VFD -leave in standby or wire in a switch

I like to use a cut off switch on my VFD's and a power light. Many machines don't get used often enough to leave them on all day every day when I am only working in my shop on the weekends and might or might not be using a particular machine. When the shop lights go out the power lights make it obvious that something still has power. To me a cut off switch is a lot more convenient than pulling the plugs or cutting the breakers that are not very conveniently located. Before the cut off switch and power indicator I would pull the plug after every use so I wouldn't leave the VFD running... that was a pain in the rear!

If I used a machine on a daily basis I would have no problem leaving the VFD's powered.
 
Reddinr said:
BTW I also unplug the coffee maker, toaster, turn off all satellite boxes, computers etc. when we're on vacation. I have only a little trust in the quality and the safety, of these "throw away" things. So I probably am a little biased on this subject.
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Don't forget to turn off the main water supply too
 
Sorry this got long...

Not all but most drives that include these large capacitors include a soft start relay / circuit to reduce the inrush current when first turned on. It is there to both avoid nuisance tripping the input circuit breaker/fuses and to go easy on the electronics of the drive. I don't know for sure about the lower-end drives. The little 3HP Asian-made drive I have on my mill has one. I have seen more than one piece of electronics end its own life when first turned on. I wouldn't say that is the cause of the failure though. There was very likely something in there that was nearing end of life anyway. For me, a failure while I am there and can react to it is better than if the failure happens with no one around.

The three main things that affect the life of the electrolytic capacitor are voltage, ripple current and temperature vs time. Ripple current is a factor of the design and application of the drive and really just leads to higher inside temperature so it is just two main things remaining that we can control, voltage vs time and temperature vs time.

The other thing about these capacitors is that they degrade just sitting there. There is an argument that keeping the power on could keep the VFD internal temperature slightly warm and keep some moisture from condensing on the capacitor, maybe helping its lifetime. The biggest factor in life-time is temperature times time. Assuming that the drive is well designed and sized properly for the motor, keeping the drive cool by mounting it with plenty of ventilation in a reasonable ambient (and protected from too much moisture) is the biggest deciding factor in its reliability. Turning it on/off daily or leaving it on shouldn't be the largest factor in reliability as long as your power system does not have significant over-voltages on an ongoing basis.

Good idea about the water supply too martik777. I once had a water-heater let go and leak for about a half day. Fortunately, just the garage was a mess.
 
All of the VFD's I have are soft starting... ramping the rpm's up over a period of time. I think this is one of the reasons VFD's can be made for so cheap these days... by implementing soft start they greatly reduce the max amount of current needed to start a motor. Which should be both good for the VFD's and the Motor.

I do not believe that most VFD's have huge capacitors to provide a huge bank of current to call on for starting motors. I believe the capacitors used are only there to smooth out the DC current coming from the rectifier.

My rotary phase converter DOES have a large bank of starting capacitors that are used to supply that huge inrush current used to get a motor moving. I recall having to use 480v starting caps in my RPC as the 240v caps I used initially kept popping.
 
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It is the smoothing capacitors I am discussing. The soft-start circuit I'm talking about (or lack there-of) is different than the motor ramp-up. It is responsible for charging the one or more capacitors on the rectifier's DC side with a controlled current when the input power is turned on. The motor ramp-up helps keep the current stresses on the switching transistors low and does allow for a smaller DC bus capacitor bank to some extent too.
 
Those RPC voltages can get unbalanced. I have one that has a high leg that runs about 260 VAC or so when it is not loaded with a motor to drive. Some of the caps in the RPC are to get the RPC motor spinning and others are to help form the third phase leg by providing a reactive load to the RPC coils.
 
Though I agree with the practice of leaving VFDs powered up, I've added E-stop mushroom buttons to my lathe and mill, both of which use VFDs. The one on the lathe is mainly there for safety. It's located at the tailstock end, just in case I can't get to the normal controls near the headstock.

As for the mill, I really don't anticipate needing an E-stop (much smaller rotating mass!), but did want a way to power down the 24VDC supply that's plugged in and "on" all the time. So I installed three sets of contacts on an industrial mushroom button. Two of them drop out the 240 volts to the VFD, the other one the 120 volts to the plug strip that serves the DC power supply, table drive, and some other accessories. I use the E-stop as an easy end-of-day shutdown. With the spindle stopped, the VFD draws very little current, and not much current on the 120 side, so I don't anticipate a lot of stress/wear on the E-stop contacts. Should last "forever."

In addition, I figger that regular use of the E-stops is "training my muscle memory," so that I know what to do in case of a real emergency.
[Muscle memory ... how a "meat head" remembers things :) ]
 
I don’t have any VFDs in my shop however I do have a static phase converter and it has an disconnect wired into the circuit. To me not having a circuit power up on electrical equipment wen not I use makes sense. Also it does provide some surge protection


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hman said:
Though I agree with the practice of leaving VFDs powered up, I've added E-stop mushroom buttons to my lathe and mill, both of which use VFDs. The one on the lathe is mainly there for safety. It's located at the tailstock end, just in case I can't get to the normal controls near the headstock.
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I seriously considered the emg stop& power to the VFD idea, But the idea of no power at the input, and the power generated by the still moving rotor concerned me that it might cause damage. It was before I found this place, but I asked on another machinist forum, and got flamed for the choice of VFD, and was told it was a dumb idea.

I did use the mushroom switch for the main power from the VFD, to control the stop/go/fwd/rev controls. After using it for a few years, I want to add the Potentiometer to add the variable speed option.

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