788 spot welder

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788 spot welder

Post by burningwings » May 14 2015 10:13pm

Does anybody have experience with the 788 spot welder sold on Alibaba ?

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788 spot welder

Post by burningwings » May 14 2015 10:21pm

Has anyone used the 788 spot welder on 18650 cell connections ? I want to build a 18650 battery .

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Re: 788 spot welder

Post by riba2233 » May 15 2015 3:24am

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Re: 788 spot welder

Post by Nobuo » May 15 2015 3:42am

burningwings wrote:Has anyone used the 788 spot welder on 18650 cell connections ? I want to build a 18650 battery .
I know some 788+ spot welder users, I'm receiving very good feedbacks of that machine lately. Is one of the two cheapest chinese spot welder machines known.

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Re: 788 spot welder

Post by Syonyk » May 16 2015 12:45am

I've just finished some teardown pictures from a repair of one - the triac blew up (110v version).

Welder details:
http://syonyk.blogspot.com/2015/05/over ... elder.html

Repair and re-engineering details:
http://syonyk.blogspot.com/2015/05/sunk ... epair.html

If you are using it on 110v, be careful and let it rest a lot. The quality of the circuit board is poor, and mine has some lifting traces, but otherwise it's a perfectly functional transformer-based spot welder capable of a decent amount of power.

I am still trying to find anyone who can explain to me the interaction between the digital interface for setting current and the CURRENT SET knob (0-16) - I know the current set knob increases the welding current or duration, but that's as much as I know, and I haven't had time to grab a scope to figure out what's going on.
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Re: 788 spot welder

Post by silentflight » May 16 2015 1:44am

Syonyk wrote:I've just finished some teardown pictures from a repair of one - the triac blew up (110v version).
Lots of good info on your blog- welcome to Endless Sphere!

What is the current limit on the circuit breaker you are running the 788+ on? I read it would need more than 20 amps when used on a 110 volt line.

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Re: 788 spot welder

Post by Syonyk » May 16 2015 11:01am

silentflight wrote:Lots of good info on your blog- welcome to Endless Sphere!
Thanks! I decided I should perhaps post as it's relevant to this thread, among others. I've had quite a few people who know what I'm working on tell me I should be posting stuff here.
What is the current limit on the circuit breaker you are running the 788+ on? I read it would need more than 20 amps when used on a 110 volt line.
15A. I haven't had any issues yet. The current draw is very, very brief - literally only a few cycles, and the welder is the only thing on the circuit when it's in use. Where on earth did you find any documentation on this? I've been trying to find anyone who knows anything about these more than just the sellers on eBay, who are almost, but not entirely, useless. I've accepted that if I want anything resembling technical information, I'm going to have to reverse engineer the thing myself. Or, at least, get a scope on the output and figure out what's going on.

I believe the fuse in the unit is a 20A fuse, so it can't be drawing much more than 20A for long. Everything about this welder can be summed up with the phrase, "Well, that's probably fine..."

If I continue having problems, I'm considering getting a 220v unit and a step up transformer, though before that, I'll probably just pair up two triacs to spread the load around. They're theoretically 30A triacs, with a 20A fuse, on a 15A circuit... so I'm hoping I just had a bad one from the factory, though if you look at the cooling (or lack thereof), I can entirely understand why they'd get hot in that location. A fan in the rear of the unit is probably sufficient to keep things cool, as long as I take it easy on the welding duty cycle.

Now I can get back to my actual goal of rebuilding an iZip Ultra pack...
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Re: 788 spot welder

Post by riba2233 » May 16 2015 11:19am

Syonyk wrote:
If I continue having problems, I'm considering getting a 220v unit and a step up transformer, though before that, I'll probably just pair up two triacs to spread the load around. They're theoretically 30A triacs, with a 20A fuse, on a 15A circuit... so I'm hoping I just had a bad one from the factory, though if you look at the cooling (or lack thereof), I can entirely understand why they'd get hot in that location. A fan in the rear of the unit is probably sufficient to keep things cool, as long as I take it easy on the welding duty cycle.

Now I can get back to my actual goal of rebuilding an iZip Ultra pack...
Adding step up transformer will only ease things on welder, but not on your power grid and installations. It would also require very large, bulky and expensive transformer.
I doubt you had one bad from the factory, it's just poor design, I've seen few of them with blown triacs. I don't know how they act in parallel.
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Re: 788 spot welder

Post by Syonyk » May 16 2015 11:35am

riba2233 wrote:Adding step up transformer will only ease things on welder, but not on your power grid and installations. It would also require very large, bulky and expensive transformer.
I doubt you had one bad from the factory, it's just poor design, I've seen few of them with blown triacs. I don't know how they act in parallel.
I know it requires a good sized transformer or a hefty inverter. That's fine. My power system can take the load, and I'll be moving in a year to somewhere with much more power available (including, if I have anything to say about it, 220v).

Good to know that blown triacs are a common problem. I suspected this was the case when the seller said the manufacturer suggested checking the triac.

As far as wiring them in parallel, it's not a great idea, but they'll usually take it just fine. I have no idea if the welder is smart enough to turn on the triac at a zero crossing or not - if it is, doubling up on triacs doesn't cause any problems, but if it's just turning it on randomly, you can get uneven startup and more load on one. It's still likely to be better than a single triac.

The fan is probably the best option for now, though.
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Re: 788 spot welder

Post by riba2233 » May 16 2015 11:50am

Yeah, good points, maybe it would be best to check it out with scope.
Can you check the temperature during operation? I ask because I'm not sure whether fan would help, since load is in ms, so the duty is pretty low.
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Re: 788 spot welder

Post by silentflight » May 16 2015 11:54am

Syonyk wrote:Where on earth did you find any documentation on this?
While shopping for a spot welder I was in communication with an alibaba seller of the 788+. I asked about the 110v units, and he replied that some people had upgraded their circuit breakers to 40 amps. I wondered whether some sellers had just replaced the cords and not altered the winds on the transformers or some such. Rather sketchy information source, but there you have it.

I like your quote "That's probably fine..." I've spent a few months in China, and that would be the optimal three word summary of my overall experience.

On the other hand, no one in the US is manufacturing inexpensive, reliable spot welders for hobbyists- so good on you, China!

Now that we have a few passionate and smart people on the Sphere discussing their solutions, all of which have positive aspects, it seems like we're leading the charge on this.

I hope you will post photos of your pack build in a thread or a link to your blog.

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Re: 788 spot welder

Post by riba2233 » May 16 2015 12:00pm

silentflight wrote:
On the other hand, no one in the US is manufacturing inexpensive, reliable spot welders for hobbyists- so good on you, China!
But there are in Croatia :lol:

But seriously, lot of people had built transformer based welder, it has it's drawbacks, but essentially it's pretty simple and much more foolproof than battery and capacitor based ones.
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Re: 788 spot welder

Post by silentflight » May 16 2015 12:26pm

riba2233 wrote:But there are in Croatia
Yes, but it isn't a fair competition. Being inspired by the beauty of the Adriatic coast as well as the beauty walking the streets, the Croatian is at an advantage.

I've found a local source for quality spot welding, but I eventually want a welder for myself. A combination of an A123 battery with a boosting capacitor and the JP welder seems like a good solution. It just seems right to use A123 cells with a mind-blowing C rate for a welder. Strapping an XL capacitor across the leads has a DocBass scifi feel to it, while completing it with a lightweight, compact unit built by a Croatian with better English than my own- seems like a 2015 solution.

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Re: 788 spot welder

Post by Syonyk » May 16 2015 12:43pm

riba2233 wrote:Yeah, good points, maybe it would be best to check it out with scope.
Can you check the temperature during operation? I ask because I'm not sure whether fan would help, since load is in ms, so the duty is pretty low.
I don't actually have a scope or data logger that can log 500v laying around. The peak voltage of a 110v circuit is around 150v (110V is RMS), and since I'm not assuming any competence without proof, I'm assuming the triac is getting slammed opened and closed, with a heavy inductive load (a transformer), at random points in the AC cycle. This means there's a very good chance that peak voltages, when the triac closes, may exceed the normal circuit voltages by a good bit (current will still flow, nowhere for it to bleed, so peaks may be high).

I'll see if I can find a way to check the temperature. Contrary to what many of my coworkers believe, I'm not actually a fully instrumented electronics R&D shop yet - I just mess with things on an as-needed basis. I may be able to change this in a year, but for now, I have no way of checking the electrical or thermal behavior of the welder at a cycle-by-cycle level.

The triac is opening and closing 4 times per weld, though (with dual pulse welding).
silentflight wrote:I like your quote "That's probably fine..." I've spent a few months in China, and that would be the optimal three word summary of my overall experience.
Yeah... I spent enough time playing with stuff back in college to learn the difference between "Complies with relevant codes, is highly reliable, and can be used by anyone" vs "Well... it'll work, most of the time, don't be stupid around it, but if you're using this you can probably repair it anyway." This welder is definitely the second.
On the other hand, no one in the US is manufacturing inexpensive, reliable spot welders for hobbyists- so good on you, China!
True. Although I'm not certain I'd call this welder "reliable" yet. If you're considering socketing your triac mounting point so it's easier to replace when it blows up, that's not a great marker for reliability. And the rest of the unit scares me as well. I have considered, depending on the success of my rebuild and subsequent uses, modifying these units with the relocated triac, a fan, and some proper heat shrink on the tubes, and reselling them in the US. I'm not sure I want to be point-of-contact for the assorted other failures I'm sure they'll have, though...
I hope you will post photos of your pack build in a thread or a link to your blog.
I did link to my blog. You should be able to find the pack teardown, at least. I don't have a pack build post yet, because it's currently in pieces in my garage. I didn't get the impression rebuilding a commercial ebike pack was that interesting to people here, though.
riba2233 wrote:But there are in Croatia :lol:
Well, you've got that whole Eastern European thing going out there, where "If you want it done, find a way to do it yourself" is much more common (and lawsuits are, per my understanding, significantly less common).

Despite the fact that "Short a lead acid starter battery across your workpiece with a few MOSFETS" (yes, I've seen your welder, and I think it's great!) is a viable way to spot weld things, that would not last long as a product in the USA. We still have plenty of people who think ebikes are cheating (because bicycling is a Proper Recreational Sport, not a way of commuting).
silentflight wrote:I've found a local source for quality spot welding, but I eventually want a welder for myself. A combination of an A123 battery with a boosting capacitor and the JP welder seems like a good solution to me. It just feels right to use A123 cells with a mind-blowing C rate for a welder and to strap an XL capacitor across the leads has a DocBass scifi feel to it, while completing it with a lightweight, compact unit built by a Croatian with better English than my own- seems like a 2015 solution.
You found a local source for spot welding? Impressive. I called around and nobody would touch lithium cells (of the few places that even knew what spot welding was).
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Re: 788 spot welder

Post by cwah » May 16 2015 2:03pm

Anyone managed to get external weldee on this?
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Re: 788 spot welder

Post by Syonyk » May 16 2015 2:06pm

External welded? ::confused::
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Re: 788 spot welder

Post by cwah » May 16 2015 2:13pm

I mean external wiring so that you don't need the 2 pin to spot weld
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Re: 788 spot welder

Post by riba2233 » May 16 2015 2:22pm

Syonyk wrote:
The triac is opening and closing 4 times per weld, though (with dual pulse welding).
On one review I've read that they are not even dual pulse.. But maybe there are some differences between versions.
Well, you've got that whole Eastern European thing going out there, where "If you want it done, find a way to do it yourself" is much more common (and lawsuits are, per my understanding, significantly less common).
Well, I consider myself to live in Central Europe, I'm only half an hour away from Italy, and have different mentality than most of the country. But yeah, I like that quoted phrase and don't see anything wrong with it :) I would say that lawsuits are only common to USA in that amount :)
Despite the fact that "Short a lead acid starter battery across your workpiece with a few MOSFETS" (yes, I've seen your welder, and I think it's great!) is a viable way to spot weld things, that would not last long as a product in the USA. We still have plenty of people who think ebikes are cheating (because bicycling is a Proper Recreational Sport, not a way of commuting).

Basically each welder does that, mine shorts battery, yours shorts power grid via transformer... Some short the capacitor.. That's just the way they work, nothing wrong with that. You can always install a fuse to be safe. Maybe it wouldn't last long as a product, but as a hobby electronics kit? Also, many people from USA buy Chinese "shit" that pose larger threat, and no one cares.
I can only feel pity for people who think that ebikes are cheating, and don't are about them. 8)

silentflight wrote: Yes, but it isn't a fair competition. Being inspired by the beauty of the Adriatic coast as well as the beauty walking the streets, the Croatian is at an advantage.

I've found a local source for quality spot welding, but I eventually want a welder for myself. A combination of an A123 battery with a boosting capacitor and the JP welder seems like a good solution. It just seems right to use A123 cells with a mind-blowing C rate for a welder. Strapping an XL capacitor across the leads has a DocBass scifi feel to it, while completing it with a lightweight, compact unit built by a Croatian with better English than my own- seems like a 2015 solution.

Thank you, that's really nice to hear 8)
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Re: 788 spot welder

Post by Syonyk » May 16 2015 2:29pm

Mine is very definitely dual pulse. I believe some of the earlier units are single pulse only, but with it set to single pulse, there is one thump, and in dual pulse mode, 2.

I see no reason extending the cables would be difficult. I don't have a need to do that right now but I believe I've seen pictures of it.

It is working again, and my pack is coming together. Slowly, as I'm letting the unit cool a lot.

I do need more fuses, though. It blew another one today, though that may have been damaged from the triac blowing.

I really think this should be considered a 220v only unit. I suspect it's much nicer that way.
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Re: 788 spot welder

Post by mcintyretj » May 16 2015 5:17pm

Burningwings, $136.16 is a good price for a spot welder

Syonyk, Not sure what a traic is, but, I probably had a similar problem with my 787a spot welder

I have the earlier version of this welder, the 787, and it looks almost the same as the 788. I used it for a 4p 15s 18650 build and it worked fine. I could not get good consistent welds on the thicker nickle tabs but it worked great on the supplied thinner tabs. When I started work on a 12p 15s battery I was doing about 20-30 welds in under 2 minutes which, I believe, is more that these units can handle. The welder stopped working. I decided to scrap all the electronics and just use a switch as shown in hundreds of youtube videos. Here is the welder today.
787 spot welder.jpg
787 spot welder.jpg (127.85 KiB) Viewed 8403 times
I just use a house light switch and a quick on-off flick of the thumb to get a solid weld. The problem I have is the black leads from the transformer to the copper leads get really hot after about 15 welds. On my battery you can see burn marks on many welds because I was in a hurry (copper sticking to nickle tabs). I needed to take a break for a few minutes and cool with a house fan before starting up again. Here is a close-up.
inside of 787 spot welder.jpg
inside of 787 spot welder.jpg (111.35 KiB) Viewed 8403 times
I also replaced the fuse with a 20 amp curcuit breaker.
fuse on back of 787 spot welder.jpg
fuse on back of 787 spot welder.jpg (80.7 KiB) Viewed 8403 times
With no face on the welder you have about 4 inches of reach for welding so I did not have to construct extensions.

Hope this helps.
Good luck!

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Re: 788 spot welder

Post by Syonyk » May 16 2015 7:43pm

... That's terrifying. How do you get anything remotely consistent with that setup?
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Re: 788 spot welder

Post by Nobuo » May 16 2015 10:43pm

Syonyk wrote:I've just finished some teardown pictures from a repair of one - the triac blew up (110v version).

Welder details:
http://syonyk.blogspot.com/2015/05/over ... elder.html

Repair and re-engineering details:
http://syonyk.blogspot.com/2015/05/sunk ... epair.html
This is really valuable info, If I get your permission Syonyk, will link this in the "18650 spot welding -how to- ULTIMATE REPOSITORY" attached to the same welder linked in the spot welders section.

Thank you very much for sharing :D
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Re: 788 spot welder

Post by Syonyk » May 17 2015 12:15am

Ok. On a keyboard. I'm going to try not to be too big an ass here, but... wow. There's a lot that's questionable here.
mcintyretj wrote:Burningwings, $136.16 is a good price for a spot welder
It's a good price for a very, very cheap spot welder. There's a reason many of the commercial ones are more expensive.
mcintyretj wrote:Syonyk, Not sure what a traic is, but, I probably had a similar problem with my 787a spot welder
A triac is a solid state switching device for mains level AC current. https://en.wikipedia.org/wiki/TRIAC It's used to make and break AC connections from a very small signal current, much like a transistor. However, they'll conduct current both ways, which is important for anything using AC (unless you want to rectify while you're in there, in which case you'd use something different). Functionally, it's similar to a relay, but much, much more precise timing-wise (fractions of a 60hz waveform) as there's no mechanical delay, and it can be cycled rapidly (relays die quickly when you do this). This is very useful for things like dimmers where you're only passing a fraction of the incoming waveform, and useful for equipment with very precise timing needs (like, say, a spot welder). The vast majority are just used as a switch, though.

If it failed, it's not a hard component to replace. Snip three leads, desolder them (you could also desolder without snipping them, but it's easier if you're not salvaging the parts), swap the heatsink to the new one, and resolder. At least in the case of mine, the physical damage was evident on the triac (it had a crater blown in it), and the seller also suggested I look at the triac, indicating it's a common failure on these.

If you had the display functioning, but it wasn't welding, it was likely the triac. If it didn't have any power, it was probably the fuse. It's entirely possible something else more complicated failed, but the mains->triac->transformer path is really quite straightforward, and the likely place for things to fail.
I have the earlier version of this welder, the 787, and it looks almost the same as the 788. I used it for a 4p 15s 18650 build and it worked fine. I could not get good consistent welds on the thicker nickle tabs but it worked great on the supplied thinner tabs. When I started work on a 12p 15s battery I was doing about 20-30 welds in under 2 minutes which, I believe, is more that these units can handle. The welder stopped working. I decided to scrap all the electronics and just use a switch as shown in hundreds of youtube videos. Here is the welder today.
I believe the 787, 787A, 788, and 797/797A are all very similar devices - they all have similar control panels and interfaces, and they're made by the same company, which indicates to me that they're probably very closely related - and I'd bet a small amount that at least some of them share circuit boards. The main difference is very likely in the transformers. That the 797 only comes in a 220v version backs this - it's too powerful to run on 110 and stay within the amperage limits. The 787 is already rated to pull "2-15A," though I find that rating on both the 220v and 110v versions, which is suspicious... I suspect it probably pulls a lot more than 15A out of the wall for 110v, but only very briefly. If I can get myself some good high frequency measurement equipment, I'll find out. Unfortunately, I need to find something radically overkill to measure this, because I strongly suspect there are some hellish transients (brief voltage or current spikes) that will fry cheaper measurement equipment.

What thickness nickel plating were you trying to weld? Honest assessments of the 787a (that don't include impossible multi-millimeter thicknesses) seem to indicate it tops out around 0.15mm, which is middle of the road for nickel strip. I went with the 788+ specifically because it's rated up past 0.2mm, and the pack I'm rebuilding came with 0.2mm, so I'm sticking with 0.2mm. Most of the included tabs I've seen with welders are 0.10 or 0.15mm thick.

I suspect I was welding at a similar rate on mine when it failed - I wasn't hurrying, but I wasn't giving it that much time to cool. The YouTube videos of these welders seem to indicate they can accomplish that welding rate, but I believe most of those videos are of the 220v version (in one case, the step up transformer makes it very clear it's a 220v unit), and as the current will be halved, it's not nearly as stressful on the unit. I don't think the 110v conversion was much more than a transformer swap and a quick change of the board power supply (if it wasn't already a switching PSU). There are no "dual mode" versions of this that run on 110 and 220, and the wiring to the transformer makes it clear why.

As for the YouTube videos, I'm not good at searching - can you please show me people building battery welders with a light switch? I see many switch controlled transformer welders, but they seem to be mostly used for welding inert chunks of metal, not highly reactive batteries. Or, more frequently, for melting things.
I just use a house light switch and a quick on-off flick of the thumb to get a solid weld. The problem I have is the black leads from the transformer to the copper leads get really hot after about 15 welds. On my battery you can see burn marks on many welds because I was in a hurry (copper sticking to nickle tabs). I needed to take a break for a few minutes and cool with a house fan before starting up again. Here is a close-up.
I don't see a "truly, deeply, horrified to the center of my being" emoticon. So imagine one.

I cannot believe you're welding batteries with that uncontrolled of a setup. This being ES, you were probably welding up a lithium pack with that.

There are a lot of issues with your design, and I'll only list a few.

The first is that you're using a standard household light switch to make and break a highly inductive load. They're designed for lights, not transformers! Any sort of switch or relay takes a very significant derating when dealing with an inductive load, because when you break them, they keep providing current, and there's typically a truly nasty voltage spike on break. If not handled properly with snubber circuits, this generally means that whatever just broke the circuit now takes a huge voltage spike, and in most devices, a nice powerful arc across the contacts. This leads to rapid pitting and high resistance in the contacts (so more heat), and on occasion, welding the contacts shut. This wouldn't matter as much for welding inert chunks of metal, but the consequences for welding a battery pack are significant.

The second is that you're using a light switch to try and control something that should, ideally, be precise to within a millisecond or so, and also, ideally, turn on/off at zero crossings of the input AC waveform. Humans are not that precise. Light switches are not that precise.

A quick survey of "how quickly I can tap the space bar" as a very loose approximation for toggling a light switch indicates I can cycle the spacebar at roughly 100ms intervals - 10 times a second (slightly less, but I'll round). The marketing for the 788+ indicates a pulse width of 1-19ms. As I haven't thrown it on an oscilloscope yet, I don't know how accurate that is, but as I'm not using the full power of the welder on my pack, I'd hazard a guess that if the marketing is close, I'm running a 15ms pulse. Maybe a bit longer, but definitely not 100ms. 100ms would do things like, perhaps, create "burn marks on many welds" - excessive current, excessive heat, flowing directly into the end of a lithium battery.

You've effectively replaced a high precision, computer controlled device with the welding equivalent of a sledgehammer. It's fine if you're banging on a wheel stuck to a brake drum, but it's not so good for anything that requires precision and a minimum of heat.

Finally, you don't seem to be concerned that your welder is running so hot you have to use a house fan (box fan?) to cool it. If anything electrical is getting that hot, and you don't know exactly what's going on (for instance, it being a filament in a bulb), it's time to step back and reconsider what you're doing. Hot electrical wiring is not a good thing.

You're dealing with batteries here, and most likely lithium cells (as I can't imagine why one would put together a 12p15s pack otherwise - 48v nominal, I expect?). Most of the popular chemistries are rather fragile, and prone to thermal runaway. Putting more heat than the bare minimum needed into them is incredibly unwise. Using a light switch controlled welder that you admit burns a lot of welds to put together a battery pack is simply stupid. My tabs are slightly warm to the touch after three welds - how are yours?
I also replaced the fuse with a 20 amp curcuit breaker.
What's the rating on the circuit you plug into, and what else is on the circuit? Many homes have 15A breakers...

Apart from that, the multiple T20A fuses (T is a slow blow rating, 20A fuse) I've blown in my welder, while not yet popping the 15A breaker on the circuit (I'm the only device on the circuit) says, "A circuit breaker is not a replacement for a fuse for something like this." Especially when your home wiring is protected by the same rating. Fuses and circuit breakers blow differently, and for a rapid current rise, a fuse is faster. Circuit breakers do not interrupt as quickly as a fuse. My frequent blown fuses also speak to the fact that I think the engineering difference between the 220v version and the 110v version are minimal at best...
With no face on the welder you have about 4 inches of reach for welding so I did not have to construct extensions.
Well, good. You've got that going for you.
Hope this helps.
Good luck!
And I hope nobody ever looks at what you've done and thinks, "Yes! I'll do THAT to weld my lithium battery pack together!"
Last edited by Syonyk on May 18 2015 12:23pm, edited 1 time in total.
Battery packs, Sunkko Welders, and more. http://syonyk.blogspot.com/

Syonyk   10 kW

10 kW
Posts: 527
Joined: May 16 2015 12:41am

Re: 788 spot welder

Post by Syonyk » May 17 2015 12:33am

Nobuo wrote: This is really valuable info, If I get your permission Syonyk, will link this in the "18650 spot welding -how to- ULTIMATE REPOSITORY" attached to the same welder linked in the spot welders section.

Thank you very much for sharing :D
You don't need my permission to link to my public blog posts. :)

But, yes, absolutely, please - link to them! I spent many hours trying to find out anything about pack rebuilding, and wasn't able to find any information on the welders other than a few pictures. Hopefully this information can help someone else out, either with picking a welder, or with repairing one.
Battery packs, Sunkko Welders, and more. http://syonyk.blogspot.com/

burningwings   100 mW

100 mW
Posts: 37
Joined: May 03 2015 11:39pm

Re: 788 spot welder

Post by burningwings » May 17 2015 1:30am

Thanks sooo much Syonyk !!!

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