DC motors run in the correct direction with the polarity reversed because the polarity of both the stator and the rotor are reversed. The only way a motor would run in the opposite direction would be if one of the fields, rotor or stator, were reversed and the other was not. This happens if you reverse the polarity of a permanent magnet motor, which gets its stator field from a permanent magnet instead of electric coils.
As for solenoids, they’ll still work too. The coils of the solenoid requires current to create a magnetic field. The movable slug is not magnetic, it’s just a ferrous metal and will be drawn in regardless of polarity. A piece of steel is attracted to both the north and south poles of a magnet, right?
And finally, when I was in college we were taught that “current flow” is from positive to negative. It makes the math easier. “Electron flow” is from negative to positive.
There was a wonderful article in the April 1956 Popular Electronics magazine about “Contropolar Electricity”. This box removed the polarity from the electricity and devices plugged into this box would perform in the opposite manner. It pictured a light plugged into the box and the bulb then removed light from the surrounding area that would normally illuminate. A soldering iron plugged into this box produced icicles on its tip. I read through the article a couple of times before I realized that it was written in the spirit of April 1 (April fool’s day).
WOW, when I posted my original question I had no idea it would get so…interesting. I asked the question because I am wiring my 36 Dodge D2 Sedan, the way it was meant to be - positive ground, I am using diagrams from old service manuals. This is my first wiring or rewiring of a vintage vehicle and I thank you all for your imput. If there is anything else I should know or be aware of while wiring this vehicle I would appreciate it. Oh yeah, one more thing, someone told me I can get away with using an 8 volt battery-he said Sears sells them-does that sound right. Thanx everyone.
Good one, Jay. My generation, we techs were taught current flow was from negative to positive, and thus current was electrons.
The engineers of our generation claimed they were taught as you say current flow was positive to negative, thus I suppose one would say hole flow, or something like that.
Over the years, I never noticed any real problem with the different viewpoint, except when someone argued about it.
You can only complete the circuit if you touch both connections to the battery. Ground and power. It really is no different from a negative ground system. In electronics class you actually learn that negative charge electrons flow from the negative of the battery to the positive. Take your pick, it is just a low volt circuit no harm from it really.
I know that 8 volt batteries were used on farm equipment to help them start more reliably. I think that the voltage regulator was adjusted to boost the output so that the battery would charge. I suppose the bulb life of the tractor lights might suffer somewhat, but the tractors weren’t driven year round at night.
IF you are rewiring your 1936 Dodge, and keeping it original, I don’t think you need an 8 volt battery. Your car, I’m sure, has vacuum wipers, hanging down from the top of the windshield. I think the passenger side and the driver side have separate motors, if your Dodge has the optional passenger side wiper. Eight, or even 12 volts won’t damage the starter motor. As I remember,the starter is actuated by a pedal on the floor that closes a switch and meshes the pinion gear of the starter with the flywheel. I don’t think 8 volts will damage the gasoline gauge. The ammeter gauge won’t care. The oil pressure and temperature gauges are mechanical. However, we never had difficulty starting our positive ground 6 volt cars in zero degree weather. My Dad owned a 1947 DeSoto that could always be relied on to fire up at sub-zero temperatures and it was a 6 volt system.
I do hope you adapt your headlights to sealed beam units if it hasn’t been done. The old bulb and reflector headlights on pre-1940 cars were so dim that you had to light a match to see if they were on. If nobody has installed turning signals on your Dodge, you may want to do that. I had to install turning signals on my first car–a 1947 Pontiac. I bought the kit from Montgomery Ward.
Yes, I do have duel vacuum wipers, and the headlights are sealed beam units and it was wired with after market turn signals. It also has a clock in the dash and a heating unit which is what originally got me wondering about the wiring. Those options are not on any wiring diagrams and I wasn’t sure if you put the power wire from the options to ground (chasis) or the ground wire to ground.
I guess i’ll go with the 6 volt battery. Thanx.
"i] DC motors run in the correct direction with the polarity reversed [/i]
Actually it depends on the motor, the ones you describe with a stator, some DC motors don’t have stators.
Electron flow IS current. By definition, current is a flowing, or passing. “Negative” is a term used to denote an excess of electrons. “Positive” is a term used to denote a (comparative) lack of electrons.
It’s useful (less confusing) to trace ELECTRIC circuits from the positive terminal to the chassis ground. But, it’s confusing to do so in ELECTRONIC circuits. An example is a driver circuit at the end of a positive-to-negative trace. How can that be a “driver”? When one thinks of that driver circuit as “driving” electron flow from chassis ground to the positive terminal, the term “driver” makes sense. It’s driving current. (Actually, it’s CONTROLLING electron flow; but, why quibble?)
Because it was believed that cars with positive grounds suffered from increased body corrosion in relation to the opposite polarity.
This belief is founded in the understanding that anodes have an oxidation reaction and cathodes have a reduction reaction. In a battery, the cathode is the positive terminal. If you notice, most ofthe corrosion on your battery terminals occurs at the positive terminal…
Ding! Ding! Ding! I think we have a winner, johnny-O, tell him what he’s won!!
"Neither wire carries any current unit a circuit is completed. The “hot” wire will (in most situations) carry 110V charge compared to ground and 220 Volt to the other leg of the circuit"
I don’t know what you really mean but the hot wire WILL be carrying the current. Of course when you touch it, the circuit is completed. ZAPP!!!
Also in an automobile, none of the circuits will shock you unless it is coming from the coil or the alternater…
DC motors with permanent magnet field poles will reverse when the polarity is reversed.
DC motors with electrmagnetic field poles will rotate the same way when polarity is reversed because both the field and armature is reversed. If the electromagnetic field is in series with the armature, these motors will even run on AC hence the name “universal motor”. Universal or series wound DC motors, are common in electric drills, saws, vacuum cleaners, etc and they run on AC or DC.
Shunt wound DC motors also run the same direction regardless of polarity but are not suitable for AC because of the field winding’s extremely high inductance.
You can go with the 8V ,it will turn better-but as Triedag says,correctly tuned it should start fine with 6V(DOES THIS HAVE ANY EFFECT ON GAS TANK SENDING UNITS?) You may screw the Bendix up from time to time(used to happen occasionally on the old AllisChalmers tractors we would convert to 12V,man those things would whiz though)Anyway nowadays,the modern multi-vis oils will her let turn easier when its cold-Kevin
I had a Sunbeam Imp (1965) that was a positive ground. After being hit by a greyhound bus, it was at the dealer waiting for a quarter panel shipped from Scotland. By the time it arrived the battery was dead so the dealer grease monkey just put in a new battery. It started and ran, but after about a mile the battery light came on so I drove right back non-stop.
I told they I wanted a new generator and battery. The mechanic said all it needed was to reverse the wires. Which he did and when he started it back up, smoke poured out of the generator. I got new batter, starter generator and a year warranty on anything electrical.
Some good ideas in these comments. However 6 or 12 volt systems arent going to hurt anyone. You have to get up over 40 volts to even get a tingle with your hands.I had several old beetles with 6volt positive grounds and the problem seemed to be corrosion on the center contact of the light bulbs.6volt systems start fine but keep the wire to the starter clean and corrosion free.
In the case of an auto battery the issue is less voltage than current, hence the big-ass spark you get when hooking up jumper cables.
However 6 or 12 volt systems arent going to hurt anyone
You can weld at 12 Volts. If you hand is near the short, it will not electric you, but it sure could put you in the burn center at the hospital.
Now ailimac, your post has certainly sparked some interesting conversation, with many off track discussions, such as the direction that electrons flow. Now it’s my turn: There are actually different schools on that. It depends upon who you learned your basic electricity from. There are as many different explanations as why current flows from pos to neg (and vice verse) as sources you can find on the internet. They all have sound, logical reasoning. As for why that american automakers decided to go with the negative ground? I did previously hear the explaination of minimizing corrosion from oxidizing, but I also heard that the big three got together and just decided to standardize the electrical systems of their cars, so I don’t know, maybe it was the guy in the room with the most convincing argument, or the loudest voice. One thing for sure, don’t let anyone near your car with jumper cables. If it were me, I’d put a big warning somewhere on the top of the battary, or somewhere, sometime, someone will hook the jumper cables or battary charger backwards, and you can just re-read some of the posts to see all the fun you’ll have changing parts.
This is truely a good thread.
The bottom line is that it really doesn’t matter to safety whether a car is positive grounded or negative grounded. Unless you complete a circuit with your body parts there’s no harm. Serious injury from electricity comes from the current flow, and as far as your body is concerned it matters not what direction it flows.
Also, whether something is subject to polarity depends on its design. I made some assumptions in my statements and others have correctly pointed out that my conclusions may or may not be true, depending on the component design.
The danger lies two areas; injury from the sideffects of getting shocked and having a current flow interfere with one’s autonomic nervous system signals. The latter is highly unlikely because the potential has to be large enough to “break down” your body’s resistance and pass current through your nerves, and connected to the right two spots to do so through a critical path. The former, getting shocked and sticking your fingers in the fan or impaling your head on the hoodlatch, is more common. Caveat: IMHO those with pacemakers should not have their head under the hood while the engine is running.
Like Jay, I’ve heard that “current flow is from positive to negative” statement. It flies smack in the face of physics, but go figure. Free electrons are traveling masses just like cars are. If all cars are going north, traffic cannot be flowing south.