Classic cars forum & vehicle restoration.

zagatoman · Joined: 31 Aug 2010 Posts: 55 Location: Sutton, Surrey

Hi all, me again with probably an easy request.

I have a feeling that my 6v dynamo on my Series M8 is not working, would anyone know a very easy way of testing. I have no experience with electrics or any fancy electrical testing equipment. I do have bulbs and wire.

Please remember a picture tells a thousand words.

Thanks, Paul
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47Jag · Posted: Mon Jul 18, 2016 7:57 pm Post subject:

Do the headlights brighten when you rev up the engine? This is a quick test.

You can buy a cheap multimeter for a fiver. Check out EBay item 201513705614. It even has a 10 amp scale.

The dynamo is 3 brush type which means that you adjust the output by moving the 3rd brush. If you look at the dynamo it will have two brushes 180 degrees apart. Then about 10 to 15 degrees away (probably from the top brush) there will be a thinner brush with the holder mounted on a slot. This is the brush that determines the current that the Dynamo delivers.

With your new DVM you can connect it to the negative (black) lead to the Dynamo output terminal and the red to the casing of the dynamo. Start the engine and see what that shows and get back to us.

Art

goneps · Posted: Mon Jul 18, 2016 11:53 pm Post subject:

There's an ammeter on the instrument panel. Does it show a charge when you rev the engine? Does the charge rate increase when you move the lighting switch to the second (winter) position?

Richard

zagatoman · Joined: 31 Aug 2010 Posts: 55 Location: Sutton, Surrey

The reason that I suspect the dynamo not working is because the ammeter not changing or the lights not getting brighter when reeving the engine. I just want to make sure before removing and getting sorted. I will try and get hold of a multimeter and do the test Art suggested.

Paul
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Enthusiastic amateur classic car nut.

Phil - Nottingham · Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham

Have you tried motoring it by disconnecting leads and loosening fan belt by jumping both D & F terminals to the battery feed (not earth)
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goneps · Posted: Tue Jul 19, 2016 11:01 pm Post subject:

If it's not charging at all then the cause might be as simple as a broken or loose third brush wire.

Richard