Chinese mini welder display adjustment ZX7-250 MINI

I bought this welder on BangGood. In the reviews, it was both praised as welding well but also criticized for having a false current rating. According to one review, its max current is around 120amps. This is fine for what I bought it for, so I won't have to fire up and drag out the huge, three phase, Czechoslovak transformer welder I have for just some small job.
But I'm annoyed that the LED display is totally false. Fortunately this is easily fixable by adjusting one varistor which sets the range of the display.
Also, I point out in the video the 180 amp fusible link, which definitely puts to rest any question whether this thing was meant to out out 250 amperes.

[@russellmatheny8677]

I have 2 of these welders. I figured out you have to correct the digital readout with a 3 resistor bias circuit using the independent supply of the meter. I used a constant resistor with two trimmer potentiometers to build a mini circuit board to correct the reading on the meter to match the actual amperage of the welder. The other trim pot you mention that you do not know what it does controls the output amperage of the machine. Yes mine to has a 180 amp circuit breaker on the buss bar, do not think that is obtainable with the circuity provided by the Chinese. I am setting mine up to run at about 130 to 140 amps then will use the bias circuit to adjust the meter reading. Also if you really want more amperage take 2 of these machines and connect them in parallel and you can run much bigger rods up to 225 amps. However with two machines running at high frequency the welding sound starts to have a high pitch noise to it in lieu of the normal frying bacon sound. If anyone needs more detail on this bias circuit I will be happy to converse with you. Thanks

[@themisk.3843]

Hello mate..I tried to correct the value on the display screen as shown in the video but I finally unsettled the other potentiometer that you mention is related to the amperage. How can I fix it? Do the amperes increase, if i turn it clockwise? Thanks!

[@andrewray822]

Just noticed your comment now. I'd be quite interested to know details of this circuit.

[@scottfrazer8376]

That would be fairly simple Andrew. BUT it might be hard to figure out the resistance values needed... IF you don't utilize a resistor "substitution box" for your preliminary testing. Perhaps "R" would be happy to provide you with the details of his particular correction circuit. Personally, I don't really give a hoot, because I already KNOW the display is showing about twice the actual output current. But another possible way to variably correct the value shown on the LED display would be to simply use a very small VARIABLE VOLTAGE regulator module, to drop the voltage in a very linear fashion. You can probably get a pack of 5 of them for around $10 to $12 on Banggood or eBay.

[@russellmatheny8677]

This is awesome info!!!! Thanks. I have my welder which I hooked up to an independent shunt with amp and volt meter to get the actual output. They said 225 amps and it actually was about half of what they said. So finally I found your viedo that shows me how to trim or adjust the digatal meter to match what the welder is putting out. Thanks Again!

[@scottfrazer8376]

ATTN: IF I had my own KZbin channel, I would make a video about this DEFECT I found and corrected in my brand new TopShak ZX7-250A 110V welder, which I bought on Banggood. Apparently, this unit was assembled using five M3x10 machine threaded screws to anchor the 3 big heat sinks in the back of the unit, near the cooling fan. This was a HUGE MISTAKE on the manufacturers part, because the heat sinks have no machined or tapped threads for the M3 x10 anchoring screws to bite into, but only SLOTS in the aluminum castings. You need to grab a standard #2 Phillips screwdriver and remove the welder cover, then use the screwdriver to check all five heat sink anchoring screws on the bottom of the circuit board, to see how many of them are loose and INCAPABLE of even being sufficiently tightened in the first place. I just replaced all five heat sink anchoring screws with some slightly bigger cabinet screws, which have tapered threads that are very similar to self tapping screws. NOW all five screws can be tightened very securely. You really don't want any of those 3 heat sinks EVER coming loose, because the result will eventually be a certain failure of the welder. ALSO....the word VARISTOR should NOT be used to describe ANY type, style or size of variable resistor or potentioemeter, because a VARSITOR is a completely different kind of electronic component.

[@vitaliryumshin6174]

the problem, it is not linear, min value in real is 54 A (shown as 24A), 66 on display is 68A real, but 204 on display is 113A. we need to correct low and high amps

[@fp274]

the first version was better, it had 3 capacytors, and the voltage adjust is on the main board lower end, i have it at 150 (with a shunt amp meter it maxed about 130A)

[@JayDustheadz]

What was the first version? The ZX7-200?

[@pearllen3514]

I didn't see it... video is dark...

[@djisydneyaustralia]

They mostly barely get 110amps but theyre fantastic. I wish i had the cash to get skids at the time i first bought them , coulsve made alot because noone had them in Australia. Now the big name brands are selling these. With small mods can achieve 180 amps stable but dont use 3.2 rods they go bang. 2.4 is ok

[@piclife1178]

Good video, thanks. Check the metal case for earth connection. My one came with a three core flex with earth wire but the earth was not connected inside the box.

[@dionisiosciascia1416]

Thanks for your review and the info you shared. Very helpful and important

[@SuperDTMF]

TOPSHACK ZX7-250. I replace fixed resistor 6K8 with 3K. LCD now shows 145A MAX. This is Ok.

[@zeljkozeljeznjak6739]

Thanx for reply. Now I realize that I have used another potentiometer. Your set up for max current on display works. Now I have window from 14 to 139. I will continue to find how to lower output current to cca 40 A.

[@andrewray822]

To be clear, this isn't changing the output current, only what is displayed on the screen. You would have to get some amp-meter if you need really precise output current, to calibrate.

[@zeljkozeljeznjak6739]

Yes I know. I intend to make new video with all info I jave now.

[@tecnology-today]

A 180 amps fuse is totally unnecessary and a waste of money for this kind of low cost machine. In my inverter such part is a current shunt for measuring the output (in the pcb there are the sense lines from the shunt to the measurement circuit). Very interesting video

[@juanrodriguez3165]

Thanks for the info.

[@johnjeronepenaflor7081]

Hi good day to you sir can you share to me what pwm ic number does the zx7 use in control board because my problem was their is no pwm signal going to igbt

[@dusanmilojevic3017]

One pots is for display and the other is for output current .

[@qaisarawan93]

I have same machine but it's tig 250 a. It has 3 pots. Using one I adjusted max current to 180amps as its max fuse readings. Earlier I fiddled with one of the other pots don't know what it could be for.?

[@kunnathupadickalmanoharan2835]

Will you please inform me where I can get the same machine circuit board

[@weldyboy-R-]

Its simple, two IGBT 60Amp, max pulsed collector current 180A , max 428Watts each..... what to expect if it fits in the palm of your hand? 🙂

[@nunyabidness-qr5vp]

wasnt that fusable link for inupt not putput

[@josesplana2073]

I can't see where you crew on board, Could you show us pls?

[@danielsouza28]

good night friend, could you check the values ​​of resistors R4, R5, R8 and R9 on this board, they control the IGBT

[@thdigas]

Thanks for useful information

[@Piano_sessionfree]

What is the blue potentiometer on the top for?

[@krzysztofnicinski8052]

I don't have the variable resistor for tuning the output number on the screen (Topshark version of the welder). What is optimal resistance on variable resistor at 130A - screen value ? Maybe You could make a new video that will sum all the topics that acurred in the comments 🙂

[@tauorus]

My welding machine didn't have a potentiometer to adjust the display, it had a fixed resistance, I put two 10K resistors in parallel, and I put them in parallel to that fixed resistor, and now it is showing 126.

[@prime553]

Are these welders safe?

[@piclife1178]

The metal case was not connected to the earth wire on the one I bought. Had to add my own earth connection.

[@zeljkozeljeznjak6739]

I tried to repeat your test, but with my welder it doesn't work that way. The display changed by 1-2 units, but the output current changed considerably. So far the max output current was 129 and now I have set it to 150 A. I have not tried further. Min remained the same 55 A. I would like to lower that to about 35 -40 A, but I don't know how.

[@andrewray822]

Do the internals look the same? Maybe the chinese have made some changes.

[@zeljkozeljeznjak6739]

@@andrewray822 Yes it looks the same. I put my answer on the top of comments.

[@sm1thers]

@@zeljkozeljeznjak6739 there are 2 blue pots close together, are you sure you're turning the correct one?

[@tauorus]

I was able to change the high and low current limits by moving the two blue potentiometers, one changes the lower limit and the other changes the upper limit, by the way the OCV of mine is approximately 102V dc, is it normal?

[@themisk.3843]

hey..i have the same machine and i am wondering if i can adjust the output voltage that i want for a project. do i have to adjust some potentiometer?

[@andrewray822]

I don't know if there is a way to regulate output voltage, kinda doubt it. What is your project?

[@themisk.3843]

@@andrewray822 i am designing a reactor that will produce hydrogen and oxygen through electrolysis

[@aloewaoson8221]

see my small test: kzbin.info/www/bejne/rZKXnH2PabWhock I checked current with UT210E, this clamp meter can measure DC currents. I think 250A rating is a 'peak current' rating. Since input is most likely 230V-16A you can have 130Amps at about 28V continously. I found about 50Amps when electrode stuck at the 50Amps selection, so I would not change the calibration. What I found about the hardware is that my input capacitors are faked and I have only 850uF instead of 2300uF. The 820uF Capacitors are only 130-140uF each. Also I miss a relay for inrush current limit at start. I had to use a cable roll to start it.

[@andrewray822]

What is the second control on yours for?