Hello,
Have been using the
Pi hat for a few years now and something burnt it out - possibly over current through a motor stall.
The motors are both 12v low current but are subject to stall conditions (not having been a problem until now).
So, I want to implement simple current protection and am thinking of connecting a polyswitch
https://www.jaycar.com.au/rxe090-ptc-fuses-speaker-protection/p/RN3462?pos=5&queryId=5acf3885558e98caf71285ec85ffe2a5&sort=relevance&searchText=ptc%20fuse
in series with each of the motors which should trip at 1.35 amps.
My question is:
Is breaking the circuit abruptly like this likely to damage the driver?
Hi Roland
A Polyswitch does not just break the circuit. When overloads occur and the switch gets to the trip point it heats up rapidly and the resistance goes high. While ever the fault condition is present the switch maintains enough current to stay hot and have a high resistance. When the power and/or the fault is removed the switch rapidly cools and normal operation is resumed.
They work very well in a static situation say as in a power supply for an amplifier where 1 amplifier could have a fault causing high current and this will be controlled instead of taking out a whole rack full of amplifiers if a fuse or breaker fails.
I have never used them in a motor situation where the start up current will be the same as stall current. They might be quick enough to prevent the motors starting if you tried to start them at full speed. If you ramp up speed with PWM or whatever they might work but if you start at full speed I think these things might be too quick. Try them anyway, you won’t do any harm but think of the above if the motors don’t start. If they have operated they will be quite hot.
Cheers Bob
Hi Bob,
Thanks for the info. I did not know they behaved like that which suggests a continuity which would not effect the driver adversely.
I am currently in the process of enhancing my control software I developed in Free Pascal to incorporate
exceleration/deceleration functions not included in this driver board so will have a normal controlled starting current ramp.
As you say it;s a matter of trying it out.
I’m supprised Adafruit don’t include current protection.
Thanks again for your input.
Cheers
Roland
If you are employing controlled acceleration at start up and speed increases then these devices will probably be OK. You will have to try it but.
Cheers Bob
