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Old Jan 06, 2007, 06:05 AM
dmt
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Noob Question: What do you do if you Charge your NiCd, but Then Can't Fly that day?

Well, what is the correct procedure?

The two most obvious choices would seem to be:

a) just let the battery sit (in or out of the aircraft?) until you eventually use it (days, weeks, months?)

Or

b) discharge it somehow.

I'll tell you what I'm doing, though I suspect you guys won't like it (in which case, I'm probably being stupid, but that's why I'm asking the question -- so I don't keep doing stupid things):

Today I charged up my two NiCd batteries at home (each for different motor gliders). The one had been trickle charged overnight in anticipation of today's flying, the other one I [fifteen minute] quick-charged this afternoon before I went out. Okay, so I went out to my field but it was just too windy. Snow flurries, significant gusts...I decided it would just be pushing it too much and eventually went back home without even getting either plane out of the car.

So, here I was at home with two fully charged NiCd batteries, and I have no guarantee as to when I'll be able to fly next (hopefully in a few days, but it could certainly be a few weeks). So, I decided to discharge the batteries, with vague ideas about preserving the proper "memory" -- a concept I only half understand. Here's the part I don't think you're going to like: I took the planes outside to the front porch (one by one, not together, but anyways...), connected up the batteries and planes, and ran the aircraft motors until the ESCs shut them off, respectively. At that point I disconnected the batteries and brought aircraft, radios and batteries back inside.

The thing I think you won't like is me running the motors without flying. I guess part of the concern is little or no load on the prop (so maybe it goes too fast?), and the other is overheating. Well, it's windy and sub-freezing outside, the cockpit covers were off and the planes were pointed into the gusty wind when running. I can't imagine they overheated. Both battery and motor were mildly warm to the touch afterwards, but nowhere near "hot". The ESC was cold to the touch.

Anyway, was what I did stupid? Dangerous? Inefficient? Unneccessary?

What do you do when you charge up your batteries but end up not flying (and have no idea when your next flight will be)?

Part 2:

Also, a similar question -- what if you end your flying session early, with still half a charge left on your NiCd battery. What do you do then? I've been just running it on the ground until the ESC shuts it off. I have a feeling that's probably going to be a big no-no though? It is winter where I am, so nothing's getting too hot for now, anyways.

Any help, instructions or advice would be appreciated.
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Old Jan 06, 2007, 07:03 AM
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Here's what I do; it may not be "correct", but it's worked for several years

Straight after a flight I discharge and then fully charge my packs using a battery cycler. I record how many mAh go back into the pack, so I can get some idea of how much they're wearing out. At last count my (probably) 6-year-old 7-cell RC2000s were still taking 1600 to 1700mAh.

Immediately before the next flight I top them up; they take 300 or 400mAh after a 3-month break.

If I miss a flight, like you just did, I don't do anything until I next need the batteries, then I top them up like normal.

I believe that memory only comes into effect if you repeatedly discharge and recharge by the same amount -- eventually the battery won't discharge any further than that amount. So, if you have too many missed flights, and therefore do too many top-ups in a row, you might have a problem. The solution is to fully discharge from time to time

Discharging using the model is not a bad idea because the ESC ensures that the voltage won't drop too far. The load on the prop is the same, or just a bit more, than it is when you're flying; cooling of the ESC is the main concern when doing it that way, plus the hassle of holding the model down Better to get, or make, a discharger if you're going to do this regularly. You can use one or more automotive light bulbs as the load, and experiment until you get a suitable amps discharge. I'm sure there's a thread about it somewhere in this forum. Then leave a voltmeter hooked onto the battery to monitor the volts.

Here's a link http://www.rcgroups.com/forums/showthread.php?t=318643
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Last edited by abenn; Jan 06, 2007 at 07:11 AM.
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Old Jan 06, 2007, 07:54 AM
dmt
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Quote:
Originally Posted by abenn
Here's what I do; it may not be "correct", but it's worked for several years

Straight after a flight I discharge and then fully charge my packs using a battery cycler. I record how many mAh go back into the pack, so I can get some idea of how much they're wearing out. At last count my (probably) 6-year-old 7-cell RC2000s were still taking 1600 to 1700mAh.

Immediately before the next flight I top them up; they take 300 or 400mAh after a 3-month break.

If I miss a flight, like you just did, I don't do anything until I next need the batteries, then I top them up like normal.

I believe that memory only comes into effect if you repeatedly discharge and recharge by the same amount -- eventually the battery won't discharge any further than that amount. So, if you have too many missed flights, and therefore do too many top-ups in a row, you might have a problem. The solution is to fully discharge from time to time

Discharging using the model is not a bad idea because the ESC ensures that the voltage won't drop too far. The load on the prop is the same, or just a bit more, than it is when you're flying; cooling of the ESC is the main concern when doing it that way, plus the hassle of holding the model down Better to get, or make, a discharger if you're going to do this regularly. You can use one or more automotive light bulbs as the load, and experiment until you get a suitable amps discharge. I'm sure there's a thread about it somewhere in this forum. Then leave a voltmeter hooked onto the battery to monitor the volts.

Here's a link http://www.rcgroups.com/forums/showthread.php?t=318643

Okay, well the ESC definitely wasn't getting hot (it's frickin' cold outside tonight!). Specifically, it was cold to the touch immediately afterwards.

So I guess the main thing you're saying though is that I don't have to completely discharge every time. In fact, you're saying you charge yours after your flight, store it charged, and then just "top it off" if it's been a few weeks-to-months.

I guess for topping off, I can just leave mine on a trickle charge overnight, essentially without any appreciable danger? Mine only has a trickle charge and a 15 minute quick charge function, with no readouts.

I only have a simple charger (and no balancer or cycler or anything) and don't plan on buying a new charger just yet (it has been working fine for me for a few years for one, and also I'm researching this whole battery thing and I will continue to do that until I have a good grasp of the issues, and then research a better charger that will best match my needs. But like I said, my present simple charger has seemingly been doing me okay for a few years now, and will surely do the same for at least the next few months).

Thanks,
-David
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Old Jan 06, 2007, 07:53 PM
dmt
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abenn,

thinking about this more, I think I see why you top off your batteries (which I was wondering about). Basically, I was doing the exact opposite -- I was discharging my batteries (down to the ESC limit) in hopes of from full charge (on the top end) down to ESC cutoff (on the low end) being the battery pack's "memory". However, I think I now see that if the batteries were to be stored for too long, the charge will eventually drop below the proper discharge limit.

For example, if my pack is 7.2v and the ESC cuts off the engine at 4.5 volts, and the radio would cut out at 4.0v; then maybe battery damage due to a "deep discharge" would start to occur at 3.75v (or something like that -- I don't know the exact numbers). If I run my batteries through the ESC/motor until cutoff (4.5v) and then store them for what unexpectedly turns out to be months, the voltage will probably eventually bleed off to below 3.75 volts (eventually well below) and the batteries will suffer "deep discharge damage".

However, if I were to store the batteries fully charged, they would never (well, maybe not "never", but it might take a year or so) drop into the danger range.

Does all that sound about right?

If so, I feel a bit foolish, as my original reasoning/actions were basically 180 degrees wrong! Oh well
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Old Jan 07, 2007, 03:47 AM
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Quote:
Originally Posted by dmt
abenn,

thinking about this more, I think I see why you top off your batteries (which I was wondering about). Basically, I was doing the exact opposite -- I was discharging my batteries (down to the ESC limit) in hopes of from full charge (on the top end) down to ESC cutoff (on the low end) being the battery pack's "memory". However, I think I now see that if the batteries were to be stored for too long, the charge will eventually drop below the proper discharge limit.

For example, if my pack is 7.2v and the ESC cuts off the engine at 4.5 volts, and the radio would cut out at 4.0v; then maybe battery damage due to a "deep discharge" would start to occur at 3.75v (or something like that -- I don't know the exact numbers). If I run my batteries through the ESC/motor until cutoff (4.5v) and then store them for what unexpectedly turns out to be months, the voltage will probably eventually bleed off to below 3.75 volts (eventually well below) and the batteries will suffer "deep discharge damage".

However, if I were to store the batteries fully charged, they would never (well, maybe not "never", but it might take a year or so) drop into the danger range.

Does all that sound about right?

If so, I feel a bit foolish, as my original reasoning/actions were basically 180 degrees wrong! Oh well
Yes, in my view storing them discharged is the worst thing you can do for the reason you've stated. I think some people advocate storing them half charged (or maybe I'm getting confused with threads on other types of battery), but that's likely to be only when you know they're going to be unused for a long while.
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Old Jan 07, 2007, 04:09 AM
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NiCds only suffer "deep discharge damage" as you call it if they are discharged at relatively high currents (like running a motor) to a very low voltage. When they are simply left to self-discharge it doesn't do them any harm even if they get right down to 0V (takes a LONG time). They may need one or two charge/discharge cycles to get back to full power when you start using them again but that's about all.

In fact the safest way to store a single NiCd cell is at 0V. It's only because they're in a pack that we have to worry about reverse charging one of the cells and so we don't deliberately discharge the whole pack to 0V.

If you just leave your NiCds in whatever state they end up in (full, empty or anything in between) and then give them a charge immediately before want to use them again they'll be fine. I have several packs over 10 years old that are still working well and I've never done anything more complicated with them.

But that's just NiCd. Both NiMH and LiPo are more fragile and need a little more care (e.g. storing half charged is for LiPo).

Steve
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Old Jan 07, 2007, 05:32 AM
dmt
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Quote:
Originally Posted by slipstick
NiCds only suffer "deep discharge damage" as you call it if they are discharged at relatively high currents (like running a motor) to a very low voltage...

If you just leave your NiCds in whatever state they end up in (full, empty or anything in between) and then give them a charge immediately before want to use them again they'll be fine.
Leave 'em in whatever state they end up in. Okay, I think I can manage that!

Actually, I think I have a good feel for how I'm going to handle this. First, I won't be anal about fully discharging a pack [to ESC cutoff] every time I don't immediately use it. On the [6 cell folded] pack I use frequently, well it only gets about 10 minutes anyway. If I land early and there's still a bit of power on it, but not enough for another flight, and if the weather is cool (or a bit windy, so I can hold it into the wind), I'll probably give it a short run to get to ESC cutoff, basically like I've been doing. I usually get two flights (or at most 3) out of it, and then there's just a bit of power left over at the end. If it's warm, I won't worry abut it.

If I realize at some point that it's been weeks and no more flights are likely in the near future (such as, I'm looking to get the damn gliders broken down and stored out of the way since I'm never using them anyway), I'll probably do an overnight charge and then leave the battery pack like that, but again, not freak out about it, like it's something I have to do.
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Old Jan 07, 2007, 05:34 AM
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slipstick, do you store your NICds in any special way (such as in a ceramic jar, or ammo box, or something like [or un-like] that) if you know they won't be used for a long time (months+)?
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Old Jan 07, 2007, 08:33 AM
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Nope, I've never really heard of a NiCd (or NiMH) doing anything it shouldn't when open circuit. I'm afraid I just keep them all in plastic boxes in the workshop.

I'm a bit more careful with LiPos though .

Steve
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Old Jan 26, 2007, 05:28 PM
no wings any more, just dust!
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DMT, yes i am a boater, however i too use nicads, as regards storage, as long as you keep the contacts from shorting you can store them pretty much anywhere, I leave mine unplugged but in the boats from time to time, in the field box, even the window sil from time to time.

so leaving them in placcy boxes like slipstick does is perfectly safe
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