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

[deckofficer]

The first 0.1 C load (32" HDTV) 11 hours 48 minutes. Cell voltages ranged from 3.06 to 2.64 so decided to do a bottom balance and then charge as a series pack as mentioned in careka's link in his post # 3175. If this works, and I'm pretty sure it will, it is by far the easiest way to bottom balance. Since it was a 0.1 C load, the changes at the discharge knee was slowed down and made it very easy to apply the PS to the lowest cell until its voltage matched the 2nd lowest cell, and then when these two cells matched the 3rd lowest (two cells in series now on the PS) bring that 3rd cell into the series charge string until all 3 cells match in voltage the highest cell. After this let the bank rest for a voltage check.

Before this balancing
2.94, 2.84, 2.64, 3.06

After balancing (done while still on the 0.1 C load)
2.85, 2.84, 2.85, 2.84

Now charging in series @ 50 amps.

Will repeat the same 0.1 C discharge tomorrow and see if the cells stay tight on the discharge knee.

[downunder]

deck officer

off thread but have you seem the info on the Torguedo 80hp electric motor

Pressemitteilungen

Cheers

[deckofficer]

I've seen the info on the Torqeedo 80 hp electric. The motor $20K, their battery another 20K and for good range you need 3 batteries. I like electric propulsion but that is a bit pricey.

[Maine Sail]

Originally Posted by deckofficer

Before this balancing
2.94, 2.84, 2.64, 3.06

This is exactly what happens when you get close to the bottom knee when doing 100% discharge tests... The problem in a house bank is that you now may be off on the charging side and the 3.06 cell may hit the upper knee sooner. Easy to combat by only charging to 13.8V and this keeps you within the safe range.

For your kayak a bottom balance is likely the best bet. For a house bank on a cruising boat a top balance is likely going to be the best bet... All depends upon how you are using the bank... EV guys often discharge to 100% DOD where off-grid/boat house banks etc. only discharge to 80% DOD thus I would argue that the top balance is more important in an off-grid bank.. Two different uses result in where you want to balance, top or bottom.

A top balance has the cells agreeing at the top end of charging or 100% SOC. A bottom balance has the cells agreeing at the bottom end or 0%..

*EV often goes to 0% thus bottom balance becomes critical

*Boats rarely if ever go to 0% but do get to 100% SOC, with multiple charging sources so top is preferred (especially if charging to 14.1V or greater).

On top of a top balance I also prefer to limit charge voltage to 13.8V - 14.0V which nearly guarantees no cell will ever get to 3.8V even if a cell were to get out of balance by 0.35V +/- WHICH IS HUGE..... My bank, at over 200 cycles to approx 80% DOD, is still in agreement out the thousandths of a volt...... Top balance is working exceptionally well for my off-grid bank and was specifically chosen because it is an off-grid bank....

[Hyprdrv]

BoatPoker,
Let me also mention this. If those are "batteries" under those aluminum covers no one puts aluminum (metal) on top of the batteries! In most cases plastic or none is better than what you have there.

Steve in Solomons MD

[Maine Sail]

Originally Posted by Boatpoker

I'm not sure the average dock walking shade tree mechanic should be allowed to buy cells of the shelf and built his own thermal nightmare. If Boeing can't get it right. Billy Bob dosn't stand a chance.

This is a prime example of why you really do need to educate yourself, as you initially stated you need to..While I agree that that installation is far from good, comparing what are most likely LiFePO4 to LiCoO2 is like comparing Bode Miller to Rosie O'Donnel in a ski race, not a very good one...

Read more and you will eventually understand why...LiFePO4 / Lithium Iron Phosphate (LFP) is a totally different technology than LiCoO2 / Lithium Cobalt Oxide (LCO). The "Li" part is about the only thing the same. LCO technology is more energy dense but also a lot more unstable than LFP...

LiFePO4 is one of the most stable & safe of the Li technologies. Is any battery 100% safe, absolutely NOT.... Not lead acid not Li not NiCad not NiMh.... Many argue LiFePO4 is actually safer than LA technology but for me I treat all batteries with respect..

This was done with a single group 27 FLA:

[deckofficer]

Maine Sail, your experience with these cells is showing. You must of got a quiet chuckle when you read last year that I did both a bottom and top balance. lol

I balanced bottom first then top, so in reality did a top balance for these packs.

That 3rd cell that dropped to 2.64 on the discharge knee, when bottom balanced now becomes the highest voltage cell on the charge knee. The 4th cell which was the highest voltage at the discharge knee after the bottom balance becomes the lowest voltage on the charge knee.

Before bottom balance
2.94, 2.84, 2.64, 3.06

After bottom balance on charge knee.....

At 4 amp acceptance (missed 5 amp)
3.55, 3.55, 3.90, 3.46

At charger shutoff
3.55, 3.63, 3.97, 3.46

At resting voltage
3.40, 3.42, 3.60, 3.36



As to us EV guys, we don't want to hurt our cells either and want cycle life. What we do want is a fast turn around time on the charger so charge voltages are higher, thus it is best that we, the EV guys should also top balance.

I will give this bottom balance a few cycles and if that 3rd cell stays high (over 3.90 volts), then I will again balance but at the charge knee. Maine Sail, your experience with these cells has you doing the right thing, for me I guess I had to experience first hand, but as usual you are correct.

[Maine Sail]

Originally Posted by deckofficer

That 3rd cell that dropped to 2.64 on the discharge knee, when bottom balanced now becomes the highest voltage cell on the charge knee. The 4th cell which was the highest voltage at the discharge knee after the bottom balance becomes the lowest voltage on the charge knee.

Spot on. I just typed and read too fast..

[deckofficer]

A bit like whack-a-mole.

[deckofficer]

Maine Sail, what is a bit odd is that after just 1 hour of an easy 10 amp load, all cells are 3.30 with no variation between them.

[senormechanico]

Originally Posted by deckofficer

I read some of the reviews. One knowledgeable user noticed that the RFI/EMI was high and kept touch pad devises like iphone, ipads not to accept touches if too close to the inverter, also same applied to charging these devises to close to the inverter. He is a HAM radio op and noticed the hash on his HF freq because of harmonics of the PWM of the waveform.

I think I'll just stay with this unit and string the extension cords during blackouts as that will allow me to swap out batteries with no loss of inverter output due to the dual Anderson plugs I put on the inverter.

There is some hash, but it isn't enough to obliterate AM radio reception on semi weak stations. The inverter is mounted in the stern immediately aft of the engine compartment. It's about 4 feet from the battery bank which is immediately ahead of the engine bulkhead in the saloon.

If I'm running my Icom 706, I'm not going to be running the inverter anyway.

[ColdEH]

Originally Posted by T1 Terry

The stuff I use is called Alminox. Use a nylon scrubber pad scrub the terminal till it's bright metal, easiest on a drill with a backing pad, these are an off the shelf item where good tools are sold. Once you have it clean and shiny, a small flat art brush and paint a film of Alminox on thick enough that it's not see through. If you are using the copper multi leaf links that come with the batteries then give the mating surface on the bottom and top leaves and paint them with Alminox as well. Have a clean large rag with you, the stuff is like Never seize and travels every where you touch if you aren't real careful.
The majority of cell out of balance problems are created by not having the terminals clean and protected at the very beginning. Give yourself a better chance of success and start the job out the right way from the very beginning, it will pay you back bucket loads over the yrs with maintenance free operation yr after yr.

T1 Terry

Thats the stuff, thanks so much Terry . !

Going to source the stuff out now and get some


Regards

[dansken]

Anyone know the equivalent to alminox in europe?

[Maine Sail]

Originally Posted by deckofficer

Maine Sail, what is a bit odd is that after just 1 hour of an easy 10 amp load, all cells are 3.30 with no variation between them.

Not weird at all, I see the same thing..... A 10A load is nothing to these cells... I see virtually no variation all the way down to 80% DOD. Even while charging at 130A they are still very much in-balance whether at 20% SOC and a 130A charge or 90% SOC and 130A charge..

[deckofficer]

Originally Posted by Maine Sail

Not weird at all, I see the same thing..... A 10A load is nothing to these cells... I see virtually no variation all the way down to 80% DOD. Even while charging at 130A they are still very much in-balance whether at 20% SOC and a 130A charge or 90% SOC and 130A charge..

So what all on the fence want to hear, stay away from the discharge knee, limit bulk charging to 14.6 volts or a bit less, no BMS, cell loggers (with high and low alarms and disconnect) for piece of mind and top balance cells for plug and play use.

Can't get easier than that for all of you on the fence about LiFePO4. The cheapest and most robust energy storage available today.

Lead is Dead.