I a looking for a schematic of a circuit to built an adjustable current source capable of delivering up to 40A.

I am building a battery with 18650 cells. These cells will be individually fused using a cell level fusing method like this:

The idea is to connect the battery to the main bus with a wire that can carry the current under normal load. In case of a short of the cell, the other cells in parallel will discharge into the short and blow the fuse. The faulty cell will be isolated.

The tricky point is to choose the correct fuse wire gauge to ensure :

• that it will not heat up too much under normal load
• that it will blow when the other cells discharge into a short.

I have looked at current tables, but I'd like to test it for real. I would need a circuit that generate an adjustable current up to 40A. I would increase the current from normal operation to fuse blow, to check the behavior of difference wire gauges.

Do you know of a circuit I could use to get this functionality? Maybe using a strong LiPo battery with some kind of current limiter?

• Is something like this out of budget?uk.rs-online.com/web/p/products/1752528 – Jack B Oct 11 at 10:24
• Come on, where did you get such idea, to fuse a battery that will blow and the remaing would take over. Most likelly it'll all blow up. – Marko Buršič Oct 11 at 11:00
• I'm upvoting because it's a good question, not because it's a good idea. I'm hoping that someone will compose an answer explaining why. – pipe Oct 11 at 11:10
• Hi Marko, maybe I had this idea because Tesla is using it in all its cars :-). See here : endless-sphere.com/forums/viewtopic.php?t=47417 – Akira Doe Oct 11 at 11:16
• okey dokey, I'm upvoting too. The Tesla guys sure made something that has to be discussed. – Marko Buršič Oct 11 at 11:51

The fuse is a device that melts due to heat loss $$\I^2 t\$$. Thinner wire will have larger resistance and will blow faster, meanhile thicker wire will blow slower at higher currents. There is also a second parameter in those fuses: the reaction time. This time can be controlled by adding a heat sink to the wire. Perhaps you have noticed that some fuses have sand inside, well in your case it will just be convectionally cooled by air.