guys, on my 37 ford flathead, im running the factory 3 bolt helmet style coil, i had it rebuilt by skip. i was told that i needed to run a ballast resistor. so a friend a gave me a part number for the one he uses... skip says the coil needs to see 4 volts not 6.... measuring the voltage with the resistor i bought, its only 2.4 volts... i noticed it feeling like it had a small misfire, like a weak spark, when leaving a show yesterday. my quesiton is, what resistor do i need and is there a way to tell how many volts it produces? this is in an AV8 coupe, thanks
That makes sense really. Sounds like the low voltage is causing it to act like a bad coil that is breaking down under load. The voltage spec is on the resistor. I was in Perrysburg with the Rollin bones a week ago. Potets car was running bad, coil was incredibly hot. They pulled the ballast and it was too high a voltage. They put the right spec ballast in and a new coil. All was well
What you need to know is the ohms rating, which is the actual resistance to current flow. The resistor you have has too high an ohmage and the extra resistance cuts the voltage more than you want. Measure the ohms of the one you have, seperated from anything else, with a volt/ohm meter, you can get one for only a few bucks nowadays.Then search around for a resistor with slightly less ohms. Caution: Make sure that you use resistor with a sufficiently high watts rating.
Read this thread http://www.jalopyjournal.com/forum/showthread.php?t=685471 Looks like you might not need a ballast with a 6 volt system. Also make sure you have a coil that doesn't have internal resistance. Here's another good one from the ford barn http://www.fordbarn.com/forum/showthread.php?t=83691
you must have one with a factory helmet style coil becuase they are externally resisted.. kinda why i had to have skip rebuild mine.......... i ran it a while without one. i just read in a few other places i need a 1.5 ohm ballast. ill measure mine and see what it says.
I would think that 2.4 volts at the coil would be a little on the low side. This is the early Ford resistor sold by Macs , shows a .6 ohm when just laying on the bench and varies when current heats it up. I like to see 4 volts at the coil on these when possible..
thanks bubba.! thats what i needed to know. about the best on anyone carries around here is .8 ohm so far.. ill try that and see what kinda voltage i get . thanks
i did some math... with a .8 ohm resistor, 12v- output will be 9.3750 volts 6v- output will be 4.6875 volts i think that is about as close as it comes.
What some do on the early fords is to byp*** the resisitor with a toggle ( momentary contact) switch and byp*** when cranking during starting ( especially hot) that way the actual battery voltage will be available to the coil while cranking with the six volts and be resisted once the engine is running. Might be worth a try?
You will see about 3.6 volts at the coil with key on engine stopped and 4.5 engine idling with that Ford resistor. The higher the RPM the higher the coil voltage will be as the coil charging inductance becomes a larger percentage of the coil on time. V8 6 Volt nominal 1.5 Ohm coil Coil current No resistor Key On Points Closed = 4 Amps Engine Idle 600 RPM Dwell 30 33 Pct No current 16 Pct Charging 2 amps 51 Pct coil fully charged 4 amps Average current at idle 2.4 amps Heat dissipation = 24 Watts Engine off 14.4 watts idling Now throw in a .6 ohm resistor which is more like 1 ohm hot Key on engine off points closed 2.4 amps Voltage at Resistor in 6 Voltage at Resistor out 3.6 Coil Current 2.4 Wattage 8.6 watts Engine idling Amps 1.44 Resistor 6V in 4.56 out The way to measure the resistance of a working ballast resistor is by measuring current and voltage drop. As the RPM increases current will drop so the resistor will cool providing more voltage to the coil reducing the RPM current drop effect, thus the name "ballast" resistor. Don't trust me, just put a voltmeter on coil positive with a ballast resistor and watch it climb with RPM. At 600 RPM Coil charging is 17 pct, at 1200 it is 34 pct, 2400 68 pct etc.
I measured mine tonight, I can't get more than 3.2 volts out of it.. I ordered a new style that will be perfect. It will start at 3.6 and climb to 4.3 volts total.. That is as close as I can get Posted using the Full Custom H.A.M.B. App!
i installed the new ballast resistor today. a .8 ohm unit. it was from MSD iginitons.. what a difference! my car has a lot different throaty sound now.. my plugs seem to be not so black, its burning all the fuel very well.. and no sputtering what so ever. very happy thats all it was.
Glad you got some success! And thanks for coming back to tell us of the success,, way too often, after the OP with the problem solves it with suggestions and help from the forum, he never comes back, follows up and reports the fix.
Sounds like ya got it. What the total ressitance including the coil ??? >8 resistor plus the coil = ?????? Thanks for staying with this project...
The resistor itself is .8 ohms. That's the smallest I can find. At idle I'm at 3.6 volts ... Driving down the road I'm about 4.1-4.3 volts. Checking resistance at the coil terminal it's about .935 ohms... We drove it a about 60-70 miles today and it was flawless. That resistor made by MSD was the ticket . And it's only 9$ at any autozone . Posted using the Full Custom H.A.M.B. App!
If you use a Ford factory (or repro) style starter solenoid then it will have a (small) terminal that can backfeed the full battery voltage to the coil side of the ballast during cranking - either onto the ballast terminal or at the coil feed terminal. That way no toggle switch to remember about. You can check it working with a light bulb at the coil - it goes brighter during cranking over.
GOOD TO KNOW! ill have to look into that. mine starts like its fuel injected. it turns over once and just fires and runs.. perfect. but that would be a nice feature to have.
Interesting post from start to finish but it feel as if there is a lesson to be learned as well. I have been involved in this problem since day one and even built a special distributor for the blown engine. ( actually yelled at him when i thought he had hung up on me once , sorry man ) Everyone has posted their fixes etc and lots of info has been downloaded. Thats not a bad thing for sure , however ........ Now that the car is fixed ( at least we hope) if you look at the specs the parts are factory value parts ! The resistor suggested is a .6 ohm (1 ohm when hot and current flowing) and i ***ume Skips coil is approx .6 as well. We do ignition distributors and systems every day and even though you have cousin Freds magic set up from 1949 and his worlds fastest flathead parts, you just cant beat the factory set up in most cases. Ignition is one of the areas the manufacture just cant afford to mess up! The vehicle must be able to run some pretty long mileage on the ignition parts and often the maker sells millions of the system to be put on the street. So the moral of the story is , that many times if we would just follow the factory service information the system would work just fine...
you hit that nail on the head.. factory parts are the best.. i think the worst is inexperiencec young guys.. ( ME!) but lessons are learned. thanks for all the help guys
I second that, I have been to Delco labs in the day and the effort they put into such details as the spark plug would amaze you. Ballast resistance and primary current are tough to understand as both are moving targets. If we say 1.5 ohm coil and 1.5 ohm resistor that's never the case exactly. At Key on Engine Off (KOEO) the coil will be it's cold resistance plus about 1 % per degree of temp. The Ballast resistor will be some value over it's room temp measurement @ 1000 degrees it is about 20 per cent for NiCr and 4 amps will heat a 24 Gauge resistor wire to 1000F. So at KOEO our 1.5/1.5 combination will likely be about 1.7/1,7 and our normal 12.6 volt battery would then flow about 3.7 amps. As soon as we start our V8 engine things change. At 500 RPM the coil is off 7.3ms, charging for about 8ms, and full current for 10 ms or so (25ms per firing. So we are now flowing about 2 amps at idle with a current peak of 3.7 or so. How can we measure the operating resistance of our components? We need an ammeter between battery and the resistor. Then we can measure our operating resistance. If the current is 3.7 amps (KOEO) and we read 12.6 in front of the resistor and 6.3 after then we know that R= E/I R=6.3/3.7=1.7 So both units Coil and Resistor have resistances of 1.7 If her had 12.6 and 5 then Resistor = 7.6 V / 3.7 A = 2.05 Ohms Coil = 5/3.7 = 1.35 Ohms Now someone like Bubba who has a Distributor tester and sees a lot of these components can give you real measurements vs my imaginary ones but that's how it works. Until you plug a resistor in the circuit and measure the avg current in the circuit and volts before and after the resistor we are probably guessing. And since the factory guys already did this, they are luckier guessers than we are.
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