Finished the welding: E-Bike Blog #11
- Tim Ellsworth
- Jun 19, 2017
- 3 min read
Welder
The welder was still not cooperating throughout the entire build. The seller that I bought it from on Amazon is also not talking to me anymore. I was able to limp along and complete the nickel strips by continuously cleaning the tips and re-welding/replacing nickel multiple times. I also found that slightly filing and cleaning the nickel and the battery contact area helped. My settings were always maxed out on the welder.
Process:
1) Settings: I experimented with settings all throughout the the welding process but I usually had all of the pulse settings in the upper left corner of the welder on and the orange current know maxed out.
2) Welding: When I first started welding and I had basically no results at all I was not paying attention. From the communication that I did have with the seller of the welder they told me that I needed to separate the lead ends for better performance. This did help the weld quality a little although I still found myself repeating welds again and again. Sometimes the best weld I got was when I had one lead on the cell and one on the nickel strip. I tried not to weld a joint more than three times. The more I welded it the worse it seemed to hold. I was careful not to get too close to the edge of a nickel strip or the edge of the positive cell cap. If the lead was on the edge it had the tendency to blow a hole in the nickel strip or positive cell caps. Below shows the way that I held the leads on a cell.
Amperage
After reading up on the amperage capability of the nickel strip that I got I decided that it would be a good idea to double up all of the series connections. I cut small strips and laid them over top the existing nickel grid that I already welded. This welding went better than the grid although I had a few instances where the secondary strip welding actually broke the initial grid off of the battery requiring me to re-weld both. I found that placing one of the welder leads directly on the battery created a better weld. As a precaution I will add Kapton tape to all of the nickel strips just in case one decides to break free and cause a short across two parallel groups.
BMS
I soldered all of the parallel group leads first making sure that I didn't get them tangled up. The hardest part was soldering the master positive and negative leads at either end. I used a suggestion from Micah Toll's book "DIY Lithium Batteries: How to Build Your Own Battery Packs" where he suggested stripping the master lead wires and soldering them along the end parallel groups (Toll p.93). This proved to be really difficult. The stripped 12 gauge wire was really difficult to manipulate and the points that I was soldering were directly above the PLA cell holders. If I took too long soldering the holders would begin to melt.
Reflections
Now that I have completed the soldering and welding of the battery pack itself I would say that I will look into alternative battery assembly methods if I choose to make another battery pack. I think that I will explore 3D printing interlocking holders with spring contacts that require no soldering as well as small bolted terminal connections that do not require any soldering except for the BMS side.
Next Steps
My next steps will be to create plexiglass covers for both sides of the battery to prevent accidental shorts. I will bolt them on using all thread that will run through the 3D printed "hole clips" that can be seen in the photo.