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Are there any fuses that i can use to protect a 18650 battery pack. I have a 2s8p which is rated at 12.6v 21.6A. one battery is rated at 4.2v at 2700mAh.

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    \$\begingroup\$ All of your numbers indicate some kind of Lithium chemistry. Based on your question and comments below, you need to stop what you're doing right now before you hurt yourself or burn your house down. These types of batteries are dangerous even to people that know what they're doing. \$\endgroup\$ – Matt Young May 2 '16 at 16:57
  • \$\begingroup\$ Do you really expect anyone to answer "no" to this yes or no question? Perhaps you should ask for what you want to know. \$\endgroup\$ – Scott Seidman May 2 '16 at 18:48
  • \$\begingroup\$ Not really a yes or no. And yea i do know what am doing. I have a pack that i use to charge my iphone and all works well. I balance charge the pack with my rc charger. I just wanted to add some safety with a fuse. So that the fuses blows when or if there a short circuit by any chance. \$\endgroup\$ – George May 2 '16 at 19:03
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    \$\begingroup\$ You should read electronics.stackexchange.com/q/230155/11684 -- there are any number of ways to screw up with lithium batteries, and over-current is only one of them. \$\endgroup\$ – Scott Seidman May 2 '16 at 20:33
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Sure, you can fuse the output of the pack. You'll want to dig into the datasheets for those batteries and see if that's peak current (likely) or continuous safe current. Design your fuse to trip accordingly.

If you need something resettable (can be reused upon removal of the fault condition), check out PTCs. PTC = Positive Temperature Coefficient. Essentially, it's a resistor that is low resistance under normal operating conditions, but as it heats up due to an over-current situation, resistance increases (hence positive temp coefficient) and cuts off the supply. Upon cooling it will become low-resistance again.

Here's the DigiKey link to PTCs so you can start selecting one for your specs.

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  • \$\begingroup\$ Does a diode be a good way to go. I know it allows current flown on one direction. \$\endgroup\$ – George May 2 '16 at 16:50
  • \$\begingroup\$ And those fuses, i am planing to connecting on each cell. Would that be better ? \$\endgroup\$ – George May 2 '16 at 16:50
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    \$\begingroup\$ @George I share Matt Young's concern about working with Lithium if you do not know what you're doing. It is hard to say what is "better" since your question is so vague. And diodes offer no protection save from reversed polarity connections, which you should make only one way to correct it anyway. \$\endgroup\$ – Joel Wigton May 2 '16 at 17:08
  • \$\begingroup\$ Yea i thought so diodes would just block flow of current. Fuses would be the best for what i need. \$\endgroup\$ – George May 2 '16 at 19:04
  • \$\begingroup\$ Yea I've seen several guys on YouTube using those fuses. But when a short circuit happens shouldn't the circuit be left open at all times ? the PTC would close it when the temp subsides and that would again cause a short. Considering the amp rating of one cell i was thinking of getting a PTC rated at 16v 3A here \$\endgroup\$ – George May 3 '16 at 5:08

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