Is My Alternator Bad?

[daisybug]

So my battery died on me yesterday, and we bought a new one. We didn't test the alternator until later last night. We tested it at Advance Auto, and it tested a 1.7 amp. They said the alternator was supposed to be 70 amp. I also heard from someone that Bugs test low. So what do yall think? Do I need a new alternator? To me that seems really low, so we ordered one just in case, (we can send it back if we need to). Also, my bug is 4 years old but it has only 35,000 miles. What do you think?

I appreciate it so much!

Daisybug

[Porkchop]

Usually with a bad alternator, you're concerned with low volts, not the amps. If it was reading 13.5 to 15.5 volts, it should be good. Lower than that, and its bad.

I tested alternators for 2 years with the same machine.

[daisybug]

Thank you so much! I really appreciate it!

[noR]

Very well could be a bad alt. But I'm not sure from the amp reading. Just haven't seen that done. But I do believe the beetle amps are in the 70, 60, 90 range... somewhere in there... 1.7 is WAY low. :P

I've known a bad alternator to cause all sorts of problems to the battery as well.

[styleandspeed]

Originally Posted by Porkchop

Usually with a bad alternator, you're concerned with low volts, not the amps. If it was reading 13.5 to 15.5 volts, it should be good. Lower than that, and its bad.

I tested alternators for 2 years with the same machine.

Sorry man, but that is not true. I work at an auto parts store and have tested hundreds of alternators, and if it is only putting out 1.7A, then it doesn't matter how many volts it is putting out.

It wouldn't be a bad idea to get a second opinion on the alternator though, because if the guy you took it to didn't know how to use the amp probe it could be the cause of those low readings.


When the battery died, what was going on? Did it happen while driving, sitting at a stoplight, or did your car just not start?

[Porkchop]

Originally Posted by styleandspeed

Sorry man, but that is not true. I work at an auto parts store and have tested hundreds of alternators, and if it is only putting out 1.7A, then it doesn't matter how many volts it is putting out.

It wouldn't be a bad idea to get a second opinion on the alternator though, because if the guy you took it to didn't know how to use the amp probe it could be the cause of those low readings.


When the battery died, what was going on? Did it happen while driving, sitting at a stoplight, or did your car just not start?

Here's a thought... at 1.7amps, how could the car be running? So the amp reading is worthless.

[Don_n_Herbie]

Off the battery till its flat

[daisybug]

Thanks much to everyone...but went and tested it again, and it's fine!

[Porkchop]

Originally Posted by Don_n_Herbie

Off the battery till its flat

Amps is current... which is pulled by ignition coil, etc. with the car running. Whether it is receiving power from the battery or the alternator, if anything electrical is running, it is pulling amps. Therefore, whether the alternator is working or not, it would show amps. The fact that is reading 1.7 amps means nothing as far as whether or not the alternator is good or bad. All it means is the inductive amp probe is only picking up 1.7 amps which could be a calibration issue or a bad amp probe (which is very common - one time dropping the probe on the concrete will cause it not to work correctly - and very few stores keep their equipment in good repair). To test the alternator, the car has to be running... which means amps are being pulled for the ECU, fuel injectors, ignition coil etc at a minimum.... that all takes more than 1.7 amps.

Therefore, I still recommend you look at the volts reading from the alternator test to see what it is showing, because surely the parts jockey can correctly hook up the machine to the + and - battery terminals. A reading under 13 volts is going to indicate the car is running off the battery and the alternator is not outputting correctly.

When I was a store manager for both Advance and Autozone this is what we primarily looked at when determining alternator status when the alternator is still on the vehicle. A better test is the machine inside because it isolates the alternator - but does require you remove the alternator. If you want to be absolutely certain, you can always have them test your old alternator when you take it in to get your core refund.

[John Koch]

With engine off attach a digital multi-meter to the 2 poles of the battery. Negative cable from meter to negative terminal and of course, positive to positive... With key in the off position, the voltage should read 12.6. This would indicate a full charge. If it reads 12.4, this indicates only a 75% charge. Leaving meter attached start engine and see what the voltage is now. It should be at least 13.8 to 14.5 volts..It may start low and increase in voltage as you increase the engine RPM's. It should never reach 16.5 volts or damage to battery and additional charging components could occurr. Next run engine at 2000 RPM and turn on several heavy draw components like the head lights, fan blower motor on 4, seat heat or rear window defrost and any other heavy draw acssesories. With RPM at 2000, battery voltage should be at least 12.0 volts for our cars...This indicates a sound battery and charging system. Also, remember that VW routes the battery voltage supply thru the generator warning light on the instrument panel. This light should be checked for proper action by turning key to the on position and observing the dash. If this light does not come on, it must be replaced before the electrical charging and supply system will work properly. Sounds cracy I know, but as per VW techs, this is indeed the case....Good Luck in all your battery and alternator problems... JK

[Pseudotropheus]

When the car is running it should be between 13.5-15.5 volts.
If while the car is running and these voltages are hard to obtain. Then the culprit could very likely be the alternator.

Also, if there using an inductive pick-up to test the amps.
You want to make sure the reading is pretty equal to the rating.

Example would be, 90 amp alt. when clamped, should be reading 90-96 amps while the car is running. if your amps are low, then it means the alt. is weak.

Also, one thing you need to check. Do a starter current draw test on the starter. If the starter is starting to go bad, you may not notice it right away, however the starter can put excessive current draw on the starting system itself giving the appearance of a bad battery. It actually happened on mine.

Battery measured 10.6v ( specific gravity ) was 1.247 ( good ).
Alterntor pushed 96 amps on a 90 amp alternator. Current draw on the starter ( while starting ) SPEC: is 140 amps. You start hittin 150-160 amps on the starter, its time to replace.

After this, the cars voltage went back to normal.

[Pseudotropheus]

Originally Posted by John Koch

With engine off attach a digital multi-meter to the 2 poles of the battery. Negative cable from meter to negative terminal and of course, positive to positive... With key in the off position, the voltage should read 12.6. This would indicate a full charge. If it reads 12.4, this indicates only a 75% charge. Leaving meter attached start engine and see what the voltage is now. It should be at least 13.8 to 14.5 volts..It may start low and increase in voltage as you increase the engine RPM's. It should never reach 16.5 volts or damage to battery and additional charging components could occurr. Next run engine at 2000 RPM and turn on several heavy draw components like the head lights, fan blower motor on 4, seat heat or rear window defrost and any other heavy draw acssesories. With RPM at 2000, battery voltage should be at least 12.0 volts for our cars...This indicates a sound battery and charging system. Also, remember that VW routes the battery voltage supply thru the generator warning light on the instrument panel. This light should be checked for proper action by turning key to the on position and observing the dash. If this light does not come on, it must be replaced before the electrical charging and supply system will work properly. Sounds cracy I know, but as per VW techs, this is indeed the case....Good Luck in all your battery and alternator problems... JK

On the indicator circuit isnt there a resistor inside there to allow that circuit to operate properly? I know alot of them, if the bulb is out, it cant complete the circuit. Like on Ford's they use a bulb and a resistor, in case the bulb goes out so the circuit is unaffected.

[wawalker]

Amperage reading will only show the load on the circuit being tested--so if the car was only idling with no "loads" (lights, stereos, windshield wipers, etc.--you get the idea) pulling amps the reading will be low.