Unusual use of M8/M9 to control a compressor

Perfectly viable.

Although anything that bypasses the switches (e.g. my first post) takes the manual switches out of the equation. I'd look at the installation effort.

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Originally Posted by Doddy

Perfectly viable.

Although anything that bypasses the switches (e.g. my first post) takes the manual switches out of the equation. I'd look at the installation effort.

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Thanks. As one of the 2 way switches is next to the compressor and power supply the installation effort is easy regarding mounting the relay, the wiring may take longer due to my electrical dyslaxia!

Cautionary note - I can't recall previous conversations and the details of the relay and whether it has an integral diode - just remember to add a diode if not part of the relay to protect the AXBB against back-emf - pretty sure it's covered in the AXBB documentation.

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Originally Posted by Doddy

Cautionary note - I can't recall previous conversations and the details of the relay and whether it has an integral diode - just remember to add a diode if not part of the relay to protect the AXBB against back-emf - pretty sure it's covered in the AXBB documentation.

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I did mean to ask why you had a diode on, thanks. The manual doesn't mention anything about back-emf or diode when connecting a mechanical relay to the isolated outputs.

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Originally Posted by ngwagwa

I did mean to ask why you had a diode on, thanks. The manual doesn't mention anything about back-emf or diode when connecting a mechanical relay to the isolated outputs.

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Hmmm, you're right - it instead refers to a relay coil with a +/- nomenclature on the coil - okay if the relay integrates a back-emf diode - I've seen relays with these - but never experienced them myself. Worth being vigilant on that topic - otherwise you can risk damage to the AXBB. Or drive the relay through a transistor amplifier (I'd always belt-and-brace that solution - but that's just me) - either way the solution requires a back-emf diode to protect the switching device.

The MK2P-S does not integrate a diode - you need to add one. Psst, if you don't have one PM me your address and I'll pop a couple in the post - I'm heading to the PO this afternoon anyway.

Quote:

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Originally Posted by Doddy

Hmmm, you're right - it instead refers to a relay coil with a +/- nomenclature on the coil - okay if the relay integrates a back-emf diode - I've seen relays with these - but never experienced them myself. Worth being vigilant on that topic - otherwise you can risk damage to the AXBB. Or drive the relay through a transistor amplifier (I'd always belt-and-brace that solution - but that's just me) - either way the solution requires a back-emf diode to protect the switching device.

The MK2P-S does not integrate a diode - you need to add one. Psst, if you don't have one PM me your address and I'll pop a couple in the post - I'm heading to the PO this afternoon anyway.

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Thanks, you have PM

Thanks for all the help folks - M8 now turns my compressor on and off - next step find a cheap solenoid valve to allow air to the cutter.

Gah, if only you'd said about the valve earlier!

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Originally Posted by Doddy

Gah, if only you'd said about the valve earlier!

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It was actually an after thought to make it 100% automatic, if you have a 24V Normally Closed valve knocking around would you swap it for a Normally Open one? No problem if not as I will just wire it up so the NO valve closes when the compressor is powered on with the manual switches.

Ah!, 240VAC coil N/C (powered to open) - from memory.