Magnetic clutch? Potentiometer/Resistor bank? DC voltage control question

[KILLDOZER]

I've got a kart on the go for my two boys, it's based on lawn tractor parts, and I would like to utilze the magnetic clutch that originally sent the power to the deck.

I played with it using my battery charger for power, and I noticed that when powering the clutch using the 2V trickle charge setting, I could (with the clutch in a vice) spin the pulley without unreasonable amounts of force required. At 12 volts, it was almost impossible to turn the pulley, and when I put the 70 amp/12V battery boost setting on - I could not budge the thing at all.

The clutch has about a 5 inch diameter steel disk in it for transmitting power, and considering it took the torque from a 16 HP Kohler Command OHV @ 3500 rpm, and sent it to a 42" mower deck with 3 high lift blades in an "instant on" fasion with out the slightest amount of slippage - I suspect this clutch could handle well in excess of any centrifugal clutch - and these things are almost free for the taking!

However... I need a way to vary the voltage, and thus the power of the magnet to allow modulation of the clutch. No I do not know how many amps this thing draws. I was hoping someone may know of an automotive application DC potentiometer, or resistor bank that I could get for next to nothing that would allow a little cheap experimentation. I need to allow for two modes: 1. a slip mode for taking off, and a lock up when off and running. I do have a couple rolls of nichrome wire which I could use to make a resistor of my own, but it would be a fixed resistance. I'm hoping for a variable resistor of some type.

Dimmer switch? Heater fan speed control? Any good suggestions?

TIA

 

[anderkart]

Cool Idea, I think I got a low cost solution for ya.

Go to a junkyard (or check on-line) and try to find an older car that had a "Hang-on" A/C system installed.
You know, not a factory A/C system but those aftermarket a/c units that shops used to bolt on under the dashboard of 50's through 1970's cars.

Well the fan-speed switches in most all those hang on a/c units had a 2 or 3-speed resistor-pack springs built right into the back of the fan speed-control switch. Those fan switches could handle up to 30-amps of current flow @12-volts, so they should be plenty heavy-duty enough for your electro-clutch.

If you can find one of those it would be easy to wire it up to send around 4-volts on low, 8-v on medium and full battery voltage on high. I could explain more about wiring one up if you can find a switch like this. If you can find an older automotive A/C shop they'll probably still have some of these switches in stock for sale.

Again what your looking for here is a 12-volt, 3 or 4-speed fan switch with 2 or 3 resistor springs (that you can see) attached directly the back side of the switch. Those resistor springs will look very similar to this pic below of a remotely-mounted fan-speed resistor pack:

It would require a bit more wiring, but you could get a resistor pack just like my pic here from any GM car made in the 60's through 80's that had a factory equipped heater or A/C, and wire it up through any 4-speed fan switch you wanted.

Those 3 different sized springs you see in my pic are simply passive-resistors that lower the voltage running through them, to whatever single input 12-volt device you want to connected them to...

 

[Bluethunder3320]

cool! i never knew such a clutch existed. pic?

so will you be able to run the engine WOT all the time and just use the switch for the throttle?

 

[anderkart]

Hey KILLDOZER,
I was thinking we could mount a Micro-switch to be triggered as your throttle pedal is pushed, so at idle the clutch would automatically disengaged:

And then that micro switches mounting bracket could have some type of adjustment you could easily reach while driving, so you could always tune the exact RPM the clutch would kick in/out.

With this system I'm thinking you might not need any type of resister or rheostat. Maybe you could adjust an engagement rpm that didn't give-ya whiplash

You'd just need a Micro switch that can handle the amperage draw of your clutch so we wouldnt need to use a relay. Electromagnets dont usually draw all that much amperage, I'm thinking a micro switch rated at 20 amp would be more than enough.

Your clutch might just slip a bit then grab and work just fine with a full 12v signal.
But the resistor-switching option could always be wired "in-line" later on if needed.

so will you be able to run the engine WOT all the time and just use the switch for the throttle?

Nope, we think his clutch might violently grab and fully lock-in instantly with a full 12-volt signal.
So it might just either stall the engine or do a big-hairy burn out every time he wanted to take off from a stop. He's just seeking a low-cost way to let it slip for a short time kinda like our clutches and T/C's do.

 

[fowler]

could u use a dimmer switch with a second (lock) switch at the end

as is known dimmer switches looses alot of current so use it to get moving then when the clucth locks the dimmier cuts out and a proper switch takes over

with this type of clutch u would be able to use it as braking like in a manual car

 

[anderkart]

However... I need a way to vary the voltage, and thus the power of the magnet to allow modulation of the clutch.. I'm hoping for a variable resistor of some type.

Dimmer switch? Heater fan speed control? Any good suggestions?

TIA

Instead of my other suggestions, I think I have a way better plan for ya here:

You could install a clutch pedal to manually actuate a Trailer Brake controller, so your clutch could slip/work just like a car with a manual tranny.

These all have a very linear, variable resistor inside that would smoothly transition between 1 and 12 volts sent to your clutch. The heavy-duty rheostat inside these could handle at least 20+ amps of current, and a manual control lever you could very easily rig up to be actuated by a clutch pedal. They even have a built in return spring, but you'd probably want to add another stronger return spring to the pedal itself.

The older style ones like my top pic should only be around 5 bucks at a junk yard and they have a longer lever that would be much easier to actuate with a clutch pedal.

These older models had a port that originally connected to your cars brake line, (and a 3rd wire that connected to the brake light switch) but you'd just skip those 2 connections and operate it manually with the lever:

_________________________

The newer style T/B controllers like the pic below also have a manual lever, its much shorter but you could extend it.

These newer style controllers dont have a brake line connection like the old style, they just get a signal from your cars brake light switch and then also used an adjustable pendulum inside for automatic trailer brake actuation. But as long as you didn't supply power to the brake light input wire, they would work just fine in the manual-lever operation mode.

Any controller you got would just have 3 wires:
A battery (+) input wire,
and a trailer brake output wire.
You wound not need (or want to) connect the 3rd wire that was intended to go to the cars brake light switch for any of these to function in the manual-lever mode.

 

[KILLDOZER]

Anderkart, thank you very much for all those suggestions - I'm just not an electrical type of guy. The switch idea will work for my kids kart as I've already determined that due to the transaxle's very low 1st gear, you can just shove the thing into gear and roll off with no burnouts. You can actually shift this transaxle with ease without the clutch - just keep shoving it into the next gear and it will slip in no problem. I was thinking into the future using this clutch set up with out any type of gearing which would require some slippage to avoid wheelies, burnouts and stallouts. I will try the yard this sat if the rain stops for some of the items you suggested.

I like this idea, because when you start thinking about it, there are many different ways to set something like this up. I'm already going to put a momentary switch on the steering wheel to cut power to the clutch when activated. This will allow the driver to rev up the engine and "drop" the clutch for wheelies and burnouts! This can't be done with a cent clutch, and should be an enjoyable feature.

Bluethunder,

This is essentially the same unit I have:

My white tractor has something quite different with a smaller driver pulley. The clutch I have has a ~5.5" dia pulley making it ideal for over driving a transaxle, I'm using a 3" pulley on the transaxle input shaft

 

[KILLDOZER]

Well it looks like the old 11HP Briggs on the kart does not have enough juice to engage this clutch. I did a quick google search and it looks like 3 amps is all the power the alternator in an old briggs puts out - not enough...

I'm going to keep this idea in the back of my head for now and just get the kart done using other means. I will likely play with the clutch again when I have an engine with enough juice to run it.

 

[kendelrk]

id use that alternator for lights and all

 

[Bluethunder3320]

pic didnt show up. i dont know if you already said why, but can you use the original engine?

 

[anderkart]

id use that alternator for lights and all

What alternator you talkin bout willis?
That pic in post #30 is an electro-clutch...

 

[Bluethunder3320]

pic didnt show up. i dont know if you already said why, but can you use the original engine?

ok, the pic showed up now. thanks for that.!