"Hot" SX-Key
Guenther Daubach
Posts: 1,321
Hi "SXers",
Currently, I'm working on an SX project for PWM controlling the motor of a concrete saw. You can imagine that these types of DC motors "eat" some power (about 240 Watts), so the power supply needs to have some "steam" as we say in German.
By some nasty error, I had a shortage between the power supply plus output (24V, 10A), and the signal ground which is separated from the motor ground. As the power ground is connected to the PE mains lead (earth), this caused current to flow from the power plus, through signal ground, the SX-Key Vss pin, the serial cable, and (as the PC ground is also connected to PE), back to the power supply.
First, I did not notice that - I was only wondering why my serial cable was getting really hot. I never experienced that before, even at the highest baud rates. So I thought, I should better turn off power now.
After finding the problem, I thought "OK, dear SX-Key - you and your SX companion in the test socket did a good job so far, but now time has come to send you two to semiconductor heaven, after I have fried you". I also was nervous that my PC's COM port might have become sick somehow after this "hot shower".
When inspecting the SX-Key, I found that the plastic of the four-pin header plug had melted around the Vss pin due to the heavy current "steamed" by the power supply.
I then thought by myself "why not give it a try". After removing some of the melted plastic, I re-connected the SX-Key, started the IDE, and - to my great surprise - both, the SX-Key, the SX, and all other components on the board worked as normal, including my PC.
Nevertheless, these ratings were "a bit" out of specs, so I do not encourage you to repeat this experiment again
.
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Greetings from Germany,
G
Currently, I'm working on an SX project for PWM controlling the motor of a concrete saw. You can imagine that these types of DC motors "eat" some power (about 240 Watts), so the power supply needs to have some "steam" as we say in German.
By some nasty error, I had a shortage between the power supply plus output (24V, 10A), and the signal ground which is separated from the motor ground. As the power ground is connected to the PE mains lead (earth), this caused current to flow from the power plus, through signal ground, the SX-Key Vss pin, the serial cable, and (as the PC ground is also connected to PE), back to the power supply.
First, I did not notice that - I was only wondering why my serial cable was getting really hot. I never experienced that before, even at the highest baud rates. So I thought, I should better turn off power now.
After finding the problem, I thought "OK, dear SX-Key - you and your SX companion in the test socket did a good job so far, but now time has come to send you two to semiconductor heaven, after I have fried you". I also was nervous that my PC's COM port might have become sick somehow after this "hot shower".
When inspecting the SX-Key, I found that the plastic of the four-pin header plug had melted around the Vss pin due to the heavy current "steamed" by the power supply.
I then thought by myself "why not give it a try". After removing some of the melted plastic, I re-connected the SX-Key, started the IDE, and - to my great surprise - both, the SX-Key, the SX, and all other components on the board worked as normal, including my PC.
Nevertheless, these ratings were "a bit" out of specs, so I do not encourage you to repeat this experiment again
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Greetings from Germany,
G