Great service

Let us know if that was in fact the problem!

Unfortunately it wasn't. So it has to be the motor, and that's where it gets really weird. I took the fan down again to see if the motor had any information. It did:

Rhine Electronic Co Ltd Model No. N-125S

I don't understand this. That's the spec for an American A/C motor, yet this is supposed to be a DC motor. In fact, the remote control receiver has:

Model: RH788R DC MOTOR CEILING FAN ONLY Ceiling fan speed control Input AC 220V-240V/50Hz LIGHT: 300 Watts max Or 300 VA DC MOTOR : 35 Watts MAX Made in Taiwan

Note that Rhine Electronic Co Ltd are in Taiwan. The motor appears to be the one on

I emailed the fan company again, but have no idea how to proceed at this stage. Looks like I'll just have to write off the replacement remote and go for a new fan. :-(

Universal motors are AC OR DC. Work with either.

This is a brushless DC motor (

The controller seems very complex. I opened it and a couple of photos are here: Receiver:

The board is glued down so I can't see under it. There are 8 leads from the long connector at the bottom of the picture to the motor, and a couple of others from the mini socket next to the antenna which might go to the led light. I assume that the eight leads are involved in not only feeding power, but also measuring back emf.

At a guess, clockwise from the bottom:

Mains input / voltage conversion MOSFETs SMPSU for logic Microcontroller for control

That looks like the RF receiver

If it is BLDC I'd expect three phase wires and three sense wires. Does that connector also supply mains?

I suppose if it's not BLDC they could be synthesising ~120V to drive the US motor? I can't clearly see what's under the heatsink but the labels could be TR for triacs?

Theo

I think everything by and under the metal screen/heatsink is related to the SMPS. "TR4" is riveted to the metal, and there is a U2K8 bridge rectifier, coil/transformer, and two 275V AC X2 class capacitors.There are also a couple of 817C optocouplers and a 6-pin IC with obscured markings. Near the other transformer is an LNK364DN AC to DC switching converter.

By and "under" the RF receiver board there's a 93C46WP 3-Wire Serial EEPROM, and what appears to be a 2904 dual op-amp. There's also a custom(?) 32-pin QIL chip.

I didn't see any mosfets, but may have missed them. Which components do you think they were?

It is. The IC is a PT4302-X ultra-low power OOK/ASK superheterodyne receiver.

I would think so, but it's hidden. I've put the fan back up just to get it out of the way.

Do A/C motors "hunt" until they find the correct rotation direction and speed?

Depends on what type they are.

Universal motors dont have a correct speed. BLDC motors without sensors will use the coils to sense everything and will do a little kick to find out where they are If they have sensors they wont.

I was thinking about the TRs. If it was 3 phase BLDC you'd need 6 MOSFETs. I can't see how many are on that heatsink. (although I suppose there could be 3 dual-MOSFET packages)

It could also use switching MOSFET(s) for the SMPSU - only one would be needed for that, although there may also be a TO220 style diode.

If there's hall sensors it may rely on detecting the particular waveform to know which direction it's turning, which it can't do when static. So a little kick may be needed so it knows what the rotor is doing.

Theo

I wouldn't have thought so but is perhaps possible. There are some BlDC motors that use back-emf and/or current sense to work out position and direction as per your wiki article. The controller won't know the starting position and may have to make a guess. It shouldn't run in reverse for more than a fraction of a turn?

Many implementations use a micro to do all the control, sensing (onboard ADC) and drive (via a MOSFET).

No point in halls - don't net you anything sensorless can do. The sensored ones normally use optical sensors I think, but its years since I had truck with one

Hi from Australia I've got the same remote receiver on our Mercator fan, been tested and not sure if it's that or the 35 w DC motor. Shuddering and hesitation. Mercator don't even want to know it. Where did you get the receiver from & price please cheers snipped-for-privacy@yahoo.com.au

I can't speak for this one, but for items made in say the last 10 years it's always worth searching on Alibaba and Aliexpress. Maybe there are part numbers on the board that will help you search. Often the parts are made by some Chinese ODM and this enables you to identify them. Sometimes parts are available (either directly, or through resellers on Aliexpress), or identifying the ODM gives you clues as to which other brands use the same parts.

Can be a detective trail but eg I've found items on there for a fraction of the price the reseller is selling them in the UK.

(Not always though - I have recently been taking apart a Vent Axia fan and it seems even the motor is a custom part from a UK company)

Theo