EEVblog #449 - Absopulse VFC500 Variable Frequency Converter Teardown

[EEVblog]

Inside the Absopulse Variable Frequency Converter
http://www.absopulse.com/pdf/sine%20wave/fc%20-%20vfc/VFC%20500.pdf

[ProBang]

Hello.

Sometimes big factories have their own standard for mains.
I know one with 200V/100Hz.
To repair their stuff you need a converter like yours.

BTW: Diodes in parallel?
I´ve learned that´s useless. One diode sacrify itself, the other one isn´t needed.
Any variations?

 

[megahz]

It sounds like a space ship!!!!

[Len]

BTW: Diodes in parallel?
I´ve learned that´s useless. One diode sacrify itself, the other one isn´t needed.
Any variations?

To quote the video:

They'll share reasonably well. Good enough for Australia anyway.

 

[opablo]

...
BTW: Diodes in parallel?
I´ve learned that´s useless. One diode sacrify itself, the other one isn´t needed.
Any variations?

Is it possible that only one is needed in terms of current specs and the second one is there just for redundancy in case of an open circuit failure of the other one ? (to increase the MTBF ?)

[Rufus]

The output isn't a transformer driven by MOSFETs. 500W at 40Hz would need a transformer half the size of the case. I'm pretty sure it will just be an H bridge with PWM modulation producing an average sine wave of the desired frequency and amplitude followed by lots of LC filtering to get rid of the PWM.

The big Micky Mouse ear on the input isn't a varistor it is a SURGE-GUARD NTC thermistor for inrush current limiting.

Next to the jumper link connecting the input board capacitors in series is space for two more which would put them in parallel presumably for a lower voltage model with twice the output current.

The performance of IEC mains filters is significantly degraded if you don't have a solid connection between the filter case and chassis.

A quote from Schaffner :-
"One of the most common problems with grounding is the installation of filters by directly attaching them to enclosures with painted or otherwise treated surfaces, in that way interrupting the ground connection and leaving the filter almost useless."

The extension of the filter case to make the flaps around the mounting holes under the plastic bezel is intended to make that connection. If done properly and their being two of them it should be more reliable (if less obvious) than a bit of green and yellow with crimps each end. That does raise an interesting question of what the finish on the aluminium chassis and cover is. Some kind of Alochrome I would imagine. You could check it with a meter

[NiHaoMike]

One of those gadgets is better known as a "Variable Frequency Drive". Most VFDs are 3 phase output, I don't see much application for a 1 phase unit. (No, you can't effectively use one to vary the speed of a single phase motor by much, it takes a two phase unit and some rewiring of the motor to do that.) Maybe try "overclocking" a cheap desk fan with that unit (maintaining the V/Hz ratio if possible), but I think the motor would lose a lot of torque and actually start slowing down at higher frequencies as the capacitor no longer provides the correct phase shift.

BTW, the part when you turned up the frequency sounds a lot like a hybrid or electric car accelerating from a stop. Or if you add in some weird sounding squeaks and buzzes at the beginning (a sensorless drive determining the rotor position) and wind up the top end frequency about 10 times higher (think jet engine), it would sound almost exactly like Brittany Benzaia's hybrid air conditioner.

[MCRIPPPer]

that thing sounds cool. it would make an interesting piece to a song. 



that is strange that the mains input is not hard wired to the case. here int he U.S. the neutral wire is tied to ground. even "non grounded" (thins without a ground prong on the plug) devices get connected to ground through the neutral wire. im not sure about how the wiring is done in other countries. maybe the device uses the neutral to get its ground connection.

[firewalker]

Is it ok to use banana socket in the output? I would expect mains socket.

Alexander.

[Ed.Kloonk]

Is it ok to use banana socket in the output? I would expect mains socket.

Alexander.

I'd expect a banana socket since the output is so widely variable. And the load is random gear which may not even have a plug or even a lead.

With a proper socket, im(h)o, the expectation is there for the output to be fairly normal like an ordinary power outlet.

If you'd have only mains appliances to test with the thing then you would have to simply make up a socket lead.

[casper.bang]

Lovely ending with the sound demo. I'm curious though, what physical cause is there for why switching regulators emit this and surely it's not the direct switching frequency (usually betweeen 100KHz and 1Mhz?)?

[peter.mitchell]

Lovely ending with the sound demo. I'm curious though, what physical cause is there for why switching regulators emit this and surely it's not the direct switching frequency (usually betweeen 100KHz and 1Mhz?)?

Generally, it isn't the regulators, but the inductors or transformers that make the noise, the magnetic forces cause them to ever so slightly vibrate.


An interesting use of such an effect is in hobby grade brushless motor controllers, where the controller uses a winding as a speaker for notification sounds.

[Phoenix]

Let's see if I can work this out from the video...

The output DC-AC stage looks pretty easy to understand. The 4 MOSFETs are in a H-Bridge configuration, with an inductor (labelled MSI 2000) on each phase outputs (not transformers). I would assume this is followed by the AC capacitor in parallel then the common mode choke before the take off point (can't quite make out all the tracks) forming an LCL type filter.

Those extra diodes are a little odd from what I can see, but they are clearly in some way anti-parallel diodes for the MOSFETs (as MOSFETs body diodes are slow). What is odd to me is that the to-220 package diodes are 45V 16A schottky diodes, but then appear to be seriesed with the axial diodes (where 2 of those are in parallel, can't make out the model number). It would be fairly easy to trace out with the board. Can you get the model of the axial diode?

If I'm not mistaken the current transformer is located on the DC side, but the current will be pulsed anyway. I guess some low pass filtering is done at a later stage in the measurement.

As for the input stage, it's a bit hard there is a lot hiding away. The label says 2x200V 1.5A, so I guess it has a 400V DC bus (which is about right for a 1phase 264V output via PWM). SG100 is surely an NTC themistor. The unit won't have regeneration capabilities as it's got dumb rectifiers in it.

I would say there is the input EMI filter stuff then a bridge rectifier (single package) on the first heatsink plate. That means the first magnetic component would have to be an inductor on one of the DC rails - for the boost PFC stage no doubt. Why the PFC needs 2 MOSFETs I don't know, but the third component on that heatsink plate is a diode (has 2 pads).

I'll take a guess at the second stage and say that the primary side of the transformer is center tapped and the two MOSFETs are in push-pull configuration. There are clearly 2 output windings (eventually seriesed) that are rectified to produce 200VDC each. What that third magnetic component is for I am not sure, as the core is shared between windings for the positive rail of both outputs, possibly just used for inductive filtering.

Cheers
Stewart

[nitro2k01]

Lovely ending with the sound demo. I'm curious though, what physical cause is there for why switching regulators emit this and surely it's not the direct switching frequency (usually betweeen 100KHz and 1Mhz?)?

Here's a spectrum plot of the recorded audio. The "weird noise" is quite obviously aliasing effects. Here's my interpretation of what I'm seeing:
There seems to be two things at play here:
1) The PWM frequency, which seems to be 10 kHz. If you put in a frequency above that limit, you will get aliasing (reflections). The 10 kHz signal itself is the band around the 10 kHz vertical line.
2) The sample rate of the sine wave. The sine wave reaches from 40-440 Hz, and it's produced from a table of sine values, which are churned out at a higher frequency, which will also be superimposed. In this case, this frequency seems to be 8 kHz for the starting 40 Hz sine wave, meaning the sine table is 200 samples big. So, the PWM breakpoint is updated 8000 times per second to begin with, and proportionally more often as the frequency is increased. The strange noises are (repeated) spectral reflections of the sine sample frequency for the sine generator, around the 10 kHz mark  See second image. Green = the actual frequency component. Blue = aliasing.
I expect the output from the terminals to filtered and much cleaner. Dave, care to scope it/spec it?

[c4757p]

here int he U.S. the neutral wire is tied to ground. even "non grounded" (thins without a ground prong on the plug) devices get connected to ground through the neutral wire.

No. No, no, no, no, no. No. Please never wire any mains equipment. 

[Fezder]

nice video, again new equipment to see

[FLL-Freak]

I was a little disapointed not to see wha the output waveform looked like under various loads. The whole introduction was on how to make a good sin wave output and we did not get to see it. For all we know it could have been a "crustry" output.

[geekysuavo]

What could be the reason for breaking out the different functions into physically separate PIC chips? Did they happen to run at odd- or non-integer multiple system clock rates?

~ Brad.

[N2IXK]

here int he U.S. the neutral wire is tied to ground. even "non grounded" (thins without a ground prong on the plug) devices get connected to ground through the neutral wire.

No. No, no, no, no, no. No. Please never wire any mains equipment. 

The original poster is absolutely correct. The neutral (white wire) is bonded to earth ground (green or bare wire) at each building's service entrance. The secondaries of transformers and other "separately derived systems" are treated in the same way. An ungrounded (floating) circuit is only allowed in specialized applications (like the isolation transformer used on an electronics test bench). Neutral and earth are ONLY supposed to bonded at the one point, and are kept separate throughout the system, with the neutral used as the current return path, and the earth only used as a safety ground and EMI/RFI/Static drain.

The grounded neutral is NOT supposed to be connected to equipment frame ground, even on devices with a 2-wire mains plug.  At one time, the frame ground wire was permissible for use as a neutral return on some types of equipment (clothes dryers and electric ranges operating at 240V, but needing 120V for timers or indicator lights), but this is no longer permitted by current codes. Such equipment is now required to be fed with a 4-wire circuit, with 2 hot phases, a neutral, and an earth ground.

[c4757p]

Neutral is connected to ground at one point, but treating it like a ground is reckless. It's just as "live" as phase. Saying ungrounded devices get connected to ground is technically correct but practically unsafe. Ungrounded devices are ungrounded.

[emcarro]

It woulg be very interesting seing that "sine" wave. But its very dificoult for an oscilloscope that kind of waves. 
The carrier frecuency would not be too high, too much noise.

[staxquad]

we were still using 25Hz hydro electrical power in some parts of Ontario up until last year 

I guess that Absopulse wasn't made for Northern Ontario.

Three generating stations on the Upper Mattagami River – Wawaitin, Sandy Falls and Lower Sturgeon, built 100 years ago, were still generating electricity at 25Hz for the mines up until 2011.

Next month, the last four 25 Hertz (Hz) generators at Wawaitin GS will cease production. That will be the end of the 25 Hz era in Northeastern Ontario.
The electricity we use in our homes is produced as alternating current, which has a frequency of 60 cycles
per second, also known as 60 Hz. In the Timmins area in the early 1900s, 25 Hz was adopted as the
frequency standard for operating pumps and motors for local mines. The Upper Mattagami River plants
had 25 Hz changed to 60 Hz through a frequency  converter, transformer and switching equipment
located in Sudbury.

They didn't mention the 25Hz lights, besides the pumps and motors.

Sandy Falls 25Hz


Wawaitin 25Hz
This was the last operating 25Hz station in Canada.


Ontario Power is a 25Hz plant built at the base of Horseshoe Falls (Niagara) by an American company.
decommissioned in 1999

[k8tek]

volt-amperes does not equate to watts. 

[staxquad]

volt-amperes does not equate to watts.

in DC it does

in AC, there's impedance, one lags the other, so can't be multiplied

[paulvos]

volt-amperes does not equate to watts.

in DC it does

in AC, there's impedance, one lags the other, so can't be multiplied

Unless you know the power factor ( cos phi ).