Well, there are many lithium fires worldwide.. Except the few that have known cause (like metal debris piercing the pack), much larger number is of "unknown cause". Heat is so intense that it is very hard to tell what actually happened. Some designs do have bad wiring, etc, but some look very good... But.. no fuses. Even Boeing have no idea what the hell is happening.madin88 said:
Samsung 25R/LG 18650HE2/ Sony VTC5 high power 18650 battery
- Thread starter Ebikebert
- Start date
circuit said:
The rules for formula student are avatible online, they are extremely boring. The pack I'm helping on is using single pouch cells of the required capacity, so there may be a special clause for 18650 cells. The whole pack comes in at 16Ah 540V nominal and a tad under 55 kg (of this, 45kg is cells). It should be able to deliver 85kW continously and ~120kW peak. There are high demands to cable isolation, pack relays, isolation barriers, no charging in car and, above all, documentation.
Did I mention this stuff is redicoulusly expencive? The final price of the pack is close to 3 USD pr Wh.
As for cell level fusing. You have a nice thing going with your 18650 kit Circuit. The downside is the cost of laser cutting or stamping these specialized sheets. As I've understood it, Tesla uses ultrasonically welded single conductor to each cell. Basically this lowers production cost and improves safety. I can see the need for fuses in a ~100p big car pack, but does the same apply to a normal ~4p ebike pack?
My opinion is that a properly designed BMS system, with thermal monitoring on all submodules, negates the need for cell-level fusing. You can find the same discussion about fusing batteries "the traditional way". In many cases it is simply a liabillity since it introduces two extra points of failure. Compared to a properly designed overcurrent shutdown system fuses are stone-age-tech.
We're abit off topic here, should we create a new thread? (Very interesting topic)
PS: I wrote this before you updated with Formula rules.
friendly1uk
1 MW
I was looking at the figures for laptop fires on planes. They are very high compared to laptop fires in general. Source's are few, but the big sony recall of millions was based on fewer numbers than we had on planes last year.
My mind goes towards the lower air pressure and how things would gas off more. Also how tiny bubbles within a pack would expand causing movement otherwise not seen. The numbers are impossible to ignore, and it is only air pressure that is any different up there. Anyone know if boeing has had fires on the ground?
My mind goes towards the lower air pressure and how things would gas off more. Also how tiny bubbles within a pack would expand causing movement otherwise not seen. The numbers are impossible to ignore, and it is only air pressure that is any different up there. Anyone know if boeing has had fires on the ground?
Ebikebert
100 W
In my opinion the bigger the pack the more safety needs to be implemented. Back on topic, both of these 18650 batteries will be in stock early in March. I will buy them as soon as the seller Supowerbattery111 has them in stock and do some load testing with them to share some real world results.
Allex
100 MW
Good news Bert! Appreciate the sharing with tests graphs.
Ebikebert
100 W
your welcome my friend, if you have any other questions about these cells i will be happy to help and see if i can get you information. 
Hillhater
100 TW
If you dismantle a Sony laptop pack, you will see a PCB with a bunch of components and connections to each cell, and temperature sensor between the cells.friendly1uk said:
It may not be a BMS but it sure looks like one and I cannot imagine what else it may be.
Allex
100 MW
Every laptop pack have a circuit board
A. Temperature sensors- monitor the battery temperature.
B. Lithium-ion cells- Store energy.
C. Voltage Converter- maintains proper levels of voltage and current.
D. Notebook connector- Used to transfer power between the battery and the notebook.
E. Voltage tap- which monitors the energy capacity of individual cells in the battery pack.
F. Battery charge state monitor- a small computer that handles the whole charging process to make sure the batteries charge as quickly and fully as possible.
A. Temperature sensors- monitor the battery temperature.
B. Lithium-ion cells- Store energy.
C. Voltage Converter- maintains proper levels of voltage and current.
D. Notebook connector- Used to transfer power between the battery and the notebook.
E. Voltage tap- which monitors the energy capacity of individual cells in the battery pack.
F. Battery charge state monitor- a small computer that handles the whole charging process to make sure the batteries charge as quickly and fully as possible.
dgrdan93
10 µW
I'm currently communicating with Supowerbattery111 to build a battery pack using Sony VTC4 cells, but after seeing this datasheet for the Samsung 25R I'm wondering whether its worth the wait for these to become available. Supowerbattery111 has advised me to use the VTC4 over the 25R for high current drain, due to its capability of 30A continuous compared to the 25R's 20A. However, comparing the datasheets for the VTC4 and the 25R, the 25R seems to have slightly less sag even at 20A continuous. With an extra 500mah capacity and probably less $, is there any reason to not go for the Samsung? I initially thought the Sony was the king of the jungle, so can someone point me in the right direction?
ridethelightning
1 MW
- Joined
- Jul 21, 2013
- Messages
- 2,010
im also very interested in the 25R cells.
any info on when they are available?
any info on when they are available?
Hillhater
100 TW
Why dont you PM Ebikebert and ask if he has tested them yet.
..i suspect he has not, or he would have said so .!
..i suspect he has not, or he would have said so .!
ridethelightning
1 MW
- Joined
- Jul 21, 2013
- Messages
- 2,010
looks like the 25Rs will be available in a week or so from supower.
Lillian said she is waiting for them to come through in the post, but i diddnt ask the price yet.
Lillian said she is waiting for them to come through in the post, but i diddnt ask the price yet.
Hillhater
100 TW
Another idea for those thinking of cell level fusing...
(possibly better done by spot welding though )
From here..http://www.youtube.com/jehugarcia
(possibly better done by spot welding though )
From here..http://www.youtube.com/jehugarcia
wow, i like this!
i think soldering the fuse wires will not hurt the battery much, because it requires only to coat a very small area with thin (about 4mm²) and this can be done very fast.
doing so, not much heat will get inside the cell or to the chemistry.
the bad thing about cell level fusing: resistance will rise, but i would accept this due to a more safe battery.
i think soldering the fuse wires will not hurt the battery much, because it requires only to coat a very small area with thin (about 4mm²) and this can be done very fast.
doing so, not much heat will get inside the cell or to the chemistry.
the bad thing about cell level fusing: resistance will rise, but i would accept this due to a more safe battery.
madin88 said:
What I'd like to see is someone testing a batch of fresh cells, soldering the tabs on one half of the group, spot-welding the other. Then measure capacity over a few cycles, IR, etc.
The amount of heat required on the battery itself (for a good solder joint) still doesn't seem like the right thing to do, but that's purely my own speculation. With old and tired laptop cells It's probably not worth stressing over, but what about fresh 25R's?
zener
1 kW
- Joined
- Jan 16, 2014
- Messages
- 353
Soldering on the flat V- side is absolutely a nogo.
Heat is the cycle killer nr.1 thats why ecar manufactures put cooling systems to the battery pack.
If you park your ecar in the hot burning sun the temperature coul'd easy go up to 60*C this reduces useable cycles massive.
Heat is the cycle killer nr.1 thats why ecar manufactures put cooling systems to the battery pack.
If you park your ecar in the hot burning sun the temperature coul'd easy go up to 60*C this reduces useable cycles massive.
Ebikebert
100 W
Hey guys the batteries will arive and get to supowerbattery111 tommorow. I will purchase the cells tommorow and once i recieve them i will tell you my initial thoughts on the cells. Pricing for the 25R cell is said to be similar to the 24R cells Remember this price includes the free tab welding service which is HUGE in helping to finish building the pack.
Pricing for the 25R cell is said to be similar to the 24R cells Remember this price includes the free tab welding service which is HUGE in helping to finish building the pack.
liveforphysics
100 TW
sardini said:
Ok. I will comment.
I think anytime you're soldering to a cell, you run the risk of locally causing thermal decomposition of the solvent/electrolyte blend, which can give otherwise healthy cells new potentials for failure modes. Though I used to do it myself for many years, I no longer recommend the practice because it's a process that is over-likely to cause cell damage IMHO.
With respect to the individual fused-link interconnect system, I think it's very cool when done right. Tesla does it right and it's a pretty amazing design. The bend in the wire needs to be perfectly curved to avoid stress-risers as the cells inevitably wiggle around. If you use straight pieces of wire, they are going to concentrate stresses and fail joints, the curve is critical for long-term survival.
There is a picture of a Tesla built Rav4 pack on ES somewhere. That is the best fused interconnect system I've seen for 18650's. The best non-fused DIY friendly non-cell-damaging interconnect system I've seen for 18650's is the no-weld, no-solder system using dimpled copper strips. I think it's an excellent pack construction method for round cells, perhaps the best of all the DIY pack build methods we've seen on ES.
Hillhater
100 TW
The one main benefit of using the "fused" cell connection system (done correctly) is that if provided protection against a "cell short" situation where one cell could internally short and if not isolated (by the fuse) would consequently short out the whole parallel string of cells. A major pack failure and potential fire starter.
But, i ask those of you who have worked with these 18650's for some time, what is the real probability of such a cell internal short, or similar local major over-current event ??
But, i ask those of you who have worked with these 18650's for some time, what is the real probability of such a cell internal short, or similar local major over-current event ??
parabellum
1 MW
Only have seen violent external short on makita pack cells (somewhere on the positive -negative separator.) Internal shorts were very peaceful events. :lol:
Hillhater
100 TW
Maybe because there were no parallel cells ??
parabellum
1 MW
Maybe, 2P is not exactly big deal. As end result they just self discharged down to 0V very quickly, was only enough heat to deform the green plastic wrap. What is internal short BTW? What exactly is shorting inside?
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