NiMH Batteries

[Phill Mainwaring]

On YOU magazine 7th dec.2008, There was a small article

on page 7 stating. (to get the most out of your NiMh rechargeable

batteries store them in a bag in your'e freezer,this will ensure

they retain power when not in use) now It's always been my understanding

that cold/freezing is the enemy of batteries, can anyone shed some light on

this statement please

[Tim Mackey]

No so. keeping them cold and partly charged is the best way to preserve them and will ensure a long service life, but will not help them to retain their charge - NiMh have a high self discharge rate, worse that NiCd

However when it comes to actually USING them, then warm is best - all batteries PERFORM poorly in the cold.

One thing you must do if refrigerating them is ro protect them from moisture, so wrap them well in airtight bags

[Phill Mainwaring]

Thanks Timbo.

I was getting a bit worried ther

Phill.

[260 Flyer]

Wrap them up, put them in the freezer. - Remove from freezer, unwrap and thaw them out.

- OR -

Just charge them before use?

[Tim Mackey]

Well I think most people do the latter - the cold storage thing is really for those peeps who want the longest possible overall lifespan from their cells, and as they are pretty cheap these days its easier to just change em after a couple of years.

[260 Flyer]

Who'll be the first to try and defrost them in the microwave?

[Phill Mainwaring]

Thanks for the suggestion Rob

I don't think it will be me

[Doug Ireland]

Be interesting to see what happens though!

[Tim Mackey]

I think it has been done actually on some silly TV programme once. I Imagine that the result would be a completely kwackered cell, and a very annoyed wife!

[Former Member]

[This posting has been removed]

[Tim Mackey]

Actually some folk reckon that Lipos ARE Ok if in freezer, but most seem to agree that "near" freezing is best.

[Former Member]

[This posting has been removed]

[Tim Mackey]

Yep

[Phill Mainwaring]

I think I will stick to my usual and throw them away

every couple of years (re cycled of course)

[Chris Bott - Moderator]

Does anyone have any figures on current capability of different capacity nimh's? I keep hearing the advice "for a receiver pack, get the highest capacity AA's you can" I'm not convinced. As we all know, 4 or more servos can take a high instantaneous current at times during a flight. So the amount of current the battery can deliver is very important. I believe that as a general rule, for a AA's at least, to get higher capacity they use thinner plates to pack more in, and thinner plates mean lower current capacity.

[260 Flyer]

Chris.

There was a thread on this subject a while ago and I ended up testing my Vapex 2600's under load. If I remember correctly the voltage holds up OK at up to 4A load.

I bought some of their Instant AA's for my camera but compared to normal NiMH's or even Alkaline cells they seem a bit 'Lightweight'.

I now use 5 X 3300 mAh sub C's for heavier loads.

[260 Flyer]

Here's the THREAD

[Chris Bott - Moderator]

Thanks Rob.
 I remember that thread now!

I must say I've had some Vapex instants and some sanyo eneloop instants and have been far more impressed with the Sanyos. 

[260 Flyer]

I had a week away in October and I just took the Instants with me this time. I used to take a charger with me and not need it, so just a fresh set of Instants in the camera this time.

The bl**dy things gave-up half way through the week .

[Chris Bott - Moderator]

My Sanyos have been great (so far)
Retain a charge for ages too.

Have you tried those Rob?  Eneloops 4 x AA

Not seen them yet as a made up Rx Pack. But wouldn't be surprised if they were available somewhere.

[260 Flyer]

You are correct!

Eneloop Rx Pack

[Chris Bott - Moderator]

Guessed so  

How much!!
That seems rather expensive?

[Tim Mackey]

Shop around Chris, much better deals to be had.

[John Mc]

I am about to committ aviation with a Venus 2 (120 size) using a 4 cell (4.8volt)  Sanyo eneloop NIMH 2000 m/ah receiver battery. I have digital servos installed.

My typical days flying is 4 X 8minute flights entailing pattern aerobatics with a bit of Knife edging thrown in. I have done this for some time with my Venus 40 (Little brother) with no problems.

 

A fellow club member suggested that voltage drop could be an issue which would mean my 2.4Ghz receiver could stop responding. He recommended bigger batteries and muttered something about Sub C. ? As an electronic Phillestine I would have fitted a 5 cell (6 volt version of the Eneloop) as the simplest solution. I read that this would increase power but reduce duration. As long as I get 4 flights this will be fine.

I have a vague memory of the use of Voltage regulators, LIPo Rx batteries and Power Boxes but this is all Greek to me and may be a massive overkill.

Any opinions on my 6.0 volt solution?

[Tim Mackey]

Either solution will work, but the difference is thus.

4 cell larger size ( sub C ) - current draw will remain same in use, as will servo speed and torque. Battery voltage will hold up better, and assuming larger than 2000m/ahr then duration will be longer.

5 cell standard AA size - current draw will increase slightly ( so shorter battery life ) servo speed and torque will increase, battery voltage will be higher to start with, but will proportionally sag more than option 1.

Edited By Tim Mackey - Administrator on 04/08/2010 20:03:59

Edited By Tim Mackey - Administrator on 10/08/2010 11:33:51