Checking a generator

Includes wiring and battery, generating system, starting system,
ignition system, windscreen wipers, lighting system and instruments and gauges.

Moderators: reidy, Blacky

Post Reply
admin_maintenance
Posts: 267
Joined: Tue Jun 28, 2011 10:52 am
State: QLD
Location: Mackay

Checking a generator

Post by admin_maintenance »

Hi all
Is there anyway to bench test a generator to see if it is any good. I tried it on a bench with a multimeter, but dont really know what I’m looking for.
Thanks
Jason
ardiesse
Posts: 1074
Joined: Thu Jan 19, 2017 9:57 am
State: NSW
Location: Sydney

Re: Checking a generator

Post by ardiesse »

Jason,

Visual Inspection First. Pop the commutator cover band off first, and inspect the inside for thrown solder. If there is thrown solder, the generator's basically bin-worthy. Pull up the brush springs. If they're weak or broken, they'll need replacing. With the brush spring held up, pull gently on the brush lead to make sure the brushes run freely in their holders. Check that the brushes are not worn out. Rotate the pulley and check that the generator's not seized. Rock the pulley from side to side and look at the commutator. If the commutator moves more than a few thou, the bush is worn, and the generator armature risks rubbing on the pole pieces. Inspect the commutator for pitting and signs of arcing. If one segment only is pitted, that means a shorted armature. Generator good for the bin. If all the segments are pitted, it means the generator needs new brushes. If the commutator is smooth, but black in colour, polish lightly with wet'n'dry.

No thrown solder? Spins freely? Rear bush OK? Brush springs OK? Brushes free in their holders? Commutator clean? Then grab a car battery, and do the following tests (Note: connections are different for Bosch and Lucas).

1. Bosch: Connect the D+ terminal to battery positive. Connect a wire with a test clip (or bare end) to battery negative.
Lucas: Connect a jumper lead between the generator body and battery negative. Connect a wire with test clip (or bare end) to battery positive.
Both: Then lightly brush the test clip or bare end against the DF terminal.
If there's a spark as you disconnect, the field coil is OK.

2. Both: Connect a jumper lead from battery negative to the frame of the generator.
Bosch: Connect the DF terminal to the frame of the generator (battery -).
Lucas: Connect the DF terminal to the D+ terminal.
Both: Connect a jumper lead from battery positive to the D+ terminal.
The generator should spin, slowly, in the same direction as it is driven on the engine.

If the generator spins in test 2, it is OK. The only other thing to check is the condition of the field coil wrapping, but it's best to pull the generator apart for that.

Rob
Last edited by ardiesse on Sat Sep 18, 2021 3:58 pm, edited 1 time in total.
admin_maintenance
Posts: 267
Joined: Tue Jun 28, 2011 10:52 am
State: QLD
Location: Mackay

Re: Checking a generator

Post by admin_maintenance »

Thanks but already worked it out. Generator is all good
User avatar
Harv
Posts: 5019
Joined: Mon Oct 08, 2007 2:00 pm
State: NSW
Location: Sydney, Australia

Re: Checking a generator

Post by Harv »

I'm storing this post in the "things I really should know how to do, but have never asked" file. Great guidance. Deserves a sticky in the Electrical section methinks.

Cheers,
Harv
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a BB/MD grey motored FED.
User avatar
Errol62
Posts: 9663
Joined: Sat Dec 06, 2014 2:44 pm
State: SA
Location: Adelaide

Re: Checking a generator

Post by Errol62 »

The one i sent you Jason?

FB ute driver, EK van project

getting my FB ute on the road
EK van on rotisserie
admin_maintenance
Posts: 267
Joined: Tue Jun 28, 2011 10:52 am
State: QLD
Location: Mackay

Re: Checking a generator

Post by admin_maintenance »

Yeah just tested it before I painted it.
User avatar
Errol62
Posts: 9663
Joined: Sat Dec 06, 2014 2:44 pm
State: SA
Location: Adelaide

Re: Checking a generator

Post by Errol62 »

Glad it works

FB ute driver, EK van project

getting my FB ute on the road
EK van on rotisserie
Blacky
Posts: 12171
Joined: Tue Jul 20, 2004 8:58 am
State: WA
Location: up in the Perth hills

Re: Checking a generator

Post by Blacky »

Harv wrote: Fri Sep 17, 2021 4:20 pm I'm storing this post in the "things I really should know how to do, but have never asked" file. Great guidance. Deserves a sticky in the Electrical section methinks.

Cheers,
Harv
I was thinking the same Harv - definitely a sticky, great info thanks Rob.
When you're faced with an unpleasant task that you really don't want to do, sometimes you just have to dig deep down inside and somehow find the patience to wait for someone else to do it for you.


Foundation member #61 of FB/EK Holden club of W.A.
Post Reply