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Old 08-07-2013, 03:06 PM   #61
BUBBAS IGNITION
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Default Re: Mallory tech answer to coil/ballast ?

Trying to help ya here ........

Trying to help you here:
from above post

The MSD Blaster series coils ( # 8302,8303 etc) are designed for electronic ignition systems with current control, not for use with a point distributor.
They have a primary resistance of .7 ohms and draw high current. Even when used with a ballast they will draw excessive current causing the contacts to burn up pretty quick.
Thats the reason the coil is hot !! More than likely drawing 8 to 10 amps ...


You need a 1.5 ohm coil ( which you do not have ) and a ballast resistor of approx 1.5 ohms as well. This would drop 6 volts at the resistor and another 6 volts at the coil negative side allowing only a small amount of voltage ( mili volts) to travel thru the contacts.
You dont want 9 volts at the coil ( only when cranking) and it really isnt about voltage anyway, its the high current going thu the low resistance coil causing the coil to heat up.

Your question was why does my coil get hot????
The reason the coil gets so hot its the wrong coil for the application...
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Old 08-07-2013, 04:17 PM   #62
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Default Re: Mallory tech answer to coil/ballast ?

Thanks! I will remove the MSD coil. It was actually MSD electronic service that told me that if it is 9 volts on the positive side on the coil I´m good, but if it is less , I would remove the resistor.

Here are the results from todays test during idle:
MSD Blaster 2 (0.7 ohms) with resistor= 6 voltage on coil positive.
MSD Blaster 2 without resistor= 7 voltage on coil positive.
Accel 8140 super stock (1.5 ohm) with resistor= 8 voltage on coil positive.
Accel 8140 super stock without resistor= 9 voltage on coil positive.

So you are saying stick with the Accel 1.5 ohms and the resistor 0.8-1.5 ohms?

Last edited by Gasoline; 08-07-2013 at 04:45 PM.
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Old 08-07-2013, 07:28 PM   #63
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Default Re: Mallory tech answer to coil/ballast ?

Quote:
Originally Posted by Gasoline View Post
Thanks! I will remove the MSD coil. It was actually MSD electronic service that told me that if it is 9 volts on the positive side on the coil I´m good, but if it is less , I would remove the resistor.

Here are the results from todays test during idle:
MSD Blaster 2 (0.7 ohms) with resistor= 6 voltage on coil positive.
MSD Blaster 2 without resistor= 7 voltage on coil positive.
Accel 8140 super stock (1.5 ohm) with resistor= 8 voltage on coil positive.
Accel 8140 super stock without resistor= 9 voltage on coil positive.

So you are saying stick with the Accel 1.5 ohms and the resistor 0.8-1.5 ohms?
Yep, but even more important , did it get hot ???
That was the issue right?
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Old 08-08-2013, 01:41 AM   #64
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Default Re: Mallory tech answer to coil/ballast ?

Thanks, I have to drive more to be certain. It did not get hot yesterday when I was testing with different coil. I wonder: How can a coil with 1.4 resistance result in higher voltage than a coil with 0.7 resistance? Should it not be the opposite?
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Old 08-08-2013, 06:36 AM   #65
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Default Re: Mallory tech answer to coil/ballast ?

The voltage across the coil is determined by both the ballast resistor and the coil resistance. If the ballast resistor is the same in both cases, the voltage across the coil will be less for a lower resistance coil. The voltage divides according to the ratio between the two. So if the ballast is 1 ohm for instance, the coil voltage will be V bat x R coil/(R coil + R ballast). WITH THE ENGINE OFF AND THE POINTS CLOSED

So with 1.4 ohms : V coil = 12 x 1.4/(1.4+1)=7v and I coil = 12/2.1= 5.7A
With a .7 ohm coil: V coil = 12 x.7/(.7+1)=4.9v and I coil = 12/1.7= 7.05A
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Old 08-08-2013, 12:39 PM   #66
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Default Re: Mallory tech answer to coil/ballast ?

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Thanks for the clarification.

However, the results that I mentioned before are taken during idle:
Accel 8140 super stock with resistor= 8 voltage on coil positive.
Accel 8140 super stock without resistor= 9 voltage on coil positive.

Done with the key on and engine off:
Accel 8140 super stock with resistor= 4.7 voltage on coil positive.
Accel 8140 super stock without resistor= 5.7 voltage on coil positve.

Is that not to low and should I not skip the ballast resistor after all?

Just so I´m doing it correct: I measure coil positive with all wires connected and multimeter red wire to the positive side and the black wire to the ground on the car?

Last edited by Gasoline; 08-08-2013 at 03:06 PM.
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Old 08-08-2013, 03:00 PM   #67
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Default Re: Mallory tech answer to coil/ballast ?

Gasoline ...A couple questions:

1- Are your key on/ engine off measurements in ohms or volts? It says ohms.

2- What is the measured resistance of the ballast resistor and the coil measured individually?

3- I'm assuming a 12V battery is being used ?

PS I did the math wrong with a 1.4 ohm coil it should be 12v/2.4 ohms = 5A, not 5.7 as I posted previously.

Is the multimeter you are using to measure the voltages a digital one?

If the 8140 without a resistor is connected to 12v, the 5.7 must be 12v or else there is something else in the path to reduce the voltage to 5.7. ( assuming the 5.7 is volts and not ohms)
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Old 08-08-2013, 03:11 PM   #68
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Default Re: Mallory tech answer to coil/ballast ?

1. My mistake, I just changed it to voltage.

2. I´m not sure what you mean. Ignition coil resistance is 1.4 and ballast resistor is 0.7

3. Yes, and I´m using a digital multimeter.

I probably have a resistance wire/loom resistance that reduce the voltage.

Skip the ballast resistor?
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Old 08-08-2013, 03:22 PM   #69
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Default Re: Mallory tech answer to coil/ballast ?

Kind of a wast of time and money to use a Unilite distributor or any with a vacuum advance, unless it's in a racing application. For street 90% of your driving is at part throttle, so your timing is retarded.
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Old 08-08-2013, 03:54 PM   #70
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Default Re: Mallory tech answer to coil/ballast ?

I use oldfashioned points. That is why I'm so concerned about the ballast or not. 9 voltage on positive on coil when running and 5.7 with engine off and key on is ok regarding to Mallory, but I trust you guys more. What do you all think?
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Old 08-08-2013, 04:16 PM   #71
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Default Re: Mallory tech answer to coil/ballast ?

You would better to go to parts store like NAPA, Macs auto has what you want.
this is for a 1957 Ford and others
B6A-12029-B
Do not use this coil on any vehicle equipped with transistorized ignition. 1964-1966 Thunderbirds offered this type of ignition as an option for the 390 & 428 engine. The ignition coil, if used in any type of vehicle with a transistorized ignition system WILL NOT WORK and may result in other electrical problems and may even burn out or damage other parts.
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Old 08-09-2013, 07:22 AM   #72
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Default Re: Mallory tech answer to coil/ballast ?

Gasoline … hope you dont glaze over here, it’s a long one!

I think the digital meter is giving you false readings when the car is running. This is because the meter is set to DC (I presume) , but the voltages are not a steady DC as the current is being interrupted by the points. Also you can get some pretty high inductive kicks back from the coil which really confuses a digital meter. That's why I keep telling people to measure with the engine off, and the points closed. Only then will you get accurate DC readings.

I asked about the ballast and coil resistance readings because I'm trying to figure out if your numbers are MEASURED or are they the mfg SPECS.

NO BALLAST RESISTOR CASE, ENGINE OFF:

Let’s assume the coil is 1.4 ohms, and the ballast is 0 ohms (not there) as stated.

From your measurements the coil voltage is 5.7v and the resistance is 1.4 ohms. This makes the steady state DC coil current 4.07 A. (I =5.7/1.4)

If there is no ballast resistor, then the loom resistance must be dropping the rest of the voltage = 12V-5.7V = 6.3V. This makes the “loom” resistance = 6.3V/4.07A= 1.5 Ohms

.7 OHM BALLAST RESISTOR CASE, ENGINE OFF:

Let’s assume the coil is 1.4 ohms, and the ballast is .7 ohms as stated.

From your measurements the coil voltage is now 4.7V and the resistance is 1.4 ohms. This makes the steady state DC coil current 3.36 A. (I =4.7/1.4)

The voltage across the ballast resistor becomes .7ohms x 3.36A = 2.35V

Now the loom resistance must be dropping the rest of the voltage = 12V-4.7V-2.35V = 4.95V . This makes the “loom” resistance = 4.95V /3.36A = 1.5 ohms

In both cases, the “loom” resistance comes out to 1.5 ohms, so that must be the correct value, and all the numbers make sense.

I would suggest that you make an actual measurement of the current with the multimeter to confirm, (with the engine off and the points closed).

If you confirm these numbers, then it is easy to calculate the peak coil current when running as follows:

I coil running = I coil stopped x 14/12 (assuming the generator/alternator is putting out 14v)

Then :

I pk with Ballast resistor =3.36A x 14/12 = 3.92 A
I pk without Ballast resistor =4.07A x 14/12 = 4.75 A

Finally to get the average running current (which determines the heat of the coil), take the peak currents above X dwell angle/45 (assuming a V8 engine)

Assuming the dwell is around 30 degrees, the numbers become:

I avg with Ballast resistor = 3.92 A X 30/45 = 2.61A
I avg without Ballast resistor = 4.75 A X 30/45 =3.16A

These current numbers seem quite reasonable to me, and its not clear if the ballast resistor is required. From the above calculations, the majority of the current limiting is in the “loom resistance” of 1.5 ohms, and not the actual ballast resistance of .7 ohms

Hope this isn’t too complicated, but that’s life!
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Old 08-09-2013, 09:34 AM   #73
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Default Re: Mallory tech answer to coil/ballast ?

I,m not a engeener ,i use parts from cars of proven desine.
You can use any parts you like,Ford 1957 coil and resister.
In all the cars i have owed i have never had to replace a coil.
I like to know for test facts of using what i run on my car.
The only thing that is known is a rsister of say 1.5 ohms.
Tests should be done when running thats what its all about.
Simple read acorss resiter 1.5x2 amps (i)=3 volt,1.5x 2.5=3.75 volts,1.5x4=6 volts.
The higher the amps the higher the volts.If the amps are to high you loose voltage to coil.
The ohms reading means nothing to me only that you have a open coil.
So my car is about 3 volts running 13.8 volts, coil is about 10 volts.thata about 5 ohms.
I don,t like digital meter,anolog meter is better.
use what works for you ,all the problem are the master blaSter, flame thrower high end parts that do,nt seem to work.Keep it simple
ever knowtis they never sell a complete packagefor electrtinic dist most always buy coil exta.
So watch the amps read across resiter 3 volt, known resister 1.5, 3 divderd 1.5= 2 amps.
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Old 08-09-2013, 12:00 PM   #74
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Default Re: Mallory tech answer to coil/ballast ?

George .... your right about 1.5 ohms x 2 amps being 3 V . That's called ohms law. But what you are missing is the fact that when the car is running, the 2A is only flowing while the points are closed. When the points are open, (about 30% of the time) the current is not 2A, its 0A. So the meter (analog or digital) is going to average these two currents and come up with what your measuring ..... 2A. But the real current flowing is nearer 4A if the ballast and coil are both 1.5 ohms. You would see the current going from 4A to 0 A as the points open and close on a running car if it was measured with a scope, but NOT WITH A MULTIMETER. It cannot react fast enough to give an accurate reading. Its kinda like your bank account, one day it has a $100 in it , the next it has $0. Over the two days the average in the account is $50, not $100.
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Old 08-09-2013, 12:47 PM   #75
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Default Re: Mallory tech answer to coil/ballast ?

B man Al
I did the test again 3 meters 2 ohms scale need batteries.
The resister is about 2 ohms and voltage is 2.6 volts ,
battery is almost 14 volts.
2.6 divided by 2 ohms=about1.3 amps.
This is getting to technical for me.
I guess if you use know correct parts there is no need for meters.
Keep them running.
George
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Old 08-09-2013, 04:20 PM   #76
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Default Re: Mallory tech answer to coil/ballast ?

George ..

Here's a test you can do to illustrate what I'm trying to say. Make the measurement you usually do with the car running. Clip the meter across the ballast resistor and measure the voltage. Lets say you measure 3V as before.

Now turn off the ignition, and turn it on again after the engine has stopped. Either the voltage will be 0 volts if the points are open ( no current is flowing) , or the voltage will increase to around 6V if the points are closed. (This assumes the ballast and coil are both around 1.5 ohms).

If you get 0V, hit the ignition momentarily until the points close.

In this case, as you have noted before, the current should be V ballast/R ballast = 6v/1.5 ohms = 4A.

From this you can see that the voltage increases across the ballast resistor when the points are closed, and the engine is off, even though the applied voltage has dropped from around 14v to 12v. The only way this can be true is if the meter is reading a reduced voltage when the engine is running due to the "averaging" going on.

Make sense?
Al
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Old 08-09-2013, 04:47 PM   #77
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Default Re: Mallory tech answer to coil/ballast ?

What can I say; I am impressed by your knowledge and I have read all posts carefully.

To sum up my problem: car shakes, dies and impossible to start on a sunny day. I change MSD 0.7 coil + 0.7 ballast resistor to a new MSD 0.7 coil and 0.7 ballast resistor, change condenser and the car starts fine again later that day. Then, the same thing occurs the day after after driving for 10 minutes. This happened once for the past seven years and that time it was caused by a bad condenser.

This time a start thinking the coil does not get enough power and the warm summer weather increases the resistance. I measure and notice that I have only have 6 volt so I change to a 1.5 ohms Accel coil and the volt increases to 8 when the engine is running (still using 0.7 ohms ballast resistor). I try without ballast resistor and volt increases to 9 when engine running.

So I am thinking that maybe I should be satisfied with 8 volt using a resistor (only 6 volt with the MSD which obvious was to low for my car). But then I am thinking that I might need 9 volt, by skipping the resistor, so I do not end up with the car shaking/dies again. But 9 volt might be bad for the breaker points - so it feels like a dilemma

I have learned that I have a wire resistance of 1.5 ohms. The question is if that combined with the 1.4 ohms coil is enough to protect the breaker points. What I did not get was the peak coil?

Last edited by Gasoline; 08-09-2013 at 05:05 PM.
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Old 08-09-2013, 06:55 PM   #78
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Default Re: Mallory tech answer to coil/ballast ?

Gasoline
I think with the resistance wire is your problem.
If you run just the wire and coil you will be ok
9 at coil and rest at wire resister must be about 3 volts.
Story my 39 was changed to 12 volt and had a resister and coil.
would start ok but stop and get gas and was very hard to start.
When I was rewiring the car 39s have a resister under dash .5 ohms.
The .5 ohms resister was in use drawing the voltage down to coil.
Lets say 2 amps x.5 ohms=1 volt taken for coil makes for hard starting.
So you are trying to use 2 resisters only need one.
Its a series circuit has to add up the battery voltage.
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Old 08-09-2013, 07:41 PM   #79
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Default Re: Mallory tech answer to coil/ballast ?

Hi George ...

I just did the experiment I suggested to you in post 76 with my model B, 1.5 ohm ballast, 1.5 ohm coil. Here's what I got using a digital multimeter.

1-Ignition off: V across ballast measured = 0 V
Comments - makes sense, as no current flowing

2-Ignition on, points open: V across ballast measured = 0V
Comments - makes sense, again as no current is flowing

3- Ignition on, points closed , engine off: V across ballast measured = 6.3V
Comments - makes sense, current is flowing and is 6.3V/1.5 ohms = 4.2A

4- Ignition on, engine running, points pulsing : V across ballast measured = 2.3V
Comments - If the voltmeter was reading correctly, and could read the peaks, it would read higher than case 3 by about 16% because of the increase in battery voltage from 12v to 14v. This would make it 7.3V instead of the measured 2.3V.

Thus the real coil current is about 7.3v/1.5 ohms=4.8A. This is what you would actually see if you made the measurement with an oscilloscope

However because of the averaging going on, there is a large error in the measured voltage, leading to the conclusion that the current is only 2.3v/1.5 ohms = 1.5 A. rather than 4.8A as calculated above.

Hope this helps to confuse the discussion some more :-)
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Old 08-09-2013, 08:02 PM   #80
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Default Re: Mallory tech answer to coil/ballast ?

Gasoline ...

Thanks for your kind words !

In your original configuration, .7 ballast, .7 coil, and a wiring resistance of 1.5, the "engine off" current would be 12/(1.5 +.7+.7)=4.1 A.

This would increase by 16% to 4.7A with the engine running due to the ratio of 14v/12V.

The question then becomes is this sufficient current for that particular coil? If it is intended to work with only a .7ohm ballast, the peak current would be 10A with the engine running (14v/(.7+.7) . If this is for a 6V coil and ballast combination it should be fine without the "loom" resistor. If however this is intended for 12V operation, the points will surely burn at 10A pk.

From where you are now, ( 1.4 ohm coil, .7 ballast + 1.5 loom, ) the points should be happy either with or without the .7 ohm ballast. If you go through the same experiment in post 76 you should be able to determine all the voltages and currents involved with your setup.
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