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Positive ground starter

Started by denise 20352, April 11, 2006, 08:43:54 AM

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denise 20352


  If I put a negative ground starter in a positive ground vehicle, will it spin backwards?

Robert Meyers

Hi,

A DC electric motor will only spin opposite direction when polarity changed if there are permanent magnets in its construction.

Dont think starter has. Some power window motors do...etc.

Why not just carefully try it on your work bench?

Thanks

Doug Houston

To reverse rotation of a DC motor, either series or shunt field, the field must be reversed with respect to the armature, or the armature reversed independently of the field winding. The way that starters are made, this cant be done. (The starter is a series motor). So,,if you change battery polarity on a starter, youre reversing both the armature and the field, and the rotation will be unchanged.

As already said above, there are some starters that have permanent magnet (PM) fields, and since the PM fields cant be changed, reversal of the armature polarity will reverse the motor. These starters are found in cars of the 80s and later years.

Bruce Reynolds # 18992

Gday Doug,

So, what actually happens when one installs a battery back the front in a Positive Ground car?

What can go wrong?

I think that there would be a few Members out there that need to know, as much as myself.

We are sitting down, waiting for teacher, Mr Houston, to enter the classroom.   Quiet there up the back.

Bruce,
The Tassie Devil(le),
60 CDV

JIM CLC # 15000

04-11-06
BRUCE, Your question re what happens if you install a battery backwards. Not much, If you have an ampmeter* it will show discharge until the battery is discharged and recharged in reverse polarity.
* dont know what happens if the car is equiped with idiot lights.

Bill Gauch

That goes against what I understood about how an ammeter works. It is wired in-line and measures the current draw through the meter. Since everything is wired on the other side of it, it measures the total current draw of the car. If you switch the battery polarity, I wouldnt think it would ever work right, since the current is being used (state changed to heat, light, sound, etc.) before reaching the ammeter.

As for switching polarity, I think the biggest impact is in the charging system. I would think you would fry the voltage/current regulation and possibly the generator and the battery itself.

All the lights will still work. There may also be other small electrical issues such as the horn relay polarity, radio polarity and other stuff I cant think of.

Robert Meyers

Ammeter actually measures voltage across a shunt. The shunt being a main feed wire between battery terminal and the vehicles electrical system. As it is reading voltage, it is polarity specific and would read opposite if battery paolarity were reversed.
Any solid state device would be damaged if polarity reversed. Alternator diodes, solid state radio, hybrid radio (tubes with output transistor, 1959 + Cad) older tube radio with solid state vibrstor fitted etc would all be zapped.

Other than that, you wouldnt notice a difference aside from the ammeter reading backwards.

Purchased a 1949 6269 with the battery polarity reversed. Owner had been driving thst way for some time!

Rhino 21150

All of the motors will spin the right way EXCEPT motors that have permanent magnets. Some starters (MagnaQuench, a GM invention) and some post 1984 window motors have permanent magnets. Those will turn backwards. Permanent magnet motors will attract iron all the time with no juice connected. No motors will be damaged but the mechanism attached to PM motors will be bent.
ALL radios will be damaged or destroyed. All computers will fry. Many sensors, but not all, will pop. Alternators will catch fire. Regulators, either generator or alternator, will burn. Generators may or may not burn, their regulator may blow up and protect them. Halogen or incandescent bulbs dont care. HID (blazing blue headlights) or fluorescent (they have power converters that use transistors)lamps will be toast. LEDs may survive, doubtful. Relays, horns, dont care. Solenoids as found in trannys and on 80s carbs, dont care. Electromechanical gauges (Fuel, oil pressure, water temp on pre 1970 cars), will read backwards, if they move at all, probably wont be damaged.
Ammeters will read backwards, right up until the battery bursts from the dead short through all the burning parts. Fuses probably wont blow because the expensive parts they protect will burn up before the fuse can pop.
I saw this happen to the 2003 GMC Jimmy that sustained $8,000 damage.
Electronics degree from Old Dominion University, 1973.

Rhino 21150

I cant wait to see what REALLY happened when Captain Kirk told Scotty to reverse the polarity on the impulse engines.

denise 20352


  This is a 70s Chrysler starter, and I assume that its series wound.  I may have to take a look at the innards and see if there is a practical way to reverse just the field frame or just the armature on the fly, but it doesnt sound too likely.

  I have a starter whose bendix (do they still call them that?) was noisy, and I thought I would save the motor to make parts for my next crane project, if I live long enough to build it.  This might turn to be a big one, with winch, trolley or telescope boom, boom jacks, stabilizer jacks, sliding ballast and slew, so it would need lots of electric motors, or hydraulic actuators, or whatever I can find on Ebay to use.  A one-way motor might work for one of the winches, with a line brake, so Ill hang onto the starter.

thanks

-denise

Doug Houston

A lot depends on the car. Lets take the case of, say a 1942 Cadillac, and reverse the battery.
First, if you dont flash the generator armature, it can cause a whopper of an over current and burn up the generator. If you do polarize the generator, it will work O.K.

The starter will operate properly.

The Ammeter (note spelling) will read backwards.

The generator regulator will ultimately fail because the points in its relays are designed for operation with a particular polarity.

The engine will fire poorly; possibly erratic. The polarity of the pulse at the spark plug must be negative for the engine to fire properly. Dont ask me why, but its a basic engine principle.

The radio will work properly, provided somebody hasnt stuck a solid state vibrator in it.

Heater blowers will operate properly.
 
lights will never know the difference

Now, on a later car:

Youll blow the electronic ignition system and the radio, if it has any transistors in it.

Yopull burn up the alternator instantly

The early Autronic Eye system will be damaged if the fuse doesnt blow. The later Guide-Matics are solid state, so kiss them good-bye, too.

If you have a computer, it will be history.

There are other numerous things in a newer car that will go bye-bye as well.

Now, how about certain model Cadillacs before 1940? For instance, the 38 and 39 radios will have the vibrator burned up, or at least, a popped fuse. There are other years with a polarity-sensitive radio. Id have to check the radio service book.

Rhino 21150

Well, you sure got a lot of advice on putting batteries in backwards...
To reverse a starter motor you will need a 4 pole double throw switch that can handle 100 amps. ummmm.... And some interesting machining skills. I did it for an electric bike. NO fun.
You need SURPLUS motors and gearmotors.
http://www.pololu.com/advice/actuators.html TARGET=_blank>http://www.pololu.com/advice/actuators.html
http://www.sciplus.com/category.cfm?subsection=18&category=174 TARGET=_blank>http://www.sciplus.com/category.cfm?subsection=18&category=174
http://www.surpluscenter.com/electric.asp TARGET=_blank>http://www.surpluscenter.com/electric.asp
Have fun!
Golf cart motors, wheelchair motors, robotics, military, all categories for Google searches.

Bruce Reynolds # 18992

Thanks for the lesson Doug,

And yes, I was referring to an automobile that was designed to use the Positive Ground system, buy the knowlege on the later stuff is also one for the brain basket.

Bruce,
The Tassie Devil(le),
60 CDV

denise


  Those are excellent links, thanks!