Hi, I have been working on an automation project using a 24v motor and an L293D driver chip and I'm having a few issues with meting plastic and popping chips. As I understand it (I'm an arduino/electronics newbie) the L293D can handle 600 mA of current, between 4.5V to 36V, for each motor/channel; with a peak output current of 1.2 A.
With this is mind I chose a DC motor with the following spec:
Model: MFA/Como Drills RE-280/1
Operating Range 12 -24V DC
Current: 0.10A (No load)
0.30A (Max Efficiency)
I tested them running at 24V. I measured the current at 0.067A when no load. Current with the motors winding a heavy load was measured at 0.20A.
To see how they would run on the driver chip I hooked an unloaded motor up to an Adafruit Motor shield V1.2 mounted on the arduino. After connecting the 24V to the external power terminals (polarity correct) I swiftly kissed goodbye to one of the driver chips as it popped. Undaunted and believing that I may have wired something wrong I wired a L293D chip up on a breadboard and connected up the motor directly; the end result was a very malformed and retched looking breadboard and a very very hot chip and a burnt finger.
I'm not sure where I'm going wrong so I'm hoping someone may help please.
Do you want a link to a Temp sensor circuit to save your fingers ?
I don't recommend connecting a FIXED 24Vdc PS for motor shields. I use a variable with adjustable current limit and start with the voltage at min and then ramp it up slowing watching the current. The PS cost $100. I've had it for 3 yrs and used it for countless projects. I bought it because I had a deadline and they wouldn't let me work overtime so I built and tested the circuit and home and made the deadline and my boss was happy. It was worth the $100. Totally. When you're doing something like that you should wear safety glasses. I once saw a little 2n2222 explode like a firecracker and the piece blew out the front of the plastic case and flew across the room and hit the wall with a ping! and bounced off the wall and landed 10ft away. If something like that hit your eye it could blind you.
The motor undoubtedly draws well over 1 ampere when it is stalled and all DC motors briefly draw the stall current when they start up. That is what is blowing the chips.
You can estimate the stall current by locking the shaft and BRIEFLY measuring the current. Start with a low voltage (like 6V) and scale up the result by 4, rather than apply 24 V.
The L298 driver is better, but even that is ancient technology and vastly overrated. Do not count on drawing much more that 1 ampere per channel, despite what all the adverts say.
I'm not sure where I'm going wrong so I'm hoping someone may help please.
You're not using a adjustable current limited variable power supply that allows you to adjust the current and ramp up the voltage (eliminating the INRUSH current).
Stall current is easily determined by measuring the DC resistance of the motor and
using I = V / R
What is the 24V supply (how much current can it supply).
If the minimum of stall current and supply current exceeds the driver chip's absolute
maximum current then you can't use that driver (without current monitoring at least).
You could consider using a heatsinked LM317 (adjustable regulator) getting it's input from the 24Vdc supply. The LM317 has foldback current limiting so it will shutdown automatically if there is a short or problem. The inrush current can be reduced using a snubber (RC) .
I don't think you don't want foldback limiting for a motor driver, as it may just jam
in the foldback state on startup or reversing. Just current limiting is fine.
Foldback means overload will drastically reduce the torque available, which
means the motor may simply stall from friction.