WTBorrow - mk4 alternator or ammeter

[MechEngg]

Anybody have a spare 90A or 120A alternator kicking around. Think my aftermarket alternator might have kicked the bucket slightly and i want to just throw a known good one in for a few days and boot around and see if my battery keeps a good charge from it.

Alternately if someone has a +200A ammeter to measure the output through my 0 gauge alternator output wire that would diagnose the problem too

Alternately to that if somebody can tell me how to properly diagnose my alternator another way it would be much help as well. Battery shows ~12.8V when ignition is off, 14.3-14.4V when the car is running but drops all the way down to the 11-11.4V range when only two compressors are on and every few days my car doesn't seem to want to start. This is what leads me to believe the alternator is putting out SOME current, just not enough.

[Stonewall]

Re: WTBorrow - mk4 alternator or ammeter

I have the one off my 2L you could borrow. Likely only a 90A though. Sounds like a bad regulator on the alternator. You could always pull it out and check the brushes.

[MechEngg]

Re: WTBorrow - mk4 alternator or ammeter

I have the one off my 2L you could borrow. Likely only a 90A though. Sounds like a bad regulator on the alternator. You could always pull it out and check the brushes.

Thanks i'll take you up on that offer. Is it on or off the car? I could come see ya sometime this week and bring that rolling frame for you and pull it pretty quick?

[roofprop]

Re: WTBorrow - mk4 alternator or ammeter

I got a 120 thats off the car, its from a TDI tho, not sure if that makes a difference. im also in cochrane.

[danosaur]

Re: WTBorrow - mk4 alternator or ammeter

You sure you don't have a parasitic drain somewhere? I don't know what kind of voltage the battery should show with the comps on, but over 11 still seems like it would be ok for short periods without killing your battery.

[MechEngg]

Re: WTBorrow - mk4 alternator or ammeter

You sure you don't have a parasitic drain somewhere? I don't know what kind of voltage the battery should show with the comps on, but over 11 still seems like it would be ok for short periods without killing your battery.

That is the next step. The battery voltage keeps draining from ~12.8 when the car is just turned off to ~~12.2 overnight then the next day its down to ~11.4 then today it was 10.5. Definitely a drain somewhere

But the voltage is very low when the comps are running so i need to get the alternator rebuilt. The 90A alternator Brent lent me shows ~13.5V when two compressors are running vs the 11-11.4V that the 200A alternator provided. Something wrong there.

[Stonewall]

Re: WTBorrow - mk4 alternator or ammeter

I am guessing it is the regulator. Did you check the brushes on it or for signs of discolouration from overheating?

[danosaur]

Re: WTBorrow - mk4 alternator or ammeter

Definitely sounds like a compounding issue. Hook up a multimeter in line with your negative post on your battery.. let it sit for 30-45 minutes and see what you get. Start unplugging things until the current drops. You've got the alt figured, at least this one is free!

[Stonewall]

Re: WTBorrow - mk4 alternator or ammeter

Multimeters are only good for 10A so that is not a good idea. Will need a DC clamp ammeter.

[p951]

Re: WTBorrow - mk4 alternator or ammeter

The car won't be running when your checking for parasitic draws, any multimeter will suffice.


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[MechEngg]

Re: WTBorrow - mk4 alternator or ammeter

Definitely sounds like a compounding issue. Hook up a multimeter in line with your negative post on your battery.. let it sit for 30-45 minutes and see what you get. Start unplugging things until the current drops. You've got the alt figured, at least this one is free!

Yup following the VW bulletin for their method of checking fuses. Thing is that i don't think it's one of the normal components such as interior circuit, thinking it's more along the lines of the FCM or airride system

Multimeters are only good for 10A so that is not a good idea. Will need a DC clamp ammeter.

I'm not using the multimeter inline, measuring voltage drop across the fuses is less accurate overall but it will help eliminate circuits. The entire fusebox inside the car is ok so that's why i'm leaning towards the airride or FCM because the airride is on the 75X circuit and my fan's aren't kicking on and i'm overheating.

[Stonewall]

Re: WTBorrow - mk4 alternator or ammeter

Why aren't you running the airride on its own dedicated power line from the battery? You could always put a relay in if you want the power switched.

[MechEngg]

Re: WTBorrow - mk4 alternator or ammeter

Why aren't you running the airride on its own dedicated power line from the battery? You could always put a relay in if you want the power switched.

Air has a constant which is from the battery and a switched from the 75x.