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Wed Jul 25, 2012 5:43 am

i've got the alternator out of the car is there any i can bench test it? please help, the charge light was on when running,,

Wed Jul 25, 2012 8:36 am

you can bench test just about any thing, but you failed to ID that Alt.
including the engine.

there are many , at least 4 types. Bosch, Mot, internal and external regs.

a photo helps. is your car a TYPE2,? if yes, why post here but you are welcome to try,but why post with out a Car year or type.?

the full tests are a load test and that needs a special setup.
but you can do many tests off car. sure can.

is it dead or alive test.?
you can check that the full on mode works. on some...
if external reg you can do far more.

if you have a load resistor of 30amps ( .5ohm 500 watt load bank)
you too can do a full load test.
a cheap way to do that is to discharge a battery 50% and use that as the load.
tell more get more.
what ALT, what is the PN, or a photo.?

yours take a diff. set up but you get the idea, right>?

Wed Jul 25, 2012 3:17 pm

it is out of my 74 super beetle, it has a external regulater, can i spin it up with a electric motor and check it for voltage?if so where do i check it has a positive pole and a plug

Wed Jul 25, 2012 4:00 pm

74
is it bosch or motorola.?
so far, i know its external regulated
some alternators will not wake up with out a battery.
but it dont take much of one, just a 12vdc lead acid battery, .
but...

one test is spin it and listen for bad bearings.
there is a no load test.
doing the on car FULL FIELD test , invites blowing up lots of lamps radio
and other electronics. so dont do that. but on a bench there is no limits.
only time and tools.

the Alternator, alone is has a field lug. it goes to the rotor, mag coil.
if you connect the field to B+ , the residual mag, in the core may self start
the alternator, just by spinning it.
meter minus to case
meter on 20vdc range
and meter Plus to the B+ large lug on the alternator
spin it by hand see if you get an output?
or with a drill at 1000 rpm or more.

one way to get it to work for sure, is just connect
any battery to the field pin, a lantern battery or what ever.
meter stays on B+ and case ground.
battery to Field pin and ground , plus to field.

this will cause a large magnetic field ,in the rotor bobbin coil.
then the alternator, then wakes up and produces a very large voltage
with nothing connected to the B+ but a meter.
Keep in mind that it can shock, you if you spin it too , fast ,so dont
put hands on B+,while spinning it. (no load)

the faster you spin the more voltage. you can even weld like this if you spin it fast enough.
this will prove its alive. (a really basic test)

for more tests , it takes a load bank. or a battery used as a load
and some very heavy wire.
and you can even connect the cars reg (pulled) and hooked up on the
bench, and with battery test away.

im not sure, if Autozone can do the Bosch or the MOT. ? (no reg)
I suspect NOT.

now the the 2nd question again.
which one..... all gens and alts are diff.

Wed Jul 25, 2012 5:49 pm

it is the one in the middle the dirty one externally regulated, thank you verry much i'll check it out tomarow,,

Thu Jul 26, 2012 5:14 am

it's a motorola? you never said. does it have markings...
if you give accurate answers we can get some accurate facts
like Pinout's, do you know that term? it means what pin does what.?

with the PinOut, you can test it.

some alts have Stator pin.
A Field DF
A ground pin D-

if it has a stator pin, ground that for the test or the B+ will be dead.

mot wiring
http://www.netlink.net/mp/volks/schem/altreg.gif

here is the R Atwell drawing that shows what needs to work and not.

the Bosch AL82N

to really test the alt.
all those diodes inside need testing. that takes a meter or running a scope.
the alternator is really a 3 phase A/C generator. 6 diodes in a group !
it rectifies the A/C into pulsating DC (can be seen on a scope)

if 1 diode open, you lose 1/3 of the full power. 50amps becomes 33 amps.

the other 3 diodes. they are the D+ boot strap diodes.
they are used to power the regulator and the field.

On the Mot gen. the dash lamp sends power to the reg and field.
this creates the beginning mag field to start up the ALT.
so on the bench wire a lamp to D+ and the test battery.
i will make a schematic for you. to see this test

best of Atwell, its all there...

http://www.ratwell.com/technical/ChargingSystem.html#testalt

Thu Jul 26, 2012 5:47 am

for you

by no means is this a full tests, Atwell lists them and shows each,
but you can do a its dead or not dead test.
it does not test all the diodes, in fact 7 diode can be missing ,or burned open and pass this test.
keep in mind its a 3 phase generator. only 1 phase working passes this test.
really, the Alternator is really 3 generators inside. if you look close... you see it.

this also lets you listen to the bearings ,with out the exh, noise... or other noises. they should purr not buzz.