Testing The VFD, Break Resistor and Wiring to AXBBE

[Phil Mayor]

Hi everyone,

So I've had the electrician round and had my Electrics upgraded, so I now have a Single Phase 32a Soccket, I'm doing bench testing and got the VFD and Spindle turning on/off (through the VFD Control Panel) and I've been able to program some of the Parameters of the VFD, but there are lots and I'm not 100% clear what some do.

Firstly I got a seperate Breaking Resistor (1kw, 60ohm) the VFD Manual says it can be wired up 2 ways - either connect the resistor to DC+ and R-, or to R+ and R-) I've done both these methods but when I stop the spindle it just slowly comes to a stop as it does without the resistor connected... I've changed the Parameters in the VFD that I found related to breaking but there's no change in stopping time, I would need this eventually as I want to utilise the ATC function and have it stop quickly (within 6sec so it can then do the tool change)

The break parameters I changed are -

Page 41
1_06 Starting DC Breaking time
1_07 Stopo Mode - Changed to 2
1_08 Stop DC Breaking starting speed - changed to 3000rpm (although I don't entirely understand this)
1_10 Stop DC Breaking time - changed to 6sec

Page 46
1_30 - Break Utilisation rate - changed to 5, but not sure if this should be higher or lower..??
1_32 - Break Resistance Tolerance - set to 60ohm as my Breaking Resistor Specs
1_33 - Break Power Resistance - set to 1000w (1kw) as my Breaking Resistor Specs

link to manual

https://www.manualslib.com/products/...s-4142539.html


I would also love to connect this up to AXBBE so I can turn it on/off and set speed through the UCCNC Software I have seen a lot of wiring diagrams on how to do it but my issue is my VFD has differently labelled terminals so I'm not confident enough to try this without help/input form here, hopefully.

The control Terminals can be found on Page 17 link above

To change Spindle Speed through UCCNC I believe I would need to

connect

AXBBE AO1 to VFD GND (I suspect this is any ground terminal, I can see 2??)
AXBBE 5V0 to VFD AI1

To turn Spindle on/off through UCCNC I believe I would need to

connect

AXBBE 24V+ to Relay +
AXBBE Isolated output 2 to Relay -

but then I'm not sure which terminals on the VFD I go to from the Relay

I've also not seen anywhere in the VFD the parameter to say I want to control this through other software...??

I would be so grateful for any help or input on any of these issues,
Sorry for the long post

Cheers,


Phil

[Muzzer]

Wonderful Chinglish!

There are 2 different braking mechanisms here.

The "DC braking" type drives a DC current in the motor windings. This is rather like driving the motor with a fixed (rather than rotating) field and it causes a drag torque on the rotor. It's not particularly good for the motor, since it results in all of the energy being dumped in the rotor or the motor. There is usually a set point for the braking current and a speed at which it starts to be applied. It can also be used to stop the motor spinning under an external torque (not a problem here). Generally for motors, the torque generated is proportional to the current. That's true for current injection too. You can increase the current to as much as 150% of the rated phase current but that's probably not ideal. There is a delay tikme before the current injection is started and the duration of the current injection seems to be a fixed duration which may continue after the motor has come to rest.

The "braking resistor" scheme simply limits the maximum voltage on the internal circuit. When you decelerate the motor rapidly, the energy is dumped back into the VFD's internal high voltage storage capacitors. If the inertial energy is sufficient and you decelerate quickly enough (so that the energy is not consumed in the VFD by internal losses), the internal voltage could rise to the point where the VFD is damaged, although the VFD will protect itself against overvoltage damage by triggering an "overvoltage fault" and disabling the output (which results in the motor simply spinning down at its own right). Without a braking resistor, you have no choice but to limit the deceleration and if you have that set too aggressively you will see that overvoltage fault. When you fit a braking resistor, the VFD can dump any excess energy into it. This allows you to decelerate at a faster rate than you could using the FD on its own.

The "braking power resistance" is the peak power rating of the braking resistor. If you have a "proper" braking resistor, it will have a specified peak power rating (in Watts) - yours appears to be 60R (01_32) and 1000W (01_33). The "braking unit used" (01_31) is the voltage threshold at which the braking resistor will start to be used - 720V seems a bit high for a 240V input VFD - for a single phase VFD I would expect that to be closer to 450Vdc. If the internal voltage never rises to this level, the braking resistor won't be doing anything. If you shorten the decel time, you should find that eventually the braking resistor will start to have a noticeable effect. Equally, if you have braking resistor turned off, you will find that shortening the decel time will result in an overvoltage fault.

A decel time of 6 seconds is pretty slow unless you have a large inertial load. I'd suggest you try shortening it down to something closer to 1 second or so. You should then find that the braking resistor actually does something. It may start to warm up slightly after a few stops from high speed - that way you can tell it's being used, if you don't have any test equipment to tell you otherwise.

Some VFDs will allow you to use both DC current injection ("DC braking" here) AND a braking resistor but they work in different ways anyhow. However, for this product, 01_07 seems to require you to choose one or the other. If you have a braking resistor you might as well make use of it.

Hope that helps a bit.

[Muzzer]

For the control wiring, you also want to look at page 13.

- Pins AI1 - AI3 (page 17) are the analog inputs for your 0-10V speed signal - unless you can generate a +/-10V signal you should use AI3. There's also a 10V supply on "10V" if you need to provide that to your controller or want to use an external potentiometer.
- The "multiple functional digital inputs" G24 and X1 - X8 are used for the "enable", "direction" or "FWD" / "REV" signals from your controller. You have to tell the VFD what functions you are wanting for those. The various schemes are shown on page 55 and 56 (their page numbers).
- Some VFDs have an 24Vdc power supply inside the VFD but some don't, in which case you'd have to provide your own 24Vdc power supply. This product says it "offers the user" 24V at 150mA on pin "P24" / "XC", which keeps life simple. This is a safe low voltage output ie not connected to mains, as are the digital inputs and the 10V analog input.

[Phil Mayor]

Hi Muzzer,

Yeah, the Chinglish is whats confusing me, im obviously no expert in electrics anyway but coupled with the Chinglish it just makes it even harder to understand...

This is all brilliant, thank you for the detaild info, I will print this off and go through it as there's a lot to take in but thank you so much!

One point on the Control Woring, you mentioned using AI3 for the +/-10v but I don't think I have that terminal, I think that's part of the PG expansion terminal that is bought separately, if that's the case would I be able to use AI1 or AI2 terminals or not...?

Cheers again

Phil

[Muzzer]

I can't easily look right now but most VFDs have a 0-10V input, not +/-10V, so I'm a little surprised. It may be you can use either of those but equally, you probably can't generate that +/-10V output on your controller anyway. I was simply going on the table on one of the pages.

If I get a chance later, I will see what I can make out.

[Phil Mayor]

Hi Muzzer, theres no rush but thanks that would be great if you could....

With regards to the Break Resistor I've been doing a bit more reading and testing with the info you provided on the VFD Parameters and had some noticable results, however, still not close to where I would expect to be with break time and i'm getting close to the top end of all the parameteres, I think the main parameter causing me issues is the 01_08 'DC Break Starting Speed' I've got this set to 3000rpm which Is the most I can set it too, and sure enough when I stop the Spindle it slows down but it takes around 17s to get to 4000rpm then as it hits 3000rpm it stops dead - total time around 19s from 20,000rpm to 0rpm - I would of expected around half that time to be honest.... I could increase both the breaking current parameter a bit more, they're both at 100% at the min and it says I could go up to 150% I thunk

Cheers,

Phil

[Muzzer]

On this VFD you can't have both DC braking and braking resistor, as they are different mechanisms and you can only enable one or the other.

That "braking starting speed" threshold is only for DC injection, whereas decel will reduce the set speed regardless of whether DC braking is enabled. Have you also tried reducing the decel time? I suggest you firstly select the braking resistor option, then start to reduce the decel time. It should then work from any speed and you should be able to get the stop time down to a second or so. If you have the braking resistor connected and take the decel time down to the point where it overvoltage trips, you can then increase it a bit and you are likely as good as you will get. On page 110, the overvoltage fault during decel is displayed as "E.ouD".

The threshold voltage (720V) for braking resistor operation doesn't sound right for a single phase / 240V input VFD. The manual says "The biggest output voltage is the same with the input voltage" - and the maximum input voltage for these VFDs is quoted as "240V". That means the internal voltage would be ~340Vdc. I would expect the braking threshold to be closer to 400Vdc rather than 720Vdc. I expect it's already set to a ~400Vdc but if you get an overvoltage fault without any obvious braking, I'd check that parameter and reduce it if necessary.

What kind of machine is this? I am wondering what spindle inertia you will be seeing.

[Phil Mayor]

Hi again Muzzer,

The Threshold Voltage is the only Parameter I've not changed, this is set at 720v I was unsure what it did, so didn't want to mess with it... I can bring it down to closer to 400v and see if that helps...

I have seen something (Page 47) that states the most power allowed for is 5 times the 'Breaking Power Resistance' (01_33) which in my case would be 5kw but I was a bit worried to increase this setting by that much, but I could do it in small increments, maybe...??

I've changed the 01_14 - 'Decel time 1' to 4 seconds (this is as low as I can get it without Overvolt) and 01_16 - 'Decel time 2' to 0.5 of a second.

at the moment I'm still not seing any noticable reduction in stop times, I can see/hear the resistor kicking in, as soon as I hit stop but till it reaches 3000rpm it doesnt kick in fully...

I've also contacted the supplier, but they usually take a few days to reply...

It's a CNC Spindle Router, so there isn't a lot of inertia compared to something like a lathe.

Phil

[Muzzer]

You should be able to bring that to a stop fairly quickly.

Are you sure you have disabled DC braking and instead enabled the braking resistor? I wouldn't expect the braking resistor to hold off until you get down to 3000rpm. It doesn't care what the speed is, only that the internal DC voltage is trying to exceed that threshold value and needs to be kept in check. That voltage surge is due to trying to decelerate the spindle rapidly and regenerating the energy back into the inverter. Which is why the decel time and threshold voltage are the only parameters that really matter here. If the braking resistor mode isn't enabled, the only thing limiting the voltage is the losses in the drive. On the other hand, 5kW should fairly rapidly burn off the RPMs.

If it's a proper braking resistor, the 5X factor should be fine as long as the "1kW" figure is a continuous rating. Ultimately the limit is the melting point of the resistance element inside the resistor. They are made of wire or foil so they have a decent thermal mass. Other, more common resistors use carbon film which can't withstand much energy before burning out.

[Phil Mayor]

Yeah, I turned the DC Breaking off by selecting the 'Stop Mode' (01_07) and Changed from 2 to 0, the only difference I can see here is when it gets to 3000rpm it stops as before but rather than stop dead it rotates freely around 5 times and just comes to a stop, whereas when the DC Breaking is selected it just stops and seems to lock in place for a second or so...

I'm not sure if it's a proper breaking Resistor, I've never owned one before so I have nothing to compare it with, it had good reviews and was around £50.00 which was mid-range....

I've attached 2 videos one with DC Breaking and one without...


https://youtube.com/shorts/_icOR_oH6J0?feature=share

https://youtube.com/shorts/789Yqw6VrgQ?feature=share



Quick update

The Chinglish has confused me again here it's contradicting itself, I've just found a diagram that says the Break Resistor should be connected to DC+ and Db as far as I can see I don't have a Db terminal..??



Also, found the ohms rating for this VFD (11kW) should be 50ohms I have a 60ohms Resistor... is this a possible issue that could be affecting the breaking time...???