ALTERNATOR TESTING

The following article was submitted by

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

WARNING ;

Be careful when running drill on alternator !

It can't be emphasised too much, spinning an alternator with a drill thus could cause damage to persons -be very careful.

(Use of a chain saw or Zip saw might be considered similar risk ; loose alternators can hurt!!)

How to test an alternator when it is off of the vehicle.

LR100 (17ACR etc) Alternator .

YOU WILL NEED;

{ 1 } Sturdy bench vice ( Perhaps a workmate will do )

{ 2 } Mains power drill ( Battery ones are too puny )

{ 3 } Old 12V car or bike battery. ( With a reasonable charge.)

{ 4 } Warning lamp, any 12V 2W or 5 W will do. ( In a socket ? )

{ 5 } Few bits of wire. (croc clip leads?)

{ 6 } Multimeter. ( To measure 12V )

{ 7 } Socket { 1/2 drive by 7/8 AF } to fit the alternator and a way of driving this with the drill. { This can be done with a bolt held in the drill so that its head is a close fit to the ½ socket }

{ 8 } Connector to the back of the alternator . { An old alternator loom from the Reliant is ideal for this }

SET UP;

{ 1 } Mount the alternator in the vice horizontally so that the fan/pulley is towards you.

{ 2 } Connect up the circuit-plug to rear of alternator, this will give you a battery lead ( with a battery eyelet if using the Reliant loom.) Take this to battery positive.

{ 3 }There should also be a BROWN/YELLOW wire in the loom which is connected to the energiser/warning lamp terminal, take this to one end of your warning lamp.

{ 4 } Take the other end of your warning lamp to the positive of the battery.

{ 5 } Connect your Multimeter on Volts across the battery.

{ 6 } Finally connect the negative of the battery to the earth/metal work of the alternator. Hopefully no sparks!

If no ready-made connector to hand, connect the larger terminal of the alternator/rectifier to the positive of the battery (B+).

Connect the smaller Lucar terminal (D+ or 61) (exciter circuit) to the warning lamp.

Finally connect the battery negative to the earth/metal work of the alternator.

WITHOUT SPARKS!

TESTING ;

{ 1 } Apply drill with (bolt) and socket attachment to alternator nut.

{ 2 } Spin drill.

{ 3 } If the alternator is any good it will ‘load up’ and load the drill in your hand, so hold firmly.

{ 4 } The warning lamp should go out and the Multimeter voltage should rise from 12V ish to 14V ish. This test is for basic function only. Full load test is not possible without an electrical full load and power to spin alternator up to say 6000rpm! (Try an engine!)

{ 5 } If alternator spins freely and voltage stays the same then alternator is dead (or your circuit is)

FAULTY ? ;

The most likely and easiest fault to deal with is the alternator brushes.

Remove the black cover 1/4 or 5.5 mm socket, remove the central plastic brush cover ( 2 more screws ) and check brushes.

If the brushes are suspect then the warning lamp won’t light in the first place.

If you want to go further, you can unsolder the three coil wires from the rectifier.

The three phase windings should measure the same across the three wires and will be just a few ohms.

A check to earth should show open circuit.

You can check the three-phase rectifier; you should find 9 diodes.

The regulator can only be checked by substitution.

Regulators and brushes used to be available as a kit, but be careful and check the bearings before spending too much time and money.

I have found that after two brush or a regulator replacement the bearings were shot.

WARNING ;

It can't be emphasised too much, spinning an alternator with a drill thus could cause damage to persons -be very careful.

(Use of a chain saw or Zip saw might be considered similar risk ; loose alternators can hurt!!)

Testing of an alternator on the car.

Easy enough. if alternator is suspect.

Is battery good enough to run lights?

Will it start the engine?

{ 1 }

Warning lamp must light up with ignition on (engine NOT running).

This completes a circuit from the battery through the ignition switch to the warning lamp.

The other end of the warning lamp goes to the alternator BROWN/YELLOW (small terminal) and thus to one of the brushes and then through the Field winding, then the second brush to earth.

(NO lamp on Means no worky)

{ 2 }

Apply Multimeter to battery.

The following voltages are not crucial, the change between states is.

Battery at rest 12V to 13V.

Start engine. Rev up. Battery voltage should rise to at least 13.5V or up to 14.5V. Higher that this means over charging, Lower means under or no charge.

This test is with ignition and battery charge only ie Alternator NOT fully loaded.

Now switch all lights on and rev engine, if voltage rises to 14V then alternator is in good condition.

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Alan Osborn ; www.aoservices.co.uk