EF3 Fuse as a Class-T Alternative?

[gigadude]

For that single case you would put a washer down first, then the bottom lug, then the fuse, then the top lug, then a washer, lock washer, and nut.

That's what I was thinking would work.

Do you think battening down the wires with p-clips would mitigate the risk of things flying around when the fuse blows? The whole shebang is inside a 12"x12" metal gutter, I have about 6" between batteries to bolt down fuse holders:



the blue sea holders are 8" long, if I mount them perpendicular to the gutter I'll have one end under the busbar. I guess I could mount them up top in the worst case.

 

[robbob2112]

Your choice, were it me I would use the blue sea holder and figure out how to make it work. I just don't like the look of that one you propose to use.

If you go ahead then secure the wires within 4 inches of the holder.

 

[gigadude]

Your choice, were it me I would use the blue sea holder and figure out how to make it work. I just don't like the look of that one you propose to use.

If you go ahead then secure the wires within 4 inches of the holder.

The VTE holders apparently do have a steel standoff under the bottom washer which makes me feel a bit better:



I'll be sure to secure everything within 4 inches. The gutter's mounted to corrugated steel atop durock backer board, if the fuses get exciting I'll get to test how well my firewall works...

 

[Drizzt321]

Well written and explained.

But we are dying to know if any of those events actually happened to you?

Well, in the first 30 odd pages of https://diysolarforum.com/threads/house-burned-down.83098 there seems to be a strong consensus that in an otherwise very well setup system, the fuses (as per manufacturer, Victron) didn't have sufficient AIC between each battery string and the bus bar, which the fire inspector pinpointed as the likely starting point of the fire.

In short (my interpretation), is likely a failed cell caused a voltage difference and all the other 6 strings (out of 7) pushed current into it. There was a Mega fuse (2000a AIC) at each battery string to the bus bar, however the AIC rating appears to have been insufficient to extinguish the arc which then seems to have gone on to melt/start the fire at the fire resistant fuse holder which I think was mounted to wood, which then proceeded to start the fire. Alternatively it cause a combustion event from the cell venting, or more cells in that string venting, or something or other. Or a combination.

In any event...this is what appears to have happened, although we can't know for sure.

 

[robbob2112]

that pretty much sums it up except to add a couple of details...

The cause - shorted cell - there was a 21minute delay between a sign of trouble and total loss of signal - in this time it is assumed the cell vented hydrogen
The fuse - while what was recommended at the build time 4 years earlier didn't take into account 7 parallel strings pushing 125amps each --- and the 32v 100amp fuse with an AIC of 2000 most likely exploded into a shower of sparks igniting the hydrogen and then the fire.

 

[Drizzt321]

Which is actually interesting to me, in that I didn't realize lithium batteries could vent hydrogen. I knew it was a not uncommon thing for a bit of hydrogen to vent with lead-acid, but didn't realize it for lithium. Or at least, as part of a "this cell is now bad" vent.

So, I learned from reading that thread!

Also I think I saw in another thread the idea that a water heater pilot light might have caused an explosion from some hydrogen buildup of lithium cell venting. So...don't put lithium batteries near a possible ignition source, enclose possible fuses/sparks away from possible hydrogen release, and have a vent near the ceiling to try and get rid of the hydrogen, or at least dilute it in concentration enough so it's not a danger.

 

[robbob2112]

When a cell shorts the percentage of gas varies with the electrolyte used and the temperature reached.... For a straight short with a cell temp of 300c or less internally the primary gas is hydrogen.. This is what you expect from an over-current or over-voltage . but the plates heat if the short is caused by a puncture like a nail or screw. When that happens they exceed 600c and the electrolyte breaks down completely ... in that case you get around 40% hydrogen, 20% oxygen, and the rest a stew of nasty gas you don't want to breath.

Lithium ion has a lot higher percentage of oxygen in the breakdown of the battery so they burn and are very very hard to put out. Basically it takes immersing it in water.

LFP is put out with a slurry of salt and a few other chemicals .... it cools it and seals it to starve it of oxygen... then the cleanup is to wear your PPE and use a shopvac once it is dried out into a powder.