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

[Maine Sail]

Gotta wonder what the acid did to this guys boat when this Trojan Battery blew up... BTW that's a lot of empty air in that case not filled with lead.......

[ebaugh]

I think you need at least automated cell level monitoring with a disconnect for house bank sized cell groups. In order to make my point, I attached 2 graphs from a Sandia Labs presentation to support the conclusion.

First, one shows that LiFePO4 is intrinsically safe. This graph shows several Li chemistries that if a cell is simply heated beyond a certain point, start to self generate more heat, adding fuel to the fire so to speak. Since we use LiFePO4, no additional heat is ever generated. But other chemistries could generate over 2 million calories on their own in a house bank sized group of cells. I'm not a chemist, but that sounds like a lot....ie. Boeing. This is a good thing thing for LiFePO4....and why there are so many of us willing to adopt.

Second, there is a graph that shows heat generated by overcharging LiFePO4 cells. This is a real risk and must be managed. The heat starts to be generated the first second a cell is overcharged, and can eventually reach near 180 degrees C based on the graph. I don't want to go there...do you? Are you always aboard to respond to an alarm? The problem that can be inferred with other chemistries, called a runaway, is the overcharging can generate enough heat to lead us back to the first graph where the chemical reaction itself leads to even more heat and more potential bad things.

But LiFePO4 simply slowly rises to its max potential at an attempted 140% SOC, by which time the cell has simply self destructed. I believe these charging tests were done on small round low capacity cells, so the results could be different, better or worse, for large format rectangular cells. But since I have a working disconnect, Im never gonna find out!

[deckofficer]

Originally Posted by Maine Sail

Gotta wonder what the acid did to this guys boat when this Trojan Battery blew up... BTW that's a lot of empty air in that case not filled with lead.......

The lead acid battery retailer that has been trolling this thread isn't going to like that picture, but for some folks the picture will be informative. It appears by the height of the battery it is a group 27. Who all remembers going to Western Auto (or other automotive parts stores) in the 60's when most all cars used a group 27, and seeing all the same size batteries with different prices and warranties, like 24, 36, and 48 month. This battery shows why, same case, different amounts of plates.

[mcarling]

Originally Posted by Dockhead

And no control device of any kind at all? Even the Balqon guy was warning against that.

The content of that email from Balqon did not give me a positive impression regarding the depth of their technical competence.

Originally Posted by diugo

The only way that's going to happen is to somehow inhibit the irreversible reverse reactions that plague the chemistry in all lithium ion cells when they are overdischarged. I hope there's a future for lithium under the hood---but it won't be found with the current set of cell ingredients.

I have $1000 that says otherwise. Care for a wager?

Originally Posted by ebaugh

First, one shows that LiFePO4 is intrinsically safe. This graph shows several Li chemistries that if a cell is simply heated beyond a certain point, start to self generate more heat, adding fuel to the fire so to speak. Since we use LiFePO4, no additional heat is ever generated. But other chemistries could generate over 2 million calories on their own in a house bank sized group of cells. I'm not a chemist, but that sounds like a lot....ie. Boeing. This is a good thing thing for LiFePO4....and why there are so many of us willing to adopt.

Two million calories (2000 kcal) is the energy in the food that I eat during a typical day.

[deckofficer]

You should all know that Balqon's main business is producing electric trucks and the majority of their personal experience is with the large (400, 700, 1000 a-hr) single cells. They are also the distributor for Winston cells and as such carry the smaller size cells and 12 volt batteries. I don't think they have any experience with the small 40 a-hr 12 volt batteries, so I would direct my questions on this battery to GWL Power.

Balqon for cells ranging from 40 a-hr to 1000 a-hr have the lowest price that I have found on their non-clearance pricing, and their clearance pricing was just too good to pass up. About the only cells left from the clearance sale are the 700 and 1000 a-hr, and I'm still looking forward to someone here putting together a house bank using those 700 a-hr cells. You could have A/C on the hook without the noise and smell of the gen set.

[diugo]

Originally Posted by mcarling

I have $1000 that says otherwise. Care for a wager?

Is that you, Mitt? I would take you up on your generous offer---but you'll need the dough when you turn your current set of LFPs into boat anchors.

[ebaugh]

Originally Posted by mcarling

Two million calories (2000 kcal) is the energy in the food that I eat during a typical day.

Looking closer...that maybe per minute at peak, not total. And it would equal raising one gallon of water 500 degrees C per minute. That's a lot of heat to dissipate at one time.....

[senormechanico]

Originally Posted by hellosailor

senormechanico-
I have some old application guides from Eveready and GE, for their NiCad and lead batteries, and both actually do remark on what we now call balancing. Except, their point is that when cells are in series, if you allow the battery to go dead OR discharged very low, any one of those cells may in fact be reversed and then subsequently be damaged or fail completely.

Maybe you misinterpreted my post.
I have four 200 aH cells with a MiniBMS.
I manually balanced them when I originally installed.
Never a problem.


Mainsail,
I'd really like to know what it was that caused that boat's battery to explode in the first place!

[diugo]

Originally Posted by Dockhead

And no control device of any kind at all? Even the Balqon guy was warning against that.

With its very well matched cells, you can safely do away with the cell-level voltage monitoring and auto-balancing features of most BMSes--but you still need to ensure that the battery's voltage never drops below 11V or exceeds 15V.

A simple $20 voltage alarm, and a $5 relay to disconnect the battery, would accomplish this.

[ebaugh]

Originally Posted by diugo

With its very well-matched cells, you can safely do away with the cell-level voltage monitoring---but you still need to ensure that the battery's voltage never drops below 11V or exceeds 15V.

A simple $20 voltage alarm, and a $5 relay to disconnect the battery, would accomplish this.

For essentially the same level of effort and cost, why not use the CellLog8?

[diugo]

Originally Posted by ebaugh

For essentially the same level of effort and cost, why not use the CellLog8?

That's the exact device I meant. But, no need to carve the battery case open and hook the CellLog up to the four cells inside. Instead, just hook the CellLog to the battery's terminals and just use the CellLog as a simple battery-level voltage alarm and relay driver.

[deckofficer]

Since so few of us are using LiFePO4, it doesn't justify a poll on a new thread, so I'll ask the poll question here.

Anyone using LiFePO4, would you go back to lead acid?


I hope all the early adopters like T1 Terry respond.

[deckofficer]

And to answer my own poll, No, lead is history to me.

[ebaugh]

Originally Posted by diugo

That's the exact device I meant. But, no need to carve the case open and hook the CellLog up to the four cells inside. Instead, just hook the battery's output wires to the CellLog as use it as a simple voltage alarm and relay driver.

If it was built as indicated in a previous post, I think I'd just remove the cells and throw away the case...then have the needed access to hook up all the wires. Otherwise, I'd just buy 40Ah cells.

[diugo]

Originally Posted by deckofficer

And to answer my own poll, No, lead is history to me.

Bob, you know I like LFP. Wouldn't have spent $850 on it if I didn't.


But if the lead acid battery in your car or truck died tomorrow, would you really put a $500 LFP in its place, along with all the proper charging, monitoring, and disconnect circuitry it would require?