Author Topic: 12 volt dynamo producing 0.5v!  (Read 525 times)

Offline owain

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12 volt dynamo producing 0.5v!
« on: 11.10. 2020 17:49 »
Hi, Abit of a follow-on from my previous post about the motorcycle lights going flat. Well, I decided to upgrade to a 12v system and install a 12v armature and 12v field coil into the E3L, with new bearings and brushes. Except now it is producing only 0.5v. Really disappointing stuff. I have since taken the dynamo apart a few more times and tried all the different combinations of old and new components (e.g. 12v field coil with 6v armature, 6v field coil with 6v armature, etc) but with no success. It can't produce more than 0.5v volts. Does anyone have any idea where I am going wrong with this? The dynamo's seem like really simple things to put together.

A few notes: 12v field coil has a resistance of 11.5 ohms. When the 12v armature rotates, the commutator oscillates slightly i.e. isn't perfectly true. Only 2/3 of the commutator is in contact with the pick-ups as the new 12v armature https://www.classicbikeshop.co.uk/12v-dynamo-armature-60w-fits-a7-a10-190mm-length-with-taper-shaft.html I have no idea if these issues will affect the dynamo's performance but if anyone could help point me in the right direction it would be appreciated hugely!
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online Rex

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Re: 12 volt dynamo producing 0.5v!
« Reply #1 on: 11.10. 2020 18:32 »
Have you tried flashing the dynamo since you rebuilt it?

Online groily

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Re: 12 volt dynamo producing 0.5v!
« Reply #2 on: 11.10. 2020 19:37 »
If you have got the polarity right (Rex's point), have you got the direction of rotation right too?
The field coil and /or brushes need connecting to suit the direction required. (A dynamo will work either way, either earth - but needs setting accordingly. If set for opposite rotation, about half a volt is what you'll see.)
The new field coil is meant to be about 12 ohms, and is designed to work with the new fine-wound armature you've got. Mix 'n match with the old bits is a definite no no.
If the armature isn't running true, then you need to look again to be sure it is assembled correctly. The commutator should run dead true to the spindle if you can check it between centres somehow. If it's not bent but doesn't run true all the same when assembled, there could be a bearing off-centre or the brush end housing is distorted.
The new brushes may take a bit of time to make full contact though. Sometimes, a gentle queeze on them can encourage a new set of bits to start - and thereafter stay - generating.
I get the feeling this is going to work properly, it sounds to me like a Q of going though the various stages to check things are set right.
Bill

Offline owain

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Re: 12 volt dynamo producing 0.5v!
« Reply #3 on: 11.10. 2020 20:00 »
Doh! I didn't flash it  *eek*...Just went back into the garage and flashed it a couple of times and reversed the direction of the drill. An output of 7.8v at 1000rpm. I'm not too sure how much I should be expecting at that speed, perhaps abit more once the new brushes have had time to seat properly..

As for commutator not being dead true. I'm afraid it is still out by a small amount. I could put it in the lathe to check if it is the armature at fault or perhaps one of the other possible factors as groily mentioned.
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Offline owain

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Re: 12 volt dynamo producing 0.5v!
« Reply #4 on: 11.10. 2020 22:13 »
Thought I'd just add this picture of the commutator on the new 12v armature. There is a decent gap between the top and the end bearing. So the commutator is only in contact with 2/3 of brushes.

On the original armature the commutator; there was a much smaller gap and the entire brush length was in contact with the commutator. Am I right to assume that this will affect the brushes ability to optimally conduct electricity?
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online RDfella

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Re: 12 volt dynamo producing 0.5v!
« Reply #5 on: 11.10. 2020 22:20 »
Is the new bearing the same as the previous one? Is the armature the same OAL? Summat amiss there.
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Online Rex

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Re: 12 volt dynamo producing 0.5v!
« Reply #6 on: 12.10. 2020 08:52 »
If the dynamo end caps are in place (and they look to be) then surely the armature is different (shorter) than the original? That gap is clearly wrong.

Offline Swarfcut

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Re: 12 volt dynamo producing 0.5v!
« Reply #7 on: 12.10. 2020 18:02 »
 Once more a good chance it's the curse of the almost fits but not quite repro pattern part.  Looks like it will have to come apart and be checked  against the original, if you still have it. If the seller says "They're all like that" then its decision time, whether to get another,  attempt to get it to fit or give it up as a bad job. The brushes should not go past the end of the commutator segments, they don't make L Shaped brushes.  Like Groily says, a new armature should run straight and true, with no movement up and down of the brushes.

 That bearing carrier looks nice and new, any error here with greater thickness of the casting and the brush mounting insulation compared to original parts will move the brushes and bearing further from the captive drive end bearing position.

 When replacing field coils, the Lucas Manual always showed what looked like a scissor jack used to press the pole piece against the dynamo body before tightening the countersunk mounting bolts. Any air gap between pole piece and body will affect the strength of the magnetic field within the dynamo body, and hence available power output.

 Swarfy.

Online chaterlea25

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Re: 12 volt dynamo producing 0.5v!
« Reply #8 on: 12.10. 2020 21:30 »
Hi Owain,
You got an E3 armature not an E3L
The short armature or dynamo is only 40 watt E3L is 60watt

John
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1963 RGS (ongoing)

Online Rex

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Re: 12 volt dynamo producing 0.5v!
« Reply #9 on: 12.10. 2020 21:37 »
Not only that but clearances between the pole piece and the rotating armature are so tight that it's possible for the armature to rub if the pole pieces aren't fully home and tight against the yoke.
If the internal screwjack tool isn't available (who's got one of those after all?) a good alternative method of fitting the field coils and poles is to fit a length of steel bar through the body and bearing on the pole then using two G clamps (one either end) pull the pole into position. Tighten the screws fully by using an impact driver.

Online trevinoz

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Re: 12 volt dynamo producing 0.5v!
« Reply #10 on: 12.10. 2020 22:27 »
I looked at the link to the supplier, the armature pictured is an E3L type.
Possibly the commutator has been placed too far onto the shaft.

Online Rex

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Re: 12 volt dynamo producing 0.5v!
« Reply #11 on: 13.10. 2020 08:28 »
I don't see how that would be possible. The comm has to be up close to the armature windings so the tails can be soldered to the comm bars.

Online groily

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Re: 12 volt dynamo producing 0.5v!
« Reply #12 on: 13.10. 2020 10:27 »
I've deleted what I tapped out a few hours ago 'cos in trying to add some measurements, I daftly measured an E3LM armature (eejit), and set out a lot of data that are wrong! Apologies.

Overall length of the BSA one, Lucas # 200752 is 190mm if it helps. Other E3L ones are shorter, at 178 and 179 mm, with the difference at the drive end.
At the brush end the bare shaft will be c 11.5mm and the comm depth 19mm if same as other E3Ls which I can measure..
At the drive end the plain section inboard of the threaded section on the Beesa one will be 9mm, threaded section also 9mm, and the shoulder at the inner end 5mm. The outer tapered section is  c 13mm and then there's the thread for the nut. Which accounts for the difference in length between the versions.
Bill

Online Bsareg

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Re: 12 volt dynamo producing 0.5v!
« Reply #13 on: 13.10. 2020 12:42 »
Can't be a E3 armature as the difference between e3 and e3l is to great. Could it be a thinner drive bearing ?
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Online trevinoz

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Re: 12 volt dynamo producing 0.5v!
« Reply #14 on: 13.10. 2020 22:43 »
Rex, it is quite possible to have the comm in the wrong place, it is only a press fit on the shaft.
I have removed and replaced countless numbers of them and have rewound more armatures than I have had Sunday dinners since about 1967 so I am aware of the correct position for the comm.
If the armature fits between the end shields and the brush boxes don't line up, the comm is in the wrong place.