View Full Version : Amp meter , max load

02-13-2007, 09:40 PM
What is the MAx load an amp meter on a 1955 6 volt car can carry when the car is changed to 12 volts ? Car in question is a '55 President. Will this amp meter carry the out put of a 60 amp alternator, 30 amp altenator? I can see a fuse is needed at the alternator and the selenoid to prevent over load in case of a short.

02-13-2007, 10:19 PM
I never tried it but my best guess is: It should show discharge instead of Charge when connected backwards. 6 Volt Studes are Pos. ground and you will want your 12V to be Neg. ground. Also there is no way it's going to take over 30-35 AMPS.

Studebakers Northwest
Ferndale, WA

02-14-2007, 06:17 AM
Yes, it will, but you have to do a little voodoo. The Ammeter only senses the current flow, so there's no actual passage through the meter part (sensor coil).
If you take a length of #8 wire, maybe a foot long and connect it between the two posts, it will shunt more of the current past the sensor coil, inside the meter. In doing so, it will reduce the amount of current the meter has to read. This will, also, reduce the amount of swing of the needle and save the sensor coil from burning out.
When I installed an 65 amp alternator (6V,pos gnd) on my 55 Pres, this was a requirement.

02-14-2007, 10:09 AM
55 Pres, you have the solution to my problem trying to keep this dash original and place an alternator into service . The old alternator instulation has the this wired without a shunt and I think that is where the heat started that wiped out my main wireing harness.

02-14-2007, 03:35 PM
I can't ascertain how your wiring got smoked, but if you hang more equipment on the car than the ammeter was designed to handle, then the internal coil for the gauge sensor will go bye bye.
I'd look into making sure that the gauge of wiring you NOW have is up to the task of delivering the amount of current you NOW use. best of luck..

02-14-2007, 06:08 PM
When I take out the old harness it will get a better idea of the cause.Old wire was brittle and frail, now burned. I would assume the original size wire can carry the 12 volt with out a problem . I purchased a new harness from Studebaker west. Is this OEM too small wire for a 55 amp alternator at 12 volts?

rusty nut garage
02-22-2007, 04:10 PM
see this website for electrical/wiring upgrades.
Mark is a very techno savy person and answers the phone himself. He will not hesistate spending time answering your questions.


Russ Shop Foreman "Rusty Nut Garage"
57 SH (project)
60 Lark VIII 2dr sd (driver)

02-23-2007, 07:53 AM
Sorry I didn't get back earlier on this, but yes, the 55 wire harness gauge will easily carry the 12 volt requirements (and more). Conversely, a 12 volt harness could never hold a 6 volt load, as the current is much too high for the wire size, to safely contain it.
The only thing I would be leery about, using an original 6 volt harness, even if it were new, is that it has a lot of cloth covered wired, that could chafe.
55 is the year the changed to plastic insulation on wiring, but they didn't change completely until a later year. I have a 55 and a lot of the underdash stuff is still cloth

02-23-2007, 08:31 AM
Double the voltage and you halve the current..for instance a 55W headlamp rated at 6 volts is the same as a 55W 12 volt headlamp but now lets do the math..Watt is voltage times amps. So divide 55W by 6 and you have a tad over 9 amp pull, now thake the new lamp 55W divide by 12 and you have approx 4.5 amps..so as 55prez says, the heavier gauge wire used in 6 volt system will easily carry the 12 volt system. The last I heard was that the industry is leaning toward 24 volts and commom buss for the newer cars with digital low power displays. As for the amp meter..how much new stuff you got wired onto the car. If you are running stock, the guage should be sufficient, only that the leads will need reversed to show proper current flow (direction.) The alternator has the capacity to output at 60 but I don't think you will ever see that unless you have a direct short to ground in the charging system. The alternator recovers quite quickly, and the output is a lot lower. The field is excited by the need for current to maintain the voltage at the lowest current output. Most alternators with full charge batteries and no load except ignition while idling have about 8 amps output..just enough to deflect your meter.. That is why you don't short out a regulator but for a second or so to verify if an alternator is the prob or the regulator is the prob. Never let any shop put a load on your car's electrical system while checking the output of the alternator to exceed 60 percent of its rating or in the case of the 60 amp alt. that would be 36 amps. A fully loaded alternator with one of them testers will take a V8 engine running at 800 RPM and flat stall the engine due to the energized field. More alternators are blown during test than was bad to begin with. Diode breakdown will be evident at 60% rating. If you are going to the common GM one wire..get the pigtail that will automatically tickle the field so it will start charging on start up..if not, you will have to rev above 1200 rpm to get the output needed to excite the field..once this field is excited the alt will continue to output below that 1200 till you shut the system off, this is for everytime you start the car. I prefer using Chrysler alternators with the dual field and the external transistorized regulator for my upgrades. Just two more wires but come to trouble shooting the sytem..just unplug the regulator, short across the two wires and read your voltmeter at the battery. 10 seconds start to finish and you know where the problem lies, no need to take the car to a shop. As for shunting the meter with a foot long piece of #8 wire..you have effectively shorted across your amp meter rendering it ineffective.. that is the need for the 8 gauge wire..if you do this, I would recommend that you install a warning light to indicate loss of charging ( the so called idiot light if you will).

As for smoking your harness..something went to ground on the main feed..look very close at the connection on your igntion switch and the wires relation ship to body ground..also on the back of the amp meter for same problem.