Test of 5 AC-DC PSUs cheaper than $1.5

I need  220AC to 5V PSU for exhaust fan controller, the trickiest part – it should be as small as possible. The main load is LEDs, same time supplied voltage should be clean enough for analog to digital conversions doing by attiny85. So I bought and test 6 different PSU. Because of seller mistake one of them turned up to be 220 to 12V PSU, so only 5 of them were tested.

All of them produces awful output exception of #1 and #3 (hilink)
The winner is #1, it’s one of the smallest (12X25X18 mm), one of the cheapest ($0.77), rated at 5V 700mA power supply.
No one of them (with exception of hi-link) doesn’t look safe enought to be treated as galvanic isolated PSU.
Here is a table for quick comparison, but out of the box (without changing capacitors or adding filters), only #1 and #3 worth to buy:

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Repairing of kitchenaid phase control board

It’s a story how I spent thee days troubleshooting 9 elements circuit when 7 of them are passive. I didn’t found what’s wrong, but fixed it.

I have  control board marked as W10354309, it’s European 220V model of phase regulator.
I don’t really understand the rules how kitchenaid marks their parts, because I found several part numbers for 220V version: 3184417, 4163707, 4163712, 9701269, 9706596, W10217542, W10538289, W10911442, W11174552, WPW10538289
(110V version have same idea and same schematic, just different values and ratings for same elements)
I don’t know why they do that. Probably because they use the same part on different models and/or under different brands.
So, I have 5ksm125 mixer and W10354309 phase control.

Service manual says, that at the first speed planetary shaft should have near 60RPM, but in my case it had near 120RPM and I was unable to decrease it by tuning control plate.

Here I should make a digression, these mixers have ability to maintain constant RPM under different load.  I was surprised when I learn how do they do that. One of the main component comes right from the steam engine era, it’s centrifugal governor which is placed on the shaft of the motor, here it is:

Yellow thing is the governor itself, black cylinders highlighted with green – weights, central pin stroked with blue is a pin which provides feedback to control plate. It works simple, the more RPM motor have the more pin extends.

Next component is so called control plate, in fact it has simple main switch and a T shaped contact. The main switch  just break circuit when you move switch lever to off. T-contact plate just shorts contacts on a plate in 3 different configuration. The white tab on a picture above is a dielectric tab on T-contact, governor’s central pin pushes this tab and changes which contacts are closed on control plate. Here is control plate from the other side:

And the last component is a phase control board, it’s basically dimmer if you google for ‘dimmer circuit’ you will find the same scheme as used in phase control board with one exception, usually dimmers have variable resistor for smooth regulation, phase control board has resistors network in which resistors shorts by control board in 3 different configuration. You can see it  behind top edge of contral board on the picture above and on closeup photo on picture below:

So, how its work together? Here is schematic from repair manual with comments and nominals added by me:

As I sad before control plate can be in 3 different states:
The first: the motor has too low RPM or doesn’t turn at all. T-contact fully closed, it shorts resistor network (R1, R2, R3, R5) completely and feeds motor with almost full sine wave (DIAC Q2 opens at around of 30V, so the start of the wave is chopped a little bit)
The third: the motor has too much RPM. T-contact fully opened, resistors network has maximum resistance,  phase control board feeds motor with minimum amount of energy (manual says that it should provide 40V RMS, I don’t understand why it’s true for both 110V and 220V version, but looks like it is).
The second: this state is somewhere in between too low RPM and too much RPM, control board shorts R1, equivalent resistance is ((R5+R3)* R2)/(R5+R3+R2), manual says that it should provide 80V RMS.

The more RPM motor have, the more central pin of centrifugal governor extents, the more it shift T-contact. When T-contact shifting, it opens circuit with bottom contact first and with upper contact next (check schematic above). When you select mixer’s speed you change distance between control plate and governor, the more distance it has the faster motor should spins to get equilibrium between the first and the third states.

Finally I can tell about my issue.
Usually when phase control is broken mixer doesn’t cho-cho at all or doing it on max speed, my story was slightly different, it had near 120 constant RPM on the first 3 speeds, next speed or two  increased RPM to the maximum, and other speeds did nothing.

When I saw schematic, I was pretty sure that I just need to replace DIAC. In circuits like this, if something works wrong in 99 cases of 100 it caused by broken semiconductor. When TRIAC failed it usually stays open or shorted (motor shouldn’t run at all or run at full speed).

I changed DIAC but  nothing changed, motor had RPM above nominal, but not the maximum. RPM was enough to extent governor’s central pin to the maximum and open both contacts on control plate.

The next suspect was TRIAC, here is only two semiconductors, if one of them is OK, the other one is broken, right? Wrong. I tried two different TRIACs without success. BTA12-600SW (it has the same characteristics like original one. Logic level gate, gate’s current 10mA , snuberless, but rated for 12A instead of 6A) and BTA06-600CW ( it isn’t logic level and had gate current around 35mA, it produced visible sparks during re-commutations on control plate, so don’t use it).

What should be suspected next? Capacitors? Both had less than 5% difference of capacitance from their nominals. I tried other capacitors, RPM of motor changed, but not significantly (in theory failed capacitors may have noticeable different capacity under high voltage, but I tested them with low voltage LCR meter).

After that I started to go crazy, I even de-solder every resistor, but they had correct values.
I spent near 3 days trying to find what’s wrong.
I had a lot of theories: failed resistor which heats when voltage applied and changes its resistance, semi-broken wires, semi-broken motor etc.
I even found a topic in which people had the same issue, but no one find the solution: https://www.electronicspoint.com/forums/threads/kitchenaid-mixer-phase-control-board-problem.241021/page-2

Soon after I started my experiments, I found that everything works as expected when I put R4 with increased value, but I wanted to find why circuit which had right elements didn’t work as it should.
At the end of the third day I gave up. I tried to replace every resistor, every capacitor in circuit and it didn’t helped, I tried to solder wires in parallel with existent,
In the end I decided to put 3.6KOhm R4 instead of original 560Ohm.

Here is my observations:

  • Manuals says that you can check phase control by putting sheet of non conductive material (like papper) between T-contact and contact which it touches, if it’s OK it should provide around 40V, but I got 50V. When I lovered voltage to 40V I got response from control plate regulation.
  • Motor starts spinning at around 9V DC.
  • Coils of stator has resistance of 7.8 Ohm each, rotor has resistance near 4 Ohm between nearest contacts, resistance of motor (between red and white wire) near 40 Ohm.
  • Circuit is sensible to element’s values, even when I tried to put capacitors with the same value I got slightly different RPM. My circuit has 1% R5, old scheme from manual has 3 resistors in series, usually this approach used when resistors have breakdown voltage less than voltage drop on them or when you want to use few cheap 5% 10% resistors instead of precise one.
  • Probably phase control boards with  different part numbers more stable. I found photos of others boards and saw that resistors have values different from values that observed. Here is an example from amazon:

Simple temperature controlled fan regulator

Some time ago I pulled out temperature fan controller from one of old ATX PSU.
With 12.2V input it provides 4.5V at 25°C and raises output voltage till 11.8V at ~70°C. After changing Q2 to higher voltage transistor and tuning of R4-R5 this divider this controller should be suitable for 12V fans with 24/36/48V input.
Here is result of my reverse engineered schematic:

One and a half port charger on TP5100 module

WARNING: Lithium batteries can be extremely dangerous when handled unproperly and lead to fire hazard. Information provided as is, you can use it on your own risk.

Before last holidays I bought cheap Chinese action camera, which came without separate charging station. Camera’s battery could be charged only in camera, charging batteries via which have few cons:

  1. You can damage camera port
  2. If you have more than one battery, you can charge only one at time
  3. You need to watch charging process and change batteries
  4. The last cons depends on camera, but usually compact devices use charger IC with linear regulation and they have low efficiency. If you don’t have access to electrical line and you bound to use power banks, efficiency could be critical.

It’s turned out that a lot of cheap cameras use battery in the same form-factor, thus I decided to share my charger.
I think the most popular solution for single-cell DIY Li-Ion chargers is TP4056 module. It’s almost plug and play solution, usually it have USB port and protection circuit, but it uses linear regulation, so it have low efficiency. Since efficiency is critical for me, I choose TP5100 module, unfortunately it comes without USB port, but it based on buck topology and should be much more efficient than TP4056.
Unfortunately these modules come without USB port (at least I didn’t found TP5100 with USB port).

Thus that project was separated in two main tasks: design carrier board with USB port and design case for charger.

Carrier board is extremely simple, it contains only Micro-USB port and place for TP5100 module.

Case also has simple design, only curlpit which I had – contacts. I made them from nickel plated strips, which I bent once to make it bit thicker:

First I had design where contacts should be inserted from side, but it was nearly impossible because of  small gap between side wall and battery holder wall. I redesigned the case in a way when contacts inserted from bottom, un-fortunatelly I didn’t take into account that wires should be soldered from bottom, so supports under contacts should be re-designed or partially melted with solderer as I did it.
To make contacts stiff I glued them in. If they not feet freely into dedicated slots, use solder iron to melt them into slots.
Before gluing them into place, you should be sure that they are long enough and battery fits properly. I supported contacts with fingers during tests. If they have right size, battery should ‘click’ into slot. My batteries stayed in place even when charger with batteries was turned upside-down.

Upper case was printed in with ‘transparent’ plastic, so I can see status led soldered on charger module:

Here is start most interesting part. TP5100 can charge two cells connected to serial, but cells will not be balanced. With a camera I frequently have one partially depleted battery and one fully depleted battery, so I cant charge them in serial configuration without balancer.
Same time it’s not recommended to connect in parallel batteries which discharged un-equally, because current which will flow between batteries will be limited only by resistance of wires and internal resistance of batteries itself.
For myself I decided that it’s acceptable risk because of next reasons:

  1. Batteries like that is not high current, so they should have relatively high internal resistance which will limit current
  2. I especially use thin wires, which have their own noticeable resistance
  3. Contacts also have noticeable resistance
  4. When one battery charges another their potentials aligns. The less difference in voltage the less current flows
  5. I’m planning to connect batteries only when charger powered up, so up to 1A from charger will aligns their potential.

When I did the charger, I connected fully charged battery with battery which was just discharged by camera and measured the current, it was near 0.17A. Batteries like that should be ok at 1C current (0.9A in my case).
I will not agitate anyone to do the same, but I find it ok for myself.

Two more precautions, this charger can be connected only to chragers which are provide more than 1A current. Newer connect that charger to laptop or PC.
TP5100 usually come with maximum charging current set as 1A. If you put 1 battery, it’s a bit more than 1C (0.9A in my case), but I didn’t observed any noticeable warming of battery during charge cycle, so you can set charge current lower or use it with 1A on your own risk.

Here is stl files for  case
Board files: board