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

[diugo]

Since the tops come off, you can also measure the individual cell voltage periodically and do a rare manual balance if needed, instead of buying a BMS.

I'm a big believer in statistical matching, simultaneously matching capacity and internal resistance. I would think there would be less chance of excellent matching if four separate cells were purchased. Note also that consecutive serial numbers does not necessarily mean a good match---every cell needs to be independently tested.

[diugo]

Originally Posted by Cotemar

Are these batteries any good for a boat house bank?
Balqon - Advanced Transportation Solution

The same WB part number exists on the Winston Battery website, where the specs are MUCH better. Which means one of three things: either Balqon isn't paying proper attention to keeping current product specs on its website; or Balqon is selling older versions of the product with inferior specs; or Balqon is lowering the specs so that it can survive the 5-year warranty period.

[diugo]

After 135 hours and 282 amp-hours later, my 260Ah bank finally hit bottom at 3am this morning. At such a low average discharge rate---only 2.09 amps---the lower knee was nearly vertical. Battery voltage fell off precipitously, from 12.4 down to 12.0V in just four hours under a load of just one amp. To protect the cells, I had to completely cut power to the RV overnight for six hours, until the sun came up.

I had done a parallel bottom balance one charge cycle earlier, with all cells well within 0.01V---but the spread was over 0.04V this morning, thanks to one high cell, which I drew down resistively before charging. They are now all back within 0.01V, so hopefully they'll stay there during the much gentler normal cycling I'll be doing for now on.

Assuming a capacity loss of 5% for sitting on the shelf for two years, the cells should be able to handle I1=123.5A for t1=2h, according to spec. With this discharge of I2=2.09A over t2=135h, my Peukert exponent comes out to 1.032. YPMV---Your Peukert May Vary.

[deckofficer]

Doug,

I'm done with my balancing of pack #2, it is spot on now. Bank #1 that I deemed good from the start, isn't as tight as #2 is now, so I'm close to done on its discharge. It has run a 3.7 amp load for 42 hours, so 155.4 a-hr and voltage of cells are 3.15 to 3.17, pack is 12.64 volts.

[diugo]

Bob, it'll be interesting to see how well the cells stay balanced across several charge cycles. How low do you plan to take your bank #1? Mine went a bit lower than planned, just over 3.00V/cell, but it was exciting to see the drama unfold---even at 3am.

[deckofficer]

3.00 volts is as low as I would go.

On long kayak trips one of the packs will power an Engel freezer that draws less than the 3.7 amps I'm drawing now and it cycles, so to see what could be 160+ a-hr at this draw from a 100 a-hr pack is quite encouraging.

[diugo]

Good, report back with final run time and amp-hours. Right now you're looking at a Peukert of 1.20---but I have a feeling your cells would perform MUCH better than spec, even at 50A. If you're willing to do another discharge test with a higher load (say, 10-20A), we could probably get you a better Peukert.

[deckofficer]

Maine Sail's test at 100+ amps tells that story, he got 425 a-hr out of his bank with cell voltages still around 3.2 volts. These cells are husky little suckers.

[Cotemar]

Originally Posted by diugo

The same WB part number exists on the Winston Battery website, where the specs are MUCH better. Which means one of three things: either Balqon isn't paying proper attention to keeping current product specs on its website; or Balqon is selling older versions of the product with inferior specs; or Balqon is lowering the specs so that it can survive the 5-year warranty period.

Yes, much better spec. at the Winston Battery website.
Balgon must just be their distributor.

Winston Battery Limited

[diugo]

> Maine Sail's test at 100+ amps tells that story, he got 425 a-hr out of his bank with cell voltages still around 3.2 volts

Right, but comparing your three-year-old 100Ah to his nearly-new 400Ah is apples and oranges. IIRC he also stopped his discharge test prematurely, making it useless for Peukert calculation purposes.

Since no two banks have the same internal resistance and capacity, everyone's bank will have a different Peukert exponent. With Peukert known, you can accurately predict run time under any load.

[NahanniV]

Just to refresh your memory of MaineSails test:

Originally Posted by Maine Sail

Holy COW!!!!!! I just completed my capacity testing and all I can say is WOW!!

She flew past 400Ah's like it was nothing. The load on the bank started at around 102A +/- and ended at 106A +/-. I ran the 100A+ load for over 4 hours straight and the pack voltage only bottomed out at 11.8V +/-. The lowest cell, about 0.01 difference than the others, only hit 2.93V.. The BMS board was not even close to alarms or LVC's..

I programmed the Victron BMV-602 battery monitor for a Peukert of 1.0 as Winston/Balquon said to. I then applied a 100A +/- load and simply counted the Ah's removed with the CE or consumed energy screen on the battery monitor..

This shot was taken as she passed the 400Ah mark.


This is where the Ah's were when the shot was taken.



I've worked on a LOT of boats and a LOT of battery systems but never, ever seen anything like this. This bank will have a very, very easy life on our boat compared to what I just did to it.........

I stopped the test at 425Ah's. Based on voltage it could have gone longer and produced more capacity. For "Clearance" cells that I paid $1032.00 for, less than Lifeline or Odyssey AGM's I am pretty impressed.

I also made a video to show the process that I will try to get uploaded.. I will likely never draw the bank this low again but boy was it impressive to watch....

BTW that $210.00 bank of "Wal*Mart batteries currently on our boat just ended its SIXTH year. They still test at over 90% of new Ah capacity and still exceed CCA and MCA with both the Midtronics and Argus analyzers.

How long do you think the LiFePo4's will last? I don't really care, as it is more for the education and experience, but I'd have to guess the way I will care for the bank I should easily exceed the Wal*Mart bank....

By then I'll be onto the next great technology, just because... The Wal*Mart bank will easily go another year or two if I wanted and most people would have never even approached three years. It's all how you care for stuff......

[deckofficer]

This is my last cycle before use. I will post the amount of nm I get out of the kayak, it looks like probably 40 nm per pack without solar.

[ColdEH]

Nobody touched on this as yet , or maybe I missed it . But if these batterries are good for 2000 cycles at 80% discharge , would you get more cycles from them if you only used them to 50% discharge ? Hmmmmm

Regards

One other thing , somebody should make a 8 cell logger/monitor/alam that is bigger, and could be mounted at a chart table on a boat .

[Talbot]

I see the advantages of the Lithium batteries, and have set up my system in my catamaran so that I can re-program my mains/generator invertor/charger, and my solar controller to the appropriate bulk and float charge.

However, I am confused by a few of the posts

1. It appears that people are using normal engine alternator regulation - or is there a smart voltage regulator that will drive two alternators and allow the correct charge rate for lithium - like a variation of amplepower's Smart regulator and dual alternator controller?

2. With an invertor/charger (victron) able to draw up to 200amps, the need for an ability to shut of the charge and the discharge with a decent relay seems like a given??

3. with all the equipment (alternator/generator/mains/solar) set up for lithium, it makes sense to convert to lithium for engine start as well. However, my single engine start battery is 1000 cca. I have looked and cannot find any lithium cells that seem be be suitable as engine start???

4. BMS and data logging seems like an essential for a bumbling idiot like me, and also some form of power available from battery display, yet I dont see any real discussion on the optimum equipment.

Help please.

[NahanniV]

Better than advertised !

Just finished my load test:

411AHA over 20h16m
Lowest cell: 3.09V
Maximum cell difference: 50mV
Lowest pack voltage: 12.41V

Recorded the whole test (see attached).

Don't know what was causing the noise on one of the inputs; Might have been my furnace or washer/dryer or perhaps just noise from the inverter I was using for a load. The monitor is hooked up with a 5pin flat trailer connector and four of the wires are a ribbon cable with the 5th one loose. The 5th wire was the problem. Any thoughts on that would be appreciated.

I had three 120VAC lights attached to the inverter for the first 5 hours, but turned off one 60W one after that since my 400W inverter was heating up and I was trying to shoot for 400AHA in 20H.

I'm afraid to post a pic of my test setup lest the UL or CSA police shutdown my workshop.

It still looks to me like I have one cell that has about twice the internal resistance of the others.

As far as I can tell these are 39 month old cells, I think that somehow MaineSail got much newer ones even though I ordered mine after him; Seems like something fishy there unless Balquon has a backwards stock rotation policy.