#104 Reverse engineering an old linear power supply
Recently I came into possession of two working ups devices from 1993. both of them had old capacitors and old 12v7a lead acid batteries inside the devices.
First thing I did was clean the cases and the PCB boards. Once that was done I replaced the old capacitors and the 12v7a batteries, then I tested both devices. both work fine but the design is old and a bit dangerous.
So I decided to reverse engineer the circuit in order to better understand the design and to see if I could make any improvements to a design I would like to make.
While reversing the PCB I noticed that the mains earth and the GND of the circuit were connected together. I also notices sone discoloration from what looks like heat between the regulator and the transformer. Also the 330 ohm resistor for the led appeared to be discoloured from what also looks like excessive heat.
With these issues in mind I also noticed that the heatsink for the LM317T was very small and close to the transformer and the mains 1A fuse was placed after the choke and varistors instead of before them.
In conclusion I decided to choose between a different regulator at a fixed voltage or a chain of 4 LM317Ts providing around 6A of peak current, Since I do not need to adjust my voltage like the original circuit I should be able to get 13.75v by using a fixed 1k and 10k resistor. I also wanted better heat dissipation and Amps so I will definitely install good heatsinks with thermal compound. Depending on the size of the enclosure I get for the project I may add a fan.
The project files and components list etc. can be found on my Github here.
Looking at other mini ups manufactures I decided to give Jiageng a go. The outer plastic enclosure looks very similar to a lot of other generic mini ups devices. I suspect they all originate from the same factory but have slight improvment’s to the actual PCB inside.
Once opened I was greeted with a beautifully soldered matt black PCB with a higher version number than the previous mini ups from Andowl.
The PCB has quality components and no mystery chips. It also has the iconic Wintonic 18650 cells.
2 differences I noticed are that all the LEDs are a dark green color (the Andowl unit had 2 different greens) and the unit powers off automatically at a low voltage so that it doesn’t require a reboot after it runs “flat”.
The unit also has flashing LEDs as apposed to the Andowl’s fading LEDs
Datasheet can be found here. Andowl artical can be found here.
After testing the generic Andowl UPS device I decided to find out if there were any alternatives in the same price range with similar features. After a few google searches I came across the SINYE TECH UPS device which has very similar features but is black in color and uses a different PCB.
After purchasing one and opening the ups I was disappointed to find out that the 4 18650 batteries had no markings on them whatsoever.. Also the main battery management IC has no identifying text on the chip. Seems like the mystery chip can of worms opens once again.
The good news is that the ups device has battery protection and has some decent components however… the actual black PCB board looks cheap unlike the good quality Andowl PCB…
Another major shock was the soldering (or should I say smoldering) of two of the transformer coil wires.. just looks ugly…
I also noticed the UPS device had a low battery LED flashing when I first switched it on and it never reaches the 100% LED even though the batteries are charged to 4.2V
Overall the UPS does function but I much prefer the Andowl Q-UP1000 UPS with similar functions it’s far more superior from what I’ve seen.
After setting up a CCTV system consisting of multiple WiFi cameras placed over my property I noticed that certain cameras were located in areas far away from AC outlets covered by my backup electrical system.
In this project I used some an old 18650 (LG makes the LGABD11865 ) from a laptop power supply. Also I upgraded my 5v charger to a 1.5A to provide enough charging and running current for the camera. The camera I am using is the EZVIZ C3W 1080p WiFi camera
Since Load-shedding has been increasing dramatically I had the need to find cheap simple and reliable power sources for there cameras (12v DC). One important requirement is that the backup system needs to fit into a small area E.G an electrical box on a pole where the camera is located.
While researching I came across the so called mini dc ups device mainly used for backing up WiFi routers at either 9v, 12v, 15v, 24v. however these devices seemed a bit overkill electronically wise and also price wise.
So I decided to opt-in on a cheaper smaller sized DIY version the components consisting of:
The components are all soldered onto a 50mm x 70mm 1 sided PCB board.
I noticed that the 4056 IC gets quite warm but doesn’t burn my fingers. The same goes for the coil. The specification is max 1A and the load I was applying was around 0.33mA – 0.670mA
After testing this particular LiPo charger PCB I noticed a few major problems the first being that the 8-pin 4056 LiPo chip is a copy of a copy… the next critical problem is that there is no protection circuitry besides the overcharge/discharge function in the 4056 chip.
This is a big problem since the chip does not switch off completely when low voltage occurs and as a result the load will periodically switch on and off unreliably before finally switching off completely. This oscillation can damage the load.
A solution will be to use a separate LiPo PCB with protection mosfets and a separate booster board.
When looking for a suitable min ups for my CCTV cameras and WiFi router I found a wide selection on takealot. After doing some research I noticed that the Q-UP1000 mini ups was listed by many vendors but at varying prices. Many companies had rebranded the device and increased their price quite dramatically.
Finally I came across a deal selling the device for under R500.00 and I purchased 2 Andowl devices. Once I received the devices I was impressed with the quality of cables and the plastic mold of the box. (There are no screws to unscrew the box simply pops open)
Once the box was open I noticed a decent PCB with all the necessary protection circuits. There are two mystery chips though.
The product was made recently (at least at the time of writing this article) and the designers made the batteries easily accessible for swaps which is awesome.
Now a negative thing I noticed is the 12000mAh claim… clearly the batteries are four 2.200mAh INR18650’s and this adds to 8.800mAh
There can be many reasons for this capacity “lie” but other than that the mini ups is looking good. Time will tell if this was a decent investment.