Phase loss error when motor stalled

Hi guys just a quick question,

Is it normal for a stalled motor to produce a 'PHL' error, which is phase loss according to the manual, or have I got something weird going on here?

It's a .75kW 3ph motor in a wood lathe, 1.5kW delta VFD-B drive. I reset it and it carries on fine but seems to be repeatable.

JoshNZ said:

Hi guys just a quick question,

Is it normal for a stalled motor to produce a 'PHL' error, which is phase loss according to the manual, or have I got something weird going on here?

It's a .75kW 3ph motor in a wood lathe, 1.5kW delta VFD-B drive. I reset it and it carries on fine but seems to be repeatable.

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Long before comprehensive building monitoring systems were common - and one of the reasons they BECAME more common, we'd lose several HVAC system blower or compressor motors every year from a "dropped phase" condition. ONE phase would get a trip-out on a breaker not ganged, or on a fuse. Near-miss lightning - local overload - wotever.

If the motor was running, it might carry-on for a long while, might "cook" itself. Or not. Some didn't fail for months - not until next off-cycle when it tried to re-start.

Look for the underlying cause. You are dealing with a symptom.

Due to the low power, and power ratio, I suspect this is used with single phase input. If so, you may need to fool it by connecting one wire to two input phase terminals.

If working from 3 phase, you may have a legitimate phase loss on the input. The unit thinks so, anyhow.

Look at wiring.

It is a single phase input I should have clarified. I have 240V live and neutral connected across L1 and L2 as the manual calls for when connecting to single phase. Are you suggesting to tie L1 and L3 together?

It actually isn't a problem, I rarely stall it. Just wanted to be sure nothing funny is going on

I am assuming this is a 3 phase input VFD and it is being used in single phase input with it derated as such. My understanding per previous discussion with Yaskawa on their VFDs in this application, is that the phase loss detection circuity kicks in when you exceed its rated current operating in this mode. So if you stalled the motor, you would get a phase loss error on their 3 phase input VFDs with single phase input. I am not aware of what parameters are monitored to trigger the error, but it occurs based on the load and possibly THD. Some VFDs cannot be run with single phase inputs as the detection circuitry is for each phase. With the Hitachi VFDs, they indicate that a jumper may be needed between L2 and L3, with L1 and L3 being used for single phase input connections in their derated mode.

On a related matter, I was wondering if some of our veteran VFD experts could comment if it there would be any benefit if one were to use two additional input diodes (sized accordingly) from each leg of the single phase input terminals, and each diode going to the unused 3rd phase terminal on the VFD (i.e. Y connected). In this manner, the input load of L1 and L2 would each be shared with L3, and may prolong the input diodes life?

mksj said:

On a related matter, I was wondering if some of our veteran VFD experts could comment if it there would be any benefit if one were to use two additional input diodes (sized accordingly) from each leg of the single phase input terminals, and each diode going to the unused 3rd phase terminal on the VFD (i.e. Y connected). In this manner, the input load of L1 and L2 would each be shared with L3, and may prolong the input diodes life?

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A "Veteran VFD expert" and I am not he, might agree unplanned thermal stress imbalance from "cold" eg; unused, modules of the diodes in a packaged array might indeed see less stress if put to work.

HOWEVER.. VFD don't necessarily operate all the same way, so, really... if the MAKER does NOT specify that be done as part of the de-rating for single-phase use, best to not second-guess them.

Were it that simple to gain a benefit, they'd either have already built it in as a strappable option, or would be selling an already-packaged option kit.

The stall could be a cause or a result. Do you know which?

The phase loss often senses ripple voltage on the bus, so a stall could do that, although the thing should not be able to do that, it should not get that ripple voltage at max current.

If it shuts down for .ripple voltage that will stall it, of course.

Might have a bad solder joint on a bus capacitor, or just a bad capacitor.

If it is rare, don't worry for now. Or reduce max current setting a bit.

It happens when I dig the chisel in, definitely a cause. I tried it more out of interest to see how everything behaves. I can have it peeling 1/4" shavings barely turning and it's happy, but the moment I bring it to a halt the error is thrown. I don't think it is reaching its current limit or it would throw an overcurrent error wouldn't it? It is well over rated the drive would cook it happily if the rotor were locked I think.

The usual phase loss detectors are either a direct voltage sensor (no voltage on wire), or excessive ripple voltage on the bus.

A stalled motor can draw 5x to 10x the full load current, so it could draw enough to increase ripple volts , especially if there is a current overload delay, could be a race as to which trips first. 150% one minute, 200% two seconds, if there is any degradation or bad connection in the capacitors, could trip on ripple.

I wonder if it is something I should mention to delta then? I doubt I'll have any luck with the seller, I kind of took a chance with it being a Chinese seller and Delta brand.

JoshNZ said:

It happens when I dig the chisel in, definitely a cause. I tried it more out of interest to see how everything behaves. I can have it peeling 1/4" shavings barely turning and it's happy, but the moment I bring it to a halt the error is thrown. I don't think it is reaching its current limit or it would throw an overcurrent error wouldn't it? It is well over rated the drive would cook it happily if the rotor were locked I think.

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Welll. You just don't really want to be doing that, yah? Poor VFD is doing the best it can do to protect you from damned foolishness, whether by sensors or the blessings of Fairy Godmother Dust.

Stalling the motor is not a desired nor recommended mode of operation to begin with, any race or tribe of machinery.

Dasn't matter if VFD or naked 3-P ..or.. Caterpiggle diesel... water-power slipping a belt.... punkawalla man pulling a rope...

I just don't push it into an overloaded range.

The only PRIZE for that leads in the fullness of time to something called a "Darwin Award", and you don't REALLY want to "win" one of those!

JST said:

The stall could be a cause or a result. Do you know which?

The phase loss often senses ripple voltage on the bus, so a stall could do that, although the thing should not be able to do that, it should not get that ripple voltage at max current.

If it shuts down for .ripple voltage that will stall it, of course.

Might have a bad solder joint on a bus capacitor, or just a bad capacitor.

If it is rare, don't worry for now. Or reduce max current setting a bit.

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That's exactly what's going on here. The Delta drives, as many other do, use the ripple current as a way to detect a phase loss. But ripple current has a lot to do with the capacitor capabilities, so when the current goes above the recommended de-rating for single phase input, the capacitors can no longer support the DC bus and the ripple increases, triggering the phase loss.

In the Delta VFD-B series however, there is no "de-rate" formula from Delta, in fact this is what the manual says:

Do NOT connect 3-phase models to a 1-phase power source.

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I happen to know from direct experience with Delta however that they CAN work, but NOT with the "50% de-rate" as some VFD mfrs claim, they need a 65% de-rate (meaning motor FLA / .35) because of the way the capacitors are designed. So for a .75kW motor, you needed a 2.2kW drive. Now that you have already bought that 1.5kW drive, and if you are not inclined to try to use it somewhere else and buy the right size, you will have to live with this "unintended feature".

One thing you can try is to change the values of parameters 06-01 and 06-02, which are the "Stall Prevention" attributes; 06-01 is during acceleration, 06-02 is during running. The factory defaults are set for 170% of the programmed motor FLA. Because of your under-rated drive situation, you can lower that to something closer to 100% of FLA. What this does however is to automatically lower the output frequency in order to attempt to shed load. That may or may not have negative consequences to a machine tool operation, i.e. your cutting speed may drop really fast and affect the cut quality. It also may not actually work because it is a Constant Torque application.

The other thing you could do is to program the Over Torque settings (par. 06-03 thru 5) to trigger one of the the Muti-Function Outputs and connect it to a warning light, telling you that it is ABOUT to trip so that you can back off on your bite.

Side note: the MAIN issue with de-rating for single phase on any VFD is actually the CAPACITORS, not the diode sizing as many people seem to think. So "sharing" across more diodes does nothing useful in that regard.

This is not a three phase input model according to the number and manual at least. It is a VFD015B21A, which would imply 1.5kW 230V single phase input.

It doesn't sound like an unreasonable occurrence given what you guys are saying anyway

If rated for 1phase input, as seems to be indicated, that should not happen.

If overloaded, it should trip on current overload, NOT on bus ripple. I am just not understanding their rating system and protection... not done the way I would do it.

Turns out the stalling is a result of the phase loss error not the cause. I was burning along today with a deep but reasonable cut, turning a bit quicker than I usually do and it gave up.

I could pull the board out and inspect the solder joints around the capacitors, or replace them. Worth getting in touch with delta for a replacement?

See what they will do before oprning up.

If nothing, not much to lose. Let it sit 10 min no power if you do open it.

Will do thanks. I'm rewiring it today with some sheathed cable for two control panels I'll make sure everything's snugged up and looks right then get in touch with Delta after that. If I don't hear from them and nothing is amiss would it be worth reflowing? Worth replacing capacitors and diodes too? They'd only be a few bucks?

JoshNZ said:

Will do thanks. I'm rewiring it today with some sheathed cable for two control panels I'll make sure everything's snugged up and looks right then get in touch with Delta after that. If I don't hear from them and nothing is amiss would it be worth reflowing? Worth replacing capacitors and diodes too? They'd only be a few bucks?

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Can't do much harm if you've done it before, but I'd not expect any real gain, either, so...
"Too late now.." but the sort of wide-range of torque it sounds as if even diameter-of-cut is handing you, this wudda been a "natural" for DC drive with its great gobs of RESERVE torque.

AC+VFD is strongest at "base" RPM and above - neat for "carbide-ization" of older metal-turning lathes if their spindles will stand the RPM (as 10EE easily do).

Dee Cee is strongest base RPM, downward, just takes up the load, holds RPM, keeps on trundling. I've got my nominal 12 FLA 10EE's DC Drive set to furnish up to 24 A for up to 90 seconds, 16 A indefinitely, AND @ 120%+ of Armature nominal AND 120% of Field Power nominal to boot.

All that's for uber-stability, not for uber-hogging, but it sounds similar to what you NEED for wotever it is you are trying to turn.

Yes, if no help from maker, DO resolder caps. A bad connection absolutely will cause the problem. I may have referred to that earlier, don't recall.

I pulled the board out just to have a look while I was reconfiguring everything today and the capacitor bank comes off in a modular strip, would be a piece of cake to work on. The terminals were covered in silicone so couldn't inspect them but I'll know for next time. Would replacing caps with higher cap value help at all?