Daddy Tanuki
Solar Wizard
I have spare class t fuses that are 80 amps I can send for testing if you need fuses
Dead short fuse trip experiment using an MRBF fuse
- Thread starter Johan
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I wish I had more time. I have all the equipment to do these tests in my lab (I've done Class T and BS88 in the past for example).
As for the BMS (I tested the JK): in many cases and faults it will be much faster to react than the fuse, but it's not the only thing I would rely on. I size my fuses based on the max current it should see in normal operation. Inverters can fail and create a dead short, but if they normally only draw 100A, a 125A fuse will do even if the cable is rated for 200A or more.
The nice thing about Class T (and BS88) is that I have yet to see them throw molten metal/plastic around.
As for the BMS (I tested the JK): in many cases and faults it will be much faster to react than the fuse, but it's not the only thing I would rely on. I size my fuses based on the max current it should see in normal operation. Inverters can fail and create a dead short, but if they normally only draw 100A, a 125A fuse will do even if the cable is rated for 200A or more.
The nice thing about Class T (and BS88) is that I have yet to see them throw molten metal/plastic around.
I think the NH00 fuses are also designed to not throw molten metal around. Same principal of an enclosed ceramic fuse surround with silica sand.
A very good alternative to class T and a lot cheaper in Europe. About $10 per fuse
on a dead short the BMS stopped it before the fuse triggered? that's damn impressive
OzSolar
Whatever you did, that's what you planned.
It really is. I've often theorized that a BMS sees the inverter's initial inrush as the beginning of a dead short thus goes into protection mode and shuts down.
Brucey
Solar Wizard
If a BMS can trip from the surge of charging an inverters capacitors then a true short should be an easier thing to detect.
Yep!
yea. I've seen them blow up too. I guess it depends on what the chip is busy doing. I assume the decision to react is all on the main micro controller cpu and not some dedicated one
If you're constantly monitoring it though you do get a head start on when you react as you say. The speeds of these electrical shorts are as fast as the electricity in a cpu though.. so the latency in a processor is higher, so it's a gamble imo
Hedges
I See Electromagnetic Fields!
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Fuses, breakers, relays are milliseconds. FETs switch at 10 or 100 kHz in power supplies.
Maybe a BMS with contactor wouldn't be fast enough. Might be enough to protect itself and wires, but possibly a fast fuse in series would get blown first (that is its job.)
I never trust microprocessor for real time. Mainly because I never trusted the programmers on the same project, but not entirely.
My hardware had analog circuitry to detect and shut down (filament or amplifier protection). Easy enough to do for the BMS, voltage across shunt into a comparator, drives a FET to discharge gate of power FETs. Only question is how fast you can get it below threshold voltage.
I would do similar for cell over-voltage, although that could be handled with polling. Maybe a state machine or dedicated uP.
Maybe a BMS with contactor wouldn't be fast enough. Might be enough to protect itself and wires, but possibly a fast fuse in series would get blown first (that is its job.)
I never trust microprocessor for real time. Mainly because I never trusted the programmers on the same project, but not entirely.
My hardware had analog circuitry to detect and shut down (filament or amplifier protection). Easy enough to do for the BMS, voltage across shunt into a comparator, drives a FET to discharge gate of power FETs. Only question is how fast you can get it below threshold voltage.
I would do similar for cell over-voltage, although that could be handled with polling. Maybe a state machine or dedicated uP.
Even if the programmers don't mess it up, it's be pretty sad if you got a https://en.wikipedia.org/wiki/Soft_error from space cosmic rays when you could have had a breaker and or fuse there 
Johan
Off-grid energy systems enthusiast.
Per request of @Pi Curio, 10 Heschen fuses (sourced on Amazon; HSPV-30; 32A; 1000VDC; I1 = 33kA) were blown while mounted in their DIN-rail fuse holders (sourced on Amazon) in the vertical position.
These fuses are filled with sand, similar to Class T fuses. The resulting current versus time plot is shown below. The legend shows the experiment number. Experiments 1 through 4 blow a single fuse. Experiment 5, 6, and 7 blow two fuses in series just to see if that makes any difference.
Here are all seven experiments on video ("Unlisted" on Youtube, so you need to use this link):
Notes:
These fuses are filled with sand, similar to Class T fuses. The resulting current versus time plot is shown below. The legend shows the experiment number. Experiments 1 through 4 blow a single fuse. Experiment 5, 6, and 7 blow two fuses in series just to see if that makes any difference.
Here are all seven experiments on video ("Unlisted" on Youtube, so you need to use this link):
Notes:
- There was no sign of external damage for fuses and holders.
- Only experiment 5 has measurement data from both the Arduino and oscilloscope for comparison purposes.
- The negative 25000A "charge current" was completely unexpected and seemed to be artificial oscilloscope nonsense at first, but this current was later reproduced on the Arduino (not shown, separate experiment). This *may* be an effect or "ringing" due to parasitic capacitance in the circuit. Anybody comments on this?
- Scopes are generally very inaccurate for measuring voltages, so they are also inaccurate for measuring voltage drops across a shunt as was done here to calculate the current.
- I estimate the Arduino accuracy to be roughly +/- 160A based on specsheets data.
- The oscilloscope accuracy seems to be roughly +/- 1800A based on specsheets data.
- See also here if you want to read more about oscilloscope accuracy.
- When torquing the screws, the side panel of the thin plastic fuse holder housing can easily crack open.
Try 50A/50mV shunt. It should give you 10x better signal to noise (10V signal instead of 1V). That -25kA peak could be due to magnetic field collapse but I doubt it would generate real current spike that high. Most likely that field is messing with your probes or scope.
I would use precision current shunt instrumentation op amp fed to an ADC and microcontroller directly mounted to the shunt and powered by small onboard battery. This way you eliminate sense wires that can pick up collapsing magnetic field interference. Or if you want to use your scope you should be using true differential probe for this to cancel out magnetic field interference. Single ended (unbalanced) probes are not good.
@Johan
I can't thank you enough for doing the gPV fuse dead-short tests.
This is above and beyond my expectations! I did not expect I'd ever get to see this fuse being properly put to the test multiple times in different configurations by someone with the talent, knowledge, and skills to do this when I made my post a while back.
For me, this is an absolute game changer and makes all the difference for my project. I will in part try to replicate the test results here in Europe just to have no doubts left about the fuse quality available here, but 10 out of 10 fuses blown is very convincing.
Your work has helped give this curious soul an answer to the question
Much obliged.
I can't thank you enough for doing the gPV fuse dead-short tests.
This is above and beyond my expectations! I did not expect I'd ever get to see this fuse being properly put to the test multiple times in different configurations by someone with the talent, knowledge, and skills to do this when I made my post a while back.
For me, this is an absolute game changer and makes all the difference for my project. I will in part try to replicate the test results here in Europe just to have no doubts left about the fuse quality available here, but 10 out of 10 fuses blown is very convincing.
Your work has helped give this curious soul an answer to the question
Much obliged.
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Hedges
I See Electromagnetic Fields!
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Makes sense if there is a loop formed by ground lead of scope probe.
dI/dt through wires of circuit under test would induce current in that loop. Shunt holds low V = IR between probe tip and ground clip so voltage appears across scope input.
Different connection scheme like BNC connected to shunt with minimum loop area formed could help. Shunt and that little loop twisted right angles to loop formed by current carrying wires might help. Squeeze the air of loop formed by the wires, even twist them.
I got Fluke i2000 Rogowski coil.
It has 20 kHz bandwidth, better than the CT I have, makes a difference for inrush measurements (may want probe with DC response for that, but I was measuring AC circuits, transformer and SMPS inrush.)
I would think shunt would be good for these 10kA or 20A measurements.
The i2000 is rated 2kA or 3kA.
Here is my attempt at testing fuse short circuit current. I used Buss AGC-2, AGC-5, AGC-10 and AGC-20 glass fuses rated for 250Vac. Setup: 44Vdc battery, 0.12 Ohm 3.8uH #18AWG wire about 10 feet long. Predicted peak current 367A. Measured peak current ~420A. Results: AGC-2 = 200A 1ms, AGC-5 = 280A 2ms, AGC-10 = 400A 5ms, AGC-20 = 420A 18ms. All fuses break an arc without exploding.
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Hedges
I See Electromagnetic Fields!
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What battery, and what prospective short circuit current?
0.12 ohms ... wire protects fuses (from exploding)?
10', 3048 mm, 3048 nH
44V/3.048e-6 H = 14 million amps per second.
If I'm seeing 1 ms/division, 200 us rise time to 200A, that would be only 1 million amps/second.
Is my reading of the screen off, or the math, or something else?
Consider twisted wires for low inductance. But it is the resistance which is keeping it from being really exciting.
0.12 ohms ... wire protects fuses (from exploding)?
10', 3048 mm, 3048 nH
44V/3.048e-6 H = 14 million amps per second.
If I'm seeing 1 ms/division, 200 us rise time to 200A, that would be only 1 million amps/second.
Is my reading of the screen off, or the math, or something else?
Consider twisted wires for low inductance. But it is the resistance which is keeping it from being really exciting.
That's the point. Wire resistance acts as a current limiter to protect the fuse. Wire inductance makes it harder for the fuse to break and arc. I use 5A fuse to protect the input of my Victron 75/15 MPPT fed from 44V Tesla battery over 20 feet of 16 gauge extension cord wire. I wanted to verify that these 250Vac rated fuses would break an arc and not explode. I measured inductance again and got 4.15 uH. Slow measured rise time could be limited by 20Mhz scope BW filter or having it zoomed out to capture entire event.
curiouscarbon
Science Penguin
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this thread is awesome!
thank you for doing these experiments and sharing the results!
it helps reduce the fog of uncertainty around how given fuses behave in the important moment.
thank you for doing these experiments and sharing the results!
it helps reduce the fog of uncertainty around how given fuses behave in the important moment.
Ignition projection not protection
I just thought of another test (thinking of possible failure modes from that recent huge up in smoke thread)
What happens if instead of an instantaneous dead short, there is a steady load applied, then create a short? Or, say a 200A rated fuse, and you load it down sustained somewhat above its rating (220A? 250A? 300A?) and instead of blowing up like in the case of a dead short, it goes through the overload time curve and then pops? Does it still extinguish any arc when blowing more slowly?
My thought behind this - sometimes catastrophic BANG blows itself out if goes from 0 to everything instantaneously. But when the fuse (relatively) slowly melts, is there a chance it could just melt and go to plasma and not actually break the circuit.
What happens if instead of an instantaneous dead short, there is a steady load applied, then create a short? Or, say a 200A rated fuse, and you load it down sustained somewhat above its rating (220A? 250A? 300A?) and instead of blowing up like in the case of a dead short, it goes through the overload time curve and then pops? Does it still extinguish any arc when blowing more slowly?
My thought behind this - sometimes catastrophic BANG blows itself out if goes from 0 to everything instantaneously. But when the fuse (relatively) slowly melts, is there a chance it could just melt and go to plasma and not actually break the circuit.
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