Lifepo4's 1000 cycles claim a load of rubbish?

[kazbluesky]

Hi, I just read that the 1000 cycles on a lifepo4 claim was rubbish because of the way the cell balancing activates the cycles (uses up the cycles) every time it balances. Can anybody confirm this? If it is true can I just stop charging when the battery is charged but before it balances and just balance it now and again? Or is this theory all bollocks?

 

[Ypedal]

I honestly don't think anyone knows for 100% sure.. fact.. etc.. it's all relative to various factors...

Personally, for me the cycle life claims are meaningless, i will never.. EVER get to 1000 cycles within 5 years.. and by this time there will be newer and greater things lol...

but anytime you are charging or discharging, the chemical reaction within the cells is happening, so ballanching the pack with the BMS draining at a few mah's is such a low rate that the cycle count equivalent at this rate is pretty meaningless imo.. Still.. i run bms-free on most of my packs.. ymmv

 

[NickF23]

Hi, I just read that the 1000 cycles on a lifepo4 claim was rubbish because of the way the cell balancing activates the cycles (uses up the cycles) every time it balances. Can anybody confirm this?

where did you read it?

If it is true can I just stop charging when the battery is charged but before it balances and just balance it now and again?

Bad idea as you risk overdischarging a less than fully charged cell.

Or is this theory all bollocks?

Yes

Personally, for me the cycle life claims are meaningless, i will never.. EVER get to 1000 cycles within 5 years.. and by this time there will be newer and greater things lol...

Same as. My nimh pack is nearly 3 years old and still performs the same as new. I keep trying to think of ways to make it die so I can get some new lifepo4 but It just keeps on surviving

 

[dogman dan]

A bms that has too high a voltage to start balancing might overcharge a cell, but one that meets the factory specs should not harm the battery. There has been some smack talked about shelf life, 5 years, 10 years, who cares? Ride your bike and you'll hit 1000 cycles in 3 or 4 years. And you'll want the newer, better one in 2 anyway.

I do think that if you have a good pack, and don't discharge to cutout, you can get by with a lot less balancing than most people think. But if you develop a runt cell, or ride to deep discharge, you might need it every charge.

The ideal set up might be like the prius packs, set them up so that the balancing happens at a lower voltage, and never charge to 100%, or discharge below 30%. You carry a lot of battery you don't really use that way, but the cells like it and last a long long time.

 

[ElectricEd]

I'm on track to be doing more than 400 cycles per year. 2 per day x 4 days a week x 50 weeks per year. There'll be the occassional 5 day week and weekend ride too.
Since installing the new style 408 and Cycle Analyst it's done 118 cycles for 3167 Km with a total of 800AH delivered.
The battery was not cycled in properly and has only been able to deliver 8AH per charge, so I am monitoring it closely. It had another 10 charges prior to the CA where I didn't limit the current drawn which was probably the cause of it's reduced capacity.
I'll be able to give a report on it's performance each 6 months.

Real world examples beat theoretical prognostications by self-interested manufacturers every time.

 

[dnmun]

keep in mind that the process of storing charge in a nicad pack is different than a lifepo4 pack.

the lifepo4 stores charge when the lithium ions are 'intercalated' in the lifepo4 crystalline matrix, inside the pores of the cathodic granules.

a nicad pack stores charge as electric potential of an electrochemical reaction, just like a lead acid battery.

i think failing to fully charge the lifepo4 because of past ideas about lipo are ill serving the user.

i repeat again, it is best to fully charge the lifepo4 to 3.65-3.7V rather than stopping the charge at 3.5V/cell because the other cells never get a chance to balance.

i think most of these bad BMS, ping battery whining complaints is because the charger does not reach a high enuff voltage to force all the cells into balance and then the pack is ruined on the the first discharge because it was not balanced initially. imho

all the 2k+ cycle numbers are for 70% max degree of discharge. 1k for 80% DOD.

so rule of thumb, #1: big pack, #2: recharge often.

result=long life. save money over having to replace your small pack too soon.

 

[kazbluesky]

Okidoki, thanks

The battery pack is about half the price of my complete bike and Ive decided that I've spent enough on this for the year - now I just want it to work and earn its keep.

I agree though, if it keeps going for a year or 2 I'll probably be wanting an upgraded battery (wether I need it or not ). 2 years from now I recon the whole industry will have changed. Recently I've seen some new Panasonic mountain bikes and foldable bikes here in Japan that look amazing (if I can figure out how to overvault them :lol: )

I read about this 1000 cycles subject here:

http://www.ampedbikes.com/forum/viewtopic.php?f=3&t=426

Thanks for the opinions, I'm probably just going to let the battery charger do what it's designed to do and keep my nose out of it's business.

 

[dogman dan]

Yes, chances are, your charger and bms are working well, and the best thing is to leave it to do it's thing and stop worrying about it.

If it acts funny though, then you may want to examine what is happening more for sure.

On the balancing thing, I firmly believe that a good pack, one with a track record for staying in balance, run to lighter depths of discharge, at reasonable c rates, seldom, mabye even never? needs balancing. In this situation, a lighter charge voltage will do no harm, and who knows, might even add even more cycles.

A pack with runt cells, or run to cutoff routinely, or run at high c rates, may need a balancing every cycle. Maybe even a extra light cycle to balance twice. It all just depends on the bike, the rider, the quality of the cells.

All last summer, I had no charger that would kick in the bms to balance my pack. Because of melted motor issues, till fall, I put the bike on the bus to get part way home. So I rode about 100 cycles with a 60% dod and a 44v sla charger. Checking the cells weekly, I never caught the thing out of balance one time. In the fall and winter, now having a 66.5 v charger, I rode to cut out a lot of times in the cold weather. The pack would get a bit out of balance then, but snap out of it in about 2 cycles

Today I will ride my 3000 mile on the battery, and have the 1 year anniversary next week. No cycleanalyst, but I monitor charging kwh, and the kwh that goes back in after a run to cutoff hasn't changed yet at all. I think the main thing on battery lifespan is a well matched system, so I keep harping, get a big one. Get a big one and have too much battery is no problem. Get too small, and you may have big problems. Given the $1000-$3000 invested in an ebike, why try to shave $200 off the most important thing in the system? You'll be happier with a smaller motor and a good battery than with a big motor and a weak battery.

 

[dogman dan]

Just read the post over there, and I hear some fuzzy logic.

"The shelves are full of bad lifepo4" ( because of the bad bms?)

"The only one that lives up to the claims is PING" ( uses the same bms, or at least the same design)

My conclusion is that if the bms fries, like a jimmywu etc , or there is bad cells in there from day 1, like a jimmywu etc. you have a battery for the shelf. The real ping difference is he doesn't force you into a pay pal dispute every time he gets a bad cell in one of his packs that makes it out to the customer. And I think a pack with 60 or so cells is naturaly less prone to a bad connection than one with 150 or so cells.

I just don't see the data that supports the thesis that extra cycles caused by a bms was the problem. Too big a motor for the battery is a frequent problem, especially if the industry standard is a 10 ah pack on a 20 amp controller.

 

[NickF23]

I think this is for SLA but the shape of the curve is constant for most batteries. Small cycles have a small effect on longevity, hence the 5 year life of a car battery despite many thousands of small cycles.

 

[Kurt]

best to fully charge the lifepo4 to 3.65-3.7V rather than stopping the charge at 3.5V/cell because the other cells never get a chance to balance.

I had no charger that would kick in the bms to balance my pack

I seam to be finding this comment a lot. Can some one explain how or why a couple of extra volts on your charging output voltage effects the balancing through the bms.

my understanding is most bms just block the current to the cells that have reached a pre determined full/max voltage lets say 3.75v. Allowing the lower voltage or less charged cells to continue receiving current until there voltage also reaches the pre determined point in this case 3.75v or for a 36v 12 cell pack 45v

So what I am asking is to know what output voltage your charger should be wouldn't you first have to know what the max charge voltage is for your particular MBS? For example what if the bms max charge voltage per cell before balancing would start was set at 3.5v per cell only requiring a 42v charger. All the cell would balance to 3.5v.

I know there is the general rule of thumb on voltage for a fully charged lifpo4 cell and you would assume your bms doesn't start to balance until at least one cell reaches this voltage but can we assume that all bms designs start to balance at the same cell voltage and all require the same voltage charger for balancing to happen.

What would a cell charged to 3.5v be 95% charged ? perhaps some bms are designed end the charge a little earlier and less voltage charger would be required to balance the pack. Some bms might be designed a little the other way and require 3.9 volts a lot would depend on the bms design.

I ask this because I have a feeling my first headway pack/changer and bms might have been designed to balance to a lower voltage and came with a 42v charger. Second headway pack came with 44.8v charger.I could be wrong just something I had been thinking about as most people don't know the specification of there bms other than the people that build there own bms.

Kurt

Kurt.

 

[ElectricEd]

A quite good overview of Lithium batteries in EVs can be found at http://eprints.soton.ac.uk/47951/01/Doerffel_D_thesis.pdf
This is a thesis by Dennis Doerffel from the University of Southampton. It refers to Lithium Ion batteries, but is actually referring to all types of Lithium ion batteries which includes LiFePO4. The info on lithium cells is quite clear and helps to allay up some of the myths that often get propagated by well intentioned but less informed people.

The interesting stuff starts at page 25, but I'd recommend reading the whole 220 page document as it has a heap of great information.

 

[NickF23]

A quite good overview of Lithium batteries in EVs can be found at http://eprints.soton.ac.uk/47951/01/Doerffel_D_thesis.pdf
, but I'd recommend reading the whole 220 page document as it has a heap of great information.

Excellent link. Not easy finding decent sources of information for EV batteries, much of the recieved wisdom and data on what is and isn't possible such as cycle life, aging good charging stratergies is transported info about consumer batteries (for example websites like 'Battery University') which really are not the same at all as they are designed for low cost and a short product lifecycle.