NiMh vs LiFe. What are the advantages and disadvantages?

[Don Fry]

I find, it’s not unusual to get the battery in a relatively inaccessible location, as it’s heavy, and CG issues says where it’s ideal location is. I would think hard about one pack, all models, as a practical solution.

[Martin McIntosh]

Just had a quick look at HK who have Zippy LiFe,  1100, £4.06, 2500, £9.10, 2100, £11.21, 1800, £9.72, 3S 1500 Tx pack, £7.63. Whether they are actually in stock I don`t know.

Rapid R/C have Zippy 1100, £9.99, 2500, £17.99, plus a range of TGY Nano which I do not particularly recommend.

 

Most of my models now have the Zippy ones in various capacities. No problems at all and most servos will easily handle 6.6V.

[Ron Gray]

On some of my larger models I use a 3000mAh Li-Fe and that is swapped between them as necessary. I also use 2000 and 2600mAh ones on other models.

 

[Nigel R]

13 minutes ago, Martin McIntosh said:

Whether they are actually in stock I don`t know

 

HK appear to have universally given up selling lithium cells in the UK.

 

[Chris Walby]

IMO for what its worth

As they were handed to me fully charged, I simply put them on a fairly high discharge rate of double my estimated typical average rate of 600mA at 1.2A to ensure that I wasn't going to be misled by being too gentle with them.

Have to disagree here, I have seen 3 small digital servos pull over 5A instantaneously against high mechanical loads and they weren’t even close to being stalled. My point is that when you need to lean the sticks and the model is I a high load situation is not the time to find out the RX brown’s out for however long. These packs state 44A max, then they should do +40A no trouble. Its like driving a car with a brick under the throttle peddle, ok until the day you need the extra performance and its not there.

 

Total delivered to the charger's cut off point of 2.9V per cell was 2250mAh for the first pack and 2280mAh for the second. 

This was what I was trying to achieve and I now know why I wasn’t, but more on this later

 

I would happily use these packs in my own models - and certainly in preference to NiMH or LiPo packs via voltage regulators.

Agree and disagree on these points.

As I see it the only way to truly know both overall capacity and actual capacity of a LiFe pack is to do a discharge and recharge test due to the very flat discharge curve and difference between manufacturers products. This means either monitoring the discharge current in the model or cycling them prior to flying (what a faff). Agreed they are better than NiMH in weight, but not as easy or accurate as Lipo to determine capacity based on voltage alone.

 

Again I am going to disagree here!

P.S. Chris was quite correct in his pricing - these are Spektrum branded batteries and Nexus list them at £39.99 a pop!  I suspect that you pay a massive premium for the OEM branding and cheaper alternatives are probably just as good.

 

“Probably just as good” does not cut it with me. I am talking about a 17 lbs model nothing else. I will be the responsible person while this thing is airborne, the safety of others and myself is paramount and I have to be able to say that I took all reasonable precautions before and during flight to avoid danger. If the packs test out okay and it has failover built into the RX then ok.

 

Knowing what I know now I am happy to use these packs in the intended model, might even use them in some others, but if I build another (Ta154 mk2) then I will use the Lipo UBEC approach not because its better, but because its far easier to determine if the battery pack is healthy or not (in my experience).

 

For me the NiMH/LiFe debate it like arguing about VHS and Betamax, technology and time has moved on, live streaming is here and now. LIPO availability, cost and performance really means neither have a place apart from the diehards who will argue until the cows have come home.

 

PS – What I have learnt is that some meters massively miss read when measuring LiFe capacity and that unless you really know your LiFe pack voltage discharge curve then you not that much wiser to knowing what’s left I the pack.

[Martin McIntosh]

I really would not trust Lipos in an i/c model having had so many puff up as I said above, 4Max excepted maybe but at what a price. No point anyway since LiFes are so cheap, light and reliable, and you should not need a regulator. (most are only 6A max anyway).

I have an 18 lb Spit and a 28 lb Hurri, each with 2x 1800 Life on 9 high torque digi servos. I no longer use snakes or kwik links due to the servo load but instead use ball links throughout and ensure that they are really free. The drain from the packs per flight is very small indeed in each case and I could happily fly either all day if I wished.

 

It is a complete waste of time using a battery tester but very easy to determine the discharge per flight and working from there.

 

And another thing, look at the price of a ready made 5s Eneloop 1900 these days.

[Chris Walby]

11 hours ago, Martin McIntosh said:

It is a complete waste of time using a battery tester but very easy to determine the discharge per flight and working from there.

Could you expand in detail how you accurately determine the remaining battery capacity between flights? Cheers

[Martin McIntosh]

You don`t. Simply see how much they take to recharge after a flight or two.

[Ron Gray]

But if you plug a checker into the battery then operate the 'plane controls that would give you the load, wouldn't it? I've just tested it on one of my models using my ISDT checker, at rest the checker showed 37%, under load (servos operated) it dropped to 25% (old Li-Fe).

[Martin McIntosh]

Please, you cannot check a life pack with any voltage or capacity checker since until they fall off the cliff the voltage will remain at 6.6. Obviously if a load is applied then this will be lower but this load must be constant, not just wiggling servos about. Forget what you used to do with NiCads, NiMis, and LiPos, these things are quite different and you may be surprised that your flying and Tx times are considerably increased. With NiMis I always recharge if they have not been used for a week or so but you would be wasting your time doing this with LiFes.

[Martin Harris - Moderator]

All my testing and the various literature available on the net shows a steady decline in voltage over the main body of the discharge so it should be possible to detect approximate state of charge with reasonably accurate measurement.  When the cliff looms and detection becomes much more obvious, there is enough energy to run an average model for several minutes but it would take poor management or extremely parsimonious battery selection to reach this point.

 

 

Terminal discharge voltage set at 2.9V per cell.  Voltage recovery on no load evident. Even from 3.06V (6.12V pack voltage) it gave 50mAh before reaching 2.9V (5.8V pack voltage) so comfortably more than enough to land safely - even with a couple of missed approaches!

[EarlyBird]

12 hours ago, Martin McIntosh said:

Please, you cannot check a life pack with any voltage or capacity checker since until they fall off the cliff the voltage will remain at 6.6.

@Martin Harris - Moderator your tests prove this statement is not true. Where did the notion of falling off a cliff come from? ?

[Denis Watkins]

30 minutes ago, EarlyBird said:

@Martin Harris - Moderator your tests prove this statement is not true. Where did the notion of falling off a cliff come from? ?

Falling off a Cliff

Comes from looking at the graph drawn of the useful voltage/ capacity

Suddenly and abruptly,

Dropping quite comfortably to zero

The term is just an observation of behaviour from a plot on a graph.

[Don Fry]

If worried, in 2021, why not fit a telemetry sensor to the Rx pack if lithium. Then the lady can shout at you when needed.

[Maurice Dyer]

On 23/05/2021 at 12:27, Phil McCavity said:

Well the advantages of NiMH are that they are cheaper, don't need a religious charging regime, can take a lot of abuse, don't need additional trickery to reduce the voltage, don't need a special charger and are much easier to obtain.

Agreed. Just use your loaf when charging, and keep a record (if) and when you cycle them. Simples.

[EarlyBird]

46 minutes ago, Denis Watkins said:

Falling off a Cliff

Comes from looking at the graph drawn of the useful voltage/ capacity

Suddenly and abruptly,

Dropping quite comfortably to zero

The term is just an observation of behaviour from a plot on a graph.

It's a term I have heard in reference to NiMh when comparing to Nicad and used as a reason not to use NiMh. It's also a term that strikes fear as the concept makes one think that control will be lost with little warning. In reality if good battery management is practiced does this ever happen? 

 

[john stones 1 - Moderator]

It's a term used for dramatic effect, anyone out there put one in using life that fell off the cliff ?

[EarlyBird]

9 minutes ago, john stones 1 - Moderator said:

a term used for dramatic effect

That's a lot of words for a Yorkshire man, why use two words when non will do (Seb Coe talking about his Dad)

 

Living close to Yorkshire (only a bridge to keep us apart) I read that to mean 'nonsense' ? yep why use two words when one will do, as my Dad would say. ???

 

 

[Ron Gray]

1 hour ago, john stones 1 - Moderator said:

It's a term used for dramatic effect, anyone out there put one in using life that fell off the cliff ?

 

Nope.

[Don Fry]

1 hour ago, EarlyBird said:

That's a lot of words for a Yorkshire man, why use two words when non will do (Seb Coe talking about his Dad)

 

Living close to Yorkshire (only a bridge to keep us apart) I read that to mean 'nonsense' ? yep why use two words when one will do, as my Dad would say. ???

 

 

As an effete southerner, this is too complicated for me.

[Martin Harris - Moderator]

Very much in line with my experience. I simply accept the false triggers if I know that they coincide with an appropriate input. I have never found the need to discharge a pack to the trigger voltage with normal inputs (set well back from the cliff edge anyway) during real world operation but telemetry gives me confidence that I have a backup to my battery management routine. 

[Martin McIntosh]

MD, Eneloops are at least three times more expensive than LiFe, need to be constantly topped up when not in use, LSD? Rubbish. They self is discharge enough to worry a modeller after a week. I still use some LSDs but Eneloops only.

Falling off a cliff means that the voltage is maintained until just before they are flat so you would need a very sophisticated checker to see the point at which they expire. Why push a flight pack that far anyway? I could probably have fifteen flights a day with many of my models but who does that? A spare pack would only cost about £7 and they recharge in 1hr.

[Chris Walby]

Okay so I have committed to using Life batteries in a model that hopefully I'll fly on a regular basis for its size, complexity and flying field wind direction  ? perhaps once a month if I am lucky for 1/2 the year. 

 

As I don't measure RX current this this leaves me with charge it up before a days flying (no problem there and could even note the charge mAh), but this just tells me what I have put in, not the total capacity of the pack. For me the only way to determine pack capacity is to discharge it to 2.95V and then recharge it and see how much goes in. This requires that I sit at home watching my charger/discharger at 0.8A time and out about 4 times outs or buy a new charger that can discharge at a higher rate. Can still do what Martin did and push it a little harder, but for something capable of 20C it might not be truly indicative of performance.

 

I still can't see how you can tell if a pack is knackered or not (loss of capacity) by just measuring the voltage or even its state of charge as some batteries seem to have a different voltage characteristic than others.

 

If anyone has any any suggestions I would like to hear them as it might save me from making a test rig and doing a discharge/recharge test each time I might fly the model. Its really not that onerous as I home balance charge the Lipos and record the capacity and charge current mAh. That way I can see the lipo performance drop off which indicates they are past their best.   

[leccyflyer]

If you're only flying the model once a month I'd have thought the simplest approach would be to charge the Life receiver pack the night before and just fly the model, just as you would have done with a NiCd pack in days of yore. The excess capacity is probably going to be so far above the likely current draw of the radio gear as to give a huge safety margin.

[Don Fry]

Chris, might I put a bit of sanity in the debate.

 

over the years we have done;

non rechargeable cells. UMMMM? Today, perhaps not.

NiCad, worked OK

NiMh, worked OK (ish) (my opinion)

LiFe, works OK, (preferred, my opinion)

LiPo, works OK (preferred, HV servo)

 

Go back, I’ve not noticed many falling back to earth, battery gone dead. 
 

Back then, we did charge before fly. If fussy, perhaps not quite full. (chemistry of cell). 
 

 

We used to go on a  500 mAh pack, 5 kilo model, 1000 mAh pack, nowadays we shiver to fly on 5 times bigger. 
 

My take, get a battery that takes a quick charge, shove it it before you go.  Fly

 

Afterwards, do an occasional discharge to prove you have bottom space before disaster.
 

 

Edited August 15, 2021 by Don Fry
No change, can’t make mind up.