Further Dynamo Problems

[derekmalcolm]

I am looking for help that is not covered in the 205 messages about Dynamos in the forum which I have now read.

I have a E3L dynamo which being part of a basket case, I have stripped and rebuilt. As part of this I have measured the field coil at 3.2 ohms and each of the coils in the armature are showing around 3.5 ohms across the commutator. The commutator surface has been cleaned and polished with wet and dry (used dry) and the bakelite cut back. The brushes have been replaced and checked to ensure that the are seating properly. The earths and continuity through the coil and through the brushes are good. So at this point all looked good.

I then flashed the coil and then tested the dynamo by motoring it - all was good with it being smooth and turning clockwise as expected.

The next test was to try to generate a voltage so with F and D shorted I drove the unit from my drill - result no appreciable output (<0.5v) when driven clockwise or counter clockwise. While this tests method is mentioned in the threads, to my mind this method relies on there being some retained magnetic field in the field core to start to build the voltage in the armature that then goes onto build the voltage in the field and so a virtuous circle is created.

Assuming that the initial retained magnet field may not be present I then separated the F and D terminals and applied 12V to the field coil and drove the dynamo while monitoring the D terminal. Result 7v at the D output.

I had hoped that having now output decent voltages that I would now be able to repeat the generator test and get an output - no such luck again no appreciable output.

So where is the flaw in my thought process, and where do I need to look for a fault.

[chris.shearwood]

The earths and continuity through the coil and through the brushes are good. So at this point all looked good..................................I then separated the F and D terminals and applied 12V to the field coil and drove the dynamo while monitoring the D terminal. Result 7v at the D output.

Do you mean you have checked to make sure no part of the field coil winding is shorted to ground? With 12 volts applied to the field coil you shouldn't have to rotate the armature very quickly to get much more than 7 volts (I think!).

[bill.bottrill]

If you can motor it there can't be much wrong with it.When you were driving it from the drill and you applied (12v) to the field coil and it started outputting 7v did you try then rejoining the field back to the D terminaL while it was still being driven and what happened.
It's a 6v dynamo isn't it so I would just be using 6v to test it.
I had a similar problem, no output when I coupled it up to my lathe, so I then tried to motor it,surprise,surprise worked a treat! reflashed it, back on the lathe ....nothing,,, so I then coupled up a 6v charger one side earth and while the lathe was motoring flashed the other charger lead across the d/f terminals I had to do it 3 times but it then started charging you could try this but be careful that you don't get everything tangled up!

[Simon.Gardiner]

...If you can motor it there can't be much wrong with it.

I did once spend a great deal of time trying get an E3LM dynamo to charge reliably. As far as I could make out all the components passed the individual tests OK and the dynamo would motor well. Couldn't get it to charge reliably on the bike.
Eventually (in desperation) I replaced the field coil and the armature with new, since when it's performed faultlessly.
I'm no 'whizz' when it comes to electrickery, my conclusion is that sometimes - and maybe very exceptionally - under 'real life' charging loads little faults show up that you can't otherwise diagnose.

SG

[derekmalcolm]

Chris
Field coil to dynamo isolation is over 18 Mega Ohms. Yes i would hope to get more than 7v but it was not running at full speed and compared to the 0.2 v I was getting with the other test configurations it seemed a big step.

Bill
thank you for the input. I have been using 12v battery as I am intending to convert the bike to 12v with LED lighting and letters on the amc website suggest that these dynamos are basically power sources that will generate a 12V output at half the current if they have a 12V regulator. you just have to rev them slightly more for them to deliver the required current. The move to LED lights will reduce my current demand to a level that is compatible with the dynamo capacity.

As to flashing the D terminal during the testing, this is in effect flashing the each of armature coils. Applying power to the F and D connections when driving the dynamo and will have the effect of motoring the dynamo at the same time. I have tried this today but so far with no effects

[bill.bottrill]

Yes,you are right,I was probably just going to connect up to the field coil as you did while it was motoring and then rejoin to the D wire.Iazy really,I can't see anyhing wrong with flashing it while motoring (with D and F joined) as it would drive it in the same direction it was turning in the lathe (I think!) it wasn't powering up anyway it worked for me, (I also had a bulb connected across the output (ie D?F and dynamo body) I forgot to say this before that's how I could see it instantly started to push out power.
As regards 12v out of a dynamo designed for 6v Alot of stuff has been said about this before, you would have to gear it up if there was a lot of town driving. Leds are good but 12v /6v ? some 12v leds don't strike with a low battery best with a magneto bike I went for 6v dynamo and an inverter to 12v for h/light kept the old horn, coil ign 6v and run the sidelights (Led's) at 6v I hope you manage to get it going I can't think of anything else bill

[nevhunter]

Running it as a 12 Volt entails a much higher field coil current which will lead to the thing getting quite hot. There's no airflow through a Lucas generator or a fan as most bigger generators have on cars.
I've seen a Lucas generator melt the commutator solder and fling the windings with just running the 6 volt headlight on continuously.
Re not keeping the magnetism. It's possible you are flashing it in the opposite polarity. (worth a try) Remove the battery from the equation (disconnect one terminal) put the headlight on and see if it illuminates when you give the engine a few revs. If it shows a discharge on the ammeter its magnetized in the opposite polarity to how it's wired.
I have a "friend" who I trust with electrics.(he does all my rewinds) who has a website which covers this on the 6V to 12 V question. chris@zochy's-magnetos.com; Nev

[admin]

The dynamo itself isn't 6v or 12v, as such
It's output is governed by it's rotational speed and the regulator.
If you spin a standard E3 fast enough, un-regulated, then you should easily see voltages up to 20v

I have had dynamos which will motor but refuse to provide their own output.
The armature segments all seemed to pass the tests but it required a new armature in the end.
Brushes have been another area of nonsense for me.

Are you are certain that you have flashed the field coil with the same polarity as you are testing for ?

battery powered drills are pants for spinning these things up, as they don't usually go fast enough.

[derekmalcolm]

Thanks Guys. I am testing the dynamo out of the bike, with sitting on the top of the battery. I have flashed it repeatedly to ensure a negative earth so I do not think that will apply. I will take John's advice on the battery drill and retest with a mains powered drill perhaps we will see some output if not it i will bite the bullet and invest in new armature and coil.