LiFePO4 Batteries

As Jon says, it is always good to have a look at the spec.
Taking the PowerSonic PS1290 spec as an example
http://powersonic.com/images/powerso...10-PS-1290.pdf

At the 5-hour discharge current of 1.44A, the specified capacity for this PS1290 9Ah SLA battery is 7.2Ah.
Richard measured 180 min = 3 hours @ 1.4 Amps = 4.2Ah.
4.2Ah of remaining capacity out of the specified 7.2 Ah means that this battery has deteriorated to 4.2/7.2 = 58% of the original capacity.
If this is a used battery, with a number of deep-discharge cycles, this deterioration is quite normal.
If this a new SLA Lead Acid battery, this is a very poor specimen.

Any rechargeable battery is a consumable.
The capacity decreases with each and every discharge-charge cycle.
The use case has a big influence on the rate of deterioration, e.g: shallow vs. deep discharge.
Looking further down the spec sheet of the Lead Acid battery, in the "life Characteristics in cyclic use" graph, you can see that this battery has a life expectancy of only about 200 deep-discharge cycles (100% discharge) and about 1100 cycles of shallow (30%) discharge.
This is why I run my batteries in parallel.

Similar calculations can be made for the LiFePO4s. I have no specification for this chemistry.
Assuming that the LiFePO4 9Ah battery derates similarly to 7.2Ah at the 5-hour current draw, Richard's measurement would indicate:
280 minutes = 4.66 hours @ 1.4 Amps = 6.53Ah or 6.53/7.2 = 91% of capacity.
Not too bad.

As said, I have all 3 of my fused SLA batteries switched in parallel. I am very comfortable with that (and no, one battery does not charge the other !)
As far as I know, the LiFePO4 packaged batteries have build-in discharge and charge protection circuits. With those, I would need to understand the spec in much detail before I would be comfortable switching them in parallel.
3U

On Saturday, May 17, 2014 2:10:06 PM UTC-7, wrote:
As Jon says, it is always good to have a look at the spec.

Taking the PowerSonic PS1290 spec as an example

http://powersonic.com/images/powerso...10-PS-1290.pdf



At the 5-hour discharge current of 1.44A, the specified capacity for this PS1290 9Ah SLA battery is 7.2Ah.

Richard measured 180 min = 3 hours @ 1.4 Amps = 4.2Ah.

4.2Ah of remaining capacity out of the specified 7.2 Ah means that this battery has deteriorated to 4.2/7.2 = 58% of the original capacity.

If this is a used battery, with a number of deep-discharge cycles, this deterioration is quite normal.

If this a new SLA Lead Acid battery, this is a very poor specimen.



Any rechargeable battery is a consumable.

The capacity decreases with each and every discharge-charge cycle.

The use case has a big influence on the rate of deterioration, e.g: shallow vs. deep discharge.

Looking further down the spec sheet of the Lead Acid battery, in the "life Characteristics in cyclic use" graph, you can see that this battery has a life expectancy of only about 200 deep-discharge cycles (100% discharge) and about 1100 cycles of shallow (30%) discharge.

This is why I run my batteries in parallel.



Similar calculations can be made for the LiFePO4s. I have no specification for this chemistry.

Assuming that the LiFePO4 9Ah battery derates similarly to 7.2Ah at the 5-hour current draw, Richard's measurement would indicate:

280 minutes = 4.66 hours @ 1.4 Amps = 6.53Ah or 6.53/7.2 = 91% of capacity.

Not too bad.



As said, I have all 3 of my fused SLA batteries switched in parallel. I am very comfortable with that (and no, one battery does not charge the other !)

As far as I know, the LiFePO4 packaged batteries have build-in discharge and charge protection circuits. With those, I would need to understand the spec in much detail before I would be comfortable switching them in parallel.

3U

I think more relevant to gliders is how deep the battery can usefully be discharged. SLA specs usually regard completely discharged as 10.5V. Modern electronics have DC-DC power supplies inside, as the input supply voltage deteriorates the current consumption goes UP, in order to supply the same currents at 5 or 3.3V to the electronics internally. Also when you hit the transmit button to announce your pattern at the end of the day, in my glider at least the current goes from about 0.6A to 1.6A. Add another 20% due to low voltage and I am trying to draw 2 amps from a mostly depleted battery, dropping the voltage further.

I don't care if I only get 200 deep discharge cycles from a $30 SLA - that represents many years of flying, the battery will decay from age before that. But the LiFe will hold its output voltage up higher when it is deeply discharged, according to Starkpower well above 12V even at 90% discharge. Another potential advantage of LiFe is that they need not be recharged fully immediately after use as they do not sulfate. Most Li battery vendors seem to recommend leaving them in a partially charged state (50-80%) for storage. So if you forget to charge it after the weekend's flying, you will do less damage to it.

On Saturday, May 17, 2014 10:09:38 AM UTC-4, Richard wrote:

I did a discharge test on the Stark Power 12v 9Ah. 1.4 amp draw got me 280 minutes.



Most of these LFP batteries come up right to, or just over manufacturer's spec. For example, I bought a bioenno 12AH battery that I tested at 12.3 AH using a fancy RC battery charger with an integrating discharge function.

T8

I am happy with my pair of Tenergy 12.8VDC 10Ah LiFePO4 batteries and have used over a dozen larger 12.8VDC LiFePO4 battery packs from batteryspace for other projects with good results too. I called Tenergy in California and these Tenergies do have the under and over voltage protection built in. If you shop around, you can get them on special with chargers included but a constant voltage power supply works fine too.

The weight is nice, the charge cycles are awesome, how long it holds its charge is really awesome and the steady output makes a big difference for radios and such. They dislike freezing temperatures more than some other options if that is an issue.

You can use your trickle charger (as long as it doesn't have an auto desulfate mode) but it is not the best idea for reasons listed and explained on here and all over the internet. Also, these are LiFePO4's so you can blast them to a charge in no time compared to a lead acid.

I wire them to the glider with inline fuses and the same connectors that I have on my chargers for convenience. Then I cover the terminals with hot glue and make handles with packing tape as my glider is a very tight fit for two 10Ah batteries. You can pull them out by the wiring (not recommended) or the slim tape handles (recommended) when needed.

LiFePO4's are starting to get very developed and produced by some bigger manufacturers so it is pretty hard to go wrong as long as they fit and meet your power needs. There are some good discussions and links on doing a power budget for your glider around too.

On Monday, April 28, 2014 11:12:01 AM UTC-6, MQ wrote:
I am happy with my pair of Tenergy 12.8VDC 10Ah LiFePO4 batteries and have used over a dozen larger 12.8VDC LiFePO4 battery packs from batteryspace for other projects with good results too. I called Tenergy in California and these Tenergies do have the under and over voltage protection built in. If you shop around, you can get them on special with chargers included but a constant voltage power supply works fine too.



The weight is nice, the charge cycles are awesome, how long it holds its charge is really awesome and the steady output makes a big difference for radios and such. They dislike freezing temperatures more than some other options if that is an issue.



You can use your trickle charger (as long as it doesn't have an auto desulfate mode) but it is not the best idea for reasons listed and explained on here and all over the internet. Also, these are LiFePO4's so you can blast them to a charge in no time compared to a lead acid.



I wire them to the glider with inline fuses and the same connectors that I have on my chargers for convenience. Then I cover the terminals with hot glue and make handles with packing tape as my glider is a very tight fit for two 10Ah batteries. You can pull them out by the wiring (not recommended) or the slim tape handles (recommended) when needed.



LiFePO4's are starting to get very developed and produced by some bigger manufacturers so it is pretty hard to go wrong as long as they fit and meet your power needs (We used to set the under and over voltage with solar charging units and analog circuits and laugh at the construction of some of the cells). There are some good discussions and links on doing a power budget for your glider around too.

On Monday, April 28, 2014 9:55:16 AM UTC-5, vontresc wrote:
So I am in the market for a new battery for my Libelle. I was thinking it might be time to upgrade to a LiFePO4 battery.



Any recommendations/reviews from the community? I've seen people using the K2 and Stark Power batteries. Any preference between the two?



Thanks



Peter

Peter I ordered mine from these folks. Have used it for a year now and very happy with it. Make sure you get with the built in BMS typefrom whoever you order from.

http://www.bioennopower.com/collecti...epo4-batteries

The discharge cited above is pretty typical for LFP batteries. See my webpage for the measured discharge curves for the K2 LFP battery. The graph shows a very flat discharge followed by a sudden drop at the end of the cycle.

http://www.foxonecorp.com/index.php/...m-iron-battery

For anyone who is interested in a K2 battery, I will be in Cordele for the Region V South contest with a few K2's and chargers on hand.


Dave Springford
Fox One Corp

Does anyone have experience charging these with a battery tender plus? I've got a new K2 10ah battery and considering a specific charger.

What indications does the battery tender give? What's a typical time to charge?

Jeff,

The LFP batteries, while they can be charged with SLA chargers, are better charged by a dedicated LFP charger. The reason for this is they need to charge up to 14.6 volts to get a 100% charge. Most SLA chargers will give only 13.75 volts and this leaves the LFP battery around 80% charged and this pretty much defeats the purpose of buying the higher capacity LFP battery.

I have LFP chargers for $30 (see the address for my webpage in my previous post).


Dave Springford
Fox One Corp

A multi chemistry charger with firmware that is upgradable to accommodate changing battery technology is a better way to go. CellPro (and other knockoffs) has several chargers that will safely and accurately charge LiFePO4 batteries among many others with one charger.

I have used a Cellpro multi 4s charger to charge my Shorai lithium iron battery which does not have a battery management system for quite a while. It will also charge a lead acid, nimh, nicad, lipo and others.

You will be able to set the charge rate, monitor the health of the cells, balance the cells (still important for a LiFePO4).