More 12v Conversion Trouble...Help a NOOB

Kaonix

Kaonix

Member
Hi guys, heres the skinny.

Car: 1941 Original Flathead 8
Problem: Car starts beautifully, runs BEAUTIFULLY then after driving for 10 to fifteen minutes car dies and wont start for an hour or so, coil is HOT to touch.

Parts:
12v NEG GRND Battery
Mallory Electronic 3 bolt replacement dist. #5072101 from Speedway Motors
First Coil: 12volt chrome job from autozone - Suspected Dead
Second Coil: Mallory Promaster 12v #29450

I have basically eliminated the vehicles wiring harness from the equation, I've sourced 12v from the battery for diagnostic to make sure I'm not missing any resistors or anything, I have the wiring correct from distributor to coil, only change is we have a dakota digital dash that requires a wire from coil - for tach lead.

The car runs ridiculously strong for ten to fifteen minutes then just dies. No sputter, no jerking, just dies. Fuel is fine, running electric pump with a regulator that is flowing perfectly.

I have tried running with the original ballast resistor under the dash and without. I'm assuming this new coil is internally resisted, it is the recommended coil by mallory to use with this distributor.

PLEASE. ANYONE HELP ME!
P.S.
I don't need any wise comments regarding how great six volts is and that I should have left it. If six volts is so great, manufacturers would still be using it. I like being able to see down the road at nite.
 
Do you have another (conventional) car that runs perfectly happily on 12V?

If so, borrow the coil and ballast off that car and try it on your 41.

I'm guessing, but it could be ballast related, but I also had a problem with the divers helmet dissy, it would fail after running a while. I read a post by GMC Bubba saying the HT can earth through to the shaft. I never fixed mine, I replaced it with a crab dissy on an adaptor. But I could see tell take signs of ht marking the shaft.

What leads are you running? If you have high resistance leads or caps, that can put an extra load on the distributor and break down the ht side if it as at all iffy.

If the coil is hot it needs a ballast, just off the top of my head.

Mart.
 
Hi Marty, thanx for your reply. I'm running a set of brand new universal v8 wires from duralast. I don't think they are the problem seeing as the vehicle just runs too good when its running to be a plug wire problem. I don't have another vehicle with a coil (well, a coil like this anyway), all my other cars are 2010+. Shouldn't the new mallory coil be internally regulated. I don't know where to look. I changed from an accel super stock coil to this one and the problem is literally identical. The coil should not be getting as hot as it is. However if the coil is internally resisted/regulated whatever, why should I need an external ballast? Don't take my questions as negative, I'm just trying to figure this out and gain as much knowledge as I can.
 
Wire in a ballast resistor and try it. If the coil is too hot it needs a resistor like Mart said. I have a Pertronix 40,000V Flame thrower and had to use a ballast resistor with it.
Bill
 
It says that you need a coil with a primary resistance of 1.4 ohms, or to add a ballast resistor to make it that, and says that coil # 447-45001 can be used without resistor

6V stock lights can be better than 12V seal beams ---the halogen bulbs I have in my A are better than seal beams, as good as some of my modern cars-better than 2 of them-just using the bulbs,all else is stock

I know that some electronic systems won't make spark without the proper resistance coil---electronics can be smart and not work if they know the system has a problem, they can shut off to protect themselves during an overload.--the coil has to be matched to the electronics

One of the reasons for 12V was with more wiring the newer cars had going to 12V meant they needed 1/2 the copper-- that cut costs
 
Kurt in NJ said:
It says that you need a coil with a primary resistance of 1.4 ohms, or to add a ballast resistor to make it that, and says that coil # 447-45001 can be used without resistor

6V stock lights can be better than 12V seal beams ---the halogen bulbs I have in my A are better than seal beams, as good as some of my modern cars-better than 2 of them-just using the bulbs,all else is stock

I know that some electronic systems won't make spark without the proper resistance coil---electronics can be smart and not work if they know the system has a problem, they can shut off to protect themselves during an overload.--the coil has to be matched to the electronics

One of the reasons for 12V was with more wiring the newer cars had going to 12V meant they needed 1/2 the copper-- that cut costs
Click to expand...

Could you possibly recommend a proper ballast resistor for my application?
and I completely understand that the electronics should be matched which is why I went with the mallory dist/coil combination. Seemed like a no brainer.
 
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Measure across the primary terminals of the coil. The value should be in the range of .75 to 1.50 ohms. Get a ballast resistor of equal or slightly higer value and wire it in. You want to get the voltage across the coil down to about 5 volts.
 
So I have measured resistance on the coil with all wires disconnected, here are my findings if this means anything to anyone

+ to -: 1.9
+ to OUTPUT TERM: 12.5k

Called NAPA and they said they have a ballast resistor @ 1.82ohms part#IC13 would this take care of it? I'm not real good with ohms law or conversions or anything, please forgive my ignorance.
 
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1.9 ohms is high for a standard coil. According to the Mallor/Prestolite site coil #29450 is an internally resisted coil and should not need a resistor. You said you're running a 12 volt converted car. If its negative(-) ground is the (-) side of the coil wired to the points? A reverse wired coil will be trouble. If it is wired correctly measure the battery voltage with the car running. You want to see no more than 16 volts.
 
It is a negative ground car now, the negative side of the coil is wired to the electronic distributor, battery shows 12.8 - 13.4 volts while vehicle is idling.
 
Suggest you contact Jim Linder (aka "Bubba") at Bubba's Hot Rod Shop in Speedway, Indiana. He posts on here regularly and does all sorts of good things with ignition systems - his specialty. He can recommend a product to suit you needs both from a theoretical and a practical perspective.
 
Kurt>>>electronics can be smart and not work if they know the system has a problem, they can shut off to protect themselves>>>

I think Kurt is correct. Seems like the coil is drawing too much current --- over 6 amps if your primary is 1.9 ohms. Your Mallory might have a thermal fuse that re-sets after a cooldown period. Try the NAPA ballast resistor that you found --- or maybe something around 1.4 to 1.5 ohms.

Jack E/NJ
 
Check the battery volts again with the engine as 1500 to 2000 Rs... are you running an alternator ?? could be over driving the system ?? when it dies, do you have voltage to the coil ?? are you running Henrys orginial, ignition switch ? that guy can not handle a big load,
Your all digital dash may be to much for the ign. switch ?? ... When it dies, jumper the ign. swithch, see if it will start...?? I would try a STOCK, STANDARD, OFF THE SHELF. COIL, not a super hot blaster 40,00000000 plus. just not needed for a good running flathead, and yes I will be running 12 volts, with the crab dist. and standard coil, with a built engine 276 inch and hot cam, and two twos.... OLD....BILL
 
I agree with the others , you need a ballast resistor. Lots of china made ignition coils out there and they wont run with 6 amps going thru them , they overheat and shot down the module.

You need between 3 and 4 ohms of primary resistance in the primary circuit to cut the amps down to about 3-4 amps .

Heres a problem like yours from a customer and the fix.....

http://www.jalopyjournal.com/forum/showthread.php?t=692933

Glad to help.....
 
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