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

[T1 Terry]

Originally Posted by OceanPlanet

Alarms only work if someone is there to hear them. Leave the lights on when off the boat for a long period, and....

You must be talking about LVC or HVC to prevent over or undercharge?

The Junsi cell loggers have an alarm port that can be connected through a boosting circuit and relay to drive a solid state relay to cut either charging or load circuits, $28 for a logging unit and $14 for a non logging unit. The cell balancing is not an issue with only 4 cells and adds a point for major failure potential.
All batteries require some form of BMS, generally it's the operator who is the monitor but simple LVC and HVC at the cell level can provide a safety net for an inattentive operator.
I can see your market for fit and forget units and good luck to you for establishing it and servicing it well. I'm just trying to show there are alternatives to the higher cost fully automated systems for the DIY types that do work and are not very expensive.
A 24v system does require more attention, still doesn't need automated cell balancing but definitely needs alarms and if possible shut off relays for the LVC and HVC, the Junsi cell loggers do 8 cells.
There is a member on the DIY electric vehicle forum who has developed a circuit board for 4 Junsi loggers to plug in so 32 cells or 96v systems can be protected and the boards can be linked to build even higher voltage systems. Way over the top for basic house battery systems but someone who was looking at combining electric propulsion with their house battery system it could be a very affordable option.
A lot of the electric vehicle people have gone away from automated cell balancing, none of he major EV manufacturers do it either.

T1 Terry

[Overlord]

Hi Terry
About 3 months ago I installed 12 hi power 200ah batteries into my boat as my house bank. I am using Dimitri's BMS.when I installed them I tried balancing them but it was a bit of a bugger trying to short out a super cell so as the others could catch up , then as another super cell was getting to the point where it was about to send a signal to my charger that it was full , quickly switching my coil of shorting wire to another super cell. Eventually I gave up. The problem I now have is that 3 of the 4 super cells reach full charge 3.6v and the fourth one only gets to 3.39v. How is this affecting my bank as a whole? How can I balance them effectively and because I have been using them this way for the past 3 months , will I have caused any damage? Is it possible that I have a bad cell ? If so how can I find the offending cell? My Hi-Power cells have those large , round lugs so I used aluminum strips about 3mm thick and 40 mm wide to join my cells. I coated the aluminum with a wax type coating. I have three 240w solar panels feeding them and a genset with 100ah charger for the dark days. So far I have hardly used the genset. I run a washing machine , water maker and all the regular appliances on a 47ft catamaran with 5 people living aboard.

[CharlieJ]

A technical point: Al bar stock is not the best choice for your inter-cell connections. The conductivity of Al ranges from 65% the conductivity of copper for pure Al to < 30% of the conductivity of copper for some of the alloys.

Ref: Eddy Current Technology Incorporated Resistivity of Metals

My recommendation is to change your inter-connections to copper bar stock cut from the same piece and to the same length to reduce any inter-cell resistance differences.

Charlie

[senormechanico]

Chris,
I have one 200 ah bank and Dimitri's BMS in my Dragonfly.

For initial balancing, I used a 12 volt car headlight for the individual cell load.
With a multimeter attached, it didn't take long to get the cells close enough for the BMS to finish off the equalizing.

[T1 Terry]

The initial balancing can be a bit like herding cats but fortunately you don't need to do it very often. Possibly a few times during the initial bedding in period but after around 3 mths of use they start to self balance each time they come to full charge voltage and then the load pulls the cells back down.
As far as one cell being a lower voltage than the others, apart from reducing the total capacity in Ah of the pack because that cell is not full, it will have no detrimental effect on the cell or over all battery pack at all. What will have a detrimental effect on the cells is charging them to 3.6v till the current stops flowing. If you are charging at high amps, 0.5C or better and stop as soon as the cell reaches 3.6v then that's fine but using a solar regulator that will tapper the current yet hold the voltage at a constant 3.6v (constant voltage charging) will damage the cell by overheating the electrolyte. Stopping at 3.5v is far safer.
How to balance the one cell that's lagging behind? Lots of methods, a DC output WallWart (those power adaptors for phones etc that plug in a power point) The output voltage of the WallWart isn't that critical but around 5V is easiest to work with. Determine the polarity and connect it across the low cell, usually these things are 0.5 amp or 1 amp so things don't happen suddenly but if you check the cell voltage every so often and have an over voltage alarm set at 3.6v the cell will slowly come up to meet the others.
If you don't have the patients of a saint one of the hobby chargers are a heap quicker. This one from Hobby King is under $20 http://http://www.hobbyking.com/hobbyking/store/__11668__HobbyKing_Variable_6S_50W_5A_Balancer_Cha rger_w_accessories.html or any from this page http://http://www.hobbyking.com/hobbyking/store/__216__408__Battery_Chargers_Acc_-Battery_Chargers.html just read through the user comments and find one that has a good rap. I have an I Max 6Sac and a Hobby King 8se that I’ve used and the I Max is probably better at maintaining a constant voltage without creeping but there isn’t much in it between them. Simply connect the supply leads across the 12v terminals of the battery pack and use that to lift the voltage of the low cell, sort of a load on the high cells and charge on the low one at the same time. The chargers can be press button programmed to a large variety of finished voltages and nom. voltages so one, two or three cells can be charged to bring their voltage up for a top balance. Some of the chargers can put out 7 amps or higher for a single cell charge but I've found even on a 200Ah cell 2 amps brings the cell voltage up within an hr max but the initial balance charge could take longer.
As far as the bus bars between the cells, always copper or copper braided cable and they need to be flexible, the ones I use (because they came with the cells) are a piece of copper 25mm wide, about 0.5mm thick with a hump bent into the middle to allow a bit of movement. Unless you have a piece of electrical equipment that is going to draw more than 100 amps from each cell that's about all you need, double them up if you need more current capabilities. I put a piece of heat shrink over the hump part to protect from accidental short circuits. EV works in Western Australia sell braided straps that are suitable for electric vehicle currents, nice looking stuff but the freight costs may be a killer. They are made in China just like everything else so possibly some of the battery sellers in the US have discovered them and stock them now, I think Jack Rickard from EVTV was saying he was going to import his own so maybe even contacting him might give some leads to a supplier. Always use a corrosion resisting compound like Alminox and lightly sand the contact faces to remove any oxide build up, you are looking for shiny metal to put the anticorrosion compound on.

No my turn for a question, tell me more about Dimitri's BMS, what does it sense and control, how much and where do you buy them?

T1 Terry

[Surf City]

Terry,

I am just about to purchase new batteries for our boat and was wondering if you have heard of new info on any lithium batteries coming out? The Sinopoly batteries are suppose to be smaller and lighter but having trouble finding a source in the US.

Thank You,

Wil

[senormechanico]

T1 Terry,
Go here:

MiniBMS

[sytaniwha]

Hi all,

I agree with everything that Terry has written regarding the charging.

As I've written before, I don't think individual cell BMS is needed for a house bank, given the low cell count, charging rates, and discharge rates. BMS control was developed for the EV market where the batteries have many cells in series and parallel, and both charge and discharge rates are very high. We come no-where near to any of those conditions.

In general, our pack is still working to our expectations. We've actually been away from the boat for almost 3 months now, without it being connected to any power supply, so it'll be interesting to see what has happened when we're next there in a few weeks. Based on previous experience, the battery will still be at the same state of charge (within measureable tolerances), and all will be fine.

We have had a problem with our new alternator regulator not putting much charge into the cells, but I haven't trouble-shooted that fully yet, and I suspect it's a regulator installation issue, and isn't related at all to the cells (this is backed up by the fact that the shore power charger works very well with them).

On the initial balancing: I had one cell that was charged higher than the others, and it took a while to bring it into the same charge range. I used a high powered (160W) resistor and connected it to the cell using car jump leads. It pulls out up to 60A, so gets the SOC down very quickly (we have 400Ahr cells), but you have to pull the voltage down below the desired voltage because the high current flow understates the cell voltage. (But it's really quick - about 10 min.s does the job). I found that I needed to play with the cell over about 5 cycles to get it into line.

I've said it before, but I'll repeat it: I think that every yacht should have low-voltage and high-voltage cutoff devices on at least the whole battery pack. That's simply because EVERY battery chemistry can be damaged by significant over-discharge and over-charge situations, and I agree with OceanPlanet that even the most diligent of us sometimes forget. But, I agree with Terry that the rates and cell numbers that we use for house banks means that cells don't really get driven out of balance, and in my opinion that means that battery level cutoffs are all that is required, not cell level.

We had high and low voltage cutoff mechanisms on our lead-acid cells, and we've kept them for our LiFePO4 cells. The same devices can be used for both chemistries if their parameters can be changed (which most can these days). We have a Vetus low voltage monitor and cut-off, and our charge devices (alternator regulator & shore charger) are smart and have charge voltage cutoff.

Following discussions on this thread (mostly with Terry), combined with experimentation, I have gradually wound the charge termination voltage down without seeing any decrease in performance. It is now at about 2.4V/cell, and that has to be better for the pack than a higher voltage. Make sure that the 2.4v is measured at the battery, not the alternator/charger.

I do think that many sailors who go to LiFePO4 cells at the moment will want some "safety insurance" because they are a less-known technology, and thus would prefer the "no-see-um, no-touch-em" approach, which OceanPlanet talks about. Most wouldn't want to go near a power resistor clamped onto one cell; in fact, most wouldn't know what it is. And that's ok in my book. So, although a number of us (few or many, who knows) are just fine without a cell-BMS, I don't think we should criticize those who use them. I personally would worry about BMS failure mechanisms as brought up by one post.

Anyway, so far I've seen nothing in our particular implementation of these cells as a house bank which would cause me to change what we've done if I had to do it again - and I'm really glad that we made the move from lead-acid technology.

I hope this helps.

Cheers,
Paul.

[senormechanico]

Although having an electronic bacground, but being a noob to these cell types, I went with the Mini BMS.
After manually getting the balance quite close, I have watched the BMS LED's during charging and the cells seem to be performing perfectly.
I agree with the possibility of a BMS fault unbalancing the cells, but the construction of unit is of high quality with conformal coating etc. so I'm satisfied with my decision.

320 watts solar, Blue Sky MPPT controller with IPN Remote, boat not plugged in and the keel cooled fridge always on. Freezer loafs along at an average temp of 10f. Batteries are never below 95% even with most days overcast around here.
I LOVE these batteries!

[bcn]

(Funny) question in that context for all the applications mentioned:

from where do you power your BMS, or non-BMS monitoring system?
An additional 12V battery? And how is this then monitored, charged and back-upped?

bcn

[senormechanico]

The BMS draws less than 100ma from the bank.
As long as daylight happens, I have a dependable backup.
No sun needed.
In the month and a half I've had my newly built Aerogel insulated fridge installed, I've never had shorepower connected, nor less than 92% battery capacity first thing in the morning (usually around 97%).
We've had mostly cloudy, rainy days during the majority of that time.
Backup is not an issue.

[I.Grind]

A little off topic, but how much power do you think you are saving with the new box? Whats your current consumption?

[senormechanico]

Originally Posted by I.Grind

A little off topic, but how much power do you think you are saving with the new box? Whats your current consumption?

I'll send you a PM.

[s/v Holiday]

Hi All,

Great thread. Convinced me to make the switch to LifePO4.

I have been shopping and need your advice. Is there any hard evidence to the cycle times quoted in the specs from these batteries? I have been told by some companies that they are all the same and the only difference is the color of the pack.

My problem is that they are roughly the same price and Winston claims almost double the life cycles. I have tried looking online and can't find any comparisons.

Also purchasing them seems a bit sketchy as I have to send money to China and then try to arrange my own shipping with no guarantees from the company I am buying from. Anyone buy this way?

Thanks

CJ

[Surf City]

CJ,

I have been looking for a source in the US, I have seen CALB and HiPower for sale on couple EV sites along with the hardware to tie terminals together. Just have not pulled the trigger yet. We are leaving in June and need to get my order together. Would like to get hands on Sinopoly batteries but have not located a source for them.

How many amp hours are you looking into?

Wil