# VFD -leave in standby or wire in a switch



## martik777 (May 11, 2019)

When I press stop, my VFD remains in standby (Can't find any settings to change this). How much current does a VFD typically draw in standby? I guess I could wire in a switch but seems like a pain to have to press stop AND flip a switch when you are done for the day.


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## Bob Korves (May 11, 2019)

I added a wall switch to turn off the VFD.  I do not find it a pain to turn it on at the beginning of a day's use and then turn it off at the end of the session.  If the machine was being used every day, I would probably just leave it on.


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## JimDawson (May 12, 2019)

martik777 said:


> When I press stop, my VFD remains in standby (Can't find any settings to change this). How much current does a VFD typically draw in standby? I guess I could wire in a switch but seems like a pain to have to press stop AND flip a switch when you are done for the day.



Very little.  I have 3 that are on continuously.  My power usage in my shop as I write this is 554 watts.  That includes 4 VFDs, 3 computers, 3 CNC control systems, lathe DRO, various battery chargers, and a refrigerator (which just happens to be running at the moment).   The VFDs are a very small fraction of that.

On the other hand, just shutting down my CNC lathe requires more than just flipping one switch:
In this case the spindle VFD is shut down at the end of the day.
Press E-stop, shuts down servo drives and puts VFD into E-stop mode
Press Control Power Off, shuts down hydraulic pump and a couple cooling fans, removes power from a couple other systems
Flip the Main Cabinet Disconnect to Off, removes main power to the lathe, turns off a couple more fans, but leaves the computer and control system up
Press E-stop on the RPC, shuts down the RPC, leaves the RPC startup VFD, and control system hot.

So flipping an extra switch at the end of the day isn't terrible.


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## 4ssss (May 12, 2019)

martik777 said:


> seems like a pain to have to press stop AND flip a switch when you are done for the day.



That statement says it all


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## Reddinr (May 12, 2019)

I switch them off.  Most times drives are designed such that leaving the power on leaves the input bus capacitors powered up and that leaves the high voltage DC applied to them and to the power transistors (340VDC at 240VAC input).  That does take very little energy.  There is also some small power draw by the electronics.  The bus capacitors are likely the single least reliable component in the drives if other components are designed in with similar margins.   I assume that the hobby grade drives have to be designed close to the edge so they can be low cost and therefore use components closer to their ratings than an industrial drive might.  So, it is likely that turning off the power for 50% of the time or more would increase the input bus capacitor lifetime since the capacitors are not charged to close to their max ratings for as long.  Also, taking them offline would _somewhat_ isolate them from power surges at night, like those induced onto the power lines by nearby lightning storms.  When they do fail, usually these capacitors fail in a reasonably well behaved way but not always.  This is why I switch mine off at night.  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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## Splat (May 12, 2019)

I pull my VFD's plug from the wall outlet.   Works for me. I don't want to leave it on, even in standby.


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## Buffalo21 (May 12, 2019)

The ones I work with everyday, on the boilers, pumps and fans are on 24/7/365, some setting in standby mode for weeks at a time, so I see no difference at home, I just leave them on. I switched over to 100% led lights in the shop, I haven’t turned them off in about 5 years.


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## CluelessNewB (May 12, 2019)

I have a switches on mine.  I may go weeks without using a specific machine.  It's not much but why waste the energy.  I also unplug unused wall warts.  Every penny I save can buy tools!


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## Bob Korves (May 12, 2019)

I find that if I watch the pennies, the dollars (and hundreds and thousands) take care of themselves...


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## Superburban (May 12, 2019)

Is it  better for the capacitors to stay powered up, or turned on and off daily? Or another way to phrase the question, is the life of the capacitors more affected by cycling on and off, or by the time it is on?

I read many years ago, that it is the cycling on and off that is the bigger factor, so most of mine have been on for over five years now.


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## MikeInOr (May 13, 2019)

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.


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## martik777 (May 13, 2019)

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.



Don't forget to turn off the main water supply too


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## Reddinr (May 13, 2019)

_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.


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## MikeInOr (May 13, 2019)

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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## Reddinr (May 13, 2019)

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.


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## Reddinr (May 13, 2019)

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.


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## hman (May 15, 2019)

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  ]


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## jdedmon91 (May 15, 2019)

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 


Sent from my iPhone using Tapatalk


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## Superburban (May 15, 2019)

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.


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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