An absolutely fuseinating question

[Ellis]

Hi all, am looking around for the various bits and bobs that we need to go LiPo, and naturally, we need fuses. The batteries we're getting can do 100a continuous and 150a burst. I figure a fuse in the region of 125a is suitable, or around there at least, but I am struggling to find one that is perfect. I would be easy and go for a 100a but I think, at least in Tormenta 2, we'll be blowing them constantly.

Where do you guys get your fast failing fuses that aren't typical sizes? The types are confusing (see what I did?), and it's a safety feature so, naturally, we want the right thing.

I suppose another question is whether you think a 125a (ish, +/- 10) is suitable for a 150a burst pack.

Thanks.

[mattsdragons]

Re: An absolutely fuseinating question

http://uk.farnell.com/jsp/displayProduc ... price=true

Not sure if its any use but taadaa

[Ellis]

Re: An absolutely fuseinating question

That's a slow blowing one mate, which I don't think will save any batteries.

[plargen]

Re: An absolutely fuseinating question

if you go for a 100a midi fuse its rupture point is 200a

if its the same with other fuses then you probably want a 75a

[plargen]

Re: An absolutely fuseinating question

found a 70a midi fuse

http://www.ebay.co.uk/itm/Midi-Fuse-70A ... 3cce163d85

[Ellis]

Re: An absolutely fuseinating question

Tormenta 2 will definitely pull 70a at times, and something about pulling power through a fuse that will limit the performance of things, whilst getting hot and potentially blowing prematurely, doesn't sound ideal! But interesting though, if they reliably blow after a short burst of say 120a and not 70a then they may be an option.

Has anyone had any positive experience with putting several smaller fuses in parallel?

[razerdave]

Re: An absolutely fuseinating question

I err on the side of caution. The fuse in Satanix is only 60A, reason being that its the continuous rating for my speed controllers. If my robot somehow draws 60A, then there is something drastically wrong and I'd rather sacrifice a fuse than almost £200 worth of speedos.

[Max]

Re: An absolutely fuseinating question

I would say you want a normal 100A fuse as this will be fine with a burst of 150A like the battery is, but it will blow if you are drawing more than 100A for a longer period of time. You could also buy a range if fuses and expirment to see what is the lowest fuse you can get away with without it blowing in normal use.

[Mouldy]

Re: An absolutely fuseinating question

blow times relative to fuse types can be found in 17th edition wiring regulations.

For automotive fuses i very much doubt tormenta will blow a 75a automotive style fuse....

In the wiring regulations book it talks about diversity of wiring, which can also be taken into account when building robots, your unlikely to stall all 3 of your motors at once, causing a fuse to blow....

Long story short ive got a 100a auto fuse in 720 which pulls over 300a... havent blown one yet.

[Ellis]

Re: An absolutely fuseinating question

Right. It does make sense to buy some and just try them. Of course the likelihood of more than one motor stalling is very low, but for example the lifter motor is an unknown quantity, for all we know it's pulling bucket loads, as it is similar in scale to a s900.

Think we'll buy some 80a and 100a ones and see how we go!

Thanks all.

Also, fusetrating. I just needed to say that.

[PJ-27]

Re: An absolutely fuseinating question

I highly doubt you'd pull enough amps long enough to damage a Li-Po, except maybe in some extreme circumstances, in which case a big Maxi/Blade/Car fuse on the Li-Po should suffice.

I'd just consider what you want to protect, so ESCs. If you burn out a motor it'll kill the esc so put a ~30a fuse there.

It would be a real shame to lose a fight beacuse you blew a fuse, but at the same time if I motor dies you've lost anyway so don't let it take more componenets with it!

Putting fuses in parallel is just more potential points of failure in your bot. I'd avoid.

[Ellis]

Re: An absolutely fuseinating question

We have have won fights having blown motors! At MMM I think we only had one fight in which we didn't destroy a gearbox and thus a motor.

I don't think the speedos will mind having a stalled 550 on them. Even two, which unless something goes really wrong, will never happen. Not only should they be fine on paper, but in practice, again, the ESCs were subject to stalled motors at MMM and they were fine.

I have an idea that may solve some of our gearbox issues anyway, which in turn should reduce the number of motors the machine eats, actually reducing stress on the speedos.

Have spoken to dad, and we'll get some 80a and 100a jobbies on the go soon. Thanks again.

[widow_twanky]

Re: An absolutely fuseinating question

Time/current charachteristics for automotive fuses are here:

http://www.littelfuse.com/products/fuse ... Delete.pdf

Can't find it for the higher fuse ratings but the curves wont change just where they are on the graph. If you scroll to the bottom you'll see the curves.

Basically for a 1A fuse you get:

Instantaneous: 10A
0.1s: 3.5A
1s: 2A
10s: 1.5A
100s: 1.25A
1000s: 1.15A

Approximate figures because the graph isn't too accurate but interpolating (which in the case of fuses is perfectly valid but doesn't give a fine accuracy) that to a 100A fuse you get:
0.1s: 1000A
1s: 200A
10S: 150A
100s: 125A
1000s: 115A

In practice they are designed to take the peak current if they're sized to take the running current. We've used a 20A fuse on two drills and a set of gimsons in BOOM! since it was built. I put a 25A fuse in Diablo and it runs no probs. Will be interesting to see wether it holds on the Wyachi's in combat but I suspect it will.

Andy