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john in SAN ANTONIO, TX wrote :
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1/22/10
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AWESOME but... Spent several months optimizing two of these units driving MTRH-34097 motors hooked up to 20:1 speed reducers using a National Instruments serial port adapter (USB to 4 port). Had no problems whatsoever with them and two serial port encoders. Upon final installation of power supplies and everything inside a nice metal case, the USB/serial ports repeated died or the controllers reported communications errors. A scope showed more than 40VAC between inputs and ground while an AC ampmeter registered more than 600 ma.
After jumpering the negative (-) terminal of the 70V input to chassis ground and soldering a small wire between the 5V input and the serial port DB9 connector shield, all problems vanished.
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