Compressor does "Clicking or Ticking sounds"

Hi, we are trying to control the compressor of a ref.

We used an H-Bridge circuit to control it. Our aim is basically an "Inverter Circuit"

http://images.elektroda.net/42_1308180076.jpg

we just used the "resistor" as a motor for representation

we have a 315VDC rail, and we are just varying the switching speed of the transistors using our PWM microcontroller.

Do you have any idea as to why there is a continuous clicking/ticking sound?

We believe that the sound might be coming from the relay of the compressor.. but we are not really sure.

The refrigerator is only a small one, about 2 or 3 cubic feet
The compressors also does not run since it is not getting cold inside the refrigerator.
Your help will be very much appreciated, thank you!

an additional question. What would happen if remove the connection in the start PIN and just directly connected the supply voltage on the RUN and COMMON pins of the compressor?

additional question, how would you identify if a compressor is Single Phase or 3Phase? the ref is old so the labels in the back are all worn out.

Hi there,

Clicking sound might be the motor rocking back and forward inside the can, or the relay.

You could substitute the start device, provided you energised the start winding by other means (for sufficient duration) at start up.

Fridge may not be getting cold if the compressor is not running, broken, or has no gas. Also, if it is actually being speed controlled it may not be running fast enough to pump sufficient refrigerant. Compressor duty cycle is normally 80 - 90% running full speed!

Being a small fridge like you say, almost certainly single phase. Measure restance between the pins to determine usual start/common/run terminals.

Hi nadre25 and welcome to our forum.
Your clicking sound could be through "Back EMF" or the klickson on the compressor? But Relay - on most small compressors there is an over temp/current bi-metal sensor safety switch called a klickson. You will have a single phase motor with two windings and three connections 1: common winding, 2: start winding and 3: run winding. For a small compressor the R could be 10s or 100s of ohms and a big (usually 3 phase) with 1 ohm or less. The start and run winding will be different on single phase where all three windings on three phase motors will be equal resistance. The start winding is usually switched off at around 70% motor speed then the run winding is switched on.

Quote:

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Originally Posted by nadre25

additional question, how would you identify if a compressor is Single Phase or 3Phase? the ref is old so the labels in the back are all worn out.

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3 phase don't have a relay across the terminals.
3 phase have equal resistance across all windings
3 phase isn't found in small fridges
If not permanently wired in, 3 phase equipment has a 5 pin plug normally, (phases 1,2,3, and neutral, and earth)

What type of compressor? 2 phase? Then you can't control the speed of it. It needs always the special starting device (current or voltage relay, special type/compressor type)
Difference between 2 or 3 phase? 3 phase 3 same windings, 2 phase 2 different windings in serial (one will be +/- 3 to 5 times the other winding)

hi Tesla, if the "clicking or ticking" sounds does come from the klickson, what solution could you suggest?

Hi HVACRsaurus,

we just cant understand why the relay ticks, where as if the refrigerator is just plugged in from the outlet without our system the relay works fine.

if we are going to replace the start device, what would you suggest?
Thanks!

Guys i'm really sorry. i forgot to mention that the electricity entering the compressor is a Square Wave, the motor will be able to see it as AC due to the H-Bridge polarities, we are able to change the direction of the current flow. But yes the problem is that there is that ticking sound.

Is the relay ticking because we are using a square wave?

Probably, the compressor needs to see full sinewave voltage at start up otherwise it will not start.

Read up on single phase motors, it appears that you are electronically biased and not electrically.

I know for fact that these inverters works flawlessly with small single phase compressors.

Perhaps you could do away with the start relay and energise the run winding directly from the inverter, however it would be best to start the compressor on equivalent of line supply, whilst energising the start winding for a few seconds (with an ordinary relay and timer). Provided the compressor did start and run, it could probably be speed controlled from then.

Nadre, Can you provide a print?