Can fuses be soldered in-line?

[Mr. Mik]

I am wondering if I could solder glass-tube type fuses straight to cables in order to reduce cost, space requirements and resistance in the circuit.

These fuses are designed to melt when the current heats them too much. How does this temperature compare to soldering temperatures?

Will the fuses just melt when soldered? Could the fuse wire be damaged by the soldering in such a way that the current rating is changed or the life expectancy reduced?

 

[Link]

The filament has to reach several thousand degrees before it'll melt, so no problem there. Issue is that the ends are usually soldered on, too, so the thing could come apart.

 

[Mr. Mik]

Thanks, Link!

I had a better idea in the meantime and have run some initial tests.

Blade fuses are much better suited for this purpose. Looks like they are made from a single piece of metal and the thin bit in the middle melts due to over-currents. I had no problem soldering them to other parts so far. And they are less likely t break than glass fuses, I believe.
But the connection between the thicker side parts and the thin part to be melted if necessary can be bent repeatedly during handling, with unknown consequences. That is avoidable with some practice.

I need to find 15A rated blade fuses and then I will run some tests to find out if hot glue is suitable to hold the fuse in place or if it gets runny again before the fuse blows. A high temperature silicone would then be needed.

But overall it looks like I will be able to attach 103 cables to the Vectux battery, each individually fused right at the point of first contact with the cell.

I also need to test cables for their behaviour under severe abuse conditions, just to be on the safe side.

Ideally I need cable that does not heat up much at all under a 12A load, is safe for continuous load at the rating of the fuses which I will use (probably 15A, 20A or 25A) and which will melt it's copper core before it melts the insulating material on the outside (in case it ever comes off the fuse and shorts the cells).
The cable needs to be thin, too, because there are many small gaps that limit the size for the individual cables as well as the 103 cable harness.

Is there a good website to learn cable basics? Cableuniversity?

 

[TylerDurden]

Soldering in fuses is a PITA when they blow... that's why they usually are in a handy spot to replace.

Car-stereo shops and even the car-audio section of the big stores have high current fuse supplies. You can still put a smaller rated fuse in them, but they have enough meat to keep from adding resistance.

 

[Link]

Yeah, if you're using bladed types, get some fuse holders like the ones ebikes.ca has. You should be able to find them locally. I know my Radio Shack has them for like $2-3 each. I use them on my bike. Easier to solder than a fuse, and no problem replacing one if it blows.

 

[Mr. Mik]

Thank you everyone!

The main issues are the sheer number of fuses needed (103) and the associated cost for fuse holders and the space restrictions inside the Vectrix battery pack.
And the added resistance which would make controlled deep discharging = reconditioning impossible without direct access to the cells.
Blown fuses are a pain, but compared what I would have to go through to get to the fuses in the first place the soldering in is a walk in the park. And I do not expect any blown fuses except for scenarios that would have ended in disaster without the fuse.

Here are some pictures of the fuses I have tried so far, and of the small space they will eventually be installed in.

The main problem so far is that the plastic melts a little bit each time I solder the fuses and they lose lateral stability, which can lead to bending of the metal thread in the middle, possibly altering it's current rating.
The mini-blade fuses are more prone to the bending problem than the standard blades.

Testing will follow.

 

[TylerDurden]

The fuses can go anywhere on those wires... middle or other end might be easier to access. You could use longer/heavier wires to get the fuses to a handy access point.

If the fuse body is weakened, vibration may cause the link to crack over time.

Those appear to be the balancing leads; why install fuses?

 

[Mr. Mik]

But if the fuses go anywhere other than right at the connection to the cell, the the cables could short out and destroy some or even all cells.
This could still happen if the wires get shorted at a time when the cells are so empty that they do not produce 20A (or whatever fuse rating I use in the end) any more for long enough to blow the fuse.

I have not done this sort of electrical project before, so I intend to over-engineer it good and proper! Better safe than sorry.

 

[PedalingBiped]

I once had a Camaro that had electrical problems. It died on the freeway, and then started up again after I wiggled some wires.
Scratched my head for a couple of weeks till a friend told me about fusible links.
googled fusible links and this is the first hit.

http://www.madelectrical.com/catalog/fusible-link.shtml

 

[Mr. Mik]

Thank you very much!

Armed with the new vocabulary I went to an Auto-parts retailer today and asked for "fusible links but not the block type"; the guy mumbled something about "they don't ask for that much any more today" and after a while we found some "Fusible Link Wire".

Much cheaper than the finished product you provided a link to: AU$3.- for 1m of 20A rated Fusible Link Wire!!!

Problem solved??? I think so!

I now have 2m of 20A and 1m of 13A rated Fusible Link Wire to play with...

I'll try to fry some under controlled conditions to determine what it really does.

Thanks again!

 

[PedalingBiped]

I found one more type.

Raychem Polyswitch

http://www.circuitprotection.com/polyswitch.asp

 

[Reid Welch]

I have soldered blade fuses a few times. I prefer to shed them of their plastic casings, inasmuch as the soldering heat embrittles the plastic.

Silicone rubber burns and can sustain flame if ignited.

I get the blade fuse out of its plastic, then tin-snip of the unneeded "beef" of the thing,
and for a fuse that is unlikely to ever be blown except in disaster, I brush the metal, solder flux paste (rosin type)
and tin-lead solder per usual.

then for insulation, very neat: epoxy putty, one or two coats, which can, whilst soft, be smoothed with wetted fingers.

High current, low resistance "disaster only" fuses might as well be crimped on and soldered: no risk then of weak spring
contacts or corrosion, ever.

But, yeah, there are times and places where removable, replaceable fuses make better sense,
if you have the room for their stowage, etc.

Also: grease of any neutral sort like plumber's grease, will ensure freedom from corrosion, water proofing against
future oxide-formation. Tin oxide is not a very good conductor. Spring-type fuse clamps must be TIGHT, but even then,
they are no electrical peer for the hard-wired fuse.

my opinions, is all,
R.

 

[Mr. Mik]

Thanks Reid, much appreciated!

I tried your suggestions and after a few false starts I'm starting to get the hang of it.

Getting the plastic off is not so easy for starters, but once I decided to just cut through plastic and metal alike whilst reducing the size of the original blade fuse, it got easier. The plastic soon falls off all by itself.

The thin fuse metal band in the middle does sometimes get bent in the process, though, and I do not yet know if this is going to reduce the current at which the fuse will open.
I will have to test this.

Is a 20A rated fuse supposed to blow at 20A or is it supposed to be able to carry 20A long-term?

The maximum current I plan to put through those wires might be 20A for capacity testing of individual cells.

For charging the maximum current which I can put in so far would be 5A, but maybe I'll get a stronger charger in the future.

The cables connected to the 20A fuses are rated at 30A.

It's all an attempt to have a low-resistance connection to the cells so I can get voltage measurements during charging and during slow, deep discharges for reconditioning if needed.

 

[Mr. Mik]

The removal of the plastic casing and enclosing the fuse wire into epoxy works well, .....BUT...


Encasing the fuse wire (of 20A blade fuses) changes their current rating! I believe this will be true for most fuses, but I have not tested it.

When I tested the current needed to open one of the blade fuses, I found 28A sufficient to blow the fuse; But, for this test I used the prototypes in which I had left the fuse plastic cover intact and covered it with some silicone sealant for stability.

But when the fuse wire is removed out of the plastic housing and then covered with epoxy putty, it requires about 40A to blow, instead of 28A. I believe this is due to the heat-sink effect of the epoxy, compared to the small air space in the original fuse cover.

I have not tested it but am fairly certain that the resistance of the fuse wire is unaffected by the epoxy casing.

For a solution I am now using the best of both worlds: I encased mini-blade-fuses (including their intact plastic cover) into epoxy. This leaves the thermal-insulating air-space around the fuse wire intact, whilst providing mechanical stability for the fuse. (The fuse becomes brittle due to the soldering heat and is not designed to be used outside a fuse holder, anyway).

I did test it: The 20A rated fuse opened at 30A when encased with the plastic (and air gap) intact.