Electrical shear pin

[puckman]

I have been looking into a electrical way to stop a motor very quickly when the setting of the motors amperage has been reached. The starters ol's do not react qucik enough. A conveyor type system is the design style i will be looking to shut down as soon as a predetermin setting has been reached. This equipment has a shear pin that is suppose to react to the torgue being put it, at times it does not function [ maybe wrong pin] don't know why.
I understand there are electronic relays that can do the same type of a job as a mechanical shear pin does.
Has anyone come accross this type of relay device and can you give your expiereance using them ?
Thanks for your inputs.

 

[Smart $]

FWIW, I'd look into getting the appropriate shear pin.

 

[ptonsparky]

Shock relay is the term. I think. I have used CTs that have a 4-20 ma output along with a CLICK plc and a low end hmi to make my own. HMI makes it easier to set parameters and track data. Spend more. Get more.

Clutches are available too.

 

[ptonsparky]

Shock relay is what I call it. Jraef called it a current sensing relay. Search "shock relay" then scroll down the page a bit.

 

[kwired]

Shock relay is what I call it. Jraef called it a current sensing relay. Search "shock relay" then scroll down the page a bit.

I'm guessing you are talking about the same thing I'm thinking of. Current sensing relay. There are some with instant contact transfer when set point is reached as well as time delayed contact transfer. They can also be used to prove that current is not too low. Say a belt or chain breaks - the current will drop without the driven load.

 

[Besoeker]

I have been looking into a electrical way to stop a motor very quickly when the setting of the motors amperage has been reached.

Do you mean physically stop i.e. get to zero speed very quickly of have the supply removed very quickly?

 

[gar]

120504-1123 EDT

With a shear pin on the output shaft you eliminate the time delay from the motor and gear box inertia, and any time delay in the control circuit. Since the output shaft is slow I will guess the shear time is in the 1 to 10 millisecond time range (high torque to zero torque).

Removing power from the motor will have a longer shutdown time.

An intermediate dropout time could be achieved with a clutch on the gear box output shaft.

You could also consider a slip clutch on the output shaft.

.

 

[templdl]

120504-1123 EDT

With a shear pin on the output shaft you eliminate the time delay from the motor and gear box inertia, and any time delay in the control circuit. Since the output shaft is slow I will guess the shear time is in the 1 to 10 millisecond time range (high torque to zero torque).

Removing power from the motor will have a longer shutdown time.

An intermediate dropout time could be achieved with a clutch on the gear box output shaft.

You could also consider a slip clutch on the output shaft.

.

Have you considered a dynamic brake if besides shuting down the motor at a given current level where braking the motor is also an issue?

 

[don_resqcapt19]

It appears to me that the OP just wants to turn the power off to the motor at a torque load slightly above that where the physical shear pin should shear. This would be a back-up in case the shear pin did not shear. He does not want to wait the amount of time it takes for the motor overload protection to operate. The "electronic shear pin" would open the control circuit and drop out the stater when it sees a load higher than the set point.

I do agree with Smart that the best solution would be to use the correct physical shear pin.

There would be a very small difference in stopping time between the shearing of the physical pin and the operation of an "electronic shear pin" that would kill the power to the motor. There would be some time for the controls to activate and open the starter contacts and some additional time as a result of the inertia of the motor.

 

[Smart $]

...

I do agree with Smart that the best solution would be to use the correct physical shear pin.

...

In this type scenario and if shearing happens often, I suspect the maintenance dept may replace the appropriate shear pin with one having a higher torque shear value, just so they don't have to replace it as often or perhaps never... analogous to a homeowner putting in a higher rated ocpd on a citcuit.

If shearing happens often with the appropriate shear pin, I'd look into installing a mechanical torque limiter... perhaps one of pawl and spring design with manual reset.

 

[puckman]

We will adventually get the right shear pin in time . But this type of electronic relay will work out to be a good backup. For what ever the reason either the wrong pin or loose chain the system fails . Thanks for all the help fellows.

 

[kwired]

Another possibility is that you want to either control the speed of the conveyor or the speed of whatever is supplying material to the conveyer and govern it according to whatever the conditions are at the output of the conveyor, instead of just stopping it.

 

[jafro]

Electrical Shear Pin

Electrical Shear Pin

I have installed dozens of Motor Protection Units (MPU) from a Canadian company called Startco. We used to use shear tips on bucket elevators with constant mega damage when the chain broke and it all ended up at the bottom. This units stops every thing immediately with no additional mechanical damage. We left the shear pins in but have not touched them in decades WWWStartco,ca