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pancho43

Newbie

Joined: 27/02/2009
Location: Australia
Posts: 10

Posted: 10:49pm 19 Feb 2014

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Good evening all you clever chappies, I hope you can help with my enquiry.

My apologies if this is in the wrong place, as my question is a bit electronic I suppose.
I have a Honda four stroke outboard that has no spark. Unfortunately parts for this 1997 model are no longer available. It has been a fantastic engine and I don�t think it has done that many hours, using no oil and up until this happened has been extremely reliable. It is fitted to a Trailer-Sailer so does not get as much use as a lot would, as I do like to sail if there is a reasonable breeze, but it needs to be reliable. I have been on u-tube and discovered how to make a GO/NOGO CDI tester and established that the CDI is ok.
On further testing I found that the primary ignition coil is faulty�open circuit. After carefully removing the epoxy covering from the coil, I found that the wire is .006 inch dia.
I have some .007 inch and some .005 inch wire, but no .006 inch.
My question is, would either of these dia. wires be ok instead.

I have purchased a mechanical counter for my lathe, so I can count accurately the number of turns as I unwind the old wire.
My fear is, would the slightly heavier .007 inch wire with the same number of turns, give a similar voltage but a stronger current, possibly damaging the SCR or some other component within the CDI, or should I use the .005 inch wire although much more delicate and easier to break.
I think that I would need to run the wire through a small nylon pulley mounted with a soft spring above the lathe to soften the jerky motion as it unwinds and then winds onto the square sectioned base or whatever it is called. Stator ??
Thanks in advance.
Cheers, Pete.

Pete

Bryan1

Guru

Joined: 22/02/2006
Location: Australia
Posts: 1344

Posted: 11:20pm 19 Feb 2014

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Hello Pete,
With wire of any size it comes down to ohms per metre so if you use thicker wire then less turns the same if you use thinner wire more turns. Now as you unwind the existing coil measure the length then work out what the ohms are. Then just use the wire you have and wind the right amount of turns. I'm in SA so if you are close I have some potting compound to encase the coils when your done too.

Regards Bryan
Edited by Bryan1 2014-02-21

pancho43

Newbie

Joined: 27/02/2009
Location: Australia
Posts: 10

Posted: 02:48am 21 Feb 2014

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Thanks for the reply Bryan.

I'm not sure I can accurately calculate the length, although I will be winding it onto an old alvey reel as I unwind the old stuff. I could try to count the number of turns of the reel, and being much bigger diameter than the coil i don't suppose it will be that many. I'll give it a go.
I'm assuming that by achieving a similar amount of ohms I would get the same current at a lower voltage. Is that correct. I'm sorry but I have never fully understood this sort of stuff.
I'm wondering whether it would be higher voltage (from more turns of the .005 in. smaller wire) or more current (from using the .700 in. wire), that would damage the CDI components or maybe even the secondary coil. this is what my main enquiry was about.
I have read that a bloke who overhauls CDI's on a motorbike forum finds that he replaces the old 400 volt SCR's that are normally fitted with 600 volt ones with great success, hence my hesitancy, as I dont really feel confident that I could do that kind of work, if the higher voltage damages my CDI.
Should I be worrying about Higher voltage or higher current, or should I just try to get some .600 in wire.

Cheers, Pete.

Pete

grub
Senior Member

Joined: 27/11/2007
Location: Australia
Posts: 169

Posted: 11:09am 21 Feb 2014

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I take that you require the coil to produce the spark to make the motor fire. If the remanufacture of the dud coil does not work, have you considered using a battery just to supply power for a spark?

The battery will go flat eventually but if you use a large deep cycle one then you should get enough out of it to run for the time period you need.

I have driven cars where the generator failed while driving and they ran for hours. I knew the generator was dead because the warning light was on and when I replaced the generator the warning light did not light up again.

Just a thought.

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 01:31pm 21 Feb 2014

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I have a friend that rewinds coils for a living and also rebuilds the CDI units.
He is based in Adelaide, but also do work for interstate and even worldwide.
I could put you in touch with Steve if you would like, he may even have a replacement coil.

I think you could have trouble unwinding the old coil and counting turns, as they are normally resin impregnated and not easy to get apart.

Steve impregnates his coils in a vacuum chamber after winding, without the resin the windings will vibrate and eventually short out.

You quote the coil is open circuit, this would imply there is a break in a wire not a burntout coil or shorted turns, try looking for the break, as it will likely be at the very end of the wire or close to the outside, removing a few turns of wire will not effect the coils operation and you may be able to repair the coil you have.

Pete.

Sometimes it just works

electrondady1
Senior Member

Joined: 12/02/2009
Location: Canada
Posts: 208

Posted: 03:57am 22 Feb 2014

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why wouldn't you just swap in another ignition coil from a similar engine?

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