Ariel Owners Motorcycle Club

Hello,
due to a charging problem i removed the dynamo.
Output test - shortcut D,F and multimeter to housing, spinned by a drill - shows very little voltage.
Using motor test - battery + to shortcut D,F, battery - to dynamo house - does it turn the other way like shown by mark on house.
Is that ok?
Dynamo is flashed to neg earth.
Brushes are easy going, but one is rather short.
Commutator is clean.
It's a E3HM dynamo but it looks restamped - look picture.
Had a look at drags, they say it should be a E3LM.
However draganfly offers brushes will they fit ?
What´s wrong?
Any help appreciated - Ralf

I can't quite read the number on your dynamo body that would tell me what it was origianlly supplied for and whether it was an E3HM or what. It isn't an LM because the 'L' indicates a 'long' dynamo, which would have 2 field coils screw, so it is a short 40 Watt dynamo. The 'M' means it is for a Magdyno but the difference is in the drive end castings that can be changed. The other differences are that the brush plate is different for clockwise and anti-clock but I suspect the differnce is subtle.
On your correctly carried out test the Voltmeter should show a rapidly increasing Voltage with revs up to 15-20Volts as there is no contoller. A low Voltage of around 0.5 Volt indicates a faulty field coil 0.5-1.5 Volts a faulty armature. Strip and clean it, scrape out the grooves in the commutator, reassmble and test again. Then start replacing bits, easy enough to do but the field coils screw(s) do need to be tight.
Managed to read the number in the 2nd picture 200285 was an E3HM, so was originally for a Magdyno. but cannot find original application.

When 'motored' the dynamo should turn in the direction it is driven in. Try swapping the field coil wires over and then testing it. Odd really as if it worked ok before and you have done nothing to it since it stopped charging then the wires should all be correctly terminated. I rebuilt my dynamo and had the same results as you are getting now. Somehow I had managed to get the field coil wires reversed and changing them over made it spin the right direction when motored and gave good voltage when the output was tested.
Regards,
Keith.

Thanks a lot for your replies.
I could change the spin direction by switching the field coil wires. But still low Voltage. Less than 0.3 V which indicates a field coil error.
Confusing cause the Motor test lets it run.
Field coil resistance shows 3 Ohm approx. which seems to be good.
Commutator looks good with clean gaps. .
I will strip it the next days.
Regards - Ralf
Keith, sorry for not mentioning. It's an old mistake. It didn't appear over night. But the daynamo never did a good job.
I use leds and don't ride at night so i had to charge the battery twice a year.
At last the ammeter refused too.

I changed the armature, now its working.
A few windings were bad.
By motor testing the armature stopped always at the same position. That's how i found the mistake.
Ralf

You can get that effect from an out of true commutator or jambing brushes True the commutator with the shaft running in a fixed steady. Nev

Ralf, I rebuilt my dynamo back in 2010 as a 12 volt unit, changing the old 6v armature and field coil for new 12 volt ones (aftermarket parts I imagine). About a year or so ago it packed up charging and, on stripping it down, I found one brush was stuck in it's holder, the commutator was burned and the armature had also just been catching the field coil shoe over about a third of its length. I checked the sealed bearings which were fine. The field coil measured 12.5 Ohms and wasn't earthing. I assumed this to be ok as it is a 12v one. On checking the 12v armature windings I found most were 2 Ohms, one winding was open circuit, and a couple were high resistance. None were shorting out with the armature shaft. It was clear that the armature was faulty. I thought the armature had been evenly kissing the field coil because the field shoe may have distorted (armature bearings being good) and, because I couldn't tighten the field coil any further, I thought I would lightly skim the armature pole faces in the lathe when I skimmed the commutator, which is what I did. Looking at the armature windings each copper wire is crimped in the commutator. With a very small file I carefully filed every crimped wire at its commutator mounting slit clean then applied some liquid flux and soldered each one home. After doing this I checked the armature windings resistance and they all measured 0.7 Ohms, a good result. Any excess solder was filed away and I was careful to ensure no solder ended up in the commutator slots. Dynamo brush holders etc. were cleaned up and the unit was re-assembled. The armature rotated cleanly no longer rubbing the field coil pole face. I then tested it and once I had corrected the crossed field coil wires it worked beautifully. Cleaning the armature winding terminations at the commutator Soldering each termination Dynamo assembled for testing.
Ralf, check your armature windings as I have done with mine as you may be able to salvage your armature as a spare.
Regards,
Keith.

hi make sure the dynamo body is making a good earth that can make it not charge very well , has i did find out when i painted my dynamo body :and the nag has got a good earth too

I have earthed my dynamo from the point where the brush is terminated to the comm end bearing body to the earth point on the magneto and then dynamo and magneto earth back to the main earth point. (In my case the lower of the oil tank fixing to the frame).

Thank's a lot for your hints.
Keith, i will follow your advise. Will clean the slits and resolder the commutator connections.
There were some high resistance windings, but no shorts to the shaft.
No idea what went wrong but the solder points look bad.
Armature didn't touch the field coil, for shure.
The New one works fine. But like you said to have a spare can't be wrong.
Ralf

PS Earth is good, dynamo house is blank at certain parts.


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