Help with VFD E-Stop

[rbertalotto]

A few months ago I decided to convert my milling machine to three phase using a 220v single phase to 220v three phase inverter. I bought a very popular inverter off Amazon. Wired it up and it is an amazing improvement to my shop. I liked it so much I just received the exact same components to convert my lathe. I have no issue using the control panel to operate all the functions I want by mounting it remotely. But I need some type of emergency stop as the "stop" button is way too small for an emergency situation. I ordered an E-Stop module from Amazon. But try as I may, I can't figure out how to install it to effectively stop the machines in an emergency. The switch itself is rated 200v/3a so with the VFD drawing around 9 amps, I can't just insert it into the power wiring. I'd rather not incorporate a magnetic relay/switch. So I want to connect it via the VFD but still have control of the attached control panel functions. Can anyone explain to me how to accomplish this. Thanks!

 

[rbertalotto]

Thinking about going this route using the 15V output on the VFD....

SSR-25DA solid state relay 3-32v dc/24-380v ac/25a Features:
This is Solid State Relay SSR-25DA 25A /250V 3-32VDC.
Input voltage: 3-32VDC
Output voltage: 24-380VAC
Output current: 25A
Working voltage: 250V
On voltage: ≤1V
One-off Time: ≤10ms
Off leakage Current: ≤2mA
Color: White
Item size: 60*45*23mm
Net weight: 98g

 

[markba633csi]

I believe that a truly electronic stop isn't the safest or most reliable way to go, although many do it that way.
The VFD could fail in such a way (theoretically) that it would be stuck on and wouldn't respond to the button.
Personally I would use a latching mechanical relay on the input side- which would require a start button as well.

Anyhow, it should be possible to connect your button to one of the control inputs of the vfd and make the appropriate
programming changes to enable it- consult the manual. Post a link to it if you can so we can take a look

 

[rbertalotto]

I have no idea how a solid state relay could fail in the “on” position. My understanding was this was why you used a solid state relay…

 

[rbertalotto]

Using the VFD as an emergency stop add a number of areas for failure. Im of the opinion that in an emergency you want EVERYTHING disconnected.No?

 

[Cadillac]

For the estop you should just have to break contact with the for/rev circuit. Or your inverter might have a estop circuit that will allow you to adjust decel times. You want to watch how quickly you stop the spindle can affect vfd. I believe you add a brake resistor if you have problems.

 

[Ischgl99]

Your VFD probably has an input you can program for your emergency stop button, but as Mark says, that is not a safe way of using an e-stop, a proper e-stop will isolate the VFD from the lathe. You don’t want to put a contactor on the wiring to the motor, you should put one on the input wiring to the VFD that will cut power to the VFD when you press the e-stop.

There are two schools of thought on e-stops, coast to stop, or controlled deceleration and then isolating the VFD. Which you use is up to you and how much risk you are willing to take. The machines as they come from the factory are coast to stop, unless you activate a brake. If you want a controlled stop as fast as possible, you will need a braking resistor for the VFD, trigger the e-stop input to the VFD, then once it reaches zero speed, open the input voltage contactor to kill power to the VFD.

 

[mksj]

Two difference purposes of an E-Stop, one is a fail safe to prevent a machine from being functional (run state on), the other is to stop the machine as fast as possible to minimize injury, this includes in some cases a destructive means (like SawStop). In most hobbyist machinist cases or single user, one wants to stop the machine as quickly as possible and also deactivate run controls as well as prevent a restart situation. In some case both methods can be achieved in that one can uses a contactor on the power in side, which drops out when the VFD is at 0 speed via the programmed inputs or one can use the Safe Torue Off (STO) function which is in most newer (not generic VFD's). Solid state relays do typically fail in the on position and also in the off position they still have some leakage, a contactor would be a better choice if used in that configuration.

External braking resistor (if supported) can significantly shorten the stopping time, older/generic VFDs tend to not have programming features that prevent an over voltage buss fault that can occur if the braking is set to aggressively or high momentum loads like in lathes. Newer VFD's have programming features which provide controlled fast braking without an over voltage error (i.e. the braking rate is controlled to maximize braking but not cause an over voltage error). Some VFD's have a programed emergency stop input with a separate deceleration rate and also will not allow a restart unless all run commands are cancelled (this include 2-wire control).

Dropping out the VFD power is not consistent with fast stopping if that is the goal of your E-Stop, otherwise if working on the machine for safety reasons disconnect the power, or if you want to prevent the possibility of a run command then disconnect the run commands (activate the STO) with the E-Stop, but beware that if you are running 2 wire control the machine can restart when you release the E-Stop. Frequent on/off/on cycling of the VFD can/will cause the inrush circuit to fail.

Example of the importance of a fast stop feature w/o a VFD buss over voltage error, my mill normally stops in 3 seconds, the other day running it at high speed (4500 RPM) with a heavier keyless chuck, on stopping it went into an over voltage error and took about 20 seconds to stop. Had this been an emergency stop situation it would have not been very good. First time this has occurred, but represents a significant issue that I need to address. This would be even more serious on my lathe.