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are fuses a good idea?
#1
hello
currwntly planning a 12s7p battery using 18650s for a skateboard, was thinking of using 2a fuses on each cell or do i just parralel each cell together, all my cells have been tested and no heaters present, and i intend using the same make of cells.
thanks
Battery is li iron using 18650s, 14s, 0p, and growing cell so far 300, untesteded.
Bms is a diy open source by stuartpittaway.
No solar yet, 
Building wind turbine, 48v im after a 48v motor if anybody has one for sale.
Cells 2000 to 2500ma.
Cells 1500 to 2000ma.
Cells 1000 to 1500ma.
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#2
Always use a fuse in my opinion a "good"cell can go bad and kill your pack
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#3
The strong recommendation is to fuse each 18650 cell in the pack. You want to fuse to blow as the rest of the pack dumps current thru the shorted out cell so you don't burn up the overall pack. The fuse must be large enough to draw the max current per cell but also small enough for 'the pack' to burn thru it if one of the cells shorts. Typically this is 2a to 10a - much discussion on the exact fuse size Smile
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#4
For skateboard no fusing. That pack need to be rigid and support high current.

I would never put cell level fuses on such a device.

Just spotweld the pack together and make sure it can take a beating. Charge it with RC charger or with proper CC CV with a good BMS that handle the balancing and if something critical happen.
If you use RC charger a BMS is really not needed unless you are keen to protect it from overdischarge.

And for people now guessing and such this is how you do it in the industry.

Whats important is that you have cells that can cope with the stress and load. No fuse can save you from a poor design from the start.
Crimp Daddy likes this post
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#5
Make sure to use a good BMS to monitor charging and keep things balanced. If anything else, it should at least give you some stats of the performance of each series sub-pack so you know early if a problem is there.
However, on discharge, you'll know when there's an issue as your range will start dropping off. Use GPS tracking to monitor your distance traveled.
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#6
(11-03-2019, 06:31 PM)daromer Wrote: For skateboard no fusing.  That pack need to be rigid and support high current.

I would never put cell level fuses on such a device.

Interesting - I thought fusing was always recommended.   Can you explain a bit why fusing is not recommenced in this case?   What's the thought process or guideline to go fuse or non-fuse.
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#7
Have you ever seen a commercial pack have per-cell-level fuses?. Its not answer to your question but the the cell level fuses was started by us due to coupling 100s  of cells in parallel and in an area for instance a shed or workshop. This along with what Tesla did to their packs. Their intention on other hand was most likely reason on swapping out the CID against a cell level fuse. On their packs they have a different system so cant be fully compared but in some areas they can

Doing that you wanted an extra level of security. That security extra added is of course not bad but you need to weight in pros and cons.
Those fuses are fragile and do not make up for any rigidity. They also only work for low current applications.

Ebike packs and small other packs i would never use cell level fuses due to this. I want rigid packs. In my world a fuse wire or other can create more issues than they solve on such a pack.

Cell level fuses in my world exist on packs for powerwalls where you have this criteria fulfilled
* They are not moving around
* You have huge amount off cells in parallel like 80p or more
* Low current
* Random built packs
* Tested with low cost testers and where you might not use ir as a factor
* 2nd hand cells
* mixed age and abuse
* Permanently mounted

Ebikes for me are
* High current packs
* They are moving around and need to be rigid
* should be built with considereation of ir and type of cells. May not always be the case though...
* lower number of cells
* Packs arent permanently mounted. (I dont call an bike or skateboard pemanent)

You can mix this a bit as you want but this is my stand in the point. Security and safety are good but you need to weight in how and why you do it against risks not doing it.

Same goes with BMS... You dont need a BMS on a pack you run the RC-Style = Charged with balancing charger.  In worst case you just drain it way beyound the max... Of course you need to make sure you cant run to high current but that can be done with proper fusing.

I have no BMS on any of my RC gear. I dont have it on most of my Ebike gear either that is swap-in out.

BUT
I have it on all ebikes charged with CC-CV or statically built packs.
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#8
Unless the fuses/cell can be solidly affixed so there is no movement, putting a fuse on something that experienced a LOT of vibrations will cause it to break prematurely.

This is also why it is suggested to have a bms that can actually report the info to you somehow instead of letting it just go on its own. Bluetooth grade bms instead of the cheaper chinesium one that one is blind to knowing what it's doing.

Or this....

(11-03-2019, 07:59 PM)daromer Wrote: Same goes with BMS... You dont need a BMS on a pack you run the RC-Style = Charged with balancing charger. In worst case you just drain it way beyound the max... Of course you need to make sure you cant run to high current but that can be done with proper fusing.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#9
Korishan but the BMS reporting doesnt give you extra safety on an ebike type pack... It gives you an indication if you hurt the pack though..
Need to distinguish between those areas on what you get and why.

A BMS should exist on every device you need it on. But its no magic thing. Reporting wont do anything good either unless you constantly check it with your eyes.... Most people never check it out.
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#10
(11-03-2019, 08:04 PM)daromer Wrote: Korishan but the BMS reporting doesnt give you extra safety on an ebike type pack... It gives you an indication if you hurt the pack though..
Need to distinguish between those areas on what you get and why.

A BMS should exist on every device you need it on. But its no magic thing. Reporting wont do anything good either unless you constantly check it with your eyes.... Most people never check it out.

Right, I was stating the reporting back so you can see visually if there is drift in a pack. But this you can see with an external RC charger if it has those abilities as well. I was not mentioning the BMS as a "safety" device, but as a "monitoring" device on the cell level, not just string-pack level.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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