I see plenty of videos testing it in the running car, but what about a junkyard alternator before installing it in the car? I can put a socket in a drill to spin the pulley. I assume you put the positive voltmeter cable on the fat + post on the alternator. Do you put the negative cable on the case? Or on one of the terminals of the 4 pin connector?
Can you bench test an alternator?
- Thread starter atikovi
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You have to know what kind of alternator you have first and ask about it at the parts store.
If you take it to a place where they rebuilt them I am sure they'll know how to test them.
If you take it to a place where they rebuilt them I am sure they'll know how to test them.
I feel guilty having them test it knowing I will not buy one from them.
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Yes, negative on the case will work. Per alternator, I would find a diagram to see if it does or doesn't need to be fed 12v. With that, you could then probably just jump from the (+) terminal to the pin on the ALT and then see what it puts out. I'd think service data should tell you per ALT what the volts or amps output should be at a certain RPM.
I could connect a battery to it if it's case grounded.
When I worked at CT in the parts dept. years ago, that was one of our regular duties.
We even had a display setup at the parts desk where we could test it right in front of the customer.
I think they all need a 12v feed to turn them on.
An alternators output is taken from the stator windings but to produce an output a wound rotor has to be exited by a 12 volt supply into producing a magnetic field. Alternator output is controlled by the voltage regulator switching the excitation rapidly on and off. I think in some cases residual magnetism in the rotor can be enough to kick start an output provided the rotor is spinning fast enough.
If you connect the alternator to a battery, that will provide the excitation and you will be able to tell if the alternator is charging by seeing the voltage rise from 12 volts or so to 14 volts.
Not nearly that simple. There are one wire alternators that use resudual magnetism to turn on. There are some that need an alternator lite.
There are some that are controlled by the ECM, and some with a regulator that is controlled by the ECM. Some have limp home ability, some do not. Some have charge voltage computer controlled. Or controlled by a termister at the battery. I suspect that some talk over the CAN bus. Auto part stores have the adapter cables to test most of them
Rod
Ragtoplvr is right, it's not nearly that simple.
I think they all need externally supplied 12VDC to power them (many get their power through the dash mounted alternator lamp). But many/most also required some kind of control signal from an externally mounted voltage regulator. The 1970s/80s/90s Chryslers had to have a Ground signal from the VR to turn them on as well as 12 volts from the ignition switch. The alternator in the newer cars are also computer controlled and that's a LOT more complex. Also a lot of alternators can output 150 Amps (or more) at about 14 VDC, so that's roughly 2100 Watts of power. One horsepower is roughly 750 Watts so even at 100% efficiency (it's not) it will take almost 3 horse power to drive the alternator if you want to test it at full power. No drill is going to do that.
Tip: Advance Discount Auto Parts will test them for free.
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The wiring schematic for the alternator connections should tell you what you have and what you need. Post them up if you have access?
I assume this alternator is a general PIB to replace?
I assume this alternator is a general PIB to replace?
When was the last time a new vehicle with a one wire alternator was sold in North America?
I do wonder about riding mowers though.
My riding mower just has coils under the flywheel with magnets on the flywheel. It's technically a generator, not an alternator.
Why feel guilty? They are offering to test the parts for free to garner good will in the hopes that when you need something you'll hopefully remember your positive experience(s) with them and purchase that next whatever part you need from them.
Just like with their Duralast brake pads and shoes - they warrant them for life even if they wear out from normal use, or as I was told by one of their employees, just bring the old pads/shoes in, tell us they are noisy and we'll give you a brand new set of pads/shoes for free (to paraphrase).
Heck AutoZone's Duralast Max pads have lasted way longer (both length of time in service and mileage) than the Wagner ThermoQuiet pads I had on two of my vehicles before the Duralast Max pads. Those will be the last pads I'll ever buy for those vehicles and I keep them until they die, are stolen, get wrecked, whatever.
Just like with their Duralast brake pads and shoes - they warrant them for life even if they wear out from normal use, or as I was told by one of their employees, just bring the old pads/shoes in, tell us they are noisy and we'll give you a brand new set of pads/shoes for free (to paraphrase).
Heck AutoZone's Duralast Max pads have lasted way longer (both length of time in service and mileage) than the Wagner ThermoQuiet pads I had on two of my vehicles before the Duralast Max pads. Those will be the last pads I'll ever buy for those vehicles and I keep them until they die, are stolen, get wrecked, whatever.
The PCM input on most alternators is actually easy to fool; I know on Chryslers which have been externally regulated since the late 80s, all the PCM input is basically a variable resistor to ground using the temperature sensor data. You can actually ground the green alternator input wire usually to have it go to full 100%.