Lifepo4 cells catch fire!

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GregsGarage
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Postby GregsGarage » Thu Jun 11, 2009 11:32 am

Hi Tom,

I don't know if its any consolation, but Team AGNI (aka Stybrook) are leading the practice runs for the ttxgp. http://ttxgp.com/index.php Race day tomorrow.

The Agni site has instructions for using the cell protectors with any charger, look for the section on using the protectors with solar panels. I believe Manzita also have some cell protectors designed to work with their chargers. Check to see if they also give low voltage protection.

No further insight to the fire, but I am working on a battery cycler to do some battery testing. It could even be used to stress some cells and see how they behave. Temp monitoring is a good idea, more important would be some over temp warning and cut off system. I believe this is necessary even with lead acid batteries. Just some simple temp switches is all that is required.
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

Sio
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Postby Sio » Thu Jun 11, 2009 1:18 pm

GregsGarage wrote:First the insurance question. My policy doesn't cover faulty components but will cover damage caused by faulty components. So, since the battery and or charger was the likely cause of the fire they wouldn't be covered. Next most expensive component was the motor, around £650 (ex vat, and since this is on a commercial policy they don't remeberse VAT). Then factor in £500 excess and loss of no claims bonus and claiming really isn't worth it. If I had implemented Peter's digital bms system with remote data logging and could show the fault was a particular cell then I would have a good case for a claim. So keep that in mind when implementing any sort of BMS.

The cells were Lifepo4, not lipo, which are supposed to be even safer than lipo. The manufacturer's claims make it appear that they are 100% safe and impossible to catch fire. I seem to have achieved the impossible! :shock:

A popular topic on various forums is using these cells without a BMS or with a very simple system. I think that this example shows that this is not the case and that if you venture outside the cells performance specification you will have trouble.

I would agree that the charger was at least a contributing factor, but that also some destructive testing of these cells would be a good idea to find out how safe they really are and what conditions will cause a fire.


Sorry to read about this terrible incident.

I am a newbie here and to the whole idea but I admire pioneers.

Many disasters and tragedies have been encountered by people who have gone first for the sake of people who follow.

This probably doesn’t make the situation hurt less but...

Tip of the hat.

Sio.

tomw
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Postby tomw » Sat Jun 13, 2009 1:37 am

Team Agni won! 87 mph!

MindMil2
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Postby MindMil2 » Wed Jun 24, 2009 7:05 am

I have bought an Elcon charger recently. I must say I like it. I only used it on bench test charging environment but it looks promising and still waits to be put into the car together with my BMS. I like it that it is sealed and quality construction. My 144V 16A model is able to put out 20Amps. When charging at 20A it was getting hot but I could easily keep my hand on it. Didn't measure the exact temperature yet but it has automatic cut-off at 85C. If needed couple of external fans could help to dissipate the heat.
I've bought the charger with CAN bus option so I am able to fully control the voltage and current for charging which means that I can be very flexible in charging algorithm parameters when charging. Some things like reducing the current when temperature of cells or charger is rising too high would be useful. It also reports the actual voltage and current which is useful when charging.
It makes a very well integrated charging solution with my BMS and battery modules. More details are in my blog http://hr-ev.blogspot.com/ . In car testing is pending.

GregsGarage
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Possible cause of fire.

Postby GregsGarage » Sat Oct 24, 2009 10:07 pm

I have recently come up with a possible explanation of what may have caused my fire. It started with a discussion on the Thundersky group about bms systems in general and I chimed in so the discussion worked around to my fire. One possibility discussed was that the fire started from my slave board. I initially dismissed this because the load resistor only dissipates 1 watt of power, and even if it shorted on, that is nowhere near enough to cause a fire. But then I started looking at some other cell failures that have been reported and a cell failing with a high internal resistance is fairly common. Peter had one of his cells fail this way and Hipower sent him a replacement under warranty. Failures like this have also been reported with Thundersky and I am sure others as well.

So what effect does a high internal resistance have on a cell under charge? When you connect a charger to a battery the voltage seen across each cell is based on its resistance. If all the cells are of the same resistance then the voltage is equal for all cells. If one cells resistance is higher then it will have more voltage across it, if it goes open circuit then it has full charger voltage across it! :shock:

So lets assume I had a high resistance at one cell, and this could also be caused by a poor connection at the cell so not necessarily a internal cell fault. My setup had the slaves switching off the main power supply to the charger and then switching it back on after the cells voltage had dropped a bit. The idea is that the load resistors on the high cells would bleed off some power and let the rest of the cells catch up. If we look at what might of happened with this setup and a faulty cell, the charger switches on and the voltage across the cell starts to climb. The load resistor gets switched on, and as the voltage climbs further the charger gets switched off, problem is when you "pull the plug" on many electronic devices the internal capacitors keep them going briefly. Add to this the fact that the charger when it was switched on had to figure out the state of charge of the pack. The charge put out a brief 10amp pulse when first switched on. These 2 factors could have caused a voltage spike on the faulty cell that burned out the picaxe controller.

Now we have lost bms function on our faulty cell and possible the load resistor has shorted on. Now if we use ohms law we find that 7 volts across a 15 ohm resistor is around 3 watts of power. Any voltage above that and the resistor is overloaded and becomes a fire hazard. From past experience I have seen a front bumper that caught fire on a car, the cause was traced to a wiring fault that connected the exterior temp sensor straight to the 12 volt battery. Since a temp sensor is just a resistor, it clearly showed what happens if you apply too much voltage to a resistor.

So that is one possible cause of my fire, and one that I think is quite probable. Once the fire got started the cells probably "fueled" it and made it worse.

Hi-power have made good on their promise to supply me a pack at a good price, so I have ordered 140x 40ah cells for my newest project, a Matiz conversion which I will detail in the conversions section. Regarding my pack and what lessons I have learned from the fire they are as follows;
    Slaves will be mounted away from cells in separate enclosure with 1 amp fuses on each cell connection.

    I am going to use Peters full digital bms, and am working on slave pcb layout.

    No scrimping on a charger, a Zivan with the proper charge profile.

    Temp sensors for each battery box.

    Cells will be clamped as per Thunderskys recommendation. Hipower says this isn't required as long as cells are operated within their specs, but I think this could help if there is a problem.

    A suggestion of Cedric's, use a timer at the mains and set it to switch off when the pack should be charged. Sometimes the simple ideas are the best! :D
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

ChopperMan
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Postby ChopperMan » Sat Oct 24, 2009 11:36 pm

Hi Greg,

Speak to Gareth at ElectroFit Zapi when you order your NG3 and ask for a LiFeBATT compatible version. This will be fitted with a suitable LiFePO4 profile that will slow the current down towards the terminal voltage and turn itself off after 40 minutes in C V mode at the terminal voltage.

It also has a remote shutdown feature as standard, a pair of contacts, which when they go open circuit shut down the charger safely, we use them connected to our battery protection module in the event of an over voltage or over temperature fault.

Cheers,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).
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LiFeBATT UK Distributor
www.lifebatt.co.uk

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retepsnikrep
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Postby retepsnikrep » Sun Oct 25, 2009 5:25 am

Greg

I concur with Ian on the charger after we had a long chat in person the other day discussing another project. I need to get myself an updated profile chip for my Zivan. Ian can you help with this or shall I just ring them?

The current Master board controls the Charger mains relay and the voltage pot.

140 * 40ah = about 15kwh pack does it not?

That's quite a high voltage 450V or so or are you going to use them in series/parallel?

If you paralell them at the cell level you only need one bms slave per group of parallel cells.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

ChopperMan
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Postby ChopperMan » Sun Oct 25, 2009 10:57 am

Hi Pete, Gareth should be able to help you. I understand the EPROM's are quite expensive, it might cost £25 including postage. But it's money well spent and a 20 minute job to fit.

Cheers,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).

_______________________________________

LiFeBATT UK Distributor

www.lifebatt.co.uk

GregsGarage
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Postby GregsGarage » Sun Oct 25, 2009 2:19 pm

Thanks for the tip Ian, I already have a NG3 from my Volvo but it is setup for gel cells, I will contact them about getting a new eeprom.

Peter, the pack is going to be configured 45s3p which will give me 144v, 120ah, 17kwh. I have some spare cells, 4 of which will be used for the 12v battery.

Greg
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

wattsin
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Re: Lifepo4 cells catch fire!

Postby wattsin » Sat May 19, 2012 12:10 pm

G'Day Guys. I know this is an old thread but I wonder if any other failures have come to light. I am looking to find anywhere in the world where a cell has resulted in a fire/failure when NOT being charged or NOT caused by wiring failures.

Regards Bill


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