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Discussion Starter #1
Hi,

Over the past year, we at EVDrive have been working on a new design for packaging 18650s into usable modules. We think this design has a number of advantages. Our modules have the following features:

--Maximum packaging density
--Cells are interconnected with Copper (over 4x less resistivity than commonly used Nickel 200)
--Integrated BMS: No high voltage wires exiting the module, only 12V power and CAN communication
--Module is potted with thermally conductive encapsulant for ease of cooling and mechanical robustness
--Any 18650 or 21700 cells can be used, so the pack can be optimized for power, capacity, cycle life, etc.
--Over 1kV isolation from cells to case, so that high voltage packs can be constructed without any troubles.


We just shipped out the first test module using our new design for a Go-kart project, as can be seen below. This particular module had the following specs:

--43.2V nominal (12S)
--54Ah
--2.33 kWh
--675A peak, 275A continuous without cooling, 450A continuous with liquid cooling
--Dimensions of 205 x 355 x 75 mm
--Mass of 12 kg

As you would expect, our modules are more expensive than Tesla packs from salvage yards. However, they provide flexibility that you may need, as they can be arranged into many more sizes, shapes and capacities. Also by using high power 18650s, they can provide far more power than a Tesla pack, if this is needed. As time goes by, we will be adding more "standard" modules into our library for ordering, but we have designed our process to be able to be customized easily and with minimal NRE costs. So, if you have a specific need, let us know and we can design just what you need.

 

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Sweet! Can we see an image as to how they can be combined/stacked? I imagine that you will allow both parallel as well as serial "stacking"?

Cheers
M
 

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What is the cooling system? Is the visible metal plate intended to be cooled by a "cold plate", or is there internal plumbing?
 

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Discussion Starter #4
The heat transfers efficiently from the cells to the aluminum surfaces--there is no internal plumbing, so those surfaces could be cooled just by air passing over them or by sinking them to a liquid cold plate, depending on how much cooling is needed.
 

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The heat transfers efficiently from the cells to the aluminum surfaces--there is no internal plumbing, so those surfaces could be cooled just by air passing over them or by sinking them to a liquid cold plate, depending on how much cooling is needed.
Thanks :) - that's what I was expecting. I assume the internal heat transfer is just by the potting material.
 

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Discussion Starter #6
Thanks :) - that's what I was expecting. I assume the internal heat transfer is just by the potting material.
Correct, although it is also a function of the extreme closeness between the cells and the housing--the potting material is "thermally conductive" but still far less so than metal, so we keep that layer extremely thin. Heat transfers far far more efficiently axially than radially in a cylindrical cell, so the heat presents itself on the ends where it is transferred right to the housing.
 

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Sweet! Can we see an image as to how they can be combined/stacked? I imagine that you will allow both parallel as well as serial "stacking"?

Cheers
M
Although you could connect them in parallel, I wouldn't recommend it--they are designed to be stacked in series; since these ones are 12S, if you wanted to parallel them you would have to parallel the strings, which can be done but is not advised. Rather, if you wanted more capacity we would just put more cells in parallel within the modules themselves.

Here you can see two of the go-kart modules connected in series for a 24S total stack:



More often than not we do modules of 12S because that fits best with our embedded BMS, but that's not a requirement and we could even do a single block of just paralleled cells if needed. Also, the embedded BMS is not a requirement...in the go-kart prototype pack there is no embedded BMS as we have not yet finished the ultra compact version of it, but we designed in the slot for it so it can be added later.

As I mentioned, we designed our process to be easily customizable, so whatever capacity is needed can be done pretty easily. The go-kart pack was 18 cells in parallel, the 16 modules below are for a monster pack that has 36 cells in parallel and are capable of 1800A peaks. We also have in the works projects that will be 24P and 48P, and will add more to our "standard library" as time goes by or as they are requested or as our internal projects require them. Our goal is to be a quick turn solution for highly customizable packs--we envision people being able to order, for example, several different shapes of modules that all have the same parallel count so people can build up a full pack that fits in their application.

 
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