I own and antique sports car with a positive ground system. I'd like to leave the car's electrical system as is and wire in a modern radio. I have heard that electrical converters can be sued to accomplish this. I never really understood how, until I read the attached article:

http://mgaguru.com/mgtech/electric/et207.htm

This makes sense to me, but I am no expert. If you are, I would appreciate your thoughts.

Any one is free to respond, but If you are just posting a guess, or your reaction, but do not really know the answer, please say so.

 

that works, but you'd need another inverter for ACC, or make a switch for ACC if you only use one inverter.

 

The metal cage it's installed into the dash with might be part of the radio's negative grounded system--I've never looked at radios with this in mind, so I'm speculating there. You could use a circuit detector (a light bulb with one end connected to +) to test it and figure out what is and isn't grounded.

Their solution was to electrically isolate the radio. If you completely encase the grounded parts of the radio (whatever they may be) in plastic, fiberglass, or some other dielectric, you'd just reverse the input voltage and the remote on/off voltages and you'd have no issues. That works, but how thick the plastic would have to be and such to ward off voltage isn't something I know off hand. An electrical engineer might be able to chime in there. I'd guess the currents are pretty mild, so I wouldn't think it would be anything ridiculous, but it might not be as simple as saran wrapping your radio.

The ACC / remote on/off switch you could do with a diode (if that's the right part name; it's been a while), but diode or whatever, it would be a switch that allows current to pass through one line when a test signal comes in at a second line.

Also, thermal management could be an issue if you decide to completely cover the radio and go for a long drive with it on (meaning if you coverd the vents that were designed for heat dissipation to keep the radio cool). For the most part, plastics are pretty good insulators.

 

The guy in the link I posted avoided the isolation method with the converter. I have used the isolation method in the past. It is always risky, as the author in the link discusses.

Thanks for your thoughts.

 

What is the ACC and why does it need a seperate inverter or switch? Thanks for you thoughts.

 

[QUOTE=Legal Bill,Sep 16 2009, 10:13 PM] What is the ACC and why does it need a seperate inverter or switch?

 

just think of the ACC as another power input, but it doesn't draw much current at all. What the ACC controls is when the unit can be turned on, like when you turn your key to accessory on your key cylinder, and off when you turn off the car.

Using one inverter, you'd only have one power output. Therefore, either the radio looses all the station memory(etc.) when you turn off the car if your main power source is switched ACC, or it will be on all the time if you connect the ACC to constant power without a switch.

Just like power input, the ACC should be +12V input in respect to ground.

 

Can I run both radio power wires to the one out-line from the inverter? Each inverter costs $100, so i don't want to buy two if i can help it.

Thanks so much for explaining this to me.

 

bill i would run the acc line to a switch first or the radio wont ever turn off, I believe... with your system it radio will always see a + signal. the acc line for a radio can be hooked to anything even a headlight interior light or something, anything that only gets a + signal when the car is on.

 

But that is the problem. Nothing gets a + signal. It is a positive ground car. I'm thinking I need to connect both wires to the converter, but put a switch in the main power line before the radio. That way, the ACC will always have power, but the main power will not come on until I throw the switch. I wonder if I could use my ignition switch as the switch? Something tells me no, because the ignition switch is carrying -12 volts and probably could not also handle +24 without a major blow out.