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Old 11-05-2020, 04:51 PM   #1
40cpe
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Default Voltage to points

I have a converted chevy distributor in my 8BA. After 3-4 thousand miles the contacts look rough. I filed/reset them and it's running good again. Wondering why they didn't last, I went to looking for the reason. I have a 1.8 ohm ballast feeding a flame Thrower 1.5 ohm coil. On a 12V system I have 5V at the coil, key on, points closed. Running I have 11 volts on the input to the coil and 8.2V on the distributor terminal of the coil with the alternator charging at 14.4 volts. Reading comments on this forum directed at 6v systems, I see 4v is recommended. I've Googled a good bit and can't find any info on voltage to the points. I'm looking for help to determine if I need more resistance, or if I just have crappy points. The ones in the distributor are Delco. Thanks for your guidance.
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Old 11-05-2020, 07:13 PM   #2
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Default Re: Voltage to points

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I have a converted chevy distributor in my 8BA. After 3-4 thousand miles the contacts look rough. I filed/reset them and it's running good again. Wondering why they didn't last, I went to looking for the reason. I have a 1.8 ohm ballast feeding a flame Thrower 1.5 ohm coil. On a 12V system I have 5V at the coil, key on, points closed. Running I have 11 volts on the input to the coil and 8.2V on the distributor terminal of the coil with the alternator charging at 14.4 volts. Reading comments on this forum directed at 6v systems, I see 4v is recommended. I've Googled a good bit and can't find any info on voltage to the points. I'm looking for help to determine if I need more resistance, or if I just have crappy points. The ones in the distributor are Delco. Thanks for your guidance.
Maybe a capacitor issue? You should have plenty of resistance with a 1.5 ohm coil and 1.8 ballast resistor! Are you sure on the coil resistance? Did you measure it?
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Old 11-05-2020, 07:41 PM   #3
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Default Re: Voltage to points

I did measure it, with a Fluke meter. It read 1.4 ohms.

How do the voltages at the coil and points look?
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Old 11-05-2020, 07:47 PM   #4
Jack E/NJ
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Default Re: Voltage to points

Agreed on a potential capacitor issue. Sounds like the ballast is about right for a 1.5 ohm coil. With the points closed, there should be 1.5/3.3 x 12.8v = ~6v at the coil input with points closed not running. So 5v sounds about right if the battery was a bit low and some resistance thru the ign switch. When it's running, who knows what you'll get especially with a slow responding digital meter. Jack E/NJ
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Old 11-05-2020, 07:56 PM   #5
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Default Re: Voltage to points

Resting battery voltage was 12.3v. With key on, points closed battery read 12.1V. The 5v at the coil was taken using a cheap analog meter and a digital meter. So the capacitor could be responsible for the 11V reading at the distributor terminal? What would be the desirable reading?
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Old 11-05-2020, 08:02 PM   #6
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Default Re: Voltage to points

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Rapid deterioration of the points can be caused by a condenser that is waaay over or under capacitance. Unless you have a proper tester, the easiest thing to do would be to swap in a good condenser. Unfortunately, that is easier said than done with the quality of condensers available today, you might just get another bad one. If it runs well with one, keep it and check the point life. You might get lucky.
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Old 11-05-2020, 08:10 PM   #7
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Default Re: Voltage to points

The test that you really need to do is the current draw (in amps) of the coil with the engine running. That reading should be around 3 amps or less. If its higher than that then there is the answer to why your points are not lasting. The condenser is very important and could be the problem. Most people have no means to test a condenser correctly so just fit a new one. You talk about voltage to the points but that is not something that can be tested normally. Only test voltage on the ignition supply to the coil. The 4 volt recommendation coil input is suggested only for 6 volt original Ford bakelite coils . I would suggest that the input voltage on your coil with engine running should be around 7 or 8 volts and not 11 volts that you are reading. Check the coil amps draw running and report back. Dont forget a small amount of high temp lube on the dist cam. Regards, Kevin.
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Old 11-05-2020, 08:12 PM   #8
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Default Re: Voltage to points

I have another capacitor I'll try and see if it changes the voltage to the points.

Thanks for the direction, I hadn't suspected a capacitor issue.
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Old 11-05-2020, 08:15 PM   #9
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Default Re: Voltage to points

Thanks Koates, I'll get that reading tomorrow before changing the capacitor.
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Old 11-05-2020, 10:16 PM   #10
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Default Re: Voltage to points

We often talk in voltages, maybe because it is easy to check, but current (amps) is what is important here and your looking for about 3 to 4 amps. The capacitor is not going to change any voltage, resistance or amperage readings you take, but a proper capacitor is going to have a big impact on points wear.

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Old 11-06-2020, 11:51 AM   #11
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Default Re: Voltage to points

I tried to check the running amps at the coil with an older Craftsman clamp type digital DC amp meter and it just jumped around between 1 and 3 amps. I then used a harbor freight digital meter in series with the coil feed wire and it varied between 5.8-6.25 amps. I don't know if I should trust either of the readings. If someone can recommend a meter we can trust that won't break the bank I'll order it.
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Old 11-06-2020, 12:19 PM   #12
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Default Re: Voltage to points

I'd trust ohm's law in the total 1.8 + 1.4 = 3.2 ohm resistance measurement. So max possible current = 14.4/3.2 = 4.5 amps running. Jack E/NJ
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Old 11-06-2020, 02:07 PM   #13
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Default Re: Voltage to points

Jack, thank you for that perspective and it certainly makes sense. Those readings were close to the advertised values for the ballast and the coil and what I got from checking with a Fluke meter. This Fluke just doesn't have a provision for measuring DC amps.

If 4.5 amps is acceptable, then I'm back to just replacing the points and condenser hoping to get a better quality?
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Old 11-06-2020, 05:55 PM   #14
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Default Re: Voltage to points

It seems these days that it's always a "crap-shoot".
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Old 11-06-2020, 07:43 PM   #15
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Default Re: Voltage to points

tubman>>>it's always a "crap-shoot".>>>


Always? Even your trash cans? 8^) Jack E/NJ




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Old 11-06-2020, 07:47 PM   #16
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Default Re: Voltage to points

Use an older analog ammeter and see what you get. Cheap digital meters do not always work very well on old cars unless it is a higher quality Fluke or such. I think 4.5 amps is on the high side and would be good at around 3 amps. Many cars I have tested are down towards 2 amps with the engine running. Engine running with the points rapidly closing and opening the circuit regulates the current to that lower figure. The higher the current draw the quicker the contacts burn out. Why do you need a FLAME THROWER coil? Half of its potential output would never be used on your engine. Use a standard ignition coil. Regards, Kevin.
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Old 11-06-2020, 07:57 PM   #17
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Default Re: Voltage to points

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tubman>>>it's always a "crap-shoot".>>>


Always? Even your trash cans? 8^) Jack E/NJ




I was referring to buying parts at your "FLAPS". Although one of mine would be a solution to the OP's problem, they are a specialty item, and therefore a little expensive. Plus, there is the added complication of mounting it externally on the SBC distributor (depending on the type used).

That being said, look at the date on the picture; several hundred out there since then with no reported problems. I'd do it, but that's just me.

Thanks for the recommendation, Jack.
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Old 11-07-2020, 10:03 AM   #18
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Default Re: Voltage to points

I remember the aftermarket stuff for the GM window type distributors were an integral point & condenser set and they were crap back then. I generally suggest purchasing Echlin brand stuff from Napa but they are now under the Standard Motor Parts banner and may suffer quality issues due to that. I always buy at least two at a time and check to see if I get any arcing on the points when I turn the car over with the cap off and a test plug plugged into the coil tower. If it's bad it will arc a lot. A good one should arc very little or not at all. The spark from the test plug should be consistent too.
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Old 11-07-2020, 10:34 AM   #19
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Default Re: Voltage to points

tubman>>> Plus, there is the added complication of mounting it externally>>>


I've always considered them an extra added attraction. The only complication is they occasionally need a maintenance buff to show off their hidden beauty . 8^) Jack E/NJ


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Old 11-07-2020, 11:17 AM   #20
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Default Re: Voltage to points

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Why do you need a FLAME THROWER coil? Half of its potential output would never be used on your engine. Use a standard ignition coil. Regards, Kevin.
I had a Pertronix unit in the distributor at one time using this coil. The name doesn't mean anything, just the ohms. I have a few more coils on the shelf, one being an old Ford yellow top coil, and none have any more resistance. I don't understand why I'm getting such high amps using the often recommended resistance. It seems like any change I make will take a good while to show the results in points life.
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