What is YOUR short circuit current?

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Oct 8, 2016
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Every person installing 18650 cells in parallel needs to know the answer to this question.

I see some people scared of the volts. I see many people not scared of anything. What I don't see, is anyone afraid of the amps.

A single 18650 cell has a a short circuit current of 50A. Multiply that by the number of cells in parallel. This is your PSCC (prospective short circuit current). 1000A can set a huge battery cable on fire within 5 seconds. Some people will have far more than 1000A.

What protection devices do you have in place to disrupt this current?

If your answer is a circuit breaker, you fail.
If your answer is a glass fuse (or any fuse where you can see the fuse wire itself), you fail.
If your answer is a HRC fuse, you pass.

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station240

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Actually some of the high current 18650's in drill and ebike batteries can do 30A, it's in the datasheets.

For those unware, it's harder to break a DC circuit than an AC circuit, as with AC the voltage drops to 0V 100/120 times a second. Hence the any Arcing can also be stopped.
 
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I did think 10A was on the low side, but he was testing ultrafire junk

Although this footage isn't Lithium, it shows the danger of low volts high amps
 

Nismo nick

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Ok i am pretty new to all of this and i understand AC v DC and amps v volts. My question is HRC regarding the fuse types?
 
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It's a sealed fuse containing sand. Any explosion is contained inside and the arc is quenched by the sand. Because of this it has High Rupture Capacity (HRC) ie the capacity to rupture (stop) a high current.

Before someone says "but my circuit breaker is rated for 6500A" first, don't believe that figure if it's from China. Second, anything over about 200A will trip but causes serious damage to the contacts and the breaker needs to be replaced.


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Nismo nick

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Ah awesome. Seems i know what they are but never knew their name. These het uses in industriul electronics. Thanks for the descrption and the diagram. :D
 

Lux_Gamer

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Oct 11, 2016
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DIYTESLAPOWERWALL said:
I put together some footage of fault currents going through batteries, cables, breakers and fuses


What is your opinion on tesla style fuses/wire fuses?
I think it is helpful beside a hrc fuse.
 

Chickey

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Oct 8, 2016
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Each cell is individually fused in my setup or pair of cells at least if they've been recovered as pairs if that makes sense. Then i have a fuse for the battery pack as a whole.

Hoping i never experience what is in the pic!
 

hbpowerwall

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DIYTESLAPOWERWALL said:
Please move this thread to the Powerwall safety section

Done :idea:
 

3nergE

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DIYTESLAPOWERWALL said:
A single 18650 cell has a a short circuit current of 50A. Multiply that by the number of cells in parallel. This is your PSCC (prospective short circuit current). 1000A can set a huge battery cable on fire within 5 seconds. Some people will have far more than 1000A.

7500A / 100kW baby!

Active fuse : 12.5mm of copper, this should work right? - <gasp>

I fall into the category of potential future example of catastrophic failure.
My pre warning system is a couple of car tyres under the rig to induce thick black smoke.

All jokes aside, heed the warnings of the pro's ppl. My powerwall is isolated by distance and the whole shed is dispensable.
 

station240

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If your using ex power tool batteries, as some are, where 20-30A is the normal current, then I expect a lot more than 50A short circuit current is possible.

Important to know what the short circuit current of you batteries are, compare that with the kA (max interrupt current) rating on your breakers/fuses. High current arcs within the breaker could be worse.
 

hbpowerwall

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so my POSSIBLE is 4000amps that's a lot of pixies to escape the fun park.

Fingers crossed me usingHRC160afusesputs me in the right place?

Moving I would like to have one of these for each pack then a forth, for the whole pack. just to make it a little easier to take one pack offline if needed.
 

Rerouter

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Jan 1, 2017
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If you can, shine a bright light source behind one to make sure its not just an opaque glass fuse being sold as a HRC (been caught out with multi meter fuses a few times) if they are indeed sand filled they should be fine,

Checking the curve for that fuse grade, to pop in 1 second would take about 1000A, and gets faster as you throw it more amperage. to 10 milliseconds at 4000A, so a full capacity short would be 1KW dumped into the wires and batteries(averaged out to 1 second), or if your wires add some resistance and bring it back closer to 1000A, it would dump 26KW over 1 second into the wiring and batteries before it popped. it seems like a crazy amount, but you will likely only need to replace the fuse holder based on the size of the wiring you have used.
 

TheBatteries

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hbpowerwall said:
so my POSSIBLE is 4000amps that's a lot of pixies to escape the fun park.

Fingers crossed me usingHRC160afusesputs me in the right place?

Moving I would like to have one of these for each pack then a forth, for the whole pack. just to make it a little easier to take one pack offline if needed.

Those fuses say 150kA, so I assume that means it can break up to 150,000 amps in a short circuit?
 

Rerouter

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Yes as a peak pulse, that somewhat de-rates based on the inductance of the system, but at the voltages you guys are dealing with, you will never see that kind of current (voltage is too low), still at that amperage, even for a very small time period your fuse holder would likely become a crater, (insane pulse of heat)

Lithium cells do actually have a small amount of surface charge that is not limited by the esr of the cell, but just your wiring to them, its a tiny amount of energy, but he does exist there, which makes rating silicon to switch it harder as the brief equalizing spike into the input capacitors of a device can be quite high.
 
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