cool video! 1. Careful about touching the transformer as the output windings possibly not safety insulated (I could see copper between the tape). I suppose if all supplies, loads, and measuring devices are fully isolated, you may be single fault tolerant for a single finger... two fingers not so much. I thought it odd that the transformer seemed to have a lot of empty volume. Perhaps they reduced the wire gauge from the original design to save money? 2. Because a tungsten filament impedance changes with temperature, the relation of true power (watts) is not as linear as you indicated for both the 1-bulb and 2-bulb tests when the voltage is not at rated levels... however, it works fine for a first order approximation. It would be cool if you had a current probe for the 2nd channel of the oscilloscope! 3. The bridge rectifier presents as a non-linear load on the source drawing most of the current at the voltage peaks (resulting in very poor crest factor as you showed on the scope). The peak currents in the windings could I guess with 20-30kHz you had chose appropriate diodes and bulk capacitance b/c standard 50/60Hz parts would not work well?
Hello, Thankyou! I am quite used to High Voltage since i was 14yo building pirate tube transmitters am/fm in Greece :-), this why one hand handling. It would Hurt and you would hear me cursing in Greek, but thats would be all :-) Btw. the Diodes used to rectify the output towards el load are ultrafast ones with a 22uf low esr cap. I don’t have current probe yet. As for the large transformer core compared to the winding, I assume the primary is less than 10 turns Center taped and the sec are ca 90-100 turns of small awg, Cheers, Konstantin
Hi Konstantin, nice testing of this cheap inverter, but i think that you have at 11:35 made a calculation error. With 230V and 213 Ohm of current limiting, the maximum current is 0,2A and not 1A. With 230V and 0,2A of current, it becomes 46Watt. Way above the advertised 30Watt limit. Also, if you use a 10 times higher C2 capacitor like 220nF, the current limit drops to 21,3 Ohm with 34Khz. With a capacitor as resistor, the higher the capacitor value, the higher AC current that can flow. But it all depends on the frequency. With 230V mains voltage at 50Hz, and 213 Ohm of current limiting value, you need arround 15uF capacitance. I can be wrong, but i think these cheap mini inverters are old stock and that they where used to drive Fluorescent lamps in emergency exit lamps powered from a 12V AGM battery in case of mains faillure. Grtz
Hi Bjorn, Thankyou, but I = U/R => I = 230/213 = 1.079 A not 0.2A and of course I mean 10x smaller Cap not Higher thankyou, was brain Fart :-) Perhaps the Transformer was from a Safety light, this is Possible. This thing is not capable of 30W, not with this Design! but the Transformer IS, as shown later in the Video with a much better Driver. Further the Transistors, the useless "Current Limiting" cap and the resonant Cap are Repurposed, Salvaged from scrap Boards, that makes the Hypothesis of emergency Lights for me even more questionable, these things have NO Protection at all, that's why I don't believe its old stock. I have seen it many times taking some leftovers (transformers, etc.) and Building something around it to be sell-able. Cheers, Konstantin
@@KonstantinGrigoriadis , you are 100% right, made also a brain fart with amps calculation of 0.2 vs 1.079A I know Ohm's law, but filled in the values in a online calculator and that used the wrong values :-) So faster is not always right :-) As for the repurposed transistors, it's weird. I get the point that they use the parts they have, but if you are a manufacturer of these small inverters, and you sell thousands of them, you also have to find double that amount of equal pairs of transistors. China sell these worldwide, but the amount of broken electronics that get send back to China is minimal. So it's weird how they get that amount of scrap parts. In small cheap wallwart power adapters i have seen that they used repurposed pcb's from another model, and you see leftovers from the cutoff red and black wires. Maybe UK versions transformed to EU or US versions, i don't know. It's good that they repurpose new (old) stock, but the use of scrap parts and sell them as new is a big scam. If you can use some of the other parts, like the transformer, then you have made a good deal, otherwise not. Grtz
Well, the amount of scrap Electronics in China is HUGE, not Minimal, and the Transistors used are Generic just mid to High Power TO200 >30V, >4A PNP Transistors, that's why you see so many different transistors on these boards, mostly dirty and old !, same with the caps taken from Scrap Power Supplies. I wouldn't see it as scam with these ultra low prices :-) I Just see it Dangerous if used in in wrong applications. Cheers, Konstantin
I can't believe that schematics is right - the PNP transistors are closed from the beginning by R1/R2. Chematics should work if swap Collectors with Emitters and swap power polarity or transistors PNP to NPN. Are you sure?
Hi Alex, thakyou for pointing it out, you are right, the schematic is WRONG !!! I cant believe I made a mistake in such a small circuit while reverse engineering really complicated ones I don't, shame on me and thankyou! It happened probably bcs in mind I had the NPN version of it. I will put the corrected circuit in my community tab and write the issue in the video description! Cheers, Konstantin
@@KonstantinGrigoriadis just in case, ZVS is not too much complicated than original Chinese Royjer, could t be possible to re-work original module into ZVS?
Hi Alex, I Plan to use the Transformer in a ZVS Topologie as Part of a Power Supply Design. To Rework the already bad Module, well all is Possible :-) but making a new PCB for it in ZVS Topologie is for me the right way, Thankyou again for Pointing out ! Cheers, Konstantin
You made a 30 minute video on a cheap Chinese inverter?? That's exactly the kind of content i'm here for! Thank you so much!
Hello, Thankyou!
Keep up with the informative videos. Cheers Dave.
cool video!
1. Careful about touching the transformer as the output windings possibly not safety insulated (I could see copper between the tape). I suppose if all supplies, loads, and measuring devices are fully isolated, you may be single fault tolerant for a single finger... two fingers not so much.
I thought it odd that the transformer seemed to have a lot of empty volume. Perhaps they reduced the wire gauge from the original design to save money?
2. Because a tungsten filament impedance changes with temperature, the relation of true power (watts) is not as linear as you indicated for both the 1-bulb and 2-bulb tests when the voltage is not at rated levels... however, it works fine for a first order approximation.
It would be cool if you had a current probe for the 2nd channel of the oscilloscope!
3. The bridge rectifier presents as a non-linear load on the source drawing most of the current at the voltage peaks (resulting in very poor crest factor as you showed on the scope). The peak currents in the windings could
I guess with 20-30kHz you had chose appropriate diodes and bulk capacitance b/c standard 50/60Hz parts would not work well?
Hello, Thankyou! I am quite used to High Voltage since i was 14yo building pirate tube transmitters am/fm in Greece :-), this why one hand handling. It would Hurt and you would hear me cursing in Greek, but thats would be all :-) Btw. the Diodes used to rectify the output towards el load are ultrafast ones with a 22uf low esr cap. I don’t have current probe yet. As for the large transformer core compared to the winding, I assume the primary is less than 10 turns Center taped and the sec are ca 90-100 turns of small awg, Cheers, Konstantin
Hi Konstantin, nice testing of this cheap inverter, but i think that you have at 11:35 made a calculation error. With 230V and 213 Ohm of current limiting, the maximum current is 0,2A and not 1A. With 230V and 0,2A of current, it becomes 46Watt. Way above the advertised 30Watt limit.
Also, if you use a 10 times higher C2 capacitor like 220nF, the current limit drops to 21,3 Ohm with 34Khz. With a capacitor as resistor, the higher the capacitor value, the higher AC current that can flow. But it all depends on the frequency. With 230V mains voltage at 50Hz, and 213 Ohm of current limiting value, you need arround 15uF capacitance.
I can be wrong, but i think these cheap mini inverters are old stock and that they where used to drive Fluorescent lamps in emergency exit lamps powered from a 12V AGM battery in case of mains faillure. Grtz
Hi Bjorn, Thankyou, but I = U/R => I = 230/213 = 1.079 A not 0.2A and of course I mean 10x smaller Cap not Higher thankyou, was brain Fart :-) Perhaps the Transformer was from a Safety light, this is Possible.
This thing is not capable of 30W, not with this Design! but the Transformer IS, as shown later in the Video with a much better Driver. Further the Transistors, the useless "Current Limiting" cap and the resonant Cap are Repurposed, Salvaged from scrap Boards, that makes the Hypothesis of emergency Lights for me even more questionable, these things have NO Protection at all, that's why I don't believe its old stock. I have seen it many times taking some leftovers (transformers, etc.) and Building something around it to be sell-able.
Cheers,
Konstantin
@@KonstantinGrigoriadis , you are 100% right, made also a brain fart with amps calculation of 0.2 vs 1.079A
I know Ohm's law, but filled in the values in a online calculator and that used the wrong values :-) So faster is not always right :-)
As for the repurposed transistors, it's weird. I get the point that they use the parts they have, but if you are a manufacturer of these small inverters, and you sell thousands of them, you also have to find double that amount of equal pairs of transistors. China sell these worldwide, but the amount of broken electronics that get send back to China is minimal. So it's weird how they get that amount of scrap parts. In small cheap wallwart power adapters i have seen that they used repurposed pcb's from another model, and you see leftovers from the cutoff red and black wires. Maybe UK versions transformed to EU or US versions, i don't know. It's good that they repurpose new (old) stock, but the use of scrap parts and sell them as new is a big scam. If you can use some of the other parts, like the transformer, then you have made a good deal, otherwise not. Grtz
Well, the amount of scrap Electronics in China is HUGE, not Minimal, and the Transistors used are Generic just mid to High Power TO200 >30V, >4A PNP Transistors, that's why you see so many different transistors on these boards, mostly dirty and old !, same with the caps taken from Scrap Power Supplies. I wouldn't see it as scam with these ultra low prices :-) I Just see it Dangerous if used in in wrong applications. Cheers, Konstantin
What's the cheap Chinese module on the left of the last circuit? I couldn't hear what you said.
Hi Samuel, now I know what circuit you mean, the black PCB, its a cheap ZVS Driver just for teating. Cheers, Konstantin
@@KonstantinGrigoriadis Thanks. Think I found it on Alibaba.
This for Example : www.aliexpress.com/item/1005004930951579.html,
or this www.aliexpress.com/item/1005003172602865.html, Cheers, Konstantin
I can't believe that schematics is right - the PNP transistors are closed from the beginning by R1/R2. Chematics should work if swap Collectors with Emitters and swap power polarity or transistors PNP to NPN. Are you sure?
Hi Alex, thakyou for pointing it out, you are right, the schematic is WRONG !!! I cant believe I made a mistake in such a small circuit while reverse engineering really complicated ones I don't, shame on me and thankyou! It happened probably bcs in mind I had the NPN version of it. I will put the corrected circuit in my community tab and write the issue in the video description!
Cheers, Konstantin
@@KonstantinGrigoriadis just in case, ZVS is not too much complicated than original Chinese Royjer, could t be possible to re-work original module into ZVS?
Hi Alex, I Plan to use the Transformer in a ZVS Topologie as Part of a Power Supply Design. To Rework the already bad Module, well all is Possible :-) but making a new PCB for it in ZVS Topologie is for me the right way, Thankyou again for Pointing out ! Cheers, Konstantin