why are lifepo4 flight packs not used very much?

[namustang1a]

I have been puzzeled to why lifepo4 flight packs are not used more and the lack of availability.

I live in a smallish flat with no garden/shed and am banned(by swimbo its her flat)) from owning lipos just incase of misshaps . I do have powered gliders using a123 hard cells but thay are limited to low amh .

The poly flight packs have good amh ,fast charging and can be run down to next to no volts, more life/charges and as far as I know don't self combust if a misshap happens,just brought a 4s pack from HK that ill be trying soon in a veron Cessna.

Any views/comments on the subject good or bad are most welcome.

Ian

[Andy Meade]

I don't think there is much difference to LiPo, it's only the electrolyte that's different, so you should treat them the same as a LiPo when it comes to respecting them when charging. i.e. no piercing, dont charge them in a model, short circuit will make them go bang if abused.

That said they do allow deep discharge, can be left fully charged, and the 6.6v pack ends up a lower voltage than a 6v NiMh when fully charged. I like them as they eliminate the BEC that would have to be used on a LiPo, and thus getting rid of another failure point, so tend to use them in large models now.

[Ben B]

The original lifepo4 cells weren't very high discharge so were less popular therefore lipos were more commonly used hence

1) better range of cells / capacities available

2) all lithum chargers will do lipos, not all will do lifepo4.

3) not all ESCs can be programmed to have a lifepo4 LVC

So it's not that lifepo4s are intrinsically "worse" than lipos (especially now high discharge lifepo4s are available). They do have a lower energy density (IE slightly heavier for a given capacity) but that's not always an issue (eg a WW1 fighter will cells at the front it's useful).

[Phil Green]

Posted by Ben B on 13/04/2016 11:03:11:

The original lifepo4 cells weren't very high discharge

I'm sorry I strongly disagree Ben.

The original LiFePo4 cells were made by A123 Systems over 10 years ago and were specified for a continuous 70 amp discharge. Thats a genuine 32C which few Lipos can match today, regardless of manufacturers 'C' claims!

Cheers
Phil

[Ernie]

Hi Ian, swimbos should never ever be told anything about our toys. Deception is the name of the game.

ernie

[Bob Cotsford]

As Phill pointed out, high discharge LiFe have been around for a long time, but were not popular because they had weight issues and being metal can cells packs ended up with more girth than a similar LiPo. Now that soft pack LiFes are available I guess it's more down to habit than anything.

Certainly for receiver packs LiFe are my first choice now but I've not tried LiFe power packs.

[Allan Bennett]

Posted by namustang1a on 13/04/2016 10:37:29:

. . . I do have powered gliders using a123 hard cells but thay are limited to low amh .

The poly flight packs have good amh ,fast charging and can be run down to next to no volts, more life/charges and as far as I know don't self combust if a misshap happens,just brought a 4s pack from HK that ill be trying soon in a veron Cessna.. . . .

As someone has already mentioned, genuine A123 LiFePO4 packs are capable of high amps, but they only come in two sizes so far as I know -- 2300mAh and 1200mAh capacity. Their amps capability is as good as most LiPos, but their weight per watt-hours capacity is greater than LiPos which, along with their limited number of different sizes, is why they seem to be going out of fashion.

In my first electric conversion (Flair Magnatilla) I started out with a brushed geared motor and 12-cell NiMh pack. I soon replaced that with a brushless AXI motor and a 5S A123 pack. Now I'm gradually going over to 4S 3300mAh LiPo packs, which weigh exactly the same as my 5S A123 and fit in the same battery bay, and which give me 60% longer flight duration.

When you talk about "poly" flight packs I think of LiPo, so which batteries are you referring to in that paragraph?

[namustang1a]

Allan Bennett..

I am referring to the lifepo4 poly flight packs(looks like a lipo ),A123's are the can cells like nimh packs.**LINK**

Ernie..

Swimbo is also involved in building and flying so no deception and I do like the quiet life.

Ian

[Grant Webb]

Hi guys.

I use lifepo4 batteries in my airborne packs exclusively these days and even my Tx (JR XG-8) runs on a lifepo4.

I have never used the A123 cells, but used to use NMiH. That is until I lost models due to black wire rot, which NMih have been blamed to contribute to.

Here is a video you might be interested in to demonstrate how much abuse the lifepo4 cells really can take. Not very scientific, but the proof is in the viewing... https://www.youtube.com/watch?v=XymqQ-YlfJ0

Edited By Grant Webb on 14/04/2016 07:34:44

[John F]

I think a bit of realistic viewing is due here. If lipo's really were that dangerous they would never be allowed for sale.

A bit of tomfoolery with a busted battery and a BBQ has led to a huge amount of myth and legend about how lipo's are almost hand grenades and should never be looked at in a harsh manner.

Of course there is a miniscule danger if you charge a busted pack but that is true for any battery out there. If it is damaged it could case a fire.

Do you have a laptop? A iPad? A kindle? Kindle Fire? A Hudl? A mobile phone of any description? E-cigarette?

Chances are that you have at least two of these devices and more than likely a collection of the above. They all have lipo's or lithium ion batteries inside them, which is a lipo in a hard case!!

[Allan Bennett]

Posted by namustang1a on 14/04/2016 06:18:40:

Allan Bennett..

I am referring to the lifepo4 poly flight packs(looks like a lipo ),A123's are the can cells like nimh packs.**LINK**

...

I wasn't aware of those; so we've now got hard-can LiFePO4 (A123) and soft-case ones, and hard and soft case LiPos.

A quick check suggests that even the soft-case LiFePO4s may be about 30% heavier than same-capacity LiPo, but they're worth considering if they don't flame like LiPos can.

[namustang1a]

John f....

I am aware of the veried uses of Lithium-ion cells,Lithium-ion being the type of cell not the chemical make up,lipo being one of them LiFe being another(see Lithium-ion on wiki).

As for lipos if treated/cared for correctly there is no reason why they should be dangerous,i think a lot of the fires etc where possably down to lack of user info in the way to handle them when first introduced , education is a good thing but accidents happen unfortunately.

Allan Bennett...

LiFepo4 poly packs have been around a few years now, yes they are heavier then a lipo but then again how offten do you add nose weight to an airframe.

Grant webb...

LiFepo4 packs are used a lot as rx/tx power which to me is odd if you realise that the power drop off is very quick much more like a fuel tank then batteries.

Thanks for the link I have seen it before, its the only one I have come a cross wilst looking into LiFepo4 safety.

Ian

[john stones 1 - Moderator]

Nimhs drop of steeper than Nicads did Ian, similar to Life, not likely to be a problem on a days flying and there's a charger sat there when back at home.

John

[namustang1a]

Thanks john I was not aware how similar the drop of was, we live and learn(field charger... top up in 20 mins fly till dark )

Ian

[PatMc]

IMO the nimh steep drop of curve is completely overstated. One myth that's developed from this is that you only have a few secs to land if you get a LV warning from the Tx.

[john stones 1 - Moderator]

Posted by PatMc on 14/04/2016 15:13:50:

IMO the nimh steep drop of curve is completely overstated. One myth that's developed from this is that you only have a few secs to land if you get a LV warning from the Tx.

Yep charge em, go fly...think less

[Martin McIntosh]

I too am slowly changing my i/c flight packs to LiFe soft shell ones. I was surprised to find that two 1800 mA/h 2S packs plus a failover switch actually weigh less than two 6V Eneloop packs. A fellow club member who recommended these cells wondered why I had gone for such a high capacity and I stated that on NiMh cells I was using about 120 mA/h per flight from each pack. I found that with the LiFe ones I was only using half that on the same model which does not make any sense to me (Savox 0252 servos).

I have therefore fitted two 700 mA/h to a new, as yet unflown pride and joy.

Does anyone use unregulated LiFe cells directly to supposedly 4.8V servos? I have not tried that as yet.

[Allan Bennett]

Posted by namustang1a on 14/04/2016 13:28:54:

... Allan Bennett...

LiFepo4 poly packs have been around a few years now, yes they are heavier then a lipo but then again how offten do you add nose weight to an airframe.

...

I don't add dead nose weight

I figure what weight of battery I need, so then I usually want to get the one with most mAh, which will be a LiPo.

I'm not giving up on LiFePO4 completely, for it's nice to have one or two models using them, so I can keep their batteries fully charged, and they're ready to go whenever I want without having to charge.

[Martin Harris - Moderator]

LiFe are supposed to be tolerant of fast partial charging, so if you are paranoid about the rapid voltage drop at end of discharge, then a quick top up between flights should allay any fears.

[Grant Webb]

Posted by Martin McIntosh on 14/04/2016 17:32:06:

Does anyone use unregulated LiFe cells directly to supposedly 4.8V servos? I have not tried that as yet.

Hi Martin.

You shouldn't have any problems running your servos from an unregulated LiFe battery - the old NiCD packs actually come off your charger at somewhere around 7.2v and take a while to drop off from there. LiFe batteries have a quicker drop off rate initially, so would in fact be a lesser risk. In any case, I believe standard servos are rated up to a max of about 7.6v.

I've been running Futaba S128's directly off 6.6v LifePo4 for a while now and never had a failure.

Cheers.

[Cuban8]

Don't forget that radios were often sold years ago with a 'dry cell' option, i.e. they came with one of those awful RX battery boxes for use with AA Duracells or similar. 'Dry' batteries are rated nominally at 1.5V each, so giving something like 6.5V for four batteries when they were fresh - the servos coped OK and as far as I'm aware, standard servos are still rated for use with X4 dry cells.

Edited By Cuban8 on 15/04/2016 07:38:50

[Martin McIntosh]

One reason I asked that is because I started a thread recently to try and determine why one aileron servo insisted on cycling from end to end frequently, despite it being replaced twice. They are HS82MG rated at 4.8 to 6V. The BEC supposedly rated at 5.5V actually gave 5.7 but that should have been no problem.

A contributor suggested that another servo may be interfering which was when I realised that the rudder has a JR 591 rated at 4.8v only. Replacing this solved the problem.

I have several of these and when I changed all i/c models to 6V they started to `wander about at will`.

The thing is that as quite correctly stated above, the freshly charged voltage of a 4.8V pack would likely be way over 5.7 for a while yet did not give any cause for concern.

I shall experiment on the bench with LiFe cells connected directly and hope for no smoke.

[Martin Harris - Moderator]

MacGregor still advise that non-HV rated JR servos are not suitable for 6V operation.

[Bob Cotsford]

Posted by Martin McIntosh on 14/04/2016 17:32:06:

I have therefore fitted two 700 mA/h to a new, as yet unflown pride and joy.

Does anyone use unregulated LiFe cells directly to supposedly 4.8V servos? I have not tried that as yet.

I use unregulated LiFe all the time Martin, though one batch of HS645s do seem more stable on a regulated supply, unregulated the neutral was wandering slightly.  I've not noticed any problem with JR servos in at least two models equipped with 2S LiFe. 

The only thing I'd be wary of with the 700s doubled up is their ability to cope with high servo current demand on larger models. Certainly with a single 700 pack I noticed a fair old voltage drop at times using 'standard' size servos if moving multiple servos at once. 1100 packs seem better able to cope, especially with digital servos in the mix.

Edited By Bob Cotsford on 15/04/2016 12:31:57

[Martin Harris - Moderator]

Interesting observation, Bob. Quite coincidentally, I used a 700 soft pack for the first time yesterday (bought 4 a while back and used the first two for a wheel brake experiment) in a fairly standard sports model I haven't used for a while which needed the NiCd receiver battery replacing. I did put a diode in series with it in order to drop a little voltage but got a couple of low voltage alarms while stick wiggling.

My previous LiFe packs have been 1100 A123s which held up without protest under load with similar diodes.

Edited By Martin Harris on 15/04/2016 15:50:13