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Centaur Ignition Coil

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Clive Brown 115/07/2021 16:27:40
720 forum posts
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I'm intending initially fitting my Centaur gas engine with contact breaker points, as per ETW, as I already have a set. I now need an ignition coil, probably 12v.

The "traditional" Lucas type of coil is readily available on Ebay, but size-wise would look rather obtrusive.

Also cheaply available are motor cycle coils such as here. I have no experience of this type. Do they work with points and therefore be suitable for my purpose ?

Any advice would be appreciated.

Clive

JasonB15/07/2021 16:42:33
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You could try the Novus coil from Minimag which is not much larger than a 35mm film canister. I've used their LT coils on a few engines.

I've used the bike type coils that you show to make buzz coils so spark should still be OK and that was on 6V dry cell.

Edited By JasonB on 15/07/2021 16:43:41

noel shelley15/07/2021 17:25:41
850 forum posts
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My Lambretta had a small ignition coil, 1.25 dia X3" high at a guess. Noel

Clive Brown 117/07/2021 18:07:16
720 forum posts
34 photos

Thanks for responses. The Minimag coils look good except for the £49 price tag, so for starters I decided to go for an Ebay "cheapie", £6.66 inc.p&p.I'll now have to rig up a test circuit to see if it does the business.

Separately, I ordered this coil mid-day yesterday and it was delivered this afternoon. Amazing for the price, and well done Hermes!

duncan webster17/07/2021 22:48:04
3584 forum posts
65 photos
Posted by noel shelley on 15/07/2021 17:25:41:

My Lambretta had a small ignition coil, 1.25 dia X3" high at a guess. Noel

Do you really want the world to know you had a Lambretta? I bought a broken one very cheap once and mended it. First time I rode it I knew it had to go. Every corner had the bodywork scraping the tarmac. Sold it at a considerable profit and went back to my proper bike

Oily Rag18/07/2021 08:51:22
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Quote:-

The "traditional" Lucas type of coil is readily available on Ebay, but size-wise would look rather obtrusive.

Also cheaply available are motor cycle coils such as here. I have no experience of this type. Do they work with points and therefore be suitable for my purpose ?

Clive, have you looked at the Lucas 4V coils used on the Triumph / BSA triples (3 x 4V = 12V!) in the late 60's? they are quite small.

The coil shown by your link is for a Yamaha 80 and I suspect it is a CDI type coil, note the single LT tab. CD ignition characteristics are infinitely different to Inductive (or Hall Effect) ignition. My old boss at Lucas described it as 'forked lightening as compared to Sheet lightening' - an excellent analogy! If it is a CDI type coil it will need to be run in conjunction with a transformer to give it a ~400V primary charge.

Duncan,

"Do you really want the world to know you had a Lambretta?"

That made my morning! Spat my Shredded Wheet all over the place!!

Martin

JasonB18/07/2021 10:07:11
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Posted by Oily Rag on 18/07/2021 08:51:22:

The coil shown by your link is for a Yamaha 80 and I suspect it is a CDI type coil, note the single LT tab. CD ignition characteristics are infinitely different to Inductive (or Hall Effect) ignition. My old boss at Lucas described it as 'forked lightening as compared to Sheet lightening' - an excellent analogy! If it is a CDI type coil it will need to be run in conjunction with a transformer to give it a ~400V primary charge.

From what I recall when I used this type of coil for open crank engines the tab is common to both coils, the LT coil is earthed via the square bar passing through the middle when screwed to the frame and the HT coil earths via the plug. The square bar through the middle becomes magnetic when circuit is complete.

As I said they give a good spark, I was using simple wiper contacts and built the coil into a Buzz coil circuit but I can't see that would affect it's use with standard points.

Brown "live" to single spade connector, Blue neutral to switch then back to -VE on battery

Mike Poole18/07/2021 12:09:26
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Posted by duncan webster on 17/07/2021 22:48:04:
Posted by noel shelley on 15/07/2021 17:25:41:

My Lambretta had a small ignition coil, 1.25 dia X3" high at a guess. Noel

Do you really want the world to know you had a Lambretta? I bought a broken one very cheap once and mended it. First time I rode it I knew it had to go. Every corner had the bodywork scraping the tarmac. Sold it at a considerable profit and went back to my proper bike

When BMW took over Cowley they had a small fleet of the C1 scooters with a roof, I fancied a go on one but never found an opportunity at night so I wouldn’t be seen, I doubt it would have been exciting as scary and exciting are not the same thing.

Mike

Clive Brown 123/07/2021 11:38:41
720 forum posts
34 photos

Quick update on my (lack of ) progress. The coil I purchased has two windings with a common point around an iron armature. The resistance of the primary is ~1.5 ohms. A lash-up test circuit didn't produce a spark unless the spark gap was virtually zero, and then it was a tiny affair, nothing like Jason's video. Jason, what were you using to trigger your coil, some sort of oscillator circuit?

I think I'll buy a conventional car-type coil which I feel that I understand better, and use this to prove the engine, although that's still some time away.

Thanks for all the comments.

JasonB23/07/2021 13:01:33
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On top of the board in my photo are a set of Buzz or trembler coil points, these simple make and break the circuit many times as soon as the points contacts complete the circuit so you get a constant stream of sparks rather than just one. Think of an electric buzzer, when circuit is complete the iron bar in the middle becomes magnetic and then pulls the buzz contacts apart, so magnet stops and releases the contact which then completes the circuit again and so on at high frequency which can be adjusted by spring tension. This is the sort of thing that Model T fords would have used.

I think I was just touching wires together out of shot in the video rather than using the contacts on the engine.

Edited By JasonB on 23/07/2021 13:05:09

Roger B23/07/2021 15:31:30
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170 forum posts
76 photos

The smaller size traditional motorbike coils are available from places like here:

**LINK**

I have used them sucessfully on my model engines.

Tim Stevens26/07/2021 20:45:14
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1494 forum posts

The smaller bike-type coils work in exactly the same way as 'conventional' old-fashioned 12 v coil-ignition coils. Same current draw, same resistance etc. They do tend to get a bit hotter if not well out in the breeze, but I use one on a vintage* car and it copes admirably. No particular reason, I just had one in good nick and a bracket to fit, so I used it.

Cheers, Tim

* vintage = pre-1931, not as per Antiques Road Show etc, where it just means 'Old but I don't know about anything that I'm getting paid to talk about'

Edited By Tim Stevens on 26/07/2021 20:50:40

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