Fuseable Battery Bar Cell Connection Designs & Sources

[deVries]

It came to my attention that even a123 26650 cells can suffer an internal short inside a battery pack. I know of someone that is building EV-car size batteries using these cells and is "fusing" each and every cell with the battery bar connected between every cell that is also designed "to melt" in an internal short or crash/accident short too. Given that one cell shorted (with a wire too) can burn/melt flesh to the bone and destroy a whole battery pack of cells I would be interested using a battery bar connection that would also be a fuse. I've seen too many pics on ES of charred fingers due to human error handling batteries too.

I've seen fusable battery bar connections similar to this shape:

But I've found no thread topic that specifically addresses fuseable battery bars, or how to design these.

Frodus made a most important point about what needs to be considered...

"The difficult thing is to have that link fuse under high current, but not to add too much resistance to the pack because of the small current path."

I'm guessing for a123 26650 cells a fuse bar between 100-150 amps per cell would be high enough AND not be too low to cause too much resistance in about a 150 cell battery.

Does anyone know how to design for this and would be willing to contribute this information to our group knowledge base here at ES? Where is this knowledge stored for reference online?

Does anyone know what the best material to use is? Copper may be too high a melting point? Nickel? Aluminum? A plated material?

Thanks!!!

 

[John in CR]

If I get into a crash bad enough to get to my batteries and create a pack destroying short, then a lost pack will be the least of my worries. Instead of fuseable links one should spend than time and money on proper mirrors, brakes, lights, brake lights, and turn signals. The bottom line is that there are typically lots of unaddressed safety concerns that should come first.

John

 

[TylerDurden]

Mr. Mik installed fuses into his Vectux (former Vectrix). Search for his very detailed reports regarding a 'manual bms'.

ps. maybe you could use this image instead of the huge one:

 

[deVries]

If I get into a crash bad enough to get to my batteries and create a pack destroying short, then a lost pack will be the least of my worries. Instead of fuseable links one should spend than time and money on proper mirrors, brakes, lights, brake lights, and turn signals. The bottom line is that there are typically lots of unaddressed safety concerns that should come first.

I changed my topic heading from: Crash/Short Safety Concern? Fuseable Battery Bar Connections

To: Fuseable Battery Bar Cell Connection Designs & Sources

My main concern besides a "crash short" is:

Just handling, installing, replacing cells, wiring battery packs can be dangerous for a possible accidental short, so that's why I'm interested in this fuseable battery bar idea... it will protect each cell from every other cell in the pack. It should help to greatly lower the risk of a major battery pack failure and heat/fire destruction and possibly severe injury.

 

[monster]

i could see it usefull for cars but ebike packs are generally small and accessable enough to run away from if the worst happens. i think the tesla has fusable 18650 cells though. in a bike crash you would be thrown from the bike. in a car crash you might be trapped in the car so its more important

 

[deVries]

i could see it usefull for cars but ebike packs are generally small and accessable enough to run away from if the worst happens. i think the tesla has fusable 18650 cells though. in a bike crash you would be thrown from the bike. in a car crash you might be trapped in the car so its more important

The point I am trying to make is that a crash is but one concern among many other equally important concerns for this battery design idea, whether the crash is in an auto, motorcycle, or bicycle. This design idea is useful for a number of other reasons. Mainly, human error, accidents (assembling & maintaining battery), and the fact a battery cell can self-short internally on rare occasions. DIY battery building is very time consuming, complicated, costly, and prone to accidental damage during assembly or maintenance. This Fuseable Battery Bar Connection is -a passive- design idea. Cells have to be connected to create the battery, so, simply, design the fuse in the battery bar connection too.

The purpose of this thread is to offer the design information about how to do this. It is meant to be a technical reference thread for those that want to make their own battery connection bars with a built-in fuse. Also, if you are a battery designer or manufacturer or know a source for this type of battery bar, then please list any Fuseable Battery Bars you know of or what you or your company offers.

 

[BMI]

Also, if you are a battery designer or manufacturer or know a source for this type of battery bar, then please list any Fuseable Battery Bars you know of or what you or your company offers.

The fuseable link in the images above which I originally posted (in reply to a question from AndyH in another thread)is from a BMI HPS factory battery pack. If anyone wants these links just ask and I can certainly order them from the factory.

 

[deVries]

The fuseable link in the images above which I originally posted (in reply to a question from AndyH in another thread)is from a BMI HPS factory battery pack. If anyone wants these links just ask and I can certainly order them from the factory.

Thanks for posting that pic, which is linked/posted from that thread to this topic.

Can you post the dimensions and material used for this fuseable battery bar? What is the cost for 50-100 of these in the USA, and who can order or stock these in the USA? Thanks!

=====================================================================

Here are some more design issues to consider for a fuseable battery bar:

Thats what you have to figure out... I've got an EE background, and it takes a bit of figuring out... conductivity of the material you're using... how much current can safely pass without fusing, how much current needs to pass before it fuses.... so continuous amps, max amps need to be calculated from the datasheets of the A123 batteries you're using. You are designing a fuse that you want to melt if too much current goes through it, but when normal current goes through it, you don't want the path to limit the current or heat up the battery pack. If all of your links get hot... and the batteries heat up, thats not a good thing either.

Its not hard, but its not very intuitive unless you have a little background in power. Its not something you're going to figure out in 30 minutes.

 

[BMI]

I will order in some of the fuseable links to keep in stock along with some other bits'n'pieces which the electric car guys find hard to find (such as orange flexible conduit for high voltage motor/controller wiring).

150A fuseable links might be a bit high a rating for many e-bikes so I will see if they are available in other ratings as well.

 

[Jeff]

I'm one of the folks fusing the A123 cells in massive parallel configuration.

I am using 10 mil nickel sheet that has been die cut for each cell connection. The link is scaled to fuse at 75A in this application.
Because of the large parallel cell count, the load applied to each cell would not exceed 20A. The fuse rating overage will accommodate thermal and mechanical influences, and still open in the event of a catastrophic fault.
Additionally, you'll need to ensure you have a gas release path. Because the application I use is so dense, there are slots cut in FR4 panels between the folded layers.

http://www.evbones.com/a123battery.pdf
Sorry about the large file, it was exported to PDF

Although this was an A123 M1 cell build, it still applies to any application where cells are parallel connected.

Regards, Jeff