Extractor Fan power supply

[budm]

Re: Extractor Fan power supply

C1 X2 cap is just a line filter cap and it connected across the L and N, the Blue disc looks to be MOV (can be verified by getting the numbers as printed on the body).
It looks like the power supply is using dropping resistors instead of dropping cap.

[redwire]

Re: Extractor Fan power supply

Sorry I don't understand what your asking me, have you drawn the attached schematic?

I drew that schematic of the power supply portion, to understand the circuit a bit better. For me it's easier to quick sketch in CADD.

Where is the timer you speak of wired in? Is it electronic or mechanical?
Are you sure this doesn't work - it's not on low speed with the pot turned to lowest speed, I see it's cranked all the way to one end.

It looks like blue is neutral, brown is line, black is (to neutral) low speed switch? I could find no manual for the fan. 4" Mixed Flow In-Line Fan - 77 CFM, Item #: WBB449252

We have to back up now, turns out it doesn't use a capacitive dropper, as budm points out. Instead, all the 10 resistors on the backside lower mains down for the MCU. It could be a 3.6V or 5V we don't know.

I'd make sure the 220uF cap is OK. You have to lift one leg to test it.
The circuit is not great for the triac, there is no snubber or transient protection for it, despite the parts being there.
I would say either we need 5V power or the triac is damaged.

[R_J]

Re: Extractor Fan power supply

The timer is the ic. The pot is for setting how long the fan runs after the switch is turned off. when the switch is trurned on , the fan starts, when the switch is turend off the fan continues to run for X amount of time (X set by pot)

PINTGLASS: what is the number on the U1 ic?

[pintglass]

Re: Extractor Fan power supply

The code on U1 is SN8P250/BSG its 14 pin.

The code on the blue component next to the 220uf cap is cnr 070471k

[budm]

Re: Extractor Fan power supply

Blue component is MOV: https://lcsc.com/product-detail/Vari...K_C273550.html

[redwire]

Re: Extractor Fan power supply

I updated the schematic. Some versions of the fan are two speed like Acme Miami AM-100, I thought it was that version.
The MCU does not have an A/D converter, it's using RC time to read the timer pot.

The triac seems to not last according to posts in other forums. People put in bigger 600V 2N6075B but wouldn't fit?
The MOV starts to clamp at 470V for a 400V triac, so I'm not sure why bother. And there's no RC snubber for it, to stop the fan inductance from making spikes.

[R_J]

Re: Extractor Fan power supply

The code on U1 is SN8P250/BSG its 14 pin.

The code on the blue component next to the 220uf cap is cnr 070471k

The ic operates on 5Volts, pin 11 is VDD (negative) pin 4 is VDD (+5v)

[R_J]

Re: Extractor Fan power supply

It could be that C1 is bad I believe it is used to isolate and couple the a/c for the 5 volt supply. If it is weak/open you won't get enough a/c to the power supply and the result will be low 5 volts
You may be having a similar issue as this thread https://www.badcaps.net/forum/showthread.php?t=80053

[pintglass]

Re: Extractor Fan power supply

Thanks for doing all this, and to everyone else that's helped, I've been trying to follow the schematic that redwire has kindly draw, but alot of it I don't understand.


What software do you use to draw with?

I have ordered a new multimeter as my current one doesn't do a capacitance test, i should receive it tomorrow. Should I remove C1 and test that first as there seems to be quite a few components that could have failed.

As you've probably guessed I'm doing this as much to learn from as fix the fan,
so thanks again I've learned a great deal.

[redwire]

Re: Extractor Fan power supply

It could be that C1 is bad...

That's what I thought too but this fan board does not use a capacitive dropper at all. Turns out it is using 10 resistors to drop mains down to the MCU's voltage. C1 is just an X-capacitor for EMI and noise, is pretty much useless here. Open C1 would not cause the fan to stutter. I thought it was a different circuit at first. At work we use Altium for schematics and pcb layout.

My guess is a bad triac or 220uF cap that is low in value.

[pintglass]

Re: Extractor Fan power supply

Could you tell me why i have around 103v on the cathode of d1?

[redwire]

Re: Extractor Fan power supply

Where was the other lead of the multimeter, between D1 cathode and ?

D1 will have 1/2 wave pulsating DC on it, so some multimters do not read that properly. I'll check my schematic again and see if I drew it right, it does look wrong ugh. The circuit is awkward as far as having a common point for measurements.

[pintglass]

Re: Extractor Fan power supply

It was more out of interest why i was asking, I,m not saying there's anything wrong with your schematic, i would't know if it was wrong to be honest.

I can't remember where i placed the other probe may well of been on the neutral.

I was just trying to figure out how the resistors are dropping the voltage.

[redwire]

Re: Extractor Fan power supply

Fixed a mistake in the fan board schematic. Now it makes sense.

D1 is a 1/2 wave rectifier supplying voltage to zener ZD1, limited by the resistors array R1-R10. I drew a simplified circuit of that section.
If you measured the voltage across D1 cathode to neutral, the multimeter sees a 1/2 sine wave and roughly should measure 1/2 of mains voltage if it has true RMS.

Neutral is usually taken as a circuit common for mains powered circuits.
But a triac driven directly by an MCU needs a negative gate voltage with respect to neutral. So the entire common for the MCU low voltage DC side is seen as say -5V with respect to neutral. It can be very confusing.
ST App note 442 TRIAC & MICROCONTROLLERS: THE EASY CONNECTION sort explains this.

[pintglass]

Re: Extractor Fan power supply

Well my mulitmeter didn't turn up today so still can't test the 220uf cap will have to wait until monday.

I've been looking at your schematic and what i don't understand is you have pin 4 of the ic as VSS where in the datasheet it says this pin is vdd? Its probably me being thick again but thought i'd ask.

[redwire]

Re: Extractor Fan power supply

I can't see where the pc board traces under the IC go.
MCU Datasheet has VDD (+V) pin 4 and VSS (GND) pin 11, I can flip the labels.

I would look at ordering a new 220uF cap and a new triac, something a bit beefier and higher voltage. Size seems to be a hassle here.

[pintglass]

Re: Extractor Fan power supply

I've tested the 220uf cap and I'm only getting about 74uf, which i think you new already, will the following caps be ok.

https://uk.rs-online.com/web/p/alumi...itors/5193848/

I'm not sure what triac to order could you give me a part number for one that you think will be suitable.

Thanks again

[budm]

Re: Extractor Fan power supply

You do not have any spare cap to try with? The TRIAC may be OK.

[pintglass]

Re: Extractor Fan power supply

No I haven't got anything close to 220uf

[budm]

Re: Extractor Fan power supply

What do you have?