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Old 07-31-2013, 06:12 AM   #41
B_man_Al
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Default Re: Mallory tech answer to coil/ballast ?

BillM thanks for the link to the coil site. Well I guess I got to eat some crow here. Didn't know that coils designed to work without a ballast resistor, have them built in! Makes sense though, to allow the primary current to increase at higher speed where the dwell time is reduced. The reduced dwell time (points closed) allows the ballast resistor to cool, thereby reducing its resistance and allowing an increase in the primary current.
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Old 07-31-2013, 06:57 AM   #42
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Default Re: Mallory tech answer to coil/ballast ?

I am struggling with a mis-fire at high revs, under load, when my engine is hot. I am still trying things one at a time to dignose the problem (ie is it fuel vapoisation or sparks).

So I have been reading this thread very carefully, and there is alot of information here, some of it hard to make out though.

My question, something that has occurred to me as I read...if the resistance in a ballast resistor increases with temperature, does the resistance in the primary windings of a coil not also increase with temperature? If so should this not also be factored in?

Cheers, Tom.
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Old 07-31-2013, 07:14 AM   #43
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Default Re: Mallory tech answer to coil/ballast ?

Tom .. Yes the coil resistance will go up with temperature as I posted in post #34. But because the ballast resistor is made from a special steel wire, it will increase a lot faster with temperature than the copper wire in the coil.

This will also happen with a coil with a built in ballast resistor. But since the two are internal, there is no way to separate the two for measurement purposes.

As posted by BillM, if the ballast resistor increases 300% ( 3:1) with temp, and the coil primary copper wire, only increases 16% over the same temp range, the dominant change will be due to the ballast resistor, though both contribute to the overall resistance change.
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Old 07-31-2013, 07:46 AM   #44
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Default Re: Mallory tech answer to coil/ballast ?

In post 36 I tried to explain what I did to determine the current and voltages associated with my 8BA coil/external ballast resistor combination on a 12V system. Key to the whole thing are two factors.

1-Do the measurements with the engine off, and the points closed. If you measure with the engine running you will get errors due to the voltages not being stable (points opening and closing constantly). If you have a scope, you can get accurate voltage measurements, but not with a multimeter.

2-Add a small series resistor ( Rsense) to allow the accurate calculation of the current, ( I coil = V Rsense/ R Rsenser) or do it directly. I used 0.18 ohms cause thats what I had, but any value that is 10x or more smaller than the coil + ballast will be fine. The lower the better to get better accuracy. This needs to be done, because the added sense resistor is designed to be stable with temp, and not vary all over the place like the ballast or coil resistance.

You can only calculate the current accurately if you know what the resistances are.

If you measure the current directly with a multimeter, then you don't need the sense resistor.

So the steps are:

1-turn off the engine, with the ignition on
2-measure the voltage applied to the ignition cct ... (ballast + coil ...nominal 6 or 12v)
3- measure the coil current , either directly or with a small sense resistor added.
4- Calculate the ballast resistance .... R ballast = V ballast/I coil
5- Calculate coil resistance ... R coil = V coil/I coil.

Check to see if results agree with the coil/ballast specs.

These need to be done quickly as the ballast and coil resistances will be changing quickly as they cool off.
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Old 07-31-2013, 07:54 AM   #45
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Default Re: Mallory tech answer to coil/ballast ?

I understand that the electronic systems need a special coil?

Bubba, can you please answer these for me;
1. Are there coils with built in ballasts, or am I missing something?
2.What are the applications (when are the different ones used) for the three different primary?) resistances that you mentioned?[/QUOTE]

WOW this thread has went on and on , some facts , some not !

The working resisitance of the coil is designed with the winding and how the windings are installed etc. I know of no coil with a internal "ballast resisitor" The working resistance is a factor of the windings. See picture of exploded coil
windings and a new winding in a delco coil. ( Both Indiana made)

The parts in a ignition system are designed for a specific current flow and voltage drop . Both must be considered in every discussion.
Once the system is designed the current draw is pretty much constant value based on system design and resistance of components.
Lets discuss voltage first. On a common 12 volt system the ballast of loom resistor drops the voltage to 6 volts and then the coil drops the voltage another 6 volts = low voltage at the contacts etc. Actually the battery is 12.2 or 12.4 volts and the extra 2-4 tenths of a volt is dropped by using a special finely stranded primary lead to the points from the coil. In reality there would be only .2 or so volts applied to the contacts in a perfect world.
Now start the engine and the voltage changes to 14.6 volts , the ballast and ignition coil would drop this extra hit of voltage as they heat up due to the voltage increase.
The current is another story. As a contact system may use a 1.5 ohm resistor and a 1.5 ohm ignition coil. The total resistance would be 3 ohms and three ohms with 12 volts would use 4 amps. 3-4 amps is pretty typical current flow for a contact ignition. This amp flow would be constant thru out the entire primary system.

The three coils we see the most ( 12 volt) are :

1-1.5 ohm coil= contact ignition system and some electronic ignitions
2-.5 ohm coil needed for current controlling electronic systems like the GM HEI ignitions etc.
3- 3-4 ohm coil used with no ballast systems as the ignition coil has it built in. Used mainly in fours and sixes as the dwell time is longer on these units and coil saturation is better.
We do not suggest these to be used on a v8 engine with smaller dwell cycles......

We also suggest using a ballast and ignition coil as this divideds the wattage of the units and lowers the heat build up by using two units in lieu of one..

pictures in next post...
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Last edited by BUBBAS IGNITION; 07-31-2013 at 07:59 AM.
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Old 07-31-2013, 08:06 AM   #46
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Default Re: Mallory tech answer to coil/ballast ?

The real issue!!!

You have got to assume that the factory did its job when they designed and made millions of vehicles and most every ignition system in all brands ran for a very long time before ever needing any service at all .......
The problems only occur after we ( all of us) modify the factory system from it factory shape and design.
I hear the comment every week: " My car is eating coils !!!" thats a easy answer the only way we can eat coils is to have too much heat and the only way we can produce too much heat is by lowering the factory ressitance of the circuit. Usually using the incorrect parts !!!
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File Type: jpg 100_9716.jpg (52.4 KB, 53 views)
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Old 07-31-2013, 10:04 AM   #47
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Default Re: Mallory tech answer to coil/ballast ?

B man Al
I want to know if you drive your car with a stock 8ba 6 volt coil and a 1 OHM resister.
I don, think you will get 100 miles.
Why would you want to do that.
Buy a 12 volt coil and matching resister , low amps about 2 amps.
ever knowtis the size of wire on 6 volt car it larger.12 volt car can use smaller wire because of less current.
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Old 07-31-2013, 11:43 AM   #48
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Default Re: Mallory tech answer to coil/ballast ?

Hi George ...

My 8BA is not on the road yet, so its only running in the garage occasionally. This is the one I did the measurements on. However I converted my 4 cyl Model B to 12v the same way in 2007 with no problems. Its been 5 yrs now and about 6000 mi. Almost all the miles are racked up on tours with the model A club, so the runs are usually all day long during the summer and fall.

The ballast resistor comes from MACS, part number A12001 and is recommended for converting 6V coils for 12v operation. I'll go make some measurements in the next day or so.

I'm curious why you think the current should be around 2A. A 1.5 ohm coil and a 1.5 ohm ballast will be around 4A peak when cold and drop to about 2-3A when hot due to the increase in resistance of the coil and ballast with temperature.

If however you take the AVERAGE current it will likely be in the 2A range because the points are open for part of the cycle, and therefore current is not flowing .
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Old 07-31-2013, 01:04 PM   #49
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Default Re: Mallory tech answer to coil/ballast ?

This is very interesting macs # A12001 what is the value of this resister.
I'm just guessing a 8ba coil needs about 3 amps to work.
When you match a resister with same value coil it works ok.
Buy adjusting resister higher or lower to match coil specs.
I guess that's a way to use and old 6 volt coil.
I did a test on mine just to see what values I would read.
I used a 12 volt coil IC13,(THIS IS SAME SIZE AS 1949 coil)and ICR 13 resister 1.82 ohms. I read about 2 amps +or-
This info is from Echlin parts book but doesn't go back to Model a.
That resister must have a high watt rating at least 20 watts.
I can see now it works for you.
Good Luck
George
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Old 07-31-2013, 10:42 PM   #50
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Default Re: Mallory tech answer to coil/ballast ?

I'm starting to understand this now. As I see it, the optimum resistance for a 12v coil would give around 3 amps? This is to prevent burning at the points. This would necessitate a resistance of around 4 ohms total. Am I on the right track?
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Old 07-31-2013, 11:16 PM   #51
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Default Re: Mallory tech answer to coil/ballast ?

Just to add to, and recap Basemans post. We arrive at the the above results using the 1.5 ohm resistor wired in series with the 1.5 ohm (12volt) coil that we should be using with a V8.
So.... when buying the resistor. Are they identified (rated?) at 1.5 ohms at operating temp (as if the engine is running) What do we buy?
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Old 08-01-2013, 07:38 AM   #52
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Default Re: Mallory tech answer to coil/ballast ?

Quote:
Originally Posted by Bluebell View Post
Just to add to, and recap Basemans post. We arrive at the the above results using the 1.5 ohm resistor wired in series with the 1.5 ohm (12volt) coil that we should be using with a V8.
So.... when buying the resistor. Are they identified (rated?) at 1.5 ohms at operating temp (as if the engine is running) What do we buy?

Yes they are rated , NAPA has a buyers guide that lists all electrical automotive products , there are many pages of resisitors ( and loom wire resistors) each oem manufacture designs the system for correct current loads etc..

This same guide also has pages of ignition coils etc ..
My experience as a technician working on these cars is that most of the time the problems are created by using the incorrect parts during a repair. Imagine a vehicle with the wrong ignition coil , the wrong resistor and the incorrect condensor all at the same time !!! We see this all the time ..
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Old 08-01-2013, 09:10 AM   #53
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Default Re: Mallory tech answer to coil/ballast ?

Well Bubba (with me) at age 60 you have enlightened me.
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Old 08-03-2013, 01:15 PM   #54
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Default Re: Mallory tech answer to coil/ballast ?

Just to keep a good thread going, and to answer George. My 32 4 cylinder with the MACS A12001 ballast resistor gives a current of 4A when not running and just turned on. (Ballast resistor cold). After a few minutes the resistor gets hot to the touch but the current only drops to 3.9 A. So there may be ballast resistors that have a 3:1 value change, but not this one. Its virtually the same over temp. The voltage drop across it is 6.15v at 3.9A which calculates to 1.58 ohms.

My dwell is set to 38 degrees, which gives a 42% make time for a 4 cylinder. So the average current would be 3.9A x .42 = 1.6A at 12V. Because the voltage increases to around 14v when running, the average coil and ballast current will be 14/12 x 1.6 = 1.9A

Al
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Old 08-04-2013, 08:32 AM   #55
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Default Re: Mallory tech answer to coil/ballast ?

The resister you are using must be for a model A coil when going to 12 volts.
the 8ba coil maybe the same ohms.
Of the testing we have done your coil must be about 2 ohms,2ampsx 3.9=7.8plus the 6.15 across the resister.=14 volt total.
my testing was 2 amps and value of coil 12 volt is about 5 ohms.
So the tests have shown there is a difference in ohms for 6 and 12 volts coils.
I,m running a 12 volt coil with low amps and has been good so far.
Macs doesn't show that resister any where else but model A section.
I don't think that's the answer for converging a 6 volt car to 12 volts.
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Old 08-04-2013, 08:50 AM   #56
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Default Re: Mallory tech answer to coil/ballast ?

Hi George ...

I just went to the MACS website. Typed in 32 ford and the A12001 came up as the resistor to use for a stock model B coil when used for 12v operation.

http://macsautoparts.com/campaign_pr...1932&make=Ford
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Old 08-04-2013, 02:57 PM   #57
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Default Re: Mallory tech answer to coil/ballast ?

I did see it in model A but didn't look in Model B
I try to get a matched coil and resister.
Seeing this is a Ford site my parts catalog NAPA ECHLIN
Says for 12 volt system point don't seem to care.
I would use IC 10 COIL, and ICR 11 Resister 1.35 OHMS
from 1956 to 1969 later but cat only goes to 69.
All this testing shows there is a difference with 6 and 12 coils.
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Old 08-07-2013, 05:03 AM   #58
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Default Re: Mallory tech answer to coil/ballast ?

Hello again!

Which is the best ignition coil for a Mallory 27 series (dual points)? Im already using a MSD Blaster 2 with external ballast resistor, but Im gonna buy an extra ignition coil/ballast resistor and keep it in the toolbag.

I was tuning the carburetor (during idle) yesterday and I noticed that my MSD Coil was getting quite hot (140 fahrenheit) and so did the condenser. Is that ok? The coil is placed in front of the engine, to the right side of the distributor.
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Old 08-07-2013, 07:09 AM   #59
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Default Re: Mallory tech answer to coil/ballast ?

Quote:
Originally Posted by Gasoline View Post
Hello again!

Which is the best ignition coil for a Mallory 27 series (dual points)? Im already using a MSD Blaster 2 with external ballast resistor, but Im gonna buy an extra ignition coil/ballast resistor and keep it in the toolbag.

I was tuning the carburetor (during idle) yesterday and I noticed that my MSD Coil was getting quite hot (140 fahrenheit) and so did the condenser. Is that ok? The coil is placed in front of the engine, to the right side of the distributor.

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 ...
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Old 08-07-2013, 01:55 PM   #60
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Default Re: Mallory tech answer to coil/ballast ?

I am at the garage right now. I measured the voltage on the positive on the coil. It is only 6 voltage with ballast and 7 without. This was strange, but perhaps why the car was shaking and finally died the other day. I must have bad wires? Is the coil bad? There is something stealing power? It is also difficult to start. The goal is to have 9 voltage on the positive side on the coil? Thanks for all the help so far.
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