Fuses or lack thereof: a confession!

[DamonHD]

Hi,

As I've re-arranged my off-grid system, in particular putting in the new LiFePO4 battery, and rearranging my small turbine to feed into it rather than my SLA for example, I realise that my system now has no fuses at all.  I have been using some of the auto-resetting fuses in the past.

Everything is protected electronically in theory, ie the Morningside MPPT and the LiFePO4's BMS, but ... um ... that's probably not really good enough, is it?

The Morningstar MMP manual shows a 25A fuse to the battery +ve and another to the load +ve, and I might as well follow the same for the LiFePO4 side (at least one in the -ve charge lead and another in the -ve discharge lead).  Does that sound OK?

I seem to remember that automotive fuses were not considered adequate for this task, even if rated to a sufficiently high current.  If not, why not, and what should I use?

What about using auto-resetting in place of some of those conventional fuses?

Rgds

Damon

Rgds

Damon

[ghurd]

I recall your wind turbine is "very small"?
Is it small enough to not do any damage if it runs unloaded in a giant storm?
I worry about some turbine fuses being undersized, resulting in a blown fuse, at the worst possible time.

I believe the usual complaint about 'car fuses' is most are only rated for 32V, and they may not quench an arc at higher voltages.
Lets face it, if your turbine is connected to a 12V battery, and the fuse is seeing greater than 32V, you have bigger issues, IMHO.

The Maxi-Fuses have a pretty big gap in them.  Maybe the same rated fuse in Maxi would be a bit safer?
I dunno.

I don't trust the self-resetting things, if the actual amps need to be limited to a critical value.
They will carry a lot more amps (%) for quite a while before they trip.
We tried a 5A greater value automotive blade fuse than the self-resetting breaker.  20A and 25A?  25A and 30A?  I do not recall.
Turned up the amps slowly, over 10~15~20 seconds?  The 5A greater fuse blew first.  Every time.
I do not believe we managed to make the breaker trip at all, but we didn't let it sit for 60 seconds at the amps between the 2 ratings.
The breaker was probably something from All Electronics.

1 cent.
G-

[DamonHD]

The wind turbine delivers so little energy that if the storm was big enough for it do do any damage I'd be losing my roof I suspect.

So the highest voltage likely to be seen in the system if something goes wrong is about 25V, ie from a solar panel Voc.

I don't know what a "Maxi fuse" is, but I'll do a little research, thanks!

Rgds

Damon

[DamonHD]

Hi again G,

How many times did I say how great it is to work opposite a B&M electronics store?

I just got myself some Maxi fuses and holders to try out:

http://www.maplin.co.uk/Module.aspx?ModuleNo=48026

http://www.maplin.co.uk/Module.aspx?ModuleNo=30444

They are so enormous I think that just holding them doubles my machismo...  The fuse holders look like bicycle security locks!

Rgds

Damon

[DamonHD]

OK, I just took the opportunity to fit one of the 30A MAXI fuses into the +ve line of my SLA, though in a not-very-good way that I will have to revisit later.

And I do have one of the 8A self-resetting things in my LiFePO4 discharge line, but that should be easier to replace with a 20A MAXI fuse in the other holder.

Because the two batteries are diode-OR-ed to supply my server I was able to do the fuse work on my SLA without bringing down the server at all, so there's a nice big glitch to zero shown on the graph!

Rgds

Damon

[SparWeb]

I'm as guilty as you are.

The risk doesn't come from high current from the solar panels, it comes from damage to wires, loose connections, metal parts falling across live terminals.  Fun stuff that happens when we tinker with the system.  The wrong kind of fault on un-fused wires can throw a huge current through very skinny wires.  If that causes a fire, then the whole system or house can go.

Yeah, I'm aware of the risks and still I don't have fuses in the right spots.  Good job getting that fixed.

[DamonHD]

I did the load side of the SLA/controller the day after, so now just have the LiFePO4 battery to decide what to do with (though it does have a self-resetting fuse on the load side)...

Rgds

Damon

[Madscientist267]

I've learned my lesson about them... sometimes... hahaha

It's a hard lesson sometimes, some harder than others. I've scorched carpet, had violent MOSFET 'venting', ahem, and a couple near misses with various projects that took a lot of time to build, only to have a fire break out in them and destroy a good portion of my work...

Never burned a house down, but I've filled rooms with smoke to the point I couldn't see...

I hate... (did I say hate? I meant HATE) fuses with a passion; sometimes they can cause more problems than I think a whoopsie would, but in all honesty, not usually. Resistance is just at the top of my list, flaky connections another, and so on and on...

They're a necessary evil, and I never leave them out of final design anymore. I'll take a little irritation rather than sleeping in a car (if I'm lucky) because I set the damn house on fire! 

Yeah, uh, get on that dude... even though your equipment probably 'works' better without them than with...

BAD Damon, I say, BAD! 

Steve

[DamonHD]

Well, I'm all fused up on the SLA side now (though at the moment I've let it get far far too low SoC Bv< ), and partly on the LiFePO4 (load) side.  I need another couple of MAXI holders to finish the LiFePO4 side...

Rgds

Damon

[TomW]

What are these FUSES you speak of?

Tom

[DamonHD]

Uninsulated metal tools less than a few mm in diameter that can touch both battery terminals at once?  B^>

Rgds

Damon

[Madscientist267]

LMFAO I call those "Quantum Fuses"... They'll most certainly blow before much heavier wire, but you never know just how much current it takes to make that happen... hahaha

Steve

[DamonHD]

I'm really really hoping never to find out...  %-P

Rgds

Damon