Testing alternator.

Bought an '87 Accord hatchback recently (2.0l, 2bbl, 5spd)... owner was
selling it because the alternator "didn't work". Seemed to me that it
worked, but not 100%. In any case, I swapped in the alternator from my
identical '87 sedan that had just bit the dust, and all was happy until
a couple nights ago: charge light flickering, dashlights dim, except
when revving high. Typical indication of bad brushes. Figured I was
doing okay trying to get home when suddenly the charge light came on
solid and wouldn't go out for anything. JUST made it home, engine
sputtering every time I hit the brakes.

So today I pulled apart the original alt. and checked it out: diodes all
test fine, field windings seem okay, no opens or shorts anywhere.
Brushes weren't too badly worn, so not really sure what was wrong with it.

Got the replacement alt. out of the car (finally - some Japanese SOB
needs a serious bitchslapping over the layout of that engine) an opened
it up... brushes were REALLY worn, but still making contact - barely.
Diodes and windings checked okay as well.

Now the only thing I can't test is the voltage regulator. Or can I?
With a stanard multimeter, that is, since I don't have a nice
super-duper alternator/starter bench tester sitting on my kitchen
table...?

I took a few readings across various terminals of both regulators, DMM
set to Diode Check, and got several readings that differed between the
two... for example, testing from "terminal A" (named arbitrarily for the
sake of argument) to terminals B and C on one regulator showed infinite
resistance, but on the other, they showed about 1200Mohms aa 1800Mohms,
respectively. Reversing the leads, the first regulator showed 1200 and
1500 (B-to-A and C-to-A), but the other, I got 1500M and infinite,
respectively. Obviously I don't know which one is "right" reading, and
it's not enough to make an intelligent diagnosis.

So... does anyone know of any way I can test the regulator? Or better
yet, know how I can hook up the alternator on the bench (ie. what goes
to what connections) and test it there, maybe spin it up with my
cordless drill?

TIA...

 

There isn't any great way to test it on the bench with common tools - it is
a lot easier to test it in service with a DMM. However, most major auto
parts stores have a test jig, where they can spin the alternator with an
electric motor and measure the output under various loads... and they will
do it for free.

Mike

 

There isn't any great way to test it on the bench with common tools - it is
a lot easier to test it in service with a DMM. However, most major auto
parts stores have a test jig, where they can spin the alternator with an
electric motor and measure the output under various loads... and they will
do it for free.

Mike

 

There must be some way to test the regulator module itself - supply
juice to the inputs, measure the outputs? As I say, all the other
components are fairly "testable" on their own and seem to be fine...

 

There must be some way to test the regulator module itself - supply
juice to the inputs, measure the outputs? As I say, all the other
components are fairly "testable" on their own and seem to be fine...

 

Maybe, but I'm not sure. Some old voltage regulators used analog drivers,
but I think all of them now are switch mode, pulsing the inductance of the
field. You could connect the regulator to the alternator and measure current
drain as you turned the input voltage up - the current should drop rapidly
as you exceed the regulator point (somewhere around 14 volts).

Mike

 

Maybe, but I'm not sure. Some old voltage regulators used analog drivers,
but I think all of them now are switch mode, pulsing the inductance of the
field. You could connect the regulator to the alternator and measure current
drain as you turned the input voltage up - the current should drop rapidly
as you exceed the regulator point (somewhere around 14 volts).

Mike

 

Cool, except it still has to be in the car for that, which in itself is
a nightmare, and at that point is wholly inaccessible Assuming one
determines which connections are which on the thing, too.

I guess that's what I'm really hoping, is to find the pinouts for the
module; given those, I may be able to at least tell, without putting it
all back together and into the car, whether either of the two regulators
I have are *obviously* faulty.

Recall that the original alternator in the car worked intermittantly,
and upon disassembly and testing, the brushes seem sufficient and
everything else I CAN test (windings, diodes) seems good, so that leaves
the regulator as "questionable".

The behaviour of the second one worries me a little, the way it was
doing the typical worn-brush thing for only a little while before
packing it in completely: again, the brushes are obviously gone, and
everything else tests fine, and I don't want to put it all back together
and into the car only to discover the regulator is pooched. A simple
works/doesn't-works test is all I'm looking for.

 

Cool, except it still has to be in the car for that, which in itself is
a nightmare, and at that point is wholly inaccessible Assuming one
determines which connections are which on the thing, too.

I guess that's what I'm really hoping, is to find the pinouts for the
module; given those, I may be able to at least tell, without putting it
all back together and into the car, whether either of the two regulators
I have are *obviously* faulty.

Recall that the original alternator in the car worked intermittantly,
and upon disassembly and testing, the brushes seem sufficient and
everything else I CAN test (windings, diodes) seems good, so that leaves
the regulator as "questionable".

The behaviour of the second one worries me a little, the way it was
doing the typical worn-brush thing for only a little while before
packing it in completely: again, the brushes are obviously gone, and
everything else tests fine, and I don't want to put it all back together
and into the car only to discover the regulator is pooched. A simple
works/doesn't-works test is all I'm looking for.

 

Is there anything wrong with taking your alternator to a parts store
for testing on their machine? Next town over has a Checker parts
store with at least one real competent guy who would test yours.


Tom Willmon
near Mountainair, (mid) New Mexico, USA

Sure it's funny! Now beam my clothes down Scotty!

Net-Tamer V 1.12.0 - Registered

 

Is there anything wrong with taking your alternator to a parts store
for testing on their machine? Next town over has a Checker parts
store with at least one real competent guy who would test yours.


Tom Willmon
near Mountainair, (mid) New Mexico, USA

Sure it's funny! Now beam my clothes down Scotty!

Net-Tamer V 1.12.0 - Registered

 

Did that. Tested fine. Put it back in the car. Now it works
intermittantly. It'll run 13V at idle, up to 14.1 at speed, but if I
start turning stuff on (lights, blower) it'll drop below 12V; ie. not
charging at all. Turning everything off again, it takes upwards of 30s
of revving to start charging again.

I'm wondering if a brush isn't in quite right, as there's a 'ticking'
sound coming from it now that changes with engine speed.

 

Did that. Tested fine. Put it back in the car. Now it works
intermittantly. It'll run 13V at idle, up to 14.1 at speed, but if I
start turning stuff on (lights, blower) it'll drop below 12V; ie. not
charging at all. Turning everything off again, it takes upwards of 30s
of revving to start charging again.

I'm wondering if a brush isn't in quite right, as there's a 'ticking'
sound coming from it now that changes with engine speed.

 

Unless you know how to rebuilt it yourself, I advise you to buy a new
alternator. Another option is to visit a car junk yard. If the manager or
owner is on a database of thousands of junk yard, he can order you one
even if he does not have one in stock. The owner or manager may even
provide a warranty for it in case it does not work. I once found a wrecked
car just like the one I owned at that time and got lots of parts off of it
for almost nothing.

 

Unless you know how to rebuilt it yourself, I advise you to buy a new
alternator. Another option is to visit a car junk yard. If the manager or
owner is on a database of thousands of junk yard, he can order you one
even if he does not have one in stock. The owner or manager may even
provide a warranty for it in case it does not work. I once found a wrecked
car just like the one I owned at that time and got lots of parts off of it
for almost nothing.