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VFDs and Emergency Stops

PaulL

PaulL

Technologist at Large
Premium Member
As per another thread, I've been refitting my power hammer with a 3-phase motor and VFD.
I'm glad I set this all up on the bench here in town before dragging it out to the cabin - it took me three trips to the hardware store to get the right spade connectors and other wiring sundries.
I now have the motor running smoothly, with a 20 second ramp in and ramp out - This should keep the solar install a little happier.
But that 20 second ramp down to protect my inverter worries me a bit in shop/heavy equipment land: It's not a very quick power-off.
So a question to all you VFD enthusiasts: What do you do for an e-stop?
I figure I can put a 20amp 2-pole shutoff on my supply, or I can do a three-pole shutoff on my 3-phase.
What's best?
 
Apparently killing the 3 PH side can do your VFD in. There should be a low voltage contact option in your VFD for ESD purposes. On my 3 PH mill conversion I have a light switch before the VFD as an VFD pwr on/off and a PA ESD switch wired into the VFD low voltage ESD contact.


canadianhobbymetalworkers.com

RF30 Basement Install

Well.... wasn't hard to disassemble. No centrifugal switch to disconnect. Lots of dust. The fan and fan cover cowling are plastic??? Should be able to do something with this. Just have to careful not to take too much off.
canadianhobbymetalworkers.com canadianhobbymetalworkers.com
 
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YYCHM said:
There should be a low voltage contact option in your VFD for ESD purposes.
Click to expand...
I've found the low-voltage contact option, and I was thinking of using it for the On/Off at the operator station - using a paddle/e-switch as you linked would do most of the job.
But that shut-down takes whatever spin-down duration is set up.
Or perhaps I should set "method to stop inverter" to "stop by itself" instead of "stop by deceleration".
The manual is a little, um, weak.
 
PaulL said:
I've found the low-voltage contact option, and I was thinking of using it for the On/Off at the operator station - using a paddle/e-switch as you linked would do most of the job.
But that shut-down takes whatever spin-down duration is set up.
Or perhaps I should set "method to stop inverter" to "stop by itself" instead of "stop by deceleration".
The manual is a little, um, weak.
Click to expand...

Don't think you want to use that PA ESD SW as an on/off, you will wear it out. Which VFD do you have?
 
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YYCHM said:
Don't think you want to use that PA ESD as an on/off, you will wear it out. Which VFD do you have?
Click to expand...
I have this one: https://www.vevor.ca/variable-frequ...p-cnc-motor-inverter-converter-p_010316855366

It looks like my best option for the time being is a single-pole/single-throw switch on the external stop line. That will still decelerate insteat of doing an immediate stop, but at least it's slappable, unlike the VFD front panel membrane button.

I have to convert the compressor as well, so I might get a better VFD with STO (Safe Torque Off) function for the power hammer and put this innexpensive unit on the compressor, which really doesn't need an e-stop.

Paul
 
PaulL said:
I've found the low-voltage contact option, and I was thinking of using it for the On/Off at the operator station - using a paddle/e-switch as you linked would do most of the job.
But that shut-down takes whatever spin-down duration is set up.
Or perhaps I should set "method to stop inverter" to "stop by itself" instead of "stop by deceleration".
The manual is a little, um, weak.
Click to expand...

Why are you using "stop by deceleration"?

My ESD SW is wired to a parameter called " Emergency Stop".
 
My VFD has a braking setting but no external resistor. I played around with the setting to figure out how quickly I could bring it to a stop. As it turns out it's not terribly fast as there's a lot of momentum in the spindle, pulleys and motor to try and slow down. If I set braking too fast it just goes to an over current situation and free wheels to a stop.
 
All VFD (at least the ones we use) have resistors built in dissipate the energy (as heat) from slowing a motor down. However to slow it down fast requires more energy absorbsion than those little resistors can provide. Some VFD's give the option to allow use external large resistors for this. Don't forget you are getting rid of the same amount of energy you put in on a fast start up in the same time frame.....lots of power.
 
On a previous inexpensive VFD I used there was a low voltage control specifically for an E-stop that would brake as quickly as (I assume) the VFD could handle. It was noticeable quicker to stop when I tested it than the usual power off command.

There should never be any disconnects between the VFD and the motor.

Higher end VFDs usually have have the option of an external braking resistor for quicker stops, I haven’t seen that on any of cheap ones I’ve used.
 
On my HAAS the 7.5HP spindle needs a big place to dump energy when you hit spindle stop or estop. When you press stop it STOPS. The energy goes into a coil that looks a lot like a stove element. It is on the top of the machine inside a metal box with ventilation holes. For my little 2HP vfd I bought the stopping resistor. It's a big coil resistor about 25cm long and 2 cm in diameter. Looks like an electromagnet. I think you need something like that for your trip hammer VFD - I guess like Rauce said assuming it supports it.
 
Here is the stop coil …
Look at the swarf up there!
 

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I have two VFDs one with a braking resistor and one without. The one with the braking resistor unspools very quickly, at least 10x faster than the original single phase motor. Pleasure to use, I need to get around to installing a resistor for the other one.
 
I'm going by memory here @PaulL - a dangerous thing in my 70s.

As far as I know, the Teco L510 I installed on the 2HP 220 3ph motor on my mill does not have connections for an external braking resistor. The 600V version does. I would not describe the Teco as an economy VFD, but it prolly isn't top of the line either. It is a highly recommended unit.

Mine does have internal braking though and it is fairly fast. I have it set for 4 seconds at 60hz. It is proportional so at 120hz it would be 8 seconds and at 30hz it would be 2 seconds. I have never tested it at faster braking, perhaps it could be faster.

I would expect that high inertial loads (such as a big chuck and big part on a lathe or a flywheel system) might reduce the maximum braking rate significantly. A mill spindle is not a big challenge.

I like your idea of switching your current VFD to your compressor and getting a better one with external braking for your mill. It might be worth a call to emotors support to see what the limits are for internal braking and which models support external. I'd be interested to know what you learn from such a call. I have found their support team to be very good and very responsive.
 
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Ok, got the motor out to the property, got it on the machine, wired up, and....nothing. lol. There were words.
Took the drive belts back on and it comes up. Stare at the manual in despair.
Eventually find the 3 settings to do with "Torque Compensation". Hmm. No units, just a number from 0-4 "bigger number may damage motor". And then clues kicked in - I still don't know the units, but it cranks the voltage at low revs, and I get to decide where high revs is. And now I have a working power hammer that my battery bank says is drawing 1.4Kw. I can live with that!
 
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