Posistor for Fujitsu

[nike123]

Does anyone know who makes these posistors?





I tried to find by logo and did not find anything?
http://www.classiccmp.org/rtellason/...ctorlogos.html
http://www.dialelec.com/semiconductorlogos.html
http://www.aufzu.de/semi/gif/

Designation on schematic is:

[Brian_UK]

Found a few sites through Google listing a 400A300-A but can't find a photo yet..

http://www.google.co.uk/search?hl=en...0&start=0&sa=N

[nike123]

Found a few sites through Google listing a 400A300-A but can't find a photo yet..

http://www.google.co.uk/search?hl=en...0&start=0&sa=N

Thanks Brian, but I didn't find anything usable!

[nike123]

By definition, posistor is a combination of a PTC (positive temperature coefficient) resistor and another resistor-element to heat it up and keep it hot.


I opened it and found only disk which gives me 33 ohm of resistance ( no mater of polarity) and two contacts made of nickel.






Disk is held in place by these contacts and positioned in center by some frame of daze (mica).



It doesn't look to me as combination of resistor and ptc resistor, it looks more like only PTC resistor.

It is available as replacement part but I need to wait 1 month.

This part is probably used to limit current to inverter, but I suppose that is current transformer task to send information about current to processor for regulation of current.
I suppose that it could be bypassed, but then inverter will be unprotected, if for some reason current exceed maximum.

What you guys think about that? Could I replace it with some fast fuse?

[Electrocoolman]

Hi Nike,

Are you sure that it is a PTC ? It could be a NTC unit to limit inrush current on first power-up.
I've used such devices in series with the primary of torroidal mains transformers which have a high inrush current and was causing MCB to trip.

Just check resistance with increase of temperature....it might fall indicating NTC.

[paul_h]

As far as I know, they do limit current inrush on first power up.
They are in the control circuit not the inverter circuit, they protect everything, not just the inverter.
I've never seen one fail, but they go open circuit when there's a short on a circuit board, AFM or condenser fan etc when you first power up the unit, cutting power to the diode bridge which powers the whole unit.
When the fault is fixed, the posistor closes circuit again.

[nike123]

As far as I know, they do limit current inrush on first power up.
They are in the control circuit not the inverter circuit, they protect everything, not just the inverter.
I've never seen one fail, but they go open circuit when there's a short on a circuit board, AFM or condenser fan etc when you first power up the unit, cutting power to the diode bridge which powers the whole unit.
When the fault is fixed, the posistor closes circuit again.

This is diagram:
Blue is neutral
Red is Live
Green is where it s supose to bee 220V but it is 0V. Therefore I taught it is faulty PTC.
When I disconect AFM from TM 102, 103, 104, 105 I got 130 V. That indicate short circuit in diode bridge. I will check it and come back with result.

[nike123]

Hi Nike,

Are you sure that it is a PTC ? It could be a NTC unit to limit inrush current on first power-up.
I've used such devices in series with the primary of torroidal mains transformers which have a high inrush current and was causing MCB to trip.

Just check resistance with increase of temperature....it might fall indicating NTC.

Thanks Electocoolman!
I checked resistance when hot and cold and it rise with temperature. It is PTC!
Then it is obvious that it protects from overload and not from inrush current.

[nike123]

Yep, I found that + part of diode bridge is short toward line. Happily it is common available part.
I will install some temporary bridge for further troubleshooting (without connected compressor and fans).
I already changed AFM because it was faulty. I hope he was the cause of diode bridge fault and that new one has remained undamaged. I will also check it.
Thanks Paul.

[stefs_cruiser]

The Posistor looks like a Murata to me, something like a PTH491A04 AR220N400
Although that measures about 25 ohms cold.

Hope this helps.

[nike123]

The Posistor looks like a Murata to me, something like a PTH491A04 AR220N400
Although that measures about 25 ohms cold.

Hope this helps.

Yes it looks simmilar. I will try to find more details on Murata page.

[nike123]

This is good literature about Posistors!
http://www.murata.com/catalog/r16e.pdf

[nike123]

And here it is, explanation of his use in my case:

3. For the control of inrush current
A switching power supply has large inrush current
when it first turns on. If POSISTOR is used, instead of
a resistor or an NTC Thermistor, the POSISTOR works
as inrush current limiter. The POSISTOR self heats due
to over current in the case of relay or thyristor’s failure
and will trip to high resistance, quickly shutting off the
current.