# Personal Experience with Prismatic LiFePO4 Cells



## TexomaEV (Jul 26, 2007)

Folks, I wanted to share some experience, I along with several other club members have had with Prismatic LiFePO4 cells, over the past year. In the hopes it helps keep others from damaging precious EXPENSIVE batteries:

1. When you build up a pack of cells, say a 12.8volt nominal battery of 4ea cells. Be sure, and place restraining plates on the end faces, bind the whole assembly with strapping to keep the cells from ever having the chance to bulge. If they ever bulge, and I've had brand new unused cells do this on their own, the internal plates start to spread apart, dry spots will develop and your capacity will slowly dwindle, to the point the battery will fail. I know this from dissecting a failed battery. 

2. Interconnecting busbars, should be sized large enough that there is very, very little noticable change in the busbar's temperature after your typical EV drive. NTEAA members have progressed to using 1" wide x 1/2" thick aluminum bars, which accomplishes several things. The posts of the LiFePO4 cells are aluminum, therefore using aluminum threaded studs screwed into the cells, with aluminum busbars, held down with a double nut system, all lathered up with "No-Ox ID A" for electrical connections. There is very little heat generation at the busbar, and the batteries operate nice and cool. Keeping the cell studs and busbars aluminum also eliminates dissimiliar metal reaction or galvanic corrosion.

3. Charge regulators, are installed on each individual cell, which once a cell reaches 3.65vdc, that particular cell stops taking on energy, shunting the majority of it over the the remaining cells. The experience has been, once one regulator comes on, showing a cell is fully charged, the remaining regulators for the rest of the pack, usually engauge within just a few minutes. If you remain within the nominal discharge C rating of your LiFePO4 cells, and you truely balance them during every charge, they want to stay balanced during the discharge cycle. Use your controller's internal cutoff setting to keep from over discharging the pack, and stay within limits of your pack discharge C rating. For the most part drive sensibly.

4. Capacitor Bank, I've only just started testing with this, but so far the results look good. What I'm proposing, is build up a large capacitor bank for the pack voltage you are using, place it between the controller and traction pack. For the most part, paralleled onto your traction pack, as close to the pack as possible. What it does, is it smooths out the pulsing of the power extraction from the batteries, that occurs when the controller requests energy. The O'Scope shows the power extraction to be in pulses, similar to what is being sent to the motor, and the capacitor bank, helps smooth out these pulses so the traction pack doesn't receive such a constant electrical shock. It keeps the energy extraction at a more constant level, thus in theory, extending the life of the traction pack, controller, along with the traction pack running cooler under load, and extending the range just a smidgen.......

For photos of what I've along with others in our www.NTEAA.org club are doing with LiFePO4 batteries, charge regulators, restraining, pack build, monitoring, etc. look at:


www.flickr.com/photos/mbarkley/sets/72157609086829232/

www.flickr.com/photos/mbarkley/sets/72157604137306905/

I hope this helps you with your LiFePO4 pack, and would be grateful for any information that you've experienced as well.


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## ClintK (Apr 27, 2008)

Great info, thanks!

Do you mind making that a "Maintaining LiFePO4 Batteries" wiki page (or mind if I do it?)?

We could probably include david85's testing as well.


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## dimitri (May 16, 2008)

Mike,

thanks for excellent info! Can we get more details about those cell regulators? I have been keeping an eye on available options, currently there are a few, with different features and cost, perhaps these can be a pretty good competition when the time comes to make a purchase. Is there a web site or a contact Email or phone number to get those regulators?

Thanks


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## TexomaEV (Jul 26, 2007)

dimitri said:


> Mike,
> 
> thanks for excellent info! Can we get more details about those cell regulators? I have been keeping an eye on available options, currently there are a few, with different features and cost, perhaps these can be a pretty good competition when the time comes to make a purchase. Is there a web site or a contact Email or phone number to get those regulators?
> 
> Thanks


I have a PDF, datasheet on the "Bat-Guard" if anyone wants it. I don't know of a way to upload it here on the Forum, it's 81K, to large to attach to this post. They are manufactured in Plano, Texas. They can be customized for AGM's or any other chemistry, voltage as well. I'll see what I can do about getting more direct info posted on the Forum.

Here's what I was able to extract from the Preliminary DataSheet:

BAT-GUARD Preliminary Datasheet 

Features: 

* Stable and accurate Voltage shunt to protect LiFePO batteries from overcharging. 
* Heat sink capable of bypassing 15 Watts of energy. 
* Reverse Voltage capability of 5.0 Volts DC without damaging internal circuitry. 
* Automotive Blade fuse to protect regulator if DC current is too high. 
* Solid State electronics encapsulated for long life and protection from debris. 
* 0.375” Ring Lug with 5” 18 gauge red and black color coded wires for connection to battery. 
* Amber LED that comes on when Regulator is absorbing energy. 
* Red LED that comes on if fuse is blown. 
Description 

The Battery Regulator incorporates precision solid state circuitry to prevent over-voltage conditions when 
charging LiFePO batteries with charging currents of 4 Amps. It contains an ultrastable voltage reference and 
shunt circuit that will prevent LiFePO batteries from reaching an overcharged state when used within design 
limitations listed. Other voltages available upon request. 

Ordering Information: Model Number: BatReg3.67 

Absolute Maximums Minimum Nominal Maximum Units Test Conditions 
DC Current 4 Amps Notes 1,2 
DC Voltage -5 3.75 
Ambient Temperature 40 C 4 Amps Current 
Power Disipation 15 Watts 

Specifications: Minimum Nominal Maximum Units Test Conditions 
Clamp Voltage 3.648 3.670 3.692 Volts 1 Amp DC current 
Current if not in Clamp Mode 225 uA 3.5 Volts 

Notes:
1) Adequate free air space to allow dissipation of power
2) Heat Sink will get hot to the touch, and may cause burns
3) If fuse blows, Battery Regulator will not be able to protect battery against over-charging.


LL Labs reserves the right to make changes at any time in order to improve design and to supply the best product possible. 


LL Labs 
Issue A, Oct x, 2008 2908 White Oak Dr. 
Plano, TX 75074 

Mechanical: Dimensions: 2.36” W x 1.38” D x 2.85” H (60mm x 35mm x 73mm) 
Storage Temperature -40 to 85 Celsius 
Operating Temperature -40 to 85 Celsius Note: derate by 0.2 Watts/C above 40C Amb. 
Mount using double sided tape Not included


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## Bowser330 (Jun 15, 2008)

"The Battery Regulator incorporates precision solid state circuitry to prevent over-voltage conditions when 
charging LiFePO batteries with charging currents of 4 Amps."

4amps is all we can charge the cell at? Maybe I am not understanding...

What is the maximum AH I can charge the pack at, say I have a portable generator that can push out 20Amps at 120V???


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## TexomaEV (Jul 26, 2007)

Bowser330 said:


> "The Battery Regulator incorporates precision solid state circuitry to prevent over-voltage conditions when
> charging LiFePO batteries with charging currents of 4 Amps."
> 
> 4amps is all we can charge the cell at? Maybe I am not understanding...
> ...


You can charge at as high of a amp rate your cells are rated to take, but as the pack voltage climbs and you are reaching it's charge out voltage, you want to taper off to 4amps or less for the final charge/balance, so at that rate the regulators will kick in and keep the cells that fill up first from overcharging while the others catch up, and stay withing the operating range of the regulators. 

The current vehicle who has the "Hot Juice Electric" BEQ1 regulators, can handle around 2amps or so, and his charger cuts back to that or less, towards the latter part of the charge cycle. The "LL Labs" Batt-Guard regulators can handle 4amps.

For instance, we're starting to work with a 100Ah LiFePO4 & 110Ah AGM hybrid pack, which is to be charged with a Zivan NG3 charger, it's programmed so that when the pack reaches it's knee voltage setpoint, it drops down to around 2amps for the final charge/balance of the pack. There will be Batt-Guard regulators on the LiFePO4 Cells, which are ganged together in 12.8vdc battery modules, and paralleled onto each individual 12vdc AGM battery. Attached to this hybrid pack will be a 44000uf 200vdc rated capacitor bank as well.

With the charger set to drop well below the regulator current limit one could just about plug in the EV, and forget about it until the next morning. I say this just because I've left a 4cell pack fully charged, on a charger for well over 10hours one day, and every LiFePO4 cell was protected during that session, using the Batt-Guard regulators. I'd recommend maybe a timer, so you didn't waste that extra energy, as you'll soon find out how long it takes for your pack to fully charge, after a few cycles.

Hope that helps, answers your question. If not let me know.


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## ClintK (Apr 27, 2008)

I threw together an article from your notes. My only change was the capacitor bank close to the controller instead of the battery pack. Please let me know if anything needs to be changed / adjusted.

http://www.diyelectriccar.com/forums/showthread.php?t=25818

Thanks again!


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## TexomaEV (Jul 26, 2007)

Clint, thanks for taking the time to put that together. I hope it helps others utilize LiFePO4 to the best, performance, the chemistry can offer them. It offers up a means of using these large format LiFePO4 cells, and not feel like they have to use hundreds of small cells.


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## dimitri (May 16, 2008)

Mike,

I have couple more questions after looking at your pictures:

- your cells are white casing, I thought TS LFP were yellow, are yours TS LFP or some other name or model?

- considering comment about sagging plates under their own weight, would it make more sense to mount cells horizontally? Even with strapping and restraining plates mounting position could make some difference over time, right? I think your fornts are horizontal but those in the back are vertical, right?

- what about temperature control? How much are they effected by ambient hot/cold weather and how much do they heat up during charge/discharge? Any consideration for insulating/venting battery boxes?

Thanks


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## TexomaEV (Jul 26, 2007)

I have couple more questions after looking at your pictures:

- your cells are white casing, I thought TS LFP were yellow, are yours TS LFP or some other name or model?

** These cells, certainly are not TS LFP, These were purchased from LionEV & Beepscom.com

- considering comment about sagging plates under their own weight, would it make more sense to mount cells horizontally? Even with strapping and restraining plates mounting position could make some difference over time, right? I think your fornts are horizontal but those in the back are vertical, right?

** The best way, from what we can tell is they need to be installed with the terminals up. There is very little electrolyte in the cells, and it tends to settle to the point the top portion of the plates aren't saturated, as there is some distance from the top of the cell to the actual plate material in the cells. Plus there's always the chance that the terminals might not have the greatest seal, and then there's that center plug as well.

** Originally John was toying with laying the ones in the front of the Fiero down, but he's since retooled his battery trays to allow them to sit up.

- what about temperature control? How much are they effected by ambient hot/cold weather and how much do they heat up during charge/discharge? Any consideration for insulating/venting battery boxes?

** Any way you could keep them at a constant temperature, certainly couldn't hurt, that's for sure. If you could keep them as close to 70F you'd probably get the best life out of the cells, but I'd have to look at the spec sheets on the LiFePO4 cells before quoting operational temps for sure. 

** I'll ask if the Fiero owner can shoot some temps of the batteries before/after a run. But the times I've been around the car, they seem relatively close to ambient temperature, with having the aluminum busbars installed.


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## Bowser330 (Jun 15, 2008)

Texoma, 

Can you tell us more about the Lithium and AGM hybrid pack?

How is it performing, and would you reccomend it to others?

Do you have to match the AH and the voltages of each pack to successfully parallel them?

Thanks,


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## TexomaEV (Jul 26, 2007)

Bowser330 said:


> Texoma,
> 
> Can you tell us more about the Lithium and AGM hybrid pack?
> 
> ...


I've experimented with Hybridizing for a year now with LiFePO4 & Pb/Acid batteries without any problems. The main experiment was merely a small LiFePO4 pack (20Ah) & 6vdc Golf Cart batteries in my E-Eclipse. There are 2ea LiFePO4 cells in series, that are paralleled onto a single 6vdc GC battery. This is done with all 13ea GC batteries in the E-Eclipse. The LiFePO4 cells have never overcharged. I've abused this Hybrid Pack with probably the worse charger possible, and still haven't harmed the cells. 

So now we're taking it a few steps further, by Hybridizing a more practical pack, using 100Ah LiFePO4 cells, and 110Ah AGM's. The AGM's derate to around 84Ah under EV use, so they match up closely to to the LiFePO4 in AH rating under EV load. This pack has 4ea LiFePO4 cells wired in series, and then paralled onto a 12volt AGM, throughout the entire traction pack. 

We aren't as lucky with the AGM's as we were with the Flooded Pb/Acid batteries to get away without having to have LiFePO4 cell regulators. The AGM's don't charge out evenly in a series charge setup, so we're seeing some AGM's fully charge before others, and then some of the LiFePO4 cells are doing the same. This should be solved for both chemistries, once we have the LiFePO4 regulators installed.

But the wildest part of this new experiment has been the results of the "Flux Capacitor". It has helped with more power to the wheel feeling of the EV, the ability to maintain higher mph with less amperage, enough to be seen immediately after installing the bank of capacitors. Even though we still have the thin cheap busbars from China on the LiFePO4 cells for now, they didn't even warm up much above ambient temperature after a quick 7mile run at speeds as high as 55mph on a road full of hills and valleys. 

So far, I'd recommend others to experiment with the idea of hybridizing if ever given the opportunity, but to keep from limiting your EV's range, try and keep the derated Ah rating of your two battery chemistries as close to the same as possible. I drive the E-Eclipse merely at 25 to 45 mph, and my typical EV run is no more than 20miles, which leaves my pack at 70 to 80% full. Time will tell with what we're able to see and do with this new hybrid pack, w/fluxcapacitor. We're still waiting on aluminum studs, installation of copper busbars, and regulators, on the LiFePO4 cells. We'll also add another "Flux Capacitor" of the same size as the first, to see if we see anymore improvements, or if it has been maxed out with the installation of the first capacitor bank.


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## Bowser330 (Jun 15, 2008)

I wish i had the skills you do Texoma...just to mention, I am from Texas originally...have since moved to southern california...

I am very hopeful for you and excited about the results of the flux capacitor bank...

I feel a hybrid pack deep cycle batteries that charge a capacitor bank is the best way to go for a long range ev with the short spurt energy of caps, Plus the absorption of maximum amps from regen...


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## Ziggythewiz (May 16, 2010)

Any update on the fluxcapacitor results?


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## winzeracer (Apr 3, 2012)

Great info, and the cell regulators look like a nice way to protect things, however for $50.00ea even for my small pack (26 cells 40ah) this would nearly double the price of my pack. So this would only be good(price effective) for HV packs.

I am still learning around here. It seems like having a BMS, even a simple one, would make this redundant? What is the advantage of running regulators and BMS? (besides having BMS shut off charger)

Thanks,

Brock
www.winzeracer.com
84v 400amp e-Kart (in progress)


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## JRP3 (Mar 7, 2008)

The cell regulators are a form of BMS, but this is an old thread and there are better, cheaper options if you want to use a BMS, like the MiniBMS advertized on the right.


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