# how to make a current limiter ?

Discussion in 'The Projects Forum' started by mejlby, Apr 24, 2016.

1. ### mejlby Thread Starter New Member

Apr 26, 2013
28
1
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: Apr 24, 2016
2. ### Picbuster Member

Dec 2, 2013
391
53
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).

3. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,971
1,135
What is (a) the motor current when free-running and (b) the stall (rotor-locked) current?

4. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,150
769
What is it with you and these pics,
Whats wrong with a simple voltage regulator like lm338 or lm317k???

5. ### Picbuster Member

Dec 2, 2013
391
53
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.

6. ### crutschow Expert

Mar 14, 2008
13,492
3,372
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.

7. ### hp1729 Well-Known Member

Nov 23, 2015
2,094
232
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?