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ES2 magdyno brushes


My ES2 magdyno has never had brushes in it although I have them. My question is what terminal(s) do they attach to?  Attached is a photo and I have highlighted the only vacant terminal I can they both attach to that or ??? 

Some guidance would be appreciated!

Cheers, Ben Tomlin


... attaches to that terminal (which should then  go to the "D" terminal on the voltage regulator); the other to the earth screw along with the field coil which is already there.

However, which brush goes to which terminal depends on rotation direction (as I remember it although Al will no doubt keep me right!).

Thanks Ian, I assume the earth screw is the one highlighted in red on the attached photo?

The rotation direction is anticlockwise looking from the same end of as the photo, hope someone can clarify which brush goes to which terminal!

Cheers, Ben Tomlin


In reply to by ian_soady


Thanks Ian, much just need to know which brush / which terminal if somebody can help....




I suggest you connect the brushes then test the direction of rotation by "motoring" the dynamo on the bench. Let's assume your ES2 is from the fifties: dynamo should rotate clockwise at the drive end, battery should be positive earth. Connect the + of your battery to the dynamo frame, connect the battery - to both the F & D terminals. The dynamo should rotate. If direction is clockwise your brushes are correctly connected. If direction is counter clock then swap over the brush terminals and re-test. You will need to adapt these instructions if you have an earlier ES2 with the inlet cam driven from the exhaust cam instead of directly from the half-time pinion, or if you have negative earth. Hopefully Al O will not have to tell me that I am "almost right" again!

Ian McD

Thanks Ian, my ES2 is from 1952 and definitely has a negative earth so your thoughts would have to be adapted as you say (but not sure how!)....just wondering what what would happen if I simply put the brushes back and watched to see what the ammeter does.....if it charges could I assume they are in the correct place?  Or if it didn't charge would it have done any damage before I swap them over?

Ben Tomlin


....if the rest of your electrical system is healthy. What you suggest will have 2 possible outcomes  - charge or no charge. But, if there are other faults present eg in the regulator/wiring/ammeter, you could still have no charge whichever way the brushes are connected. The "motoring" test is a reasonable indication of a healthy dynamo (although not a guarantee). It is a question of testing each element of the system to establish what is good and what is suspect. The adaptation needed for the "motoring" test with negative earth is to connect the battery - to the dynamo frame, and the + to the F&D terminals.

Hope this helps, Ian McD


.. test works (just connect the reverse of what Ian McD originally said, ie negative to the dynamo body and positive to the F&D terminals) then put a voltmeter between the commoned F&D terminals and the dynamo body and spin the dynamo up using a cordless drill (in the same direction as fitted to the bike). You should get a few volts showing depending on the speed of the drill. If this works, refit the dynamo and connect the voltmeter isn the same way and run the engine. This will spin the dynamo faster and you should see well over 12 volts at engine speeds of 2 - 3,000 rpm.


If we didn't know that this dynamo was off this model yet it can motor in either direction (depending on input polarity) what difference does it make? for charging?   Its just a matter of  testing the output terminals and connecting to appropriate earth arrangement isn't it?

 Only other observation to make is the speed when motoring.  If its more efficient one way or t'other, then that is the direction that would give the higher output.

Just curious....

 Where is Al when you need him... 




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