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To flash a dynamo

Submitted by paul_standeven on Tue, 10/07/2018
Forums
Electrical

My lights died on the way home last night. Battery run flat due to non-charging by the dynamo (Lucas E3L on a Dominator). It has been off the road for 30 years, so I think the dynamo needs flashing. How do you do that? The bike is of course + earth. The battery (a pair of Cyclons in parallel for 6V) is dead flat, but I have a 12 V car battery on hand

I think that you disengage the dynamo from its drive, connect positive battery post to the dynamo body, and negative battery post to the D terminal on the dynamo, and let it motor for a few seconds. Is that correct?

Paul

Submitted by paul_standeven on Tue, 10/07/2018

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I have just been sent a link to DynamoRegulators site:

http://www.dynamoregulatorconversions.com/polarising-a-dynamo.php

The gist is that you remove the two dynamo leads (D + F), take a feed wire from the non-earth side, and touch it to the Field terminal on the dynamo several times until you get a blue flash. That's why it's called 'flashing' the dynamo.... Then it should charge as normal.

So I had the right idea, but the wrong terminal on the dynamo. That's why it is sensible to check before you do something you have never tried before.......

Paul

Submitted by peter_arnull on Tue, 10/07/2018

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Previously terence_rafter wrote:

A few things to check. Brushes are OK. Check for oil on the commutator as this can prevent the dynamo from self-exciting.

Peter

Submitted by alan_osborn on Wed, 18/07/2018

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And again. Remove any/all wires from Dynamo. Connect a wire from the 'live' terminal of the battery to F for a moment, it will flash when being removed. Job done. The battery being connected as you intend to use it ie Positive earth has Positive to earth. No need to remove drive or 'motor'.

Submitted by paul_standeven on Fri, 20/07/2018

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I checked the dynamo output following the instructions on 'Matchlessclueless.com'. Remove the dynamo and field wires, join the two terminals together with a wire, and check the voltage at idle and fast idle. I got 4V at idle and 14V at fast idle. Figures so good that I think the dynamo will cope easily if I fit a 12V regulator. Does the DynamoRegulators item simply fit in place of the Lucas regulator?

Paul

 


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