OllinBoards - Cell Level Fuse

Continuing the discussion from Balancing/Equilibrium Board vs BMS. Whats the difference?:

This is how we are currently assembling our packs. This is just a basic mockup, we also apply a strip of fish paper over the brass strips before sealing the packs in heat-shrink for added electrical insulation. Nickel tabs are spot welded to the li-ion cells and the fuse wires are soldered onto the the tabs allowing for a serviceable connection. I’ll post more photos with greater detail while we complete our latest build.

Cell level fusing is probably the best way to insure a failing cell does not take out an entire parallel pack of cells throughout the lifetime of your pack. This allows us to string together huge links of paralleled cells and build battery systems with incredible range without worrying if a faulty cell will ruin someones day a few years down the road.

All together the packs measure under 22mm after heat-shrink is applied.

If anyone is interested in these feel free to send us a message.

.stl file on thingiverse: http://www.thingiverse.com/thing:1712459

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Beautiful, are those custom cell holders?

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Gorgeous! :slight_smile:

Yes they are, I still need to make a few changes to speed up the print time but this is the final design for the beta builds.

Will these Tesla style packs last with all the vibrations of esk8ing?

I have to handed it to you :wink:
that is a clever solution. you are really a resourceful individual Mr. Clark.
Kudos to you :thumbsup: :thumbsup: :thumbsup:

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Will these Tesla style packs last with all the vibrations of esk8ing?

They handle vibration very well, probably much better than nickel strips since the wire helps isolate any movement from tearing the tabs from the cells.

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The wires seem awful thin, are they able to carry higher currents?

The wires are sized according to the cells capability and internal resistance. Length and gauge play an important role here, for 20 amp cells you want a fuse that blows at 22 to 25 amps. If a cell begins to fail the inrush from the other cells in the pack quickly blow the fuse before any damage is done.

You still want to run a fuse on your main terminals in the case of a short circuit in your electrical system.

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Does the fuse need to handle (Max Continuous A ) or Max A of the Cell …

example: (20A C vs 30A)

Awesome idea and great design !
Do you mind sharing telling what material the wire is made of ?
And how it will be connected to the cell and the strips ?

Let me know when you find an 18650 cell that can do 30 amps continuous. :slight_smile: If you size the fuse too high it defeats the purpose of the fuse. If you are pulling 6000 watts constant from a 12s6p pack then you should probably switch to prismatic lipo’s. High discharge 18650’s shouldn’t really be driven too close to their max constant rating. This chart gives you an ide of what happens and the level of voltage sag you can see at different loads. With voltage sag you will also see massive heat buildup.

Do you mind sharing telling what material the wire is made of ?
And how it will be connected to the cell and the strips ?

The fuse wire is nickel plated copper and they are soldered to the underside of the buss bar. Not shown in the photo is the welded nickel tabs, after they have been spot welded the cell fuse is soldered to the tabs.

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I meant a cell like the LG HG2 is good for 20A cont. or 30 A peak .

Thanks @chaka

Maybe you could apply this to largers cells like the A123 systems ANR26650M1-B 2500mAh which can do up to 70A.

And just one final question if you don’t mind.
Did you do tests on when these nickel plated copper wires break at a certain current and did you put that into a formula ?

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The fuses are essentially “slow blow”, meaning small peaks will not cause the fuse to break circuit. Even a direct short on the mains takes a bit of time before the fuses start popping off. Look at that chart and you will see that individually the cells drop below 3.3v right away at 20 amps. Best to build a bigger pack or switch to A123’s and higher gauge fuses if you need that much power.

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I really don’t know how many Amps my Single pulls, i just read about people here saying sometimes they are pulling like 60A going up hill ?

The cell fuse idea in itself is great and the implementation that you have done here is superb in its simplicity.

But @chaka what implementation do you have for knowing when a fuse have blown once the pack is sealed ?

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I think this is really important for DIY crowd to get these packs designed well.

What about OBC offering some kind of affiliate program that certifies reliable and safe pack design?

Maybe call it high performance standards or something.

Wouldn’t need to be expensive but would give buyers more confidence if they knew their expensive pack were going to last more 6 months to 1 year because it was reviewed by an respected designer.

Could also increase the expertise out there to use reclaimed batteries from laptops to make affordable large packs.

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That is one of the great aspects of these styles of pack. A failed cell doesn’t cripple your ride, you can still make it home if something goes wrong. Clear heat-shrink allows for easy inspection if you notice a loss of range or an unbalanced pack.

@CSN Tesla has already set the standard with this type of assembly. Unless you think Tesla Motors isn’t well respected? :wink:

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