Reverse engineering of DoCreate DHJ567 handheld spot welder

[spleenharvester]

Hello everyone

I attach a schematic and teardown photos for the DoCreate DHJ567 handheld spot welder. I bought this welder for temporary use while my supercapacitor welder was waiting for replacement parts. It cost only £24, though there is a screenless version available for £17.

Performance: The absolute maximum it can handle appears to be 0.15mm of pure nickel. Reliability was not great - welds were very inconsistent, ranging from weak attachment to burning through the strip. However, I was able to build a 5S2P pack without losing any cells. It's a bit difficult getting the weld probes to sense continuity too, which makes it difficult to use when delay is enabled.

Hardware: It uses a simple 3.7V pouch cell that is run through a boost converter up to 5V. Four NCE30H29D MOSFETs are used to fire the weld pulse. The MCU is a Cmsemicon CMS8S6990N. Programming pins are exposed but presumably you need Cmsemicon's programmer.

It's not the best but it's impressive how they have been able to bring it to market so cheaply, and would probably work well in someone's collection if they don't want to splash the cash on a supercapacitor welder.

DoCreate DHJ567 Spot Welder Schematic V001.pdf

[sam_sam_sam]

I have one of these as well but it does not have the screen it has a row of LEDs that you set the welding current by I suspect that the battery cell is shit because it runs down quickly from what I remember and I do not think that it is a high current capacity rated battery cell that is the first problem

I am going to do a very detailed analysis of this battery cell and see what it really can do at what load and what does the discharge graph curve looks like

I have to finish some testing that I still working on then I will set up the 40 amp battery testing machine and do a 40 amp load test and see what voltage values I get and for how long but I going to this test outside just in case the battery cell burst into flames I can throw it in the driveway and put out before it gets out of control

I have to also take some measurements of this pouch battery cell and see if come in a high current capacity battery cell and how much it cost because the high current capacity battery cells are 2 or 3 times the cost of a low current capacity battery cell I am not referring to amp hour rating that speck is different from current capacity

Because the discharge current / voltage curve looks different from a high current capacity versus a low current capability battery cell and generally speaking the high current capacity battery cells have a lower amp hour rating not always but the cost is considerably higher than a low current capacity battery cell with nearly the same amp hour rating

On a side note I have a battery operated battery tabbing welder that also has a low current capacity battery pack cells but the high current capacity battery cell is about 5mm wider and will not fit in the enclosure correctly but adding an extra battery cell made a big difference in it performance even though it was still a low current capacity battery cell

So if a high current battery cell is not going to fit correctly I will just get another low current capacity battery cell and see if the performance is better or not

Or

I will just put a much bigger battery pack that I bought from Battery Hookup that is brand new and it has 70 battery cells in parallel which is what I bought it for originally but then I found a different brand of battery operated battery tab welder that also has the same issue about the battery draining very quickly when welding with it ( which I thought I might use in this welder too but it might not not be a good idea or option because the battery tabbing bolt holes are very close to the edge of the circuit board that is the main reason I sighted away from doing this in the first place on this one that is being discussed on in this post the circuit board can be made to support the battery cables and I do not have to worry about the bolt holes breaking into pieces


I have one very important question to ask you where are the welding connections are on this circuit diagram because I do not see them unless you named it something else just curious about this

I will post the results here when they are available

[CapLeaker]

I know you using this to spot weld batteries together for a pack. Call me ignorant, but I just solder mine.

[spleenharvester]

I have one very important question to ask you where are the welding connections are on this circuit diagram because I do not see them unless you named it something else just curious about this

It's Weld+ and Weld- at the top right

I know you using this to spot weld batteries together for a pack. Call me ignorant, but I just solder mine.

Yes a lot of people on Reddit get upset if you do that lol. I don't know how much it really matters in practice, but spot welding is a lot quicker for large packs either way.

[CapLeaker]

A lot quicker? You’d need to almost manufacture or repair batteries a lot to make it worth while. For that one battery pack here or there, I’ll keep soldering.

[sam_sam_sam]

A lot quicker? You’d need to almost manufacture or repair batteries a lot to make it worth while. For that one battery pack here or there, I’ll keep soldering.

I will do this from time to time but keep in mind that if the battery temperature goes to high then the pressure CDI will trip and you would not have any voltage output so use solder that has flux and do not spend much time on the positive end of the battery cell the negative side is little bit more forgiving but a little bit harder to solder you can do it but just keep this in mind when doing this procedure

[CapLeaker]

I will do this from time to time but keep in mind that if the battery temperature goes to high then the pressure CDI will trip and you would not have any voltage output so use solder that has flux and do not spend much time on the positive end of the battery cell the negative side is little bit more forgiving but a little bit harder to solder you can do it but just keep this in mind when doing this procedure

True. That's why one needs a way soldering hot and fast plus surface preperation... and I got what I need to make that possible. My way takes longer, yes... but I don't make or repair enough battery packs to justify.

[spleenharvester]

A lot quicker? You’d need to almost manufacture or repair batteries a lot to make it worth while. For that one battery pack here or there, I’ll keep soldering.

I bought mine for building two 10S4P packs - 2 welds * 2 terminals * 40 batteries = 160 welds per pack. It starts to become a faff real quick.

Plus it's a good investment if you want to build e.g. tool batteries, I broke out the welder again to build a bunch of 5S2P Milwaukee packs.

[CapLeaker]

Yeah… see… I don’t do any amount nor that battery size either. I mean I get it why someone needs to have it. I suppose if I had to do that what you did, I’d look at something like that probably too.