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are fuses a good idea?
#11
well i did plan a really good design where the fuses would be protected, as for the correct fuse it could be reaally difficult to fit the correct one as im sure cells characteristics would change a bit i may just fit fuses and see how it runs, i have two motors on the way, i do intend just using the same cells recycled ones only my best ones, will definatly find out what their discharge current is and use that, didnt think about that so thanks, i will use these fuses or simular if i can get a speck sheet, and lay out a small pcb it will be reayy well protected

https://www.aliexpress.com/item/33012231...b201603_52


yes i am going to use a bms, a lot of skateboards just use new cells without a bms, think it would be ok for a while....

i did concider no bms, just thought about balancing it every couple of charges, but that cheap chinese bluetooth one is pretty good
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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#12
As Said i would not use fuses...
I would either Charge with RC Chargere
With balance function or CC cv with bms

Just make sure having Main fuse.

That way you have a solid battery that Will work
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#13
(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.

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.

This, 100%

(11-03-2019, 07:37 PM)OffGridInTheCity Wrote:
(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.

Its extremely rare to find cell level fusing on packs for applications like this "high performance batteries"... ebikes, skateboards, RC, hoverboard, powertools...  

The packs are not large enough... meaning that your current requirements are large enough that you cant reliably put a small enough fuse for it to really matter.

The fuse would be sized such that even if the cell shorted out, it might not blow with the inrush from the other cells.

All you are doing at this stage is adding a point of increases resistance, heat, voltage drop, fragility in construction.

I do however treat and maintain my packs very similar to how people would in the RC world.  Balancing charger, with no BMS, and diligent monitoring of general health.  Noting capacity, balance, and internal resistance... just like many do in RC.
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#14
(11-03-2019, 07:59 PM)daromer Wrote: 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.
This recap makes perfect sense - thank you!
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