Inverters

[Latte]

Hi Guys,

I seem to be on courses every month at the moment and this months was Inverters.

I must say i was impressed. Using a 3 phase compressor on a 240volt system looks good. No motor motor rating for start up just a gradual build up. Even more from what i can see with all the transformers and capacitors on the board the only two thing that can go wrong are either the compressor or the board.

Has anyone had any inverter problems out in the field yet or are they as the manufactures say ultra reliable and too new to have faulted yet

Regards

Fatboy

[Daddy Cool]

Inverters have been around for years, they have evolved somewhat, with more fancy electronic's. In general i would say they are reliable, but have been slighted by dodgy engineers demanding new PCB's as the inverter board has failed. i recently spoke to one of my old techy supports who works for a manufacturer, they had a new apprentice start, and his first job was to test the inverter PCB's that came back under warranty. Having spent all day he was left with a pile of 'ok' boards, and none that were not ok. They went back into their boxes and back on the shelf! For what it's worth, i was also chatting to an old fridge boy, and he was won over by inverters, but said ' i don't know how they work, they just do, but then i don't know how my phone works, it just does, so what do i care'

Do they explain how they work on your courses?

[Karl Hofmann]

I love Inverters, they solve a lot of problems for me since nearly all of my work has to be connected up to single phase supply and for nearly all domestic installations, connection to the ringmain is within regulations (Excluding some of the larger stuff used in conservatories)
One of the most annoying things about cap start compressors is the "Thud" when it first fires up, which can be a major issue for many housholders.

Although I am going a little deaf, I do have to concentrate quite hard to hear when the compressor on a Tosh or Sanyo fires up

Every unit that I fitted this year was an inverter

[daddymac]

I've found inverters to be good too, as you can have a reasonable size system on a single phase supply. In most premesis, you're hard pressed to find 3 adjacent "ways" in their dist boards! They also ramp up smoothly rather than banging a 80amp surge when they start!
On dist boards... be careful when wiring into and existing board with harmonised cable!! Confusing, and potentially very dangerous!

[Latte]

Do they explain how they work on your courses?

Hi Daddy Cool,

Not so much of a technical course as a general overview. Fault codes, basic technical stuff really.

Explained single phase 240ac gets converted to DC before getting converted back to 240AC 3 phase for the compressor.

It's like most courses, you don't gain anything really until you get out in the field with them. As yet i have never had a problem with one that does tend to suggest that they are more reliable than the old style units (Well LG anyway).

The course was very good though, Toshiba - held in Welwn garden city at FM/AMD site. I have all the technical info that tey give you but for some unexplained this year it's gone mental going up to christmas and havn't had chance to even look at it yet

Regards

Fatboy

[iceman007]

Only thing you have to be wary of is a bad compressor is easily capable of wrecking an inverter. We've had them ruin base amp boards and TM modules etc, but that aside we only install inverter systems because they are more efficient, as the capacity is closely matched to the load, unlike fixed speed systems.

[Daddy Cool]

Hi Fatboy (may i call you fatboy without appearing rude?)

I did sit through an all day course that my old company (manufacturers) were running as a trial and we were the guinea pigs. general opinion was that it was too deep into electronics, and not really of much use in the field. the basics were useful to understand, but the full on in depth bit was a bit heavy.

[Latte]

Hi Fatboy (may i call you fatboy without appearing rude?)

No Problem, Go into any suppliers up this way, NRS/HRP and say Fatboy they know who you are talking about.

I look on it as a compliment, i could get called a lot worse

regards

fatboy

[rbartlett]

Inverters have been around for years, they have evolved somewhat, with more fancy electronic's. In general i would say they are reliable, but have been slighted by dodgy engineers demanding new PCB's as the inverter board has failed. i recently spoke to one of my old techy supports who works for a manufacturer, they had a new apprentice start, and his first job was to test the inverter PCB's that came back under warranty. Having spent all day he was left with a pile of 'ok' boards, and none that were not ok. They went back into their boxes and back on the shelf! For what it's worth, i was also chatting to an old fridge boy, and he was won over by inverters, but said ' i don't know how they work, they just do, but then i don't know how my phone works, it just does, so what do i care'

Do they explain how they work on your courses?

Whilst this is no doubt true, the worse thing is to price just the compressor and find it won't run.

best to price to swap out all the 'bits' as you know then you are starting afresh. pricey for the customer but better for them to get a price and know that's it.

nothing upsets people to hear half way through "err it's gonna cost you another xx grand" as they -

a) immediately assume you are trying to rob them
b) you're incompetent for not correctly diagnosing the job in the first place
c) they are going to have to wait another week before it's fixed

cheers

richard

[Abe]

Whilst this is no doubt true, the worse thing is to price just the compressor and find it won't run.

best to price to swap out all the 'bits' as you know then you are starting afresh. pricey for the customer but better for them to get a price and know that's it.

nothing upsets people to hear half way through "err it's gonna cost you another xx grand" as they -

a) immediately assume you are trying to rob them
b) you're incompetent for not correctly diagnosing the job in the first place
c) they are going to have to wait another week before it's fixed

cheers

richard

I adopt one policy, which saves me a lot of stress
As Richard says..........Nothing worse then going to customer at a later stage and saying.............Ohh, by the way, your valve looks dodgy....

I change everything that looks suspect or is past its sell by date.......

Nothing works, functions like a New Part

Also............Whenever you try to save your customer a few bob.........you end up paying...

Why??

Let him suffer the pain......

I always say to myself, All these years, did he bother to have units serviced? Answer.........No

But............Moment he has a prob, you are his best freind, and he wants you there like............NOW

All my stuff is going bad, they cry out pitifully

Well..............Did they think about a back up system??

Like heck they did.

Tell him simply..............Dont make Your Problem My Problem

[Renato RR]

I dont see that any of you in replaes use tehnical languige.Do anyone really know work principle of frequency regulated compressor.I know realy litl about inverters but seams to me that I am not the only one.

Renato RR

[Lazarus]

Hi people,
My first posting so be kind.........

Have used Inverters of different types and considerable size for years in Industrial fridge.... fairly amused by the 'Latest technology' thing with air conditioning.
Installation wise probably 90% of my work is Inverters, mainly Panasonic...
Though must say i am now a little disapointed... Panasonic reply to fault codes... its your PCB board... but the indications i have are for the compressor..... Duly changed board at there insistence.... 2 months later my customer is now happy with his new compressor.
Another ongoing case with an inverter ducted unit... fault codes show interconnecting wiring at fault.... checked , replaced , checked again.. it is good. Panasonic then say they cannot identify which board is at fault, but it is one of two.... send me both boards please.... one arrives, installed ... no effect. 6 months later after many episodes i will not bore you with ... still waiting for the other board with a very upset client... No i will not be using Panasonic Inverter ducted units again until they get there act together here!!!
Are spare parts slow for this manufacturer just in Spain or is this a wide spread problem.... !!!!

[Peter_1]

Alle the posts were airco related but we use the VFD's mainly for refrigeration purposes.

We use the T-verters form Taian (Teco/Westinghouse) and the last 4 were controlled by a special (cheap) Carel controller.

[Temprite]

G'day all

When doing a voltage output check on an inverter PCB. I have been offered two methods of checking by various technical sources for airconditioning.

1.Remove compressor leads and turn unit onto cooling (or forced cooling) and measure voltage between UV/UW/VW

2.As above but measure voltage from DC- on diode bridge to U,V and W.

Which is the best way?

Also we all know that a faulty compressor can take out a PCB. But what if it is seized?
You cant confirm that by checking the windings. If you put in a new PCB the minute you start the unit up you take out the new board. How do we confirm seized compressor before purchasing new board?

Regards.

[tonto]

Aiyub,

You make such true comments about a minority of customers... We installed at a previous job I was working at, some custom made cake and sandwich displays, 3 years later condensor motors start to seize and then in turn eventually the compressor fails all due to condensors that were not cleaned from the beginning.... Customer winges and bitches reckons we are thieves even after recommendations have been made to service the equipment... In the end I say to the man do you buy a car and not service it or check the radiator fluid??? And from the customer I recieve a long silence....

[phil68]

The environmental test chamber manufacturer I was working for about 15 years ago dabbled with inverter controlled Rotocold compressors to control capacity as the chamber reached setpoint. The compressor would gradualy slow as the chamber neared setpoint & be barely ticking over once setpoint was reached, to gain close control. Unfortunately the company went to the wall before this set up could be developed fully for that application.

[ozairman]

G'day all

When doing a voltage output check on an inverter PCB. I have been offered two methods of checking by various technical sources for airconditioning.

Which is the best way?

Also we all know that a faulty compressor can take out a PCB. But what if it is seized?
You cant confirm that by checking the windings. If you put in a new PCB the minute you start the unit up you take out the new board. How do we confirm seized compressor before purchasing new board?

Regards.

I would say output across the compressor leads is a more valid way of testing than output to the DC ground. As you probably know the inverter module artificially creates 3 phase from a high voltage DC power supply ~380VDC. The DC Inverter compressors in most AC units (ie japanese brands) are wound in star and the inverter module has six transistors inside it, a pair for each winding of the compressor. The inverter sequences the switching of the transistors to alternately switch two of the compressor windings to the positive side of the supply and one to the negative leg, then in the next sequence two legs to negative and one to positive. This is sequenced to create a rotating magnetic field to make the motor spin. If you have seen inside a Fisher and Paykel "smartdrive" washing machien they basically do the same thing.

As its the switching to positive and negative DC then looking at the output of UV/UW/VW is more useful than looking at U-N etc.

As for checking the compressor a seized compressor is not going to take an inverter pcb out, more likely to cause a location fault or an overcurrent protection fault. A shorted compressor will toast the inverter pcb very quickly. The only way to check a compressor is with a 4 wire resistance measuring device that can measure milliohms and a megger. A lot of these compressors have winding resistances of less than 2 ohms and are critical to 5% imbalance. Fieldpiece make an adaptor called an AMR1 which attaches to a normal multimeter to do low ohms measurements that works well and costs about $160. A megger is the only way you are going to be able to pick up a short to earth but noone seems to carry them these days.

HTH

[Temprite]

Thanks ozairman.

I had a compressor on a LG kill a board recently.

Outdoor board was no good, checked windings of compressor, which according to their tech support were OK. Also checked to earth also but not with megger.

Was told to replace outdoor PCB which I did.First start up and the outdoor board is toast again.This time they told me to replace compressor and board which I did. Now all works OK.

Asked how to avoid this in the future and they said there is no way of telling.

Might start checking every time with a megger

Regards.

[Cofreth]

Thanks ozairman.

I had a compressor on a LG kill a board recently.

Outdoor board was no good, checked windings of compressor, which according to their tech support were OK. Also checked to earth also but not with megger.

Was told to replace outdoor PCB which I did.First start up and the outdoor board is toast again.This time they told me to replace compressor and board which I did. Now all works OK.

Asked how to avoid this in the future and they said there is no way of telling.

Might start checking every time with a megger

Regards.

Probably the PCB got toasted not because of a grounded compressor,therefore, even with a Megger on hand may not diagnose the problem.

[star882]

I guess that those inverters just need better design. My friend Christina Mahoney helped design the compressor inverter, preregulator, UPS, and system power supply for a quad Britney server. She said that the inverter will survive a locked rotor (overload will activate and inverter will shut off). A short will blow the B+ fuse, although the inverter itself should survive. Even if it does not, there's only 4 MOSFETs and 1 triac to replace.