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I feel as if i should know this but, I have a '76 B and I've been having some ignition trouble. Reading one of my manuals it states that my car might have a 6 volt coil. How would I tell? and what would happen if I placed a 12 volt coil on the car by mistake? Thanks, MACK /ubbthreads/images/graemlins/cheers.gif
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Coil voltage
- Thread starter Mack
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kennypinkerton
Yoda
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If'n it's stock... you get 12 volts to the coil at startup...and then it drops to 6 or so volts by the balast resistor, and a relay (one of the only 2 on the car).
I've based this info on mine... Some diffeneces did occur on the 1976 to 1977 year model. This might be one of them. /ubbthreads/images/graemlins/confused.gif
Call in the group... /ubbthreads/images/graemlins/grouphug.gif
I've based this info on mine... Some diffeneces did occur on the 1976 to 1977 year model. This might be one of them. /ubbthreads/images/graemlins/confused.gif
Call in the group... /ubbthreads/images/graemlins/grouphug.gif
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Mack, All the information I have says that all MGBs use a 12 volt coil. Maybe someone else has some different info. on this. Some coils are mounted differently, but as far as the info I have goes, thier all 12 volt. I dont know about the voltage drop to 6 volts while running, but anything's possible! What I can't figure out is, why in the world would the manufacture build a car with a 12 volt system and have it run on 6 volts? To me,that doesn't even make sense! I've got to do some more research on this! PJ
dklawson
Yoda
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The quickest test is to mark and disconnect the low tension wires on the coil. Use a multimeter to measure the resistance across the coil's bare spade lugs. If you get something close to 3 ohms, its a 12V coil. Anything between 1-2 ohms is for a ballasted ignition system (6V coil).
Lucas' practice where a ballast coil is fitted was to run a pink wire from the ignition switch to the coil (+) terminal (the wire is a resistor...not just a wire). If you see a pink wire to your coil, that's another give away. Ballast coils also have another wire connected to the coil (+) terminal. The additional wire goes to the starter solenoid. While you're cranking the car on the starter this wire delivers full battery voltage to the coil to make starting easier.
Lucas' practice where a ballast coil is fitted was to run a pink wire from the ignition switch to the coil (+) terminal (the wire is a resistor...not just a wire). If you see a pink wire to your coil, that's another give away. Ballast coils also have another wire connected to the coil (+) terminal. The additional wire goes to the starter solenoid. While you're cranking the car on the starter this wire delivers full battery voltage to the coil to make starting easier.
Keoke
Great Pumpkin
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[ QUOTE ]
Doug, do you know the reason for the ballasted coil? I've heard of droping voltage to the points so they would last longer and resist burning, but this is the first time I've heard of droping voltage to the coil. PJ
[/ QUOTE ]
PJ, the only way to drop the voltage to the points is to drop the voltage at the coil.---Keoke
Doug, do you know the reason for the ballasted coil? I've heard of droping voltage to the points so they would last longer and resist burning, but this is the first time I've heard of droping voltage to the coil. PJ
[/ QUOTE ]
PJ, the only way to drop the voltage to the points is to drop the voltage at the coil.---Keoke
dklawson
Yoda
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The reason for the ballasted ignition system is not to extend the life of the points, it's to improve starting. Mismatching coils to the rest of the ignition system can shorten point life.
To put this succinctly.... When the starter operates it pulls the operating voltage of the car down because a large portion of the available power is going to the starter. On an unballasted (standard) ignition system this can cause a significant reduction in the voltage supplied to the coil and in turn to the spark plugs.
Somewhere along the way, someone figured out that if you put a 6V coil on the car, the spark would be hotter. However, this 6V coil, because of its lower internal resistance, drew more current through the points causing them to burn out quicker. Obviously what was needed was a way to temporarily supply higher voltage to the 6V coil during cranking and only 6V during normal running. The solution was to connect the 6V coil to the starter solenoid so it got all the available battery voltage while cranking. Once your engine starts and the solenoid disengages, power is supplied to the coil through a ballast resistor (or resistor wire) in series with power coming from the ignition switch. The current flowing through the ballast resistor drops the voltage supplied to the coil to around 6V. This gives the best of both worlds. High voltage to the coil during cranking, and 6V at the coil while running.
The serious problem with points life happens when you use a 6V coil on a standard ignition system. This causes too much current to flow through the points. If you go the other way and put a 12V coil on a ballasted ignition system, the car may start but may have problems delivering a good spark in "normal" run mode.
To put this succinctly.... When the starter operates it pulls the operating voltage of the car down because a large portion of the available power is going to the starter. On an unballasted (standard) ignition system this can cause a significant reduction in the voltage supplied to the coil and in turn to the spark plugs.
Somewhere along the way, someone figured out that if you put a 6V coil on the car, the spark would be hotter. However, this 6V coil, because of its lower internal resistance, drew more current through the points causing them to burn out quicker. Obviously what was needed was a way to temporarily supply higher voltage to the 6V coil during cranking and only 6V during normal running. The solution was to connect the 6V coil to the starter solenoid so it got all the available battery voltage while cranking. Once your engine starts and the solenoid disengages, power is supplied to the coil through a ballast resistor (or resistor wire) in series with power coming from the ignition switch. The current flowing through the ballast resistor drops the voltage supplied to the coil to around 6V. This gives the best of both worlds. High voltage to the coil during cranking, and 6V at the coil while running.
The serious problem with points life happens when you use a 6V coil on a standard ignition system. This causes too much current to flow through the points. If you go the other way and put a 12V coil on a ballasted ignition system, the car may start but may have problems delivering a good spark in "normal" run mode.
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Does a 72 have a ballasted ignition system? I remember putting a new coil on the car just before puting it in the barn almost 20 years ago. I'm using the same coil and I'm pretty sure it's a 12 volt coil. Seems to start and run great. What do you think? PJ /ubbthreads/images/graemlins/tongue.gif
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Well, you know what they say,(who ever "they" are), If it aint broke, don't fix it! She has a Lucas coil on her, bought from a British Leyland dealer 20 years ago, (The same dealer I bought my Land Rover from), with 12 volts stamped on it, and she runs great. /ubbthreads/images/graemlins/nopity.gif Nuf said. PJ
kennypinkerton
Yoda
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Here I go thinking again...
I think for sure that Doug is right on this one. Seems like the way I know it anyway for a stock (late model in my case) setup....
.... BUT, I think that the (gold) Lucas Sport Coil (and other aftermarket one's) are 12v coils... not to be used with a ballast resistor. So they give more spark, but they are wound to basically do the same thing at 12v that the stock coil does at 6v. If I'm wrong... Somebody can come slap me and tell me "the way it is". Until then that's what I think. /ubbthreads/images/graemlins/thumbsup.gif
I think for sure that Doug is right on this one. Seems like the way I know it anyway for a stock (late model in my case) setup....
.... BUT, I think that the (gold) Lucas Sport Coil (and other aftermarket one's) are 12v coils... not to be used with a ballast resistor. So they give more spark, but they are wound to basically do the same thing at 12v that the stock coil does at 6v. If I'm wrong... Somebody can come slap me and tell me "the way it is". Until then that's what I think. /ubbthreads/images/graemlins/thumbsup.gif
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Kenny, Doug gave me some info on how to test the coil to see if it is a ballast coil. As soon as the "B" gets back from the paint shop, hopfully Friday, I'm going to check it out. The car runs great but now I'm really curious about the coil just in case I need one. At least I'll know for sure which one to get. Thanks for your input. PJ /ubbthreads/images/graemlins/thumbsup.gif