2F ignition coil voltage with ballast resistor

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Nov 30, 2005
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Hello,

The question:

Is 5.6 - 6V on the the coil + to ground the correct voltage for this ignition ?

Background:
My points keep burning after less than 2500miles. A hole in one side and a pillar on the other side.
Someone before me fitted an Accell 140001 Super coil. The original 1.5Ohm ballast was kept in place but the additional 0./85Ohm resistor that comes with this coil was never fitted.
I do not have it.

The static voltage on this coil + to ground was 10.7V with points closed. Quite high.

Since I cannot get a 0.85Ohm ballast resistor at a reasonable price, I decided to replace the coil with a AccuSpark 1.5 Ohm Sports Coil for Ballast/Resistor Ignitions.

I fitted that on the weekend, again with the original 1.5Ohm resistor in place. The instructions mentioned I should get ~9V on the coil + to ground.
But I only get 5.8V there. (I previously had 10.7V).

The engine seems to run fine.

I want to have this right as the next step is electronic points.
 

ToyotaMatt

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Hello,

The question:

Is 5.6 - 6V on the the coil + to ground the correct voltage for this ignition ?

Background:
My points keep burning after less than 2500miles. A hole in one side and a pillar on the other side.
Someone before me fitted an Accell 140001 Super coil. The original 1.5Ohm ballast was kept in place but the additional 0./85Ohm resistor that comes with this coil was never fitted.
I do not have it.

The static voltage on this coil + to ground was 10.7V with points closed. Quite high.

Since I cannot get a 0.85Ohm ballast resistor at a reasonable price, I decided to replace the coil with a AccuSpark 1.5 Ohm Sports Coil for Ballast/Resistor Ignitions.

I fitted that on the weekend, again with the original 1.5Ohm resistor in place. The instructions mentioned I should get ~9V on the coil + to ground.
But I only get 5.8V there. (I previously had 10.7V).

The engine seems to run fine.

I want to have this right as the next step is electronic points.




i offer this Genuine NipponDenso OEM Toyota Parts Solution for a POINTS System







93916250-ADD4-4380-A70F-1CF602ADE20B.jpeg
AA9130B9-D698-4E2A-9333-4E8DD4FF9F44.jpeg
 
Last edited:

ToyotaMatt

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I really wanted to know the cI rrect coil voltage.
Surely this is known?



between what 2 points ?


KEY ON ?

KEY OFF ?


photos would really help here since you have replaced some but NOT all of the OEM parts ?
 
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It is a series resistance or voltage divider situation. If your have two resistors in series with equal resistance and then put 12V across the circuit, you will measure 6V at the midpoint between the two resistors. Since he only measures 5.8, this means that the resistance of the first resistor (in this case the ballast) in slightly higher than the second resistor (the coil). This is not a large enough difference to matter.
 

Engineer8000

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As @Pin_Head states it depends on the coil and ballast resistor values. 5.5 to 6v is not unheard of. But ultimately this is the answer. The condenser absorbs the back emf from the coil when the points open, if it is bad then the points take the punishment and burn up.

As long as you get a reliable spark, it runs fine and the coil does not get hot, then everything is OK. If the points burn, then you may need a new condenser.
 
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Messages
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It is a series resistance or voltage divider situation. If your have two resistors in series with equal resistance and then put 12V across the circuit, you will measure 6V at the midpoint between the two resistors. Since he only measures 5.8, this means that the resistance of the first resistor (in this case the ballast) in slightly higher than the second resistor (the coil). This is not a large enough difference to matter.
So you all agree that 9V on this coil is totally out of the question, given the resistance values?
The company's instructions are not correct.
 
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I am however still interested in what the voltage actually is on an original setup.

Surely someone has those details?
 
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What value of resistor does the coil instructions say to use?
The original resistor, 1.5Ohm.
And thanks for the pictures and verification.
There is a lot of false info out there and it seems to get repeated.

BTW, I am also an electronis engineer. I like your setup. I had a HP 5420 scope like that many years ago :)
 

Engineer8000

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I would say the instructions are faulty. With a 1.5 ohm resistor and 1.5 ohm coil, you are never getting 9v there.

I used Tek scopes forever but got a smoking deal on this HP. It took some time to get used to the controls but I find I like it better.
 
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At 9V, the 1.5 ohm coil will sink more current and power and may produce a higher voltage spark, depending on the RPM and inductive time constant of the coil. As long as the coil does not over heat, it will be fine. Pertronix advertises its “Flame-thrower” 1.5 ohm coil as a super performance coil for use without a ballast resistor, which is really just a 6V coil. Anything more than what is needed to make a reliable spark under all circumstances encountered is just wasted energy. It does nothing for performance. Auto manufactures know this, which is why they just provide a reliable ignition coil And leave the people who are fooled by performance hype to the aftermarket con artists.

I still have my Tek vacuum tube O-scope with the neon bulb timer, but it is in the attic and I am not getting it down for any foreseeable reason.
 

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