Nicads

[Lee Morgan]

Hi All

I have bought an aeroplane off Ebay there you go I said it!!!

I have put 3 towerpro 9G servos in and I have a gws rx to go in, No comments on the gear used up to now please unless your going to fund better gear. I need a small battery pack for it, Needs to be a square setup AAA set at 4.8V, I just cant find any.

Help would be great, Google ain't your friend.

Best regards

Lee

[Bob Cotsford]

I made mine from 4 AAA nimh cells from Maplins - pretty cheap at £1-99 if I remember correctly.

[Alan B]

Hi Lee

I do the same.  usually Aldi or Lidl  Costs range between £1.99 - £2.49 for a 4 pack       Ni - MH AAA or AA  About 750 mAh on the AAAs   2500 mAh on the AAs 

I get a battery lead from the local model shop for £1

Bit of solder and shrink wrap and you got a high capacity set up for about £3.50

Regards Al

[flytilbroke]

Try Overtec

Overlander/Overtec

[Tim Mackey]

lee....wait til you come up if you can, as I have some you can have.

NIMH though...NOT NICADS ...why do ya want cadnium??

[Lee Morgan]

Thanks for the offer Tim, I have some on there way NIMH's not cad's, I need them before I come up so that I can maiden my Jap C**P , I wouldn't want to make a tit of myself now would I!!

Lee

[Mouldy]

But if you dont, wheres the entertainment????

[winchweight]

As an eBay user, search for Vapextech. They will supply all your NiMh (instead of nicad and better) needs, cheaply and with good quality, high capacity batteries.

[Tim Mackey]

But I dont think they do complete packs ? As for making up batteries with spring loaded holders, or half assed attempts at soldering together cells which are not designed for it, I would NEVER recommend that for a flight pack, especially one in a combat wing !!!!!!

[Slopetrashuk]

I never put Nimhs in gliders unless they need to be really small.

I'm a cold weather man. Too many crashes.

Andy

[David Ashby - Moderator]

My model shop keep telling me that NiCads will disappear soon - environment issues with their disposal....

[Slopetrashuk]

Your model shop is wrong. The tree huggers keep falling foul of the emergency services around the world (especially alpine and cave rescue etc.) who keep telling them that their torches, de-fibrillation sets and radios will not work at low temperatures, postponing legislation.

Li-Po's are no better than Nimh's at low temperature.

Don't you read my stuff?

[Tim Mackey]

CORRECTION.

Vapex do indeed supply ready made up packs - my bad as they say these days

http://www.vapextech.co.uk/acatalog/copy_of_High_Power_Model_Control_Batteries.html

Having said that, I still wouldn't use 'em ! for the reasons already stated, and resolutely confirmed by Mr Glider himself

PS Andy, although not a huge glider fan, ( or even fan of huge gliders ) I read your stuff

and commend anyone else to do likewise, as you obviously have a vast experience in this sport, and write very well. Please send the cheque to My home address

[Terence Lynock]

I never put Nimhs in gliders unless they need to be really small.

I'm a cold weather man. Too many crashes.

Andy

Hi Andy,

                If the worst happens you can always overcharge a li-po and warm your hands on it..................,

regards,    Terry

[Mouldy]

Guys, whats the problem with Ni-Mh at low temps then? And what temps are we talking about??

A lot of my tools ar on Ni-Mh and I havent seen much in the way of problems with them. Or am I missing something??

[Slopetrashuk]

Nimh performance really starts to deteriorate belo zero, but you must consider a glider fliers weekend away.....

From my column - Nov 2006 (apologies for the long read.....Oh and I had to split it into two posts..)

At around this time last year there were a number of high profile crashes out on the slopes which were all attributed to failure of the models receiver battery pack due to reduced winter temperatures. I started to dig into this at the time but when I’d finished my research the weather had warmed up and it would have been pointless bringing it to you as a reminder to be careful.

The crashes (about 7 in all) all had a number of things in common. All the models were using Nickel Metal Hydride receiver packs; On the day of the crash the temperature was well below 0°C; The models had been charged more than 24 hours before the crash and all the crashes occurred on the first flight of the day. Suspicious eh?

Well no not really. When armed with the facts it’s clear to see that NiMh cells are a poor choice for use in these type of conditions compared to the environmentally unfriendly Nickel Cadmium battery. A fact which almost on it’s own has prevented the tree huggers from outlawing the humble NiCad already.

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Since the chemical reactions inside rechargeable batteries become weaker when the temperatures are extremely low, the batteries will not be able to provide their usual performance. This is a common characteristic of all batteries and is related to the cells Polarisation. This is the ability of the cell to move ions within the electrodes.

Take note of the two diagrams attached which relate available discharge capacity of both NiCad’s and NiMhs to the ambient discharge temperature. (These were taken from information provided by the Eveready Battery Company).

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Whilst both graphs display a run down of capacity to -20°C ambient (Batteries are unaffected by wind chill) I’ll accept that it is unlikely you will find yourself exposed to these temperatures whilst flying. It is actually impossible to be still in -20°C for more than a few minutes before the onset of hypothermia!

You may experience though as I have, regular temperature drops down to -7°C or -8°C. This is especially so if your slopes tend to be fairly high.

You can see that at -8°C and no load, a Nickel Cadmium battery (fig 1) will give just 70% of its nominal discharge capacity (i.e. a 1000mAh battery will deliver just 700mAh), whilst an equivalent Nickel Metal Hydride battery at the same temperature would supply just over 500mAh (Fig 2). Of course with a load applied and with old or rarely cycled batteries, these figure drop dramatically, as does the terminal voltage of the cells. At an ambient temperature of -5°C to -10°C or so, the electronics in Tx, Rx, or servos can also stop working reliably.

Flying for one hour with a 6 servo sailplane with all digital servos has a consumption of 0.5-0.7 Amps. A typical draw with all digitals on a F3B model on the winch during launch will regularly peak at 3-5A but currents draws of up to 8Amp have been measured. Bind up a surface on the slope or pull some very hard turns and you’ll be hitting somewhere near the same values.

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[Slopetrashuk]

The prospect of problems then is very high. Consider this scenario.

You charge your best slope ships NiMh battery pack looking forward to a nice weekend up the hill and load up the car on Friday night ready for an early start on the Saturday. The overnight temperature freezes everything and you wake up to light snow and a frosty motor. You plod your way up the hill to meet your mates and rig your model. You choose your pits but the air is a whiteout and it’s obvious that you won’t be flying for a while. Nevertheless you put your model in the snow on the deck and chew the cud with your mates over a flask of hot coffee giving it an hour or so. Despondent you pack away and head off home leaving your gear in the car overnight to try again on Sunday. Again you need to defrost the car on your way to the hill and again you sit your model down in the snow whilst you have a first brew to warm your mitts up. At around lunchtime you launch your ship into freezing but booming air and let rip around the slope with some grin inducing moves at high speed, despite the pain in your fingers from the growing cold. 15 minutes in and everything suddenly goes sluggish very quickly. Your model gives one last wave of a wing tip as a fond goodbye before plummeting to its death on the valley floor. You head down to pick up all the bits and trudge back to the waiting crash investigation committee. The battery checker appears and low and behold it shows red. “Well It’s had a full charge” you moan………….

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Sound like somebody you know?...............

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If you plan to slope soar in sub zero conditions this winter, here’s some solutions:

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• Use NiCad’s or high capacity NiMh Cells (The biggest you can fit).
• Charge before flight and intermediately if necessary, warming the cells before you do so.
• Use 5 cell packs if your gear can stand the voltage.
• Use high quality cells avoiding cheap ‘consumer’ products.
• Don’t leave your gear in the car in freezing temperatures before flying. Keep it’s ambient temperature above freezing.
• Fly for short periods checking the cells under load after each flight.
• Keep a very close eye on the quality and condition of your receiver battery packs and replace as necessary.

As a last point I did some research to try and determine if Lithium Polymer receiver packs (through a voltage regulator) would be a viable alternative to NiCad’s under these conditions. Various manufacturers were unable to provide me with any worthwhile data regarding capacity against temperature, but with the bits that I have pieced together it would seem that they are no better than Nickel Metal Hydride cells in this application. I really need to discharge a pack in the freezer and find out for myself........as if!

 Andy.

[Lee Morgan]

I am fairly new to all this, 3 years actual flying or somewhere near, I wouldn't dream of putting my gear on snow or in the car the night before, BUT I get your point Andy and thank you for sharing it with us,

I find it difficult enough to fund models wihout doing stupid mistakes that can be avoided,

Best Regards

Lee

( don't fly if you'r hands are blue)

[Mouldy]

OK bud. Were talking sub zero temps then or maybe ambiants of 4 and below.

Ill be safe then!

[Tim Mackey]

One point in favour of Lipo though is that when used with a regulator ( which almost all applications require ) although they will show a drop in performance at these low temperatures as you rightly say, with the right LV alarm system fitted ( such as the combo alarm /regulator I featured in my article on using LiPo in your radio ) you will receive a loud alarm signal as they drop off to around 6V, and this will still be enough to supply a working voltage to the radio, and enable you to land for a recharge / exchange of pack.

Incidentally, one COULD use the alarm /regulator device with a "conventional" pack of cells like nicads, but it is designed to operate the alarm at 6v, so careful selection of the number of cells in your pack is required if you wish to retain the alarm function. 4 nicads will be around  4V when flat, but only 6V (maximum) when fresh off charge, so thats no good,  5 cells will be 5V and 7.5 respectively, and will sound the alarm at their nominal figure of 6V ( 5 X 1.2V ) so 6 cells will probably be about right - 6V when "flat", 9V fresh off charge if lucky, and nominal 7.2V.

Of course a similar LV alarm could be easily constructed for a few pounds which will alert you when ANY pack reaches pretty well any voltage you set, but I am straying off topic here and frankly, if you want to stick with nickel technology, then stay with Nicads for cold weather.

[Terence Lynock]

Hi Folks,

                 a low warning circuit diagram is at http://www.webx.dk/rc/lipoly/low-volt-alarm.htm and could easily be modified to give a audible warning instead of all those LED's, if you need any BC847's I have about 300 of the things but you need to be able to solder surface mount components to use 'em,

                        regards,            Terry

[Tom Sharp]

A chap of my aquaintance who works for an local emergency lighting firm told me a little while ago that battery munufacturers had stopped making Nicads. But there are still billions in stock, enough in fact to last well past 2010.

Is this true?

[Slopetrashuk]

Doesn't look like it from this:

http://www.chinasourcingreports.com/csr/Electronic-Components/Batteries/p/CSRBAT/Executive-Summary.htm

Nicad comment at the bottom.

Other manufacturers probably stopped because with the Chinese flooding the market they can't afford to compete (just speculating).

Andy

[Mark Lubbock]

Hi All, 

Back to the thread, If you need a really small battery, use a PCB mounted 4.8v 110mAH battery as used in maintaining power to electronic systems. Some are nicad, some Nimh, but all the same capacity. They sell them in Maplins & RS. I have used them for years in lightweight models, they are made up from button type cells similar to the DEAC's of yesteryear & lose very little charge in storage-I just checked a model that has not been flown for 5 years & the radio still works without charging!!!

I think they weigh about 1oz