[mhackney]

I've read everything I can here and on the web about e-stop circuit design. I think I get the theory and what I need to do to safely shut down my machine (A Grizzly G0704 CNC conversion). Now I am trying to make the design decisions for MY circuit! There are so many options and it isn't clear which are the most cost effect, safe, etc. Here are the devices/circuits I need to manage:

1) I'm controlling my spindle with a KBMM-125 which is in turn controlled manually with a POT and via Mach with a CNC4PC C6 board. 20Amp

2) my control box with a CNC4PC C35 BOB, stepper drivers, 48V power supply. the C6 board, relay for the flood coolant, 5V and 12V wall warts for the various devices. 15Amp

3) an 850 GPH 120V pump for flood coolant. 5Amp

4) e-stop signal to Mach

So, I need a safety relay to switch these off when interrupted by the e-stop. First, I find that these safety relays come in 24V and 120V options. It seems that a 120V safety relay would be simpler in that a separate 24V power supply would not be required. Is there a cost consideration (i.e. the 120V version is significantly more expensive?)? How about having 120V run through the e-stop switch. Many seem to be rated for that.

Second, since my spindle needs a 20A contact, what is the best way to deal with that? Are relays with four NO 20A contacts available and affordable?

Figuring out what's available for a cost effective solution is challenging!

cheers,
Michael

[underthetire]

ALLEN BRADLEY CONTACTOR 100-A09ND3 COIL 120VAC | eBay

[mhackney]

Thanks underthetire. I came across those on eBay myself. I wasn't (am not) sure if these are rated for the 20A spindle motor though. If you look at the label closeup in the listing it says its rated at 1/3 HP at 100V single phase and then 9A. Am I interpreting this correctly?

cheers
Michael

[underthetire]

If your using these to switch a motor on and off, no. If your using a drive unit, your not supposed to switch the motor output side, only the input side.

[mhackney]

Thanks, good point, I do plan to switch a KBMM-125 motor speed controller (input side). It is configured for a 1.5 HP motor drawing up to 16AMPs. At this max rating, the spec sheet says 24 RMS Amps AC line current.

I have this speed control on a dedicated 20A circuit in my workshop. Will this one work?

cheers,
Michael

[Al_The_Man]

You can go with the Safety Relay, but if you want a cost effective style, use a low voltage control circuit for a hard wired E-Stop, place all emergency stops etc in this string, a Ice Cube relay with 4 PDT contacts, the industry standard is 24vdc but you can use 12vdc.
This relay would then control a contactor coil such as pointed out, I prefer Telemecanique DIN style, they are abundant on ebay.
A contact on the I.C. Rly would advise mach a E-stop has taken place, the main contactor would switch spindle motor and servo/stepper supply.
BTW, you can switch the output of the KB as long as you use a contact on the I.C. relay to close the I1 & I2 contacts on the KB.
See manual.
Al.

[mhackney]

Thanks Al, now my head is swimming again! I thought the intent of the Safety Relay was a "1 box" solution? My biggest challenge is I don't know how to spec what I need. I can't find any contactors that support a 20A 120V. Relays I can find.

cheers,
Michael

[Al_The_Man]

Ebay 160712191568
More than you need.
Al.

[mhackney]

Thanks for the link. I scrutinized the label and searched on the part # and can't find the specs regarding the # of NC contacts and whether it is the 24V, 110V or 220V version.
cheers,
Michael

[mhackney]

Ok, I found that this is a 120V for the control coil - the G6 on the back is the designator (and the 120V label too!). The 24V version is -B7.

And it has 3 main and 1 NC auxiliary poles.

So, the question remains, is there an advantage for using a 24V control voltage / loop with relays to control the contractor or simply use a 120V control voltage with an e-stop switch rated for 120V?

regards,
Michael

[Al_The_Man]

The 24v is advantageous because of the safety factor, the small control relay contacts for switching the various monitored functions, including a high current contactor coil.
BTW, these contactor coils can be replaced easily to low voltage versions if needed.
Al.

[mhackney]

Thank you Al, that's what I thought. I don't really like the idea of 110V going through an e-stop button that I press!

I think I am going to go the 24V circuit route and use an ice cube relay and the 24V version of this contactor.

Thanks for the help! I'll post back when the parts are in and wired up.

cheers,
Michael

[mhackney]

Jeese, now I'm confused on what the purpose of the 4PDT relay is? I ordered a 24V contractor. Wouldn't the 24V volt wire this in directly with the e-stop and limit switches, etc?

Michael

[Al_The_Man]

The I.C. relay is to do the low level switching, and then switch the contactor for the High current devices, AC motors, Spindle etc, you could use the contactor itself if you fit a 24v coil, but in all probability you will need a clip-on auxiliary contact block on the contactor for various function such as advising Mach etc.
Al.

[mhackney]

How does one setup the 24v power supply so that it comes on and stays on during an e-stop so the system can be reset? Do folks typically use a 24 V wall wart type of supply on a different (non e-stop protected) circuit?

cheers,
Michael

[Al_The_Man]

See the Category 2 diagram.
A retaining contact is used on the relay to maintain the start/reset button.
Also http://static.schneider-electric.us/...0140CT9201.pdf
Al.

[mhackney]

And this is why you are called "Al The Man"! Thank you Al.

I've ordered my components. I'm putting all of the power supplies and gear in a separate box and all of the low voltage control stuff in a separate box. I currently have everything in 1. All I need to do is move the 48V power supply and a couple of wall warts. I still need to get a wall wart for the 24 V safety circuit but those are easy to find.

cheers,
Michael