P2) 416 OFPPk (Design & Development)

Design & Development

First and foremost, the design will need to be simple.

It takes more brains power to be simple than more complex design. Simplicity is rather not easy to come by. Many considerations have put into this simple and yet it needs to fulfill the basic feature. Simple will also mean that each part will have more functions on its own. That'll also means less part to take care and less part to assemble. Another most important consideration is the user.
Can the user assembled easily without much effort?
Can the user change the configuration?
Does it allow future expansion?
Is it fused?
This are some of the important question during the design phase... anything is possible or omitted.

Basic Battery Pack Design

Generally, most DIYer or battery maker will have their battery pack mounted in the battery holder like this picture below. After which they put the nickel strip, spot-welded or soldered it to the bus wire. This is a proven design that many manufacturers & DIYers have adopted.

This is great in most extent and is compact to the minimum. The issues most people will come across is the assembled the pack. Spot weld and Soldering is required during this process. Not that practical if you just starting to build power pack. Spot weld do consume a lot of energy and also a safety concern.

In-order to build a DIY battery pack, the first consideration will be what configuration will most DIYers used. Going small or go big?

As below, this is the first design & build using 4 x 7 configuration. I did a prototype and it function as what I have in mind. The only issue is the structure, it need to be improve. Back to drawing board.

While redesigning the pack, I realised that for this 4 x 7 pack to upgrade to a Powerwall capacity will be a huge task... lots of 4 x7 is needed. So I gather more information within the DIY & Ebike community. The most popular configuration in DIY or Powerwall is 3S, 4S, 7S, 13S & 14S. For ebike, it can go to up to 16S. So I took the minimum and maximum to come out a 4 x 16 configuration.

That's where 416 Open Frame Power Pack Kit (OFPPK) is born.

Pack Design

Have spend countless hours, countless design, researching the best and easy way to secure and have the consistent contacts thru out the whole pack... it is not easy. Finally manage to figured out and implement it on this 416 build. The improved version vs the 4 x 7 is much more robust.

How does it work?
The principle is using compression. Compression is like a wire connector, once you compress and lock, it will maintain that position. So what I did was to use a short nickel strip on each cell, goes thru a slot on a thick acrylic plate. Another acrylic plate will tie to this plate act as a cell holder. I then placed 4 long nickel strip all the way from end-to-end to link all the cells connection together. When both side of the plate is tied together, it creates a solid mating on the battery contact as well as the long connected nickel strip. All the cells will have consistent pressure and maximum contact surface. This will be similar as the normal Spot weld format.

Termination

The 4 long nickel strip will travel all the way to the termination point where a Nickel termination plate that will join all together by 10 M5 screws. This is where series, parallel or BMS connections can be done easily using cable lug or ready made connecting plates.