Topic: At what point do you stop using AA Nimhs?

After studying the various battery and servo load characteristics for my 50cc Sukhoi I am now left questioning battery selections for my next model. Prior experience tells me that a good old Wot 4 with 5 standard servos will fly happily on a 4.8v 600mah  pack but what about my YT Magic formula 3D?

This 60” model will be powered by a 91 and has 6 servos (5 digital) and huge surfaces.

Its not a huge model so I would expect to use AA batteries as below AA Ni-MH 6V 2600mAh  150g High drain performance(up to 10C (another spec says 7.8Amps)

The alternative would be an SC 3300 mAh Ni-HM Twin at 260g (30 Amps)

I just don't trust hi-capacity NiMh...

Had a number of these with inconsistent charging and discharging times... So anything over 700mah goes to sub c

2 off A123's 2300mAh in series may need a diode in series also , virtually no self discharge, 140g weight for both cells

So instead of using AA cells should we be looking at 2/3 A cells?

these 'look' the right shape and seem to give decent output current althouh they have lower capacity than AA cells and are a lot lighter than SC.

Realy do not want to go to A123 on my smaller models.

I just don't trust hi-capacity NiMh...

Had a number of these with inconsistent charging and discharging times... So anything over 700mah goes to sub c

Same here. Lost 2 models to high capacity Nihms that had a cell die very suddenly. They were always charged on the Nihm setting of 2 chargers and never at a rate higher than about 0.75c

So instead of using AA cells should we be looking at 2/3 A cells?

these 'look' the right shape and seem to give decent output current althouh they have lower capacity than AA cells and are a lot lighter than SC.

Realy do not want to go to A123 on my smaller models.

2/3 a are better than AA, but I still wouldn't go for too high a capacity. (keep below 2000mah and you should be okay)


  Tom

2/3 a are better than AA, but I still wouldn't go for too high a capacity.


  Tom

2/3a are okay at 1500mah ish.  They have a max discharge of about 15amp/hr which is not bad (twice that of AA).  As I understand it is a common size in rc cars. 

Thanks for the responses so far althoughpart of the original question remains unanswered.

When do you stop using AA cells?  Is it based on number of servos, size of model, engine capacity, weight, a combination of these or something else?

Think that I may be going for 2/3A cells at 1600mah or A123 for heavier loads upto 26cc models

I've stopped using Nimh in all planes. I use either the 1100mAH or 2300mAh A123's.

Thanks for the responses so far althoughpart of the original question remains unanswered.

When do you stop using AA cells?  Is it based on number of servos, size of model, engine capacity, weight, a combination of these or something else?

Think that I may be going for 2/3A cells at 1600mah or A123 for heavier loads upto 26cc models

I don't think anyone can give you a definitive answer, all the above come into the equasion along with your style of flying, how many flights and how long is each flight in a session? Are you prepared to recharge between flights? What weight can the model carry without effecting performance? Your own pesonal prefrence and probbably a few more I can't think of right now.


  Tom

when you think that the current draw will exceed the max output of the battery less whatever safety margin you deem to be appropriate, I guess.  Cold weather obviously adversely effects many batteries.

I've stopped using Nimh in all planes. I use either the 1100mAH or 2300mAh A123's.

2nd the above i am slowly moving over to A123 cells
Ron

Not a conscious decision but looking at my fleet over the past two year I have NOT used AA MiMh above 700mah.

And I only use 700 on models less than a .50 and four servos or less.

Anything else gets a Sub C...

For those a123 users, what battery programme do you use to charge them?

I have been using the AA 4.8v packs from Vapextek 2600mah for some time.  They have been in my Mystic which has 6 tower pro 5010 servos, engine is a 22cc Zenoah and I have never had an issue with it and those servos do a lot of twiddling when I fly it.  They have been both fast charged and also over night with a ordinary Futaba tx/rx mains charger, I always check battery capacity with a checker that puts a 1amp load on before every flight (which I do pretty much with any aircraft) and find the Vapextek to last extremely well and will give 6 full tank flights or basically a mornings flying at our club (we only seem to fly mornings).

For those a123 users, what battery programme do you use to charge them?

life is the setting on my charger like the old nicads you can fast charge at the field to get more flying time
Ron

For those a123 users, what battery programme do you use to charge them?

Stuey, A123 cells are LiFePO4 chemistry. I think that most chargers simply call this a "LiFe" program.
A123 is just a brand name.

It does seem that many modellers are uncomfortable with AA NiMh cells, especially the very high capacity types.
I have just bought a couple of 2000mAh Eneloop packs one 4 cell and one 5 cell to try, but I suspect that before very long I will be using either a123 or Lipo receiver packs.

I don't think anyone can give you a definitive answer,

  Tom

Not after a definitive answer just your own personal decision making process.  Its your choice and if it works that is okay.

Your selection criteria sound right to me, so when do you stop using AA packs?

Your selection criteria sound right to me, so when do you stop using AA packs?

When I find I have an issue with them which to date I have not.  The only sub-c's I use are on my 1/4 scale pup but that's purely for ballast anyway otherwise it would be on ordinary Vapextek 4.8V 2600's

For those a123 users, what battery programme do you use to charge them?

Have just bought my first A123 cells Stuey and find I now have to buy another charger with a LiFe programme. Neither my Pro Peak nor my Triton can handle them.

Robin

I think A123's are overkill for a small model like that but hey if thats what you want to use go for it.
The figures you quoted for the digital servos drawing 10c and 7.5c are in a fully stalled state, your not pulling anything like that even in full 3D snap mode. Heck the plugs for the servos are only rated at 5 amps max and thats just for a few seconds. They melt beyond 30 seconds or more

I fly 40%'s down to little old 50cc planes on hard 3D and use A123's mostly because I dont trust Lipos but before 123's became popular I used NmH packs of various types from AA to 2/3a which I buy and still do from Nobs in the US.

http://www.hangtimes.com/sportrxpacks.html

Most of my models use JR 8711's which you will know is one of if not the highest drawing servo out there and my older Nim packs where fine.

It’s “horses-for-courses”. 
I have a 28cc petrol engined Spitfire which uses nine servos, but it has a fairly unstressful existence so I don’t mind it running on a 2,600 Mah “AA” cell Hydride pack.

I also have a 50cc petrol engined 3-D machine which only has six servos, but I wouldn’t dream of using “AA” cells in it.  It uses A123 cells, but I have also used Lipos and Sub “C” cells in these more demanding machines.

B.C.

When I find I have an issue with them which to date I have not.  The only sub-c's I use are on my 1/4 scale pup but that's purely for ballast anyway otherwise it would be on ordinary Vapextek 4.8V 2600's

Okay, as a rough guide, I would be happy to use up to 2100 AA Instants/Enloop in a most 90f/s powered warbirds,Wot4/Acro Wot etc Anything over that up to large petrol I would use up to 1300 AA, 2/3 or 1100 A123s, if I needed to keep the weight down. Anything larger or with a lot of digitals or if weight wasn't a problem, 3,300 SubC or 2300A123s, but in the end it would come down to "gut feeling".



   Tom

As i slowly change over to Spektrum receivers I am fiinding that some of my models have flashing LED's at the end of a flight.  Looks like I will be updating to 6v AA upto 10cc then SC or A123 for bigger models.

The A123 do look good, a 6.6v 2300 pack weighs almost the same as a 6v AA but can deliver huge current without fading.  A bit costly though!

Realy do not want to go to A123 on my smaller models.

Any particular reason Simon?
Two 1100 A123s will fit anywhere...   you dont have to use the larger M1 cells...  

Phil

My thinned down fleet runs to 32 models, most have AA cells, a few on SC and three on A123.

Dont want to change to A123 across the board but will probably go that way on new builds.

AA 6v is only £7 an 1100 A123 is £19 so nearly 3 times the price!

I've had a look at the usual suspects to supply A123 cells and can't see much.

Where are you buying the 2300 cells?

stu k

Go to electricwingman http://www.electricwingman.com/2s-a123-battery-packs.aspx they are 9in the sidebar on the left.

Very good (best UK that I can find, beats HK too) prices for proper twin lead packs.

Simon

Mine are all from Dewalt drill packs, off ebay.
Phil

Mine are all from Dewalt drill packs, off ebay.
Phil

And just how much do they cost to make up?

I looked at going that way but at over £7 per cell they didnt seem worth the effort and cost when compared to new cells in a factory welded pack.

This was 3 years ago before any made-up packs were available. They were for an electric race bike project, which is, erm...,  'ongoing' you might say 
They cost next to nothing to make up, a bit of wire and a deans? Its no effort at all. Maybe made-up packs are cheaper now, I dont know, I wont be buying any for a while - I've 70-odd cells left... 
Phil

And just how much do they cost to make up?

I looked at going that way but at over £7 per cell they didnt seem worth the effort and cost when compared to new cells in a factory welded pack.

I never put nimh batteries in any of my planes, bought a stack of 4.8 V 1000 mAh nicads from overlander and field charge them to top up, In some of my a/c I have switched becs and 2 cell  lipos usually use 1000 or 1600 mAh ones and field charge as necessary.
Nimh for me are real bad news, also I regularly check the switches and buy hd futaba ones, ok the price makes your eyes water but to me they are the best, and the only reason I choose those over jr is that the futaba ones will then fit any battery plug without bodging.

Thanks Simon & Phil, I'll be looking into getting some
regards
stu k

Don`t think I`ll go the lipo route for an rx batt, just waiting for A123`s to be cheaper than the planes, so sticking to instants for now.

chaz@2b