Marine coil?

[chrishewett]

No replies to my post requesting info on suppressing electrical interferance so can anyone answer me this?
It has been suggested to me that the reason I am getting problems with the engine interfering with the echo sounder is that I am using an ordinary car coil. I can buy a "marine coil" from Fairways Marine for £45 + the governments bit. The question is: will it be any different from the coil I am using and will it stop the interferance? All they can tell me at Fairways is that it is the coil they always fit and they have never heard of any problems like mine.

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[Jean]

Tracing interference is not necessarily simple and trying a different coil type, I'd suggest, probably not the answer (but, you may be lucky!). Generally, interference could be air bound via radiated magnetic/electric fields (hence need to look at cable runs/segregation) or conductor bound (along the wiring, hence appropriate suppression needed). Regarding "appropriate" suppression, either trial and error or specialist kit needed to check it. Remember too, when checking wiring segregation, not just the 12v supply to the unit, but also the transducer cable and appropriate screening. Hope this helps.

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[mickshep]

Used ordinary car coils on my old Stuart Turner 10 hp. no problem. bought several bits off Fairways;
a) Starter button---------poor quality & 4 times the price of identical switch from 1 of the mail order marine stores.
b) Charge light for control panel,-------- fitted with screw in bulb in a bayonet fitting, also manytimes the price of identical fitting elsewhere.
c) On/off/on ignition switch. very good quality ----- again at inflated price.

A friends engine did have interference problems, the source of the problems was the points. he cured it with a suppressor which was attached to the engine in the area of the points cover, how it connected electrically I do not know. I do remember having to do something similar when fitting a car radio,(when cars had points) Hope this is of use. Cheers, Mike.

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[paulrossall]

You need to make sure your transducer cable does not go anywhere near your engine. I would pull the transducer cable back to where it goes through the hull and plug it directly into the depth sounder leaving the cable loose in the cabin and see if that makes any difference. If it doesnt at least you have eliminated one possibility. It is a matter of slowly eliminating possible causes.

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[andyball]

I'd be a little surprised if a "marine" coil was much different in stopping the interference.

Assuming the sounder cables (power supply and sensor) are well away from the engine, I'd start by checking the points(?) & condensor....then try a resistor plug &/or cap.

With troublesome radio interference, I've fixed it before by supplying the radio straight from the battery terminals (+ & - )...not using any existing wires that feed the engine. Could be worth trying that with your depth sounder.

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[chrishewett]

The display is still affected when the transducer cable is disconected so I assume it is not the cause of the problem. I have tried a completely seperate power supply and that made no difference. The points have a capacitor anyway, is that not a suppressor? As for wiring runs, in such a small boat there really are few options. I have considered trying to shield the echo sounder or engine completely but am unsure what material to use. Thanks for all the thoughts sofar.

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[qsiv]

In that case the interference is on the DC supply side, or worse the alternator is feeding a significant AC component to the DC system.

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[chrishewett]

Dont quite understand what you mean. Do you mean the power supply to the sounder? The engine has a dynastart system and the problem is there when it is in start or charge mode.
Chris

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[qsiv]

In that case it would almost certainly be interference - but I've not often come across interference at a level that would have such a big impact (unless the sounder is very susceptible to interference on the DC supply).

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[mickshep]

I'm no expert, but, As I understand it the capacitor stores some of the charge that is released when the points open. Like a small rapid charge/discharge battery, the suppressor prevents the interference which can occur with an electrical discharge and is a small but similar looking object, I could be wrong of course but we definately fitted them to our cars when we fitted a radio. Mick

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[chrishewett]

You seem to have a lot more knowledge than me on the subject. Any suggestions as to the type of material I should use to attempt some shielding? I still dont understand what you mean by "interferance on the DC supply"
Chris

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[andyball]

"interferance on the DC supply" just means it reaches your depthsounder via the + & - leads. Since you've tried an independent supply & found no improvement, this is fairly unlikely to be the problem....& even if it is, it's likely a problem with the ignition or dynastart on your engine.

Did this problem suddenly arise? or has the depthsounder just been fitted & always suffered when the engine runs?.

A "3.3 supressor" between coil+ & earth was probably a capacitor...if this worked before & doesn't now: suspect points &/or condensor problems & look at these.




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[chrishewett]

I fitted the echosounder last season and had the problem immediately. I fitted the suppressor and the problem was solved but I didnt use the boat much after that. Over the winter I started the engine several times and had no problem with interferance but soon after I put the boat in the water I noticed that the problem had returned. I assumed the suppressor had broken down but with new ones the engine would not start. New points and condensor were fitted last year. The engine still runs well as long as I dont fit a suppressor to the coil.
My head is begining to hurt with this one! I always believed that all problems were solvable but I am begining to doubt it now.
Chris

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[andyball]

righto

Forgive the b.obvious suggestions....?

you're certain you've connected the new supressor from coil+ to earth...not to the contact breaker side of the coil?

if ok then maybe a prob. with the condensor/points even though they were new last season- something will explain why same size supressor stops the spark when worked fine before.

Could be condensor, points gap/condition, dodgy plug/cap, low voltage reaching the coil (check w/points closed) or even the coil.

Everything's solvable, but sometimes substitution is easier.

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[DMGibson]

As another contributor has already commented, it is extremely difficult to diagnose interference problems this way.

However, a thought from reading your original post where you said the engine stopped running when you changed the capacitor make me wonder whether the capacitor across the points has failed. This unit is NOT for suppressing the electrical interference, but is an important part of the circuit for generating the spark. One symptom of failure is that the points burn out very quickly, another is that the engine is difficult to start, and another is that it causes a lot more electrical interference. Just to clarify things a little, this capacitor is connected to the junction of the points and the coil, with the other end to the chassis (usually through the capacitor body).

A suppressor capacitor is connected to the other end of the coil, which is also connected to the battery through the ignition switch. This capacitor has no effect on the running of the engine, only on the amount of electrical noise produced by the ignition.

Another thought is that the dynamo or the regultor could be causing the problem - have you tried using the echo sounder with the dynamo disabled? Suppressing interference from them is even more fun!

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[brianrunyard]

Have you tried a suppressor on the supply side of the coil?

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard