How to bench test alternator

[Perry]

Hi,

I have an alternator from a 98 sidekick kicking around here that I can’t remember if it’s good or not and I was going to sell it  to someone. If I put a drill on the pulley nut and spin it, with the ground lead of my tester on the alternator body and the positive lead on the big stud I only show about 0.5 volts. I know some alternators need to be wired up a certain way to show charging. Not sure if this is the same. I looked at your diagram and was wondering if the charge “sense” circuit needed to be recreated.

Thanks!    

[fixkick]

Hi,

I have an alternator from a 98 sidekick kicking around here that I can’t remember if it’s good or not and I was going to sell it  to someone. If I put a drill on the pulley nut and spin it, with the ground lead of my tester on the alternator body and the positive lead on the big stud I only show about 0.5 volts. I know some alternators need to be wired up a certain way to show charging. Not sure if this is the same. I looked at your diagram and was wondering if the charge “sense” circuit needed to be recreated.

Thanks!

what a great question, how to test any alternator off car,  all auto-stores (most) have that machine in the store, to test alternators.  
go there and ask? .
one top failure is not alt dead but bearings shot and makes huge noise spun. fast. and does spin way faster than engine.

98 sidekick, G16 or J18?//??? they are not the same.

the only real test is on any motor spinning and a real battery in place.
try to know that the internal regulator inside, must NOT THINK (detect) that there is a MISSING battery , nor shorted, or the ALT reg, shuts it all down, to prevent 2 things.
1: blowing up a battery (acid flying) and not wreck it self. trying.
2: if battery missing it will not want to run, due to huge possible factors of going over 15vdc and blowing up all electronics in the car and  busted bank account there.


now to answer the question. actual
first off the alternator will  be dead 1/2 the time if the dash idio lamp is missing , the lamp is the self excitation current to get the alternator to boot up, and make power.
the fact is , some alts have residual magnatism in the rotor and self excite ok, but is a coin toss that.

off my charging page is this. G16 ONLY !

1. first is  a real battery.
   
2. then the lamp
   
3. then black-white jumped to B+ big stud , or the alternator will be dead.
   
4. must  be spun fast enough to wake up the REG.  (on car 800rpm is engine but alt is way faster 3 times?) IDK ratio. It say over 200 RPM on ALT.( finger raised to wind)
   

most alts wake up at 600 RPM engine actual. alt spins 3 times faster, see that tiny pulley on alt?>yah. (2" over 6" is 3:1) by seaman's eye.



 
here is REG guts, if lamp is missing, R1 is dead, if there is residual mag. Diode Trio wakes up and feeds R1. and magic happens.
the reg must go online of the rotor coil is dead and so be ALT,  what  cool schematic no?   some cloned ALTS  will  act different !(clone =  random 3rd party makers)
the sense wire is never optional.

[Perry]

Thanks for the detailed response as always. I tried it without the lamp first. I jumped back/white to the big stud (battery positive) but had no luck. I will try again with the lamp added. The lamp goes on white red and the other side ground, correct? I will let you know what I find out.

I would rather not have to installed the alternator to find out if it works. No where to bring it to get tested on a Sunday. And I don’t think any shops around here have complimentary testing. (No autozone, etc.)

[Perry]

Also, maybe a dumb question but it doesn’t matter which was it spins, does it?

[fixkick]

I thinks so,  the stator and diode bridge works, and so would the rotor. but the nut might come loose, not sure that.
clock wise from front. normal. 
but OMG , never tried that ever. I will ask the wind generators guys.

a valid test is under load, and full RPM
or at least partial load, and minimum RPM. 
alternators only work at min. RPM,
here is the top GM alternator spec, this is alternator  RPM not engine , engine spins about 4 x less.  so 2000 divided by 4 is 500 rpm on engine, but that is missing so 2000 is it.
this fact is why alternators best generators out in 1960s.



the electrics don't care on rotation, the fields generated (mag) are  not reversed only direction is changed, and the slip rings do not care either, so should work backwards CCW.

[fixkick]

the wind mill power generator pages shows this.
"Typically, the lowest speed at which a car alternator is able to generate 12VDC is about 1,800RPM."
my Delco chart above shows same.
so spinning it by hand does nothing.


the math and faradays laws are here on topic.

https://digitalcommons.calpoly.edu/cgi/v...ntext=eesp


in the auto store the machine there has huge fast electric motor to spin it up.
the suzuki is 5000 rpm crank shaft and x4 is 20,000 rpm alternator. (the pulley ratio dictates that)

[Perry]

So I finally got it figured out! A couple things I learned:

1. The charge light needs to be hooked up for it to work
2. it seems to only want to work when spinning clockwise (when looking at pulley)

When I first hooked up the charge light it would not work, this is because I hooked one side of the bulb to the spade connector where white/red goes and the other to ground (light a normal light). But after looking at the diagram again the white/red goes to the spade on alt and the other side goes to the battery(+), the spade is grounded when no charge is being put out. The the back/white spade goes directly to battery (+) or big stud on alt.

When the charge light would not come on at first I almost gave up and brought it to recycle, good thing I double checked.

video for those who are interested: https://streamable.com/vh8u80