Electricians view required on fuses

[testdruif]

Hey there techies!!

I was wondering if an electrician could shed some light on the below:

The fuse: uk.rs-online.com/web/p/resettable-wire-ended-fuses/5176916/

Can I/we assume that this fuse works by heating up when there is too much current going though it and thus in a closed environment such as a boxmod (aluminium) would cause melting of wires (and maybe the battery next to it) if it takes to long to open up the box and get the battery out?

A) In a mod where space is limited, could/would you recommend another type of fuse that is resettable or easily replaceable?
B) In a mod where the board itself has an input limit of 7 amps, would a fuse matter?

[Super-Shiny]

Cheers testdruif

[Super-Shiny]

Also posted this over at Breaktru: breaktru.com/smf/index.php/topic,1042.0.html

Might get some more imput

Damm link never work

[Super-Shiny]

testdruif some info so far:

"The only reason for the 2 fuses in parallel, instead of 1, is that it cuts the resistance in half so the parallel fuses minimally affects the resistance. "

"3 amp fuses are used in tandem to lower resistance and get 6 amps nominal. Trip current is more like 10a"

Taken from here: www.e-cigarette-forum.com/forum/battery-mods/446513-dna-20-parts.html

If any of that helps i don't know

[smarties]

Is this what you are looking at (sorry haven't got a clue how to do links)



en.wikipedia.org/wiki/Resettable_fuse

7 amps is a lot of current to have in your hand

[a1laserboy]

According to the documentation LINK the units are recommended for use in Lithium cells and battery packs, and rechargeable battery packs and chargers. From that I would say that heat within the unit won't be a problem. If wires could warm up from current draw through them, then the wires are not big enough to take the load. Also, if you are worried about hot wires generally because of the environment, you can get higher temperature rated wire then regular pvc insulated wire.

Does the board need to have an external fuse? if not, then there is no need for it. If you want to be safe, then make sure you use wire that is big enough to take the maximum current the battery is able to output from the battery to the fuse. Does the board not have it's own over current protection onboard?

The unit you have asked about has a fairly slow trip time - 1.7 seconds. Also, it is a 4A fuse, but saying that, they also state that the device may withstand higher interrupt current at lower voltages. The 6.9A bit is the maximum trip current that is safe, I assume that beyond that, the unit will be irreparably damaged.

[a1laserboy]

Jan 6, 2014 19:45:43 GMT smarties said:

7 amps is a lot of current to have in your hand

Some 18650 batteries can output a maximum 30A continuous which is reachable by using a 0.14 ohm coil on a freshly charged battery at 4.2V. 7A would be a 0.6 ohm coil which is becoming a normal resistance for some.

[Greg]

Jan 6, 2014 19:44:39 GMT Super-Shiny said:

testdruif some info so far:

"The only reason for the 2 fuses in parallel, instead of 1, is that it cuts the resistance in half so the parallel fuses minimally affects the resistance. "

"3 amp fuses are used in tandem to lower resistance and get 6 amps nominal. Trip current is more like 10a"

Taken from here: www.e-cigarette-forum.com/forum/battery-mods/446513-dna-20-parts.html

If any of that helps i don't know

That's incorrect, if you have a 3amp fuse and 3 amps flows through it then it will blow in a finite time given in the data sheet. If you put two two 3 amp fuses in parallel then assuming each fuse has the same resistance then if 3 amps flows through each fuse they will both blow in the finite time. It won't take 10 amps to blow the fuses. If 10 amps were to flow, 5 amps through each fuse then they would blow / melt quicker than the finite time in the data sheet.

[Super-Shiny]

Jan 6, 2014 20:09:36 GMT Greg said:

Jan 6, 2014 19:44:39 GMT Super-Shiny said:

testdruif some info so far:

"The only reason for the 2 fuses in parallel, instead of 1, is that it cuts the resistance in half so the parallel fuses minimally affects the resistance. "

"3 amp fuses are used in tandem to lower resistance and get 6 amps nominal. Trip current is more like 10a"

Taken from here: www.e-cigarette-forum.com/forum/battery-mods/446513-dna-20-parts.html

If any of that helps i don't know

That's incorrect, if you have a 3amp fuse and 3 amps flows through it then it will blow in a finite time given in the data sheet. If you put two two 3 amp fuses in parallel then assuming each fuse has the same resistance then if 3 amps flows through each fuse they will both blow in the finite time. It won't take 10 amps to blow the fuses. If 10 amps were to flow, 5 amps through each fuse then they would blow / melt quicker than the finite time in the data sheet.

Can you recommend a fuse then that will work well with 2 x 18650 batteries and the requirements of the DNA20D board?