I realized that I got extra space while designing the board (5cmx5cm) for my numitron driver board so I decided to add a USB I/V monitor into it.
[attachment=2] Unlike the others out there that uses polyfuse as a short-circuit protection, mine uses TPS2051C which is a Current-Limited USB Power Distribution Switch. I chose it because: 1) ULVO at 4.5v 2) Output enable pin 3) Fault output pin Currently, I'm using it together with a multimeter but in future there will be another board stacked on top of it. Running a mcu and a oled/lcd display. The fault pin will be attached to the mcu interrupt pin. When the IC triggers a fault, the mcu will disable the output. And reset it by pressing a button. Just like a circuit breaker.
BTW I have 5 extra pcb to give away. If you're interested let me know, I'll send you one. Or perhaps a DP free pcb give away?
While waiting for ebay parts to arrive for my DC load project, I thought of having a go at attempting to fix the Weller DS701E solder/desolder station which I've gotten it a while back. I have no idea when this model was produced and googling for datasheets and manual comes back with nothing. [attachment=5]
My first approach was to look for visual signs of component failure and everything looks fine. So, next is to probe the temperature control board. Check out the old school pcb routing. The board gets its power from the 12vac through 1/2 wave rectifier, filter cap, 7805 regulator and another filter cap. Initially, the voltage measured at the regulator was 7v at the input and 4.2v at the output. The filter cap was quite warm. Tested the cap ESR was 0.7ohms and not shorted. My capacitor meter was only limited to 200uF max. So I concluded that the cap has lost its capacitance over time. Replaced them with what ever I have in my junk bin and it works like a charm. Did some quick calibration with a thermal probe. [attachment=4]
I've decided to replaced all the caps just in case. Im actually surprised that there are very few ICs in one of these. [attachment=3]
Phillips caps. When was the last time you heard of them? I know they were acquired by some company, Vishay was it? [attachment=2]
An overall shot of the internal. The transformer is rated at 24v 280va. Which took up most of the weight. [attachment=1]
I've also took the opportunity to strip the old paint with a wire brush. Some fine sanding and elbow grease and finally a couple of clear coat. Tried to create the brush alu effect. Unfortunately, the desolder tool wasn't working, it dint get hot but the pump works fine though. Looks like another job for another time. [attachment=0]
Here's my attempt to build a 4 ch electronic load. I'll be using IRFP240 Nch mosfet. Each could dissipate 150w of heat @ 25°c. Specs: Should be able to sink at least 5A per ch. Able to combine all 4 ch to aggregate into a single high current ch. [attachment=2]
Testing current measurement with an INA169 high side shunt sensor. I might use the ACS712-20A hall effect sensor instead. [attachment=1]
Li-ion batts makes great power source. They can easily source high current. These are sanyo cells I've salvaged from a lenovo laptop battery pack. Test @ 12v,5A Ambient temp 28°c Case temp 85°c Heatsink temp 40°c [attachment=0]
Task left - Op amp loop - Sort out the current sense - Get a DAC for current set - Get a microcontroller - Get some lcd for display - Write the code (ughh) - User interface - Somesort of data logging sd card perhaps?
Today I've decided to test the efficiency of the different design of HV SMPS that I've built a while back. I used a 240v neon bulb which I salvaged from a panel mount light indicator. The bulb draws about 1.5mA and I've used 2 pieces. MAX1771 have the best efficiency but comes with a pricey price tag.
So I decided to make a well padded case to store my development boards. The anti static foam came in 1/4" thick so I have to glue them together using white glue. I didn't let the glue fully dry and went ahead to store the boards. Took just a day to destroy everything. Gotta do some damage control and try to salvage what I can. And just to think i got my lauchpad a day ago. Collateral damage: Arduino uno, ti lauchpad, usbtiny isp, usbasp isp, usb UART.
