[Newbie] VFD Undervolt Error with SVC

[mksj]

Specifications are for constant rated power, you need to account for overload which you have set to 150% which is typically 1 minute, shorter time frames it can be 200%. The VFD is probably trying to pull higher current and the more it tries the more the voltage sags and the higher the current drawn on the input wiring. Efficiency of the motor is lower at low speeds/loads, the converter should be able to handle the motor current if the input voltage wasn't sagging.

Reading the manual your are limited to SVC or V/F, you would not want t add an encoder for FVC, Try a lower carrier frequency like 10 or 12kHz (maximum is model specific and often requires derating), try to set the overload torque to a lower value say 120% instead of 150%. There is a parameter for low input voltage, but clearly you are seeing voltage sag on the input side and this should be corrected first. This VFD also uses an input voltage doubler to raise the buss voltage for 380V output, this will effect the efficiency of the VFD. P8-18 = 01 start protection should be on.

Surprising there no guidance on fusing, breaker or wiring size, etc. You can look at other VFD manufactures manuals that give some guidance on these issues for the rated input voltage/size of VFD.

 

[mMcFab]

Specifications are for constant rated power, you need to account for overload which you have set to 150% which is typically 1 minute, shorter time frames it can be 200%. The VFD is probably trying to pull higher current and the more it tries the more the voltage sags and the higher the current drawn on the input wiring. Efficiency of the motor is lower at low speeds/loads, the converter should be able to handle the motor current if the input voltage wasn't sagging.

Hmm, ok I should be able to work with that. I think given recommendations on sites like https://buildyourcnc.com/FAQ/14904 among others, I'm feeling fairly sure my breaker and fuse should still be a safe bet. I don't wanna go too big (on my fuse/breaker ratings) and create a risk that way either, I'd rather have a sensitive switch+fuse than an unresponsive one (plus I can't go much bigger. My house is on 40A and each sub-breaker is max 20A, so there's no way I can go bigger (on the fuse/breaker) without tripping the whole house)
So I guess my plan is to keep increasing wire thickness to minimise the "resistance->heat->more resistance->more heat" thing until I can actually trip something, then bump up those components if they prove to be a problem. The 10v reduction in voltage sag just by using slightly bigger wire I think helps push me in this direction, and I think I gotta cut out the extension cord stage for sure
Thank you btw! I knew efficiency was worse at lower speeds, but I guess it's got a bigger impact than I thought

 

[mksj]

Wiring doesn't work that way, the breaker protects the wiring, you can always use a larger size wire with a smaller breaker but not the other way around (it is varies by electrical code and device you are powering). It is also a function of the length of the wire, etc. You should be able to run it on a 20A breaker, that would be the minimum. Dial down the torque overload until it doesn't trip the VFD and decrease the carrier frequency.

 

[mMcFab]

Thank you! I will be bumping up those wire sizes and tweaking those parameters. Soonest I can try it out is Wednesday I think, but fingers crossed this gets it going (though you have described the breaker and wire pairing rules the same way as I understand them - larger wire ok with smaller breaker - so I'm not sure what part of wiring doesn't work in what way, I've edited my prior post to clarify that when I'm talking about "not going too big" I'm referring to the breaker/fuse ratings, not the diameter of the wire, I think I wrote it a bit confusingly)
[I now have 4mm2 wire on the way, with any luck I should be able to eliminate that variable on Monday]

 

[den-den]

I believe you identified the problem: "It's 230v normally, drops to 190v on average once the motor powers on with dips as low as 185v." The power supply is not adequate.

 

[mMcFab]

I believe you identified the problem: "It's 230v normally, drops to 190v on average once the motor powers on with dips as low as 185v." The power supply is not adequate.

...i'm gonna keep my fingers crossed about the wire gauge + extension cord thing for now since a modest increase in thickness reduced the dip already, because a generally inadequate power supply would be unfixable My power supply is the grid, and this would just add to the long list of things I hate about the house I live in. My 2.2kW tablesaw runs fine here which kinda gives me hope, but it has a very different configuration
I mean I guess an alternative is a 1.5kW servo motor setup until I get to move somewhere better, they're just a little pricey compared to the cheapest motor and VFD on the market . Or maybe I just run it in V/F mode, that's gotta at least have a little more torque than a lil DC motor... I hope...

 

[rabler]

I'm certainly not a code expert, but my understanding is that in the U.S, the national electric code specifies a maximum drop under load of 5% at the outlet for your wiring. Of course your cord may add some additional drop, but another 10% is not reasonable. Either you have a bad connection somewhere, or your wiring is undersized.

Keep in mind circuit breakers don't blow instantly. I.e., a 20 amp breaker is not suppose to trip at less than 20 amps. It may take considerable time at 22 or 23 amps. Your VFD is much more sensitive than the breaker, as a breaker only measures current not voltage.

I would caution against running it in V/F mode. You're masking an underlying problem that potentially creates a fire hazard, but more realistically could significantly shorten the life of the motor and VFD.

The reason the motor runs at some arbitrary (slow) speed in sensor mode is that the VFD doesn't have a connected sensor. Speed sensors are additional features on some motors. WAG, the VFD is trying to spin up the motor and is looking for a speed sensor input, without a valid input it is defaulting to some meaningless behaviour.

 

[mMcFab]

I'm certainly not a code expert, but my understanding is that in the U.S, the national electric code specifies a maximum drop under load of 5% at the outlet for your wiring. Of course your cord may add some additional drop, but another 10% is not reasonable. Either you have a bad connection somewhere, or your wiring is undersized.

Keep in mind circuit breakers don't blow instantly. I.e., a 20 amp breaker is not suppose to trip at less than 20 amps. It may take considerable time at 22 or 23 amps. Your VFD is much more sensitive than the breaker, as a breaker only measures current not voltage.

I would caution against running it in V/F mode. You're masking an underlying problem that potentially creates a fire hazard, but more realistically could significantly shorten the life of the motor and VFD.

The reason the motor runs at some arbitrary (slow) speed in sensor mode is that the VFD doesn't have a connected sensor. Speed sensors are additional features on some motors. WAG, the VFD is trying to spin up the motor and is looking for a speed sensor input, without a valid input it is defaulting to some meaningless behaviour.

With that information in mind then, I guess if the voltage drop is still >10v (My limit for applicances after the main breaker is also 5% here) after beefing everything up and removing extensions (there's probably a good 40 meters of cable between the main breaker and the VFD right now between the shed cable that runs from the house and my "convenience cable"), I think I will just pack everything into a box and just not put anything at risk unless I move somewhere better set up for this stuff. I've seen some of the wiring in this house and it doesn't exactly leave me optimistic I'm gonna leave this with a success on my hands

Thanks for the advice, everyone! At least I know what the issue probably is now, which is more than I knew before

 

[mksj]

A 40M extension cord of small size will cause the voltage to sag significantly given the size/Hp you are trying to drive. Something like 1.5 mm wire at 15A would drop the voltage around 12-15% and maybe more if the VFD was trying to pull higher current instantaneously. I also would be concerned about the rest of the wiring if you are plugging that into a socket and not directly connecting to the panel breaker. At least in the US, the breaker size does not mean that the wiring is also rated at that current on a continuous bases, it is typically 80% of the breaker rating. Breakers also have different overload curves based on current over time. You should not replace the breaker with a larger one if you need more current. The VFD in SVC mode does not need an encoder, but at the end of the day your input voltage is sagging significantly to trip an error on the VFD.

 

[mMcFab]

A 40M extension cord of small size will cause the voltage to sag significantly given the size/Hp you are trying to drive. Something like 1.5 mm wire at 15A would drop the voltage around 12-15% and maybe more if the VFD was trying to pull higher current instantaneously. I also would be concerned about the rest of the wiring if you are plugging that into a socket and not directly connecting to the panel breaker. At least in the US, the breaker size does not mean that the wiring is also rated at that current on a continuous bases, it is typically 80% of the breaker rating. Breakers also have different overload curves based on current over time. You should not replace the breaker with a larger one if you need more current. The VFD in SVC mode does not need an encoder, but at the end of the day your input voltage is sagging significantly to trip an error on the VFD.

Yep, I do not intend to increase the breaker rating at this point
If I had to guess without directly measuring it, I probably have a hard limit of about 20A continuous on the internal wiring of the house (fairly sure it's not gonna be 30A, definitely not more and the main breakers pop well below any of those numbers), plus I think the concrete shed was an add-on with also not-so-thick wiring in it too. I've pretty much ended up giving myself the worst set up possible, and then got confused when it didn't work. Egg on my face, I guess
If we owned the place, I would've paid to rewire the place a long time ago. The owners seemingly just ran a long wire from a utility room to the shed, which is not very thick either. There are more than a few indications the place was built as cheaply as possible.

I am indeed using a wall plug, so aside from everything else I'm also hard limited to the 16A a european schuko plug+socket can handle (I think that may only be short-term though, continuous may be more like 10-12A, it's surprisingly difficult to find a definite answer), and since I don't think I should be wiring anything directly to the mains at the moment, I will just give up on this if I can't mitigate the issue until I have the opportunity to move somewhere with a better wiring setup and a little more confidence. I think I've taken enough risks with this so far, and I've clearly got more I need to learn before I start trying anything like that