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Power & LiFePO4 Chemistry - Charging ?


mikefilosa

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I am interested in trying an LiFePO4 battery in a new setup - 40 or 60ah.

The investment cost here is pretty steep, so I don't want to make a mistake!

 

They are often sold with marketing that commends their utility as replacement block batteries for any standard or AGM block that we use conventionally.  (As our market is rather small for such a manufacturer, these larger blocks seem to be aimed at the golf cart / handicap scooter crowd.)

They all seem to use 14.6v as charging voltage, leaving a battery that's fully charged at 12.8-13.2

 

I've also seen mention of the preference to use a PCB in the battery build which "spreads" out the charging amongst the cells in an even fashion and enhances performance. 

 

I have not been unhappy with my conventional AGM blocks, but have been thinking about this newer, MUCH lighter approach before I retool for my next big project.  These batteries also have exceptional lifespans.  And,  I am also looking to build this myself as a cost saving measure....

 

So....  I am getting very conflicting reports about charging them up. 

One source says my PSC PowerMax will be just fine for charging and distribution. 

Other sources say there is a "specific charging regimen" involved in their use -

This could be true, or could be an easy excuse to sell chargers - the chargers don't seem very sophisticated or different at first glance.  The presence of a PCB installed IN the block would seem intended to "smooth out" the charging process, but hey, what do I know?  Just a guess....

 

Does anybody have any experience with a larger LiFePO4 homebrew setup, and charging?

And just as important, has anyone HAD, or know of others that have had, a LiFEPO4 casualty, tragedy, catastrophe, or other unwanted career-changing consequences from experimenting with this latest greatest chemistry?

 

Any insight will be greatly appreciated, carefully compiled, and shared for the masses....... 

 

Thanx

 

MF

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Michael:

 

all of my power is DIY.  I have never had an issue.  I buy my cells and chargers from Batteryspace.com.  Reasonable price and, you will occasionally find a good value.  For LiFePO4, a general rule is $1/watt.  Significantly under that and you are in value-land.

 

I would suggest switching to a higher battery voltage.  Something in the 24-30 volt range.  I say that because there are very efficient  DC-DC voltage converters that will bring anything within 22-30 volts down to a constant 13 or so volts.  If you start out with a 12-13v battery, the cut-off voltage is not that far down and, in my experience, as the voltage drops below 12volts our gear has to work harder (read as less efficiently) to stay on.  I realize this is extra weight and space for a converter, but that's how (my cart) rolls. 

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Michael -

Awesome idea, going 24 - 30volts and then stepping down towards 12v - ish...

 

Firstly, your experiences with LiFePO4 have been good, using simple conventional charging process, correct?

 

I have several good ol' PSC PowerMax units - I believe they are created for 12v charging, feeding 13-13.8, and will charge one or two blocks simultaneously, carefully and by design, enabling you to operate AND charge whilst plugged into anywhere between 100-240v.

They distribute 6, 12, or 18v via 6x 4p xlr outputs based on your selection of Pins 2 (6v), 3 (18v), or 4 (12v) in the cables you make or buy to connect to your gear.  

 

So - I doubt if I can safely charge battery blocks to 24-30 through these trusty workhorses and achieve your desired effect.  Do you have special chargers built into your system, or do you externally charge overnight exclusively? 

Nothing wrong with that at all !

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Hi Mike,

 

I've been on the same (but very slow) mission as you. I have a PowerMax on my cart and have spoken to Ron at PSC. He's pretty confident that the LiFePo batts would work fine (charging and discharging). I linked him to the batteryspace.com page for 12v versions (which I think I got from a post that Jeff W. made). However, the people at batteryspace were a little more hesitant. I can understand where they're coming from (we're using this for a different application than it was intended). I didn't mean to ask them if they thought it would work, I was inquiring with them about alternatives in battery dimensions so it would fit in my cart. So that's where my journey has stalled out at the moment. 

 

So...I wanted to say I think you're probably on the right path. And I wanted to post so I can easily find this page again so I can follow your progress. 

 

Josh

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hi michael,

i used diy lifepo4 batteries for the last 2 years exclusively, but with lesser capacities ( 20 ah ), put in small pelicases. weight reduction is stunning and they proofed to be at least as robust as sla's

i did the first pack with just 4 plain cells in series, no protection board. i cannot recommend this at all, as the cells will absolutely die , especially when overdischarged. also, the cells voltage will drift over time, reducing the effectively usable capacity. so, some sort of balancing circuit is recommendable.

the places selling those cells are usually carrying a variety of different protection circuit boards in their sortiment, also pcb's with integrated balancing circuits, which i use ( eg. http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=5175 ).

generally, lifepos need a slightly higher end charge voltage than sla's. as chargers i use ctek car chargers with 14.7v end charge voltage, which are primarily laid out for leadacid, but will charge lifepos ok. never tried a designated lifepo charger as there was no need until now. i guess the powermax chargers will be ok, as they are also designed to charge sla's. they might not charge the battery to a full 100% , but they wont damage the cells due to a slightly low end charge voltage.

the discharge curve of lifepos is very flat and voltage under load is quite stable. so, a topped off battery will start around 13.4v and then quickly settle around 12.8v , from where it drops towards 12v until nearly empty. the voltage drop in the end is very steep, so if voltage falls under 12v, the battery is basically flat.

marco

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