Jump to content

NiMh vs LiFe. What are the advantages and disadvantages?


Recommended Posts

I started out using 500-600 mAh Nicad batteries to power the receivers in my models in the late 1980s. I found that I could fly all day with no problems. When NiCads were no longer readily available I started using NiMhs.

 

Nowadays I use 1600-2500 NiMhs in my models which are mostly traditional sports, vintage or trainer models though I also have a 1/6 scale BE2e and an incomplete DB Sport & Scale Auster. 

 

I use a Spextrum DX9 transmitter, Spektrum receivers and Hitec servos. I see that quite a few pilots are using LiFe batteries these days. What are the advantages of using LiFes instead of NiMhs?

 

Link to comment
Share on other sites

Life, hold charge forever, tough as old boots, has a long service life, delivers as much current as any power hungry digital servos might desire, can be charged at high rates, no false peaks,  smaller, lighter.

Nimh, none of the above.

if concerned about higher voltage output, invest in a good Ubec/switch and you end up with a reliable power source.

I like life packs.

 

  • Like 1
Link to comment
Share on other sites

1 hour ago, Don Fry said:

Life, hold charge forever, tough as old boots, has a long service life, delivers as much current as any power hungry digital servos might desire, can be charged at high rates, no false peaks,  smaller, lighter.

Nimh, none of the above.

if concerned about higher voltage output, invest in a good Ubec/switch and you end up with a reliable power source.

I like life packs.

 

Hi Don

 

Do LiFe batteries have a higher voltage than NiMhs?

 

What is a Ubec?

 

Do you mean invest in a good Ubec, or in a good switch or in a good Ubec-switch?

 

Do you know of a good supplier of LiFe batteries and Ubecs?

 

Regards

 

David

 

 

 

Link to comment
Share on other sites

My micro helo, a tiny beast, has a 60mha life battery that doesn't splats non of the above advantages.

 

I was not old when it failed. Does not hold a full charge, won't even lift the tiny helo and dies after 30 seconds it so.

 

Tried getting a new battery pack be t due to lock down and carriage restrictions, are unobtainable at present.

Link to comment
Share on other sites

Hi David,

Like you I have used NiMhs and also used LiFe batteries and for a while I switched to LiFe batteries as they were lighter etc, however, I had a few which failed without warning and only a few charges into their use and so I went back to NiMhs batteries. I later I tried the  LiFe batteries and these have been good so far, so I now use both, not in the same model, but if I need a little more nose ballast I try a NiMhs battery, if your need to add extra weight may as well make it useful weight.

My models are mostly IC powered with spektrum radio. For Ubec's I get mine from 4Max in my electric models.

Regards

Robert

Link to comment
Share on other sites

56 minutes ago, David Davis said:

Hi Don

 

Do LiFe batteries have a higher voltage than NiMhs?

 

What is a Ubec?

 

Do you mean invest in a good Ubec, or in a good switch or in a good Ubec-switch?

 

Do you know of a good supplier of LiFe batteries and Ubecs?

 

Regards

 

David

 

 

 

David, this is one of mine, from hobby king, it is switchable, 5 volts, or 6 volts, nice toggle switch, input volts  as you want. About 10 euro, but Miniplanes or Topmodel do them. I don’t think mine is anything special, just a lot better than a slide switch.
 

But in my experience standard servos do not need switching the voltage down. Futaba run happily on the full voltage, I think Hitec do, I think some of the JR servos don’t like the full voltage. Don’t quote me on this paragraph, check, but there is a lot of information on servos out there.

Re batteries, I use the Hobbyking units. 100% reliable, but again, I don’t think they are anything special.

 

edit bit. Yes life batteries do about 7 volts full charge, as against about 6.6 volts for 5 cell nimh packs. 

4FB20475-FA9E-401A-AF13-7B3500EA7810.jpeg

Edited by Don Fry
Link to comment
Share on other sites

11 minutes ago, Don Fry said:

......

Re batteries, I use the Hobbyking units. 100% reliable, ......

 

 

That's a big claim Don - for any product.

 

Regarding pros v cons. I think Don has got the pros of LiFe and Phil has got the pros of NiMh about right. I'd just add that branded Eneloop NiMh's are the ones to go for, and a further advantage of NiMh's in your case are that they are a straight swap for what you are using now,

  • Like 1
Link to comment
Share on other sites

I now swear by LiFe packs because they are ultra reliable, never lose their charge, very much cheaper and lighter than NiMh`s, charge in an hour from flat and will suffer a lot of abuse. I use an 1100 TGY one for bench testing only because it got squashed almost flat in a prang but still retains a full charge.

I prefer the Zippy or HK ones but could not get hold of them recently so have some Nano Tech 1600`s. The Nano NiMh`s are notorious for puffing up after one flight but these are OK so far. They do not, however, hold their charge as well.

The other plus point which I cannot explain is that even after several flights they take very little topping up compared with other types.

 

A UBEC is a universal battery eliminator circuit similar to the BEC`s on ESC`s so you can drop the 6.6V to 5 or 6. Watch out because some require a minimum 2s Lipo so will not work on a 2s LiFe. I cannot get these at the moment but on the `better stuff` I like to use a Failover Switch which couples two packs together and has two Rx power outputs, switching out one pack if it fails in any way. Input is a minimum 4V and output 5.9V.

  • Like 1
Link to comment
Share on other sites

I did forget one disadvantage which is that there is absolutely no way to tell the state of charge since they will always read 6.6V until they fall off the cliff but mine have never got anywhere near that stage anyway.

I also have four Tx`s with TGY 1500 3s LiFe. These are smaller and lighter than the original 8s NiMh`s, a quarter of the price and a recharge is more a case of `oh, I suppose I should do it sometime` rather than a necessity.

Link to comment
Share on other sites

Mmmmm, so you don't have a charging regime as they never go flat and read 6.6v untill they fall off the cliff ?

 

Do you log flying or radio on time, a modern computer tx/Rx could do that ??

 

In the old days you could get a nicad tester, saying capacity, and cycle the cells, I had one years ago...

 

The tx had a gauge giving an indication of battery power left over..... I assume modern radio gear has this as well ???

Link to comment
Share on other sites

My theory of the anomaly of the apparent lower discharge is that with the higher voltage comes faster movement to the commanded position - i.e. for the same energy requirement (watts) the current is lower (P=VI) so the recharge in mAh will be lower than anticipated with the equivalent NiXX pack.

 

While there were some dubious quality NiCd packs sold prior to the introduction of NiMH by firms with well known names, good quality packs that have not been abused may well still be serviceable and if their performance is monitored, failure is likely to be more predictable than the sudden decline often experienced with NiMHs.

Link to comment
Share on other sites

RG, no of course I don`t wait until they may be flat. It was just a figure of speech to illustrate that they will last much longer than even larger capacity NiMh`s. On my Tx`s the voltmeter will drop by about 0.1 to 0.2V long before the pack is even 1/3rd discharged. I now rarely get more than 500 mA/hr back into a 1500 pack.

 

I disagree that the packs in a model discharge less because a 5s NiMh would be getting a bit flat if the voltage was much below 6.6 even though they are theoretically only 6V.

I would not expect to recharge more than 150 mA/hr after three x 10min. flights with seven digital mini servos. A NiMh would require considerably more than this.

Link to comment
Share on other sites

21 hours ago, David Davis said:

I use a Spextrum DX9 transmitter, Spektrum receivers and Hitec servos. I see that quite a few pilots are using LiFe batteries these days. What are the advantages of using LiFes instead of NiMhs?

 

One of the largest disadvantages of LiFes - for you - is that you already have a fleet fitted with nimh.

 

 

 

20 hours ago, Don Fry said:

Life, hold charge forever, tough as old boots, has a long service life, delivers as much current as any power hungry digital servos might desire, can be charged at high rates, no false peaks,  smaller, lighter.

Nimh, none of the above

 

Disagree.

 

Caveat - I'm going to assume we are talking eneloop or vapex instant, or similar reasonable branded low discharge nimh, with a decent charger.

 

As close to like-for-like as I could find.

 

6.6V 2000mA LiFe pack, volume 48cm3, 90g weight, rated discharge max 4.8A, rated charge max 1.6A, £19

4.8V 2500mA nimh pack, volume 43cm3, 118g weight, rated discharge max >6A, rated charge max 2.5A, £6.20

 

nimh charges quicker.

nimh has higher discharge current

nimh is smaller

life is lighter (by 1oz)

life is 3x more expensive

 

Charge retention on nimh is also excellent.

 

Numbers gleaned from vapex:

https://www.vapextech.co.uk/66v-2000mah-life-rechargeable-battery-vapextech-sq

https://www.vapextech.co.uk/4-8v-battery-pack-48v-2500mah-nimh-instance-sq-vapextech-rx

 

If your digitial servo setup outstrips the max current capability of the nimh pack, you are into territory where the RX power block is also too small along with all your wiring, you need bigger wiring, a distribution block/board and/or maybe multiple batteries for your creation. The pinch point is not even the battery; the average standard servo style plug (battery, switch, receiver, everywhere) is only rated around 3A continuous, I believe.

 

 

6 hours ago, Martin McIntosh said:

I would not expect to recharge more than 150 mA/hr after three x 10min. flights with seven digital mini servos. A NiMh would require considerably more than this.

 

Excuse the question, but, how?

Link to comment
Share on other sites

8 hours ago, Martin Harris - Moderator said:

My theory of the anomaly of the apparent lower discharge is that with the higher voltage comes faster movement to the commanded position - i.e. for the same energy requirement (watts) the current is lower (P=VI) so the recharge in mAh will be lower than anticipated with the equivalent NiXX pack.

 

With respect -

 

That's back to front, current is higher for higher voltage, motors in servos are not perfect resistive loads but still follow that basic rule.

 

Watts are a measurement of power not energy.

 

Link to comment
Share on other sites

I am with Nigel 100% on this topic. I have been using Life packs for five years, and they have turned out to be brilliant. Cheap, Lightweight, hold their charge well, fast to charge etc. With a bit of testing / checking, its straightforward to know how much is being taken out of the pack each flight and charge accordingly.

Link to comment
Share on other sites

This is why I look in here and elsewhere, things have changed so much in my 22 year break in RC aeromodeling, I am out of date and need to learn, re learn stuff.

 

So a modern intelligent battery charger will do what my nicad checker/charger would do, and more, and the modern tx will do more than the now old tx would do.

 

Progress...

 

Still on the merry-go-round for now. I do not invisage having a model with more than 4 servos for now, but realise the practicality of 5 servos, ie. 2 aileron servos, but that's for a year or twos time.

 

Stay safe out there, safe flying is no accident.

 

Ps, the problem with forums is we cannot hear and see each other so miss visual/audio info, emphasis, manner, tone, smiles , meaning etc...

Link to comment
Share on other sites

My experience with life cells is disappointing with my Hitec Flash 8 TX. There was no longlivity in use in the TX and even new Hitec packs did not extend the flying times same cell packs,   changed to a 2 cell lipo now gives me confidence I will not be getting low voltage alarm from tx when in flight. Not been confident to go down Rx packs staid with enoloops

Link to comment
Share on other sites

58 minutes ago, Keith Berriman said:

My experience with life cells is disappointing with my Hitec Flash 8 TX. There was no longlivity in use in the TX and even new Hitec packs did not extend the flying times same cell packs,   changed to a 2 cell lipo now gives me confidence I will not be getting low voltage alarm from tx when in flight. Not been confident to go down Rx packs staid with enoloops

I have had my Flash 8 for three years and never had a problem with the LiFe battery.

Link to comment
Share on other sites

3 hours ago, Nigel R said:

 

With respect -

 

That's back to front, current is higher for higher voltage, motors in servos are not perfect resistive loads but still follow that basic rule.

 

Watts are a measurement of power not energy.

 

The point I’m making is that the energy required to move the servo is the same so the process happens faster. I simplified the explanation and properly, should have referred to watt.hours

 

With a higher voltage for the same energy requirement over a shorter time, the current is lower so when recharging we put back fewer mAh than for a lower voltage pack. 
 

As I said, just a theory and perhaps not very well explained but there must be an explanation of why so many of us have noticed that LiFe packs discharge less than the NiXX packs they’ve replaced. 

Link to comment
Share on other sites

Thanks Martin - understand now.

 

I think some experimentation would be needed to determine whether total energy needs remain the same across different pack voltages, but for now let's assume the same total energy is needed. In that case, a lower voltage pack needs to put out more Ah to provide that total energy. However, does that mean it is 'discharged more' than the LiFe? I think comparing only the Ah from one pack to a another pack of different voltage is not apples for apples.

 

 

Link to comment
Share on other sites

It really boils down to a question of "horses for courses"! Both battery types have their pros and cons. LiFe packs are typically 3.3 volts per cell, making a two cell pack 6.6 volts. Most "old school" servos can handle the slight excess voltage, but JRs in particular do not tolerate excess voltage well. While many people say they are using JRs with LiFe packs, it WILL shorten their life span. Eneloop NiMhs are relatively cheap, readily available and reliable. However, pen-cells in general do have a slightly high internal resistance which limits their ability to supply power-hungry heavy duty servos. I've found that 3300 sub-C NiMhs have plenty of capacity and are quite capable of handling heavy duty servos. They also hold their charge well, despite not being Eneloops! I use them a lot in helicopters.

 

You can reduce the voltage of LiFes with a regulator - or even a simple diode in series. A silicon diode typically has a volt drop of around 0.7 volts. However, both these solutions include another potential point of failure in the power supply chain. My preference is to keep the power chain as simple as possible, with as few components as possible between the battery and receiver / servos.

 

I much prefer using LiFe to LiPos for receiver supplies. They are much more robust, and much less prone to catching fire! For powering the thrust motors in a model, you really don't have much choice other than LiPos, but both LiFe and NiMh are a better solution for the radio supply IMHO.

 

In short, If you have high voltage servos (or servos that will work happily at a consistent 6.6 volts) then use LiFe. Otherwise, use NiMhs.

 

Finally, because LiFes have a cell voltage of 3.3V, a 3-cell pack makes an ideal substitute for the 8-cell NiMhs found in older transmitters (9.9 V versus a nominal 9.8V for NiMhs). They are also MUCH safer to charge "in situ" than LiPos!

 

Just my 2Pp worth! ?

 

--

Pete

 

  • Like 4
Link to comment
Share on other sites

One of the reasons I stopped using NIMH was the issue of a cell going down, but showing a full charge (the three other cells were "carrying" the dud cell). So the scenario was:

Fully charge pack as usual.

Use both hand held and on board voltage checker to confirm voltage ok / in the green.

Fly.

After a couple of minutes, notice everything has gone "soggy".

Land asap.

Check individual cells with a multimeter, and find that only three cells showing a voltage.

Hence the three carrying the fourth.

 

As far as price goes, the Life 1100 packs I use are £4.06 each. Eneloops are a LOT more expensive.

 

I did some trials in the early days with various models from vintage to full on 3D models:

 

Fully charged charged Life pack and took voltage reading.

Flew models for exactly ten minutes.

Recorded voltage reading again.

Charged and recorded how much was put back in to battery.

The 1100 packs are generally good for at least 6-8 safe flights, depending of course on the servo type etc etc.

 

 

Link to comment
Share on other sites

Nigel R., you seem to have everything back to front here. LiFe`s are about 1/4 of the price of NiMh`s and very, very much lighter, charge from flat in under an hour and are considerably smaller than an equivalent NiMh. I need to use nose ballast to re balance a model which has been changed to these.

See the above post by Simon.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...