EVE identifies Grade B cells using new marking Method [Reposting from General]

[Alkaline]

In my RC car days once a lipo fell below 80% it would rapidly fall to like 5% within 10 - 15 cycles. Its not a gradual decline, its a fall off the cliff drop.

 

[curiouscarbon]

In my RC car days once a lipo fell below 80% it would rapidly fall to like 5% within 10 - 15 cycles. Its not a gradual decline, its a fall off the cliff drop.

thank you

 

[justgary]

IIRC, the new EVE specification says discard at 70%, not 80%. Perhaps their long term testing showed more life.

 

[toms]

why 80% of original charge capacity, is my curiosity.

dendrites might have formed?

That’s the usual failure mode. If you use your cells conservatively you will prolong the failure.

 

[Substrate]

From a diy standpoint, what is the warranty on your BMS?

Your cells might be fine for 4 years, but then one day a fet in the bms welds itself in a closed condition, and takes a cell down to zero behind your back. You replace it, but that one is 4 years younger.

Or, your power needs have increased, and you buy another system anyway. I suppose you could tack on an addition that is 4 years newer, but now always keeping an eagle eye on the others...

On the road to a franken-bank when you consider possible failures..

 

[RandyP]

From a diy standpoint, what is the warranty on your BMS?

Your cells might be fine for 4 years, but then one day a fet in the bms welds itself in a closed condition, and takes a cell down to zero behind your back. You replace it, but that one is 4 years younger.

Or, your power needs have increased, and you buy another system anyway. I suppose you could tack on an addition that is 4 years newer, but now always keeping an eagle eye on the others...

On the road to a franken-bank when you consider possible failures..

Do the FET's always fail (weld themselves together) Closed, or do they sometimes fail Open ?

 

[augiedoggy]

Do the FET's always fail (weld themselves together) Closed, or do they sometimes fail Open ?

Like solid state relays they typically fail closed... typically contacts of any type dont stick and weld themselves to nothing so it only makes sense they would typically stick on. If the failure was catastrophic ive seen the circuit open back up but ive seen most mosfets stick closed.

 

[740GLE]

In my RC car days once a lipo fell below 80% it would rapidly fall to like 5% within 10 - 15 cycles. Its not a gradual decline, its a fall off the cliff drop.

Lipo is the same as Lifepo4?

Kinda apples and oranges, no?

 

[brum]

Nope, different types of cells. LiPo are the 3.7V high current cells. They are usually used for RC models. And usually these are pouch cells packed in 2S-6S packs and rated for high current in the 20C - 40C range. These are the "dangerous" cells.

My first cells were LiPo 3S 2200mAh rated for 20C. The brand was Turnigy. They were used for 8 or 9 years as a power source for DIY camping lamps. Each year they got 10-20 cycles discharged to below critical levels (8.5-9 volts). Last year I got rid of them. They were badly swollen, but still, they were pulling very close to the initial capacity.

 

[RandyP]

Like solid state relays they typically fail closed... typically contacts of any type dont stick and weld themselves to nothing so it only makes sense they would typically stick on. If the failure was catastrophic ive seen the circuit open back up but ive seen most mosfets stick closed.

FET's are not relays. I think they generally fail open, there are no contacts in a FET. I think their semi conducting material burns open.

 

[augiedoggy]

FET's are not relays. I think they generally fail open, there are no contacts in a FET. I think their semi conducting material burns open.

I understand they are not mechanical relays but they are both forms of electric relays/switches. (there are no contacts or moving parts in a solid state relay either)

As a field engineer I can think of a particular board in a particular machine ive been servicing for years that has a tendency to have any one of 6 small mosfets used to control heaters and maintain printhead plate heaters on an industrial printer fail. Its so common I replace the mosfets myself now with tweezers and a magnifying glass. When those relays fail they visibly to the naked eye and sometimes they cause the heater to stay on causing an overtemp erro and sometimes the heater doesnt come on but more often than not the heater sticks on. ive seen other larger mosfets fail open or closed as well while repairing flat screen tvs as a hobby.

I also own a small brewpub and I use about 30 larger SSRs in the control panels I built to mainly control heaters and pumps of the electric brewery.. While failure is rare they also typically fail in the "on" position. the cheaper generic "fotek" brand SSRs are natorious for this and if you google it you will see what I mean.

heres some good data on mosfets

Difference between SSR and Power MOS FET | FAQ | Singapore | Omron IA

https://www.mouser.com/pdfdocs/MosfetE-book.pdf

 

[Bud Martin]

I replaced lots of shorted out power MOSFET's, the only time it is measured as open circuit is when the die is blown into pieces.

How and when MOSFETs blow up - Power Electronic Tips

www.powerelectronictips.com

 

[augiedoggy]

I replaced lots of shorted out power MOSFET's, the only time it is measured as open circuit is when the die is blown into pieces.

How and when MOSFETs blow up - Power Electronic Tips

www.powerelectronictips.com

I was second guessing my own memory.. I do think it depends on the mosfet and circuit though. I can think of a certain series of sanyo tvs that had a common mosfet failure that would open the circuit and cause no audio on the tv... I probalby repaired a half dozen or so with that same failure.

 

[Just John]

FET's are not relays. I think they generally fail open, there are no contacts in a FET. I think their semi conducting material burns open.

FETs are semiconductors designed for controlling large amounts of current. The physics of how this is done means they are much more likely to fail as a short.

 

[740GLE]

Nope, different types of cells. LiPo are the 3.7V high current cells. They are usually used for RC models. And usually these are pouch cells packed in 2S-6S packs and rated for high current in the 20C - 40C range. These are the "dangerous" cells.

My first cells were LiPo 3S 2200mAh rated for 20C. The brand was Turnigy. They were used for 8 or 9 years as a power source for DIY camping lamps. Each year they got 10-20 cycles discharged to below critical levels (8.5-9 volts). Last year I got rid of them. They were badly swollen, but still, they were pulling very close to the initial capacity.

So again, how does it apply that if a LiFePo4 cell is at 80% capacity, it is considered trash and capacity will fall off the cliff same as you’re LiPo cells?

I don’t think you can apply LiPo experiences/expectations to LiFePo4 cells.

 

[brum]

I'm just telling what LiPo is. And nowhere I'm telling that LiFePo4 will behave like LiPo.

LiFePo4 is considered safer and with longer life. LiPo cells have shorter life and are more dangerous.

 

[Alkaline]

Lipo is the same as Lifepo4?

Kinda apples and oranges, no?

No lipo is lithium ion polymer it is 3.7 nominal and 4.2v fully charged. It has the highest energy density but also most kaboom potential.

Generally used in phones, thin laptops, and rc planes and cars.

Threy can have discharges of 20-70c so huge energy bursts.

 

[Alkaline]

Check it?️

 

[BiduleOhm]

No lipo is lithium ion polymer it is 3.7 nominal and 4.2v fully charged. It has the highest energy density but also most kaboom potential.

Generally used in phones, thin laptops, and rc planes and cars.

Threy can have discharges of 20-70c so huge energy bursts.

Phones and laptops don't use LiPo batteries, they use NMC Li-ion ones. AFAIK LiPo are only used in the RC world, everything else is either NMC or LFP Li-ion.

 

[toms]

So again, how does it apply that if a LiFePo4 cell is at 80% capacity, it is considered trash and capacity will fall off the cliff same as you’re LiPo cells?

I don’t think you can apply LiPo experiences/expectations to LiFePo4 cells.

How have you been seeing LiFePO4 fail?

My experience is when they are down below 80% of original SOC, you can no longer use their rated discharge current, and they do “fall off a cliff” in a similar fashion to other lithium chemistry.