discarging nicd and nimh how?

[stalion456 0]

hi all, I would like to cycle my both nicd and nimh battery but not sure how, they are both 4 cells 4.9v I usually charge them at 300mha, at how many mha would you discharge them and howmany v's.

Thanks

William

[arun 0]

I normally discharge to 1v per cell for NiMh - so 4v for your packs. A discharge rate of 0.3A should be fine. I don't use NiCds due to their limitations compared to NiMh, but my understanding is their charge characteristics are similar, but they are more sensitive to over/undercharging - maybe someone who uses them will comment.

 

In terms of actually doing the discharge, a half decent digital charger should handle this for you and will cycle them up/down a preset number of times to remove memory effect. Something like this should be fine, and is a worthwhile investment:

 

http://www.giantshark.co.uk/power-a606- ... 05325.html

 

Alternatively, connect a suitable light bulb across the terminals of the pack to discharge, but you'll need a multimeter or similar if you want to accurately know when to stop!

[stalion456 0]

Thanks for the info I think I will give the nicd a miss as it is a spare anyhow and I have been told the same , I have a good charger such the one on the link above detailed, how often should I cycle them? I usually charge them after every day out but I never fully discharge them.

[arun 0]

If you are flying regularly, I'd recommend cycling them on return from the field, then topping them up the night/morning before you fly. If not flying regularly, maybe cycle them once a month if you can be bothered! You might want to look at Sanyo Eneloop NiMh packs - these have a low self discharge so once cycled on return to field can be left fully charged and will be ready to go still weeks later.

[snakeyme 0]

i use normal AA battery carriers for battery packs inside planes and i get 2800mha Ni-mh batteries off amazon, they cost me £2.97 for a pack of 4 and are called palocell, they take about 4 hrs to fully charge and will last for 2 weeks in a digital camera used everyday.

 

Just thought id mention that

[stalion456 0]

this is what I have found, is this the one you meant?

http://www.brentfordrc.co.uk/scripts/pr ... oduct=2001

[arun 0]

Yes, they are the ones. If you shop around I'd like to think you can get them a few quid cheaper than that, but maybe they have gone up in price.

 

If buying new packs, no reason I can think of to buy 4.8v in a typical IC plane - go for 6v. This is a must for Spektrum receivers to avoid brownouts, and gives a better safety margin for Futaba. Also, 6v = faster+stronger servo reaction.

 

http://www.overlander.co.uk/sanyo-enelo ... -flat.html

Edited October 15, 2012 by Guest

[arun 0]

i use normal AA battery carriers for battery packs inside planes and i get 2800mha Ni-mh batteries off amazon, they cost me £2.97 for a pack of 4 and are called palocell, they take about 4 hrs to fully charge and will last for 2 weeks in a digital camera used everyday.

 

Just thought id mention that

 

Not a good idea if you mean you are using loose cells. Straight out the BMFA book:

 

"(b) The use of dry cell batteries in airborne battery packs is strongly discouraged and they must never be used in the airborne pack if you have four or more servos operating." (page 24)

 

Long story short, if one shakes loose during flight, you're out of control. Also not all loose AA batteries can deliver the current requirements placed on them by multiple servos (normal or digi)

[Bravedan 106]

To dot a few "i"s, etc.........

 

NICAD is an environmentally dangerous construction no longer on normal sale (due heavy metal cadmium content). It would be best to take any NICAD out of circulation by proper disposal means, not normal refuse, as soon as possible. NIMH is the superseding technology, in some ways (like charge retention) not as good, but that's the way of things!

 

Some servos (and some gyros) are NOT safe for five NIMH cell batteries, i.e., voltage above a fully charged 4 cell battery. This particularly applies to a lot of the fast servos used on Helicopter tail drives but the limitation can appear almost anywhere, including servos on general sale and widely used in planes, and you should check the specific servo(s) data carefully before using 5 cell. When the manufacturer says 6v max, they usually mean it literally, so bear in mind the fully recharged voltage of your pack, not the nominal running voltage.

 

Loose AA clip in battery carriers are fitted to Tx's like Spektrum DX6i, JP Planet, Futaba ground use sets and lots of other low end units. However, using them in ANY flight pack where they are subject to a lot more vibration, landing impacts and g forces is a really BAD idea! Using them in any pack driving more than a couple of micro servos and an tiny ESC on basically a small "toy" type airborne model is adding an unacceptable risk to the safe operation of the model and those around it.

 

You can get perfectly adequate chargers which include cycle and discharge for NIMH and LiPo such as the X-Charger B606 for less than £25.

[stalion456 0]

Thanks Arun, I think 20 quid it,s worth getting a few of the 6v as you said better safe then sorry, I was using 4.8 as this was the basic requirement, so in a nut shell 6v is better than 4.8v.

[stalion456 0]

Hi Dan,

I have a good charger that I purchased at avicraft for 50 quid it does cycles and charges all batteryes, I just wasn't sure on how to discharge them, for example this morning I have tried to cycle my 4.8 2000mha pack, I have set the mha rate at 0.5 and the voltage on 4.8 but when I press the start discharging button it will go off in a few minutes and display dry and then it will go to charging mode, now I know that the battery as 75% capacity still left have a battery checker and also I have charged it yesterday and only had a couple of flights, I must admit I am a bit confused what am I doing wrong?

[Trevor 25]

These people do Eneloop packs cheaper than the Overlander ones. I have a couple of them and they have been okay.

http://www.component-shop.co.uk/html/lo ... harge.html

 

 

I usually only cycle NiMh packs once a month and just top them up before each flight. I thought NiMh packs don't suffer from the memory issues that NiCd packs did?

[arun 0]

Hi Dan,

I have a good charger that I purchased at avicraft for 50 quid it does cycles and charges all batteryes, I just wasn't sure on how to discharge them, for example this morning I have tried to cycle my 4.8 2000mha pack, I have set the mha rate at 0.5 and the voltage on 4.8 but when I press the start discharging button it will go off in a few minutes and display dry and then it will go to charging mode, now I know that the battery as 75% capacity still left have a battery checker and also I have charged it yesterday and only had a couple of flights, I must admit I am a bit confused what am I doing wrong?

 

You probably need to set the voltage to the stop voltage. In this case it should be set to a discharge rate of 0.3A and a stop voltage of 4.0v, not 4.8v. Basically what is happening is the charger is measuring the battery voltage, seeing it is less than 4.8v and stopping. But you don't want it to stop until it gets to 4.0v!

[stalion456 0]

dahha that makes sense how silly was I thanks for that.

[snakeyme 0]

i probably shoulda mentioned this before but i wrap the loose cell battery carriers in insulation tape so that only the contacts are visible and then put the whole thing in a tightly cut piece of foam (the stuff that usually pads fuel tanks) and its so tight that its a struggle to get it in, this is what i do to stop them coming loose

[stalion456 0]

These people do Eneloop packs cheaper than the Overlander ones. I have a couple of them and they have been okay.

http://www.component-shop.co.uk/html/lo ... harge.html

 

 

Now that's what I call value for monie.

[stalion456 0]

why go trough all that bother in fiddling around just buy the right staff, so you don't have to, I don't believe you go trough all that just for a battery I think you just realised that you said a silly think and afters Aruns comment about the Bmfa book you though you would had a comment just so that you are covered.It can be spotted a mile away mate !! not being rude but less B......t.

[stalion456 0]

Bull.... you just said that so you don't sound stupid... I don't believe that you go trough all that no way it makes no logical sense !! unless you are one of those that just tries really hard to comment on everything without really knowing what there talking about?

or your just one of those whom likes to make his life a living misery with stupid time wasting theories. Witch one is it?

[arun 0]

i probably shoulda mentioned this before but i wrap the loose cell battery carriers in insulation tape so that only the contacts are visible and then put the whole thing in a tightly cut piece of foam (the stuff that usually pads fuel tanks) and its so tight that its a struggle to get it in, this is what i do to stop them coming loose

 

They still can't necessarily handle the current draw from servos however much you tape them up. Just because AA batteries look the same, does not mean their internal structure (aka resistance) is the same. Why risk a model/go against the safety recommendation for the sake of a few quid? Do keep in mind that in the case of public injury and resulting investigation by BMFA insurers, this kind of thing could jeopardise your coverage which could be financially very significant for YOU.... you have been warned!

[Martin 0]

Just to put some of the things on this thread in perspective, have a look at the discharge graphs on http://www.eneloop.info/eneloop/technol ... acity.html . Note that NiMH batteries (both the low-self-discharge type and the high capacity type) have a long section with quite a stable voltage around the 1.2-1.3V mark, and that this is quite stable across the three different current drain graphs (100mA, 500mA, 1000mA).

 

It's quite possible that if you discharge to 1.2V at a reasonably high drain rate (like 300mA) then you're only reaching the start of this flat section. Discharging to (say) 1.0V (I have even seen people suggest to go down to 0.9V) means you should definitely be at the end of this region.

 

Reading the BMFA handbook section, they appear to use "dry cells" to mean "non-rechargeable primary cells" - i.e. alkaline or other similar battery technologies. Looking at the discharge graphs should show why this is - an increase in current drain on a partially-discharged alkaline battery causes the voltage to drop very rapidly. This would be likely to lead to receiver brownouts and other unwelcome effects.

 

There is a separate statement (p24 ©) "Do not rely on the spring type battery contacts in battery boxes." and a recommendation (p24 (d)) on what to do when using individual rechargeable cells in the few transmitters which do have spring contacts (e.g. Spektrum DX6i).

[Trevor 25]

In addition to what Arun says, the battery and holder terminals can easily corrode and break contact whereas packs are welded or soldered to prevent this from happening. I agree with Arun, be safe and use proper packs.

[Martin 0]

I think it's not just the risk of the batteries coming loose. You also have the problems that you're relying on spring pressure to maintain a good low-resistance electrical contact (vibration could reduce this), and that because the contact area between spring and battery end is actually quite small you can have a small amount of corrosion on one or other surface which makes a significant difference to contact resistance.

 

The problem with a dodgy high-resistance contact is that it may well work when everything's on the ground and there isn't much drain, but it could cause problems when you're in the air, your pack isn't at 100% capacity, and you have all your servos working at once (especially fighting to maintain position against in-flight loading of the control surfaces).

[hotrod 0]

Re 4.8v vs 6v

As I understand it for a given capacity of battery the 6v will not last as long as the 4.8v as you are using more volts.

Please correct me if I am wrong

Rod

[arun 0]

Re 4.8v vs 6v

As I understand it for a given capacity of battery the 6v will not last as long as the 4.8v as you are using more volts.

Please correct me if I am wrong

Rod

 

This is my understanding, happy to be corrected. I assumed be "last as long" you mean for a single discharge, as against total life before it goes in the bin. If it is the latter, the answer is probably, "it depends"

 

Capacity is measured in milli-amp hour (mAh) which indicates how many constant milli-amps of current can be supplied by the pack for one hour.

 

So if your servos pull on average 1A, a 2000mAh battery will last two hours irrespective of voltage. During the course of discharge voltage obviously drops gradually (see Martin's graphs above). Indeed it may also drop temporarily if you try and pull excessively high current, say during an aggressive manoeuvre that makes that servos have to work very hard to hold their position.

 

So ... at some point that voltage may fall below a safe limit for operation of your plane which will be before you have used up all of the theoretical capacity of the battery. If anything for our use, I would expect a 6v battery to last longer "in the field" than a 4.8v one as its voltage remains above a safe level for Rx/servos for longer, hence avoiding brown out.

[Martin 0]

Re 4.8v vs 6v

As I understand it for a given capacity of battery the 6v will not last as long as the 4.8v as you are using more volts.

Please correct me if I am wrong

Rod

 

I think different people have shown different things for this, and there are a lot of different factors at play. Something like a receiver probably draws a more or less fixed current regardless of voltage (but may well get hotter at a higher supply voltage, as with simple linear BECs on small ESCs). Servos will move faster and provide more torque (again getting hotter), but will draw more current in doing so (partly mitigated by the fact that they are moving the same distance at a faster speed so are moving for less time). At the same time, drawing a higher current from the battery will reduce the usable capacity due to things like internal resistance. The real effect will depend on so many different things (models of receiver and servos in use; battery technology, quality and charge level; specific flight loads) that you may never get a definitive answer of how much this affects things.

 

Personally, I think the benefits (more speed and power from servos, larger safety margin against receiver brownouts) outweigh the disadvantages (25% more weight on pack, possible slight reduction in flight time). If I ever do get to the point where the weight or flight time is a problem then I've always got the option of LiFe (or just swapping for a fresh NiMH pack after a couple of flights)...