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Topic: PC damaged by bad Circuit (Read 3151 times) previous topic - next topic

TRanger

Yeah, I knew better and feel like a moron.  I wanted to post here for two reasons, one to provide an example of what can happen and two, to inquire about how to protect the PC in the future.

I looked here: http://arduino.cc/forum/index.php/topic,124547.0.html and on a much older thread and didn't see a good solution.

I was working with this H-bridge motor controller:

http://www.ebay.com/itm/DC-12-30V-5A-H-bridge-Brush-Motor-Driver-PWM-Brake-For-Smart-Car-Arduino-/170916785405?pt=LH_DefaultDomain_0&hash=item27cb6f2cfd

The documentation isn't the best.  It has four terminals on the output side.  Two for power (B+ and gnd) and two for the motor (M+ and M-).  There are six on the "input" side.  B+, ground, enable, pwm1, pwm2, vt and ct.  At the time of the incident I did not have a data sheet for the motor driver chip - it is a L6201P.

The datasheet is on this page: http://www.st.com/internet/analog/product/63228.jsp

I had a 24V, 5A external power supply for the output side.  It has a circuit breaker on the 120V side and a 6A circuit breaker on the 24V size.

The Arduino was wired to the input side of the controller as follows:

5V to B+
Pin 4 to Enable
Pin 3 to Pwm1
Pin 5 to Pwm2
Gnd to Gnd
CT and VT not connected.

The Arduino was powered via USB from the laptop PC

So..... after everything was connected, I turned on the line-side cb and then the output cb and ..... poof! I shut off the cb (still had my hand on it - it doesn't take long) and disconnected the USB cable.  The PC display was blank.  I could smell a hint of released electronic smoke.

The PC came back to life after pushing the power button.  It was like it went to sleep or something.  (BTW - it is 6 month old, win7 64b, Dell precision something or other WORK computer).

The Arduino was dead, TX RX and power on LED's were lit.  I checked voltage on 5V and it was 4.4V, 3.3V was 3.3V.  I figured I fried both processors on the board.

Here's the moron part.  B+ is B+.  The 24V on the "output" side is connected to the first pin on the "input" side.  I put 24V on the 5V Arduino pin.

So I broke out Arduino #2 and couldn't load a sketch.  I don't recall the exact error, but it contained "synch".  The IDE looked like it finished loading, but couldn't confirm?  So, I figured I would reboot to get back to square one.

The PC would not reboot.  It posted and then hung.  It is still in that state.  I installed Ubuntu Live CD to make sure all my data was there and the drives appear to be ok.

I have interfaced to other industrial stuff, like solenoids, VFD's etc... and I have used opto-couplers.  In this case, I didn't think the pwm would work across that interface.  I also thought I needed 5V for the driver chip (wrong) and don't have a 5V supply handy.

Anyway, other than "don't do THAT", what advice is there to avoid cooking a PC across the USB line.




JoshD

I always avoid connecting the arduino to anything over 5v for the first time while the USB cable is plugged in.  Even if I plan to have it connected to get data from it later, I always start with the arduino running on battery power.  I wasn't sure if it was possible to damage the PC before, but after reading this, I'm thinking the paranoia was justified.

Have you opened up the PC to see what happened?  Maybe you'll get lucky and it's just a blown cap somewhere!

TRanger

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Have you opened up the PC to see what happened?  Maybe you'll get lucky and it's just a blown cap somewhere!


Sort of.  I took off the back cover and see that it is truly 10 lbs of stuff in a 5 lb bag.  I was planning on just taking out the HDD's.  Since it is a company PC, that's as far as I want to go.

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I always start with the arduino running on battery power.


Or even a wall plug, just no USB. 

Coding Badly


Good quality powered USB hub.  It may or may not help but, for the modest price and the chance that it will help, it is worth using.  I believe optically isolated hubs are available.

By coincidence, I just dropped a hub in the trash that very likely failed from Arduino and "industrial" related abuse.

Trion

#4
Dec 15, 2015, 09:21 am Last Edit: Dec 15, 2015, 09:38 am by Trion Reason: CT and VT pins?
Thank you for posting here about this motor driver, TRanger!

I came here because I also bought Wingxine / Wangxin / Wingxin miniIBT motor drivers and the documentation (which I am attaching here) left important questions unanswered, especially about the "B+" pin.

I agree that it's dangerous to have a section "input ports" in the documenation when it contains an output pin with the full voltage of the battery!  :smiley-eek:

I wonder if this board supplies 5V or 3.3V somewhere? What are those VT and CT pins? Can I use them to measure the amount of current and voltage provided to the motor?

I.e. for CT, 3.775V means the motor is drawing 5A?
And for VT, 3.529V means the voltage supplied to the motor is 30V? What about 48V then?

raschemmel

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I.e. for CT, 3.775V means the motor is drawing 5A?
And for VT, 3.529V means the voltage supplied to the motor is 30V? What about 48V then? 
The way I interpret that documentation, those two  pins are for use with an arduino analog input.
The VT has an 1/8.50 ratio to the input. 1.0 Volts on the VT pin , means the motor voltage output is 8.50V
2.0 V on the VT pin means the motor output voltage is 2* 8.50 = 17V an so on.

The same applies to the CT. The CT pin 1/1.3245033112582781456953642384106 ratio of the motor current. 
If the motor current is 1 A, the CT pin voltage is 1/1.3= 0.775 V.
Motor current = 2 A => CT pin = 2/1.3 = 1.51 V
                      3 A => CT pin = 3/1.3= 2.265 V
                      4 A =>  CT pin = 4/1.3=  3.02 V
                       5 A => CT pin = 5/1.3 = 3.775 V

If you read those two pins with analog inputs you can monitor and display motor voltage and current on an LCD.

Trion

Yes that's my understanding as well. So we have two more output pins in the "input pins" section...  >:(

raschemmel

They should be labeled Motor Voltage and Motor Current

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