DIY HI POWERED PACK: First time, General questions

Ohbse said:

Jonathan1981 said:

it would be awesome to find a cheap mold-able material the could do that. I was thinking something like mixing aluminum powder into a soft two part epoxy and molding a thin layer around each cell?..... thoughts, links etc???? just trying to think of a cost effective DIY cooling solution for such a large pack..

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Wax. http://www.allcelltech.com/index.php/technology/pcc-thermal-management

Phase change temperature can be varied with composition to target the sweet spot for optimal cell performance/lifespan.

The downsides are primarily mass and complexity. In many circumstances you would be better off taking the mass dedicated to the cell cooling and adding additional active material in the form of more cells. More of the same cell with the same power demands lowers per cell heating OR more cells allows for a more 'power' focused chemistry while hitting your energy requirements, again reducing per cell heating due to lower IR.

Essentially to maximise performance and longevity, you should use the largest possible pack you can package. The higher % of mass of your vehicle is active material (cells OR motor) the higher system efficiency will be in general.

On my latest skate prototype, over 75% of the total weight is in cells or motors. Next one will be even higher. On my bike the proportion is about 60%.

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Ohbse said:

Jonathan1981 said:

it would be awesome to find a cheap mold-able material the could do that. I was thinking something like mixing aluminum powder into a soft two part epoxy and molding a thin layer around each cell?..... thoughts, links etc???? just trying to think of a cost effective DIY cooling solution for such a large pack..

Click to expand...

Wax. http://www.allcelltech.com/index.php/technology/pcc-thermal-management

Phase change temperature can be varied with composition to target the sweet spot for optimal cell performance/lifespan.

The downsides are primarily mass and complexity. In many circumstances you would be better off taking the mass dedicated to the cell cooling and adding additional active material in the form of more cells. More of the same cell with the same power demands lowers per cell heating OR more cells allows for a more 'power' focused chemistry while hitting your energy requirements, again reducing per cell heating due to lower IR.

Essentially to maximise performance and longevity, you should use the largest possible pack you can package. The higher % of mass of your vehicle is active material (cells OR motor) the higher system efficiency will be in general.

On my latest skate prototype, over 75% of the total weight is in cells or motors. Next one will be even higher. On my bike the proportion is about 60%.

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Jonathan1981 said:

yeah, my pack is big so there there will definitely be wiggle room. I'll probably just put a temp sensor in there and turn down the draw if anything spikes....

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SamRich said:

If you use a cycle analyst it can automatically reduce current based on battery temp, motor temp and SOC

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Jonathan1981 said:

anyone have experience with these?

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Ohbse said:

Jonathan1981 said:

anyone have experience with these?

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Good, but not quite as good as the 30q

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Jonathan1981 said:

So has anyone experimented with a liquid tight battery enclosure/container and putting dielectric fluid in it, perhaps with a small pump to keep things circulating? Seems like a no brainer.

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fechter said:

Jonathan1981 said:

So has anyone experimented with a liquid tight battery enclosure/container and putting dielectric fluid in it, perhaps with a small pump to keep things circulating? Seems like a no brainer.

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This has been discussed in some other topics. Distilled water was tested and won't work because it doesn't stay distilled and starts to corrode everything. Most oil-like liquids are flammable. Non-conductive and non-flammable liquids made for this kind of application are very expensive. Phase change material may be something to look at.

Others have used potting to completely fill the space between the cells and the enclosure. Potting conducts heat better than foam or dead air space. The outside of the enclosure will typically get plenty of air flow and stay near ambient.

Another approach is to build the pack with enough space between cells to allow air flow and put a small fan inside the enclosure to circulate it. The enclosure can be sealed to keep water out.

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