I have a frozen drink machine and for some reason it froze up the other night and stripped the plastic gear that operates the mixing paddle. Is there something that I could buy to put in line with the paddle motor that when it got to a certain amp draw that it would shut the power down to that motor? Thanks Michael

 

There are several ways to go about it but less knowing the current and voltage hard to make a suggestion. Also depending on the machine most have a freeze stat to prevent from happening what just happened.

Ron

 

Its a cheap unit from China $700 and has been running fine since I got it. (2 Months) Woke up one morning, half of the mix was a giant block of ice. Of course the gears are just plastic, so it just stripped the mixer gearbox. I haven't check to see what its drawing yet for that part of it. Will take some measurements once the parts come in. Thanks

 

I wonder if it froze first, or if the gears stripped first and the lack of motion allowed it to freeze solid.

 

I am guessing that the motor is an AC induction motor, and so liiting the current with an AC device will be a bit tricky.

 

I would be checking the thermostat first, chances are that's why it froze..

 

One option, which may be effective but is certainly NOT efficient, is a series resistor so that the motor will stall before stripping the gears. It may also be useful to add some sort of slip-clutch arrangement so that the gears will not strip when the stirring part becomes jammed. . That is probably the simplest effective option.

 

Wife's washing machine has a plastic drive link between the motor and the gear box. If ever the gears become jammed the plastic drive is the break point. It broke once and we never figured out why. I replaced that link with the correct one and the washer has been working for many years. No reason why it might have hung up.

Had an electric chain saw with a plastic gear between the motor and the chain. As chain saws do - they bind up. And that plastic gear is the break point. Replaced that twice on a single job. That chain saw - - - I don't know where it is today. But I stopped spending money on gears. I went out and bought a REAL chain saw. One with a clutch.

I'm wondering how hard it would be to make a torque sensor. And if it were easy, the next question would be where to put it. But if the torque became too high the motor could be tricked into shut-down. And to reset it the user would have to shut the machine off and turn it back on. Of course, after the ice block has melted.

The thing that I focused on was the fact that it's a "Chinese" machine. Plastic gears may be their way of preventing a big disaster with a small one. A plastic gear is easier to destroy than a whole machine. Or a jammed machine without a breakaway point can become a fire hazard. OR perhaps you can get a metal gear and let things jam up. When the motor heats up a thermal breaker can trip, shutting down the unit until it's thawed and then the breaker gets manually reset. The key is to knowing the motors startup/stall current and running current. Then you have to decide where the "Break" point is to be set. Can't be the startup current. The motor has to start up. Can't be the stall current either for the same reason. Unless there's a delay built into the sensing method so as to allow starting. Should a jam occur, a prolonged current draw can indicate a fault and shut down the machine.

 

Tony just hit on the solution, at least sort of. Use one of those thermal current limiters in series with the motor. And glue it to the motor so that as the motor heats the current is vastly reduced. That would be cheap, effective, and very repeatable, plus not needing any effort to reset it.

 

The reason why I went with a manual rest point is because if the unit freezes up it's going to take some time to thaw it out. In that time period the motor may cool sufficiently and rest and again try to restart a frozen unit. With a manual rest, the user is aware of a problem that may have its roots in another part of the machine. "Why did it freeze up in the first place?" would be the first question I would want to answer. Plus, having a thermal breaker that self resets - like the breaker on a refrigeration unit such as a refrigerator or an air conditioner - means stressing the motor over and over, which may likely lead to premature total failure of the motor. With the refrigerator example, if the compressor is running then suffers a momentary loss of power, the back pressure of the freon will prevent the compressor from restarting. The motor will overheat and go into thermal shut down. When it cools sufficiently it will try again. If the freon back pressure is still too high the motor will again cycle through the heat. It will do that until the back pressure of the freon has dropped sufficiently to allow the compressor motor to restart and restore normal function. It may take a few minutes for the pressure to drop. Could take five minutes. But it takes a lot longer for a block of ice to melt sufficiently. A manual reset point allows the user to decide when to try restarting the machine.

Remember @MisterBill2; the motor is 100% jammed. Actually, it's the arm that jams. The plastic gear breaks and the unit survives. With a metal gear if the arm jams, the motor will completely stall. And remain stuck until intervention. You would have to be able to reduce the current nearly completely. And I'd fear that a motor that isn't running at full power may allow the arm to freeze again, and more easily.

 

All valid points, Tony. And certainly the very big question of WHY did it freeze needs to be answered.. The one similar machine that I have worked on had a solenoid valve to control which loop got the cooling,, and I am not equipped to replace a malfunctioning valve in the freon line. so that repair went elsewhere. And possibly this appliance also ha such a valve. So there is some detective work to be done now. And I still recommend some form of overload disconnect before those gears.

 

I am leaning towards the mixer quit which caused the freeze. When I first got the machine the freeze cycle was way to high and froze the mix and stopped the paddle. which I think I caught pretty quick, saving it from getting totally stripped. But since its been running fine for 2 months, I was thinking it took some damage from the initial freeze and then just finally let loose. When the part come I will do some testing.