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Low voltage at the coils

  • Thread starter Thread starter LarryA_Texas
  • Start date Start date
L

LarryA_Texas

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I know there is a coil relay mod for this and I'll probably do it but this seems kinda strange to me so I thought I'd ask:

1982 GS650 E

Voltage at the battery 12.35
Voltage at the fuse panel 12.10

Voltage at the coils with all wires connected; 9.6
Measured this voltage at the orange/white connector blade.

When I DISCONNECT the Black/yellow wire from the right coil the voltage jumps up to about 12

With that wired connected and the white wire disconnected from the left coil the voltage stays at 9.6

(In other words; there is good voltage at the coil when the black/Y wire is disconnected from the right coil but there is a drop when it's connected properly. The white wire on the left coil has no affect on voltage whether connected or not)

I wired in a different coil and got the same result: significant voltage drop when the right coil is connected.

With the old coils connected I wired in a different igniter box. Same result; good voltage when the black/yellow wire is not connected but a significant (1.5 to 2 volts) drop when the black/yellow wire is connected.

Removing the signal generator had no affect. The voltage drop is still there even if the SG is not connected at all.

As a last resort I pulled the black/yellow wire out of the harness looking for a cut or something where it might be shorting out. Nothing...just one straight, clean wire from the igniter connector to the coil plug.

Any ideas?

And, yes, this is having a significant impact on starting. There isn't enough voltage for ignition when the starter button is pressed. The starter engages but there is not enough spark to ignite.
 
12.35v is pretty low for battery voltage. Poor connections add to the problem, so coils and ignitor ( both connected) see even less. Less than 10 volts to ignitor might not let it work right. And when you hit starter button, system voltage drops even more. Scoop a wiring diagram off Basscliff's site and you should be able to figure out how to jury rig jumper wire from battery positive to ignitor plug orange/white wire to bypass the harness. The plug is under seat -top right side- IF IF your bike is similiar to mine.
 
LarryA_Texas said:
I know there is a coil relay mod for this and I'll probably do it but this seems kinda strange to me so I thought I'd ask:

1982 GS650 E

Voltage at the battery 12.35
Voltage at the fuse panel 12.10

Voltage at the coils with all wires connected; 9.6
Measured this voltage at the orange/white connector blade.

When I DISCONNECT the Black/yellow wire from the right coil the voltage jumps up to about 12

With that wired connected and the white wire disconnected from the left coil the voltage stays at 9.6

(In other words; there is good voltage at the coil when the black/Y wire is disconnected from the right coil but there is a drop when it's connected properly. The white wire on the left coil has no affect on voltage whether connected or not)

I wired in a different coil and got the same result: significant voltage drop when the right coil is connected.

With the old coils connected I wired in a different igniter box. Same result; good voltage when the black/yellow wire is not connected but a significant (1.5 to 2 volts) drop when the black/yellow wire is connected.

Removing the signal generator had no affect. The voltage drop is still there even if the SG is not connected at all.

As a last resort I pulled the black/yellow wire out of the harness looking for a cut or something where it might be shorting out. Nothing...just one straight, clean wire from the igniter connector to the coil plug.

Any ideas?

And, yes, this is having a significant impact on starting. There isn't enough voltage for ignition when the starter button is pressed. The starter engages but there is not enough spark to ignite.
Click to expand...
To clarify:

As I read your post, I understand that the question you are asking is:

"Why does the voltage drop when B/Y is connected?"

This sounds like there is extra impedance across the circuit. You've already checked for an obvious break or cut, but there could be something happening inside the insulation that you cannot see.

Have you checked the resistance across that one wire?

Just shooting in the dark a little. Electrical is not my strong suit (yet). I hope I'mnot going to muddy the question with the following.



The wiring diagram I'm looking at for my 650G shows B/Y connecting back to the R/R.

Could it be a bad ground connection or a closed contact drawing power somewhere else in the B/Y wiring?
 
BigD_83 said:
To clarify:

As I read your post, I understand that the question you are asking is:

"Why does the voltage drop when B/Y is connected?"
...
Could it be a bad ground connection or a closed contact drawing power somewhere else in the B/Y wiring?
Click to expand...

Well, the question would be "any idea why disconnecting the right coil would allow the voltage to climb to normal when disconnecting the left would have no effect?"

I sorta feel like if I do the relay mod I'm masking a problem somewhere else. Good point about checking the ignition; I'll do that soon. Also will look for resistance in each of the wires involved.

This bike has been an electrical 'problem child' for a while. If I can lick this low voltage at the coils thing I'll probably have cured it. (hard to start and weak battery) I just don't get what could be different about the left and right coil.

By the way; 7.5 ohms on both coils when checked on positive and negative blades.
 
Leakage current!

What is the resistance across the primary and secondary windings in the black/yellow coil?

Edit: I didn't see the last part of your post.
Hmm.

Does your voltage drop any differently if you attach the black/yellow trigger to the other coil? (IE switching white trigger with black/yellow trigger?)
 
Last edited:
Were you checking the battery voltage with the key ON?

Try to get the bike running, then measure the battery voltage and the coil voltage, then compare them.

If your battery had 12.35 volts before you turned on the key, it would have a bit less when the key is ON.

Why does one coil affect it and not the other? Because there might not have been current going through both coils.
I am not sure exactly how the ignitor trigger mechanism works, but I think one triggers on a positive pulse, the other triggers on a negative pulse.
Depending on where the crank stopped, you might only have one coil enabled. If you stopped the engine at random points in its rotation,
you might find the other coil is the one that will affect the voltage.

This is another reason I suggested having the engine running for your tests, as both coils will be seeing the same current through them.

.
 
Steve said:
Were you checking the battery voltage with the key ON?

Try to get the bike running, then measure the battery voltage and the coil voltage, then compare them.

If your battery had 12.35 volts before you turned on the key, it would have a bit less when the key is ON.

Why does one coil affect it and not the other? Because there might not have been current going through both coils.
I am not sure exactly how the ignitor trigger mechanism works, but I think one triggers on a positive pulse, the other triggers on a negative pulse.
Depending on where the crank stopped, you might only have one coil enabled. If you stopped the engine at random points in its rotation,
you might find the other coil is the one that will affect the voltage.

This is another reason I suggested having the engine running for your tests, as both coils will be seeing the same current through them.

.
Click to expand...
Good point about the crank rotation, Steve. I inadvertantly (i.e. was a dumba**) left the key in the ON position with the battery tender connected, and when I checked on the bike the next day the left coil (and only the left coil) had gotten hot enough to melt the dielectric grease off the spades such that it dripped onto the engine and floor before solidifying like candle wax.
 
Just do the coil relay mod. I resisted for a year or two and cleaned every connection and switch I could find - had very similar readings to you.

I couldn't get my head around how it could make such a difference - I was sure there had to be some other way or something I was missing. I even replaced points for a dyna and then the coils (even though they tested good...) mind you I also saw it as a bit of an upgrade.

But it's a sweet thing to see full voltage at those coils.
 
Coady said:
Just do the coil relay mod. I resisted for a year or two and cleaned every connection and switch I could find - had very similar readings to you.

I couldn't get my head around how it could make such a difference - I was sure there had to be some other way or something I was missing. I even replaced points for a dyna and then the coils (even though they tested good...) mind you I also saw it as a bit of an upgrade.

But it's a sweet thing to see full voltage at those coils.
Click to expand...

At 10 amps, it only takes 0.1 ohms to get a 1 volt drop between battery and coils. So just a little corrosion in either the ignition switch or the starter switch will cause these drops. If you live in a humid area, trying to keep the contacts that clean is gonna be a constant battle.
 
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