AXBB charge pump fault

[john swift]

Hi Charlie

I am surprised the the charge pump output has failed again

I would of thought the combination of the diode added across the relay coil to control the back emf
and the 27 ohm resistor to limit the current if the relay was ever short circuited
would of protected the FET

Can you measure the voltage between the CHP O1 and -24V terminal

when the output should be ON and OFF

and if possible the voltage across the 10K resistor on the PCB

knowing the voltage between the 74HC14 GND pin 7 and output from pin 2
will help

I would expect it to be 0V when OFF and +3 to +5V when ON

from the FET data
Gate Threshold Voltage = min 1.5V to max 2.5 V

John

[CharlieRam]

Hi Charlie

I am surprised the the charge pump output has failed again

I would of thought the combination of the diode added across the relay coil to control the back emf
and the 27 ohm resistor to limit the current if the relay was ever short circuited
would of protected the FET

Can you measure the voltage between the CHP O1 and -24V terminal

when the output should be ON and OFF

and if possible the voltage across the 10K resistor on the PCB

knowing the voltage between the 74HC14 GND pin 7 and output from pin 2
will help

I would expect it to be 0V when OFF and +3 to +5V when ON

from the FET data
Gate Threshold Voltage = min 1.5V to max 2.5 V

John

Sorry for the late reply, so I managed to check a couple of voltages before the battery died on my volunteer again...really should remember to turn it off! It reads 9v when off and 24v when on when the relay is connected. but I had a brainwave and it works so unless you say it's a bad idea I'm going to stick with it...
The charge pump only activates the relay when the software is active and reset state is inactive, the problem was that it wouldn't then shutoff on reset or estop so I have used an opto isolated relay on another output which is the true state of reset and settable in uccnc. This means that the relay isn't active unless the software is active and reset is not. It also protects the AXBB against any other issue causing the charge pump failure..

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