Thyristor powered pulse motor - with video

[Slider2732]

Got a problem of understanding here.

I was looking for MOSFET's and whatnot on old PC monitors earlier and found what looked like a small transistor, but with odd numbering.
BT169D
Googled the datasheet and got this: BT169D Datasheet pdf - Thyristors logic level - Philips

The thing is about these, they are used as latches. A small current comes in at what would be a transistor Base and the unit switches on....and doesn't stop conducting.
I've found out that there is a mode where they shut down once the input current goes below a certain level and, presumably, that is what's happening here, hundreds of times per second. However, it should then latch, as online circuits for buzzers and other triggered alarms show.

I don't really know, but the motor runs well

There is a 1K resistor on the middle triggering leg. The Negative supply comes in on leg 1 and leaves on leg 3. I would think it's a bit like a MOSFET, but again have no real idea. Only other thought is that the collapsing coil AC is backing up via skin effect and causing the switch (a multi-strand 7 wire).

What's goin' on ?

Here's the video - please do note I must apologise, the vid says DT169D, not BT169D.

YouTube - ‪Thyristor powered pulse motor‬‏

[Farmhand]

Hi Slider, What you got there is a logic level SCR or thyristor, it's kinda like a Diode with a trigger, a rectifier of sorts, when the voltage go's down through zero volts in an AC supply the SCR switch's off so it only lets power of one sign through. Silicon Controlled Rectifier.

I find this site better for datasheets.
BT169 pdf, BT169 description, BT169 datasheets, BT169 view ::: ALLDATASHEET :::

When using DC they might not turn off, but do if a reversal happens. It's a switch so you made it work, good job.

That one will turn on with only .5 of a volt.

Cheers

[Slider2732]

Thanks Farmhand
I usually use those guys for datasheets too, leaving the search box on a tab and just typing in as and when I find anything when salvaging. However, the 'Quick View' of PDF's is also neat, in Chrome at least.

I understand the normal methods of switching, when relating to a DC input...which is where i'm still unclear on the operating method here. On/Off with Latch is how I understand thyristors, or at least that's how I used to understand them.
So, you mean the AC is indeed doing the switch action ? reversing the diode operation quality and letting it begin a fresh cycle ?

Hmm, If that is the case, then the Hall position would be important for exactly collapsing ? same as any coil setup on a pulse motor. Or maybe not, the Hall merely turning off the coil to collapse the coil and generate the AC that switches the thyristor.

And in which case, if the latter is correct, the video i'm uploading now might just challenge another tenet of pulse motors
It's weird, again, gimme a few minutes for it to finish uploading and i'll post the link.

[Slider2732]

Here's something that raised my own eyebrows so high up, that I wondered if i'd have to scrape them off the ceiling !

Tested with 3 different single filar relay coils the effect in the video below doesn't work.
Tested with 2 different 7 strand multistrand RomeroUK connected coils it does work.
Any single filar coil that has been tested doesn't even run with a thyristor.

The position of the Hall sensor is non governing...the coil can be placed anywhere and the motor runs.
Always at the same speed.
Always only the one speed
Rotor wobble is induced at different voltages, but not large speed increases or decreases.

YouTube - ‪Coil anywhere, motor keeps on running‬‏

[penno64]

Hi Slider,

Interesting video.

You need to consider what components remain in the original fan motor.

Remember, internally you have coils on a core. Your unit could be
inducting into the internal coils and using the original rotor magnet.

Maybe this will help to understand what is going on.

Pull apart the fan and remove the magnet & coils. Simply keep the bush
for the shaft. Reassemble and test again.

Penno

[Slider2732]

Interesting, thanks.
This one has no gubbins from an original fan, but the original fridge magnet type ring is still present, to serve as a flywheel (the intention anyway). The neo's are superglued now, so i'll see about removing the ring and run a test.

[Slider2732]

Here we go, ring magnet and metal holder removed.
Still runs

YouTube - ‪Penno's pulse motor question‬‏

[penno64]

Hi Slider,

That was quick work.

I have to stop my CONVENTIONAL thinking.

I will be attempting this experiment later today but can tell you, if I move
my coil even slightly, my rotor slows or stops.

Will report back later.

Penno