Charging coil resistance?. 1980 Yamaha 40 BM

[elliotgr]

Hi Can anybody help. The charging coil (the one that supplies the power to the CDI) has blown. As it is an old motor, it probably is easier to wind the coil myself. Any idea of what the resistance should be?

[boscoe99]

205 ohms brown lead to blue lead. Plus or minus 20%. At 68 degrees F.

Don't forget to check either of the leads to ground. There should be no connection to ground.

[cpostis]

205 ohms brown lead to blue lead. Plus or minus 20%. At 68 degrees F.

Don't forget to check either of the leads to ground. There should be no connection to ground.

You are my CIA guy!!

Now, questions come to me. I am assuming elliotgr is going to measure the circumference of the coil wire (gauge), find out the ohms per thousand feet of new wire, and calculate the length of the coil wire he needs for the resistance you posted?

Does amount of turns need to be considered?

[99yam40]

I would think number of turn needs to be counted

[boscoe99]

I think that the diameter of the wire would be measured to determine the needed wire size.

The number of turns should not affect the resistance as long as the total length and diameter of the wire remains the same. But...

Voltage generated when a magnet passes a coil is a function of the number of turns of the wire in the coil. More coils means a higher voltage. Amongst a number of other things of course.

So, the same number of coils should be used if and when the charge coil is rewound using the same gauge wire as was used in the original coil.

I appreciate folks that take the time to do something like this.

[cpostis]

I think that the diameter of the wire would be measured to determine the needed wire size.

The number of turns should not affect the resistance as long as the total length and diameter of the wire remains the same. But...

Voltage generated when a magnet passes a coil is a function of the number of turns of the wire in the coil. More coils means a higher voltage. Amongst a number of other things of course.

So, the same number of coils should be used if and when the charge coil is rewound using the same gauge wire as was used in the original coil.

I appreciate folks that take the time to do something like this.

No idea of the gauge wire on the original. But, I looked at magnet wire resistances for a 40 gauge 1,000' for the purpose of discussion. It is 1,079 ohms.

So, elliotgr would need about 190' of this 40ga magnet wire to get 205 ohms resistance. Say (again, for discussion) his iron core is equal 2.5" in circumference and after the coil wraps the coiled wire winding is about 4.5" circumference. Average would be 3.5".

Number of turns should equal about (190' x 12)/3.5".
That would come to about 650 turns.

Do you think just being sure you wind the proper gauge magnet wire of the resistance length needed on the core tight and even would be accurate enough? I'd probably make a rig to use on my drill press to do this?

What ya think elliotgr/Boscoe?

[boscoe99]

I think I would buy a replacement OEM coil.

[cpostis]

I think I would buy a replacement OEM coil.

Might be tough to find one for that 36 year old motor!

[elliotgr]

Thanks for all the responses. The charging coil was 120 to 150 ohms according to an old manual I found. The two old coils I had both measured 135 ohms but gave different issues. One would not idle, the other would not let the motor go past 3/4 throttle. Must have been breaking down under load. But I did it the easy way. Measured thickness of wire. Got resistance per meter for the wire which was 0.18 mm thick and 0.679 ohms per meter. Meters required = 206 m. So wound on 206 m by eye based on previous thickness of coil and then slightly over-wound it. I made a simple jig on the lathe and ran at slow speed. Took about 5 minutes to wind. I then stripped back small part of varnish on wire to test. Result 139.9 ohms. So sealed it with epoxy and back into motor. Motor starts and revs. Now to test under load on the weekend. Will let you guys know how it went.

[boscoe99]

Might be tough to find one for that 36 year old motor!

Just a phone call and credit card away.

6H4-85520-00-00 YAMAHA COIL,CHARGE

[cpostis]

Just a phone call and credit card away.

6H4-85520-00-00 YAMAHA COIL,CHARGE

Now how did you find/confirm this Agent 99?. It is the same for this 1980 motor?

[cpostis]

Thanks for all the responses. The charging coil was 120 to 150 ohms according to an old manual I found. The two old coils I had both measured 135 ohms but gave different issues. One would not idle, the other would not let the motor go past 3/4 throttle. Must have been breaking down under load. But I did it the easy way. Measured thickness of wire. Got resistance per meter for the wire which was 0.18 mm thick and 0.679 ohms per meter. Meters required = 206 m. So wound on 206 m by eye based on previous thickness of coil and then slightly over-wound it. I made a simple jig on the lathe and ran at slow speed. Took about 5 minutes to wind. I then stripped back small part of varnish on wire to test. Result 139.9 ohms. So sealed it with epoxy and back into motor. Motor starts and revs. Now to test under load on the weekend. Will let you guys know how it went.

Hope you find positive results! If I ever need a coil wound, I'll call you!!!

[boscoe99]

Now how did you find/confirm this Agent 99?. It is the same for this 1980 motor?

If I told you I would have to kill you. You are to be kept alive and around for other useful purposes. Therefore, I cannot disclose the method to my madness.

[elliotgr]

The coil I have is different to the one shown. Only one brown wire from it. The other end is earthed to the former. But it runs and idles smoothly on the trailer. Hopefully it will perform once in the water on Saturday!

[99yam40]

Thanks for all the responses. The charging coil was 120 to 150 ohms according to an old manual I found. The two old coils I had both measured 135 ohms but gave different issues. One would not idle, the other would not let the motor go past 3/4 throttle. Must have been breaking down under load. But I did it the easy way. Measured thickness of wire. Got resistance per meter for the wire which was 0.18 mm thick and 0.679 ohms per meter. Meters required = 206 m. So wound on 206 m by eye based on previous thickness of coil and then slightly over-wound it. I made a simple jig on the lathe and ran at slow speed. Took about 5 minutes to wind. I then stripped back small part of varnish on wire to test. Result 139.9 ohms. So sealed it with epoxy and back into motor. Motor starts and revs. Now to test under load on the weekend. Will let you guys know how it went.

It would have been good to have taken peak voltage reading of the old coils and your newly rewound one so you could have compared the readings.

Also if the old ones were breaking down the volt meter would have shown that by monitoring the voltage while the problem showed up.

very strange one would break down at idle and the other at higher RPMs