Lucas ignition coil question
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o0norton0o
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Each 6 volt coil should have a resistance of about 1.5 - 1.8 ohms each that means the total resistance for using a pair of 6 volt coils is between 3 - 3.6 ohms (6 volt coils are wired in series on 12 volt systems) If you use 12 volt coils they are wired parallel. I use a single 3 ohm dyna coil with dual leads and prefer it to both the other two double coil systems....
o0norton0o
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L.A.B. said:
I did not know that!!! (since I have a '70)
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Even though the spark coils are wired in parallel on a points type ignition system, no two sets of points are closed at the same time. So basically current alternates from one coil to the other coil. The primary resistance of the spark coil is very close to the resistance of the ballast resistor and seeing how they are wired in series you should have a voltage drop of approximately 6 volts across each spark coil. You should also have approximately a 6 volt drop across the ballast resistor so that the added voltage drops between the ballast resistor and each spark coil should add up to 12 volts. If the primary resistance of the spark coils and the ballast resistor fall within factory specs and the total of your voltage drops between the spark coil and the ballast resistor do not add up to 12 volts that would mean that you have resistance built up in your wiring which needs to be corrected.
If you have an electronic ignition system and you are running your spark coils in series and still using a ballast resistor, you need to remove the ballast resistor because you will have too much voltage drop across each spark coil.
Peter Joe
If you have an electronic ignition system and you are running your spark coils in series and still using a ballast resistor, you need to remove the ballast resistor because you will have too much voltage drop across each spark coil.
Peter Joe
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illf8ed said:
Actually I'm wrong. total voltage is 3.5v plus 3.5v for two coils in series plus voltage drop around 5-6v from the ballast resistor = 12v plus. Therefore 3.5v at each coil across the low tension terminal is what would be expected with the ignition switch on and the system powered. Again folks see my original post. Set up is all stock with Lucas 6v coils and points/ballast resistor.
Thanks
o0norton0o
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illf8ed said:
As LAB said, you test your coil by measuring it's resistance, which is measured in ohms.. Honestly, I didn't know why you were asking about volts... Sorry, I wasn't clear.
Deets55
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David,
I'll give it a shot.
When I was testing my coils I don't recall having to look for that number. I believe the two important things to check were the overall resistance and to see if there was a short. I think it was something like 1.7-1.9 ohms per 6 volt coil. I am sure you might be able to calculate the final voltage using 12dc into the coil at what ever resistance the coil is but I am not sure if that is necessary. I have no information in front of me now so this is just my best guess. FWIW even after testing the coils that way it did not pinpoint the problem, the end result was they were failing under load and when hot. After eliminating everything else I bought a new set and that solved the problem. Hope this helps.
Pete
DogT
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Yes, resistance check across + and - is better than volts. 6V Lucas coils 1.7-1.9 ohms, 12V 3.3-3.8 ohms. Also check from ground to the HV center. It should be infinity. This is with everything disconnected from the coils. Actually I have a good 6V coil on my bench right now and between + and - I read 1.85 ohms which is OK. From either + or - to the HV center I read 5.4K ohms and HV to ground is open, no reading. I've had the wires to the + or - disconnect inside coils and of course that doesn't work much. Make sure you take into consideration the meter lead resistance which can be upwards of .7 ohms when measuring the + and -. It should also read infinity from + or - to the case.
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I didn't post that my resistance measurement that was 2.1 ohms as that wasn't my question. This value is normal, but with power on I checked voltage for verification 3.5v. Since coils and ballast resistor are in series the voltage measurement seems in line with normal. Conclusion the coils seem to be OK.
Thanks everyone
Thanks everyone
maylar
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illf8ed said:
With the engine not running, when one set of points are closed you'll see 6V (ish) on one coil and 6V across the ballast. The other coil will have no voltage across it. Be aware that as you turn the engine and points open, there will be a spike of a couple hundred volts there that can give you a nasty bite.
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Deets55 said:
Good point. Pretty tough to run the bike up a hill under load with a cold engine. As soon as it is under load the temp is already up. More food for thought. I'm leaning to just replacing the whole ignition system with Tri-Spark and new coils. The other issue is my cam timing which I checked and corrected (was 15 degrees retarded). Unfortunately I need to recheck as my thinking at the time may be suspect. This goes to which side of the degree wheel is BTDC or ABDC. Result after cam timing change is the engine won't start. Frankly I think I'm getting to old to continue messing with Commandos. If they weren't so sweet when running perfectly, I'd give up.
o0norton0o
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illf8ed said:Right now thinking it's not so easy.I'll get it eventually.
... It's not that hard... If you make a mistake like calculating the crank rotation the wrong way, everything after that point is moot... Honestly, I think it's harder if a person is clueless and is just following a manual to set up points. That doesn't seem to be your case at all....
It's just my opinion, but I think points, condenser, ballast resistor, and lucas coils are really more work than they are worth. A boyer IE and a dyna dual lead coil are a "set it and forget it" for me for 25 years... I've taken off the timing side cover to do modifications and just made a visual note of the boyer magnet's position when I disassembled it. I did my work, then reassembled and set magnetic rotor back into position by "eyeballing" it, starting the bike, and micro adjusting it with the strobe light which took less than 10 minutes...
I am sure there are people who will argue that points work well enough for them... Electronic ignition and a 3 ohm dyna coil are simple to set up and less complicated to run. They are reliable and don't require fiddling... Certainly it's your call on your bike,...
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