Electric help please

[electrajohnt]

Is it a Voltmeter or a Multimeter? If it's a Multimeter with a 10 amp (or more) dc current range then you can wire the meter in series with the load (bulb) and measure the current flowing through the load using the current range of course and note that many multimeters with such ranges have a dedicated terminal to connect to not the usual dc volts and Ohms ones .

I suspect that you can't spin the dynamo fast enough with your drill. I have found with my Lucas dynamos (all two of them) that the bulb is very reluctant to light when doing the "F wired to D" test on the bike and it's not until the engine is running at significant speed that it will suddenly cut in and illuminate the bulb.

All may not be lost ....


Alan

Ok thanks, It is a multimeter, I have had it years but only used it for continuity and voltage. Occasionally for resistance. I am not that conversant with its full capability. It appears it will read DC current, see attached photograph of the page in the instruction book. I will give that a go tomorrow. As MickD suggested I stripped it and cleaned, bit if fine wet or dry on the bit where the brushes run and also ran a knife point along the segment gaps, still will not light the bulb

[electrajohnt]

Just read the article Mr Greybeard directed me to. Seems like I could need to “flash” the dynamo. This dynamo belongs to a Venom that, whilst In very good condition, has not been used for many, many years ( not used properly for more than twenty years and last started about ten years ago) Due to our enforced lock in I decided to get it out and recommission, which I have now done, except for the charging and horn that is. So maybe I need to reenergise the field windings. Could someone direct me how to do that please.
JohnT

[Groily]

Have you tried Spriddler's suggestion using a 12v bulb? Or pre-heated a 6v one to help it light? Often, a lower wattage bulb will get things going - 21w 12v bulbs are good for this - and then you can hook another one on if/when things start to go. If a pair of them brighten nicely, that's 42w and a decent test load.
Wait till the dynamo 'kicks in' and is producing the volts you mention, then hook the bulb on. Don't attach the bulb first. You can probably feel a strong torque reaction on the drill when the dynamo excites - that tells you when it's doing its stuff.
The fact that you have had it motoring says you have put battery current through the field already, and delivering good 'no-load' voltage suggests to me that it may well work. The field shouldn't need flashing again. Motoring is not definitive but it is indicative, and if there are no 'dead spots' - 'chugging' - as it spins (which you can feel if you lightly pinch the spindle 'twixt thumb and finger while it runs) it's a good sign. Dead spots tell you that one or more of the armature windings is defective.
But anyway, to flash it, all you have to do is touch the chosen battery live side terminal, negative in this case I think, momentarily to the F terminal of the dynamo (with the dynamo body earthed to the battery). You can reverse the polarity at will. Note that it doesn't affect the direction of rotation of the thing - that is controlled by which way the field coil wires are attached inside, or by which brush is live and which is earthed. When motoring, it should turn in the direction it is meant to go on the bike. There may be an arrow on the dynamo body, and it may even point the right way, although equally it may not, as any dynamo can go either way, with either polarity.
If you have a squirty can of contact cleaner, it's worth aiming it at the commutator while the dynamo spins, just as it is also worth giving the brushes a very gentle squeeze while things are in motion, to help with the contact.

[Mick D]

Here's a slightly more sophisticated test rig -

Too much information.

Shame its for an alternator/rectifier system and nothing to do with a dynamo

[DM2]

Shame its for an alternator/rectifier system and nothing to do with a dynamo

The test box can't tell the difference between a dynamo or an alternators rectified output.

The DC input with the 1 ohm load resistor will check the dynamo is working fine, ok it will only dump 36W into the load resistor (as long as you dont over rev the dynamo to get more than a 6v output) but will still show if the dynamo is working.

[electrajohnt]

Eureka,
Not got a clue why, after reading the latest suggested tests etc. I went into the garage, put a 12v 21amp on and it lit up, tried the 6v on and that lit up too.
Thanks everyone for your help, I'll put it on the bike now, hopefully it should work.
JohnT

[electrajohnt]

I'm back, guess you knew I might be, unbounded joy did not last long.
Put the dynamo on the bike, rotated it with the drill, hoping to see a flicker of movement at the ammeter (the ammeter works ok, it shows varying states of discharge dependant on what lights are switched on) no movement on the ammeter when the dynamo is rotated.
I decided to check continuity from dynamo forward. First port of call is the cut-out.
Selected Rx10k on the meter setting.
Below is a photograph of the underside of the cut out, from left to right the connections are labelled: D, E, A, F.
From both D and F terminals on the dynamo I get a full range swing on the multi meter for all the connections on the cut out. Not sure why but this does not seem correct.
As you can see the cut out is effectively sealed by the bent over tabs, do I need to straighten them to get inside and investigate the further?
OR,
Could I achieve something by adjusting the two screws shown the other photograph?

JohnT

[DM2]

Your test meter set on R*10K range wont tell you much as you will get a reading through the various shunt and seried coils inside the regulator.

Please don't play with the adjustment screws as you will only dig yourself into a bigger hole.

Disconnect the A wire on the regulator, spin the dynamo with the drill and see if you get a voltage output on the D terminal on the regulator, that will tell you if the contacts feeding the F coil are making a good connection.

If that is ok look for a voltage on the A terminal which will tell you if the cutout contacts are closing.

Most likely you will need to take the cover off and clean the contacts.

[56G80S]

http://www.jampot.com/forum/viewtopic.p ... 2&start=20

someone else's story on this.

More years ago than I want to recall, I threw out the original MCR2, fitted the replacement that you have. Threw that away and fitted an electronic regulator from Al Osborne.

Then everything works.

Johnny B

[SPRIDDLER]

Can't help with the meter resistance readings but the dynamo seems to be o.k. so there may simply be a broken or corroded connection between 'A' at the regulator and the headlamp switch.
Do you get a voltage reading between 'A' on the regulator and Earth with the dynamo turning? If so, check for continuity between 'A' and the other end of the wire where it arrives at the headlamp switch.