Cell monitoring

[RossW]

presumably the one with all 12 good cells??  Looks like one could almost identify this set within the other one...

Same bank of 24 cells (48V). But 3 identified "weak or suspect" cells removed and replaced with three cells from my now defunct secondary bank. (Yes, it means I'm now having to make do with 500AH until I seal the deal on the new LFP bank)

[offgridQLD]

What about just using a product like this  for $27.....

https://www.hobbyking.com/hobbyking/store/__9282__Cell_Log_Cell_Voltage_Monitor_2_8S_Lipo.html

I have a few of them laying around and have been using them on multiple cell batery projects for years. They have provisions for 8 cells each and can log the data via USB I made up some extension leads for the harness wires to make it a more practical length for larger battery projects , They have a audio alarm for under/over voltage. They can be calibrated and a lot of the setting are user adjustable. Great for a quick visual to of what each cell is doing.

[zoneblue]

We are all wondering how Ross's new lifepos are going too.

[Westbranch]

You do want to make sure you do NOT overcharge a cell like this one was (destructive test)
http://gwl-power.tumblr.com/post/70017866727/test-the-winston-lifepo4-cell-160ah-short-circuit

[RossW]

We are all wondering how Ross's new lifepos are going too.

I'm madly saving up to double them and ditch the rest of my lead-acid entirely.

I'm really pleased with their ability to soak up current, how stiff they are, their multiple-poor-days charging performance is.
They're small, light and tight. In short, I've nothing bad to say about them at all.

[Westbranch]

Ross, have you managed to (really) stress test them yet?

[RossW]

Ross, have you managed to (really) stress test them yet?

Oh boy, you had to ask, didn't you?

19 days ago, my old original inverter @*#& itself at 5:25am.
After operating flawlessly for 10 years and 6 days, it just plain gave up.
Not quite sure of the events however. Piecing what I can back together after the event, the day before we had poor sun, but I thought we'd make it. Daughter had just moved back home after 4 years university, so my guess as to how much power we were going to use may have been a little wide of the mark.

Graphs indicate that some (unknown) additional and non-trivial load applied around 1am, volts started to drop quickly with the cells low SoC, and battery volts got "low" (48V) about 5am. Inverter called for the generator. Genset had run - for exactly 5 minutes. Looks like the inverter had failed to sync, reason unknown. Batteries continued to drop. At (near as I can tell) 43V the inverter shut off and/or died.

43V is about 5V below anything I've ever let them get to. That's down to 2.69V/cell for the LFP.

With a dead inverter/charger, I couldn't even just run the genset to put some charge into them. Was several more hours before I had some sunlight and could divert 100% of that power to the LFP bank.

Managed to get them at least into absorb by that afternoon. A couple of weeks on, and they seem to be behaving exactly the same way they were before the event...

There is no sign of any mechanical issue (bulging) and there was no sign of any significant temperature rise at the time.

[ClassicCrazy]

Here is where the real battery abusers lurk - on the electric bicycle forums - lots of info
http://endless-sphere.com/forums/viewforum.php?f=14

[Westbranch]

CC, can you narrow the search for some disaster in waiting for us, or similar discussion to what we are covering?

tks

[ClassicCrazy]

CC, can you narrow the search for some disaster in waiting for us, or similar discussion to what we are covering?

tks

You asked about stressing out Lithium batteries - here are some stress tests done on various chemistries including LiFePo4
http://youtu.be/dree0rTr1HM

[Westbranch]

Wow, determined, they should call him the destroyer! 

[ClassicCrazy]

His goal was to really test Lithium batteries to find out what happens in real world possibilities  - high heat, over voltage, punctures, etc.  Obviously those were extremes but make you really understand that caution is always advised with such high energy sources .

[fca]

Hi Ross . How does this project boards end up I setting up a new battery bank and I want to add cell monitoring.
Can't find anything ready to buy for leadacid cells . I want exactly what you show, measure single cell voltage and temperature .
Did this work for you, did you sell these boards ?
My goal is to have them connected to board like arduino that than will serve that info by modbus/tcp to my scada app.
Please get in touch .
Regards