Inliners International Forums General Discussion Electrical ballast resistor

does anyone know how many ohms ballist resistor I need for an accel super coil(the big yellow one) im running it on a 1954 chevy 235.

It should have came with one. But if not you should be able to get one from any parts place who sells those coils. accel even has their own. So do many others Mallory,MSD so on.

A (factory) Chevrolet one will work too. They were used from 1955 thru 1962.

The main thing is It's wire wound in a ceramic housing. They get very hot making the reduction from 14V to 6.8 etc.

Your 54 is converted to 12V, right??

The 'universals' are around 1.50 and you can even buy 'variable rate' ballast resistors, I think MSD's is just 0.25, you can use pretty much any of them, but like John says make sure they have a good porcelian heat sink. I like to use a low resistance like the Mopar or MSD, I have no proof, but I think it gives me a hotter spark.

yes my 54 it came with a delco remey 12v genorator and converted the rest. thanks for the info

Dear Steve;

Okay then;

I would go with the Accel product, as the resistance may be 'mated' to the coil's primary winding and this IS 'an aftermarket' item. Also, look on the box/instruction sheet to see if one is required. Some coils have them 'built in' or have a 'heaver gauge' primary that stays 12V.

I wasn't aware there was such a varriance in (ballast) resistor values. There's no need to vary the size (resistance) of the primary winding much as the higher HV comes from a larger secondary etc.

There's a 60,000 volt (coil & resistor) combo on e-bay for under $20. But don't get "caught up" in the HV concept, as It's not that cold in Texas.

thanks John I think I will look on accels website becuase I bought the truck with the coil on it . I only drove it around the block a few times before I took it apart to restore it; I was told that it was six volt, but It was acctually 12v as I started to notice as I took the truck apart. So it should have one built in it, im going to doublle chech just to be sure
thanks again

S;

Accel wants their coil to run @ 8-10V which is more than the stock GM coil, using a distributor with points.

It says to make the measurement with the Ing. switch in the "run" position. This will be whatever the battery voltage is (engine not running) and around 14V when it is, don't forget.

Steve, the large yellow Accel coil has a very low primary resistance. The important parameter here is the current. Shoot for ~3 amps with points and you will be OK. Greater than 4 and point life really suffers. I am using two series 1.5 ohm ballast resistors in a 24V system.

Jon, the reason that the primary resistance is lower is that the primary inductance is also lower. A lower primary inductance will result in quicker saturation which is needed for the shorter dwell times in 8 cylinder engines and/or high rpm.

thanks Jason ill do that

Jayson is correct with the induction theory.

However; You will still need to make the voltage measurement (engine running) to make sure it meets the coil MFG standards (8-10V) etc.

I would check the voltage first (even W/O engine) just to get an idea.

If you have 8-10 volts across a 0.7 ohm coil, you will have too much current through the points.

J;

This may be true, but that's what Accel says to run on their coil. This is higher that the 6.8 GM uses because their primary winding is different etc.

The few degrees of dwell (over 30) for the higher current flow shouldn't really matter in his case, as the # of 'coil saturations' is 2 fewer than a V-8 (in real time) for each rotor revolution.

Happy trails.

Jon, Accel recommends that the supplied 0.85 ohm ballast resistor be used in addition to the vehicle's original ballast resistor (right off the Accel website). Assuming that the original ballast resistor was 1.5 ohm, the current will be 4.6 amps and you will have 3.22 volts at the coil. This current value agrees well with the accecpted limit of ~4 amps through points. In practice, the current will less because the resistance of the ballast resistor increased with temperature. I have no idea where your 8-10 volts comes from. If you had 9 volts across the coil, you would have 12.86 amps through the coil and points. Clearly too much. Another point to ponder. IF the Accel Supercoil's only difference from a standard points coil is the primary inductance, you would actually have worse performance. Can you guess why this is?

I got that from the FAQ section, on the Accel website.

It did seem high as most coils (with resistors) run much less. I just figured it was for their special need and who would know more about that product but the MFG??

It won't hurt to run it lower (using the value you said) to save the points, as it was running W/O any, which would be 14V.

The 'true test' here, would be to run it using their product line & see how long the points last. Then adjust the imput voltage if needed.