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philjd26
21-11-2007, 07:17 PM
hi, can anyone tell me what ditermines the speed at which the transtors for inv switch...is the dc voltage increased to the transistor module or is there a signal? i know that inverter speed is controlled according to back pressure/temp,discharge pressure/temp etc...

rgrds phil

Brian_UK
21-11-2007, 09:50 PM
Transistors can switch at mHz if required and there will be a signal from a sensor going through the control system to the transistor.

TRASH101
22-11-2007, 01:05 PM
Hello PhillJD

the rate at which the "transistor" switches is exactly the same as the "hertz" reading i.e. cycles per seconds. The relationship between sensor arrays and final output is as you`ve identified software driven. The sensors are decoded to digital value and matched as an address to a known value stored in memory which is then used as the output to drive the Astable* which forms the correct "wave" for that phase.The D.C. voltage is there purely as a "reservoir" to drive the Astable. This is of course the basic Invertor and various clever things can be done to manipulate the waveform for better drive characteristcs.

Hope this helps a little.

*Astable- A circuit that has no stable condition and oscillates and a frequency governed by circuit values. In analogue electronics that can give a perfect sinusoidal (sine) wave:cool:.

philjd26
22-11-2007, 11:51 PM
Hello PhillJD


*Astable- A circuit that has no stable condition and oscillates and a frequency governed by circuit values. In analogue electronics that can give a perfect sinusoidal (sine) wave:cool:.


hi trash,

nice one learnt something ther! would astable feed transistors? my thinkin of a transistor is it sends out pulses of voltage at whatever mhz per sec,so your saying that the astable dictates th dc voltage to the transistors and powers up each transistor accordingly or??

cheers phil

TRASH101
23-11-2007, 12:08 PM
hello phill,

The DC voltage is determined by the available AC voltage before the RECTIFIER. The rectification stage gives your primary DC and may be used "raw" or regulated before it feeds the main transistors or amplifier. the astable/s affects the amplifier/s as an independant control circuit behaving like signal driving a solenoid valve to create the correct wave (pulse) shape.

If you search for wheatstone bridge that will give you an example of single phase rectification. (treat the diodes as one way valves) this will help you visualise the flow.

good luck phill:D

Thermatech
24-11-2007, 07:49 PM
Most VRV / VRF systems will tend to have slowest compressor speed at around 30 hz & max compressor speed at arround 100 hz.
Although the exact max speed will vary depending on each model.
Most VRV / VRF systems have a control board & an inverter board.
The control board monitors the system operating data like all temperature sensors & pressure sensors & calculates stuf like superheats & subcools. The data is all compaired with ideal targets which are in the softwear program.The control board then sends a command to the inverter board for the required compressor speed / hz which is needed to meet its target conditions.
But some manufacturers use fussy logic control. So the system does not instantly react to the current data but also compaires it to the data it has been receiving over the last say 10 or 15 mins. The control board is constantly calculating the data trend & adjusting the compressor speed in responce to the trend not the current operating data.
This prevents the sytem over reacting & making the compressor constantly speed up & slow down. However this does mean that the system will only slowly ramp up compressor speed which can be frustrating when you are working on the system & need to see it respond.
Split systems often only have one circuit board but in principle work in a similare way.
If you have a good multi meter you can measure the frequency at the compressor terminals or on most VRV/VRF systems you can moniotor the control frequency on the outdoor control board digital display provided you know how.
Although you can hear the compressor ramp up & down it can be useful to know the exact compressor speed when you are trouble shooting some problems.

stuartwking
24-11-2007, 11:28 PM
Thanks for asking the question Philjd, Learned something from it.Just wanted to see a great post with some real good replies. thanks guys.

philjd26
25-11-2007, 02:57 PM
cheers fellas... understand operation alot better thanks

rgrds phil

hendrag
25-11-2007, 08:35 PM
I run a course on refrigeration electrics covering inverters at Eastliegh college. click here www.mylg.co.uk/downloads/Eastliegh%20Week%207%20inverter%20theory.doc (http://www.mylg.co.uk/downloads/Eastliegh%20Week%207%20inverter%20theory.doc) for a copy of the notes on this subject. Its a simple explanation of how inverters work. Hope its of some use

regards

hendrag LG tech manager UK