I need to control a dc 12v motor that it will switch off at a certain amperage does something like that exist off the shelf

 

Do you want the motor to switch off when its current gets low, or when its current gets high.
An off-the-shelf circuit breaker will switch off the motor when the current gets high and when it starts.

 

Yes, what's your price point? Industrial or just a home project?

Ron

 

Thanks for replies I am designing a product that when it stops against an object it will move the object until the full load amps are reached and then the power disconnects. It must not work as a trip switch but like a limit switch. I cannot use limit switches

 

A stationary motor draws maximum current when stopped, also when it begins running, because it is stopped before it begins running. It is called "Inertia".
Your product will also draw a fairly high current current when it reaches an object that is stopped (unless the motor has a high amount of momentum), then as it pushes the object the current decreases and does not increase unless the loading on the motor increases.

 

Thank you, I just want to know if there is a device that measures the amps and when over a limit switch the motor off.

 

Thanks for replies I am designing a product that when it stops against an object it will move the object until the full load amps are reached and then the power disconnects. It must not work as a trip switch but like a limit switch. I cannot use limit switches

Yes, monitor the current across a shunt like a fractional ohm resistance and amplify and measure the voltage drop across the shunt. That will be proportional to the current level. Run that into a comparator so when a certain limit is met it disconnects. You were asked what to do then? Also you can likely just buy a small module to do this, simply put an off the shelf turn key solution. There are dozens of current sensing and monitoring solutions out there.

Ron

 

Didn't you hear me?
1) An electric motor draws its Maximum current when it is started. Then the current sensing device will switch it off.
2) When the device reaches an object and begins to push it, the motor will draw a high current and maybe be switched off.
3) The motor current decreases (becomes less) as it is pushing an object and the current sensing device will not be triggered.

 

Didn't you hear me?
1) An electric motor draws its Maximum current when it is started. Then the current sensing device will switch it off.
2) When the device reaches an object and begins to push it, the motor will draw a high current and maybe be switched off.
3) The motor current decreases (becomes less) as it is pushing an object and the current sensing device will not be triggered.

Actually there is a good point in that. You want a short delay in your current sense. Depending on the motor it will draw stall current on start. You want to note what AG mentions so you don't get bit in your design.

Ron

 

Thank you, I just want to know if there is a device that measures the amps and when over a limit switch the motor off.

The circuit you seek is called a "Stall detector" circuit and there are quite a few of them published.