Battery and Alternator Info Required

ksaudi · 15-02-13, 05:20 AM

Re: 5-10-1990 - Audi Quattro Coupe 20V - 2309 cc - 5 Cylinder -
Chassis No: WAU ZZZ 8 BZLA 018736 - Engine No: 7 A 014151

I do low mileage but have not had starting problem except for last few years when battery has gone flat after a few months.
My battery supplier says battery is fine but has asked me if I can find out exact Battery and Alternator spec (amps) for the car. Cannot see any label on the Alternator which has been changed in the past. My Audi mechanic tells me that the alternator was probably 120 amp but there were a few 90 amps about and the Battery was 63 amp.

Can anyone kindly give me definite figures or tell me how I can obtain them?

Thanks very much.
Keith

John. · 15-02-13, 08:48 AM

Regardless of alternator and battery, if the parasitic drain is too high then this will discharge the battery.
I have the same model of coupe.....have left it for 1 month and had no problems. I'll try and check today the battery spec.
Most multi-meters have an amps function....easy to test(drain), not as easy to trace a problem if there is one though.

John.

msh · 15-02-13, 11:35 AM

What mechanic said could be true, apart from the fact that I doubt that there was 120A alternators in B3 cars - IIRC on more luxurious C3 cars there was only optional 110A alternator, which I'm not sure if ever was fitted on B3 from factory, while 120A alternator came only with multi groove belt.

When I will have need to replace my battery, I will go for biggest possible to put in battery tray [which will be diesel battery of about 85 Ah capacity], currently I've installed 110A alternator but in the future I'll go for 120A alternator.

As for leak testing - most cheap-ass multimeters have only 200 mA max current, which is not enough, unless measurement is done with skill, as some devices might draw considerably more at the moment when power is restored. Some time ago I tried to measure power drain in such a way, which resulted in blown multimeter fuse. Next time I will use mechanical ampermetre, as it doesn't have any fuses, while it will be able to survive current spike. Otherwise I agree with John.

John. · 15-02-13, 03:42 PM

Checked drain, first pic shows without alarm on.
When alarm was set the current draw blipped up to 0.04amp now and again.(pic 2)
The third pic was with an amp clamp on as well, this is a great tool for checking alternator output and the likes but as can be seen in the picture is no-where near as accurate for drain testing as the multimeter.
Battery fitted to my car is an 096 type, 680 amp cold cranking amperage(doesn't show a figure for reserve capacity)

mikes2 · 15-02-13, 03:53 PM

Standard alternator on the 7A was 90A unless the car had air conditioning. These came with 110/115A versions

ksaudi · 16-02-13, 06:13 AM

Thanks for all replies. No air con, so it looks as though alternator should be 90 amp.
My battery supplier is more used to seeing alternator output on an Audi of at least 85 plus and wondered whether mine at 76 amp was keeping up with my 74 amp battery - he is accustomed to seeing a 10 amp plus buffer between battery and alternator, hence his wish to know battery and alternator spec.
Could I get your opinion on whether you think low alternator output combined with short journeys/low mileage could be the problem?
Thanks
Keith

msh · 16-02-13, 08:35 AM

Short journeys/low mileage could be problem with any alternator. This winter I'm additionally charging my 6 years old battery around once a month as my usual daily trip is 1,4 kilometres to work and after 12 hours the same distance back, which apparently is not enough to charge the battery.

As for weak alternators - even 65A [came on smaller 4 pot engines] is enough if care is taken and especially if the car is equipped with aux gauges, allowing to monitor voltage. Back in the days with 65A alternator I was able to use simultaneously engine, headlights, heater, cd player + amplifier and heat something - either my arse or rear screen.

John. · 16-02-13, 11:03 AM

Keith.
A point of interest......it's not the alternator that decides how many amps goes into the battery, it's the battery.(ohms law)
If you have a 120 amp alternator or an 80 amp alternator, if the battery only wants 30 amps then that's all it'll take. But if you were using a further 60 amps(unlikely) in running the car, this is where the 80 amp alternator would fall short(30+60=90).
If your battery has been tested as ok then assuming nothings draining it then a trickle charger might be the answer.......a car battery is designed to supply a high amount of power for a short time(cranking engine), not designed for a tiny drain over a long period......a charger/conditioner would overcome this.
I suspect your car is fine(hey, it's a 23 year old Audi !)......it's the infrequent running that's the problem.

John.

15-02-13, 03:53 PM	#5
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	Standard alternator on the 7A was 90A unless the car had air conditioning. These came with 110/115A versions __________________ 1991 90 quattro 20v sport 1991 90 quattro

15-02-13, 08:48 AM	#2
John. 4 ring whore! Classic Audi Club Member Join Date: Mar 2011 Location: Scottish Borders. Posts: 7,540	Regardless of alternator and battery, if the parasitic drain is too high then this will discharge the battery. I have the same model of coupe.....have left it for 1 month and had no problems. I'll try and check today the battery spec. Most multi-meters have an amps function....easy to test(drain), not as easy to trace a problem if there is one though. John.

15-02-13, 11:35 AM	#3
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	What mechanic said could be true, apart from the fact that I doubt that there was 120A alternators in B3 cars - IIRC on more luxurious C3 cars there was only optional 110A alternator, which I'm not sure if ever was fitted on B3 from factory, while 120A alternator came only with multi groove belt. When I will have need to replace my battery, I will go for biggest possible to put in battery tray [which will be diesel battery of about 85 Ah capacity], currently I've installed 110A alternator but in the future I'll go for 120A alternator. As for leak testing - most cheap-ass multimeters have only 200 mA max current, which is not enough, unless measurement is done with skill, as some devices might draw considerably more at the moment when power is restored. Some time ago I tried to measure power drain in such a way, which resulted in blown multimeter fuse. Next time I will use mechanical ampermetre, as it doesn't have any fuses, while it will be able to survive current spike. Otherwise I agree with John.

15-02-13, 03:42 PM	#4
John. 4 ring whore! Classic Audi Club Member Join Date: Mar 2011 Location: Scottish Borders. Posts: 7,540	Checked drain, first pic shows without alarm on. When alarm was set the current draw blipped up to 0.04amp now and again.(pic 2) The third pic was with an amp clamp on as well, this is a great tool for checking alternator output and the likes but as can be seen in the picture is no-where near as accurate for drain testing as the multimeter. Battery fitted to my car is an 096 type, 680 amp cold cranking amperage(doesn't show a figure for reserve capacity)

16-02-13, 06:13 AM	#6
ksaudi Grown up member Classic Audi Club Member Join Date: May 2010 Posts: 51	Thanks for all replies. No air con, so it looks as though alternator should be 90 amp. My battery supplier is more used to seeing alternator output on an Audi of at least 85 plus and wondered whether mine at 76 amp was keeping up with my 74 amp battery - he is accustomed to seeing a 10 amp plus buffer between battery and alternator, hence his wish to know battery and alternator spec. Could I get your opinion on whether you think low alternator output combined with short journeys/low mileage could be the problem? Thanks Keith

16-02-13, 08:35 AM	#7
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	Short journeys/low mileage could be problem with any alternator. This winter I'm additionally charging my 6 years old battery around once a month as my usual daily trip is 1,4 kilometres to work and after 12 hours the same distance back, which apparently is not enough to charge the battery. As for weak alternators - even 65A [came on smaller 4 pot engines] is enough if care is taken and especially if the car is equipped with aux gauges, allowing to monitor voltage. Back in the days with 65A alternator I was able to use simultaneously engine, headlights, heater, cd player + amplifier and heat something - either my arse or rear screen.

16-02-13, 11:03 AM	#8
John. 4 ring whore! Classic Audi Club Member Join Date: Mar 2011 Location: Scottish Borders. Posts: 7,540	Keith. A point of interest......it's not the alternator that decides how many amps goes into the battery, it's the battery.(ohms law) If you have a 120 amp alternator or an 80 amp alternator, if the battery only wants 30 amps then that's all it'll take. But if you were using a further 60 amps(unlikely) in running the car, this is where the 80 amp alternator would fall short(30+60=90). If your battery has been tested as ok then assuming nothings draining it then a trickle charger might be the answer.......a car battery is designed to supply a high amount of power for a short time(cranking engine), not designed for a tiny drain over a long period......a charger/conditioner would overcome this. I suspect your car is fine(hey, it's a 23 year old Audi !)......it's the infrequent running that's the problem. John.