# PowerFlex 40 Not power up ( no display)



## amperee (Sep 23, 2015)

Hi all,

I am new here, hope can get some help about the PowerFlex 40 VFD have no display, I already check line voltage and fuses, have power feed to the drive, but still not power up, please help.


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## Black Dog (Oct 16, 2011)

amperee said:


> Hi all,
> 
> I am new here, hope can get some help about the PowerFlex 40 VFD have no display, I already check line voltage and fuses, have power feed to the drive, but still not power up, please help.


Bump!


Welcome to the forum amp.:thumbup:


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## triden (Jun 13, 2012)

Are you using single phase or three phase line configuration? If single, make sure you are using L1 and L2.


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## JRaef (Mar 23, 2009)

amperee said:


> Hi all,
> 
> I am new here, hope can get some help about the PowerFlex 40 VFD have no display, I already check line voltage and fuses, have power feed to the drive, but still not power up, please help.


Is it brand new out of the box, or was it working fine and now it stopped, or did you buy it used and are just discovering the risk of buying used equipment?

The PF40 does not have any internal fuses, the power supply for the electronics is taken directly off of the DC bus. So either you have a dead power supply board, or your DC bus is open. There are terminals for DC bus on the drive, marked DC+ and DC-, so using an appropriately classed meter set to DC, capable of the appropriate voltages involved (see below), you can read the DC bus level. 

If the VFD is 230V, the bus level will be around 310VDC
If the VFD is 460V, the bus level will be around 635VDC, so make sure your meter is safe for up to 1000VDC before connecting it. Also realize that after you kill power to a drive, the bus caps (if powered) remain powered for quite a while after killing line power.

If there IS the correct power on the DC bus, you have a bad power supply board. If not, read on.

How that can happen is that you have a defective "pre-charge" circuit. In order to avoid having the inrush current from charging the capacitors cause damage to the caps or other components, there is a "pre-charge" circuit that places a current limiting resistor in series with the caps for a second or two when you first power up the drive, then the resistor is taken out of the circuit. On larger drives the resistor is removed via a relay contact that shorts around it, on smaller drives there is what's called an NTC resistor, where NTC stands for Negative Coefficient of Temperature. That resistor starts off with a high resistance, then the resistance drops as the temperature rises (negative coefficient). So it is a high resistance when you energize the drive, but that resistance drops to nearly nothing in a second or two. But if that resistor (or even the one that is shorted by a relay) is burned out, then NO electricity gets to the caps, and thereby the DC bus. No energy on the bus means no energy to the power supply, so no display, electronics etc., so "No VFD for you!"

If this was a used VFD or one you have had for a while and it just stopped working, the likely cause is that someone attempted to perform braking with the VFD, but without using the external Braking Resistor. The VFD can do a LITTLE BIT of braking by using that internal resistor mentioned above, because when not being used for pre-charge, it is also used to bleed off the capacitors safely. But the risk is, you burn out the resistor and end up with a dead drive. That resistor is not easy to replace, and the time it would take you is likely worth more than the cost of a new drive.

If this is a brand new drive out of the box that you purchased from an authorized AB distributor, return it for warranty replacement.


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## Mech247 (Apr 1, 2021)

amperee said:


> Hi all,
> 
> I am new here, hope can get some help about the PowerFlex 40 VFD have no display, I already check line voltage and fuses, have power feed to the drive, but still not power up, please help.


I know this is old, but for those that experience this, it usually happens after the drive or cabinet has had power off and things cool. A heat gun will revive these problematic drives (or many other electronics with the same issue powering on when cold). It will continue to behave this way each time it cools and you want to power it back on so it is something you will want to replace but, in cases where you need to transfer the parameters or need to get it going in a pinch, heating the drive will only take you a fraction of the time to get it going. Then you can work on transferring parameters to a new one after getting it going again.


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