This is new territory for me so pardon my ignorance but what must be done/changed when converting a Ford model A with 24 stud flathead from 6 to 12 V. Battery (obviously )Starter, Coil, dynamo, plugs, fuses if any. Anything else??...
You shouldn't need to change the starter; I have done several 6-12V conversions and the 6V starter has always lived -obviously not a good idea to crank it for several minutes at a time. 6V horns are usually OK on 12V too. Bulbs need to be changed to 12V. Fuses may need de-rating as the current will halve for the same wattage of bulb on 12V.
You should look at any fuses, the generator/alternator obviously, all lamps, the ignition system at most may need a new coil or a ballast resistor added to the circuit. If your ignition coil primary resistance is 3 ohms or more (measured across the coil + and - terminals) you shouldn't need to do anything; less than that and a new coil OR ballast resistor will be needed. Any electric gauges (except for an ammeter if present) will need the voltage dropped; a later Ford 'gauge regulator' will fix that (Ford used 6V gauges well into the 70s on 12V cars). If you have an ammeter, make sure it's rating is at least equal to the new charging system output. If you convert to an alternator, I'd recommend changing to a voltmeter instead. Any other electrical devices (radio, electric wipers, fuel pump, etc) should be changed out for 12V bits.
Fuses are sized to protect the wire, and if you are not changing the wire, then the fuse size should not need to be changed. They will carry about half as much current, operating the same circuit at 12v vs 6v. If it has electrical gauges, you might need to reduce the voltage to them, but it depends what type of gauge. The ammeter will likely see less current if you use an old 12v generator, but could see more if you put a modern alternator in. Look at what size wiring is recommended for whatever it is you are using...if the wire needs to be thicker than what you have, then you might have issues with the ammeter, if it has one. But it's hard to say without knowing what you have. so...for the best advice, give us a lot more information about the car.
That's true, but limiting fuse size to 125% of the actual connected loads will, in the event of a fault, reduce the stress on connections, switches, etc and reduce the chance of fire in connected components.
On my flatty, I changed out the coil and went from a generator to an alternator. You can keep the 6v starter. It'll work for years in a 12v system. The rest of the electrical on my build went to 12v from scratch. Be sure to replace your fuses and some electrical to handle the load if you are not using a new harness.
Yep, fuses would be half the amp load of the 6V system. Horn, bulbs, gauges and coil. The wiring will be 2x as big as it needs to be for 12V. I am running 12V in my AV8.
Depending on the generator you may be able to just change to 12 fields. makes for a better generator if you can do that the 6v armature wound stronger. The Voltage regulator will need to be changed. No need to change the fuses the fuses protect the wiring not the appliances that the wiring supplies. The points don't care all they are is a switch, but the coil will probably need to be changed and you'll need to add a ballast resistor in most cases. You'll need a start circuit wired in to bypass the resistor on start. Dynamo is generator correct?
buddy says he has a diode the lets 6v gauges run on 12v... some ameters excluded... i will call and ask for a part # if you need it...
That would be a 6volt Zener diode- don't use a standard silicon diode. You can make up a 12 to 6v regulator to run anything which may cook on 12 volts (heater motors, wipers, etc), as long as it has enough current capacity. Something like this: Use a LM7806 where it says "78XX"
Some flatties had a heater hose size nipple attatched to a curved flange, they went in the water hoses to add a heater... One of those nipples could let you add a temp sending unit to an A if you want... This one had a sender in it...
Model A's only have an ammeter and no fuses. So fuse circuits appropriately. Model A's are probably the easiest ones to convert over. Get the correct coil/ballast resistor and the ignition is set. Do not use the stock ammeter with an alternator, they'll fry. Run neg ground. Don't worry about the starter, they are cool with 12V neg.
Nice info! I used this in my model A with '39 gauges but did not use the second transistor, I guess that second transistor is for higher current loads. Thanks!
Your'e right, the transistor ups the current capacity. The LM7805or LM7806 is good up to 1Amp with a heatsink. That transistor (MJE3055) is good for 10amps, also with a heatsink.
Comments on the ammeter. If you have an original treat it with respect as the new ones are junk. The voltage won't be a problem but the current might. Go over 20 amps for too long and you will fry it. My solution is to run a bypass wire so some of the current goes around the ammeter. You can't just get a new ammeter as they are the wrong diameter and probably too deep to fit the original gauge panel. Charlie Stephens
If you have the original lights get the bulbs from Ron Francis Wire Works, https://www.ronfrancis.com, (800) 292-1940 or someone that handles his products. Ask for the "Brite" bulls. They go right into your sockets and work very well. Charlie Stephens
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