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

[JohnInBKK]

"Accurate" SoC Measurement

Quantum Magnetism (Q-Mag) from Cadex seems most promising. This was mentioned in another thread by "Conachir", but ignored.

I have only just come across this method and have yet to identify any commercial BMS' using the technology.

Here are a few links:

Battery Fuel Gauge: Factual or Fallacy?

Measuring State-of-charge - Battery University

BTW - this is an excellent thread and I will be quizzing the pros (Maine Sail and the like) later this year when I build a 700AH - 1000AH LiFePO4/Solar system!

Thanks to all.

[sparrowhawk1]

I've been living" off grid" for 20 years and this is the first time I've heard of using magnetism to determine SOC. Keep up the good work everyone.

[Maine Sail]

Originally Posted by JohnInBKK

"Accurate" SoC Measurement

Quantum Magnetism (Q-Mag) from Cadex seems most promising. This was mentioned in another thread by "Conachir", but ignored.

I have only just come across this method and have yet to identify any commercial BMS' using the technology.

Here are a few links:

Battery Fuel Gauge: Factual or Fallacy?

Measuring State-of-charge - Battery University

BTW - this is an excellent thread and I will be quizzing the pros (Maine Sail and the like) later this year when I build a 700AH - 1000AH LiFePO4/Solar system!

Thanks to all.

I own and have tested perhaps one of the best accepted voltage SOC gauges on the market, the Smart Gauge. EnerSys, the makers of Odyssey TPPL batteries has in-house tested this product and loves it.

Sadly it FAILS to track LiFePO4 accurately.. I mean falls flat on its face. The voltage changes are so small that even after 15+ cycles, two to 100% DOD and back to full, the rest to 80% DOD and back to full, it is still off by more than 25%... The Smart Gauge does work well on lead acid but falls flat on its face when presented with the extremely flat curves of Li....

I would LOVE to see a voltage only method for determining SOC from LiFePO4 but I have serious doubts about how accurate it can be. The new CALB CA series cells have an even flatter curve.....

The Cadex method sounds interesting but only time will tell... It also seems as if they have no product yet that would fit our needs.

A simple Ah counter like the Victron BMV-600 runs $155.00 to $200.00 and works remarkably well..

[AlamedaEyes]

Great post for someone considering a Lithium install. The discussion re series and parallel is also interesting. Connecting the parallel buss in the centers to equalize buss resistance made me consider another wiring mode. If you look at the 2nd drawing. Starting at the plus side of the bank. If you take the first series wire to the left and move it to the top of the drawing then leave the second one in it's current position. The third series wire would go back to the top of the drawing. I think that makes it so that each cell has to force its electrons through exactly the same length of copper. Each cell will have a different proportion of plus and minus buss, but exactly the same length of total buss.

Does this address the buss resistance problem or are we talking resistance of the connection of the buss bar to the actual cell.

Originally Posted by sytaniwha

Sorry if my description led to decreased clarity, rather than increased.

I've attached a pdf of some hand-drawn diagrams that hopefully help clarify what I meant. I've used blocks rathr than circuit diagram symbols to try to make the representation of the physical cells as clear as possible.

Comments on each configuration in the drawing are:

1) This is the "Pacific High" configuration, with 6 lead-acid equivalent "batteries" of 4 parallel cells, connected in series to provide the wanted capacity. As Roetter and others have commented, it isn't ideal from an electrical viewpoint because with 12V across each series group, there is a greater chance of individual cells becoming un-balanced. It was probably done this way because it allows drop-in lead acid replacement modules, which can be a less intimidating way to change technologies for some people.

2) This is a representation of the photo of the yellow cells which Roetter posted just after the "Pacific High" post. Because the cells are paralleled first, each group of 4 parallel cells is held to the same voltage on charge and discharge, which is why it's preferable to example 1). However, with the connections between the parallel sets being on the bottom cells, the other cells in each set have higher resistance due to the extra links they go through (e.g. the top cells have 3 extra links of resistance on both the +ve & -ve terminals). This means that the voltage each cell receives under charge is slightly different due to the higher resistance path. Although probbaly not important in any given cycle if you use good links, over time this can cause some change in cell balance. The ideal is to have identical resistive paths for each cell within a battery.

3) If you just have a single link between each parallel cell set, then this is a better set-up than 2 because it moves the links between sets closer to the physical centre of each set, thus reducing resistance path imbalances.

4) This is the ideal situation, where every cell in each parallel set has the same resistive path. It does take a lot more links, which may be significantly more expensive. You could, of course, have custom copper plates made which each have 8 holes in them and drop over the sets of connectors on adjacent parallel strings to do the same thing. Probably overkill.

5) I would say that this is probably the best compromise, which largely evens up the resistive path, but with fewer links than 4.

I hope this helps clarify what I am trying to say.

Fundamentally I believe that there are 2 points which are important:

1) If you have both parallel and series connections, connect parallel sets in series,
2) Construct your inter-cell links to try to get the same resistive paths between all the cells.

I hope this helps.

Cheers,
Paul.

[gael]

Originally Posted by JohnInBKK

"Accurate" SoC Measurement

Quantum Magnetism (Q-Mag) from Cadex seems most promising. This was mentioned in another thread by "Conachir", but ignored.

I have only just come across this method and have yet to identify any commercial BMS' using the technology.

Here are a few links:

Battery Fuel Gauge: Factual or Fallacy?

Measuring State-of-charge - Battery University

BTW - this is an excellent thread and I will be quizzing the pros (Maine Sail and the like) later this year when I build a 700AH - 1000AH LiFePO4/Solar system!

Thanks to all.

Thanks for fwding these threads. Very interesting in the medic' contexts.
I can understand this is a promessing approach if the total generator internal impedance must be kept low as possible.
Also I have noticed the overall accuracy should be in the range of +/- 5% for Li ion battery and I assume for always a same discharge profile.

For my view, evaluating the House Bank capacity measuring only Volts is just not possible with a flat discharge curve.
Instead adding few milliohms to the bank internal impedance for a current sense ( the big shunt resistor...) is not big deal compared to the full wiring resistance.
For my LiPo banks I'm using the "Coulomb approach" with the Victron monitors.
Compared to a 6digits Amps meters, the Victron current sense is within 2% accurracy. Overall I estimate the bank capacity measurement is better than 10% . But now this figure must be linked to the usage profile (high C , low C discharge ect..)
Well, I'm not sure this clarify something but as the battery capacity is a "fuzzy concept" I feel the simpler is better.
Cheers
Gael

[hellosailor]

New Polymer Could End Battery Fires, Quadruple Efficiency | Autopia | Wired.com

"New Polymer Could End Battery Fires, Quadruple Efficiency"

Another possible game changer.

[gael]

Originally Posted by hellosailor

New Polymer Could End Battery Fires, Quadruple Efficiency | Autopia | Wired.com

"New Polymer Could End Battery Fires, Quadruple Efficiency"

Another possible game changer.

Hopfully scientists are still moving on!
New Polymer Could End Battery Fires, Quadruple Efficiency | Autopia | Wired.com

[CarstenWL]

... hope it is ok to ask another question related to charging LiFePO4 batteries with an hydrogenerator in this thread ...

Watt&Sea has some new hydrogenerators and I am looking to install the Cruising 600 (600 Watts - 48 Amperes in 12 Vcc) on my 41ft cruiser together with 4 Thunder-Sky / Winston 400Ah (WB-LYP400AHA) in parallel.

It seems the only parameter you can program on the converter of the Watt&Sea units is the output 'charging' voltage (just double checking with my supplier).

- To what value should this voltage be programmed?

Infos on the newer Watt&Sea models can be found here:
http://tinyurl.com/plsw2jt
http://tinyurl.com/nwow9aq
http://tinyurl.com/njon97j

More thoughts?Thanks,

Carsten

[Maine Sail]

Originally Posted by CarstenWL

... hope it is ok to ask another question related to charging LiFePO4 batteries with an hydrogenerator in this thread ...

Watt&Sea has some new hydrogenerators and I am looking to install the Cruising 600 (600 Watts - 48 Amperes in 12 Vcc) on my 41ft cruiser together with 4 Thunder-Sky / Winston 400Ah (WB-LYP400AHA) in parallel.

It seems the only parameter you can program on the converter of the Watt&Sea units is the output 'charging' voltage (just double checking with my supplier).

- To what value should this voltage be programmed?

Infos on the newer Watt&Sea models can be found here:
http://tinyurl.com/plsw2jt
http://tinyurl.com/nwow9aq
http://tinyurl.com/njon97j

More thoughts?Thanks,

Carsten

Depends upon where your BMS HVC is set to? What BMS are you using? I personally don't like to see Winston cells charged beyond 14.2V, THERE IS ZERO NEED TO DO SO, but personally I feel 14.0V or lower is even better. IIRC the W&S cruising controller is set for 14.3 & 13.8V... A diode could be used to drop the voltage below 14.3V so it does not interfere with a BMS.

The BMS I use executes HVC at 14.2V so you ideally want to be 0.1V - 0.2V below that to prevent HVC triggers this puts you in the 14.0V range for charging Winstons..

That said if you are driving an AP, loads etc. it is unlikely the W&S would get to absorption voltage. If it does you can simply lift the leg.....

[mitko512]

Hi, I have a question regarding the implementation of OVP when charging from one or more chargers (solar/mains/B2B)

Would it be feasible to implement it by simulating high temperature to a charger with a temperature sensor, or by simulating very high total voltage, both triggered when a cell is high?

Eliminating the standard temperature sensor (except possibly for measuring its characteristics), we would connect the temperature sensor input of the charger via a relay to two resistors that correspond to a low and high temperature (selected to provide normal charging voltage as well as sufficient room for control). The relay could be controlled by the CellLog alarm output so that in case of cell over-voltage we simulate a high temperature to the charger and it brings the charging voltage down. Obviously, it would also be possible to implement a smarter design with a micro-controller that would control the charger's output voltage smoothly via the simulated temperature, based on individual cell voltage.

Similarly, some chargers have separate voltage sense lines and a circuit to completely shut off at, say, 16V (12V system). Connecting the sense line to the battery via a relay that can also be switched to a 16V+ source would provide another way of controlling the charger. Some chargers won't recover automatically after entering this mode, and in any case it would be strictly on/off,but even then it could be used as a secondary protection supplementing the temperature-based one.

Unfortunately, I can't remember any more if I thought of this myself or read it somewhere, possibly even here (but can't find it right now)?

[roetter]

Quick report on my latest Balqon order.

I ordered 8x700Ah cells beginning of March. They shipped about 10 days after order (counting weekends) and arrived about 16 days after the order in Annapolis.

This was my most painless order yet (my 4th order).

[folivier]

Glad your order shipped so quick. Mind telling us how you placed the order?
Who you talked to? Or did it online?
Hopefully they are getting their order system working better now.

[georgec]

Originally Posted by roetter

Quick report on my latest Balqon order.

I ordered 8x700Ah cells beginning of March. They shipped about 10 days after order (counting weekends) and arrived about 16 days after the order in Annapolis.

This was my most painless order yet (my 4th order).

I am glad you received your cells. It seems the only cells they are shipping are what they have in stock. Were your cells new or used? 700AH cells are too tall to fit into my battery compartment so I ordered 8x400AH cells. I ordered them in December to take advantage of their free shipping promotion. Their original delivery estimate was 6 to 8 weeks. 16 weeks and still no batteries. I have checked with them a couple of times and they are still waiting for a delivery from China. Fortunately I am not in a rush for them; at least not yet. Looks like I'll be buying CALB's, but at a much higher price. 8x400AH from Balqon would have been $3520 delivered.

[Jd1]

Since 400 Ah (at $440 each) are not available from Balqon, what is the next best place to order that size of lithium battery from? All I have managed to find are at about $100 premium over the Balqon price

[georgec]

I received a quote from calibpower.com for $500 per 400AH cell with $390 shipping to NJ.