Single phase, two cap motor

Thread Starter

s34n

Joined Jan 1, 2024
19
Not quite electronics, but someone might know.

ABAC B2800B air compressor, with Single phase Tipo M80-2M 2.2kw motor.

The electric motor has a winding to earth, so its being replaced.

But when having a look at the wiring, it looks as though it has two run capacitors? I thought Id seen something similar before, but online searches dont seem to bring up much on how its connected to the windings.

Four wires come from the motor,
One black, connected to Live.
One white, to a 35uf capacitor which is looped to another 40uf capacitor.
First red, connected to the other side of the 40uf cap.
Second red, connected to Neutral.

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A link to another forum (not to promote it) where someone else is talking about the same model of air comp, where they have posted a number of pictures of the wiring and disassembled motor.
https://www.mig-welding.co.uk/forum/threads/abac-b312-100-compressor.132146/

It looks as though there is no centrifugal switch, or anything else to disconnect one of the caps.

Just wondering how the circuit works?

Cheers
 

MaxHeadRoom

Joined Jul 18, 2013
28,758
Translates to:
Insertion time 1.5"
Repetition period 6"
I would expect that to be seconds?
Are you sure about the values? I would expect one, Run cap, to be much lower, The time stated in seconds is a typical limit for a start cap version.
Can you post a pic of the caps?
 

Thread Starter

s34n

Joined Jan 1, 2024
19
Translates to:
Insertion time 1.5"
Repetition period 6"
I would expect that to be seconds?
Are you sure about the values? I would expect one, Run cap, to be much lower, The time stated in seconds is a typical limit for a start cap version.
Can you post a pic of the caps?
If you follow the link in the top post, someone has posted pics of the caps and wiring for that motor.

Searched for the B05000X400G24FFFM capacitor, and it seems to have a built in timed switch if going by this similar one.
Link to similar cap
 

MaxHeadRoom

Joined Jul 18, 2013
28,758
The fact that it is marked as per #6 would indicate it possibly includes the typical current relay that is normally external.
i.e. detects when the start current has dropped and then drops out, opening the cap.
 

Thread Starter

s34n

Joined Jan 1, 2024
19
Sort of sounds like their doing it based on time with electronics, but who knows.
Maybe someone has info on this style of cap? I'm not finding much on searches.

Cheers
 

MaxHeadRoom

Joined Jul 18, 2013
28,758
Typically It is done externally to the motor with a current relay, it is possible there could be a small one internal in the cap.
Is there any resistance measured across any two of the leads?
 

Thread Starter

s34n

Joined Jan 1, 2024
19
Had a look at the one fitted to the air comp I was looking at.

Its capacitor is slightly different, a 40uf 262/CR404U. Some of the label has rubbed away, but it has the insertion time as "Autotarabile".
Measuring the resistance both ways just gave the usual charging as on a normal cap, quickly going from 0 to OL.
Wired it to live and neutral on its own, and it ramped its current up to 3A and sat there. Didnt leave it powered up to long, maybe 3-4 seconds.

Also measured the resistance between the motors leads.

B - W = 3.4 Ohms
B - R going to 40uf cap = 1.1 Ohms
B - R going to neutral = 1.1 Ohms
R - R = 0.0 Ohms
R going to 40uf cap - W = 4.5 Ohms
R going to neutral - W = 4.5 Ohms

Kinda looks like its just a CSCR motor with a funny start cap.

Cheers
 

MisterBill2

Joined Jan 23, 2018
18,928
I am fortunate to not have had to deal with such devices, as it seems that verifying that they function correctly would be a bit of a challenge.
 

MisterBill2

Joined Jan 23, 2018
18,928
Given the complaint, " The electric motor has a winding to earth, so its being replaced. ", I suggest a careful very close examination of the motor to see if that accidental "connection to earth" could be fixed.
And another suggestion is that if the motor is a standard physical size, that a more common frame size motor with a more standard arrangement be used as the replacement. Most air compressor drives are belt coupled and so that may even provide a cost reduction and an efficiency improvement.

Of course it might also require a pressure unloading scheme if one is not present.
 

Thread Starter

s34n

Joined Jan 1, 2024
19
The windings had failed an insulation resistance check, no signs of contact or damage with the housing on the wires going into the motor.
The caps both tested ok value-wise, but I also dont know how your best to test the built in switch.
I might pull the motor apart out of interest, and try something with the cap.

They went with replacing the motor with a Techtop ML90L-2, I think.
Came with 50uf and 250uf caps and a funny electronic centrifugal switch, a RECS-220P.

RECS-220P English starts on page 16

Initially programmed it with the compressor belt off, trying to follow the manfacturers instructions. It started fine with no pressure in the air tank. But on restarting with 6 bar, it was stalling the motor.

Reset the switch, and programmed at full load. Seemed to work ok.

It seems to have a pressure relief for the short length of pipe between the comp discharge and check valve on the tank.

Cheers
 

MaxHeadRoom

Joined Jul 18, 2013
28,758
The RECS-220P appears to be a typical start current relay, they ensure the start cap is only in circuit for a couple of seconds, any great deal longer and you lose the capacitor.
 

MisterBill2

Joined Jan 23, 2018
18,928
I would never expect a motor to start with that much of a torque load. That is why I always provide a means of relieving the pressure when the pressure switch opens. usually that consists of a check valve between the compressor and the air receiver tank, with a small normally open solenoid valve to vent the compressor side to relieve the head pressure. That greatly reduces the starting current Some installations have a pressure switch that provides a pressure release when the pressure switch opens, but the plumbing for those is more complex.
There may be a leak in the check valve , and it may also be that a greater volume is required to allow adequate time for the motor to develop running speed and torque. Pneumatic check valves have been known to fail partially. I have had that problem in the past because of thhe seal material in the check valve not being compatible with the compressor lubricant mist.
 

Thread Starter

s34n

Joined Jan 1, 2024
19
Sorry, not a pressure relief safety valve. But as your talking about a pressure switch/valve that dumps the pressure in the short length of pipe when it stops the comp. It seems to be working, giving a little release of air shortly after the comp stops. And the pullys are easily turned by hand.

And sorry, not programming the switch at full load, but at maximum tank pressure the comp restarts at.

Running current with the belt off was only around 2.5A. 230V

With the tank at 6 bar and discharge pipe vented, starting current read with a clamp meter peaked at 22A, and within a second the start cap is being dropped out. Running current at about 8.5-9.5A. Doesnt seem too bad.

Maybe the check valve or dump valve is intermitently not working correctly.
 
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