# how to make a current limiter ?

#### mejlby

Joined Apr 26, 2013
28
Hi All

I have a 24 VDC motor that I want to turn off when the current exceeds approximately 500m amp
and I want to be able to regulate the current limit from 300m amp to about 1 amp

I want to protect the motor to be destroyed if it becomes overloaded

I hope someone can help me with a circuit and explain how it works

Best regard

Mejlby
Denmark

Last edited:

#### Picbuster

Joined Dec 2, 2013
1,047
use a 50milli Ohm resistor in series and measure the voltage as function of the current.
feed this into an amplifier( opamp) 1amp does 50mV gain x 50 and feed into cheap 8 pin PIC use two ports analogue in one for current other for pot meter allowing to set cut-off current compare and use a fet to cut-off voltage.
Advantage with Pic; you can easy omit switch off at temporally current peak( eq switch off when the current is for n milliseconds above, by pot, selected value).

#### Alec_t

Joined Sep 17, 2013
14,314
What is (a) the motor current when free-running and (b) the stall (rotor-locked) current?

#### Dodgydave

Joined Jun 22, 2012
11,303
use a 50milli Ohm resistor in series and measure the voltage as function of the current.
feed this into an amplifier( opamp) 1amp does 50mV gain x 50 and feed into cheap 8 pin PIC use two ports analogue in one for current other for pot meter allowing to set cut-off current compare and use a fet to cut-off voltage.
Advantage with Pic; you can easy omit switch off at temporally current peak( eq switch off when the current is for n milliseconds above, by pot, selected value).
What is it with you and these pics,
Whats wrong with a simple voltage regulator like lm338 or lm317k???

#### Picbuster

Joined Dec 2, 2013
1,047
Nothing wrong with it but it's not as flexible as I like to see it.
Like implementing hysteresis, slow start, rpm versus current used to calculate mechanical load.
And as a real Picbuster I have to use pic's make them jump, swing and even make thee or coffee (smile).
But again nothing wrong with lm series.

#### crutschow

Joined Mar 14, 2008
34,452
How much voltage drop can you tolerate?
Can you put a sense resistor in the return line?
An LM317 used as a current-limiter will drop a minimum of about 2.5V.

#### hp1729

Joined Nov 23, 2015
2,304
Can you deal with a microcontroller? Nothing special about PICs, any of them would work that have an analog port. Do you need to just limit the current at some point or shut power down and wait for a human to reset the overcurrent condition?