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

[Lagoon4us]

Originally Posted by diugo

Lagoon4us, my plan is to use my existing Morningstar TS-45 solar charge controller---and its high voltage disconnect feature---to disconnect charging whenever 13.5 volts is reached, and reconnect charging when the bank falls to 13.1. (I will disable all the normal lead acid features, ie absorb, float, equalize, and temperature compensation.)

For cell safety, I'll use a separate cell voltage monitoring circuit to disconnect the battery (via a shunt trip breaker) if any cell goes outside the safe 3.1-3.5 volt range. Plus audible alarms to alert if outside the normal 3.2-3.4.

So you are planning on using a redundant controller to only connect between 13.1 and 13.5 volts, if so we also have the exact unit and it too will be redundant....

If correct it sounds a cheaper option.

[deckofficer]

Originally Posted by Maine Sail

For the price of the 3010EX, below, it is pretty tough to beat and 3X the current output of the 3A model......

They make a 3010EX which is 10A for $149.00

Just ordered, thanks Maine Sail.

[diugo]

Originally Posted by Lagoon4us

So you are planning on using a redundant controller to only connect between 13.1 and 13.5 volts, if so we also have the exact unit and it too will be redundant....

I wouldn't exactly characterize my TS-45 as redundant, as it's the only way I plan to charge my new batteries. I like the fact that it can be programmed with a laptop to work with batteries it was never designed for. Ironically, it may well do a better job of handling the LFPs than it did with the AGMs.

[deckofficer]

I ran the pack much lower this time, 36 hours on a 30 watt load, 1080 w-hr. I only stopped because one cell dropped to 2.81 volts, highest cell at 3.24 volts. I have now used jumpers to put the 4 cells in parallel to bottom balance. After 6 hours the cells are 3.22, 3.23, 3.21, 3.21. This is a slow process, as rate of charge (balancing) is dependent on voltage differential, and 0.43 volts is a lot for imbalance but not much for a fast transfer of electrons.

[Lagoon4us]

Originally Posted by diugo

I wouldn't exactly characterize my TS-45 as redundant, as it's the only way I plan to charge my new batteries. I like the fact that it can be programmed with a laptop to work with batteries it was never designed for. Ironically, it may well do a better job of handling the LFPs than it did with the AGMs.

Ok so your choice is definitely the TS-45 as it can be tailored to suit the LFP's more so, good.
Now comes my dumb questions:-
1) You'd be using this only to regulate the solar?
2) What AC charge system are you using that also matches LFP's?
3) What regulators are you using on any engine driven main engine?

Cheers just trying to understand more about this option.

[Lagoon4us]

Originally Posted by deckofficer

I ran the pack much lower this time, 36 hours on a 30 watt load, 1080 w-hr. I only stopped because one cell dropped to 2.81 volts, highest cell at 3.24 volts. I have now used jumpers to put the 4 cells in parallel to bottom balance. After 6 hours the cells are 3.22, 3.23, 3.21, 3.21. This is a slow process, as rate of charge (balancing) is dependent on voltage differential, and 0.43 volts is a lot for imbalance but not much for a fast transfer of electrons.

Bob do you stop now satisfied that they are quite close?

Cheers

[deckofficer]

Originally Posted by Lagoon4us

Bob do you stop now satisfied that they are quite close?

Cheers

I'm going to leave them in parallel for another 6 hours, then charge at 50 amps in series. If this doesn't work, I've ordered the adjustable power supply as per Maine Sail, will discharge in series, then put them back in parallel and charge at 10 amps at whatever voltage Maine Sail recommends. I'm guessing maybe 3.7 volts?

[daddle]

Experts: Why not charge with four parallel chargers at the nominal 3 volts? It's there a technical reason not too, or only complexity and availability? Such a unit might also be designed to regulate the voltage across the cell at the bottom limit too.

[deckofficer]

Originally Posted by daddle

Experts: Why not charge with four parallel chargers at the nominal 3 volts? It's there a technical reason not too, or only complexity and availability? Such a unit might also be designed to regulate the voltage across the cell at the bottom limit too.

I'm no expert, and don't play one on TV, but since it is you, and you have a SC 50, which I respect, I'll give it a try.

The nominal voltage on these cells is 3.2 volts, and if charged at 3.2, would take a long time to reach that voltage as the differential would be so small as they reached 3.2.

I have a single 12 volt, 50 amp charger with a lithium profile. I just bought and waiting for delivery a adjustable 0~30 volt, 0~10 amp switching power supply which I'll use for balancing. I don't want to buy 4 of these for my 12 volt batteries, or 16 of them for my future 48 volt inverter/propulsion bank.

[hellosailor]

Bob, how often do you intend to so this battery charging dance? Routinely, or what?

It is sounding like you are proving the point of the companies that insist a fairly expensive BMS really is necessary, i.e. the same way that lithium packs in laptops have long been monitored and charged on a cell-by-cell basis, making their battery packs rather expensive because there's a charge management system built into each one, looking at each cell, or pair of cells.

[deckofficer]

I'm hoping for a balance on these 2 1/2 year old cells, and once balanced should be able to charge to full on the 50 amp charger and no more chasing errant cells. These two packs will be tossed in and out of the kayak and the yard with an inverter to run power tools. I hope not to have a BMS on them for this rather physical use. I did buy one and was thinking of running one pack with it to see if they are really needed if you start out balanced.

[goboatingnow]

Originally Posted by hellosailor

Bob, how often do you intend to so this battery charging dance? Routinely, or what?

It is sounding like you are proving the point of the companies that insist a fairly expensive BMS really is necessary, i.e. the same way that lithium packs in laptops have long been monitored and charged on a cell-by-cell basis, making their battery packs rather expensive because there's a charge management system built into each one, looking at each cell, or pair of cells.

My experience. ( its not in a marine field) is that after the initial balancing , such as bob is doing. You rarely see the need to balance again , particularly with sub C charging and discharging. I am not personally in favour of sophisticated BMS, cell monitoring is useful however. I find the best way to initially balance is just to parallel the cells and do a few cycles.

In laptops and others ( a design area I'm very familiar with) there are many reasons for quite sophisticated cell chargers , monitors.) firstly you have LiPO and other sensitive chemistries. Secondly the cells are regularly emptied to virtually zero ( well to a minimum voltage ) charge and discharge are often multiple C environments. In particular pre qualifying charge is important etc. ( as are sub zero protection ).

It's not really useful to infer certain assumptions from small format Li cells into large prismatic Li ferrous cells used in a typical boat environment.

I have to say this thread though is a store of experience.

Dave

[diugo]

Bob, thanks for the info on the cells. Great that you are not waiting til spring to test them!

Hellosailor, regarding the dance and proving the need for the expensive BMS, it's way too early to tell that yet---one needs to go through several charge cycles and see how well the cell voltages stick together (or not). If the cells are well-matched and currents are kept under 1C, a BMS might be a big waste of money.

That said, I do believe a small $30 multi-cell voltage monitor/alarm gizmo (such as the CellLog 8) would be a prudent investment.

Daddle, by parallel chargers, I assume you mean a separate charger for each cell? Because in service, you always the cells connected in series, not parallel. Multiple identical chargers multiply the cost as well as the chance that one might fail.

Lagoon4us, I'm actually a solar-only RVer, not a boater. So I don't have to worry about multiple charging sources.

[daddle]

Originally Posted by diugo

... by parallel chargers, I assume you mean a separate charger for each cell? Because in service, you always the cells connected in series, not parallel. Multiple identical chargers multiply the cost as well as the chance that one might fail.

Okay, cells in series. That does up the number of chargers. But makes each one smaller. A charger regulator is not an expensive item. I am thinking business opportunities. How many cells are folks here using? And what is the typical C of the cells in boat applications?

What worries me is the use in this discussion of the words "might" and "probably" regarding cells needing balancing. I never accepted those words in my engineering career they would certainly get one fired.

[goboatingnow]

daddle

In small cell applications, individual cell charging is the norm, usually using a chip that integrates most of the work. In fact as you point out , it can be cheaper to have 4 10A chargers then a single 40A.

I currently have on the bench , 4 small SMPS units capable of being used in that way , in fact I am the proponent of parallel capable small chargers ganged together to make a big charger, less points of failure.

What worries me is the use in this discussion of the words "might" and "probably" regarding cells needing balancing. I never accepted those words in my engineering career they would certainly get one fired.

There is huge amounts of probably in engineering!!,

One of the reasons is that there is no exact determination. If you want a belt and braces answer then the correct one is that active cell balancing is needed for LI technology. If you want an answer based on observation of large prismatic Li cells in sub C charging and discharging environments , the answer is cell balancing is not required on a regular basis.

your mileage may vary.