Dynamo Voltage

Information relating to the Matchless G11 or AJS Model 30 600cc twin
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Joined: Tue Jul 26, 2011 9:01 pm
Location: ST AUSTELL UK

Dynamo Voltage

Postby mattwhite » Sun Aug 07, 2011 2:05 pm

Hi
i am new to the club so hello everyone,

I am currently having trouble with my dynamo my battery is not charging and my lights are not working! i am reading 0 volts on the dynamo with the engine running am i correct in thinking i should be reading between 6-7 volts with my meter set to ac from the two terminals on the dynamo ? oh and the bike is a G11 1956 matchless.
Any information would be gratefully received .


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Dynamo Voltage

Postby Groily » Sun Aug 07, 2011 3:00 pm

welcome matt.
Not on ac, this is a dynamo so dc.
To test for output from the dynamo with the engine running, you need to disconnect F and D terminals at the dynamo, link F and D on the dynamo with a short bit of wire (plenty of posts on this hereabouts) and then measure from the link wire to the frame or dynamo body with the engine running. At low revs there should be a few volts, rising to mid teens or more with rpm. Using a bulb (headlight sized is good) between the linked wires and earth is better for testing for real output. If it lights at low revs - don't rev too high with a bulb there or you'll blow it - then the dynamo is working. And the problem is at the regulator or elsewhere.
Do your lights horn etc work if the battery is (charged up and) in circuit? They should - so it could just be that your main feed from battery to ammeter isn't right and no charge can get to the battery? Good luck!

Posts: 2
Joined: Tue Jul 26, 2011 9:01 pm
Location: ST AUSTELL UK

Dynamo Voltage

Postby mattwhite » Sun Aug 07, 2011 3:25 pm

Aha i am showing my electrical ignorance here i thought the regulator not only regulated the voltage but also acted as a rectifier ac to dc, the brake light and headlight worked while there was charge in the battery but it is now flat, i will do as you said to test i did search elsewhere on the site for similar forums but didnt find any. thanks for the swift reply.

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Dynamo Voltage

Postby Groily » Sun Aug 07, 2011 4:58 pm

I was assuming it's a dynamo matt from what you said!
If it's an alternator model (if indeed there are alternator G11s?) - it's inside the primary chaincase bulge, mounted on the end of the crankshaft - as opposed to a cylindrical lump across the front of the crankcase with two leads coming to it - which is the Dynamo.
Very different territory if an alternator system. Then you'd want to be testing on the ac scale for ac volts across two of the leads (or perhaps the only two leads) that emerge from the primary chaincase. In which case you might have a regulator/rectifier, or just a rectifier, or a rectifier plus zener diode.
Tell us more if you don't have a dynamo!

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Dynamo Voltage

Postby en7jos » Mon Aug 08, 2011 1:23 am

Assuming you have a dynamo system, this might help:
[url="http://www.matchlessclueless.com/how-to-guides/lucas/testing-lucas-dynamo/"]How to test a Lucas dynamo[/url]
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