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Author Topic: BOB relay low voltage  (Read 135 times)

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BOB relay low voltage
« on: August 07, 2020, 11:15:14 AM »
Hi, I hope I'm asking in the right place here.

I'm having some trouble with the relay output on my generic Mach3 breakout board.  Our machine has been running without major issue for a number of years, but recently the relay to trigger the plasma torch has been acting up.  Upon triggering the torch in software the relay on the bob clicks on, but the relay it drives had become intermittent.  I replaced the external relay first, but had the same issue.  Next, I checked the voltages in and out of the bob.  Have a clean 5v from the power supply, and a clean 5v at the 'pc5v' ports, but am only getting about 3v out from the relay once triggered...

I've also tried swapping out the bob for a fresh spare, but am having the same problem, only 3v out from the relay...

The bob in question is the typical, generic 5 axis board found any number of places, and had been working fine up until recently, when it started acting up after a few cycles on and off.

Has anyone else had this issue?  I was pretty sure that the bob relay was supposed to put out 5v, as I had never had a prior issue with running a 5v relay from it before, but perhaps I assumed wrong and just had good luck previously?

Thanks in advance for any help or tips that anyone might have.
Re: BOB relay low voltage
« Reply #1 on: August 08, 2020, 06:02:52 AM »
sounds like the coil resistance of the relay is dragging the BoB output voltage down.
Why don't you use a transistor, diode and a resistor and then you could switch 24V and use
an industry standard relay coil voltage?

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