Misc: Charging Systems Dynamo Testing

[Robert Watson]

Ahhhh These things suddenly arrive whilst thinking of something completely different.

The engine sprocket is 35T
The generator sprocket is 28T so this is a speed up drive not a slow down.
with the generator turning 1000 RPM the engine is only turning 1000 X 28 /35 = 800 RPM. so barely above an idle. The podtronics likely wouldn't kick in at that speed. I know mine running on a Miller likes to see a bit of revs and then if charging is required it kicks in.

You're probably OK!

 

[Chris Launders]

I always use a 3000 rpm mains drill, and it may sometimes take a few goes to kick in, I did one for a mate, all new stuff, tested perfect, motored fine, it didn't kick in until about the 10th attempt. The best way of testing is to run it at this speed with a 12v headlamp bulb instead of the meter as that's only telling you the voltage, not whether there's any current.

Best dynamo understand/test/repair site "Matchlessclueless"

 

[bmetcalf]

See Appendix IV in KTB.

 

[greg brillus]

Genny's rely on resdual magnetism to "Kick in" some take more revolutions to do this than others. You may have to rev the armature to 2000 or 3000 rpm for it to come "On line" then it will hold a charging output lower than this figure if all is well.

 

[LoneStar]

Thanks for the replies! I did indeed have the gear ratio backwards, as Robert points out, so my test is at a measly 800 rpm engine speed. I can see where this isn't very meaningful, as others note too, so will need to either find a faster drill or just install the dynamo on the bike (when ready; many months of work still ahead) and see if it charges.

The wiring conversion to Lucas spec, as per KTB, had already been done. I modified it slightly as required for the Podtronics, which involves connecting the field coil wires to F and D terminals rather than F and earth. But once a jumper wire is installed for testing without the regulator, there's no effective difference: full output from the armature brushes is available to the field coil, as if the regulator was "full on".

 

[oexing]

Checking my photos I´d say the dynamo spins faster than the crank, 28 teeth on dynamo sprocket and 35 on crank, so a quarter faster. But I don´t think you´d get much out of 1000 rpm on the dynamo. Try to test it at 2000 rpm with direct 6 V supply to the field winding for max magnetic field . Yes, not a lot of power to hope from these devices anyway.

Vic

Sorry, disregard, I was too slow to reply.

 

[Peter Holmes]

Have you looked in KTB

 

[Robert Watson]

Have you looked in KTB

From post 15 a couple of hours before you

The wiring conversion to Lucas spec, as per KTB, had already been done.

 

[LoneStar]

I've ordered a drill capable of a mighty 3000 rpm, which ought to be a valid test.

Vic suggests using a battery to energize the field coil. My understanding was that regulators, both old mechanical and new electronic, don't typically feed battery current to the field coil but instead rely on the "bootstrapping" effect from the armature output. This requires an initial, residual magnetism in the field coil shoe, hence the need to restore this via flashing in some cases.

But I could be wrong on this - anyone know? I can see it being a useful design feature in a regulator to provide initial current to the field coil.

 

[oexing]

Most continental bikes had charging lights, no ammeters, so via that bulb the dynamo got some current for easy charging start, no residual magnetism required - but is normal state anyway. I´d think any electronics on these dc dynamos may hinder the build up of voltage in the dynamo as diodes like to sap any small charge being produced at very low speeds - not so with old regulators. That sapping of initial low voltage is the reason why a modern ac 3 ph alternator will not produce any power with an empty or wrecked battery. I don´t mean the permanent magnet type alternators but the automotive kind like in BMWs or Guzzis with rotor and its slip rings for field generation . The set of diodes and electronic regulator prevent any small voltage built up from residual magentism in the rotor. You really need a small battery to start the alternator charging. Many decades ago I had to drive home from Scotland to Bavaria , no lights as I think the battery had died there - or was it the rotor ? Had no further problems as the Earles BMWs had a great magneto on the camshaft, just no lights with dead 3 ph alternator.
So for a simple test of the Miller D 6 I´d hook 6 V to the field connector for testing output without the regulator messing up results. At 2000 - 3000 rpm there should be a good 6-7 V and some lighting on bulbs for checking real power.

Vic