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Fuse wire index
I am starting this thread as a place to park info I find about possible fuse wire I may use in the future. I am hopeful that it may prove useful to others. please post fuse wire you have used in the past, and the results you achieved.

CAT5 wire:
A friend recently suggested I should look at CAT5 wire as an option. CAT5 cable is used for Ethernet grids in a home and uses wire that has been used in the past for "land line" telephones. CAT5 cable typically contains four twisted pairs of 24AWG solid copper wire, 0.50mm diameter, 0.020-inch. This means one foot of CAT5 contains eight feet of 24AWG solid copper wire.

edit: some CAT5 cable uses the slightly smaller awg26, 2A continuous, 4A temp peak, blow at 20A...0.40mm dia-0.016 inch

A quick Google shows 3.5A continuous, and 5A temporary peak for a single 24AWG conductor. I am looking at using two wires per cell as a fuse, so dual-24AWG should handle 7A continuous and 10A peak (to reduce voltage sag and wire-heat). If I am drawing 1A per cell under normal loads, and my paralleled groups are at least 10P (or larger), I suspect a cell with a cascading internal short would flow 20A+ to blow the fuse(es), and that would be only 2A per cell in a 10P group...and a larger P-group would be even safer if using dual-24AWG.

edit: ajw22 below lists the "blow" current at 29A for a single solid copper awg24 (58A for double fuses)

By this I mean that an individual cell fuse-set would blow at a P-group per-cell amp-draw that would not damage the remaining cells. More cells in the P-group would result in a lower amp-draw per cell during an "incident" from an internally shorting cell.

I am trying to get away from spot-welding onto the NEGATIVE end as much as possible. Solder may require a two-second contact, but the temps are roughly only 360F. A spot-weld only takes 1/4 second (250-milliseconds?), but nickel requires roughly 2600F to melt into a solid contact. In the pic below, wire tips have been flattened by a hammer and pre-tinned before connection to cell...

(many spot-welding manuals specify to avoid welding onto the center of the negative end. Internal construction shows that the center is where the jelly roll is connected to the shell during construction. Added heat in that spot may loosen that internal connection)

[Image: file.php?id=253561]
Note that its not what 1 cell can flow but what all other dump into that cell!! And if you have 100 cells in a pack we talk about 2000A....

And dont over think the fuse wire. Its generally best to get proper fuse wire. They will last longer. All other wires that you potentially get from shielded places will deteriorate in air depending on how they are coated. A roll of fuse wire do not cost much at all and then you get the correct size instead of doing double the work. Work is money in the end as well Wink
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That 3.5A continuous / 5A peak current for copper AWG24 is what it can comfortably carry without heating up much. At least not enough to degrade the insulator. It will only break at around 29+Amps! So I think you'll want to use much thinner wire, if you're using 18650s. I think most people use something between AWG30~35.
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Thanks for the info, I appreciate the tips.
Further to daromers comments, proper fuse wire is:
- tinned so it corrodes less vs bare copper.
- designed to melt at a lower temp vs copper wire, this leads to more controlled "xxx current = blown" results.
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I don't have the reference handy (insert here later), but fuse wire is very similar in composition to lead-free solder. For lower currents, the fuse wire is preferred, but...when a fuse-wire blows, it can spray conductive splatter onto all of the nearly components.

This conductive splatter is typically not an issue due to the small volume. However, it is a consideration. If you are building a small battery that must provide higher currents (a portable suitcase battery/inverter, perhaps?), then using a glass-encased fuse, or copper wire might be preferred (copper would have 1/4th the volume of splatter compared to a similarly-rated common fuse wire). Just a thought...
(06-10-2019, 02:00 PM)spinningmagnets Wrote: ...............when a fuse-wire blows, it can spray conductive splatter onto all of the nearly components.............

After watching several fuse wire tests and at what amperage they glow, and then interrupt with melting slag and spatter, I will prefer to encase this action in a glass enclosure for any of my packs. Glowing wire is meant for hairdryers and toasters not powerwalls.

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