Powerflex 70 Braking Resistors Red Hot

Hi, have an issue with a Powerflex 70 that has been installed with braking resistors. The resistors are sitting at 200 degrees Celsius. The motor being driven by this inverter is a vibrating conveyor that runs continuously 24 hours a day without stopping. Have checked parameters 161, 163, 145 and 155 and they appear to be correct. There is a identical machine whose resistors are 30 degrees Celsius. Have compared the important settings and they appear the same. The problem inverter shows a constant fluctuation of drive current between 10-16A over a second or two. The healthy inverter shows 10-11A. Online the diagnostic menu shows Input Phase loss at a value of 32000 and flashes yellow. The healthy inverter has a value of 2000 at this parameter. Have checked input voltage and all stable on three phases. Output current when measured near the motor (clip on ammeter) shows no fluctuation and is steady on all three phases.

Is it possible it could be the motor/physical mechanics causing this to happen? Both inverter and resistors were replaced a couple of months back and looks like the heat has been there a while as the panel wiring has become brittle. Resistors are identical in both machines.

What is the DC Bus voltage? Are the resistors rated correctly?

What kind of vibrating conveyor ? There are many different types.

If the conveyor is driven by dual symmetrical unbalance agitators, then there is usually no regenerative power in normal operation. When stopping there can be very significant regenerative power.

If the conveyor is driven by a motor and a mechanical excentric link, then the conveyor can alternate between being driven and driving when it goes from up-stroke to down-stroke. If possible you can possible get the VFD to just absorb the energy if you lower the DC voltage. This so that there is more reserve between the up and downstroke.
If that is not enough, you need a bigger resistor.

Are there more than one motor on the conveyor ? If so, are both driven by the same VFD ? If not, one motor can drive the other and cause regenerative load on the other VFD.

Does the problem conveyor move smoothly ? It could be that it has hit a resonant frequency. This can cause all kinds of problems, incl. the current fluctuations you see and that it sometimes is generating regenerative power.

Is it possible that due to some mechanical linkage, the conveyor is being driven by some external force ? In that case it constantly tries to brake the load.
edit: Such a 'linkage' can even be through the foundation of two neighboring conveyors.

Some great suggestions, thanks. There are two identical machines next to each other. One has a problem the other does not. I will have to check the physical conveyor for neighbour interference. Although 100% identical the conveyor on this one has been repaired in the past (mechanically). One machine was a constant 47Hz and the other one 49Hz (no stopping or accel/decel all day/week long). I could change the freq on the bad one to match the good one?

Is the DC voltage is an editable parameter? I do not have online access at this moment as the machine is in a remote factory. I see parameter 12 is a read only value for DC. Should I be able to lower this in a Powerflex 70?

SCUBA NooB said:

One machine was a constant 47Hz and the other one 49Hz (no stopping or accel/decel all day/week long). I could change the freq on the bad one to match the good one?

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2 Hz difference can mean a lot. Going slower usually means that stroke gets greater, and greater possibility that the conveyor drives the VFD on the downstroke.

SCUBA NooB said:

Is the DC voltage is an editable parameter? I do not have online access at this moment as the machine is in a remote factory. I see parameter 12 is a read only value for DC. Should I be able to lower this in a Powerflex 70?

Click to expand...

I dont know PF70. Other VFDs I know you can specify the DC voltage.

Repeat:

JesperMP said:

What kind of vibrating conveyor ? There are many different types.

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Btw. usually the manufacturer specifies the operating frequency or permissible range of the operating frequency.
Same with the unbalance weights (if this kind of conveyor is used). There is usually a max value these can be set to.
Vibratory conveyors are notoriously iffy of operating within certain parameters. If you try to go outside these, you will very likely have breakages sooner or later.