering or on in the dash / dials.

ICP have an alternator which says it's 3 pin but only looks like 2 pin in the picture...so I can call them to check.

But, theirs is rated at 90 Amps, where as my Yuasa battery says it's 110 Amps. Will the ICP one still be ok? (provided it is actually 3 pin like mine on the car at the moment)

https://www.importcarparts.co.uk/par...or&searchPart=

I don't know the part number for the alternator in the car at the moment, only that it's the original factory alternator. It could well be 90 Amp, but I don't know.

 

http://opposedforces.com/parts/impre...llustration_2/

23700AA521

110amp as standard

 

Just to add current part number is now 23700AA522 (may help to widen search)

 

The output of all altednators is lower at tickover. You should be a le to maintain 13.8 to 14.2 volts above about 2500rpm.
Your warning light only indicates a fault, not that you're drawing more current than the alternator can supply.
All alternators convert engine power into electricity. If you draw a lot of current from the alternator, it takes more power. This can cause a rev drop on tickover. However, the engine ecu should compensate for most of it.
If you need spend a long time on tickover, consider load shedding. I suggest you fit a seperate Voltmeter to monitor your battery supply.
Unless you've fitted a lot of high power electrical accessories, you're unlikely to overtax a 100A alternator. 100A is 1200 watts. That's a lot of light and heat going somewhere.