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Forum Index : Electronics : Reverse engineering a TL494 based Chinese
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LadyN Guru  Joined: 26/01/2019 Location: United StatesPosts: 408 |
When reading this forum I came across this interesting TL494 based Chinese boost converter often claimed as 1200W, 1500W or even 1800W https://www.aliexpress.com/item/1200W-20A-DC-Converter-Boost-Step-up-Power-Supply-Module-IN-8-60V-OUT-12-83V/32767522358 .html I quickly ordered it but I am surprised to see no schematics for it online! I spent a few hours looking for detailed pictures of the unit and see that it has: 1. Output voltage control 2. Output (or input?) current cutoff (often mislabelled as "constant current" setting) 3. ULVO (input voltage cutoff) Have anyone else on this forum looked at this board? Hi hotwater, are you talking about this specific board or another boost one? |
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zaphod Regular Member  Joined: 03/06/2018 Location: United KingdomPosts: 93 |
Why would you buy something if you don't know what it is ? Personally I have an aversion to Chinese rubbish with no specification and probably lifted from some application note so long ago nobody can remember and all the parts replaced according to local availability and economy, the phrase "can of worms" comes to mind! Cheers Roger 1Kwp DIY PV + Woodburner + Rainwater scavanger :) |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Fair question. I decided to spend my pocket money on it because it seems to me, that on this forum: 1. a few people have already looked at this exact convertor and understood it way well than I possibly can 2. almost everyone here is happy to share their knowledge and bring newbies like me up to date so I/we can be productive I am hoping these members share what they have learned and then we can start controlling this using a microcontroller like the blue pill |
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mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
That link had a space in it. 1200W-20A-DC-Converter-Boost-Step-up-Power-Supply-Module-IN-8-60V-OUT-12-83V I can't help, but look forward to seeing what you come up with |
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| ltopower Regular Member Joined: 08/03/2019 Location: United KingdomPosts: 64 |
I quite frequently buy some itemes when they are lacking full details because they seem to be ok and only trial and error sometimes really gives you the idea as to what they really are and can do. The units are quite ok, they seem reasonably efficient, reliable, easy to repair.. I used one with a 600W wind turbine, one of the variable resistors allows you to pull the input voltage down to whatever level you want, so i used one as a low wind input device, stepped up the 18-22V from the turbine to charge the 48V battery. Really windy I just bypassed the unit (or increased the voltage level) as the wind turbine was then able to output 48V and charge directly... 1.2kW out of a 600W unit, not ideal and a few strange noises in a storm. This was all experimenting and learning at the time. |
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| azhaque Senior Member  Joined: 21/02/2017 Location: PakistanPosts: 117 |
Natasha, Are you thinking what I am. I have the same idea. Use this Board in conjunction with an Arduino (say) and make an MPPT controller. I have been researching this idea for a while. My need for such a system arises because I am currently using 4 Nos. PWM controllers from EPSOLAR for my off-grid system. The next logical step is to go MPPT. The main hurdle in this approach is the cost of MPPT controllers. If we can manage one on our own it would be really cost effective. SolarMike is already working on one while Madness has developed on already. Maybe we can build on their work and develop something useful. Have you received your board from China. When you do please share with us the numbers of the various integrated circuits used thereon. We should be able to divine the circuit out of that. Here is a link to a bigger one with a video. https://www.aliexpress.com/item/1800W-40A-CC-CV-Boost-Converter-DC-DC-Step-Up-Power-Supply-Adjustable-Module-DC-10V/3285 7772579.html?spm=2114.search0104.3.115.3b821a25PESXwY&ws_ab_test=searchweb0_0,searchweb201602_8_10065_10068_319_10059_10 884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536_10902,searchweb201603_16,ppcSwitch_0&algo_expi d=293ae1a8-aa5d-4f27-9fae-866cd1d303f2-16&algo_pvid=293ae1a8-aa5d-4f27-9fae-866cd1d303f2&transAbTest=ae803_3 azhaque |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
I had trouble with that link. try aliExpress 1800W boost Cheers Andrew |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
That is exactly right! I want to use the ESP32 as the loop modifier. Want to work on this together? I paid $23 for mine just to get a version with all ICs marked and I now have them. TL494, LM358 and a small onboard 5V buck to power itself. Feel free to purchase the cheaper ones that do not have ICs marked. My current problem is that the board is smaller than I expected it to be and with my vision I need a good magnifying glass to trace it. Are you also interested in tracing it? I have some pictures and @ltopower sent me much more detailed pictures as well |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Is a boost-converter a good starting point for a MPPT battery charger? Normally panel voltages are higher than the battery voltage. I look forward to a circuit diagram for this unit, maybe it will help explain the problem I have been having with a lower-power version using the same PCB. I suspect that this is doing something strange at low supply voltage, ie below their rating of 10V. Dave |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Good question Dave, Depends on the use case I think. I am not designing or using this for battery charging. My use case is that I don't want a battery. I only want to offset grid usage by the available solar power. So while a buck convertor is needed to charge battery (V_PV_out >> V_BATTERY), in my case, a boost-converter is needed (V_PV_MPP_out << V_GRID) specially if I want to load share with V_GRID (rectified grid). The warpverter comes in if I NEED AC OUT so my DC and AC needs are taken care of. The challenge with using a pure uC based MPPT boost-converter is that the uC has too much to do all at once. I am hoping to outsource the boost-converter math to this boost-converter and let the uC (ESP32 in this case) just worry about the MPPT part. In theory. I would really like to continue that thread and am sad you gave up. Maybe we should start this project first and armed with that knowledge resume that thread. |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
Natalie, you want to use a micro and a DAC as a control reference in your feedback mechanism? Thats fine, does the ESP32 have a DAC ? I'd be wary about using a boost topology if you are after high power and or have a large voltage difference between input and output. You could potentially put a lot of stress on you caps, diodes, and so on. In this case, imho, a transformer based design is called for. If your input voltage is close, then fine. As Tony or Mike has said in Dave's thread, you need to watch the "negative impedance" of a boost circuit on a solar panel. If I understand your application; that is you're creating, say, a 120Vdc buss , supplied by rectified mains and by diode isolated solar (via a boost converter). You want to feed maximum load demand by the solar, but mains can top up or take over where solar in insufficient. As in Tony's power source circuit. How many panels, wattage? how many panels in a string, Voc and Vmp? Cheers Andrew |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I think you would be far better spending your money on hooking up more series connected solar panels, and increasing the voltage that way. Cheers, Tony. |
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| LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408 |
Thank you Andrew, Tony. There is a significant possibility that my inexperience and naivety is moving me in this direction. Yes, I intend to series connect 3x 300 Wpp, 30Vmpp, 9A Isc panels. This specific boost convertor has a suicidal design where it does not monitor the maximum current that can flow through it to maintain load regulation. So, on startup if the load draws enough current to cause a heavy draw from the input, AND the source can oblige, this specific boost convertor will happily go along even if the di/dt exceeds its nominal values in a misguided attempt at load regulation. This of course makes this specific boost convertor go boom very easily. Additional current sensing circuit might mitigate this challenge? Now, this is not of consequence, I don't think, if PV Panels are connected to this boost convertor directly: PV Panels naturally limit current so as long as Isc < nominal Imax of the MOSFET + Diodes, I think we should be fine. However, this excludes an alternate design that Tony suggested that hooks up a capacitor bank to the PV Panels that really addresses power point hunting very simply. Tony's design of a capacitor bank goes very nicely with a transformer based step up (boost?) convertor though. So if this boost convertor adventure turns bad, I will have to start learning about transformers, how they work, how to wind them, test them etc. For now, transformer cores are really turning out to be a real issue. The ones on eBay are not only expensive (shipping can exceed cost of transformer) but they are not spec'd properly. The companies that sell transformer cores with nice datasheets want hundreds of dollars for a 1kVA capable core. So for me, the route would be to use less expensive salvaged cores but that requires me to figure out specs by running tests on them, which I am currently not equipped to do (although it's on my TODO list). |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
I agree with Tony, get a 4th panel and series the lot  Whats the Voc? ~38v |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Things like house bricks, lead acid batteries, and steel transformer cores are just too damned heavy to ship economically any distance, so buying local is the only option. Your best bet might be recycling someone else's unwanted junk. Scrap metal merchants and the local rubbish dump may turn up something if you are both patient and persistent. Phoning around some of your local solar installers may turn up a deceased grid tie inverter that is not economically repairable. That sometimes happens because the company that made it is no longer in business and there are no circuits or information. They would usually be more than happy to get just scrap metal value for it. Cheers, Tony. |
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Techie007 Newbie  Joined: 25/10/2020 Location: United StatesPosts: 3 |
I too have been looking for a schematic for these Chinese boost converters, and came across this thread early in my search. Having found no schematic anywhere, I decided to make one myself and share it here for others who may be interested:  QS-4884CCCV-1800W schematic.png They are surprisingly well made, and are capable doing 1800w if the input/output voltages are high/close enough (e.g. >48/60v; the inductor overheats otherwise). The maximum rating of the Schottky diodes combined is 40a, and the output terminals are rated at 30a. They even have ingenious reverse protection by using a mosfet backwards! They have Over Current Protection, where it throttles back if the input current goes too high (not sure how well it works though), which is separate from the Constant Current circuit. However, they have one glaring design flaw: The blue UVP LED drops too much voltage, causing a danger zone in the 5-10v range where the converter tries to run but has too little voltage to fully drive the switching mosfet or to turn itself off, which can burn up the mosfet when under load. This isn't helped by the nearby feedback capacitor (between pins 1 & 2), which makes the UVP circuit incapable of reacting fast enough or regulating the input voltage, sending it into dangerous spasms instead. I would strongly suggest replacing the UVP LED with a red one and knocking the feedback capacitor off the circuit board as a fundamental design modification before using these converters. The feedback capacitor can be replaced with a 10-100k resistor to reduce noise and minor oscillations when regulating the input voltage if desired. Another couple shortcomings is the lack of Over Temperature Protection, and a fan that has two speeds (on and off) with a tendency to vibrate (where the axle starts oscillating in the bearing, dragging the impeller RPM way down and reducing cooling). I am successfully using these boost converters as mini-MPPTs in a partially/occasionally shaded 36v solar system, specced at 1000w/board. Loaded panel nominal is 30-35v and battery float is 43v, so the boost converters do a decent job with UVP set to 32v and the modification above in place so it can function correctly, regulating the input voltage. The advantage this setup has over a traditional, high voltage MPPT system is that partial shading over one panel doesn't take out an entire series array section. As I've watched the system function and adjusted the parameters manually, I realize there's a bit more power to squeeze out in full noon sunlight (panels work better at 35v), and in heavy clouds (panels work better at 30v), and at dusk (panels drop below 30v and work best anywhere from 15-25v). Hence the need for a schematic so I can add basic (passive) Power Point Tracking, Variable Fan Speed, and Over Temperature Protection. The modifications are quite simple: 1: Remove the 22K CC pullup resistor (between TL494 pin 15 and 5v). This leaves the CC circuit hanging at minimum power (~250mA out), regardless of the CC adjustment. 2: On the underside of the circuit board, connect a 30v zener diode (adjust according to the start of your power point curve) from Vin to a 10k resistor connected to the non-grounded lead of the CC potentiometer. This will cause the CC adjustment to rise starting at the input voltage set by the zener diode. 3: Remove all the fan control components except for the PNP transistor and its 4.3k pulldown resistor. 4: Bridge the two pads behind/parallel with the 4.3k pulldown resistor. This should connect the left lead of the thermistor to the transistor's base. 5: Bridge the two pads between the two TL431s, where the 10k resistor used to be. This should connect the right lead of the thermistor to ground. Now the fan speed will gradually increase from stopped as the heatsink warms up. Just be careful not to short the thermistor during operation or you will blow the transistor as there's no series base resistor (by design; we need the highest sensitivity we can get so the temperature curve isn't too wide). The temperature threshold can be adjusted by changing the value of the 4.3k pulldown resistor. 6: Now that the fan speed is variable, we can add OTP. Solder a 10v zener diode from the positive fan lead to the top lead of the UVP potentiometer (should be connected to LM358 pin 3). As the fan approaches full speed, the zener will start conducting, rapidly raising the UVP point, causing the UVP LED to light and the boost converter to throttle back or even stop completely until the heatsink cools down a little. 7: Another change I am contemplating is to break the signal ground trace and connect signal ground directly to main ground. The rationale is that the solar power point is in relation to input current, not output current. Additionally, the CC circuit can't go any lower than 250mA (out), but testing has demonstrated that it can go down to about 100mA with the main ground, which eliminates the ground loop caused by the 100uF 12v filter capacitor, and includes the input current (as measured by the circuit board traces) in the CC measurements. This may provide better power point tracking performance in the heavy clouds to dusk range. Regarding these boost converters being used as MPPTs, there's a guy on Reddit who actually replaced the TL494 switching logic with an ESP32, resulting in active power point tracking, WiFi connectivity, and a nice, visual web interface! |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Hi Techie007, Thanks for posting this. I still have a couple of these units gathering dust because I could NOT get them to work as MPPT boost supplies. The "one glaring design flaw" possibly describes one problem I had. Having a schematic might help me understand why I had another problem, ie switching in different R values for Uvp as an attempted digitally-controlled MPPT boost supply. davef |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Yes Techie007, thanks for reverse engineering & posting the circuit, an excellent effort. I am fairly confident though that there is an error with the over current protect sense part of the schematic. The 2K resistor on pin 5 of the LM358 should go to the load side of the current shunt (the same as the connection net Csense ), else it cant see the actual output current. The circuit appears to act as a maximum output foldback current limiter (limits the PWM duty cycle once the threshold is exceeded), the input under-voltage appears to operate in a similar fashion reducing output PWM to reduce power throughput. I assume the output shunt is around 1.2 to 1.3 mOhms which would allow for an output current ~ 40A+ before the over current protect kicks in. The first regulator also appears to be shown pinned incorrectly. I believe the 13.5V regulator IC is an AP1609 or exact equivalent and the pinning is out by 180 degrees. For the sake of adding a few buffer transistors to properly drive the 3 indicator LEDs from the 13.5V supply I think it could have ended up a much better design. Lastly to remove ambiguity of exactly how to perform the modifications, a few pictures would help to ensure what needs to be done for the less technical readers. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| Techie007 Newbie Joined: 25/10/2020 Location: United StatesPosts: 3 |
I'm very confident that the OCP circuit is drawn correctly—it took me awhile to understand how it works. I too thought that the positive input on the LM358 should go to the current sense shunt, but it does not: It is clearly connected directly to the signal ground bus through the 2K resistor, which creates a resistor divider with the slight internal input pullup of the LM358, raising it slightly above ground. The current feedback actually comes from the inverting input, through the parallel 100 and 120ohm resistors, which explicitly avoid the nearby signal ground bus (that the 2k resistor is connected to!) and are connected to power ground by a through-hole via. Thus, the OCP circuit is measuring the input current (voltage dropped through the circuit board traces) instead of the output current. Hence my convoluted way of drawing those resistors up to power ground instead of staying in the visual envelope and drawing them down to the signal ground bus for a cleaner look. Ironically, I have tried unsuccessfully to switch that op-amp to a positive-input based output current sense, because I don't need the OCP function (each unit is only connected to 1000w of panels), and I could really use a "voltage overregulation" function, where the output voltage is linearly boosted under higher current loads to compensate for wiring losses (output of that op-amp would be reconnected in some way to pin 2 of the TL494). But I haven't had success so far—unlike the TL494's op-amp, the LM358 seems to just get "stuck on" when dealing with voltages that close to zero on the positive input. You're probably right about the buck converter chip. On my boost converter, its top has been completely ground off, obscuring both its part number and its orientation. Combined with a small bar running across the "top", I assumed its orientation was upright, just like the LM358. Judging by photos found online, it appears that whoever made the 1500w boost converters with the four-lead input block didn't grind that chip, but everyone else did. Sadly, none of the photos are clear enough for me to read their part number. It also looks like that unit uses pin 8 (or pin 4) of the chip, whereas it appears to be unconnected on my 1800w unit—so I don't know for sure if they're using the same chip or not. I personally think that their using LEDs as "or diodes" while simultaneously functioning as indicators was brilliant—lower component count and slightly higher efficiency, since the current would be flowing anyway. They just needed to consider the blue LED voltage drop and the LM358 drive overhead! If they had omitted the OCP feedback capacitor and swapped their use of red and blue LEDs (so blue for power and red for UVP and OCP), it would've saved them money (red LEDs are cheaper), the 5-10v "fry zone" would be eliminated, the color coding would make more sense (red for warning), and UVP would regulate the input voltage properly. They could've also eliminated the 75k power LED resistor by putting the power LED in series with the 200k voltage adjustment knob, resulting in a constant current over the entire adjustable voltage range for that LED. They could've saved even more money and eliminated a TL431 plus a few resistors if they had tapped into the TL494's 5v reference and adjusted a couple resistors instead of creating a 10v reference just for the fan. Or saved even more money removed all those fan control components like I did, adding variable fan speed and OTP in the process! The output shunt is too small for any of my meters to read. I plan to calculate its resistance by putting one of these boost converters under a controlled, high load and measuring the resulting voltage drop. After confirming a few things and performing a few more tests, I plan to update the schematic and post some visual material regarding the changes I've made to these converters. Thanks for the AP1509 part suggestion, that does look like the chip they're using—or at least a plausible replacement!  Edited 2020-10-30 03:38 by Techie007 |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
The whole purpose of presenting a schematic is to enhance the understanding of the circuit for others to follow or reproduce. The OCP circuit relies on either the pin 5 terminal going positive WRT pin6, or the pin 6 terminal going negative WRT pin 5. If it is relying on a voltage drop formed on a PCB track then that can be considered as a resistor or shunt and should be drawn as such. As it is currently drawn it is wrong as it is drawn as equipotential points and cant work. So I stand by my original point that there is an error as presented ! Had someone decided to lay out their own circuit without the special knowledge you enhanced on in your second attempt it would not work unless by accident. Pin4 of the buck converter (on/off/shutdown) pin should be tied to ground if unused. Does the output resistor/shunt exist as a part or is it a PCB trace also ? Its a shame that their cheap? brilliant? implementation oscillates and carries on and needs extra work to function properly (assuming the mods do actually fix it 100% for all units). I would not do it their way. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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