How to Test Alternator - FD3

[leeroy_25]

Guy\'s can someone tell me how to test if my alternator is working.. I have an issue wth my battery light coming on. (explained in another thread)
http://www.mazdarotaryclub.com/forums/showthread.php?t=62220

Am I correct in thinking if I connect a mutlimeter to any live feed and measure the voltage when the engine is running if I am getting 13.5V or more I am getting a charge okay?
Now if I do not then I want to check if charge is leaving the alternator as this is one I have jst swapped over!
So what do I need to measure from to check it properly? There is the main live wire and a two pin lug to choose from. Can I run the car with the plug off to measure from the pins if need be?

Thank you
Lee

[FEED Addict]

connect you multi meter to your battery and check what you got to start with (12.7v ish), then start the car and check again (alternator is now running 14v ish), then wazz all your fans, heaters, wipers,lights, etc on and see what the voltage is should still be quite high (13.5v+)

[ashc]

if there are still concerns after those tests, there is a guide in the mitchell full factory service manual using a ohmmeter with the unit off the car.

[leeroy_25]

Thanks guy\'s.. testing the unit off the car??!

Okay.. I\'ll have a look in my manual.. So there is no on car test?to see if power is coming out of it then? As in directly at the alternator..

Cheers
Lee

[ashc]

not what i meant! follow garys instructions first, that will give you a pretty good idea if the alternator is duff.
but if the problem is intermittent or wildly swinging voltages etc it might be the coils or brushes on the way out, you\'ll then have to test the resistance as per the manual and or disassemble the unit and replace the brushes.

[FEED Addict]

If you get as far as fitting new brushes don\'t forget to clean the \'com\' segments (just gently rub a screw driver or fine hacksaw blade inbetween the copper) and bed the new brushes in by fitting them and honing them to the radius of the \'com\' with a bit of polishing tape.

[DR SCHNITZEL]

I have just got a voltmeter its by gunson. id love to be able to use it for checking more than resistance. ill google it at lunch, so many dial settings. i wish i understood them

[FEED Addict]

I use a Fluke! but got this when i was out on the tools fixing machines!:Tongue1

[leeroy_25]

Hi Gary, it may just be a case of a dudd battery? Here\'s hoping! My battery has gone dead again after only a couple of days which included a 4 mile drive of which 3 miles I had the Alternator light on? I am guessing that should not kill the battery so quick? Anyway. Is the failure in the alternator the brushes then? the one I took off everything seems fine inside.. The diodes or whatever the little canisters at the back connected into the windings are all looked fine. Not sure if they fail and leak like a capacitor?
What is the \'com\'? Please confirm..
Is there anything on the shaft side/core of the alternator that can result in it failing as I only had a back plate part to swap over complete with the outer windings? I hav another core but a fin needs straightening out so it spins freely in the housing.

I should get a battery and fit it Thursday with luck then can do some voltage tests. Does anyone know if a low voltage would cause the ABS light to go on? Also what is the reason the oil and water warning lights come on with the alternator light for?

Thank you
Lee

[MaLicE]

when my alt died last and it was running low voltage (it might be that your battery wont take any more charge) all the lights on my dash were on... have you tried charging your battery? is it a fluid type battery? if so does it have fluid in it?

[leeroy_25]

I think the battery is a sealed unit.. I will check. It appears to take at least some charge.. but I would need to physically charge it to see how much.. I did notice that the green Indicator cell in it that is supposed to glow when it\'s charged doesn\'t glow green anymore.. Even after a lot of charging! Not sure how reliable those indicators are though?
Thanks
Lee

[leeroy_25]

Just to confirm. I last charged the battery last week.. fitted it on Thursday night.. car sat until Sunday.. Then I went for a 4 mile drive in the evening.. lights and fan on.. Warning lights all came on about 1 mile into the drive.. Then car sat again until today.. Went to fire it up this evening and battery is all but dead.. Measured 9 volts with my meter.


Lee

[MaLicE]

i would say its dead then mate, the indicators seem pretty accurate to me, go buy a new one and slap it in, or borrow one from another car and give it a try!

[FEED Addict]

so what your saying is with a fully charged battery (3-4 days prior) you can start the car from cold and run for about 4 miles and the alternator/battery charge light is on for 3 of them! (sounds like alternator is not charging the battery to me)
 
start again dude and test in this order-
 
1:- charge battery up again and test voltage=
2:- connect battery and check voltage (at battery terminals)=
3:- start car and check voltage (at battery terminals)=
4:- Turn all your gubbins on heaters,lights etc and check voltage (yep you guessed it)=
 
 
1= voltage should be at least 12.5-13v
2=very similar to (1) dependant on alarm expect a little drop.
3=should be 14+v ish
4= should be slightly less than (3) if this is down to or less than (1) then your alternator is knack\'d, you could fit new brushes, clean comutator (contacts brushes rub) and meter out rotor windings (should be balanced) (set meter to ohms)
 
 
or take it to an auto electrician who will do the above test in 5mins and may do a drop test on the battery too for a few quid!

[leeroy_25]

I got a good battery sorted today. So I aim to fit and test it tomorrow. Aside the checks at the battery suggested above I have read the manual about testing the alternator and it gives you the expected voltages at each terminal when the car is at idle.. Only thing I don\'t get is it says you cannot earth the main terminal \'B\' on the alternator or the \'L\' terminal which goes to the warning lamp when the engine is running? How on earth do I test them with my voltmeter then? It also says you cannot run the car with the plug going to L and S disconnected!

Any advice please so I don\'t blow anything up that isn\'t already blown!

Cheers
Lee