# Powerflex 400 won't shut off



## just the cowboy (Sep 4, 2013)

The first part of the problem I could understand, wrong side of shield hooked up voltage induced on wires holding in circuit or control not a real dry contact, some type of solid state relay. I have seen inputs not turn off due to leakage.

BUT as for outside vs inside no guess.


----------



## pjholguin (May 16, 2014)

What is the voltage on the line to the dry contact? Is it DC?



eesnerd said:


> We have a Powerflex 400 VFD driving a 40 hp submersible well pump on an ungrounded delta 480-Volt system. The well is 700 feet from the drive and we have a dv/dt package installed. The drive is started from a dry contact in another building over about 100 feet of twisted pair, shielded cable with the shield grounded at one end. When we started the system up, it worked fine but would not shut off. It could only be made to shut off if the dry contact were replaced with 120 Volts operating an ice cube relay stuck inside the VFD cabinet, using the dry contact on the relay. I tried mounting the relay just outside the VFD cabinet and it again would not shut off. Anybody have a problem like this?


----------



## Wiresmith (Feb 9, 2013)

is it really ungrounded delta or corner grounded or high impedance ground?


----------



## JRaef (Mar 23, 2009)

On an ungrounded delta system, you would have had to pull the ground reference jumper off of your PowerFlex drive (or SHOULD have). When you do that, you lose some of the benefits that provided, one of which is a safe place for common mode noise created by the drive to go to. So now you likely have a lot of CM noise bleeding all over everything, and in 24VFD circuits, that can sometimes create enough energy to keep a signal high once it has GONE high, meaning it in essence "latches" in. The noise isn't enough to energize the circuit, but it's just enough to KEEP it energized.


----------



## MDShunk (Jan 7, 2007)

Wouldn't be the first time someone thought they had a dry contact and actually had a solid state relay or solid state output. Takes a bit of a real load to turn them off.


----------



## oliquir (Jan 13, 2011)

maybe just a small load ( 2-3k resistor) on the vfd input could eliminate the noise on the 24v input of the vfd.


----------



## paulengr (Oct 8, 2017)

You are getting inductive pickup on the signal cable. Either from the floating drive or could be basically anywhere since ground is sometimes a conductor, sometimes not. This is why ABB basically says their drives don't even worm on ungrounded deltas.

I have no problems with resistance grounds but an "ungrounded" system is grounded butt it's grounded through system capacitance. It will be flaky operation forever. Insurance companies (particularly Factory Mutual) has all but banned them. Every arcing or nonarcing fault is coupling AC or DC onto ground too which bleeds everywhere. And if the drive isn't at least grounded to the motor no matter what the line side is as per ABs installation requirements you are puking common mode noise and RF everywhere and especially DC inputs will do all kinds of strange things.

Do a visual check. Then take a spool of wire, say a box of CAT 5. Measure resistance of the spool. Now use it as a multimeter led extension and measure resistance from the motor frame to the drive ground. If the resistance of the full loop (motor to drive, and returning back through the spool of wire) is more than twice the resistance of the spool, you have a bad ground. No substitutes with drives.

Follow the IEEE color book standard for low voltage control signals. PM me if you need it.

Sent from my SM-T350 using Tapatalk


----------



## eesnerd (Apr 4, 2018)

Thanks for the suggestions. The dry contact is a contact of an ice cube relay and the jumper is in fact pulled. The comments about common mode noise make good sense and, over the next week or so, I'll try loading the input or adding a common mode filter such as a pair of small capacitors. There is a #6 dedicated grounding conductor in the pipe to the motor, but I can't verify the connection at the motor end, so I might try the multimeter extension.

This is my first appearance here and I'm impressed with the depth of all the responses. I'll be back.


----------



## mikey383 (May 21, 2012)

I've seen this same issue with a triac output card and an Allen-Bradley 700-HN121 relay. When the output turned off, the relay stayed energized. The leakage current is enough to keep the relay coil energized, but once the relay was removed from the base, there wasn't enough current to energize it unless the output was re-energized.

Changed the relay to a larger one, and haven't had the issue since.


----------



## micromind (Aug 11, 2007)

mikey383 said:


> I've seen this same issue with a triac output card and an Allen-Bradley 700-HN121 relay. When the output turned off, the relay stayed energized. The leakage current is enough to keep the relay coil energized, but once the relay was removed from the base, there wasn't enough current to energize it unless the output was re-energized.
> 
> Changed the relay to a larger one, and haven't had the issue since.


The A/B HN-121 is a socket, I bet you meant a type HK relay. 

The coil current of an HK relay @ 24 DC is about 20 mA. If it's 120 AC, it'd be about 10 mA. 

It wouldn't take much leakage to keep the contacts closed........lol.


----------



## mikey383 (May 21, 2012)

micromind said:


> The A/B HN-121 is a socket, I bet you meant a type HK relay.
> 
> The coil current of an HK relay @ 24 DC is about 20 mA. If it's 120 AC, it'd be about 10 mA.
> 
> It wouldn't take much leakage to keep the contacts closed........lol.


You're right. I keep getting those part numbers confused for some reason. 

I think it was a 700-HA series that I replaced it with.


----------



## micromind (Aug 11, 2007)

mikey383 said:


> You're right. I keep getting those part numbers confused for some reason.
> 
> I think it was a 700-HA series that I replaced it with.


Those are the tube-base relays w/10 amp contacts.....they might be 15 though, can't remember.

Those coils take a bit more current so leakage isn't much of a problem. 

Another problem I've had with the HKs is if the wire for a 120 AC coil is run in the same pipe as 480 for a long distance, capacitive coupling will cause it to not drop out when de-energized.


----------



## mikey383 (May 21, 2012)

micromind said:


> Those are the tube-base relays w/10 amp contacts.....they might be 15 though, can't remember.
> 
> Those coils take a bit more current so leakage isn't much of a problem.


Yep, those are the ones. I used the HKs on several drives that I installed up until that issue happened. It worked fine for a year or two, then suddenly the drive wouldn't stop. I've been using the HAs since then, unless it's being controlled by a relay output card.


----------

