Title say it all -- on a little road trip in a '50 Plymouth, would be nice to keep the phone topped up.
Here are a couple of web sites that might give you ideas.
First, add a negative ground cigar lighter adapter to your car.
Second, rewire your charger cord to swap the positive and negative leads. Be sure to mark this cord as a "special" if you do.
I have charged a gps device from 6V but charge is slow and will not keep up with draw. Might work for a phone with minimal usage.
My iPhone5 charged on 6v in the T just fine, but exchanged it for iPhone6.
This 6 uses 5v 1 amp juice, but won't charge on 6v in the T. Gets a message says charger device not compatible, tried some other charge units but all say the same on 6v in the T.
All these chargers work fine in the modern on 12v. Go Figure
The old Garmin NUVI charges OK on 6v in the T.
Chris, I use a speedometer app on my phone that will drain the charge in a few hours. I looked at some of the charging options and read several comments of how it will work, or won't work. Bottom line is a phone is 5V and your charging system may hit as high as 8V. I didn't want to chance it on a $700 phone!
I mounted a lighter receptacle out of sight under the dash and ran wires under the seat of my T to connect to a small rechargeable 12V sealed battery that is about 2.5"x3"x4" (there are many sizes available) Then I used a lighter plug-cell phone charger (12V) available anywhere and kept my phone plugged in all the time while in the car. The battery lasted all 4 days of the tour without charging. When I do need to charge it I use one of the "maintainer" style trickle chargers. It is easy to take the battery out of the car since it uses spade terminals to connect the wires, so it can be charged in a hotel room if necessary.
Thanks for the replies. My device is an iPhone 5. The particular concern is the Plymouth's positive ground, as the T and modern cars are negative.
The voltage in a running and slightly charging Model T system is around 7.2 - 7.5 Volts. The regulated voltage in a USB plug is 5 Volts and the batteries are typically 3.6 Volts.
It should be possible to make it work, but it all is about how much voltage loss there is in the USB charger. The milage will vary - some are better than others. My Samsung S4 can last the most of a day with GPS running (very power consuming) in my T using one of my USB chargers.
I find this to work good enough to not start fiddling with 12 Volt conversions.
The problem with charging devices is that the first thing the engineer looks at is the supply voltage and then designs his charger accordingly. If the supply is a car with a 12V battery then he likely designs in a battery disconnect circuit with a threshold around 10.5 volts or so because a 12V battery that measures 10.5 is totally dead and nothing would normally be gained by connecting to it. As others have pointed out, the newer phones are expensive so the engineer wants to protect the phone by not having it connected to things like a dead battery. The simpler el cheapo charger designer doesn't care about anything but hooking up the path and lets the owner see if it works. No voltage checking of the source with an accompanying warning message probably allows the thing to work but then a low input voltage level might in fact be harmful to the phone if a less than full charge results. There are devices called DC to DC converters that can rather easily convert 6V to 12V and they can easily also allow you to have the input being positive ground 6V and the output being negative ground 12V. The rating of the converter must be such that its output current can supply the maximum needs of the device you want to use. If you are going to plug your expensive Iphone into the thing you need to make sure you know what you are doing. This is not a place for tinkering but it really isn't rocket science from an engineering point of view. The main problem is that you each have slightly different needs and that is where the trouble may start since something that works for one smart phone may not work at all with another even though they are basically similar in their needs. The assumption that one size fits all is false or at least can be false and an expensive phone is not a good testing device for experimenting.
I had a converter for 6 volt positive ground to 12 volt negative ground in an old truck for a 12 volt radio. For some reason, when I would use the aftermarket 6 volt blinkers the radio volume would lower to almost inaudible with every blink. I don't know how I had all that wired, I was 16, but the 12 volt output pulsed which might not be good from what John Reagan said. I might not plug mine into my driver car anymore because the lights do crazy stuff.
When you convert from 6V to 12V that is called a "step up" or "boost" type of converter and you must pay particular attention to having really good heavy wires on the 6V side and also mount the thing as near as possible to the 6V battery so as to keep the 6V connections as short as possible since the DC current in the 6V side will be MORE than DOUBLE the amount of current taken from the 12V output. For light duty applications you can move the thing further away but you always need to make sure you are using heavy low resistance connections on the input 6V side.
You can purchase mini rechargable batteries that plug into your phone and extend its use for many hours. They hold a charge for months and are handy when needed.
Reversing the polarity is easy. Buy a socket and wire the supply to the outer side and ground the inner. Of course you will have to mount it in a insulated fashion (block of wood comes to mind). Easy to test by just hooking the socket directly to the battery as I have described !!!
Electronic supply houses such as Mouser sell a small module that is a voltage doubler, 6 to 12 volts and good for almost an ampere, you can wire it for ether polarity to cigarette lighter receptacle. Brad.
Thanks everyone for your comments and suggestions. Agree that an easy mod could have done the trick for me, but given that I was already on an eight-hour road trip, nothing other than "yeah I've done it, had no problem" would have been of immediate help.
I'm am thinking now however, about fabricating one of the step-ups into a gizmo that could be plugged into a 6-volt lighter and used in various cars. My friend's '50 Plymouth and my own '47 Dodge are both 6-pos and both cars we road trip in frequently.
Why not charge it off a Charger Pack. You can get a 10KmAh charger for less than 20 bucks. It's probably enough to charge an iPhone several times over. I have two of these I swap use on a digital night scope. I've run the high draw scope for about three hours at the range and the battery pack never dropped an indicator. (Charge status.) It will fit in a cell phone MOLLE pouch or an AR-15 magazine pouch.
Here it is installed in a Butt Stock magazine pouch powering the night scope.
The only problem with "booster packs" and other battery packs is that you must remember to charge them up before you use them or they will be as dead as the battery in the device you are plugging into the booster pack.
I don't see it as problem if you have the where with all to remember to recharge your phone. You can charge the battery pack when you get home along with your phone. It will stay charged for many months and ready for the next trip.
You can fabricate as many problems as you want but the battery pack is still the best solution for portable reserve power. And you don't need a different converter for each car (6v/12v).
Another possibility is a 12 V solar charger. VW has one with a factory part number. You can find them on ebay.