[bladehunter]

Well I've finally made a start after collecting "The Bits".

Anyways I'd thought I'd do it back to front and get the electronics sorted then get onto the mechanical side. Reason being the electronics I can get locally, the mechanical bits have to come from Overseas.

The electronics are going to be contained in 2 19" rack enclosures, a 3U one for the stepper drives & PS and a 2U for the BOB and other sundry logic. The stepper box is complete and functioning (all wired up correctly 1st time) and now I'm thinking about the E-Stop.

Do I or should I on a E-Stop condition

1. Cut power to the mains supply and have a 1 to 2 second delay in shutting power to the stepper drives due to the PS caps discharging.
2. Cut the 48V rail to the drives via relays and leave the mains untouched. I do have a power switch to turn off the mains.
3. Use a couple of relays to disconnect the Step signal to the drivers. Thereby leaving the steppers in a "held state".

Personally I'm tending toward the second option as I can wire up a relay and a pushbutton as a NVR switch on the 48v rail. The E-Stop will do any disabling of equipment and will just inform Mach of the E-Stop condition.

If this seems a bit confusing I can post up some pictures\diagrams in the morning.

Cheers
Rob

[doorknob]

It may depend on the specifics of the drives that you are using, but switching off the DC supply to the drives is often not recommended because it can damage the drives.

So it may be better to use a combination of signalling Mach3, cutting off the AC to the power supply input via a contactor relay, and turning off the spindle through a relay or vfd.

[bladehunter]

Apart from the delay the from the caps discharging in the PS what's the difference between cutting the mains and cutting the 48v rail ?

[Bubba]

Inductive kickback from cutting the 48VDC rail can(will) fry the drive and/or motor due to voltage spikes.

If you cut the mains, the voltage can decay peacefully or it can be done quicker by means of a bleed resistor or cutting in a smaller bleed resistor by means of a relay.

[bladehunter]

Cheers Bubba, much appreciated. Any advantages/disadvantages from switching Active or Active\Neutral via relays?

[Bubba]

bladehunter,
I am not completely sure of the terminology that your using here, but I think your talking about cutting one or both legs of the mains side? IF I understand your electrical system there (and I am not 100% sure on this one) you have 220V and isn't one side at ground/earth??? If it is, I would only switch the hi side voltage. That way, IF something were to happen, you still have the machine grounded/earthed.
Hope I have made myself clear and it is correct.

[bladehunter]

We have a 3 wire system. As shown below


The case is earthed.

[Bubba]

Based on what I have always been told (and I am no electrician) you only switch the "active side".

Hopefully one of your countrymen with proper knowledge will jump in and correct me if I am wrong or agree if correct!

[Flexo!]

hi Rob, Good to see another southern hemisphere BF20 build!

On my setup I switch both active/neutral.

Generally I think its unsuitable to E-stop at the core voltage supply level - either to the stepper drives or their supplies. Steppers tend to shift position when powering up and down, and to a lesser extent when mach3 E-stops (usually to the closest Full Step I believe?).

Mach 3 stops sending signals when in Estop mode, so generally a simple input switch is suitable as an Estop. Its very safe, and very instant. A "charge pump" is highly recommended as it halts everything when mach 3 is inactive, so it stops relays switching on randomly when the computer powers up.