What is a good protection method?

T Chap

I have a master controller with a bank of RJ45's on it, each with a different wiring scheme going to different devices. On one port, there is a BLDC motor cable that contains

Hall1
Hall2
Hall3
5V
GND
Encoder A
Encoder B
Limit Switch pulled up to 5V via 10k

On the other ports there are signal lines, serial i/o lines, power, etc all ranging from GND, 3v3, 5V. On a few rare occasions an installer has plugged in the motor cable to one of the wrong ports and killed one of the Hall sensor outputs. I am not sure which port is the port that causes the problem because the installer never keeps track.

As a method of protection, I am considering a buffer module that sits between the motor and the master, that contains a resistor on each line of the 8 lines. Any suggestions on a value to offer protection against killing the encoder and hall sensors by plugging into the wrong ports? I was thinking 200 ohms.

davejames

...myself, I'd need to see the schematics before suggesting anything.

No chance of changing the type of connector to physically prevent improper plug-in?

T Chap

I cannot change the connector, or connection location at this time as there is a lot of fabrication built around the 8 ports. The CAT5 is the only type of connector I would want guys in the field trying to repair or replace. So my only option is to build a module that offers some protection. This is a rare problem, just an extra precaution.

Even if I posted schematics, in the real world the installer still may wire up a cable wrong or use some non standard wiring.

xanadu

Maybe use keyed RJ45 connectors for that BLDC port?

Gadgetman

Colour code the ports?

T Chap

The port is a 4 port RJ45 and I don't see any options for the SMT style 4 port in various colors for each port. The I have warning stickers etc on the port and cables, but in the real world I need a fail safe. Any suggestions for resistors in the lines?

T Chap

The hall sensors have an output such that the BLDC driver IC holds the outputs to 6.25V. The hall sensor pulls the voltage lines LOW when active. Since the hall sensors are what get killed, I am assuming that may be happening is that the hall sensors are seeing a direct 5V voltage when connected wrong, so that when the sensor wants to pull the line low, it cannot because it is a hard 5V versus 6.25 pulled up via resistor. That's why I am thinking about a 200 ohm on all 8 lines, then even if the outputs see a 5V direct voltage, they would likely survive.

http://sccatalog.honeywell.com/pdbdownload/images/ss40.series.chart.1.pdf

Beau Schwabe

If the order of connections are the same as what you listed, then everything is centroid on the power and ground, which means that if the connector is reversed, so is the power and ground polarity.... to me that would cause potentially more problems than anything else.

kwinn

T Chap wrote: »

The hall sensors have an output such that the BLDC driver IC holds the outputs to 6.25V. The hall sensor pulls the voltage lines LOW when active. Since the hall sensors are what get killed, I am assuming that may be happening is that the hall sensors are seeing a direct 5V voltage when connected wrong, so that when the sensor wants to pull the line low, it cannot because it is a hard 5V versus 6.25 pulled up via resistor. That's why I am thinking about a 200 ohm on all 8 lines, then even if the outputs see a 5V direct voltage, they would likely survive.

http://sccatalog.honeywell.com/pdbdownload/images/ss40.series.chart.1.pdf

I was going to suggest resistors, but would suggest a somewhat higher value, say about 470 ohms. That would limit the current to just over 1mA.