hello,

my gas combi condensing boiler stopped working recently due to a fan failure.

I took the fan apart and found worn bearings, which I've replaced and also an opened fuseable 10R 5 watt resistor inline from ACLIVE, along with 2 out of 5 shorted IRF830 mosfets.

i'm new to BLDC theory so doing my research on it at the moment, but wondering generally what kind of pwm signal is used to run these kind of motors. I was guessing a 5-12v, 100hz-10khz, 50% duty square wave for starters but hope someone can comment on this.

the motor itself has 4 stationary coils, with a plain magnetic rotor attached to the shaft, only 2 electrodes are used to power the coil windings.

the fan is supplied 6 wires (HS hall sensor, PWM, sig GND, AC LIVE, AC NEUTRAL, and chassis GND) with a 240v ac supply.

the datasheet http://www.farnell.com/datasheets/1648153.pdf states a 24v dc nominal dc voltage, 7200 rpm and 40watts rating.

I think the fault may have been caused by either the faulty bearings, or voltage spikes due to power outages. there is evidence of light arcing between LIVE and GND, with some carbon deposits between 2 tracks, where it is dusty and dirty. these boilers have no surge protection built in, which is an easy way to rack up profit on these parts (£200 approx for the fan and another £200 for the main system pcb if it's blown)

I'm in the middle of drawing the schematic, which is a little tricky as although the top side of the pcb is through hole and only 21 components complex, the bottom side is large scale surface mount and has a thin layer of been green epoxy making it difficult to read the ic codes. might be needing a microscope for that part. from the ic's i can read they are high side drivers.

are there any good tutorials out there for how BLDC motor controllers work ?

the mosfets are rated at 500v, 4.5A, 70W 1.5 ohms drain-source. 10v max gate-source and are made by international rectifier.

Can I use modern vishay replacements to replace the 2 faulty ones, or should i replace all 5 with the same type ?

does it matter if they have a higher spec, but same drain-source ohmage ?

any help much appreciated,
thanks

 

I have my doubts that the motor is a BLDC. With only two phases (four coils) a BLDC would have a minimum of six coils, since all of them I'm aware of are three phase.

Is the rotor really magnetic? If so it could be a imbedded magnet induction motor also known as a permanent magnet synchronous motor.

As to the Vishay instead of International Rectifier mosfets, Vishay acquired a lot of the older IR part numbers so manufacturer name doesn't matter as long as the specs are the same or higher. Unless the board is easy to get to I'd replace all 5 at once.

 

thanks for replying shortbus, yes the rotor is definitely magnetic, it attracted all the bolts when it was in the bag.

i'll post some piccies so you can have a look.

imbedded magnet induction motor - could be, I wouldn't know as I'm still new to motors, just rebuilt a treadmill motor with new bearings and need to repair one of the motor controller boards. need to do a fair bit more reading about em.

 

there are some pictures up at this url http://s1300.photobucket.com/user/reapairman/library/

here is the stator and the rotor:

 

You are well ahead of me, repairman, but I've had a similar issue to yours with ebmpapst boiler fan. On the pcb, the first sm component on the +UB line is labelled 'F' - the input fuse and is o.c. - any idea of it's value? - can't see the underside as haven't unsoldered it yet. It's series resistor also looks o.c. No sign of burning and MOSFETs all seem OK, but underside was mildly coated with deposit after pervious (unrelated) incident. Can't ID the board - too many etched labels, but sticker says 0710L11-05, AT 190308, 24532. Can't find a replacement. [ALPHA CD35C]. Any ideas, please. Remainder of fan, rotor, bearings, stator in fine condition.