1949 Fastback 12V conversion

[kimkbh]

Hi guys,

Due to a couple of reasons and a frequent usage of a vintage caravan, I have decided to convert my Fastback to 12V. Its not because of any 6V issues, its mainly that I cannot use 6V on my caravan.

So I would very much like some tips from you guys, since its my first conversion.


Thank you in advance

Kim

[johnwalker]

12V bulbs, voltage reducer on the fuel and temp gauges and 12V generator/regulator. The radio is the hard part as they don't do well with just a volt-a-drop. 

[bcroe]

Due to a couple of reasons and a frequent usage of a vintage caravan, I have decided to convert my Fastback to 12V. Its not because of any 6V issues, its mainly that I cannot use 6V on my caravan.

So I would very much like some tips from you guys, since its my first conversion.  Kim 

Are you also changing from positive to negative ground?  Most stuff doesn't care, anything
with a permanent magnet field (motors, gauges) will matter.  If there is an ammeter, the
leads will need to be reversed, if kept wired in.  Using an alternator requires some wiring
changes, mostly removals.  A large alternator might require larger wire to the battery. 

Generally the radio doesn't care about polarity. if it doesn't have a 6 pin (syncronous)
vibrator or permanent magnet scan motor.  A 12V to 6V buck converter of sufficient
capacity will do it.  Some people have a radio "modernized" by installing new internals,
but it would be possible to wire tube filaments in series strings of 2, and changing the
power trans to one from a 12V radio.  Or plug in the 12V version of each tube (6SQ7
to 12SQ7, etc).  Bruce Roe

[harry s]

'49 is negative ground.     Harry

[TJ Hopland]

What does the car have to operate in the caravan?   Just lights?  And I assume you sometimes have the caravan connected to a 12v car too?     If you are content with the 6V car and everything is working it would seem like it may be less hassle to build a little relay box so that the 6v car was just signaling a 12v system in the trailer.   This would mean the trailer would have to have its own battery but with the size cost and life these days that may not be an issue unless you really need to run the stuff for a very long time.    You could build the box with the correct connectors for each end so it could easily just be unplugged and removed if it was not needed.

[Jay Friedman]

I agree with TJ Hopland that if it's merely for the rear lights on the caravan (tail light, brake light, directional signal) you don't need to convert to 12v.  Besides what TJ wrote, an alternate way would be to temporarily hang (bolt on or clamp on) a pair of after-market tail lamps on the caravan with 6 volt bulbs and just run a hot wire and a ground wire from each of the '49's tail lamps to the temporary caravan tail lights.  It might work too.

[bcroe]

I agree with TJ Hopland that if it's merely for the rear lights on the caravan (tail light, brake light, directional signal) you don't need to convert to 12v.  Besides what TJ wrote, an alternate way would be to temporarily hang (bolt on or clamp on) a pair of after-market tail lamps on the caravan with 6 volt bulbs and just run a hot wire and a ground wire from each of the '49's tail lamps to the temporary caravan tail lights.  It might work too. 

I'm inclined to agree.  Maybe install a 6V and a 12V bulb in each light, each with its own
wiring to plug into a 6V or 12V car.  Or put LEDs in there, or just mount a second set of lights
next to the existing.  Bruce Roe

[kimkbh]

12V bulbs, voltage reducer on the fuel and temp gauges and 12V generator/regulator. The radio is the hard part as they don't do well with just a volt-a-drop.

Thanks for your input John.

I am not using the radio, so that is easily taken care of. However I would assume that I need a bulky reducer for the heater, or does it run fine on dobble the speed?

[bcroe]

I am not using the radio, so that is easily taken care of. However I would assume that I need a bulky reducer for the heater, or does it run fine on dobble the speed? 

If you convert to 12V, better disconnect the 6V radio or remove the fuse. 
Otherwise someone will turn it on and burn out all the tubes.  Best heater
fix is a 12V motor if one fits, but its speed reducer resistors need changing
out as well.  Bruce Roe

[gene harl]

I changed my 51 to 12 volts using 2 6 volt optima battery's  with a center tap ... 12 volts for the lights,, starter,,  ing.  ect.   6volts for  radio, gauges, blowers,,, works good..
Gene Harl    CLC 22406

[bcroe]

I changed my 51 to 12 volts using 2 6 volt optima battery's  with a center tap ... 12 volts for the lights,, starter,,  ing.  ect.   6volts for  radio, gauges, blowers,,, works good..  Gene Harl    CLC 22406   

That means the batteries will not get equal charge/discharge.  The result will
considerably shorten their life.  Bruce Roe

[Philippe M. Ruel]

I agree with TJ, relays are the way to go.

Use a deck of 6V relays, that will be able to work from the 6V master circuit, and will deliver current to the 12V slave circuit - no matter the slave circuit voltage, what matters is only output current amperage.

Does your caravan feature "old style" lights, i.e. turn lights integral with brake lights ? Then you need a 4-relay deck, one for tail lights+license plate, one for back-up lights, one for LH turn/brake light, one for RH turn/brake light.
It can be hidden somewhere in the car trunk, the slave circuit being fed by a 12V battery in the car trunk as well.

[Jay Friedman]

I run my own '49 fastback completely on 6 volts, including long trips, with no technical problems whatsoever.  (The only exception is a modern 12v under-dash radio-cassette tape deck which is powered through a Trippe 6v-12v inverter hooked up to the car's 6v system.)

As mentioned in my earlier posting, I feel you are making the project of getting lights to the back of your caravan more complicated than it need be.  I still think you can mount auxiliary lights on the back of the caravan, similar to those used by tow trucks on the cars they tow, that can be powered from your '49's 6 volt system.