Hi, I am using an ULN2830 to drive 5 DC motors. I am connecting everything pretty much the way it is presented here
Motors are switched on/off for short periods and never two at the same time. An external power supply is used to power both the Arduino and the Motors (though Vin)
I am wondering is there any danger of inductive load to return back and destroy arduino pins?
Your subject line has the wrong part number I think - we are talking about the ULN2803, not 2830?
So long as the COM terminal (pin 10) is connected to the +ve supply for the motors the internal diodes will handle inductive spikes. The video neglects freewheel diodes altogether alas, which is never a good idea with inductive loads. The ULN2803 itself will be the first component to risk destruction in this scenario.
Incidentally the DPDT relay circuit shown in that video lacks free-wheel diodes too. It is effectively an H-bridge and needs 4 diodes.
Hi MarkT, thanks for the reply. So if I connect the Vin from Arduino (which is used to provide +5v to each one of the 5 Motors) to pin 10 on ULN2803 it should be fine?
What Arduino are you using? In case it's a 5V board like a Nano, UNO etc. then the following applies:
Either Vin is between 7V and 12V so that the Arduino can make its own 5V from it using its onboard regulator. Or you are applying 5V from an external source, but that should go to the 5V pin on your Arduino, not to Vin.
I am sorry you are right, I am using an external 5V power supply and connecting it to the Arduino (via 5V pin) and also using it to provide 5V to all the motors (by splitting the wire and using a breadboard). Then the ULN2803 is used to Ground each DC motor and let it work. So if I connect the (common for Arduino and DC motors) power supply to pin 10 (COM) of ULN2803 the diodes will protect it?
Yes, the protection diodes for the transistors in the ULN2803 are onboard the ULN2803 chip itself.
I see, so 5v at COM is engaging the diodes if I understand it correctly. This should work then I guess with diodes protecting against inductive load
Uhm, that combination of words doesn't make sense to me, sorry.
The diodes are there to handle the reverse polarity spike that comes from the motors and channels it to Vcc/5V where it's harmless, to put it simply.
According to the datasheet, yeah. And of course provided that your motors will run as desired at such low voltage. I assume you've looked into that aspect.
sorry koraks, I meant that providing 5V at the COM (pin 10) of ULN2803 is making the diodes work. Yes, my motors work with 5V so it is fine!
I started the thread because I noticed today that one of my ULN2803 was damaged and I was not sure why the internal diodes did not protect it. I had the pin10 unconnected, so a good lesson!
Ah, yeah, I see what you mean now. Yes, it does! And yes, this certainly could explain your damaged chip; well done!
Hmm actually I revisited the circuit and noticed that I had in fact connected the IC's pin 10 to +ve. Strange, what could have damaged it then? I am using actually two input pins controlling two output pins per motor for extra amperage and security but it seems that none of them is working in one of the motors so I guess it's clearly inductive load that created the issue... I cannot understand
Keep an eye on the temperature of the ULN2803.
The chip has a saturation voltage of 1volt@200mA (4volt for the motor),
meaning if your five motors only draw 200mA each, then the chip will dissipate 1watt.
The chip could be 73 degrees C above ambient (see datasheet).
So which motors are we talking about?
Leo..
Yes, I thought about it. I use toy DC Motors operating at 5V. The thing is that I have used small heatsinks on the chip (with thermal paste) and the motors are turned on/off separately (never two at the same time) and not for long times (something around 1-3 seconds) followed by small pauses (again around 1-2 seconds) occasionally there are also longer pauses (around 15 seconds). It is an installation in a museum so it works for long periods. It was working fine for months but just a few days ago one of the two ULN2803 got damaged (actually only two of its outputs)
Perhaps those motors developed friction, possibly due to wear of the installation?
No no, the motors work fine. I replaced the IC and the installation works fine again. I am just curious about what could have caused it. I am not an electrical engineer so I wonder are those ICs very sensitive?
To an extent, yes - as you've noticed. But since the cause of the malfunction isn't known, it's hard to tell if a different choice of components would have prevented the defect.
Hi,
Have you actually measured the total motor current while your project is working?
Thanks.. Tom... 
Actually not, do you think it could be an issue? I guess it should be around 0.4-0.5 A
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