dynamo output problem

[Rich]

I have a conundrum with a E3L dynamo, I have tested the field windings and have a reading of 2.8 ohms also I have cleaned and undercut the commutator and have a reading across each section of approximately the same reading, I dont have a growler so cannot test it any further. The brushes are good and it is wired correctly. Also flashed the dynamo.
I  connected the F and D together and put a wire to earth and connected them to a battery and it motors smoothly, however when I put it in the lathe and ran it up the correct way, with a volt meter between F&D and earth with the lathe running as far as it could I get less than 1 volt output.
I have double checked all of the above and still no joy.
Can anyone throw any light on this problem

[groily]

How fast does your lathe go? Often needs a good deal of revs to get one to cut in, especially if it's being capricious. Close to 2K rpm isn't rare. Suggest try mains powered drill applied to drive end with dyn in vice, which should spin at 2-3000rpm, see if it cuts in with no load on, D&F together etc. If it shows loadsavolts, then hook a bulb on too. Preferably 12v, start with about 25W (car flasher bulb is good). That, if it lights and burns brightly with revs, starts to tell you a story that ought to have a happy ending. (Assuming direction of rotation is right, that is.)

[Rich]

I lent my dynamo to a friend while I rebuilt his dynamo with a new old stock armature, I presumed that the loan one was charging as it motored on a battery, however it never charged on the bike.
The dynamo I rebuilt for him when run up in my lathe gives 9 volts+ so although I dont know the exact revs of the lathe it is fast enough to run up dynamo's, previous ones have worked in the lathe. The direction is as the arrow on the dynamo casing

[Bsareg]

With brushes isolated, there should be an open circuit between body and commutator? If not,you may have an armature short.

[CheeserBeezer]

Step by step guide here. May help....
https://docs.google.com/document/d/1KAPtZqORs9czjkkTNl4UgyUu5qanqxAp/edit

[Rich]

I honestly cannot say I checked that, but if a short was apparent then I dont think it would motor smoothly on a battery, and it is doing that ok. But I will check that tomorrow.
Thanks Cheeserbeezer for the link how to test the dynamo, I do actually know all that by heart having had dynamo powered bikes for over 50 years, also I have all the lucas manuals, but this one is strange and obviously either the armature is faulty or I have missed something so simple I just cannot see it YET!!!

[KiwiGF]

I have a conundrum with a E3L dynamo, I have tested the field windings and have a reading of 2.8 ohms also I have cleaned and undercut the commutator and have a reading across each section of approximately the same reading, I dont have a growler so cannot test it any further. The brushes are good and it is wired correctly. Also flashed the dynamo.
I  connected the F and D together and put a wire to earth and connected them to a battery and it motors smoothly, however when I put it in the lathe and ran it up the correct way, with a volt meter between F&D and earth with the lathe running as far as it could I get less than 1 volt output.
I have double checked all of the above and still no joy.
Can anyone throw any light on this problem

In my experience it will be the brushes have a high enough resistance to prevent “self starting” - a check you can do for that is to put a current through the field and then see if it generates properly (in the armature). You can put 6v straight onto a 2.8 ohm field and it will take a bit over 2 amps which will be ok and not overheat it, albeit I personally would only run it like that for a minute just to do the test.

[Jim S]

I have been going through the same problem, doing the same checks as you have done, swapping out brushes and cleaning connections etc. I have also connected 6 volts to the field winding and spun the armature at about 1200 rev/min and I got about 6 volts output. But it still didn't work on the bike.

I found this video on youtube:
https://m.youtube.com/watch?v=lmjFzukDhqI

My armature failed 2 of the 3 tests. I placed an order for a new armature.

As corrective action, I have installed LED headlight bulbs to reduce the load on the poor dynamo.

[trevinoz]

Motoring the generator does not prove that it is any good. An armature with an open circuit will still motor at 6V but usually will not at less than 4V.
Testing with a multi meter between segments is a waste of time unless you have a voltage connected across the commutator and do a "drop" test across each pair in succession.
Usually if the generator motors and no useful voltage is produced when driven, the armature has an open circuit in one or more of the coils, there are 12 of them.
a sign of an open circuit is a "flat" on one or more commutator segments, easily spotted as it is the dimension of the brush and may be slightly blackened.

[Jim S]

Trevino
Help us out here.

In my case, using an ohm meter, I got about 0.7 ohms between adjacent commutator bars except in 2 locations where I got open circuit readings. I got the same, taking readings on commutator bars 180 degrees apart, with 2 open circuit readings. Is this not an indication that there is a problem with the armature?

Also, if there is an indication of a short circuit between any commutator bar and the armature stack, isn't this also an indication of a problem?

I guess I (we) are looking for a clear and easy set of checks that would help lead us to a decision to chuck out the armature or not, keeping in mind that access to a growler may not be easy.

I would appreciate your added input.

Jim

[Bsareg]

I've had dynamos with open circuits between segments that were cause by dry solder joint or a broken wire where it enters the segment. Might be worth a close look.

[Rich]

the armature is shorted between the segments ,i.e. the windings so I am now trying to source a good armature, thanks for all your inputs

[trevinoz]

Jim, I never use a growler, too much mucking about when I can get better results quicker by "drop" testing.
Reg is right suggesting that you check all of the solder joints. A common cause of open circuits is thrown solder from over heating but the windings are usually slightly cooked.
Broken wires at the commutator are generally caused by loose commutator segments, a good idea to check before the comm disintegrates with dire consequences.
It seems as though you have 2 open circuits, if you had 1 you would most likely not detect it with an ohmmeter. Also check for "flats" on the segments.
Probably time for a new armature or rewind.

[Jim S]

Trevinoz/BSAReg

Attached is a picture of my armature commutator end. The wires from the windings that are soldered to the commutator segments are covered with wound string and set with epoxy. Are you suggesting that I cut this covering away in order to see the solder joints at the segment ends?

I have already written off this armature and ordered another, but it would be interesting to see if the solder joints have been affected as you have  mentioned.

[Bsareg]

What have you to lose, and you might find it's simply dry joints.