Correct Ballast Resistor

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Oct 7, 2002 | 02:19 PM

fatfenders

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From: Iowa

Correct Ballast Resistor

I am installing an aftermarket harness (Haywire brand) in my 53 F100 with Duraspark Blue grommet module and stock distributor, and an MSD Blaster coil. I have a question regarding the proper resistor. My harness instrutions and I believe the Ranger station recommend a resistor in the 1.3 - 1.5 ohm range. (Which I bought) I was looking through the instructions for the Blaster coil and the recommendation is a .8 ohm resistor or resistor wire. Which recommendation should I follow?

Thanks
'fenders

Oct 7, 2002 | 10:18 PM

Mike W

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From: Central Kali

Correct Ballast Resistor

I did a quick calculation. Assuming the coil is 2 ohms, the 1.5 ohm ballast resistor would let 4 amps flow and the coil would run at 8 volts. The .8 ohm would let 5 amps flow and the coil would run at 10 volts. I would use the 1.5 ohm. The coil would dissapate 32 watts with the 1.5 ohm and 50 watts with the .8 ohm. (this assumes the coil is sitting there with a constant current going thru it)

Oct 8, 2002 | 07:46 PM

fatfenders

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From: Iowa

Correct Ballast Resistor

Mike

Thanks for taking the time to calculate it. I would not have known where to start. I also rechecked the Ranger Station site and their minimum recommendation is .8 ohms, not 1.3 ohms. I'll use a .8 and we'll see how it works. Is there a general rule for target voltage at the coil or does it depend on the coil manufacturer.

'fenders

Oct 8, 2002 | 08:55 PM

thelonerangerxlt

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Correct Ballast Resistor

[updated:LAST EDITED ON 08-Oct-02 AT 09:59 PM (EST)]Fenders, I like to see around 7-9v at the coil, with the engine off, key on. The running voltage will vary with the alternator output, battery condition, accessories that are on, etc....For a "hands on" test, grab the coil housing after it has idled a few minutes. If it is unusually hot (too hot to touch), put a higher value resistor on it. By the way, the coil will run hotter at idle than it will at higher rpms, because of the dwell time.

78 Bronco Ranger XLT, 351M, 4-sp, Trailer Special

Oct 8, 2002 | 09:16 PM

Mike W

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From: Central Kali

Correct Ballast Resistor

" their minimum recommendation is .8 ohms ", this tells me to not go below .8 ohms. Not that 1.3 would not work. The Blaster coil may be able to handle the .8 ohm ok, but will the duraspark hold up with the extra current? If you had a points system, I would expect the points to burn out faster with the lower ballast resistor.

I run MSD ignition systems where the coil functions as a step up transformer. Instead of trying to push a lot of current into the primary to get the high voltage output, the primary gets a pulse of maybe 400 volts. The windings ratio steps this up at the secondary.

Oct 9, 2002 | 03:01 PM

fatfenders

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From: Iowa

Correct Ballast Resistor

Mike and Lone Ranger

Would I be correct then in expecting the least possibility of trouble with a 1.3 ohm resistor, provided my coil voltage is in range when I'm done? As you can see from my gallery, we aren't going racing here. I needed a coil and the MSD Blaster coil matches my truck color very nicely.

'fenders

Oct 9, 2002 | 08:51 PM

Mike W

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From: Central Kali

Correct Ballast Resistor

I would go with the 1.3 ohm. A 75 manual gives a spec for the stock coil of 1 to 2 ohms. The ballast is 1.3 to 1.4 at 75 degrees F. To check the coil voltage jumper the coil neg to ground. A 72 spec (points) lists 6 to 8.1 volts as ok. If outside that range, replace the ballast.