Howto bench test an alternator?

[gordontytler]

I have my alternator in a vice and I am ready with my volt meter, battery and drill but I am not sure how to wire it up.

My profile has an album with a picture of the circuit diagram. It is almost identical to this http://i275.photobucket.com/albums/jj287/naskeet/VDO-Alt-W-Tach.jpg .

My alternator has B+ , D-, W and D+ connectors and the regulator is inside.

Should I connect the battery to W and D+ and measure the voltage between B+ and D- when I spin it with the drill?

 

[volvopaul]

I have my alternator in a vice and I am ready with my volt meter, battery and drill but I am not sure how to wire it up.

My profile has an album with a picture of the circuit diagram. It is almost identical to this http://i275.photobucket.com/albums/jj287/naskeet/VDO-Alt-W-Tach.jpg .

My alternator has B+ , D-, W and D+ connectors and the regulator is inside.

Should I connect the battery to W and D+ and measure the voltage between B+ and D- when I spin it with the drill?

Before you do that, you need to excite it otherwise it won't charge by wiring a bulb across the warning light terminal.

What amazes me is why electrical engineers and engineers don't test alternators on the boat where sometimes the fault lies in other areas than the alternator itself .

 

[gordontytler]

Before you do that, you need to excite it otherwise it won't charge by wiring a bulb across the warning light terminal.

What amazes me is why electrical engineers and engineers don't test alternators on the boat where sometimes the fault lies in other areas than the alternator itself .

The proposed connection from W to the battery "-" and D+ to the battery "+" was for intended for the rotating coil excitation current. Perhaps I also need to connect D- to the battery "-" to bias the diodes.

I know at last one of the BMW / Mercruiser D 636 engines has faulty wiring or relays and suspect at least one of the alternators is also faulty.

On the sea trial neither produced any charge.

The charge warning light and tachometer are dead for the starboard one, which is on the vice at home. The light and tachometer work on the port one but it doesn't charge. I would guess the wiring is OK on the port engine and the starboard alternator on my vice might working. Fortunately these engines have no computer so I only need to swap some relays between the engines to identify the problem. But there are 8 combinations of relay swaps multiplied by 2 alternators.

I have swapped the warning bulb and it is fine. I may swap the wires to the tachometers.

Trouble is it is out of the water and the hose and oil drum need to be moved if I want to start the other engine. Suppose I could remove the water pump impellers and run the engines dry for a few minutes for each test.

 

[VicS]

Should I connect the battery to W and D+ and measure the voltage between B+ and D- when I spin it with the drill?

No

Check the connections in the engine manual. Hopefully you will be able to confirm that

B+ is the battery + connection ( ie the main output terminal)

W is the connection for a tachometer

D+ is the warning light connection ( without which it will probably not function)

D- is the battery negative connection.

I do not know what you are hoping to achieve

To carry out a meaningful test you need a voltmeter to measure the output volts an ammeter to measure the output current and a means of applying a appropriate load to the alternator.

I suggest that with an obvious lack of knowledge you should take the alternator to an automotive electrician who will have a proper test rig and the means to diagnose any faults.


BTW there are no pictures viewable in your album.... perhaps you have not asked for them to be moderated

 

[gordontytler]

..
BTW there are no pictures viewable in your album.... perhaps you have not asked for them to be moderated

Thanks. I will knock up a rig to simulate the boat and its load. I like technical problems and am working my way down the 500 posts on this forum with the word "alternator". It would be no fun asking someone else to do it. I got a prize for physics at school but that was along time ago

fingers crossed.... the picture should appear here

 

[VicS]

That confirms B+ is the main positive output terminal, W the output signal to a tacho, D+ is the warning light connection but I don't know why it would also go to the starter relay.

 

[Prospect and Sunray]

D+ is the warning light connection but I don't know why it would also go to the starter relay.

I would say that connecting to the starter relay on the warning light circuit is correct, as the alternator will only be energised when ignition is on. Same system as on my boat, different but effective

 

[david_bagshaw]

dont forget if the test does work, you will get a substantial torque reaction at the drill, apart from needing a pretty beefy one any way.


I have a 60 A alternator connected to a briggs mower engine and had to remove thr regulator, as the alternator would take all the engines power and bog it down,to a stall. So I dont imagine you will get a meaningfully measurable output, however it will determine if it is capable of any output.


B+ to batt +

casing and d- to batt -

Bat + via a small bulb to DF for excitation current


spin drill, be ready for either a build up of reactive torque, or a sudden kick as reg cuts in.

if no reactive torque

1 wiring wrong
2 drill not fast enough
3 reg nackered, or other fault.

if bulb flickers, most likely drill not powerful enough, rather than diode probs etc.

Easier method take to car alternator repairer & pay, do your thing first then take, and pay less as they will know by discussion you know something about it.

 

[gordontytler]

Thank you all very much for your advice so far.

I connected the rotating coil directly to the battery (D+ , W) and started the drill. I measured 13.8V induced on my stator coil. You are right about the force. I small engine would be needed to test the regulator in situe like this. It's not conclusive but enough reason to put this alternator on the engine with the working charge light and tachometer and take the other one home for the same test.

 

[david_bagshaw]

Many years ago when trying to fix an alternator prob with an external reg, I fully wired it in "engine room " installation mode, ie completely ignored any of the boat wiring, wire directly to battery, and a bulb for the field current, just to prove to my Dad the alt was not at fault but the yard wiring was the problem. It would definitively prove the alt works and where your problems lie.