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

[ebaugh]

Originally Posted by Lagoon4us

Exactly Bob, how long has your system been running and with nil incidents? Cheers

Long enough to conclude they are at least initially far superior to lead acid. But the life cost depends on real cycle life data. We have some positive reports from the EV and solar users. And some from other users on the thread. But I want to see 1500-2000 usable cycles reported before I declare complete victory.

Charging can be an issue, I still have problems with my older Magnum inverter/charger. And have workarounds or solved some initial BMS issues. But it's not in the bag yet. Hence all the discussion here. The discussion is great, I just don't want someone to think all the finer points need complete resolution before considering the battery for adoption.

[T1 Terry]

Originally Posted by Lagoon4us

Exactly Bob, how long has your system been running and with nil incidents? Cheers

Mine has been running a bit over 2 yrs, maybe 750 cycles to 50% or lower. I can't say it's been without incidents though, they have had a few discharges into the 2v area and a few charges into the 4v plus area but it didn't kill them, they still seem to be functioning fine. It's about the life cycle of lead acid now, so every cycle from here on is a bonus.

T1 Terry

[deckofficer]

Originally Posted by T1 Terry

The 48v system is an interesting one. It actually measures out nicely to 15 lithium ferrous cells. As 3 groups of 5 cells, each group has a voltage operating range of 15v to 17v, this is very close to the perfect operating voltage for 12v solar panels.
I plan to run a 48v system in my big bus project, both house power for the 5kW inverter and power for a hybrid drive assist electic motor, most likely AC so I can gain the benefit of regen braking. I plan to use 3 individual Junsi cell loggers and timer circuits and simply toggle the solar on and off to stop any cell going over 3.6v, the charger side of the inverter will be set to 50v cut off, 3.3v per cell, the solar can do the rest.
There is no reason why the same system could be set up for the two chargers, the Zivan is a good programable charger and the Dual Pro I believe can be also programmed for each chanel to stop charging just that little bit before all the cells were full, then the solar finishing off the job.

The C20 rating for a lead acid battery is Peukert's effect being taken into account. Good manufacturers give tables showing the reletive capacity at different C rates. Peukerts isn't really the method for calculating the losses in lithium ferrous batteries although the effects are similar at very high discharge rates. Proffessor Jay Whitacre refers to it as the Warbird (sp) coeffecient, it is very reliant on the cell build, the thickness of the material coating, each design build is different. The thinner the material, the higher the C rating before the Warbird kicks in but the lower the cell capacity, the thicker the coating, the earlier in a the C rate the Warbird kicks in but the greater the storage capacity. This is one thing they have in common with lead acid batteries, it's the difference between starting batteries and deep cycle batteries, just on a much higher scale. Some of the high current cells are up around the 20C mark before the Warbird kicks in, but their capacity is only around 10Ah.

T1 Terry

Terry,

I've played with some numbers for a bus to RV conversion using electric drive. My electric Smart Car consumes around 275 w-hr per mile at 55 mph. I figure by the hp required to hold 60 mph in a 40,000 lb bus conversion, it would consume 1000 w-hr per mile on a level road. So for a $55K in LiFePO4 cells, 5600 lbs, 273 KW-hr, you'll have an electric range of 200+ miles. All the newer RV parks offer 50 amp service, so one day of sucking down 10 KW per hour, you get another 200 mile charge. Makes you feel like your getting your money's worth when the park is charging $50 a night and you put $36 worth of electricity into your battery bank.

[T1 Terry]

That has been thought about :lol: Basically, this set up will be for assisted hill climbing and steep hill starts with a bonus of regenerative braking. My bus conversion will be around the 10 ton mark and dragging a VW Kombi (think they are call a transporter or similar in the US, but it's a campervan) a framed behind, at 48v the motor would be huge, as would the cabling. Some of the caravan parks are 2,000miles apart over here, that would require a big battery bank. We are set up for 100% free camping, i think it's call boon docking in the US. It's a self propelled 36ft long by 8 ft wide by 7ft 6" headroom air conditioned one bedroom apartment.

T1 Terry

[mrm]

Originally Posted by Lagoon4us

I guess the resistors generate heat but i would think part of the process of the BMS that switches the 'overvoltage' to a resistors has cut charge off to the pack simultaneously?

Cheers

I think an approach used in laptop packs is to bypass a cell with overvoltage condition while allowing other cells to charge. This is not practical with high capacity high amperage banks, though. At least this is what I think I observed looking at open laptop packs.

[mcarling]

I'm not sure, but it seems that some readers here may not realize that the minimum, nominal, and maximum voltages for LiFeYPO4 batteries (including Winston) should be approximately 10% higher than for LiFePO4 batteries.

[Lagoon4us]

LiFeYPO4 have these been mentioned much? Seems your quite correct...

[ebaugh]

Originally Posted by mcarling

I'm not sure, but it seems that some readers here may not realize that the minimum, nominal, and maximum voltages for LiFeYPO4 batteries (including Winston) should be approximately 10% higher than for LiFePO4 batteries.

This might seem the case on first blush based on the maximum voltage specifications. But it is not indicated on the two attached discharge graphs at lower C rates. At 50%, both cells show very similar characteristics. I think it's more based on different manufacturers opinions then a substantive difference in the cells.

[Lagoon4us]

The guy's i'm buying from list them with Yttrium, was this material dropped in the cells description or are they chemically different the graph i attached is for LiFeYPO4

[mcarling]

Neither of the two graphs above are for straight LiFePO4. The first is for LiFeYPO4 (yttrium added) and the second is for LiFeMPO4 (unspecified metal added).

[ebaugh]

Originally Posted by mcarling

Neither of the two graphs above are for straight LiFePO4. The first is for LiFeYPO4 (yttrium added) and the second is for LiFeMPO4 (unspecified metal added).

it's true both of these have slightly modified chemistry. But pull up a CALB spec, my Internet is too slow to upload this time of the day in the San Blas. You will find the same basic discharge curve. That's my point, Im not sure there are practical differences in how they need to be treated in normal operation.

[ebaugh]

Originally Posted by Lagoon4us

The guy's i'm buying from list them with Yttrium, was this material dropped in the cells description or are they chemically different the graph i attached is for LiFeYPO4

The Winston MSDS shows LiFeYPO4 still. They call it Yttyia there, but that might be bad translation.

[mbianka]

Originally Posted by ebaugh

Charging can be an issue, I still have problems with my older Magnum inverter/charger. And have workarounds or solved some initial BMS issues. But it's not in the bag yet. Hence all the discussion here. The discussion is great, I just don't want someone to think all the finer points need complete resolution before considering the battery for adoption.

Charging is the the bugaboo isn't it? Ease of charging is an important issue especially for those cruisers who are not that tech savy as many here are. I'm pretty happy with my current Gel and AGM setup and the pretty much trouble free charging systems that I have used for the past five years. I'm still not prepared to jump to these newer more expensive battery technologies before I see more of a track record and know that I won't be fretting over the balance of individual cells and/or temperamental BMS electronics that will be expensive to repair or replace.
Still, I'm glad there are a number of folks here who are early adopters of these battery technologies. Hopefully there will be some standardization and bullet proof charging solutions coming down the pike so one does not have to fuss too much over these LifePO4 battery banks. That's what diesel engines are for.

[deckofficer]

Capt Mike,

You were an early adopter of electric propulsion, why not LiFePO4 when your AGMs need replacing? If this thread has proved one thing, that would be you get a lot more bang for the buck, both on purchase and ratings of the cells. My (2) 12 volt packs of 100 a-hr each, if rated like a LA at the 20 hour rate would probably be 160 a-hr, add to that 80% DOD vs 50% DOD, and 2000 cycles vs 500, well you get the picture.

[SailFastTri]

Would be interested in what you all think about this product 12V 100Ah,StarkPower 'UltraEnergy" LiFePO Lithium Energy Storage Battery as a "drop in replacement" for LA batteries?