# Jogging Reverse as a brake



## dronai (Apr 11, 2011)

Worked on a troubleshooter today at a carwash. Breaker tripping to a disconnect where the guys bypassed and removed the fuses at the disconnect, to a 3 phase motor to a large rinser to spin dry the rags and towels. The controls were just gutted and spaghetti wiring in the control box. The guys removed the control on one single phase motor and just put a cord on it and plugged it in for the washer. They must have tried and failed for the bigger 3 phase motor and caused the short. 

There are no Ol's and the 3 phase motor originally had a forward and reverse switch. I found one working contactor out of the 4 that were in there, and used that. Lost my reverse, but they were using it for braking the motor. 

Doesn't that cause damage to a motor or the shaft by using reverse for braking ?


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## Southeast Power (Jan 18, 2009)

Plug reversal.
Not intended for a fully loaded motor.


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## oliquir (Jan 13, 2011)

did make some control panels that use reverse for braking 3 ph motor for 0.5-1 seconds but those were only for emergency braking.


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## John Valdes (May 17, 2007)

Dorian. Its not so much about the motor as it is about the mechanical load.
Can the attached load handle the reverse jogging?

Can a brake motor be used in lieu of the reverse jog option?


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## JRaef (Mar 23, 2009)

Plug braking is about as hard of duty as you can exert on a motor, shaft, gears or pulleys, everything in the system, INCLUDING the contactors. Most likely the spin dryer was not designed for that, it was likely reversible so that it alternated direction on each subsequent use in order to keep the wear and tear on the bearings more evenly distributed. But some smart guy decided to adapt it for plug braking. The workers likely are paid based on how many cars they get through the wash, so waiting for the spin dryer to coast to a stop was costing them money. But they wouldn't care about the cost to fix the machine...

If they want to brake it fast, use either a brake motor as John suggested, or if they don't want to replace brakes because of wear, they can use electronic braking. But if you use electronic braking, you need to add a timer that limits their duty cycle. Every braking cycle puts as much heat into the motor as a starting cycle, so if you calculate the Starts-per-Hour capacity of the motor and load, you have to cut that in half if you are braking, and double the rest period between cycles. 

Higher cost alternative #3 is to use a VFD with a Line Regeneration Module that turns the motor into a generator and pumps that energy back into the line so the motor stays cooler. They can be added to most VFDs, even the cheap ones. You could also use a VFD and a Dynamic Braking Resistor, but that too will have a limited duty cycle and it's likely these guys would burn it out too. The Line Regen module has no limitations.
http://www.bonitron.com/m3545.html


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## dronai (Apr 11, 2011)

John Valdes said:


> Dorian. Its not so much about the motor as it is about the mechanical load.
> Can the attached load handle the reverse jogging?
> 
> Can a brake motor be used in lieu of the reverse jog option?


 I was worried about a heavy load of wet towels and the speed at which it gets going with a really long coast to stop. I figured it's pretty hard on all of the mechanical attached.



JRaef said:


> Plug braking is about as hard of duty as you can exert on a motor, shaft, gears or pulleys, everything in the system, INCLUDING the contactors. Most likely the spin dryer was not designed for that, it was likely reversible so that it alternated direction on each subsequent use in order to keep the wear and tear on the bearings more evenly distributed. But some smart guy decided to adapt it for plug braking. The workers likely are paid based on how many cars they get through the wash, so waiting for the spin dryer to coast to a stop was costing them money. But they wouldn't care about the cost to fix the machine...
> 
> http://www.bonitron.com/m3545.html


 You nailed it
Owners too cheap to buy a motor brake


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## John Valdes (May 17, 2007)

Dorian, If this is a centrifuge, disregard everything I said as from memory, you are not dealing with a simple 3 phase motor.
Speed and design being the major differences. 

I would look at similar applications to see how they accomplish braking.


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