DC12V 12A car window motor - what spec for a 220V PSU?

[jim hardy]

During testing you had observed the motor beginning to run hot

window motors aren't expected to see continuous duty...

 

[marcophys]

I will check the motor without worm drive.

I was wondering what is making it a two speed motor, depending on polarity.
I attempted to remove the motor outer casing from the spare motor, but even after heating the screws they weren't budging.
I'll come back to that operation.

Re the fuse
I found a BS1362 5A fuse.
I then opened the charger.
It's a West German Absaar Type 108 NE/D2 with a push button fuse.
However, the fuse has no data on it whatsoever, but T 25 F appears on the underside data sheet.

The Fuse is top left
Wired from the Ammeter to Output.

The fuse button is out and is on a spring.
I presume it must trip on heat.

Any thoughts?
Should I still install the BS1362 5A fuse?

Re motor duty
This is to be seen.
The motor isn't running continuously.
By necessity it is fully enclosed in plastic (as per the earlier photo).
It's a roomy enclosure, but heat will dissipate slowly through the plastic.

I could have it wired to the standard foot switch - but It would mean more stopping and starting.

In Use
It seems to be running freely without signs of protest.
I'm going to complete all the planned operations, and then run some more tests.

 

[jim hardy]

I was wondering what is making it a two speed motor, depending on polarity.

That's interesting, and when you think about it they might have done it on purpose.
One way it's lifting the window which is a several pound load plus friction.
Other way it's lowering the window so runs unloaded.

To get same up and down speeds for aesthetics one would do something to slow unloaded "Down" speed to match loaded "Up" speed.
I've no idea what they did.
Perhaps some clever mechanical trick with friction in the worm drive; ME's are brilliant at such things
perhaps a third brush; a mundane EE trick
perhaps a few turns around the permanent field magnets to slightly aid or oppose them ?

Now you've got me curious - next one i find i'll take apart...

 

[marcophys]

I think that it must be electrical... it is almost perfectly twice or half speed.
Minor difference will probably come from increased friction one way:

Engine Barrel 1.7 Kg
Clockwise = 35 rpm - 6 V
Anticlockwise = 68 rpm - 7.80 V

This voltage was measured only a few inches from the motor at the end of approximately 10m of 1.5 sq mm cable

I've had another look at the screws holding the motor casing.
The problem is that I can't get a T bar in play due to the screw proximity to the casing.
That leaves the screw driver.
Also the screw heads are not hard.

Having already tried with heat, I can see that this would come down to 'drilling out'.
With so much to do, the motor must remain a mystery for the time being.

 

[Asymptotic]

Re the fuse
I found a BS1362 5A fuse.
I then opened the charger.
It's a West German Absaar Type 108 NE/D2 with a push button fuse.
However, the fuse has no data on it whatsoever, but T 25 F appears on the underside data sheet.

Absaar may be calling the red buttoned device a fuse, but it actually is a push-to-reset circuit breaker wired in series with the charger DC output. Can't say what the "T 25 F" marking means. 25A seems a high current rating for this purpose; Absaar type 108 charging output is 11 amps, and a 15A breaker sounds about right. If the charger is operational with the button out then either it comes out farther when in the tripped state, or it is tripped, but the breaker contacts are welded together.

I presume it must trip on heat.

Many circuit breakers are thermal-magnetic in nature. Long-duration, marginal overloads cause trips due to thermal effects while magnetic principles are used to quickly clear severe overloads and short circuits.

Should I still install the BS1362 5A fuse?

Is the BS1362, 5A fuse in the line cord plug? Or are you asking whether one of these are appropriately rated to provide motor protection?

 

[marcophys]

RE T 25 F
I found this catalogue:
http://www.sensata.com/download/klixon-circuit-breaker-thermal-catalog.pdf

On page 4 it shows all the breakers with very similar red buttons.
On page 6 & 7 there are the specs showing temperature rating at 25 deg C

Perhaps therefore: T (temp) 25 F (fuse)

Re potentially welded together
I note that the Klixon buttons are a similar distance out.
This isn't hard data, but...

Certainly my fuse button seems to be out a good distance (6mm).

I have spoken to Absaar, but the charger is pre the experience of the technician.
So I've sent him an email with the photos etc.

BS1362, 5A fuse in the line cord plug?
Yes it fits in the sprung in-line fuse holder.
It's a touch shorter than the original, but the spring handles it.

 

[jim hardy]

BS1362, 5A fuse in the line cord plug?
Yes it fits in the sprung in-line fuse holder.
It's a touch shorter than the original, but the spring handles it.

hmmm

The original fuse, provided with the motor is a straight 15 Amps (30mm x 6.3mm).

Automotive fuses will be rated just 32 volts
Check , it should be written on one end.
Don't rely on an automotive fuse to interrupt line voltage for it might or might not do it. Get a proper 250 volt rated fuse. Any good hardware store should have them , or look in junk electronics (dead PC power supply?) .

 

[marcophys]

hmmm

Automotive fuses will be rated just 32 volts
Check , it should be written on one end.
Don't rely on an automotive fuse to interrupt line voltage for it might or might not do it. Get a proper 250 volt rated fuse. Any good hardware store should have them , or look in junk electronics (dead PC power supply?) .

It is suggested that the auto fuse be replaced by the BS1362, 5A fuse in the line cord plug.
The spring tension is fine.

The original auto fuse was rated at 15A.

 

[jim hardy]

It is suggested that the auto fuse be replaced by the BS1362, 5A fuse in the line cord plug.

Ahhh, thanks for clarification.

I see BSC1362 (a new term to me) is a British standard for line fuses !
http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/product-datasheets-a/Bus_Ele_DS_2042_TDC180.pdf

Wikipedia:
https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets:_British_and_related_types

BS 1363, 13 A plugs socket-outlets adaptors and connection units is a British Standard which specifies the most common type of single-phase AC power plugs and sockets that are used in the United Kingdom.

Learn something every day... Thanks !

old jim

 

[marcophys]

Ha!
Nice data sheet find... good share.

When I searched, the BS site wanted £65 to view the data sheet.
So annoying, particularly as it's a common or garden 'gold standard' that was created in 1947, and modded to include the 5A into the standard in 1973.

As an aside... I see that you've successfully avoided the global debate about BS1363, as to whether this is the ultimate 'plug & socket' connector system (it's best avoided)..

I note that 'fuse users' (everybody) are now advised to weigh the fuses before use to confirm authenticity.
Anything less than 2.2g should be discarded.
Mine is 2.4g
http://www.bs1363.org.uk/DTI_warning_on_Counterfeit_Fuses_web.pdf

Here's a link to a counterfeit BS1362 fuse test page, with a nice video at the bottom, showing a fake fuse exploding on short circuit.
http://www.pat-testing-training.net/articles/fake-fuses.php

Or if you really want to go anal, and see how prime time TV educates the public on fuses... here is the first 10 minutes of a program devoted purely to the the subject of fuses.


I love it!... it's all down to the sand.
Hence why I proclaimed that I'd found a BS1362 5A fuse.
I thought oooh... that's a good one

 

[jim hardy]

I love it!... it's all down to the sand.

I'm a believer in sand . It's the arc-quenching medium in fast acting semiconductor fuses like Shawmut 101's.
I've dissected many a fuse for post-mortem forensics on electrical failures ...

Counterfeit fuses ? OMG thanks for the head-up.

 

[marcophys]

Counterfeit fuses ? OMG thanks for the head-up.

I know... it's horrifying.
... and you can no longer rely on print quality as the flag.

Previously everything about them (counterfeits) were crap.
... but now they have the printing to perfection, and they are flooding the market.

It's not the cost of the sand... it's the fact that this entire element of the production line isn't included.
Take away 'sand management & implementation' and everything becomes as easy as a wire , two caps, and a printed enclosure.
... and within that remaining structure... anything goes.

... and apart from electrical failure scenarios...it impacts on quality producers and jobs...
So it's good that TV producers are kicking out these warnings at prime viewing hours.

... Anyway... I've completed surface densification today.

 

[jim hardy]

... and apart from electrical failure scenarios..

Heaven forbid one of those fuses winds up in somebody's multimeter.

This is video of the explosion that might result (don't worry it's a demonstration filmed with a dummy)
whiteout from fireball lasts 'til 22 seconds

 

[marcophys]

Densification left a polished finish.
Static densification doesn't.

1st phase surface removal media is extremely sharp.
Therefore, on impact a cut occurs, even when the iron surface is passing at the speeds discussed.
Round ceramic dust media must be delivering a glancing blow.
In fact, this is as predicted, though I didn't consider that a polished surface would be the result.

I can get the speed down to 29 rpm @ 5.3V 4.7A (using the slow charge switch on the charger).
35 rpm @ 6V 5.1A (using fast charge switch)

(It looks like that 5A fuse is too light)

If I drop the voltage again, by say by increasing the supply cable length, the Amps will increase again.
Is this problematic to the motor?

 

[marcophys]

I added 8m of cable:

26 RPM 4.4V 4.5A

So the volts dropped and the amps dropped.
I expected the amps to rise.

I have to presume that the extension crocodile leads shouldn't be used.
This last measurement was taken with the meter probes screwed into connector blocks.

What I'll do is add another 8m of cable - it's a 4 wire cable - I can simply solder the ends).
I'll measure again using the same system.
This way we should get a genuine difference between the two.

 

[marcophys]

A further 8m cable... so approximately 26m in total.

21 rpm 3.8V 4.35A.

The motor seems to be rotating fine.
The volts are up and down... so the reading is best median.

I've started, so I'll continue.
The goal is to get it to 10 RPM.

 

[marcophys]

This is better.
We have 45m of 1.5 sq mm cable.

With the barrel mounted on the turntable:

11.5 RPM 2.8 V 4 A​

The motor seems to turn okayish... but there is a tight spot, so it slows and speeds up within one revolution.
... but this is to be expected.

The only question is whether the motor can function at this setting, on an ongoing basis.
I will remove the enclosure cover, and simply touch the motor to judge whether it is getting hot.

 

[marcophys]

Ha ha!
The big news that we've been waiting for...

I ran the motor continuously for 10 minutes, and was able to hold my hand on the motor.
It was getting hotter constantly, but thinking of shower temperatures, my guess is that after 10 minutes it reached around 45 - 50 deg C.
To 5 minutes it had barely warmed.

I don't know what the fail point will be, nor the cool down period, but it definitely seems workable.
When I think of typical motors that run for say an hour... you can't even touch them because they are so hot.

Does anybody have any thoughts on this area?

I need to test densification at the new speed, but knowing the speed that one's hand moves over clean iron, I am very confident of success.
11.5 RPM is a crawling pace.
I'll confirm this.

Other exciting news
The enclosure contained ceramic media (what?)

I once saw a doc on the development of a new torpedo.
The camera crew were there for the first trial in the test pool.
It sank!
(I scoffed)
The journalist, in horror, said "but it sank".
The prototype engineer was totally unphased... he said "they all do, the first time".

I take back my scoffing.

The enclosure was unpacked from its polythene wrap - a new stock item.
But the gasket had parted in one place.

Yet only one place - and with no outlet... why would the ceramic media be looking to ingress?
The answer is of course positive air pressure.

While the filter is the cost of a small bungalow... it struggles to cope at the 'micro particle level'... so extraction is advised to be restricted
... otherwise the media (the cost of the car in the garage) will be extracted through the filter... and we don't want that.
Hence, there is a slight positive pressure build up, sufficient to find any failings in the enclosure system.

Thankfully, due to the weight of the dust, and the lack of air movement in the enclosure... it looks like the particles have entered the enclosure and for the most part dropped (there was no dusting on the motor itself).
However, this is a cautionary tale for electrical engineers.

The moral of the story is to check the gasket, even when dealing with a new enclosure.
Just the daily differing air pressures might cause an enclosure to breathe.
Then imagine the motor getting warm, heating and expanding the air... forcing some out through the shaft seal?

I'm not sure... the seals are tight.
... but it does raise the question of 'to breathe or not to breathe'?

The ideal must be a diaphragm - say between the lid and box.
Then you could have a hole in the lid (facing down).

The air pressure would be equalised by the diaphragm, ensuring that there would be no external or internal pressure on the shaft seals.

Eliminating the cable

Prior to moving to a PWM system... can the cable be simply replaced with a resistance?
If so... what sort of values should be in the ballpark?

Note: just seen a typo in the previous post... it should read 35m of 1.5 sq mm cable.

 

[marcophys]

Found a dimmer switch rated 250V AC 40 - 250W
Can this be used?

 

[marcophys]

Diaphragm made, exactly as first suggested.

I put a 3.5mm breather in the furthest corner from the gear box.
I then blew in.
... nothing at first (and I was thinking what?)... and then that was it; the cavity was filled and pressurised.

So the enclosure can breath, while the motor remains sealed.
Warm air or cold air, the diaphragm will absorb the pressure differential.
This should prevent any ingress of media between the seals and drive shaft.

 

[jim hardy]

Found a dimmer switch rated 250V AC 40 - 250W
Can this be used?

It will be an experiment with i'd estimate 60% chance of success.
It'll either work fine or wreck the dimmer, so if it's one you already have and don't mind sacrificing...

I have an extension cord with a lamp dimmer & receptacle in a box at one end just for experiments like this. One side of receptacle gets full voltage, other side is through dimmer. In US that's easy because our receptacles provide for separate feeds.

Try it with a lamp first . Then set it to minimum , plug in the charger and bring voltage up slowly while listening for unusual humming in your transformer.
Asymmetry in the dimmer output will make the transformer hum and run hot but it should self-announce by those symptoms..
You might feel a little line frequency vibration in your motor but that's expected.

Keep this thing safe. PF is wary about inexperienced people working with line voltage.
Be sure you put the dimmer and receptacle in an outlet box and all connections are safe from tiny fingers in your household that are curious...
Your work in post #29 looks pretty good so i don't mind suggesting you give it a try.
I think over there you have fused appliance cords - one of those sounds like a good safety feature. I don't like 240 volts , the sparks are too big for me...

old jim

 

[marcophys]

Thanks Jim for sharing that idea.
Yes I'm fine with wiring and general electricity... it's the development theory that I lack - I always have to do a lot of reading

Life is a constant learning process; and even when we know something in an associated field... we don't know all it's implications.
Here's a perfect example, just rediscovered now.

Q. Why do we need control over our electrical supply?
A. Because all the French cook at midday ​

We know this, but yet, it still can catch us (me) out.
I wanted to test densification at the newly achieved low speed.
I was all set to go, and hit the switch.
All I got was a pleasant hum, and a turntable that wasn't turning.

At least we can see that we have discovered the limits of motor operation - and we are on them.

This also explains why the test measurements are inconsistent.
French electricity, in all respects, is to a low standard.
Momentary power outages are frequent, especially if we have a bit of rain.

Turntable speeds
We have a 4 speed system - 2 with the motor and 2 with the PSU (battery charger)

                 RPM

 Charger Normal      Charger Quick

     Motor               Motor
Slow      Fast      Slow      Fast

 11        19        30        42

Because the slowest speed is on the limit, it needs to rise to perhaps 14.
For this reason, densification was tested at 19 rpm

The result was almost perfect, or perhaps perfect depending upon the desired finish.
There was a very slight shine, yet even speckling of the iron surface.

Clearly, everything is dependent upon diameter, but with the current cylinder, 14 would be ideal.

Next job: The dimmer switch.

 

[jim hardy]

Next job: The dimmer switch.

I hope it works . I never used a dimmer with a battery charger, might try it out if i can find my test box. Quit using it when i got a fine ten amp Variac...

 

[marcophys]

Dimmer controlled socket

I found a BS1363 MK socket with switch and indicator lamp (there is a God).
It has seen good service, and it intends to keep on giving.
(It's face could benefit from surface enhancement )

The dimmer is 240V AC 40-250W

The live mains supply lead passes through the dimmer.
The Earth and neutral leads pass direct to the socket.

The switch and socket were mounted on a convenient insulation panel:

Dimmer Control Test

Battery charger connected, the dimmer was wound up.
A quiet buzz could be heard.

The turntable is connected to the charger via 10m 1.5 sq mm cable.

Test 1
On normal or low charge setting - with the dimmer at maximum output
Slowest motor setting (clockwise)

3V DC is seen at the motor.
16 rpm is achieved
The motor hums

There is zero adjustment available on the dimmer at these settings.
Any reduction stops the motor.

Test 2
On normal or low charge setting
Fastest motor setting (anti-clockwise)

The dimmer provides adjustment
12 rpm was achieved
2.5V DC is seen at the motor

The fast motor setting is the best (for whatever reason - it's still a mystery to us).

Working at these minimum levels, may be highlighting any fluctuations in the mains supply.
The motor seemed to initially struggle, and then settled down and ran well.

Test 3
On high charge setting (!)
Fastest motor setting (anti-clockwise)

The dimmer provides adjustment
10 rpm was achieved
2.V DC is seen at the motor

Note: At this power setting, the turntable will not start unassisted
14 rpm @ 2.5V DC appears to be an acceptable minimum or thereabouts, without supply voltage regulation

Conclusions
The slow motor setting (clockwise) can now be dispensed with.
Anti clockwise runs better, with barely any variation of speed within 1 rotation (must be worm drive associated).

Jim's dimmer switch mod has proved successful in providing motor speed control.
I note Jim, that you suggested that the transformer would run hot, and forewarned of the motor hum.

From this... are we considering this to be a simple test... and at some point a more suitable motor control should be implemented.
Either way, we have learned a great deal.

Drawbacks
The only drawback derives from the fluctuating mains supply.
I've yet to monitor this but I guess it could easily range from 220V to 250V.

Is it the case that a mains supply voltage regulator is required?
Example - (this was at the top of the ebay page)
http://www.ebay.co.uk/itm/Voltage-Regulator-Adjust-Motor-Speed-Control-Dimmer-Thermostat-AC-220V-4000W-/282425934168?

or this one with a fan:
http://www.ebay.co.uk/itm/AC-220V-4...or-Speed-Control-Controller-Fan/192027019684?

Would something like this always give a stable output, if set to lower than the minimum voltage supply?
In effect, a dimmer, but with known voltage output, and perhaps no negative 'buzzing' overheating effects?
Or is this cheap kit missing what is required?

I'm guessing that the PWM controller system would still require a DC voltage regulator, to enable standardised settings for rpm?

I'd be quite happy using Jims dimmer switch concept... it's just a question of whether it is fundamentally flawed for long term use.
(and even if this is so... it has proved invaluable for test purposes)

 

[jim hardy]

I note Jim, that you suggested that the transformer would run hot,

Thanks for the feedback !

Feel of it.
What worries me is your dimmer looks to be second hand and voltage to the motor seems to have dropped.

Asymmetric power from the dimmer will apply some DC to the charger's transformer . It should NOT be operated with THAT condition. It will hum loudly and get very hot.

Those are the easiest symptoms to see.

If you can measure voltage across the charger's primary winding (and i don't see a convenient place in your pictures)
read it with a DMM set for DC about 50 or 100 volts scale. More than a couple volts DC is too much,

Why , you'll naturally ask ?
We're handing the dimmer a largely inductive load now instead of the resistive one it's designed for.
So double check your transformer for buzzing, running hot, and best test is for DC content in the AC applied to its primary.
Most DMM's when set for DC will filter out the AC so long as you're not overranging them drastically. Don't try to measure DC content of a 240 AC wave on the 2 volt DC scale, but 100 volt scale should work and 50 might.

You need to have less than 1% DC content.

The heart of a lamp dimmer is an electronic switch known as a 'thyristor" .
Asymmetric firing of thyristors used to burn up relay coils in my nuke plant. They'd check fine on the bench at room temperature but when the thyristors got to operating temperature (~110F) they developed DC content. We found it first with oscilloscope and current probe, later learned that trick with the DMM set for DC.

So that's why i am sensitive , perhaps overly , but better safe than _{you know} ...
I'll feel better if you run it a while and feel of the charger's transformer .
Measurement of DC content would put a number on that qualitative test and be very reassuring.

I'd hate to be the guy who led you to burn up a battery charger because of a defective lamp dimmer.

Learn from my hard knocks it's easier that way, and share yours ? That's what we do here, share our experience.

old jim

 

[marcophys]

What worries me is your dimmer looks to be second hand and voltage to the motor seems to have dropped.

The dimmer is second hand... it was used to power a normal bulb in the 90's - probably 100W.
The voltage to the motor definitely dropped... it dropped by an additional 25m 1.5 sq mm cable.

IE. We achieved similar conditions by replacing the cable with the dimmer switch on maximum setting.

Asymmetric power from the dimmer will apply some DC to the charger's transformer . It should NOT be operated with THAT condition. It will hum loudly and get very hot.

Those are the easiest symptoms to see.

Forgive me, but I'm finding this statement ambiguous.

Are you stating that, fundamentally, the dimmer WILL apply some DC to the chargers transformer
,,, and therefore... regardless of the useful tests, it should NOT be used on a day to day basis?
OR
Is this warning only applicable if the transformers hums loudly?

Either way... my feedback is that the transformer exhibits a very low noise buzz.
You can hear it, but it's not much.

If you can measure voltage across the charger's primary winding (and i don't see a convenient place in your pictures)
read it with a DMM set for DC about 50 or 100 volts scale. More than a couple volts DC is too much,

Why , you'll naturally ask ?
We're handing the dimmer a largely inductive load now instead of the resistive one it's designed for.
So double check your transformer for buzzing, running hot, and best test is for DC content in the AC applied to its primary.
Most DMM's when set for DC will filter out the AC so long as you're not overranging them drastically. Don't try to measure DC content of a 240 AC wave on the 2 volt DC scale, but 100 volt scale should work and 50 might.

You need to have less than 1% DC content.

From this, I believe that you are asking me to meter the live and neutral at the MK socket (post dimmer switch).

I can confirm that your eyesight is still good
Absaar has cunningly masked the primary leads with a particularly delicate plastic enclosure, that has been glued together.
But the plug flex is only 1.5m.
Therefore I can disconnect the dimmer panel - open the plug, and insert it, with the exposed pins available.

With the dimmer reconnected, I can sample the modified supply to the transformer.
Yes?

The heart of a lamp dimmer is an electronic switch known as a 'thyristor" .
Asymmetric firing of thyristors used to burn up relay coils in my nuke plant. They'd check fine on the bench at room temperature but when the thyristors got to operating temperature (~110F) they developed DC content. We found it first with oscilloscope and current probe, later learned that trick with the DMM set for DC.

So that's why i am sensitive , perhaps overly , but better safe than _{you know} ...
I'll feel better if you run it a while and feel of the charger's transformer .
Measurement of DC content would put a number on that qualitative test and be very reassuring.

I have another dimmer switch... it will be transferable.

On with the testing......

Notes:
I wish that I understood this transformer .

 

[marcophys]

Measuring the Dimmed live feed
... at DC setting 200V

The reading is up and down, varying from a peak of 1.3V DC to 0.1V DC.
This is a repeating cycle, that hovers mid range then goes up... and then down.
... but max is always momentarily 1.3V DC.

Therefore well under the 2V DC that you warned about.

 

[Tom.G]

We're handing the dimmer a largely inductive load now instead of the resistive one it's designed for.
So double check your transformer for buzzing, running hot, and best test is for DC content in the AC applied to its primary.

Just add an incandescent lamp (60W - 100W ?) as a parallel load for the dimmer. That reduces the inductive load phase shift and makes the dimmer behave much better.

 

[jim hardy]

Are you stating that, fundamentally, the dimmer WILL apply some DC to the chargers transformer
,,, and therefore... regardless of the useful tests, it should NOT be used on a day to day basis?
OR
Is this warning only applicable if the transformers hums loudly?

The latter

Either way... my feedback is that the transformer exhibits a very low noise buzz.
You can hear it, but it's not much.

That's expected. Instead of a smooth sinewave it is receiving a 'chopped' approximate sinewave with sharp leading edges.


I think you'll be okay.

Forgive me, but I'm finding this statement ambiguous.

I was worried about the reduced voltage but you explained it as extra cable.
Sorry for the confusion . I should have said "If you have there an asymmetric behaving dimmer, hum and transformer heating will be the most obvious symptoms ."

The reading is up and down, varying from a peak of 1.3V DC to 0.1V DC.
This is a repeating cycle, that hovers mid range then goes up... and then down.
... but max is always momentarily 1.3V DC.

If the polarity sign on your meter shows for that measurement sometimes + and sometimes - then you have very good symmetry and no worries at all.
If it was always same polarity, feel the windings and the core after a few tens of minutes or an hour of operation.with no load on it.
If they're not uncomfortably hot to the touch i think you're fine.

Asymmetry puts a small amount of DC into the transformer. That causes the core to approach saturation heating it
and more current through the primary winding heating it too. Secondary winding will be heated only by thermal conduction outward from core and primary which is slow.
Those effects will be most noticeable near maximum "brightness" .

I'm oversensitized to this, probably.
As i said we had trouble with asymmetric thyristors in 1970's.
Burning up a hundred dollar relay wasn't an issue.
But when that relay tripped the nuke plant it cost my employer a literal million bucks for fuel oil to replace the megawatts we didn't make that day.
So i have a lot of my own "midnight oil" invested in tracking down what was killing those relay coils . Taught me a lot about inductance...

Thanks for tolerating an 'old fire-horse' . We've found no smoke but diligently checked for a potential cause of it.
If you build these motor drives for your friends , make that DC measurement and pick out dimmers with minimal DC content.
Probably the lamp dimmer people won't test their products for that parameter because a little DC is of no consequence to an incandescent lamp.

Congratulations for your inventive project . We learn SO MUCH MORE by doing than by just reading about doing , eh?

old jim

 

[marcophys]

Just add an incandescent lamp (60W - 100W ?) as a parallel load for the dimmer. That reduces the inductive load phase shift and makes the dimmer behave much better.

Wiring a 40W lamp in parallel to the Transformer feed
Haha... thanks Tom... it worked!
The buzzing dropped substantially - barely perceptible (as you'll see in the video below)

You've just jumped the development process... thanks for contributing

If the polarity sign on your meter shows for that measurement sometimes + and sometimes - then you have very good symmetry and no worries at all.

Metering the DC voltage
The video shows a number of DC voltage tests.
YouTube allows the video speed to be reduced... but even at normal speed, the +ve -ve cycle is evident.

Video Notes (Important)
The video shows a very noisy motor that masks the 'hum'.

This was just bad luck due to the speed at max dimmer - a speed that happened to resonate.
The noise resonates through the metal grill (dropped in position) and is amplified by the cabinet.
This was probably due to the gearing.

When making a video, one is time limited, when attempting a single take (which I was doing).
A better test would be to have slowed the motor down (to move out of resonance range).

I did this after making the video.
Here's the big news!

At reduced dimmer setting:

10 revolutions in 25 seconds NO LAMP (2nd test 27 sec)
10 revolutions in 21 seconds WITH LAMP (2nd test 22 sec)​

There is also a small reduction in motor hum.

Therefore, not only does a parallel lamp aid the transformer...
... it also aids the motor.

Having repeated the tests... there is a very clear difference between 'with and without' the lamp.
This means that the secondary coil is affected by the lamp - fact!

4 x 25 seconds = 100 seconds (40 revolutions) - without lamp
4 x 21 seconds = 84 seconds (40 revolutions) - with lamp

Therefore, by adding the lamp we see a 16% improvement in motor efficiency.

Note:
No change in efficiency is witnessed by increasing the lamp wattage to 100W.
Therefore, at this moment in time, it may be possible for those of you with the theoretical knowledge to consider a suitable replacement.

I'm thinking... a simple +ve -ve component bridge within the MK socket, that would replace the bulk of the lamp.

Ha!
This project keeps on giving

Here's the video
I would definitely consider slowing the video down to 0.5 speed (at appropriate moments).
This allows you to see the flipping between +ve & -ve DC that Jim mentioned.