Since I am last one with the word "cheap" in my post, suppose it is addressed to me.eTrike said:Could you please define cheap and compare cost per wh?
You certainly need balance wires, not for balancing itself but for supervision. It leads to another questions answer, you can arrange your series in flashlight style if you figure how to make balance connections. Cells will generally stay balanced if they are new and used in not abusive manner but if 1 cell is defective in some way then your pack is a ticking bomb and you should know it before avalanche happens.rick (nova scotia) said:I certainly like the idea of no solder/weld packs.
I'm an E-bike newb, waiting for my new Stunner, but already thinking about a "spare" battery. And thinking of building it myself. the first question that came to my mind was could I series together in a flashlight manner. Which led me to this thread.
Thanks for answering my question. I believe I came across the figure 9 pounds of force is enough.
Keep in mind I'm new, another question is; since the pack would easily be disassembled in winter (or more often) how necessary is balancing wires, assuming you start with new, and equal cells ?
My design is coming along nicely in my head, so long as it don't get crushed.
IdleMind said:I agree with the post above, you need to have a method to know that the groups are in balance as well as confidence that all cells are good. An advantage of these type of assemblies is that they can be disassembled and each cell checked or tested.
Spring tension is dependent on many factors, I am using 8 to 10 pounds and it's been working well for me. I have about 200 miles on this pack and happy with it's performance. This is a lot more spring force than a typical flashlight.
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Here are some factors to consider
1--how much current are you pulling--I have a low power setup and seldom draw more than 10 amps. I charge at 3.5 amps.
2--how much actual surface area do contact points provide. I use brass nuts as contacts and depending on fit the contact area could be the area of the nut or just a point contact. Some guys have formed bumps into the copper plates, this may be a better technique if the bumps are slightly flexible and provide more contact.
3--how well are the cells contained to prevent side to side movement. High spring force can help keep every thing tight
A gallon of water weighs about 7.5 pounds, just to think about to help get a feel that this is fairly high force.
Jonathan in Hiram said:Great idea, I love it.. A couple of modifications come to mind due to what I already have on hand. Pure copper foil tape with conductive adhesive, two layers put sticky side toward each other with brass or copper washers in between the layers to make the bumps.
Neo disc magnets for the spring compression on one end of your cell stack, copper foil tape again with magnets sandwiched between the adhesive layers and other magnets arranged in the end cover to compress the stack. I'm only thinking this because I have a couple of hundred of them right now.
I had a different kind of build planned but I like your idea enough to give it a try I think.