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Nickel based batteries

A guide to using and charging

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Batteries demystified - part.1

Batteries demystified - part.1

Think you know all about Li-Po batteries? Tim Mackey has the definitive guide - 9/4/09 Subscribers Only

Batteries demystified - part.2

Batteries demystified - part.2

Tim Mackey takes a close look at any battery that isn't a Li-Po! - 15/4/09 Subscribers Only

Malcolm Fisher12/08/2011 22:20:14
579 forum posts
7 photos
I'm using some seven cell NiMH batteries in my two electrically powered planes. I want to know what type of Lithium based battery would make a suitable replacement.
For one model, I think a new ESC would be required as I don't think that the LVC can be adjusted from the setting for the NiMH battery.
Both are "can" motors and one ESC can easily be changed for LiPo operation so that one at least is no real problem. I just need to know whether to use a two or three cell pack to replace the NiMH.
PatMc13/08/2011 00:42:55
3715 forum posts
476 photos
I used 2s lipo as an alternative to 8 nimhs in a vintage model with a geared 480. Never had any problems but I never ran it down to LVC as the duration with lipos was so much longer. I used a bigger prop with the lipos to get the same power with the lower voltage.
I've just upgraded the model to a brushless with 3s lipo - first flight with the new power will be when we have a decent bit of weather.

Edited By PatMc on 13/08/2011 00:44:53

Malcolm Fisher13/08/2011 19:53:21
579 forum posts
7 photos
Thanks for that Pat,
What capacity lipo did you use?
One of my NiMH batteries is 3800 mAh and I've only once run that down to LVC as a test to get an idea how long it would last at WOT - not that I fly it that way as a rule.
The others are much smaller in a park flyer type Cub, and these always hit the LVC when I fly it.

Edited By Malcolm Fisher on 13/08/2011 19:54:43

PatMc13/08/2011 20:49:49
3715 forum posts
476 photos
Hi Malcolm, with the 480 brushed motor I was using 2s 2100 rated at 20c. I would have used lower capacity but happened to have them to hand.

Edited By PatMc on 13/08/2011 20:50:34

PatMc13/08/2011 21:03:01
3715 forum posts
476 photos
For some reason I was unable to complete the above post & couldn't edit it either.
I was going to add - that the 2s lipo battery weighs 120g whereas the 1050mAH 8cell battery it replaced weighed 180g. The model's AUW was just over 1Kg.
Malcolm Fisher13/08/2011 21:15:26
579 forum posts
7 photos
Thanks Pat,
The large NiMH battery I have weighs just short of one pound - well over 400 grams. Part of my reasoning for changing is a weight saving measure - it lasts for a full afternoon's flying using the motor as "an old man's tow line" in a powered glider.
I don't know the weight of the smaller ones but they are only AAA cells of 650 mAH capacity. Duration is the reason for looking at replacing those. I suspect one decent LiPo would give a longer flight than all three of these I have do.
PatMc13/08/2011 22:00:18
3715 forum posts
476 photos
Malcolm, I have an OD 9ft motor glider that started with 7 cell 1900mAH sub C nicads & a geared 600 motor that has been upgraded in stages to now having 3s 2200mAH lipos with a brushless outrunner. The AUW weight has dropped from 1.8Kg to 1.5Kg
With the nicads I got about 3 or 4 slow climbs per charge running down to LVC & a total duration of around 20 - 25 minutes without thermal help. Now I get 5 or 6 faster climbs to much greater altitude with at least double the duration per charge before I get bored & land. I'm using a pre lipo ESC so rely on a count down timer on the Tx set at an accumulated 4 min of motor run time but I usually land before that's reached.

This is it with the brushed motor & GB.

This is it with a lengthened nose & brushless.

Malcolm Fisher14/08/2011 21:59:35
579 forum posts
7 photos
Hi Pat,
I like your glider. If there is a plan push it at young Ashby.
In my case the two models are a CC Lee Piper Cub and an Easy Pigeon. The latter was bought after returning to slope flying and having several trips out in conditions with no slope lift. Being a Yorkshire man, the thirty odd mile round trip with no real stick time, apart from the short flights with the Cub, hurt - especially as I could have flown that on the nearby football field... The EP at least gave me some stick time and I have enjoyed it's flying capabilities. So far it has been flown in zero wind speeds - the original requirement - and with wind speeds of over 40 mph measured on a friend's meter.
I am not sure if my Tx has a suitable timer, but as I have difficulty hearing its low battery alarm, I probably wouldn't hear an accumulative timer either. Could possibly use my mobile phone with its ear piece though so that might be worth considering.
I have bought a brushless motor to accompany the ESC I won in the Forum prize draw some time ago and am looking at building something for this or converting an existing model and in that case I will be looking at a suitable lithium based battery. I do have a compatible charger which I bought so that I could monitor the capacities of my other radio equipment and do some cycling of TX and Rx batteries as well as having the capability of field charging..
I've never reached the "bored" state when slope flying and can remember one flight lasting nearly three hours with a Kamco Kloudrider on the slope then flying it back to near the car at the bottom of the slope when it was time to come home.
PatMc14/08/2011 22:19:07
3715 forum posts
476 photos
Hi Malcolm, the count down timer I use is only because the ESC pre-dates lipos.
The model is now quite old now & probably a bit too big for a magazine plan. I fly it quite often at my local slope (200 yards away) when the winds too light for most other gliders. It has a couple of fixing points for a Flycam & I've posted a couple of videos taken from it.
tom clarke09/01/2012 18:39:11
26 forum posts
1 photos
hi people.. im doing my first large 3d model and need help with batteries, i have two identical 6v 3300 nimh packs to go into the plane, can i have one as a back up or how do i run both packs safely? (plane is 50cc sbach with 5 savox 20kg digis hence the need for lots of battery power) i know lipo is the way to go but never had a problem with nimh and the plane balances with both packs upfront.
Mart4925/07/2014 18:15:41
259 forum posts
5 photos

Help please!

I'm a Lipo man, but just bought a slope soarer to take away with me this summer. It comes with 2300mah Nimh 4.8v battery, and I'd like to know the best setting to charge it with. Any help and advice appreciated.


Martin Harris25/07/2014 19:29:10
7635 forum posts
190 photos

If it's a second hand battery, I would bin it - I've seen too many NiMH batteries fail unexpectedly after a couple of years to risk it.

If it's new, then charge it the first time at 1/10 C (230 mA) or as close as possible for 16 hours then subsequently charge at at least 1/2 C (1650mA) up to 1C if you're using a delta peak detection charger. NiMHs are very prone to triggering a false peak and not recharging fully especially if charged at a low rate.

Rotten substitutes for proper NiCds!

Mart4925/07/2014 20:05:09
259 forum posts
5 photos

Martin, Thanks. Its new. Looking at my charger, it appears that it charges in A rather than mA. Not wanting to cause an problem, is it the same@ Either 2.3A or should it be .3A. Sorry - failed physics at school many years ago....

Edited By Mart49 on 25/07/2014 20:05:37

Daithi O Buitigh25/07/2014 20:12:49
1291 forum posts
44 photos

The cells are probably 2300 mAH (1 mA = 1/1000 Amp) so they would be 2.3 Amps. To charge at 1/10C you would then be using 230 mA which is 0.23 Amps

john melia 115/08/2014 05:07:17
1770 forum posts
24 photos

Tim whats an EVM ?

robert chamberlain29/09/2017 06:11:24
67 forum posts

Hello all,---I recently tried to charge up my Hitec trans with the included wallwart unit. The trans had been sitting for about 3 months and I thought I would give the 7.2 nickel metal batt a charge. Usually this doesn't take all that long but this time I left it connected for about 3 hours. The little red light stayed on and it never went to green as usual so I figured all was well. Boy, was that batt HOT ! I could touch it ,but it was more than just a little warm. So-----either the wallwart went crazy or the batt has a problem. Could it be that one cell went dead and the charger kept trying to bring the voltage up? It did read 8.2 on the trans screen, however. Maybe the other 5 cells now are over charged?

I measured the output of the wallwart on another batt and it showed 80 MAH. I was thinking of cutting open(carefully ) the bat to see if a cell was dead. Are these wallwart chargers just trickle chargers? I would think not if they had both a red and a green light.

Maybe I'll just make up a cable and charge it from my charger( assuming the wallwart goes directly to the battery and not through some circuits inside.----Any thoughts would be appreciated.!

Oh, while I am here, what is a good setting for the MV /cell cut off for the peak detection charge? I owe you

Bob C

ChrisB29/09/2017 08:09:46
1207 forum posts
34 photos

I use the wall chargers for charging all our NIMH aircraft, from 600mah to 4500mah. I check the output and resistance twice a year. They all trickle at 70-150 (depending on the charger) and won't stop until you switch them off. Its usually down to the battery playing up rather than the charger in my experience.


robert chamberlain05/12/2017 06:31:09
67 forum posts

hello all,---My charger is set to the "default" setting which looks like around 7mv for the cut off on NIMH batts. When the charger says "fully charged" , I can test the batt and it is indeed not fully charged. I noticed that I can hit the button again and it will continue charging again for a short time. I assume the mv is a little low if this can be done. I have the safety features all set ,--time, capacity, temp etc . Any suggestions on a safe mv to set the charger on? Thanks for any advice,---Bob C in Kansas, USA

Dave Bran05/12/2017 06:41:22
1892 forum posts
5 photos

NIMH chargers work by sensing the negative dip that occurs as a pack reaches full charge.

If you repeat charge the charger will attempt to charge until it gets another negative dip, which might be a while, and during this time you are pumping more current into the pack that it does not need.

Because it appears to charge again, that does not mean it was not fully charged in the first place.

robert chamberlain13/01/2018 06:16:42
67 forum posts

Hello, just had an Enlope 5 cell pack made for me. I was told it was 1900 MAH using AA cells . It is nicely done with shrink wrap and glue but I can not peal it apart to see the charging rate. The builder didn't have any idea. Before I cut into the wrap can anyone tell me if they are any different from other NiMH units? 10% or 1C?

I have some similar NiMH cells sold as "fast charge" but when I looked, it said 10% overnight.

I read Tim's piece above and found it interesting, but still have questions. -------------Bob C

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