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Voltage to coil??

earlfor

earlfor

Forum Guru
Past Site Supporter
TGSR Superstar
Charter Member
On my 750E, with the bike not running, my multi meter shows 12.8 volts at the battery and with the ignition turned on, the meter reads 10.2 volts into the coils. It seems to me this is an excessive drop. Can anyone tell me their standing battery voltage and voltage to their coils so I can compare? I could accept 1/2 volt drop or so, but 2.6 volt drop?

Bikes been running rough and is getting worse. Its now bad enough that its unridable. I've already checked, fuel, carbs, plug caps, plugs, battery, ignition timing, and replaced points, so I'm reasonably sure its low system voltage (due to faulty wire, bad connection, switch, etc) or a coil going bad. I have my doubts about a coil as all four plugs are burning about the same and all four plugs are firing. I'n thinking it has to be a wiring harness problem due simply to old age. :-) If anyone has any other ideas,.......I'm all ears. :-)

Earl
 
I hope this isn't bad. I just checked my '78 1000 and it has 11 at the battery (it's real cold here and I haven't started it for a while) and 7 at the coils.

Steve
 
I think 11 volts would be a pretty well discharged battery and any load is going to pull the voltage down quickly. BUT... living in south FL and not dealing with batteries in really cold weather, I couldnt say if your voltages are normal or not.

Earl

Wheelie said:
I hope this isn't bad. I just checked my '78 1000 and it has 11 at the battery (it's real cold here and I haven't started it for a while) and 7 at the coils.

Steve
Click to expand...
 
Re: Voltage to coil??

earlfor said:
On my 750E, with the bike not running, my multi meter shows 12.8 volts at the battery and with the ignition turned on, the meter reads 10.2 volts into the coils. It seems to me this is an excessive drop. Can anyone tell me their standing battery voltage and voltage to their coils so I can compare? I could accept 1/2 volt drop or so, but 2.6 volt drop?

Bikes been running rough and is getting worse. Its now bad enough that its unridable. I've already checked, fuel, carbs, plug caps, plugs, battery, ignition timing, and replaced points, so I'm reasonably sure its low system voltage (due to faulty wire, bad connection, switch, etc) or a coil going bad. I have my doubts about a coil as all four plugs are burning about the same and all four plugs are firing. I'n thinking it has to be a wiring harness problem due simply to old age. :-) If anyone has any other ideas,.......I'm all ears. :-)

Earl
Click to expand...
my battery is stored for the winter Earl, i just checked it and was getting about 12.5 volt reading, electrics are my weak point, so i dont know if thats good or bad :roll:
 
earlfor said:
I think 11 volts would be a pretty well discharged battery and any load is going to pull the voltage down quickly. BUT... living in south FL and not dealing with batteries in really cold weather, I couldnt say if your voltages are normal or not.

Earl

Wheelie said:
I hope this isn't bad. I just checked my '78 1000 and it has 11 at the battery (it's real cold here and I haven't started it for a while) and 7 at the coils.

Steve
Click to expand...
Click to expand...
I do it tomorrow Earl--I just saw the post.
 
this is one of the reasons why I re-wired my bike so that instead of having all the power go through the ignition switch, I have it wired so that the ignition switch energizes a relay, that provides power to everything.

big improvement in power getting to everything.
 
Re: Voltage to coil??

Well Wrench, 12.5 is probably a good voltage to maintain for a battery in storage. I wanted to know the end value and the voltage drop in the bike's electrical system due to harness resistances. I'm a gonna be a good guy this time and not make you put the battery back in the bike and check all those things. :-) :-) :-) eh eheh

Earl

[quote="wrench
my battery is stored for the winter Earl, i just checked it and was getting about 12.5 volt reading, electrics are my weak point, so i dont know if thats good or bad :roll:[/quote]
 
Thanks Scotty. :-) :-)

Earl

[quote="slopoke
I do it tomorrow Earl--I just saw the post.[/quote]
 
earlfor said:
Thanks Scotty. :-) :-)

Earl

[quote="slopoke
I do it tomorrow Earl--I just saw the post.
Click to expand...
[/quote]
I think i need to check that out for myself also-I never did
 
Scotty, I've gone throught the electrical "trail" in the harness for the ignition system. When I posted this topic, I had a 2.6 volt drop between the battery reading and what actually arrived at the coils. I've clean/replaced connectors/switches and a few wires and cleaned up grounds and my voltage drop at the coils is now .6 volts. I have 12.6 at the battery and 12.0 arriving at the coils. I dont know if this is normal/average.

Earl


[quote="slopoke
I think i need to check that out for myself also-I never did[/quote]
 
I also put a few relays in to reduce voltage drop. They directly apply power that used to go through the ignition switch and back again to the fusebox, headlights, and the power from the stator that used to go from the lighting circuit, through the lefthand light swtitch then back to the rectifier (silly idea and a nasty little switch!). I think the elctrex solution may directly control all three stator circuits, therefore solving the last problem area. All the original switches are use to turn the relays on and off.

I have also found that the fusebox connectors (I have the old round ones) where they clip around the fuse can build enough resistance for the electrics to play up. The solution is fine wet and dry cleaning of the fuse clip surface where it contacts the fuse.
 
earlfor said:
Scotty, I've gone throught the electrical "trail" in the harness for the ignition system. When I posted this topic, I had a 2.6 volt drop between the battery reading and what actually arrived at the coils. I've clean/replaced connectors/switches and a few wires and cleaned up grounds and my voltage drop at the coils is now .6 volts. I have 12.6 at the battery and 12.0 arriving at the coils. I dont know if this is normal/average.

Earl


[quote="slopoke
I think i need to check that out for myself also-I never did
Click to expand...
[/quote]

Earl .6 volts doesnt sound so bad--ancient garbage wire from japan is the reason for that. and the crazy route that the power must take as stated by saaz
 
The voltage drop is related to the resistances of the wires and connectors and also to the current through the wire. If there is no current - there will be no voltage drop. My point is, I guess, that the voltage drop you see across any wire will change with the applied load or how much current you are drawing.

Just doing my part to add confusion to this topic. 8O
 
This is what I found for Open Circuit Voltage on standard batteries (measured when battery is not in use after stabilized - not used or charged for period of time, e.g. 30 min).

Battery Charge Level vs. Voltage

100% 12.7
75% 12.5
50% 12.2
25% 12.0
Discharged 11.8

So I would say your battery is fine. When you turn ignition on, the current starts flowing and the voltage drop would occur inside battery (because of internal resistance), and in cables. As I remember voltage is proportional to current and resistance. So I would check the voltage on battery before and after you turn the ignition, and follow up all the way to the coils. You should be able to find easily which part has the majority of voltage drop (resistance).
 
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