Great service

[Jeff Layman]

We see quite a few messages here about poor service, so I thought I'd post one concerning exceptionally good service.

Almost 9 years ago I installed a ceiling fan in our new conservatory. The fan was pretty expensive, being a remote-controlled DC fan, 6-speed and reversible, with a LED light. It has been used extensively over the years. A week ago I found it would barely turn, at only one speed, and no reverse. The light worked. I emailed the company explaining the problem (

), and a couple of days later got a reply suggesting that the remote receiver control was faulty. The reply stated the all-in cost of a replacement (including VAT and P&P), and a pdf of instructions on how to fit it. I phoned in the order yesterday at 3pm, and the remote control receiver, together with a new remote transmitter, arrived at 11am this morning by 1st class post.

[Davey]

Let us know if that was in fact the problem!

[Jeff Layman]

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

120Vac 60Hz 0.65A 38W Conforms to ANSI/UL STD 507 Certified to CSA C22.2 No 113

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

, but the number is slightly different (125NS instead of N-125S).

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. :-(

[The Natural Philosopher]

Universal motors are AC OR DC. Work with either.

[Jeff Layman]

This is a brushless DC motor (

which appears identical to mine). The info here seems to apply, especially the second paragraph as the fan definitely often starts in reverse and then seems to work out it needs to go the correct way (when it is working properly!)

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

Receiver additional board

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.

[Theo]

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

[Jeff Layman]

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?

[The Natural Philosopher]

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.

[Theo]

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

[Fredxx]

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).

[The Natural Philosopher]

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