Dynamo Testing (TC)

[SteveW]

I need to test my dynamo and I'm unsure as to how to go about it. I've seen guidance on testing it when on the car, but as I'm in the middle of rebuilding my engine, I need to do a bench test. It's been sat in a box for a long time, so I guess that I need to repolarise (flash) it before I do any other tests, so if anyone can point me to a step by step bench test guide, that would be great. Attached is a picture, could someone also confirm which terminal is which.

[Steve Simmons]

This isn't my strong suit but I'll give it a crack...

You will need a way to spin the generator to the equivalent of 3000 RPM engine speed (calculate for pulley diameter differences). I believe the only real test you can do without specialized equipment is to make sure it puts out voltage. Connect a volt meter to the D terminal (the larger of the two) and the other to ground (any bare metal on the case). Spin up the generator to appropriate speed as mentioned above. You should measure 2-4 volts. If no volts, check the brushes. If brushes are OK then your armature may be bad. If you get rapidly rising volts with increase in RPM, you may have a short somewhere.

With more sophisticated testing equipment, you can do more tests including load, which measures amp output / resistance. If you have an electric shop nearby, they should be able to test it for you, often for free. I think certain auto parts stores do this for free also (here in the USA at least), although the young guys might not know what to do with a generator.

Edit: Here is a more complete description: http://www.tcmotoringguild.org/techinfo ... checks.pdf

[Duncan M]

He may be talking about how to hook it up to a 12V power supply to test if it will spin as a motor. I never found that was a particularly useful or good test for a dynamo.

Keep in mind that a replacement armature is not obtainable anywhere, so treat it like gold.

After sitting 60 years I found the only thing really wrong with my dynamo was the fields tested abnormal with an Ohm meter. The insulating paper (between fields and case) had gotten brittle and cracked. Replacement of the special paper was all it needed. When it was all apart I did common sense cleanup and maintenance. Been working just fine for 6 years.

[Steve Simmons]

If it spins when 12V is applied then you know that it's at least functioning. Brushes, etc are good. But it doesn't tell you much else.

[SteveW]

It seems that the best way of testing one is to have the whole of the electrics installed in the car. I guess at this stage all I want to do is something that lets me know if it has a chance of working. I'm aware that doing the wrong thing can damage an otherwise servicable unit, hence the request for advice. I'm not that keen on treating it like a motor and pushing current through it rather than spinning it and seeing if I get a voltage.

How about I spin it up as suggested by Steve using a drill (I think that I would need a battery drill that I can run in reverse).

[frenchblatter]

Steve, do the test to see it spins, It's very easy to remove the dynamo when the engine is running and NTG can get it overhauled in a couple of days.

To check a dynamo - disconnect the wiring, then join the two connections on the dynamo together with a bit of wire - rig a jump lead from earth to the case (if it's not on the engine) and then touch a lead from +ve to the joined up wires - the dynamo should run as a motor (make the fan belt very loose first!). If it motors - it's fine.

You will need to reverse the above advice as you have positive earth.

[Steve Simmons]

Just keep in mind that it's unregulated, so don't spin it too fast. I wish I had the specs handy on what the actual generator RPM is at 3K engine RPM.

Here is another test from the late Dave Dubois. It was likely written for a C40, but I'd imagine the principle is the same.

Double-check the generator/dynamo - once correctly polarized - by disconnecting the wires from its
terminals, connecting the two terminals together and connecting a multimeter, set to the 50 volt scale,
between the two jumpered terminals to ground (note: for best results use an analog meter not a digital
meter). Start the engine – DON’T rev it!! - just slowly increase the revs, watching the voltmeter. It
should get to 20v by the time you get to 1000 rpm. DON’T exceed 20v. If the voltage stops increasing
before reaching 20v, the generator needs repair. If the generator checks out reconnect the wires to the
dynamo. Connect the multimeter between D terminal of the regulator (brown/yellow wire) and ground,
again start up and slowly increase the revs watching the voltmeter. The voltage should rise then
stabilize at about 14.5v, if it goes higher again don’t let it go over 20v. If it stabilizes at 14.5v it is
charging OK. If the D terminal shows only about 1v there is a disconnection in either the brown/yellow
or the brown/green between dynamo and control box, or a fault inside the regulator.

And here is more info that may help, straight from the Lucas service manual...

[Duncan M]

This link tells you how to check Ohms on field coils--on bench. Original TC dynamo has two field coils, like the first picture at top.

http://www.dynamoregulatorconversions.c ... inding.php

Getting into very esoteric areas, here. Many auto electric places would not have a clue how to do this or render repairs.

[SteveW]

Thanks for the advice.

I've tested the field coils and I get 6.9 ohms, which is exactly right according to the link that Duncan provided. I then connected a multi meter between the D terminal and ground and spun up the dynamo using an electric drill driving a socket on the pully bolt. I couldn't spin it very fast due to the speed of the drill, but it registered a volatage. Overall, I think that's good enough for the moment and I'll do a more thorough test when I can run the engine.

I then went to test the starter motor and got stuck because I know that the pull switch that attaches to it is in my garage somewhere, but it was evading capture so I'll have another look later.

[Ray White]

I then went to test the starter motor and got stuck because I know that the pull switch that attaches to it is in my garage somewhere, but it was evading capture so I'll have another look later.

I know the feeling. Frustration doesn't begin to describe it. I have a black hole in my garage that Stephen Hawking would have been proud of!

[Steve Simmons]

One of the best things I ever did was to spend an entire week emptying every cabinet, every shelf, every dark corner of my garage and organizing the parts into car/part type. Then I bought a whole bunch of cheap plastic storage bins of varying sizes and put the parts in those, then put all the bins back in the cabinets. Every plastic bin has a label on the front so not only do I know it's in there, but I can see through the clear plastic. Not only has my life become a whole lot easier, and not only can I find parts much, much faster, but I've saved money because I don't have to buy parts that I already own anymore.

One of the TC part cabinets...

[SteveW]

That's what I did and I even took a photo of what was in each box. However, the starter switch isn't in its box and doesn't seem to be in the other ones either. Presumably I took it out for some reason, but I cannot for the life of me think why I did that or what I did with it.

[frenchblatter]

Steve, if you stop looking for it, you'll find it.... works for me every time.

[SteveW]

I'm 100% certain that it will turn up the day after I buy another one.

[bloodysalmon]

Steve, I have a spare you can have so when around pop in ... Chris

[SteveW]

That's great Chris, thank you. By the way, Lou says that your not allowed to move.

[SteveW]

I'm a scientist by training, so I like to think that I have a rational (if a somewhat Newtonian) view of the world, so I'm struggling with this...

For the last couple of days I've been searching my garage high and low looking for my starter switch, but without any success. Yesterday, Norman Verona predicted on here that I would find it as soon as I stopped looking for it. Of course, being a rational scientist, I knew that this wasn't true. This morning (again on here, so there is evidence), Chris Blood said that I could have his spare, meaning that I had no need to look for mine any more. This afternoon, I walked into my garage to do something else and within 30 seconds I had found my switch!

Norman - if you have a moment, could you send me a PM with next weeks winning lottery numbers please?

[bloodysalmon]

well i'm blowed ... excellent news of course but this does set a precedence for finding the things you need ... um, what am I looking for in life?
Steve, I've 2 of those Y shaped pipes ... have a look for a Z-shaped one and you never know!!!!