Hello guys,
I have this circuit to control a claw. Everything works fine with a small motor, but when i use the claw ( around 6v - 3A ) the MOSFETS can´t deal with it. They get hot and fail.
To get the 6v from the 24v battery i use the arduino PWM ( with analogRead in 490Hz pins).
I am not reaching the problem alone. I would really appreciate some help/advice.
Thank you
sergiodocarmo:
To get the 6v from the 24v battery i use the arduino PWM ( with analogRead in 490Hz pins).
The Arduino PWM does not produce 6v. It produces and On Off current which is 24v for 25% of the time and 0v for 75% of the time. The average is 6v.
I'm not going to comment on your Mosfets because I am not expert on them. I do note that you have not told us exactly what Mosfets you are using.
...R
Thank you for your answer Robin.
About the PWM, that was exactly what i tried to transmit. The power source has 24v but with a 25% duty time the motor "sees" it as 6V.
In the jpeg attached you have the components references. the mosfets i am using are the IRFZ44N.
The IRFZ44N is not a logic level MOSFET. It is quite likely not to be fully switched on with only 5V driving it and that's probably why it gets hot.
Steve
Hello Steve,
If you see the jpeg attached, you'll notice the mosfet is getting at the gate around 12v. It's being driven by an optocoupler (4n35) and has two 2,2k resistors as a voltage divider from the 24v battery!
Thank you fo your answer.
@sergiodocarmo, please make your images visible in your Post so people can see them. See this Simple Image Posting Guide
...R
Robin2:
@sergiodocarmo, please make your images visible in your Post so people can see them. See this Simple Image Posting Guide...R
Done, thank you!
To get the 6v from the 24v battery i use the arduino PWM ( with analogRead in 490Hz pins)
No, PWM doesn’t work like that. You’re putting 24 volt pulses on a 6 volt motor so you’re most likely exceeding the current rating of the mosfets. The bottom line is that if you have a 6v motor, you need a 6v supply.
WattsThat:
No, PWM doesn’t work like that. You’re putting 24 volt pulses on a 6 volt motor so you’re most likely exceeding the current rating of the mosfets. The bottom line is that if you have a 6v motor, you need a 6v supply.
I am not qualified to comment on your suggestion that the current limit of the OP's Mosfet may be exceeded. However with a suitable Mosfet there would be no trouble running a 6v motor using PWM from a 24v supply - just don't turn the power up too high.
...R
You need 2 more kickback diodes, anode of each to one side of motor, cathodes of both to +24V.
And 2 new MOSFETs. Don't like those high resistances on the gate circuits, might slow the gate capacitance charge / discharge time too much, keeping the channel in the linear region too long, causing heating.
