Extractor Fan power supply

[pintglass]

Hi
I've attached an image of the power supply i'm trying to repair.

The fan works fine if i bypass the timer circuit.
I'm guessing that the x2 capacitor could be at fault as the fan stutters when it is switched on.

Could the issue be that the capacitive dropper has lost capacitance so increasing resistance.

I was looking at ordering the following replacement component

https://uk.farnell.com/kemet/r46kf31.../2763160?st=x2

but it states that it is not for use in "series with mains" type applications.

Does this mean that it just won't last very long( just like the original ) or does it mean it could fail short circuit with obvious consequences.

[stj]

Re: Extractor Fan power supply

for mains you need an X2 class cap.

i dont know why the kemet one warns against this unless it has very low current handling.

[redwire]

Re: Extractor Fan power supply

Kemet and Vishay explicitly state some of their X2 caps are not suitable for use in capacitive droppers. I think it's a lifetime issue due to the high ripple currents that are seen? There is a film cap failure mechanism where the capacitance just gets lower and lower, in series dropper applications.

I would measure across ZD1 that will tell you if it's a power problem. The zener ZD1 and 220uF cap, they also fail with age.

[pintglass]

Re: Extractor Fan power supply

I'm not sure what voltage i should have across ZD1 so don't know if it will be correct or not.

[budm]

Re: Extractor Fan power supply

It will be <10V for sure since the filter cap is rated at only 10VDC. Look up spec sheet of U1, that will give you a clue what the ZD1 will be.
For now you can check the resistance of ZD1 in both directions to see what you get.

[pintglass]

Re: Extractor Fan power supply

From the datasheet for u1 it lists these specs so i assume its 5V

0.2 ELECTRICAL CHARACTERISTIC
(All of voltages refer to Vss, Vdd = 5.0V, fosc = 4MHz,Fcpu=1MHZ, ambient temperature is 25C unless otherwise note.)
PARAMETER SYM. DESCRIPTION MIN. TYP. MAX. UNIT

Operating voltage Vdd Normal mode, Vpp = Vdd,25C 2.4 5.0 5.5 V
Normal mode, Vpp = Vdd, -40C~85C 2.5 5.0 5.5 V

Am i measuring in dc or ac?

[R_J]

Re: Extractor Fan power supply

It would be better if you posted the ic number or the datasheet.

[pintglass]

Re: Extractor Fan power supply

Sorry this is the data sheet for u1

https://datasheet.lcsc.com/szlcsc/18...SG_C337782.pdf

[R_J]

Re: Extractor Fan power supply

The VDD voltage for the ic will be +5 volts, so the voltage across the cap will likely be +5vdc. Is VR1 the speed control for the fan?

[redwire]

Re: Extractor Fan power supply

It looks like 5VDC power is used for the MCU. The MAC97A6 triac needs around 5mA to turn on and R12 is 1k.

So I would expect around 5VDC across ZD1 and the 220uF 10V cap.

[pintglass]

Re: Extractor Fan power supply

The VDD voltage for the ic will be +5 volts, so the voltage across the cap will likely be +5vdc. Is VR1 the speed control for the fan?

Vr1 is for how long the fan stays on after its switched off, or power removed from the switch live

It has a permanent live and a switch live, hope that makes sense.

[R_J]

Re: Extractor Fan power supply

The fan works fine if i bypass the timer circuit

how did you bypass the timer circuit? It could be the triac is driven by a PWM signal from the ic and the fault could be with the fan and not the drive circuit. or if the output of the ic just turns the triac on and off with a logic high or low, the triac could be faulty.

[pintglass]

Re: Extractor Fan power supply

how did you bypass the timer circuit? It could be the triac is driven by a PWM signal from the ic and the fault could be with the fan and not the drive circuit. or if the output of the ic just turns the triac on and off with a logic high or low, the triac could be faulty.

To test the fan i just connected a wire from the neutral terminal on the input connector to the A/N point on the board, so i was just basically bypassing the triac as the triac is on the neutral line.

I have tested the triac and it did seem ok.

I've tested for voltage on the + terminal of the 220uf cap and I'm only getting about 1.8v thats with one probe on neutral and the other on the + terminal of the cap, am i doing this correctly?

[budm]

Re: Extractor Fan power supply

You need to check the DC Voltage on the cap by putting each probe of the meter on the cap legs.
BTW, I see that the AC terminal block has 3 wires, Brown = LINE, Blue = Neutral, so what is the black wire connected to on the out side world?

[pintglass]

Re: Extractor Fan power supply

You need to check the DC Voltage on the cap by putting each probe of the meter on the cap legs.
BTW, I see that the AC terminal block has 3 wires, Brown = LINE, Blue = Neutral, so what is the black wire connected to on the out side world?

The black wire is the switch live, which is then connected to the physical switch to turn the fan on and off, but when the physical switch is turned off the permanent live (brown) allows the fan to continue to run until the timer turns it off.

[pintglass]

Re: Extractor Fan power supply

I'm getting 3.7v dc across the 220uf cap and the same across the zener diode(zd1)

I'm getting 103v on the cathode of d1 and 3.7v on the anode.

Should i be getting about 5v across the cap and the zener diode?

[redwire]

Re: Extractor Fan power supply

The capacitive dropper C1 is under high stress (missing a resistor for low ripple current, and it's half-wave) - check C1's value is not low. You'd have to sketch a partial schematic, not sure where D1 cathode goes.

See if it stays at 3.7V when it's trying to have the fan on (using more current driving the triac). I think it's a 5V design, although the MCU can run from 2.4-5.5V it has brownout/low voltage detect programmable at 2.0V/2.4V/3.6V but at low voltage say 3.6V not much current is available for the triac.

Why is the LED not populated, but the 680R resistor "ZD2" is there, strange.

[pintglass]

Re: Extractor Fan power supply

The voltage across the 220uf cap and the zener diode stay the same if I switch the fan on or off.

The only reason i can think of for the led being left out is that this pcb could of been used in many different versions of fans, in my case there is no hole in the cover so it would not be seen anyway.

I have attached an image of the underside of the pcb highlighting the point where the diode comes through the board, it then connects through the 2 banks of resistors to the live side of the fan.

To be honest I've been trying to sketch a schematic but im not sure I'm drawing things correctly as its hard to see if things are in parallel or series, I'll keep trying with that.

[redwire]

Re: Extractor Fan power supply

The circuit is weird, it doesn't make sense why C1 is across the triac?
This is duct fan WBB449251 4" 77 CFM?

[pintglass]

Re: Extractor Fan power supply

The circuit is weird, it doesn't make sense why C1 is across the triac?
This is duct fan WBB449251 4" 77 CFM?

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