ozzieflyer

Some questions on LiFE Batteries.

How long do they keep their charge, i.e if I charge them last Saturday and don't use them, are they right to go this Saturday?
How do I measure their charge? i.e. coming form NiCd's or NiMh's you could use a battery checker to "know" the charge in the batteries. How do we accurately do that with LiFe's?

How far allowable is it to use them and be safe, say an 1100 mah pack, down to 25% (when I figure out how to measure 25% capacity).

Thanks

TimBle

I've been using Hyperion Life battery packs now for over a year.

I find they hold their charge for months with very little self discharge. I have charged a pack and stored it. Fitted it to a plane 4 months later and it showed the same voltage  it had 15 min off the charger 4 months later.

Measuring their capacity is a bit of a problem. there are battery checkers availble that measures voltage against an ideal curve and interpolates the capacity. These are reasonable accurate but trend to be conservative (A good thing). the Hyperion EOS Battery checker is such a device.

Some folk prefer to charge a LIFE battery pack , fly it for a fixed perid of time say 20 min and then recharge it to measure what has been put back into the battery. they then have an idea of current draw per min. My reservation with this is that on no two flights will he current draw be the same.
However again approximations are good enough if he user is clever enough to recharge when capacity ius reaching 30%.

I have found thedrop off voltage for the Hyperion LiFePO4 packs to be around 6.2V.
thereafter you are within 5% of a broken plane. I never fly a plane with a LiFePO4 pack at voltage lower than 6.4V (excluding those packs that have a nominal voltage of 6.4V)

A.T.

Following might assist:
Optima Transceiver (RX) - Battery set up for Nitro/Gas models #1 - caution re NiMH & Alert re LiFE.

BarracudaHockey

My Feedback: (11)

The good thing is they charge fast so nipping a charge after a few flights is no issue.

jester_s1

Measuring the charge put in after a few flights is not as accurate as a measured discharge because some of the charging current goes toward heating up the battery, but it does get you in the ballpark. Lithium based batteries do not benefit from being used up like NiCd's do, so flying to about 50% capacity and topping off is best.

Silent-AV8R

If your LiFePO4 packs are getting hot then something is wrong. My Hyperion packs stay room temperature even when charging at 4C. I use the tiemd discharge method. I have found that the Hyperion (and other) voltage testers are way over conservative. Generally by at least 10% to 15%.

CustomPC

There are now several manufactures that make switches or devices with built-in mAh counters. These are semi useful for eyeballing the usage but the model has be on the ground to read it. The pilot needs to check the mAh used from the pack before he takes off and decide whether there is enough charge remaining for a safe flight.

Personally, i'm using a telemetry current sensor on my Multiplex radio. The sensor measures current and mAh used and stores the sum of the usage in it's memory between flights. I have a constant real-time readout of remaining capacity and an alarm when the pack reaches a preset usage. The receiver also monitors the voltage and triggers an alarm if the voltage drops.

pilotpete2

That certainly is true of Nixx chemistry, but with A123's or Lipo's the difference between the measured discharge current and amount of current needed to recharge is more than close enough for Govamint work. I've never been able to detect any temperature rise in any Lithium based battery I've charged[8D]
Pete

BarracudaHockey

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You could over engineer it all day long.

Or you could fly a couple of times and see how much you put in. Figure out your safe flights, and take a flight or two away as a safety margin.

FWIW I do an average of 325 per flight on my 50CC gassers, flying 3D with 5x 7955 servos and the ignition running off the same pack. I charge after 4 flights.

pilotpete2

Exactly[8D]
Pete

a1pcfixer

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What are some of the better LiFe/A123 balance chargers available?

I've heard some say the FMA CellPro 4S Gold is great, but it only does a single pack at a time?

TimT2000

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Where, who, Please share! I need 14 of them. Switches that is, not devices. The one I knew about was discontinued for rework.

Tim

BuschBarber

My Feedback: (2)

I use the FMA Cellpro 10S. It can charge up to two 5S packs at the same time. You are limited to 10a, or in the case of 5a packs, 2C. Both packs have to be the same number of cells and have to be discharged similarly or the charge takes much longer. The packs are charged in Series, so the charger sees two 5S packs as 10S.

FMA makes a Powerlab 8 charger that can charge more than two packs and at up to 40a, I believe. It charges the packs in Parallel. Each pack still has to be the same number of cells.

You can charge through the Balancing Taps only, or through the Balancing Taps and the Charge Leads. You can see the Supply Voltage, Charge Current, Total mah In, Elapsed Time, Pack Voltage, Individual Cell Voltage, and Internal Resistance of each Cell. It also displays a representation of the amount of charge left, as Fuel Percentage.

TimBle

Not sure that there is huge difference between most of the computerised chargers. Ihave been using a Turnigy Accucell 6 for 18 months and it charges the LiFePO4, A123, LiPO, LI-ION (3.6V) much better than the the industrial chargers Ihave for some of them.
It balance charges, and provides a on charge display of the cell balance. It works and its extremely cost effective. I know plenty of folk who also have great success with the iMax chargers

4*60

My Feedback: (41)

+1

rmh

The FMA10 S as mentioned above -easily the top of the heap
As for all the attempts at counting amps and using 6 volts as a cutoff ??
N F W- do it at your own risk.

Talk to guys who have some long time experience with the LIFE/A123 cells
Forget the guesswork. Some history:
The real reason for using the A123's (the best of the lot) was to keep voltage to servos as high as possible under loads.
This required technology which would supply high current levels throughout entire charged capacity.
The only close competitor is LIPO
The downside ,is a technology which has a severe drop at extreme end of capacity
For example -on my test station( two 1157 bulbs )- the output is at 3.3 v per cell for 75%of the cycle
(full cycle is almost exactly 30 minutes) at the end say 27 minutes the voltage fades - and when it hits 3 volts it quits in under a minute.
Recharge at 4 amps is possible, immediately- no problem
How good amp recording devices really are - I really don't know.
The relative weight of the cells to the total model weight is low - so I always doubled the possible battery needs
at field recharge -using a good balancing charger is quick- usually 15 minutes for my setups
The best part is NO friggen regulators needed so the failure points are minimal-
mainly you just need good wiring and a simple failsafe switch.

ozzieflyer

Check this out,
http://www.boomarc.com/products/162-...lliswitch.aspx

pretty cool. But i haven't tried one but have heard its good.

Silent-AV8R

FWIW here is a discharge comparison between a Hyperion LiFePO4 pack and a pack made with the Sanyo Eneloop cells. 500 mA load.

ozzieflyer

I guess my concern is, even though you calculate and know what you normally use, so you can estimate when to charge, with out a checker, you have no way of telling if a servo or something suddenly drew more current than normal, so reducing the capacity, way below the safe level, then 'OUCH' occurs.

ozzieflyer

That is a really good chart to look at.

TimBle

Its a good char tot illustrate a point but its not correct. The Hyperion packs hit 6.6V and gradually drop to 6.5V so that straight flat line should have a slight slope to it.
Its that slope the battery checkers look for because they measure the LiFe batteries to .001 of a Volt.

rmh

These two cell types are for completely differing uses.
The ENELOOP is a very high shelf life - low current app.
as such they are unbeatable
an example would be a TX pack whre the AA size makes them easy to fit. also cameras an all kind of low current stuff

The LIFE cell is for high current uses
prices are faaaar different too

Silent-AV8R

The point for this thread was not to imply or compare the ENeloop cells, but rather to simply show a constant current discharge curve. I did do the chart originally to show the difference in curves in order to highlight that Eneloop cells have a much higher voltage drop at a given load due to their higher internal impedance. I think they are great for transmitters and very low load airborne use. Higher load uses I would not use them.

Silent-AV8R

How is it not correct? It was obtained using actual data, not some theoretical concept. It is real data. BTW - I have found the Hyperion "checker" to be horrendously over conservative. It will always tell me that my packs are 10% to 15% lower than what I end up putting back in them. Checker says I am at 30% of capacity and the Hyperion charger will only put back in 55% to 60% of capacity. Both the charger and checker then read 100%. My Hyperion checker only measures, or at least only displays, to 0.01 volts as well.

rmh

The FMA "fuel guage" is also not accurate - not even close
again it shows a number which never equals % of remaining power
Here is the rub:
depending on the rate at which you suck power from th e batts- the "remaining power "will change

stated differently if the outrush is extremely high, the cells change temp and measuring will not be accurate (kinda like that ENELOOP chart - it makes the ENELOOP look like a cheezy cell - -but the current is of course beyond design specs.)
I see over n over comments about 2.4 rx failing -when in most cases - the failure is simply a failure to provide voltage req'd under load
Selecting wrong battery is a classic screwup
classic evaluation is "the battery was still almost full"
means nothing if the load is high enough.