I’ve been in the process of building a 14S7P 18650 GA 50 Amp Cont soft pack for some time now. In the process I’ve learned a whole lot about battery building and exactly how challenging it can be. Once of the real struggles I’ve had is finding a decent battery spot welder that doesn’t break the bank. For this project, I ended up using 2 different battery spot welders, both purchased from eBay. This article will discuss the pros and cons of both welders as well as making suggestions of what you shouldn’t waste your money on.
The first spot welder I purchased was off eBay since that was the cheapest place I could find. There are a plethora of welders out there on eBay and Aliexpress just search for “battery spot welders”. This welder had some serious limitations. The biggest problem I found was that the welding tips only go two cells deep. This works fine if you’re building a hot glue pack and can just glue on cells as you go, but if you are using a plastic stencil pack then it can be seriously difficult to build a large pack. The pack I was building used a total of 98 cells, was 5 cells deep and weighed about 12 lbs. It was incredibly difficult and fatiguing to try to spot weld that pack. I ended up bending the metal contacts so that it would go 3 cells deep, but it was very difficult to do that and often it would slip and make a big spark. The welds with this unit were very good, because the electricity did not have to travel very far, the power you set at the machine tends to be close to what you get on the welds. With the second welder I purchased with remote battery welding leads, I would only get about 1/2 the energy I set the welder at because of the long wires that the remote leads had.
After using this first welder for a few hundred welds, blowing 3 fuses, and tripping the circuit breaker in my house several times the unit just died. Since it had been more than 30 days since I bought it there was really no recourse, I emailed ontheway_2012 on eBay who said I was out of luck. I would not buy from them again, nor would I recommend this welder even to someone I didn’t like. For giggles I took it apart and the inside construction of this unit was laughably bad. They used hot glue everywhere to hold things together and everything about the inside of this unit looked very sketchy.
I finally decided to splurge as my pack was now half built, and not being very useful to me in that state. I ended up settling on a welder with remote leads because it was such a pain to have to hold the battery up for several hours on end while I was welding it. It was also very tricky getting that third row of welds in with the bent leads. This new welder was much nicer and even comes with a cheapo soldering iron which I have yet to test. You can use it with the leads on the box and weld it like you used the first welder by pushing the battery pack up and the welds automatically zapping the battery when there was adequate pressure. It also shipped with a foot switch which in tandem with the remote leads. At first, it was a little unnerving watching the lead wires jump every time I did a weld, but after a while I got used to it and was able to focus on the task at hand. I messed around with the settings but ended up setting it to 8 pulses with the power up at maximum with the remote leads. Full power is a complete overkill if you are using the leads mounted directly on the box because you end up getting a lot more of the power through the welds. It worked fine just a bit over 1/2 way up when welding cells using the pressure sensitive welding leads directly the box. Higher than that and you will start melting through the nickel strips.
Instead of doing multiple welds on same 18650 battery in quick succession I ended up doing one weld at a time on each battery and then jumping to the next one. The batteries got pretty hot from the welds and I was worried that the batteries would blow up in my face if they got too hot. Speaking of batteries blowing up in your face you should ALWAYS use eye protection when working with welding lithium batteries. If you don’t do this then really there is no hope for you. Really.
The remote welding leads got very hot when I was doing too many welds in a row too quickly. At first, it was unsettling but it was a great way to get me to slow down. I suspect that I destroyed the first welder by doing too many welds too quickly and burned out something in the welder. When the first welder stopped working it would act like it was working but then it just wouldn’t actually weld. Kind of like me, at a real job. I would pretend to work as soon as the boss walked in, then as soon as they walked out, it was right back to the video games. That’s why I have to work for myself, because no one else can put up with me.
The one thing I’ve learned through the whole battery building process is that it’s really not worth your time and energy to undertake a battery building project. If you can find a decent 18650 pack already built then chances are it will be cheaper and less frustrating to just buy and use that battery than to try to make your own from scratch. If you’re interested in learning about how to build batteries yourself and are looking for a cool and fun ebike project, then by all means, you should do it, but if you’re looking to save money & time then you’re going to be disappointed. Kind of like the time I really, really wanted that Optimus Prime transformer for Christmas and then when I finally got it and realized it wasn’t a real living robot I cried myself to sleep.
UPDATE : I loaned the expensive battery welder to a friend of mine and the fuse blew, then after it was replaced the fuse holder actually melted. I guess you get what you pay for.