Dynamo confusion

[bikerbob]

Sorry to bore you with another dynamo problem but am totally confused so please bear with me. Just before Christmas I thought the dynamo bearings were noisy although charging OK with belt drive and DVR2 regulator. Bought new bearings stripped dynamo and relaced bearings when back on the bike no charge,but while the dynamo was stripped the armature rolled off the workbench onto concrete floor assumed armature now broken although no physical damage. Looking at rest of dynamo decided to completely overhaul the dynamo bought a kit new armature, field coil, brushes and new end cap. Rebuilt the dynamo still no charge, have done a number of tests connected F and D run the dynamo only getting 0.10volts on multimeter,done resistance check on F terminal getting 3.2 ohms D terminal 1.9 ohms. Stripped the dynamo again but can find nothing wrong done continuity tests on the segments all OK rebuilt the dynamo supported in lathe run up to 700revs anti clockwise still only getting 0.10 volts. Have checked the wiring also flashed the dynamo to no avail,have tried running the dynamo as motor on the bench with battery connect F and D terminals together connect to neg terminal. positive terminal to dynamo body dynamo runs clockwise swap battery  terminals around still runs clockwise is this correct any advice would be very welcome. I have stripped and rebuilt dynamos before but never had this problem. Help

[Bsareg]

Sound like you need to reverse just the field coil to get anti clock rotation. Reversing the battery won't do it as you are reversing both magnetic fields. Don't forget to flash the field to the correct polarity for your bike

[bikerbob]

Thanks for the quick reply but I had already flashed the dynamo to the correct polarity before I ran the dynamo as a motor.

[groily]

Wasn't at all clear whether you'd ended up with negative or positive earth after swapping the battery connections. Motoring it with the battery connections reversed from what you have on the machine reverses the polarity automatically.
But it certainly sounds as if the field coil wires need reversing (or the brushes) to get the rotation correct, as Bsareg says.
But on your main point, 700rpm won't do it anyway. It will typically need more than that, maybe double, for it to kick in.
If you hook the thing to a drill with a socket over the drive end, whirr it the way it is driven on the machine, there may well be plenty of output. Up to 20v-odd at speed without loads on if it's working properly. Once kicked in it should light bulbs brightly.

[bikerbob]

I have checked how it is wired and it is correct and I did flash it before carrying out the test on the Lathe I only tried running as a motor as a last thing read about it somewhere. When I overhauled the dynamo I put it back on the bike started the engine and was really surprised to see no charge on the ammeter even increasing the revs a bit. So will do as you advise tomorrow and run with higher revs in the lathe my drill does not have a reverse so can only run anticlockwise in the lathe. Thanks

[Bsareg]

If rotation is clockwise when motoring the dynamo the field or brushes MUST be reversed to get it to motor anti clock as it needs to be driven in the same direction as it motors

[bikerbob]

Thanks for that info will swap the brushes over tomorrow and try again. This is how I wired it up the post also showed 2 sketches which have not copied.

Looking directly at the end of the dynamo, and if the dynamo is wired typically the following is how it is wired. The two wires which come out through the top of the brush carrier plate are the field coil wires.  Normally the wire which exits through the right-hand hole has a small sleeve on it and is earthed with a small screw just above the bearing. The left hand field wire is connected to 'F'. The left hand brush is earthed with the right hand field wire. The right hand brush goes to 'D'. Before testing, flash the dynamo (negative lead of a battery to 'F' and positive lead of battery to earth -  a quick tickle(!) should be all you need). Connect F and D together with a bridge wire. Connect any point of the bridge wire to a 12v bulb, then the bulb to earth on the dynamo. Then spin the dynamo anticlockwise with a drill to test. Bulb should glow very brightly at about 1400 r.p.m. If all is well remove the bridge wire before putting to use.

[Bsareg]

Seems about right,trouble is many dynamos have seen more strips than teasey weasey raymond ( Google him ) and you can't trust the direction markings on the casing

[bikerbob]

Have just been in garage done as suggested and reversed the brushes connected to battery and dynamo now runs anticlockwise as it should, put dynamo in lathe run anticlockwise up to 1350 revs and am getting 8.16 volts on the multimeter assume this is correct if so will put dynamo back on the bike Saturday. Hopefully this has fixed everything thanks for help.

[groily]

Sounds much more like. 1350rpm driven directly is roughly the same as 1000rpm engine, and what you're seeing is about right I reckon. If you were to load it with a bulb at those 'lathe' revs, the voltage shown on the meter would drop (by how much depending on how big the bulb was) - but that would be normal too. I think you've cracked it and she should now be good to go. Hope so!

[Zander]

After faffing about with other things, I've returned to the dynamo enigma.
long story short, I've run it in the lathe and done the meter bulb tests.
What happens is that the bulb illuminates at high revs and dims at lower speed - all ok.
Then, if I stop the lathe, obviously lamp goes out, but won't kick in til the revs are high.
I'm now going to fit it and see what happens.  The PO has written " new innards" on the reg., so hopefully that'll work.

[Bsareg]

When the regulator is in circuit the small amount of residual  magnetism generates enough current to pull in the cutout which then boosts the magnetic flux for normally operation. Without the regulator you will need much higher higher revs.

[Zander]

Thanks for that Bsareg.  Hopefully the regulator will provide the necessary kick

[duTch]

 So how did b-Bob get on?

[trevinoz]

Reg,
The residual magnetism allows a small voltage to be generated which is fed to the F terminal via the regulator contacts.
When the voltage reaches the pre set values for the cut out and regulator they will operate, the cut out to connect the generator to the battery, the regulator to limit the voltage.