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VFD auto restart after load disconnect

solvej

Feb 23, 2022
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Feb 23, 2022
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My VFD has arrived and I got the 3 phase well pump running, driven by solar / lion battery. The VFD gives the pump a soft start, which works good. The pump has a water pressure switch build in, so that when 5 bars is reached, the pump disconnects the power line. When water is used and water pressure falls below 4 bars, the power is reconnected. Problem is that this reconnect creates a huge peak current which causes the battery manager to disconnect the battery. (So far I've only build one of the 6 battery packs.)
I'm looking for a way to setup the vfd so that it will soft start when pump reconnects. I've come up with several ways that did not work.
1) Set "U0-65: Upper torque limit".
Problem is that battery manager disconnects faster than the VFD is able to limit the current.
2) Turn down the max voltage and frequency. (The relation between the two is currently linear. This can be changed.) The minimum voltage/frequency needed to reach 5bar is 175V/39Hz. Setting this as max values, still triggers the battery protection when pump reconnects.
3) Make the VFD stop when pump disconnects. Then restart at some time later. Either after a time delay or at load detection. I haven't figured out the settings to do the resume. The settings I have done is:
p9-49 Fault protection action Load becoming 0, Err30: 2 Continue to run at 7%, resume to set frequency if load recovers (This setting seems to do nothing)
p9-63 protection on load becoming 0: 1 enable (If this is not set, the output stays at set voltage and frequency when pump disconnects, no error is displayed)
p9-09 fault auto reset times: 20 (This seems to do nothing)
p9-11 fault auto reset delay: 25.0s (This seems to do nothing)
To my mind, if either of p9-49 or {p9-09 and p9-11} did what the instructions say, my problem would be solved. I suspect that there is a setting somewhere that needs to be set in order for the others to take effect. (That has been the case with other settings I've done.) Does anyone have an idea of what that could be?

The vfd in question is the Nflixin 9600 2.2kw
http://nflixin.com/en/?p=103

Function list as pdf is too large for file upload. It can be found in the download section of the nflixin website.
 

Bluejets

Oct 5, 2014
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Motors draw large current on startup, well known fact.
Limit the power available during this time on this particular motor may do damage to the windings.
 

solvej

Feb 23, 2022
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Feb 23, 2022
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That's true. But still, a motor that runs for a while before it breaks down is more useful than a motor that doesn't run at all.
I've set p0-19 Acceleration/Deceleration time unit = 0.01s. That is the shortest possible acceleration time, and it is enough to not introduce the startup current issue. If I could make the vfd willing to resume after load is reconnected, either by detection or timer, I think this thing would be able to live without human interaction.
 

Tha fios agaibh

Aug 11, 2014
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I would make pressure switches control the start/stop commands and not disconnect line power to the drive.
For safety you can add a high pressure switch to kill power, but use your 4-5 bar PS for the forward enable cmd.
Then put your Acc/Dec back to about 0.5s to limit current.
 

solvej

Feb 23, 2022
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I would too. But it is build into the pump. I can't access it.
 

Minder

Apr 24, 2015
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Disconnecting the VFD defeats the object of the soft start.
The input to a VFD is a 3ph bridge rect followed by very large bank of capacitors, at switch on these are a high load across the supply, defeating any ramp-up setting in the VFD.
.
 

Martaine2005

May 12, 2015
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Not sure what’s going on here but would thermistors be able to clamp the inrush current?

Martin
 

solvej

Feb 23, 2022
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I think the setting
p9-49 Fault protection action Load becoming 0, Err30: 2 Continue to run at 7%, resume to set frequency if load recovers
sounds exactly what I need. Just that it doesn't do anything except for changing the display from "Err30" to "A30" when load disconnects, and it keeps a out voltage at about 2V. So it seems to do the first part - Continue to run at 7%. But it does not resume when load recovers. I wouldn't be surprised if there is another setting somewhere that is stopping that from happening, If so, my issues will be solved by finding that setting (which I haven't been able to). If not, I'll probably need to install another pressure switch to control the vfd that responds on a lower pressure than the one build into the pump.
 

Tha fios agaibh

Aug 11, 2014
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How is it wired? I would expect the pressure switch to turn on a 3 pole motor starter in an accessible location.
 
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