LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[electric1]

Originally Posted by witzgall

No, I do not believe so, but I will check. These shunt only at the top end of charge, or do they shunt anytime when the voltage is X different from the other cells?

The tap is to the wire coming directly from the cells, lead to the main board. it is not directly connected to the cell boards - they are also connected to the main board, but at a different terminal.

Chris

Shunting is only above 3.5V, so there wasn't any. Did you confirm voltage reading with trusted voltmeter at the same tap points where Celllog is connected? Maybe Celllog is misreading the voltages.

[Opie91]

I have been following this tread for a while and just wanted to say thanks to all you trail blazers of this new technology.

I must admit to being skeptical at first. I've done some model rc car stuff with lipo batteries and have seen what happens to them when the are overcharged, its not pretty. That being said, LiFePO4 seems to be a different story and it appears to be the future of marine batteries. After spending some time doing some research they appear to be quite stable, safe, have outstanding capacity and be quite resilient. I think a LiFePO4 bank may be my next bank.

Keep up the good work!!!

[deckofficer]

Stay tuned to this thread Opie91, we will keep you posted. I hope to be the first to use LiFePO4 for a propulsion/inverter bank (if Capt Mike doesn't beat me) larger than the propulsion packs for my electric kayak. 2.6 KW-hr vs 75 KW-hr. The tests I've run my cells through has convinced me Lead is Dead.

[T1 Terry]

Originally Posted by NahanniV

Terry: How old are your cells with "700 plus cycles".

Originally Posted by NahanniV

You seem to know a lot about these cells, do you have any data on maximum calendar life ?
My cells are the older Thundersky LFP circa 2009.

My two battery pack, connected in series parallel at the moment, are 50/50 new and old technology cells, a mix of 3mth old and 3 yr old in parallel. The experiment was to see if there was an issue with mixing the technologies in a house battery application. If there is a problem, I haven't seen it yet, I am at about the average cycle life for lead acid batteries now, every over night discharge is in excess of 280Ah from a 720Ah pack, the pack spends about 50% of it's time below the 60% SOC mark, more than 30% of it's time below the 45% SOC mark, as mentioned before, at least 5 cycles down to below 0% SOC if the AH drawn are deducted from the advertised capacity.
Calendar life as apposed to cycle life, as long as they are treated right, stored for long periods at around 60% SOC with no continuous draw to flatten them, there doesn't seem to be much of a limit, the answer is an unknown.
Actual cycle life staying within the max and min cell voltages of 2.8v and 3.6v and discharge under 0.5C also seems to be a bit of an unknown, none have died yet. The only fatalities appear to be a result of neglect, over voltage charged or discharged to zero volts and held there.
We a have a member of the local RV lithium group that bought some ex scooter 40Ah Thundersky cells, the old LFP technology. Some of the cells only read 0.4v, but he removed the BMS modules and recharged them to 3.6v till they were no longer drawing current. They have been in service as aux fridge batteries when camping and outboard motor batteries for around 18 mths since, every cell recovered and has provided faultless service, they can be killed, but it's not all that easy.

T1 Terry

[T1 Terry]

Originally Posted by witzgall

I tried to "tap" into the wires leading from the batteries to the BMS yesterday for the Celllog 8s, and found that while it would show voltages for each of the cells, the voltages were obviously in great error. For example showing 3.14v for once cell, 3.41 for another, when in fact they were all around 3.3X within 10mv of each other. Any ideas why the values were so off? I am guessing that because I was taping so close to the board, it is measuring the voltage of the board, and not the cell?

PS - remember, I have my cell boards centeralized, not like the current Housepower bms.

Chris

The cell logger uses the positive reading from on cell as the negative reading of the next cell, if something pull the positive low one one cell the reading will be low, but the reading of the next cell will be high, it's a give away that something is wrong and the readings need to be double checked and the cause of the reading being pulled low needs to be determined and rectified.
If the problem cells were side by side, I'd first ceck the connection at the positive cable for the low cell, if that's good and the voltage reading is the
same at that point, disconnect the wire at the BMS board and see if it makes a difference, it may be telling you there is a dodgy BMS board if the cell voltages weren't high enough to have ther resistor shunt active.

T1 Terry

[Lagoon4us]

Why do the suppliers give contrary info on charging levels to what is largely discussed in this thread?
The following is the email i received back regarding ensuring my MPPT suited:-

Hello Frank,


thank you for email.

Our cells and batteries are operating with following :

Cell - 3,65V balancing voltage, 3,95-4V first time charge

Battery - 14,6V balancing voltage, 16V first time charge

Balancing voltage may be 3,65-3,75V (14,6V - 15V).

I believe your MPPT is fine for the battery.


Best regards

Pavel Radomersky
Export department

i4wifi a.s.
Prumyslova 11/1472
102 00 Praha 10
Czech Republic

[hellosailor]

And today, Winston and the LiFePO4 industry all miss another major sales and PR opportunity:

-----------------------------------------
Airbus Abandons Plan to Use Controversial Batteries in New Jet By NICOLA CLARK

Published: February 15, 2013 NEW YORK TIMES

PARIS — Faced with a potentially prolonged investigation into what caused batteries on two Boeing 787 Dreamliner jets to catch fire or emit smoke last month, Boeing’s European rival, Airbus, said Friday that it had abandoned plans to use the same battery technology [in favor of Nickel Cadmium!] on its forthcoming wide-body jet, the A350-XWB. ....
-----------------------------------------




Apparently Airbus wants nothing to do with lithium-anything, which may speak to confusion and reputation more than product. Still, that speaks to the image the whole industry has, and needs to address.

[goboatingnow]

Actually I beleive this was just Airbus doing a quick market reaction rethink rather then any evaluation on technical merits.

Dave

[hellosailor]

Yes, and considering what it costs Boeing eveyr minute those Dreamliners are on the ground and they have to pay damages for airlines who aren't flying them...It boggles my wee little mind that Boeing keeps saying they're going to fix this. Instead of just grabbing something else off the shelf. Safer, heavier, whatever, something that would put the planes in the air again. Apparently the FAA bars to this are worth the hundreds of millions in damage payments?

There's still a HUGE opportunity being lost, and one has to ask why no LiFePo4 maker has been smart enough to hold a press conference and say "XYZ Co. Offers Boeing a Safe Battery Alternative!"

They'd rather squabble about who has the sole worthwhile patents?

[goboatingnow]

one of the problems of course is that LFP is not a drop in replacement for LiCO. I know this to my chargrin in my most recent design project. big difference betwwen 3.2 nominal and 3.7 cells

dave

[Lagoon4us]

Aviation and medical instruments take years to apply any item, no matter how good, let alone new technology and have legal insurable acceptance in the market, the ramifications calculable and refused by an actuary until totally safe.

How the overheating has occurred must be by outside influence or bad QA both unusual to say the least.

[hellosailor]

Oh heck, the overheating is no mystery. Every airline knows, they overheated because the circuit was resonant to cell phone frequencies, and some passenger turned on their damned cell phone once too often, too close to the battery.

Or maybe, it was terrorists, training signal mirrors and laser pointers on the battery area of the plane. Yeah, we could blame it on them.

Or, leakage from the weather radar reflecting back and focusing down some strut.

No doubt it will come down to something equally esoteric and mundane, one of those "You're never going to believe this" moments like Grace Hopper's team actually finding a moth in the computer.

I kinda feel like Ricky Ricardo waiting to hear how Lucy gonna 'splain this.<G> Considering the early history of many aircraft that folks have considered 'old reliable' for many many years, this is a small glitch. And apparently a very clever one.



Dave-
" LFP is not a drop in replacement for LiCO" and neither one would give them the convenient nominal 36 volts for an aircraft. But the odds are, some engineer can take 11-12 of the lower voltage cells and tweak some regulation to get a working alternative to a "37" volt 10-cell pack. That's what engineering is all about, right?

[bill good]

Re Boeing battery. The materials used within the battery case appears not suitable to keep safely spaced any cell which failed plus missed the condition where other than planned high current paths could develop & cause other cells to be able to pass destructive high current. The metal battery case, metal cell case & earthed via large high current straps & maybe shielded cable to the cell BMS unit? All normal in aircraft installation for RFI/EMI. The disconnect protection would have had to be designed at the neg & pos to have prevent this melt down. The internal materials used looked as if it would melt at temps well under the 600 degs C that would have developed & would have added to the mess. This double failure of the Boeing battery is still under investigation a month after the event & the chain reaction was due more to how the battery was made & not the type of chem used IMO. LIFEPO4 could have produced as much current & heat if the cells were made in the same way. I can't see the same internal current disconnect protection in prismatic cells as in the cylinder cell. We might want to start a thread to cover the Safety use of these cells as there has been at least one fire on a boat resulting in a total loss. Murphy lives on.
Regards

[goboatingnow]

That's what engineering is all about, right?

Q: What is the definition of an engineer?
A: Someone who solves a problem you didn't know you had in a way you don't understand.

Q: When does a person decide to become an engineer?
A: When he realizes he doesn't have the charisma to be an undertaker.

Q: How can you tell an extroverted engineer?
A: When he talks to you, he looks at your shoes instead of his own.

Q: Why did the engineers cross the road?
A: Because they looked in the file and that's what they did last year.

Q: How do you drive an engineer completely insane?
A: Tie him to a chair, stand in front of him, and fold up a road map the wrong way.

[Adamante]

Originally Posted by bill good

... as there has been at least one fire on a boat resulting in a total loss.
Regards

Which boat?