# TESLA style cell level Fuses



## BobK (Mar 6, 2009)

Thanks for the video jehu

It surprises me that more people are not trying to do this.

The fuses look like a good idea to me.

Im really interested in how this works out. Keep the updates coming!


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## dougingraham (Jul 26, 2011)

Jehu,

Your test in the video was different than what you are doing on the real pack. You should probably try it again with the actual pack setup. With the fuse wire attached to the brass bus bar it will take longer to heat up and it will handle more current because of that. I would think anything between 8 and 10 amps would be ok.

Looking forward to more Electric Samba Adventures!


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## Karter2 (Nov 17, 2011)

Since this is primarily intended as protection for a shorted cell, i would not think the actual maximum current limit is too critical.
10,15,25 amps would be minor compared to the current drawn by a shorted cell.
On a separate point,.. are you comfortable with the potential risk of internal cell damage resulting from soldering directly onto the can ?
The heat could make a significant difference to the cell capacity, performance, and cycle life.


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## dougingraham (Jul 26, 2011)

Karter2 said:


> Since this is primarily intended as protection for a shorted cell, i would not think the actual maximum current limit is too critical.
> 10,15,25 amps would be minor compared to the current drawn by a shorted cell.
> On a separate point,.. are you comfortable with the potential risk of internal cell damage resulting from soldering directly onto the can ?
> The heat could make a significant difference to the cell capacity, performance, and cycle life.


Certainly a good solid short would be able to pull significant current but the problem you want to avoid is the one where the cell sort of kind of becomes a resistor and sits there draining the rest of that module all the time. For that situation you want to to blow at a level not too far above the peak current requirement.

I have heard the risk argument about soldering to cells since I started soldering to NiCds in the early 70's. Yes, you can damage the seals or worse if you do a poor job of it but it is also fairly easy to not cause any issues. The fuse wire to the cap is a piece of cake compared to soldering a heavier wire.


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## Karter2 (Nov 17, 2011)

dougingraham said:


> the problem you want to avoid is the one where the cell sort of kind of becomes a resistor and sits there draining the rest of that module all the time. For that situation you want to to blow at a level not too far above the peak current requirement.


 Presumeably there is no way of knowing how much "drain" a weak cell would put on a string of parallel cells.
..it could be 10, or more amps, but equally it could be 1 amp or less,.
So a fuse is no guarantee of preventing that type of failure.
Isnt that what a BMS is intended to do ?



dougingraham said:


> I have heard the risk argument about soldering to cells since I started soldering to NiCds in the early 70's. Yes, you can damage the seals or worse if you do a poor job of it but it is also fairly easy to not cause any issues. The fuse wire to the cap is a piece of cake compared to soldering a heavier wire.


 Even the finest wire solder joint still requires the can surface to be "tinned" for the solder to bond to the metal of the can.
Some of these 18650's have been shown to be very susceptible to that heat transfer . This is one of the reasons that most commercial pack construction ( power tools, lap tops, Tesla, etc) do not use soldered contacts.
Spot welding and ultrasonic welding are the industry standards for 18650 packs.
Battery spot welders for home use are as cheap as a good solder station these days. ( probable cost less than all the solder needed for those thousands of cells ! )


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## onegreenev (May 18, 2012)

A weak cell can be carried by the other parallel cells but a shorted one needs to be removed from the string to prevent a cascade disaster. So that 6 to 12 amp fuse wire would be fine. The cells connected to a buss bar is fine too. The power is pulled off the buss bar. I noticed that tesla uses a large plate over the cells with those holes for connecting the fuse wire. The metal is set above the cells. 

I was thinking of using some way to secure the buss bars so they don't move around in the event of a sudden stop like you'd find hitting a tree or something. 

When Jack put his A123 cells in plastic they could not handle that heat generated by the resin curing. They shorted and blew apart. I agree that the excess heat could damage some of the cells and that spot welding the wire would be better. 

Jehu wants to continue using solder. I tried soldering some cells in the past and had one hell of a time getting solder to stick well. Im more concerned about the solder just coming off the end of the cell. 

Pete


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## sunworksco (Sep 8, 2008)

Under $300.00 delivered.


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## sunworksco (Sep 8, 2008)

Perhaps the plastic battery framework could be milled to allow the copper plates to be countersunk and epoxied into place to keep them in position during an accident.


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## Karter2 (Nov 17, 2011)

> Jehu wants to continue using solder. I tried soldering some cells in the past and had one hell of a time getting solder to stick well. Im more concerned about the solder just coming off the end of the cell


 I can understand that, its a very easy, (reversible) method..but..
Faced with thousands, i would look for the quickest , easiest method, which is where a spot welder has an advantage.
.i have only ever tried a few cells at a time, and even with the correct solder, that was a chore.
Also , it seems to me that if you have gone through the pain of testing, selecting, matching etc,..cells for a large pack, the last thing you want is to risk affecting the performance of a few of them by the very process of pack assembly. ( it going to be really hard to find individual weak cells in large pack like this )
I guess you could retest all the cells for capacity, IR, etc, after tinning the ends, and leaving only the quick touch of solder to fix the wire fuses to minimize the risk of faults.


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## lithiumlogic (Aug 24, 2011)

I'm interested in those frames - are there any that offer greater cell spacing? Cell spacing is one of the ingredients Tesla use to achieve safety to prevent fires propagating. In climates like we have here in the UK, forced air cooling would probably be just as good as liquid.

The trouble is, if you go for wider spacing, you're then going to end up with a pack that will be lighter than an LFP of the same size, but which holds no more power cubic metre for cubic metre. And generally, volume, not weight, is the limiting factor for vehicles.

In an electric motor glider, for example, you have a lot of space in the wings and weight is more the issue, so this approach could hold promise.


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## lithiumlogic (Aug 24, 2011)

Jehu, I do think your bus will go a lot further when you get the windows in. Is there more you can do to improve the aerodynamics? I saw your Christmas project summary video, showing the metalwork, with the vehicle upended.

You could install a flat panel to cover the bottom, it should improve your highway miles quite a bit, the underside of that bus looks very open as it is! This would have the advantage of not significantly altering the appearance.

Does it still have that roof rack? That must cost a few miles too.


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## aeroscott (Jan 5, 2008)

are those cell tops, caps on top of the cells?


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