The way I built my compression frame, it extends well above the height of the terminals. Anything I place over the batteries will rest on the frame, not the terminals/cables/lugs.
LiFePO4 prismatic cell short circuit current and main circuit protection
- Thread starter sduser
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I'd just run the two bundles in the alt layout of sense wires inside some fireproof loom. That way it prevents the ability to scuff to the terminals and if they do short/overload some other way it's contained and will certainly become an open circuit in the loom.
Also not mentioned here but always best practice to keep the sense wires all the same length!
ArthurEld
Solar Wizard
I'm thinking about switching to the original layout. It seems safer to me.
And it will be easier to make a flip open cover
And it will be easier to make a flip open cover
John Frum
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If you don't mind my asking, why do you feel its safer?
Is there something specific that you are avoiding?
ArthurEld
Solar Wizard
If I short the original configuration less cells are involved. It's almost impossible to short all cells on the original layout.
But the alternate layout has the + and - right next to each other. And you can easily short a bunch of cells all down the middle of the battery.
pablo fiasco
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I'm going to do a little table top research. Someone mentioned that electric wire insulation burns. I found that counter intuitive so I tried and indeed it does. So long as there is a flame it burns. Remove the flame and it goes out. Same with the insulators on terminal crimps. 2 types of heat shrink I've tried so far went on burning without an external flame. I'm gathering up every kind of material I can find around the homestead and will post results eventually. Meanwhile anyone heard of Starlite? Or intumescent paint? There's some far out materials I want to try set fire to.Don't put plywood or cardboard over the batteries. I have to go out and remove mine.
Fire!! Never cover LiFePO4 with wood!!!
New adventure.. I went inside the battery room. As the exhaust fans where working, and they are temp based, I felt OK to close the door. I used wood (MDF) to cover the cells and sit on top, and to prevent accident if something falls 2 left over pieces, 10mm, but strong enough to sit on, as...diysolarforum.com
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I think that's what is meant by "self-extinguishing" vs "non-flammable"?
ArthurEld
Solar Wizard
I wonder about the plastic cover on these fuse holders - https://www.bluesea.com/products/5007100/Class_T_Fuse_Block_with_Insulating_Cover_-_110_to_200A
It says-
It says-
- Insulating cover satisfies ABYC/USCG insulation requirements
- UL 94-V0 base resists high heat
Hedges
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I've never met anyone who had been killed by not wearing a seatbelt.
But I have seen many cars with punched windshields.
Similar for helmets; one of mine has some nice circular patterns in the paint.
pablo fiasco
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It's interesting to think things through. Not so interesting to let Google do it for you. I sometimes get diametrically opposite answers. Anyway, one does ones best and then lets go. If you want your boomerang to come back first you have to throw it.
ArthurEld
Solar Wizard
There is another thing I am trying to avoid. Arcs.
I think there is less arc potential across the battery when the cells are lined up in 1P series
ArthurEld
Solar Wizard
This is a crappy representation of the bad short I had. The yellow line shows where my tool shorted.
The red is showing the current path changing directions and moving toward each other. I think that makes a difference.
The two current paths are already trying to reach each other which causes more arc potential right there. And that aided my tool keeping the sort connection even though it fell away from the terminal.
I have no proof but I think this makes a difference.
When there's more arc potential a short is more eager to happen. I don't want that.
The red is showing the current path changing directions and moving toward each other. I think that makes a difference.
The two current paths are already trying to reach each other which causes more arc potential right there. And that aided my tool keeping the sort connection even though it fell away from the terminal.
I have no proof but I think this makes a difference.
When there's more arc potential a short is more eager to happen. I don't want that.
pablo fiasco
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I've been down a dozen times. One time over the bars down a flight of stairs on a mountain bike. My feeling is that what you can't risk losing is not worth having. Just me setting a bad example. Not giving advice.
ArthurEld
Solar Wizard
I got knocked off a motorcycle going 70 mph. If I didn't have on a cheap novelty helmet I'd have a flat spot worn into my scull just like the one on the helmet.
pablo fiasco
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Not DOT or SNELL? Say it weren't so.
ArthurEld
Solar Wizard
I think I did stick a DOT sticker on it. We're way off topic
pablo fiasco
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Yep. Become DIY philosophy. Let's try to focus. (Largely my fault I think. Sorry.)
I know I'm a bit late to join this discussion, but am hoping for a sanity check on a fuse I want to use.
I need a fuse that is somewhere between my max load of about 130A and the max current rating of my cables, 188A. It could potentially see the full force of a 450Ah 8s LiFePO4, so I think I want a high interrupt rating. Class T fuses below 225A are a real hassle to obtain in Australia, and expensive.
My reading of the specifications seems to indicate this NH fuse will work. I'm a bit unclear whether the "Rated breaking capacity: 120kA" on page 1 of the data sheet applies to DC or just AC. Details for the 160A version are on page 3.
Product page link
Data sheet
I'd really appreciate if anyone can help me decipher the data sheet.
I need a fuse that is somewhere between my max load of about 130A and the max current rating of my cables, 188A. It could potentially see the full force of a 450Ah 8s LiFePO4, so I think I want a high interrupt rating. Class T fuses below 225A are a real hassle to obtain in Australia, and expensive.
My reading of the specifications seems to indicate this NH fuse will work. I'm a bit unclear whether the "Rated breaking capacity: 120kA" on page 1 of the data sheet applies to DC or just AC. Details for the 160A version are on page 3.
Product page link
Data sheet
I'd really appreciate if anyone can help me decipher the data sheet.
There's insufficient information. It's rated to 250Vdc but you're right -- the breaking capacity isn't qualified with AC or DC. It looks like it's mostly designed for an AC circuit so I personally wouldn't choose it.
Class T fuses are expensive ... that's part of why I moved to a quality DC breaker. Maybe you'll have more luck sourcing a breaker?
According to the product page specifications, that is an AC fuse, not a DC fuse. Only once in the data sheet does it have a rating for DC, on page one.
In the below product brochure for NH fuses from Eaton it says:
If it was me, I would find a fuse specific to DC applications.
Hedges
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Not a lot of room between 130A max load and 188A rating.
How did you come up with 130A?
What I would do is consider:
Watts (maximum continuous output of inverter, not surge)
Vbat (minimum battery voltage as seen at inverter, low bat cutout)
Efficiency (at max watts, not "peak")
125% (margin to avoid nuisance trips)
112% (RMS of ripple current in DC supplying sine wave power)
If 1200W, 10V minimum, 90% efficiency
1200W/10V/0.9*1.25*1.12 = 187A, that would be OK.
Note that nominal 1200W/12V = 100A (ignoring efficiency), so my recommended fuse size would be 87% higher.
Can you use larger cables with 225A ampacity, so 225A class T fuses could be used?
Based on the internal resistance rating I've seen for LiFePO4 cells, I estimate 20,000A short circuit current, which is exactly what class T can handle.
Would like fuses sized so they never blow except in case of a short.
For motor loads, good to have a breaker which will trip after a delay with "locked rotor amps" so motor can start, but is protected from overheating if stalled.
Ok, you've confirmed my suspicions. I'll look for something different. Thanks.
This is actually on my charge circuit, so the max current under normal conditions would be from the solar array. I have 12 panels in parallel (Electrodacus system), each with Isc of 8.78A so 105A. A 1.25 safety factor puts max output at about 130A. The only time the fuse would really be relevant is if I dropped a spanner across the charge busses, which would effectively short the battery, hence the need for HRC.
This would be overkill on cable size, but would solve the problem. Might be a good solution if I can't locate a fuse.
Hedges
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OK, you already included the 1.25 factor.
Electrodacus and Isc? Meaning PWM, no current boost from a switcher?
Charge controller, so ignore my 1.12 factor for ripple current supplying inverter.
The two currents for you to consider are maximum from PV panels, and short circuit being backfed from battery.
Perhaps if you connect this circuit after a class-T fuse (that protects inverter cable), then it doesn't need the same AIC for fault current. But it isn't clear to me a main fuse provides "current limiting". The curves I've seen show class T can interrupt 200 kA (AC) while protecting parts with a 20 kA rating. But it doesn't do the same with a 20 kA fault.
The US NEC for wires/fuses from PV panels calls for 1.56 safety factor. That's the usual 1.25 to avoid nuisance trips, plus another 1.25 in case extra reflected illumination causes higher than Isc. I think this puts you at about 160A minimum fuse and wire ampacity.
Electrodacus and Isc? Meaning PWM, no current boost from a switcher?
Charge controller, so ignore my 1.12 factor for ripple current supplying inverter.
The two currents for you to consider are maximum from PV panels, and short circuit being backfed from battery.
Perhaps if you connect this circuit after a class-T fuse (that protects inverter cable), then it doesn't need the same AIC for fault current. But it isn't clear to me a main fuse provides "current limiting". The curves I've seen show class T can interrupt 200 kA (AC) while protecting parts with a 20 kA rating. But it doesn't do the same with a 20 kA fault.
The US NEC for wires/fuses from PV panels calls for 1.56 safety factor. That's the usual 1.25 to avoid nuisance trips, plus another 1.25 in case extra reflected illumination causes higher than Isc. I think this puts you at about 160A minimum fuse and wire ampacity.
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