Bitzer Octagon compressors

[RONB]

I am currently commissioning some Searle CCU recip packs.I have had some trouble with one of the Bitzer Octagon comps.When I ran the comp up for the first time it sounded tight and was pulling high amps.It is a 50/50 PWS and the windiing resistances are around 2.4 ohms on both windings.The comp dose not have a conventional oil pump but a centrifugal pick up which feeds directly to the crank.I have 420 volts between phases on both windings.As the comp is brand new and the feedback I have recieved from the supplier, that the comps are fully checked and tested that there must be some other reason for the problems I am having.I was wondering if anyone else had had any such problems with the comps.

[Renato RR]

8FC70.2 or 8FC60.2,and give me
evaporating temp.
condensing temp.
readings by ampermeter
R 407C or what

Best regards,
Renato

[Snowman123]

Fist step is to make sure you have oil pressure, may be running in reverse. Some compressors recip can only run one way due to the type of oil pump. Also part wind comps need a delay between each winding of 3 secs min.

[Peter_1]

We install mostly Bitzer.

A Bitzer can run in every direction, so the oil pump isn't an issue.

You have PWS...have you measured the 3 lines separately and wasn't there one line which pulled more Amps then the other?
It can be that one of the windings is turned inside the opposite way so that it's magnetic field is counteracting the other 2.
Your resistance reading will be correct but the Amps will differ.

Some Bitzers are limited in maximum LP, if you go over it, then Amps will be too high.

Are all the bolds tightned well, also at the underside of the plastic connection block? Sometimes the amps are correct when measuring unloaded but as soon machine starts, the loosen contact will pull more Amps.

You said .. both windings...is it not a 3 phase motor then?

What type of compressor do you use? All the same type on the pack?

Keep posting what you found ,we can learn from it.

[NoNickName]

Yeah, like peter said it looks like winding A is wired CW and winding B is wired CCW or viceversa.

[Peter_1]

But I'm still confused about the 2 windings

If a winding is wrong connected, then this is a factory fault because it happened inside the compressor.

You should call your supplier because this is a warranty case and they should pay you to solve this.

I'm working this day on an Octagon and I will have a look once if (!!!) you can change it.

[Peter_1]

Another possible cause which I searched for some hours in the rain: compressor 1 has power cable A and B (50 +50%) and compressor 2 has C and D. If B and C are interchanged, then everything works fine as long as both are running.

As soon one stops, motor which is still running comes to half power. But the magnetic field generates a new voltage in the other non-energised winding so that you can measure a voltage on the outlet of a non-energised relay of the stopped compressor.
Do you understand what I mean?

[NoNickName]

No, how can there be 4 wires in a PWS. There must to be 6.

[Peter_1]

I was talking about power cables, not wires.
1 cable for the 1st motor, 1 cable for the 2nd motor.
A PWS has 2 cables with each 3 wires, so 6 wires total/compressor.
A PWS motor always has 3 windings.

Is this more clear?

[NoNickName]

I was talking about power cables, not wires.
1 cable for the 1st motor, 1 cable for the 2nd motor.
A PWS has 2 cables with each 3 wires, so 6 wires total/compressor.
A PWS motor always has 3 windings.

Is this more clear?

No, a PWS has two windings, three wires per winding.

[Andy]

No, a PWS has two windings, three wires per winding.

Nick,

Us Irish will translate

The wiring was mixed up on the job Peter was talking about.

It ran fine if both the compressors with the mixed wires were running together.

But if one stopped only one set of the Part Wind was being fed on the other running compressor and the compressor overloaded.

Kind Regards. Andy

[Peter_1]

Help , I have to rewire all my compressors and especially all the Bitzers I've installed the last 20 years!

How do you connect 3 wires to 1 winding?
A winding has 2 ends

You can't make a rotating magnetic field with 1 winding in a 3 phase motor.

A PW motor is basically a 3 phase motor and a second 3 phase motor winded through each other, mostly wired 50/50, sometimes 70/30.

I give up.

Perhaps an interesting link for some: http://www.thermagroup.com/documents/Issue2.pdf

[Peter_1]

And what was funny, we started up under full load, everything worked fine for at least half an hour.

The switch cupboard was located in the basement, pack standing outside the building.

Measured AMP's on all comp --> all lower then FLA.

Looked around a litlle bit, went back to the switch cupboard and Comp 1 overload had tripped.

Reset it, let it run, measured AMP--> normal.

Have to say, we were running on an generator. So I thought, generator fault???

Monitored it some minutes (pack under full load).

Looked to the generator, looked around a litlle bit, went back to the switch cupboard and oeps... overload of COMP 2 was tripped.

Reset it, measured and AMPS of COMp 1 and 2 , everything normal.

I started raining very heavy, it was already around 10 PM, I was tired working the whole day.
And the other day, the engineering office was coming to verify everything.

You coudl imagine that I was really p**d of.

[NoNickName]

A winding is something different than a wound wire, peter. So a winding is a set of three wound wires, eventually 2, 4 or more poles, with 3 ends. Then the three wound wires can be connected star or delta or star star in case of PWS.
Hope it is clear know. No need to rewire your bitzers, at least not for this reason.

[Peter_1]

No, it isn't clear, but never mind, I gave up already.
I know when I have to quit.

http://www.infolytica.com/en/coolstuff/index-dcmot.html

[Andy]

A winding is something different than a wound wire, peter. So a winding is a set of three wound wires, eventually 2, 4 or more poles, with 3 ends. Then the three wound wires can be connected star or delta or star star in case of PWS.
Hope it is clear know. No need to rewire your bitzers, at least not for this reason.

The Irishman will try again

Two compressors

Two set of wires

Wires mixed up from one compressor to the other

Hope this helps

Kind Regards. Andy

[Peter_1]

I see from your first post you followed my explanation.
Perhaps not in best English but because you understood it, then it can't be that bad explained.

Andy, what's the difference between a cable and a wire? Does a cable consists of wires?

[Andy]

I see from your first post you followed my explanation.
Perhaps not in best English but because you understood it, then it can't be that bad explained.

Andy, what's the difference between a cable and a wire? Does a cable consists of wires?

Yep the wire is the conductor or conveyor of the electric.
The cable is a collection of one or more wires in an insulated cover

Kind Regards. Andy

P.S I am lucky that english is my first language, otherwise I would not understand anything

[TONY_MF]

your problem is overcahrge during commissioning

[Peter_1]

How can the current be high due to overcharging on a semi-hermetic Bitzer, mounted on a pack?
Explain this once fo me because I can always learn something new.

[S.M.Gokhale]

Hi,

We had a similar problem. While commissioning a 15 H.P. two-stage Bitzer semihermetic - the compressor would trip within a few seconds of the second winding coming on load.

Checked the current - it was showing 154 amps. As the compressor suction and discharge pressures were not abnormal checked the wiring.

It all boils down to a very simple solution (in fact this is the right way of cabling for part winding start which we did not know at that time) - Keep the phase sequence same from incoming cable to the Motor Control Panel right upto the compressor. A sketch is enclosed.

In our case inside the Motor Control Panel R & Y were interchanged for one of the windings (This creates no problem with star-delta starting). Once the fault was identified and corrected all was well.

[D.D.KORANNE]

FOR octagon series, why use part winding scheme ?
Connect the motor terminals in star wound position & operate with DOL starter . Pls look up in the terminal box , it says , 400 V Y.

[750 Valve]

I understood what you were saying Peter, even in 2006

[NoNickName]

Despite, a PWS motor still has got 6 terminals, which are the terminations of 2 internally connected stars. 3 wires per winding, the other three plus three are connected inside the motor. Maybe this sheds some light on a 4-years old thread.

[kaelte_technik]

normally part winding motors especially bitzer is with taggings in the terminals as U1, V1, W1 (for the first winding) and U2, V2, W2 (for the second winding) and since it is a part winding there must be two contactors for each winding plus and time delay for the entry of the second winding which is normally 1 sec. there must be a set of cables with 3 wires each so all in all there will be six wires. each set of cable will go to each contactor and windings. there must be some mixed in the 2nd windings wiring if it is tripping upon start up and with high amps. If it is a DOL start which is normally with octagon it will be depending on the connection if U2, V2, W2 is bundled together then the connection is STAR and you will only have 3 wires that will connect to U1, V1, W1 if it is DELTA U1+U2, V1+V2, W1+W2 and you will also have 3 wires to connect.

[NoNickName]

Yes, kaelte, but too many people forget the basics, and arrange a lunch with a dinner with what they scrounge up.