6v positive ground converted to 12v neg ground, wiring two way convertible top motors

Thread Starter

jmikkelsen

Joined Feb 20, 2017
6
Okay, I am just a simple accounting teacher fumbling my way through working on my 75 year old Dodge convertible. I have been reading about electric motors and switching online, but I am having a hard time finding the last bit of insight to get the wiring done. I'd like to know if it matters to the life of the motor, safety, or otherwise which direction the power flows.

Here's the situation:

The convertible top system runs two electric motors driving a gearbox reduction to a set of screw extenders instead of the more modern hydraulic systems.
The motors originally ran in a 6v positive ground system.
The electric motors have three wires coming out of each of them.
The red motor wire on each motor is connected to one of the brushes on the commutator.
Green is connected to another mysterious part of the motor internals.
Black is connected to yet another part of the motor internals.
None of these three wires has continuity with the steel motor housing

Switching power from the green wire to the black wire reverses direction of the motor. The motor doesn't seem to care which direction the power flows. It works the same if I hook positive 12v to the red wire and move the ground from the green to the black wire to reverse direction; or if I hook the ground to red and move the ground from green to black to reverse direction.

I'd like to hook the red motor wire up to ground. This way I'll be able to run the positive power through the dash switch and have no power to the motors unless they are running. Maybe I just feel weird hooking a red connection up to ground? Am I going to cause any problems hooking it up this way?

Thank you,
Jon
 

Thread Starter

jmikkelsen

Joined Feb 20, 2017
6
One last thought, now that I am hooking these 6v motors up to 12v, is their speed going to go twice as fast or will they just use 1/2 the amount of the 12v power and run at the same speed as they did under 6v? If the speed will change, is there something I can do to adjust it down?

Yikes, how many other things do I know nothing about?

Thanks!
Jon
 

profbuxton

Joined Feb 21, 2014
419
I would suggest that you could connect the red wire to chassis and then switch power to either the green or black to drive in either direction.
As long as the motor has no internal connection to chassis.
As far as 6V and 12V operation is concerned, be aware that connecting to 12V will make motor run faster and use MORE current and will most likely burn it out. Its doubling its supply. You wouldn't connect a 110V appliance the 220V would you? You need some way to reduce the volts to correct motor design volts (6V).
Also be aware there may be some form of limit switches in the system to switch motors off when end of travel is reached so you will need to ensure that motor stops when end of travel is reached.
 

shortbus

Joined Sep 30, 2009
7,443
Back in the day I rebuilt and drove many vehicles that were originally 6V but changed to 12V. Things like heater motors and gauges, a voltage dropping resistor was used for them. But starters and other stuff like overdrive solenoids or even a top motor were just ran at 12V. Non of the last things ran for enough time to do any damage to them. The gauges and heater motors stayed on for a longer time so they got the droppers.
 

Thread Starter

jmikkelsen

Joined Feb 20, 2017
6
Good stuff folks, thank you so much for the input. I did read somewhere on the internet that the motors will run the same speed with 12v as they ran with 6v but that's just some random internet source and now I have two opposites to settle. I did look around and there are 12 to 6v step down converters able to handle 20amps of power for $35 so that could be good. Besides, I did power these up direct to the battery and they ran quite a bit faster than I expected so I am inclined to expect this 12v double speed tip is the right one to follow. I don't expect the short run times would hurt anything, but I do think the ultra fast top run up and run down would present a host of problems.

Thanks Prof for the wiring guidance, I like the idea of switching the input power so much better than switching the grounds.
 

Thread Starter

jmikkelsen

Joined Feb 20, 2017
6
Then I was just thinking, it might be nice to have a progressive switch that goes slow when barely on and faster when switched all the way on. Wonder if such a thing exists.

And too, the original wiring diagram I came across shows a control relay that I think is supposed to do something like stopping it when it gets overloaded, ie the end of he push and it starts cramping. Not sure about that of course.... I was thinking I would just need to turn off the switch when it gets close to fully extended. Maybe I need to rethink that end game. Thanks for making me think more about that.
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
Higher voltage definitely increases the RPM, a down and dirty way to drop the voltage that won't be so affected by current is to wire a string of diodes in series with the power lead.
You may get away with 5 or 6 to make a difference.
Cover with heat shrink tubing.
It may be worth a try for a couple of $.
Max.
 

#12

Joined Nov 30, 2010
18,190
Here's an idea: Install a 6 volt battery and use relays to power the motors with 6 volts. Is it cheaper to use a 6 volt battery and build a slow charger for it, than to build a 12V to 6V regulator that has to carry the whole motor current?

Probably a bad idea because the 6V battery will fail more often than a 12V to 6V regulator.:(
 

shortbus

Joined Sep 30, 2009
7,443
At one time they also made batteries just for situations like this, they had a built in tap for half of the cells in a 12V battery. You wired stuff for 6V to the center tap of the battery. Didn't sell very well because people found out you could just drive a screw in the correct position in the battery top and hit the cell bussbar on a standard 12V battery. This was back when batteries still had a thick tar top and hard rubber cases.
 

Thread Starter

jmikkelsen

Joined Feb 20, 2017
6
Progress!
I am going to buy a 12v to 6v step down converter, that sounds like a nice clean and proper set up. I need to know what amperage converter to get. So I hooked up my 12v batteries through my multi meter to measure how many amps each motor draws in 12v. Right when I connect power the meter spikes to about 15amps, then the reading disappears. This repeats each time I start it up. I am guessing that is draws that 15amps to get the motor going then since there isn't any load on the motor, it just spins without drawing hardly any power? I tried both multimeters and got essentially the same result with both of them.

I am stuck again, and hope somebody has enough experience with this start up reading to have an idea of the amperage I need to supply. Maybe knowing that each motor is about the diameter of a can of Comet cleanser and is about 4" high will help........

Not sure here, but I sure enjoyed hearing your earlier insightful thoughts and I am hoping for more.

On a related note:
Two 6v electric motors walked into a bar.

No, no they didn't actually,. They couldn't get through the door because they kept going in circles since one motor was running faster than the other.

Anyway, that came to me when I was worrying about the one rusty motor not keeping up with the other motor and potentially twisting the convertible top into bits as they moved at different speeds. Both motors are cleaned from their 75 years of dirt accumulation and are running super now. I am sure they'll get into the bar just fine.

Thanks,
Jon
 

profbuxton

Joined Feb 21, 2014
419
The 12 to 6 volt converter is the way to go. To find the correct load current best bet is to install motors and run them from a 6v source and measure the loaded current as they drive to the end stop. Don't know how you propose to stop the motors at end of travel, limit switches or some sort of overload device(but that seems dodgy).
 

Thread Starter

jmikkelsen

Joined Feb 20, 2017
6
The 12 to 6 volt converter is the way to go. To find the correct load current best bet is to install motors and run them from a 6v source and measure the loaded current as they drive to the end stop. Don't know how you propose to stop the motors at end of travel, limit switches or some sort of overload device(but that seems dodgy).
Coast to a stop? That's the plan anyway. Hopefully I can let go of the momentary switch reliably enough. I wired it all up from the motors back to the dash and jumped it to the battery terminal to see what would happen. They run super fast with 12v! But they do stop easily enough when they run out of travel, up or down. I didn't have a 6v power source, and the step down converter I found was cheaper than a powerful enough 6v battery so I bought a 20 amp converter to try. I will check the current draw when I have that set up installed.

I wonder, what happens if the motors draw more power than the 20 amp converter supplies? If it runs slower without any damage, that's probably better. I am no hurry to rush the top up at full throttle. If running slower causes motor troubles, that's going to make me feel awfully silly for ruining everything.

If the draw is higher than the step down converter supplies, do the converts just try to keep up as best as they can, or do the converters melt down and go all Samsung and explode in flames?

There's some pretty sketchy stuff in there, I know. Your thoughts and better ideas are appreciated!

Thank you,
Jon
 

shortbus

Joined Sep 30, 2009
7,443
Coast to a stop? That's the plan anyway. Hopefully I can let go of the momentary switch reliably enough.
That's what they did back in the day. No fancy limit switches or such, with power windows and tops. No one was texting or talking on their phone while working the power accessories. No extended warranties, so if something broke you paid out of pocket to get it fixed. :)

You may want to consider, after finding the amp draw, putting a automotive automatic resetting circuit breaker in the power wire. They were used in headlight circuits a lot back then, so they are kind of "period" correct if that's a concern. And as time went by they started using them in power accessory circuits.

Just one of many places selling them - http://www.wiringproducts.com/automotive-circuit-breakers
 
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