Switching polarity

Unknown

So, I'm about done with my 12 v conversion. I’m considering going for negative ground now.



It appears I can switch polarity fairly easily (basically, swap poles on the coil.) as far as the car’s ignition and starting systems are concerned. As the starter is field / armature based, it will spin the same direction regardless of polarity. Thanks Park W for all the info.



I’m concerned that the radio won’t think reversing polarity is vary funny. I’m thinking I’m going to run it off a 6v non-isolated power supply, but when I mount the radio back in the dash, it will be grounded, and probably expect it’s traditional -6v input.



So, do old vacuum tube radios care about polarity? The tube heaters won’t care, but will anything else?



I know full well the heater fan and clock winder will both run backwards, so I’ve got to isolate those from ground and wire them up.



I’ll provide a writeup when I’m done with this.



Thanks;

-Chris

Unknown

your radio is not polarity sensetive in a stepdown, some 30s models are, the heater and clock will work fine, you have it right use a voltage drop for radio and reverse leads on coil, be sure to use a ballast resistor bnetween key and coil, (Ign wire) good luck, BILL ALBRIGHT

Park_W

As Bill says, the heater motor and clock are fine ... they aren't polarity sensitive. I prefer to use a resistor with the clock, as even on 6v they have a tendency to burn the contact points over time (which can cause the problem H308 referred to). Running one on 12v just aggravates the point-burning problem. The design of the radio's internal power supply is what determines whether it's polarity sensitive or not. Bill's certainly had a lot of experience with these radios, so I'd take his word that the stepdown ones are not.

Unknown

bill a wrote:

your radio is not polarity sensetive in a stepdown, some 30s models are, the heater and clock will work fine, you have it right use a voltage drop for radio and reverse leads on coil, be sure to use a ballast resistor bnetween key and coil, (Ign wire) good luck, BILL ALBRIGHT

What value (and wattage) should the resister be? Will the coil draw much current?



And thanks!



-Chris

Park_W

Whether you need a ballast resistor depends on the coil you have. Some 12v coils have a ballast resistor built in. To make sure I was getting a "matched" coil and resistor, I used the ones NAPA shows for the '56 Hornet 6 ... Echlin coil IC-14, resistor ICR-13. As an alternative, Echlin IC-12 has the built-in resistor. The advantage of the separate resistor is that, by using the right starter solenoid, you can wire it so the resistor is bypassed during cranking, applying full voltage to the coil for that brief time. A suitable solenoid with the extra connection to do this is NAPA ST-81.

RG53Hornet

Radio should be ok w/ + or – ground. I built an electronic voltage regulator for mine so it always sees 6.8 volts (neg ground) when the vehicle is anywhere from 10-16 volts. I’ve played it for hours multiple times while I’m working on the car, it has not complained yet. I used a 70's MoPar ignition ballast resistor in line with the clock, and after I shortened the internal spring, it keeps good time.

Unknown

Park W wrote:

Whether you need a ballast resistor depends on the coil you have. Some 12v coils have a ballast resistor built in. To make sure I was getting a "matched" coil and resistor, I used the ones NAPA shows for the '56 Hornet 6 ... Echlin coil IC-14, resistor ICR-13. As an alternative, Echlin IC-12 has the built-in resistor. The advantage of the separate resistor is that, by using the right starter solenoid, you can wire it so the resistor is bypassed during cranking, applying full voltage to the coil for that brief time. A suitable solenoid with the extra connection to do this is NAPA ST-81.

Park is right on about the resistor and coil selection. My Terp 8 is 12V and has been that way for 4 years now. Originally I used a MOPAR resistor and the original type 6V coil and it ran beautiful till it got warm , then it would stumble and run like crap at low speeds. Changed to a coil made to use with a resistor such as late model Mopar and runs fine and smooth at all times. The coil was breaking down, also used a Ford selenoid on the 6V starter to give full 12V at starting.

Unknown

Park W wrote:

As Bill says, the heater motor and clock are fine ... they aren't polarity sensitive. I prefer to use a resistor with the clock, as even on 6v they have a tendency to burn the contact points over time (which can cause the problem H308 referred to). Running one on 12v just aggravates the point-burning problem. The design of the radio's internal power supply is what determines whether it's polarity sensitive or not. Bill's certainly had a lot of experience with these radios, so I'd take his word that the stepdown ones are not.

This brings up a an intriguing question, at least to me. I have also converted Doc to 12V and used the resistor for the gauges (8V). Interestingly enough, the clock was not a factor in re-wiring it, as it is mechanical. Just wind it (after I re-built it) and it keeps perfect time. Apparently, y'all have some that are electric. Is the mechanical clock rare, or maybe the electric's were options? or year specific? What does everyone else have?



Russell

Park_W

Electrics were standard on Commodores and Hornets. Supers came with mechanicals.

Unknown

Park W wrote:

Electrics were standard on Commodores and Hornets. Supers came with mechanicals.

That must mean that mine has been switched at some point. I kinda like the mechanical ones . . . they are very nice pieces.



Russell

[Deleted User]

Russell, my mechanical clock in the Pace still works great as well. Though you have to keep winding it.



Jay :-)

Unknown

YOUR MECH CLOCK CAME FROM A WASP OR SUPER, DO THE UMERALS MATCH THE SPEEDOdsssssssssss?? iF THEY ARE THE SAME, SPEEDO FACE WAS ALSO CHANGED, GOOD LUCK, bill albright

Unknown

bill a wrote:

YOUR MECH CLOCK CAME FROM A WASP OR SUPER, DO THE UMERALS MATCH THE SPEEDOdsssssssssss?? iF THEY ARE THE SAME, SPEEDO FACE WAS ALSO CHANGED, GOOD LUCK, bill albright

Yes, the numerals on my clock face match the speedo. I guess at some point the electric clock stopped working and was replaced with the mechanical. They must have also changed the face of the speedo to match. It looks good as it is, I suppose I'll leave it as it is.



Russell

[Deleted User]

I have two 54 Hornet Specials, one has an electric clock and the other has a wind up. Both work fine but I am partial to the electric, cause I keep forgeting to wind the mechanical.

Bob Hickson