The Stovebolt Site Forums The Shop Area The Electrical Bay Help with correct coil to use

The 235 I recently purchased came with a NAPA Ichlin IC-12 coil. Says "12v use with external resistor" and “use external resistor” on the side. The PO had converted his truck to 12V and I will do the same. I just want to confirm this is the correct coil to be using. If not, what should I purchase?

Thanks

Yes, correct. To be used with a ballast Resistor.

Here's a selection of the correct resistors from Rock Auto:

https://www.rockauto.com/en/catalog/chevrolet,1960,c10+pickup,3.8l+235cid+l6,1489472,ignition,ballast+resistor,7052

Jerry

Thanks Bartamos and Jerry. All 4 of those resistors look alike to me. Thanks for the link Jerry.

You'll also need the 12 volt type foot start switch with the small side terminal for the resistor bypass wire. Rock also shows a listing for that item. Search their website for the 1957 C-10 with a 235 for a "starter solenoid". That's not the correct name, but that's how it's listed.


I lied- - - - -they corrected the listing!

https://www.rockauto.com/en/catalog/chevrolet,1957,truck,3.8l+235cid+l6,1326091,electrical-switch+&+relay,ignition+starter+switch,4700

Jerry

I’d see about finding an NOS Delco Remy on eBay. I had a go around with the modern replacements having higher resistance than the stock one.

If the ballast has the right resistance, the "Ignition on- - -points closed- - - -engine not running" voltage at the coil + terminal will be approximately 9.5 volts.
Jerry

Anyone know what the correct Ohm value should be? I always thought that was one of the most important aspects of choosing the correct coil.

The resistance of the coil primary winding will be a factor in how much voltage the resistor drops, since the resistor and the primary winding are in series with each other. Half an ohm difference in the coil winding resistance will make a big difference in the voltage drop you can measure with the circuit conducting. Measure what the circuit is actually doing- - - -don't rely on some chat room "expert's" pontificating- - - - -including mine. If you don't know enough about DC resistive circuits to understand the readings you're getting, find someone who does.

Terry- - - -I'm 60 miles south of you down I-65- - - -drop in sometime and I'll show you exactly what I'm talking about with a multimeter.
Jerry

This is one of those, "it never goes away" questions. Hotrod has the practical solution. He always does. If you want the more "technical" solution, then this is for you. The points are a switch. There is a limit to the current that switch can take. Some Engineer figured out how much current those points would take and still live. His or Her math was based on 6 volts. "Cause that was what they worked with at the time. Simple IRV equation. I(current) R(resistance) and, V(voltage). Ohms law. Add the coil, and you get a new set of numbers. Reactance. That is AC resistance. The coil is an Inductor. 6 Volts becomes 20,000 Volts and you get a spark. For those who like math, Voltage equals Current times Resistance. V=I(R). If you measure the coil resistance, multiply that by the Voltage, you will get the current through the points. Kinda. Sorta. Cause the D.C. resistance is close, not correct. So what to do? Relax. This is car and truck stuff. No rockets here. So we then(around 1954) go to 12 Volts. No one is gonna pay an Engineer to recalculate because, that takes money. Same switch, and same coil, add a cheap resistor. Problem solved. That is the "Ballast" resistor. Back to our kinda/sorta problem. Coil D.C. resistance is matched to the ballast resistor. Problem solved. Then sometime around 1967 those sneaky makers hid the "ballast" resistor inside the coil. The true 12 volt coil was invented. Sorta. But, no "ballast" resistor is needed, "cause it is built in. Same switch, same coil, same resistor, new can. Some where the hotrod guys got in the mix. Bigger spark for higher compression. They wanted more power. Use more current. That worked, and burned up points. Change the number of turns inside the coil. That worked, and messed up the current. Burned up the points. So, you now have to match the coil to the resistor. Or, use a "12 volt" coil. Are we having fun yet? Hotrod and his practical solution. Winner.

Good points, Steve. When I start getting into discussing inductive reactance, and also condenser charge/discharge times, and the fact that at highway speed, the switching is happening 60 times a second or faster, most folks' eyes glaze over and they start to snore. Also take into account that I spent 30-something years trying to "educate" a bunch of inner city ghetto gangbangers who knew a lot more about stealing cars than fixing them. "Practical" is my default setting. I can also talk "technical" with a select few people who are capable of having an intelligent conversation on the subject. My electrical engineer younger brother who also has a doctorate in plasma physics used to call me for auto repair advice on occasion!
Jerry

I have a 1954 3100 with the original 235 that has been converted to 12v. After several years of running with a 6v coil and from what someone told me a Chrysler ballast resistor the 6v coil finally died, I replaced it with a coil from NAPA. Part # MPE IC12SB $34.49. I also didn't want to take a chance so I replaced the ballast resistor (NAPA calls it a Coil resistor) with Part # ECH ICR13 $15.99. I have been running both for 6 months and no issues. Truck is running great and firing as it should. I did nothing but replace those two items.

Jerry, Thank you for the invite. When I can secure a kitchen pass I'll give you a call. My truck needs to be driven and Delrose has some great back roads.

Cheers,
Terry

You're welcome anytime! Nashville is a good place to be from- - - - -a LONG way from! I was born and raised there, but the city I grew up in was not the same when I returned from California in 1980. I spent 20-something years running the auto shop at McGavock High School before the "Educators" closed down all the vocational programs that actually taught kids how to work for a living! I retired in 2011 and never looked back!
Jerry