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Member postings for Tim Stevens

Here is a list of all the postings Tim Stevens has made in our forums. Click on a thread name to jump to the thread.

Thread: A dynamo question: rotation direction?
13/05/2019 17:23:28

Windings correctly connected (using a truly magnetic compass) and away it goes, the right way round.

I still wonder why it motored the wrong way with field coils alternately the right, and the wrong way, round. Ho hum.

Cheers, everyone - helpful as always


12/05/2019 15:55:43

Aha - I think I have discovered my problem - or at least one of my problems. When connecting the coils I fitted the steel centres to each coil, and used a small current and an old plotting compass to check the polarity. Now, though, I have checked again with a new compass, and I have four poles the same way round. All I can imagine is that I am getting old and dafter (true) or the the old compass had lost any magnetism it ever had (quite likely, I think it came from a cracker about 4 moves ago ie 30+ years), and simply was attracted to the first magnetism it saw.

So, I will now reverse the winding connections of two opposite poles and try again.

But this does not answer vthe question fully - it should have declined to rotate altogether, surely?

Robert - I am in Knighton, Mid-Wales, and you are welcome to come if you wish, but give me a day or two to change the connections, re-tape etc, and rebuild, ready for a further test session.

Regards, Tim

PS for Sale - vintage plotting compass, only used by two old ladies to go to church.

12/05/2019 14:29:24

Robert G8RPI: A very helpful (1960s*) summary which is a reminder of stuff I already have at my fingertips. [See latest edition of the Vintage Minor Register newspaper.] So, unless I am missing something, I am no further forward. Thanks, though - the answer ought to be in there somewhere so I conclude that my fault(s) is/are fairly non-standard. Perhaps I have inadvertently fitted two N and then two S coils, rather than NSNS, or even three of one and one of the other. But I don't see how that would give the symptoms I have - so perhaps I have got two things wrong at the same time.

* For interest - I suggest this date for these reasons:
1. only as late as 1960 was the third brush system on the way out:
2. The diagrams show the mainly post-WWII positive earth wiring;
3. The typeface only became generally available in about 1960 - before that it was Times property.

Thanks anyway. If all else fails can I parcel the thing up for you to look at ... no, I thought not

Regards, Tim

12/05/2019 11:52:26

Nimble: Yes, it would but changing the field current direction should change the movement, and it doesn't.

Nicholas: Yes, tried that (along with all the other tricks I know about) - makes no difference.

Trevor J: It is a CAV dynamo - but they were owned by Lucas at about the same time ?1930. My problem is that I have reversed the field connections and it made no difference. I guess that the dynamo number will not be much help as I am not clear how much of it is original, etc. For certain the barrel with the field windings is not the same as the original (but seems identical in appearance, dimensions etc.)

Vintage engineer: They cannot be reversed end to end as the connections won't reach; nor back to front as the curved shape is wrong; nor moved round one place as the slots for the through bolts won't line up. So, I swapped the field connections (which should do the same thing as your suggestions) and it made no difference.

Russel: There was a third brush, but it is not used. The field windings were 'earthed' at the third brush, in effect, but I have connected this end (of the new thinner windings) to the earthed armature brush. And I agree - I can't understand what is happening either.

So - I am going to spend some time with a plotting compass and a low-voltage supply, to see what exactly happens to the field magnetism in various wiring conditions. I'm hoping I don't have to start again with another rewind ...

Regards, Tim

11/05/2019 23:20:11

There is a certain amount of confusion - sorry. I start with a few facts in clarification:

1. The existing field coils were duff, so needed rewinding anyway. Therefore 'Just fit a regulator' does not address the issue.

2. I am not (yet) trying to test whether it generates. I know it motors and I need it to motor in the other sense. Motoring does not rely on a small amount of residual magnetism, as the field coils are energised by the applied voltage. The residual magnetism is only relevant when I test it as a dynamo. And in any event, I have tried flashing and while I did pass current, it made no difference.

3. The reason we have a cut-out on a traditional dynamo circuit is to stop the dynamo, when the engine stops, trying to turn as a motor. It is trying to turn in the direction it normally runs, so I am trying to test my dynamo to see if it will motor - but it does so the wrong way round.

4. Swapping the brush connections won't help in this case as one of the brush holders is earthed, or, more accurately, only one holder is insulated from earth.

5. Swapping the field winding end to end is surely the same effect as swapping the brush connections? This is what I have done and it makes no difference - that is my problem.

6. The problem is not to do with positive or negative earth wiring. A good dynamo will motor in the right direction whichever system is applied (but doing this the 'wrong way round' is likely to set up the residual magnetism the wrong way for charging the 'right way round'[close parenthesis].

So, thanks, everyone for your helpful replies, but we're not there yet.

Regards, Tim


Edited By Tim Stevens on 11/05/2019 23:22:28

Thread: What makes your bristle?
11/05/2019 18:38:47

If there is a problem with tooth goo running down inside the device, would it not make sense to brush your teeth while hanging upside down?


Thread: Honing motor cycle small ends
11/05/2019 17:02:03

Goodness, it was 50 years ago, and I can't see through the fairing ...

But if the bike was used in the TT between 1974 and 1980 I expect I scrutineered it at least once.

Cheers, Tim

11/05/2019 15:12:39

Bending the rod to get it as near as possible was standard practice when I was in the business. Almost my last job at BSA was aligning the little-end on one of the first B50s - then I finished the assembly and put it on the brake.

And if you know anyone who could use a complete Hennan and Froude brake, do let me know. I know of one in the UK which needs a new home for not too much dosh.

Cheers, Tim

Thread: A dynamo question: rotation direction?
11/05/2019 15:02:13

I am restoring a dynamo from an Austin 7 about 1930. The owners needs 12v so I have rewound the 4 field coils with new thinner wire, carefully (I thought) checking the winding directions LRLR. Connect it all up and test with the Field and Output connected together to live, and the body to earth. It motors round as expected, but the wrong way round. So, I rearrange the connections of the field winding set so their current is reversed, leaving the brush connections the same. And once more, it goes the wrong way round. Where am I going wrong?

Conventional shunt dynamo, four field coils, brushes at right angles. No third brush or other complications.

PS: yes, you guessed, this is a follow on from my Empire Tape query for which you were all very helpful - thanks.

Regards, Tim

Edited By Tim Stevens on 11/05/2019 15:03:47

Thread: Which thread for T nuts
09/05/2019 17:31:00

The nuts need to fill the slots with a little clearance for swarf, etc. Which studs you use - as long as they fit within the slots - is up to you, so M8 would be OK but not so rigid, should you need it, as M10. Or, if you like, use UNF or BSF threads - but if you have a variety of thread choices, stamp the size on the T-nut so you don't get cross threaded, literally

Cheers, Tim

Thread: Pulse Jet Carburator
09/05/2019 17:14:44

Clever things, pulse jets. You start with a working two-stroke single, with a reed valve inlet and tuned resonant exhaust system, and you take away the engine and just join the rest together. Exhaust dimensions limit the frequency, so with a model I guess the sound is not at all reminiscent of a V1?

Reed valve petals can be made by spark erosion, electro-etching, and in extremis, nail scissors. But why not a flutter-box as used in the device mentioned above?

Cheers, Tim

Thread: Threading 1/8 stainless steel
01/05/2019 18:00:15

It might be that the rod is hard-drawn, so the surface has been work-hardened in manufacture. If your job does not need the top end of the high-tensile capability, try the effect of softening the rod with heat.

Cheers, Tim

Thread: A Unique Word?
27/04/2019 17:10:37

Isn't the point about words that they should all be unique? A quality which I recognise is not at all common in English, though.

PS highhanded


Edited By Tim Stevens on 27/04/2019 17:12:52

Thread: Coil binding tape = Empire tape? Suppliers?
27/04/2019 17:08:03

Hello Jason

Yes, I have ordered wire and varnish, but they seem only to have self-adhesive glass-fibre tape, and I am not sure this will enable the regular tightening as the wrap is applied. And what is the effect of heat on the adhesive, I wonder?

Thanks anyway.

Phil - I have asked the Empire Tapes firm by email, as I cannot find the 'right stuff' in their listings. Perhaps the only users now are in China and India, and use local stuff? Thanks.


Thread: The Chocolate Fireguard as designed by Mercedes Benz
27/04/2019 16:51:46

Could it be (I suggest cautiously) that the general run of drivers of Mercs, Audis BMWs etc seem to be totally incapable of looking under the bonnet, or finding the toolkit (if any) or understanding any of the bits or warning lights etc? So the number of truck rescues for them is high. Whereas those of us with second-hand fiestas, skodas, etc, will have a go ourselves, first, and might not need a rescue truck?

Or in other words, some people are ashamed to have cars which need attention, while others are ashamed if they need attention by someone else.

Cheers, Tim

Thread: Coil binding tape = Empire tape? Suppliers?
27/04/2019 16:43:30

I should have said, of course - a UK supplier would be helpful, but other sources are not excluded, just slower, usually.

And it is only the field windings I am renewing.


27/04/2019 16:31:51

I am rewinding a dynamo and I have located supplies of enamelled copper wire. What I also need is the cotton (?) tape to wrap the windings. It used to be called Empire tape but then, we used to have an Empire. So, what is it called now, and is cotton still the better material? Or glass fibre or what?

Many thanks


Thread: Dialect expressions
18/04/2019 15:50:29

Liverpool lads have a way of reducing all their words to a diminutive. One of my students said ' I was going past whizzy ozzy on my placky and I ran out of petty' - so I knew he was riding his moped (plastic fantastic) past Whiston Hospital when he ran out of petrol.

In Dudley I was once accosted by a pre-school lad asking 'Ow dam yeow?' I think it was his birthday and he wanted to know how old I was ...

cheers, Tim

Thread: No 20 machine oil
08/04/2019 17:41:14

I think the answer will depend on the country where the instructions were written, Adrian. Rather like hat and shoe sizes, I'm afraid - so offer a bit more detail and someone (from that country, ideally) might be able to help.

Cheers, Tim

Thread: LED light array
08/04/2019 17:35:49

Er, might it be worth rotating the clear cover so that the majority of LEDs can shine through the clear areas? 10 degrees should be OK for the two outer rings and at least half of the innermost ones.

Cheers, Tim

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