LiFePO4 prismatic cell short circuit current and main circuit protection

[HRTKD]

I'm pretty sure you could take a battery cable and connected to the terminal of a 280Ah cell. Clamp on to a welding rod with the battery cable and touch it to the other terminal. ? You'd get some welding action from 3.4V.

You first!

 

[pablo fiasco]

I'm pretty sure you could take a battery cable and connected to the terminal of a 280Ah cell. Clamp on to a welding rod with the battery cable and touch it to the other terminal. ? You'd get some welding action from 3.4V.

I guess it depends on how you define welding. Sparks or a puddle. Anyway, fly at it. Post a video.

 

[curiouscarbon]

ok, is anyone familiar with the concept of a FET/capacitor array used in conjunction with contactor/relay and current sensing?

a digital arc arrestor

using a resistance vs time model of a given contactor

current sense indicates over current condition. capacitors are at 0V and FET array drivers engage. current flows into the capacitors.

the contactor coil is disengaged with timing such that the capacitors have peak inrush current at or slightly before the arc is expected to have formed.

when the contactor is fully open, disengage FETs and bleed off charge with big resistors

any device being sold that does this?

like a SiC array with a bunch of good heatsinks and ultra caps or something.

eg this SiC MOSFET and this 3400F supercap

 

[ArthurEld]

I guess it depends on how you define welding. Sparks or a puddle. Anyway, fly at it. Post a video.

If you do it long enough the terminal will melt off. I didn't say it would be a pretty weld.
Sadly my cell welding experience wasn't caught on film. I shorted 24V with a 1/4 ratchet and socket.
It was worthy of film.

 

[ArthurEld]

Except that this isn't normal atmospheric condition:



Look at what happens in the video below -- the connecting arc is small and requires close proximity. The disconnecting arc is shockingly enormous (no pun intended).

I spend a lot of time thinking about the time I accidentally shorted my battery.
And I never could figure out what I touched to cause the short.
Now I realize you don't have to touch anything. You can have an arch more than 1" long.

When I saw a flash and heard the noise it freaked me out and I dropped my 1/4" ratchet with a deep socket.
I thought the deep socket was enough to keep me away from everything.

It kept sparking for what seemed like a long time. So, I grabbed the wrench and pulled it off.

Another thing the confused the hell out of me was that the socket stayed connected. I dropped the wrench so how could the deep socket stay on the nut and the handle reach all the way down and touch the other busbar?

The socket didn't have to stay on the nut and the handle didn't have to touch the other busbar. They just needed to stay within an inch or two because of the archs.

@AussieInSeattle said he was using an insulated wrench that had a little piece that was uncovered. He probably got bit by the arch too.

 

[carbon60]

Anyone found insulated sockets suitable for a DIYer? All I've found are the expensive pro-level kits.

 

[HRTKD]

Wrap them in masking tape as needed. Temporary insulation is fine. I'm not going to buy dedicated sockets just for working around my batteries.

 

[carbon60]

Wrap them in masking tape as needed. Temporary insulation is fine. I'm not going to buy dedicated sockets just for working around my batteries.

Yeah, that’s wise. I figured I’d use them whenever I had my torso jammed into some hole shared by electrical where it’s hard to maneuver, just to avoid damaging anything. Particularly when working on friends stuff…

 

[ArthurEld]

Electrical tape works good if you don't mind gumming up your tool. Two layers in some spots.
One day I put my wedding ring between a terminal and my BMS and it shocked me. The space between the two was bigger than my ring.
I don't wear my ring anymore.

 

[sduser]

Electrical tape works good if you don't mind gumming up your tool. Two layers in some spots.
One day I put my wedding ring between a terminal and my BMS and it shocked me. The space between the two was bigger than my ring.
I don't wear my ring anymore.

Silicone rings are great for folks that work around electricity.

 

[carbon60]

One day I put my wedding ring between a terminal and my BMS and it shocked me. The space between the two was bigger than my ring.

I'm starting to see a pattern here, maybe it's your body chemistry?

 

[HRTKD]

I'm starting to see a pattern here, maybe it's your body chemistry?

What? A shock through the wedding ring isn't a good way to rev up the romance? Let me show you my shocked face. It's around here somewhere...

 

[timm]

Earlier in the thread, there was mention of placing fuses between the cells of a battery. If one of those internal fuses were to blow, what's the impact on the BMS positive lead?

 

[cinergi]

Earlier in the thread, there was mention of placing fuses between the cells of a battery. If one of those internal fuses were to blow, what's the impact on the BMS positive lead?

Fuses between each cell would be the equivalent of disconnecting any of the BMS leads -- many BMS'es would be destroyed by doing this.

 

[barbixy]

The trouble with some fuses like the MEGAs I'm using to connect two BYD modules is you can't tell if they're blown, and if you have multiple parallel strings you'd never know unless you noticed a capacity drop.

I soldered tiny wires parallel to the fuses to act as a indicator. I did tests and that wire pops at 22 amps.
View attachment 37783

Do we need to worry about this with connecting two 100ah Battleborn batteries? Where would we put the fuse there?

 

[pablo fiasco]

If you do it long enough the terminal will melt off. I didn't say it would be a pretty weld.
Sadly my cell welding experience wasn't caught on film. I shorted 24V with a 1/4 ratchet and socket.
It was worthy of film.

Maybe do it again with cameras rolling. How long do figure it would take to melt a terminal off? I'm sorry, what kind of battery and how big and what voltage were we talking about? I've lost the start of this thread.

 

[ArthurEld]

Maybe do it again with cameras rolling. How long do figure it would take to melt a terminal off? I'm sorry, what kind of battery and how big and what voltage were we talking about? I've lost the start of this thread.

I will do my best to be sure it doesn't happen again. You are welcome to learn from my mistake or make it yourself.

I think most of the aluminum melted and exploded off of the terminal immediately. But that didn't break the connection.
The stud burnt off and disintegrated. The busbar melted. All that still didn't break the connection.
The arch didn't stop until I picked up the ratchet. I don't know what would have happened it I didn't remove the ratchet.
I suspect it would have burned everything possible until there was nothing left to arch to.

I shorted on half of a 48V battery. The stud nuts seized on the cells that were involved in the short.
Since the terminal is destroyed on one cell, I can't use it. The other cells seem to be fine.

So, this lightning bolt from hell only cost me about $100. But it reminded my of the ticking time bomb I have in my garage.
I have to do what I can to reduce the likelihood of this happening again. And it seems like I should try to warn others.
But so far no one wants to hear my warning. They think I'm a party pooper. I'll give up soon.

 

[pablo fiasco]

I will do my best to be sure it doesn't happen again. You are welcome to learn from my mistake or make it yourself.

I think most of the aluminum melted and exploded off of the terminal immediately. But that didn't break the connection.
The stud burnt off and disintegrated. The busbar melted. All that still didn't break the connection.
The arch didn't stop until I picked up the ratchet. I don't know what would have happened it I didn't remove the ratchet.
I suspect it would have burned everything possible until there was nothing left to arch to.

I shorted on half of a 48V battery. The stud nuts seized on the cells that were involved in the short.
Since the terminal is destroyed on one cell, I can't use it. The other cells seem to be fine.

So, this lightning bolt from hell only cost me about $100. But it reminded my of the ticking time bomb I have in my garage.
I have to do what I can to reduce the likelihood of this happening again. And it seems like I should try to warn others.
But so far no one wants to hear my warning. They think I'm a party pooper. I'll give up soon.

How about we crowd fund you a new battery if you do again for the cameras?

 

[DerpsyDoodler]

I will do my best to be sure it doesn't happen again. You are welcome to learn from my mistake or make it yourself.

I think most of the aluminum melted and exploded off of the terminal immediately. But that didn't break the connection.
The stud burnt off and disintegrated. The busbar melted. All that still didn't break the connection.
The arch didn't stop until I picked up the ratchet. I don't know what would have happened it I didn't remove the ratchet.
I suspect it would have burned everything possible until there was nothing left to arch to.

I shorted on half of a 48V battery. The stud nuts seized on the cells that were involved in the short.
Since the terminal is destroyed on one cell, I can't use it. The other cells seem to be fine.

So, this lightning bolt from hell only cost me about $100. But it reminded my of the ticking time bomb I have in my garage.
I have to do what I can to reduce the likelihood of this happening again. And it seems like I should try to warn others.
But so far no one wants to hear my warning. They think I'm a party pooper. I'll give up soon.

I’ve heeded the warning. Don’t stop warning people. Even if 1 person listens, its worth saying.

I didn’t heat the heat shrink, but it’s unnecessary. It serves its purpose.

 

[ArthurEld]

How about we crowd fund you a new battery if you do again for the cameras?

Send me some cells and I'll do it. I'm more worried about it happening when I'm not there to put out the fire.