BTN01 - what is it?

[WaveyDipole]

Can anyone help me determine what this component is please?

The board is an extractor fan timer board. The connector visible in the picture is for the fan motor (rated 220V, 45W). One terminal is wired direct to live, the other is wired via this component in a TO-92 package to neutral. I am guessing that it is a thyristor or triac as I can't imagine anything else so small handling mains AC voltage, however, I am not sure and have been unable to find any datasheet. The TC4001BP IC is a quad 2 input NOR gate. The centre pin on the BTN01 device is connected via a resistor to the output of one of the gates. The board has a handful of discrete components and a preset to set the 'ON' duration.

Sorry the photo is a bit fuzzy. It was difficult to capture with the phone camera.

[John M0GLN]

As you say there's not much info' about but according to an advert on Amazon it is,

Product Name : Triac Thyristor;Model : BTN01
Blocking Voltage : 600V;RMS on-state Current : 1A
Pin Size : 14 x 1.27mm/ 0.55" x 0.05" ( L* Pitch);Body Dimension : 5 x 4.5 x 3.5mm/0.2" x 0.18" x 0.14"(L*W*T)
Weight : 4g (2c3f72d6-1b26-11ea-9a1e-4cedfbbbda4e
Package Content : 30 x Triac Thyristor (Contenu de l’emballage: 30 x thyristors Triac

this is the advert, but it does look like a different package.
https://www.amazon.co.uk/Aexit-Silic.../dp/B07CWTH665

John

[WaveyDipole]

John, thank you for finding that information. A triac certainly makes sense given that this is an AC application. The package is the same. The camera angle of my photo is a bit mis-leading.

What is a "Triac Thyristor" though? I thought triacs and thyristors were separate (although related) component types with a triac passing AC, but a thyristor being basically an SCR and passing only DC. So is this some kind of hybrid?

Well, I think I have managed to track down a datasheet:
https://www.datasheet4u.com/datashee....php?id=860112
It is described here as a triac, so I guess that Amazon listing description is a bit of seller keyword spamming?

I also thought that neither device can be turned off once triggered so I am puzzled how the circuit manages to turn the fan off after X seconds? I can appreciate that it must have something to do with C2 discharging via R4/VR1 at a rate determined by the setting of VR1 but I can't quite understand how turning off the light switch triggers the countdown and turns the thing off. I have attached the reverse engineered circuit diagram as far as I can make it out. Also, why is the switching on the Neutral side?

[WaveyDipole]

Further experimentation shows that the triac can be turned on and off just be supplying a voltage to the resistor in series with the triac gate. The triac can be turned off simply by removing the voltage. It doesn't seem to respond very well to being driven with a PWM source. It just stays either on or off. I was hoping I might be able to regulate the speed this way.

[Herald1360]

Triac in the neutral side is easy to drive from logic with its supplies referenced to neutral. The fan doesn't care.

PWMing the triac gate won't work because once turned on it stays on for the rest of the half cycle. You might get somewhere with phase delayed turn on but the motor's likely an induction type which doesn't respond very well to voltage control.

[Terry_VK5TM]

You need cycle skipping to control the speed.

I E you turn on the triac for x cycles and off for a few cycles - note that some motors do not respond well to this form of control.

I think there was a motor speed control project based on this principle in EPE magazine recently (ish).

Phase control is another option, but this tends to generate a lot of electrical interference if not properly suppressed.

[WaveyDipole]

Thank you. That all makes sense. Phased control looks a little more complex and the circuits I have seen so far involve a potentiometer (as in light dimmer control) to adjust the phase angle. From what I can see it also seems to require a trigger reference from the mains AC cycle.

I am working on a project to control the bathroom extractor fan using an ESP. The existing timing is so erratic that it seemed anything would be an improvement. I am experimenting with a spare fan controller board and a 40w light bulb to simulate the load of the 45W fan. I was a simple matter of lifting a 1.5k resistor in series with the triac gate and inserting an opto-coupler between it and the circuit DC supply. The Arduino interfaces vi athe opto-coupler which is sufficient to turn the fan on and off as required. According to the datasheet, the triac gate could be driven directly, but it just seemed safer to use an opto-coupler.

The fan would run at full speed while someone was having a bath or using a shower and for a defined time afterwards, but it seemed to me that if the fan could run at much reduced speed (and noise level!) to provide background ventilation for an extended time afterwards might contribute to reducing the level of black mould in the bathroom. Its only a theory though. Adding phase control would certainly make the project somewhat more interesting.

[Lucien Nunes]

To expand on Herald1360's comment, the fan motor will be a shaded-pole induction motor, the speed of which can be controlled to some extent by voltage (either by transformer or by phase angle control.) However, unlike say a DC permanent magnet motor that can be proportionally and smoothly controlled all the way down to zero, induction motor speed tends not to be very stable when significantly reduced below maximum. In any induction motor, speed is primarily determined by frequency, as this governs the rotation of the magnetic flux vector around the stator (1500 or 3000rpm on 50Hz.) The rotor of an operational motor runs a little slower, typically 1425rpm vs 1500rpm synchronous, causing the rotor cage winding to cut the magnetic field, inducing current and generating torque. The difference between synchronous and actual speed, called slip, increases with torque and with reduction in supply voltage, since lower voltage means less magnetising current, less flux, therefore more slip needed to produce a certain amount of rotor current and torque.

Because a fan has a smooth (although non-linear) torque-speed curve, on reduced voltage the speed drops until the torque-speed curves of motor and fan cross. In effect, it is a weaker 1500rpm motor still trying to achieve 1500 rpm, slower only because of the load torque. The practical effect of this is that even if the voltage supply is stiff, as the speed it reduced it becomes increasingly dependant on the air loading of the fan impeller, so you might find backdraughts or variations in airflow through the house affecting the fan speed considerably.

When experimenting using a lamp load note that it is non-inductive, while the motor is significantly inductive and will produce a lagging current. Whether this is important depends on how you are detecting the supply voltage phase and how you are firing the triac. Better results are obtainably by hard firing relative to the actual supply, compared with a simple 2-wire circuit as used by most conventional triac twist dimmers. The motor may also buzz when presented with a chopped waveform, this effect is likely to be very dependent on the exact construction of the motor; one might be objectionable, another almost silent. Conversely, reducing the magnetising current slightly does often make induction motors run more quietly, as the vibratory forces proportional to flux are reduced.

[WaveyDipole]

Lucien, thank you for the detailed explanation. This all seems to make sense and I am beginning to understand that at best this will be very much trial and error with low chance of success, and at worst case is likely not to work at all. I actually am now beginning to think the latter is nearer the mark given the fan has an inductive motor. As everyone quite rightly points out, this type of motor does not respond very well to voltage changes. It is probably better to keep it simple and stick with plain on/off control on a timer for now.

It might be worth an experiment to see whether the motor can be made to run a bit quieter with a slightly reduced power input but I will bear in mind that this might not be at all possible to achieve.

[GroovyG]

For what it's worth, there was an article in Elektor a few years back that suggested switching the fan in response to the temperature of the hot water pipe to the shower. I eventually got round to construction of this device and can say that it seems to work very acceptably, allowing the fan to run on until the water in the pipe has cooled to the set point.

[Refugee]

Originally Posted by GroovyG

For what it's worth, there was an article in Elektor a few years back that suggested switching the fan in response to the temperature of the hot water pipe to the shower. I eventually got round to construction of this device and can say that it seems to work very acceptably, allowing the fan to run on until the water in the pipe has cooled to the set point.

That is not easy with an electric shower.

[Cobaltblue]

Our fans run with a combination of timer and humidity in our bathrooms a long as I remember to turn on the lights

Cheers
Mike T

[WaveyDipole]

Originally Posted by GroovyG

For what it's worth, there was an article in Elektor a few years back that suggested switching the fan in response to the temperature of the hot water pipe to the shower. I eventually got round to construction of this device and can say that it seems to work very acceptably, allowing the fan to run on until the water in the pipe has cooled to the set point.

Thanks for the comment. If the sensor were in a position where it can sense the hot water feed to both shower and bath that would allow it to deal with both. The shower pipes here are within a stud wall and not easy to get to although perhaps under the floor or in the boiler cupboard might be possible.

My plan was to have the sensor inside the vent pipe just above the shower. Both temperature and humidity should rise in response to either a bath or a shower, although it may take longer to respond for the bath. Since air temperature and humidity vary throughout the year but shouldn't vary appreciably over a few minutes, one could presumably have to look for a sudden rise of both parameters in the space of say 2 or 3 minutes and have it turn off as the temperature/humidity approaches levels prior to the sudden rise. In that respect, the water pipe idea is probably simpler to implement. I will give it some thought.