Ballast resistor.

D

Darrell Kinnan

Junior Member
Installed a new ballast resistor on a rough running 37 engine. Started the engine and the resistor started smoking. Put the original back on, it's made out of ceramics, it didn't smoke but reach to 300 degrees. Should the resistor run this hot, if not, what could be the problem? Obviously the new ballast resistors can't stand the heat as they are not ceramic.

Always grateful for your help,
Darrell
 
They do get warm, not sure of the actual temp.
If this is ignition resistor, they still make ceramic ones. Do a search for part number. It has been discussed here before.
 
If the coil is drawing to much current....being partial shortened or some other issue the resistor will heat up more then it should.
They should heat up a fair bit...that´s part of the design.
Those chinese bambo versions from the company whos name we shall not mention ;) are just plain junk...you´re better of fixing your old one...
 
The resister is about .5 ohms but you must have a watt rating of 10
See if you can get one on line .5ohms 10 watts
 
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See if you can get one on line   .5ohms 10 watts
Ignition ballast resistors have a positive temperature coefficient; as they get hotter their resistance increases. Normal power resistors have a neutral temperature coefficient so don't react like ballast resistors. There was a post recently that listed different values of ballast resistors from NAPA I believe. That would be what one would want if you need a special resistance.
 
All of these are higher value than what you need for a stock Ford application.

•#ICR23 – 1.20 ohms
•#ICR11 – 1.35 ohms
•#ICR34 – 1.40 ohms
•#ICR37 – 1.60 ohms
•#ICR35 – 1.80 ohms
•#ICR13 – 1.82 ohms
Lucas* 3BR (1.3 - 1.4 Ohms)
Mopar* DCC-4529795 (1.40 Ohms)
Accel* ACC-150250 (1.35 Ohms)
Standard* RU-4 (1.35 Ohms)
Standard RU-23 (1.20 ohms)
Standard RU-37 (1.40 Ohms)
 
We need to know if this is a stock 6-volt system. Resistors use some power to drop voltage and control current since they are a load device. They will get hot so they use ceramics & place them on a board that can take some heat. Ford generally placed the board in an area where they will be somewhat protected from hazards.
 
I think the 6 volt coils need about 3 amps or 4.5 volts to work. With no special meters ,only a volt meter if you measure 1.5 volts across the resister that should be good. By putting a larger 1.5 ohms you cut the amps to 2 amps and the coil voltage to 3 volts. So with a .5 ohm 10 watt this should work if you can't find a original resister.
 
Be careful you use the right resistor. If you use one with too much resistance it will reduce the juice to the plugs and soot them up so much they will misfire.
If you see black sooty plugs your resistor is too big.
 
Init1 said:
Be careful you use the right resistor. If you use one with too much resistance it will reduce the juice to the plugs and soot them up so much they will misfire.
If you see black sooty plugs your resistor is too big.
Click to expand...

This sounds like more of a guess than fact. Truth is the engine will
run good on 4 volts to the coil and also good in the 3.5+ range but
when you get below 3.5 it may not even start. In the lower range
sometimes it will start just as you release the starter the engine is
still spinning and the voltage to the coil increases from the voltage
increase when the starter disengages. Much over 4 volts will cause
the points to arc and pit them. G.M.
 
Here's what I'm getting with the engine not running:

6 volts on the battery
2 volts at the coil
6 volts on the ignition side of the resistor
2.5 volts on the coil side of the resistor

Is the resistor taking too much from the coil? Engine starts but runs real rough.

Darrell
 
Darrell Kinnan said:
Here's what I'm getting with the engine not running:

6 volts on the battery
2 volts at the coil
6 volts on the ignition side of the resistor
2.5 volts on the coil side of the resistor

Is the resistor taking too much from the coil? Engine starts but runs real rough.

Darrell
Click to expand...
I like to test when running, measure across resister.
I would buy a resister from
Resistor Fuse Terminal Block
1933 - 37
40-12250
dennis-carpenter
about $30 looks like original.
 
Darrell Kinnan said:
Here's what I'm getting with the engine not running:

6 volts on the battery
2 volts at the coil
6 volts on the ignition side of the resistor
2.5 volts on the coil side of the resistor

Is the resistor taking too much from the coil? Engine starts but runs real rough.

Darrell
Click to expand...

Several issues here, but the big one appears to be the voltage drop across the ballast resistor. The coil needs a min of 3.5v (as already stated) and is better at around 4.0v. The battery should be greater than 6v not running, more in the 6.2-6.3 range and somewhere above 7v running.
 
If the coil is shorted out having a lower resistance then it should have you get readings like this.
Or if the ballast resistor has a bad connection between the resistance wire and the connection points giving it a higher value then it should have.
Is the coil heating up more then normal ?
 
Thanks for all replies. I've learn that ballast resistors can get red hot. I put the old one back on and it seems to be working ok with at least 2.5 volts to the coil. Waiting for Skip to rebuild the coil and have received a distributor rebuild back from Cliff Green. Hope to be on the road soon. DK
 
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