Re: 23rd Sedan with AC

Posted by DavidPackard On 2017/6/20 23:17:53

I can't resist!

This appears to be a 'center tapped' 12 volt system. The two smaller gauge wires would be connected to the 6 volt center tab. This type of electrical system allows for dual voltage, common polarity, power. I suspect the starter is connected to 12 volts, as is the AC. The rest of the car remains 6 volt. I equally suspect the polarity has been switched to negative ground ( I surely would and then again I would also power the ignition system with 12 volts).

The only piece of electrical equipment that is polarity sensitive is the radio ( I think ). Given that the original radio may or may not work, cost of vacuum tubes, and 12 volt negative ground power is now readily available, a modern radio could be installed somewhere in the car. The power to the OEM radio is easily disconnected.

I don't have any experience with the overdrive solenoid, but give that those small automotive relays work with either polarity at the pull-in coil, I would think the OD solenoid would work OK.

I've been told that heater blower motors will reverse direction when the polarity is swapped. The good news is that air will still flow in the correct direction, albeit at a reduced flow rate. The blower wheel vanes had been optimized assuming a known direction of rotation, and swapping polarity just blew all of that science into the water and the flow rate goes down.

If the starter still has 6 volt field pole windings that's a bit of a gamble. Except for a 6 volt to 12 volt conversion on an old VW bug years ago I would change, or modify, to a 12 volt rated starter. The Bendix drive life will be far less at the elevated starter torque that results from the higher voltage. I've also heard that the 'nose' of the starter housing may be a weak link, but fortunately have no firsthand experience breaking starter housings. The really good news is the starter will spin in the correct direction independent of the polarity. I'm still scratching my head over that fact.

This isn't a complete change-over to 12 volts, so the good news is that none of the bulbs need changing.

The generator idiot light (if so equipped) may be a casualty unless the alternator has the provision for that feature. Many Delco 10 or 12-SI units ( the alternator in the photo looks like a later model ) will have a location to connect the idiot light. The current to 'light the light' also excites the alternator and the unit will produce full voltage at a lower speed. Sometimes these older cars have a smaller crank pulley diameter and need a little more idle speed, or a smaller than normal alternator pulley to have full voltage at or near idle speed. If the car has an ammeter I'll have to go get a sheet of paper and figure-out how to wire that . . . it could also be a casualty. The two wires from the center tap could be just to buck the ammeter so it stays in the middle all of the time. A voltmeter would let you know if the full system voltage is about 14 vdc (everything is OK), or 12 vdc (something is broken) in either case. I'm working on a Zener driving a LED circuit as a poor man's voltmeter.

You can buy many 12 volt batteries center tapped for dual voltage, but I don't believe I've ever run across one of the 19 inch long, 4 inch wide units center tapped. Two six volt batteries won't push the cost over the top . . . especially considering how much expense is avoided by keeping most of the car 6 volts.

I think I would have built a bit of a cover for batteries and slap a 'Willard' decal on it to hide a bit of the complexity. I also paint the tops of the Optima batteries semi-gloss black, and take the 'stickers' off.

The AC compressor appears to be mounted where the generator normally is mounted.

dp