Safest NiCd discharge?
 

NOTE:I mixed up NiCd and NiMH for obvious reasons. I meant NiCd NOT NiMH!!!

I need to discharge my NiCd pack because there's been a few games where it would die because I couldn't charge it the night before. I couldn't charge it cause I didn't know what was left of at and for how long to charge it. I don't want to screw up the NiCd memory but I also want full power before a quick game. I could buy another pack but I have other priorties such as a vehicle so I can actually drive to the store and pick one up.

So aside from hooking it up to an electrical motor and letting it run till it stops, what's the safest way to discharge a NiCd battery pack???

NiMh don't have memory effect. ONLY NiCd does. Also, NiMh crap out if you discharge them 100%, worst than not discharging NiCd batteries.

http://www.airsoftcanada.com/showthr...ht=battery+faq
There is quite a bit about Ni-Cd cells and how to discharge them properly.
As for what to use to properly discharge a cell. Most high end chargers have a variable discharge setting, I assume this is the best option. I have also seen other products like the TM discharger on the battery page from 007 airsoft, not sure how this would work compared to a charger.
http://www.007airsoft.com/products/htm/consumables.htm

1) the whole NiCad "memory" thing is generally blown out of proportion by people who don't understand how batteries work and fail to charge them properly: unless you're regularly and consistently draining your batteries to the exact same level and the recharging, over and over, "memory" is not an issue.

2) All rechargeable battery packs (NiCad, NiMH, LiPo, Li-Ion, etc) have a finite cycle-life, that is they will eventually wear out and die after being charged/discharged a number of times. How you care for your batteries will extent or shorten the lifespan of your pack. Artificially discharging your pack just pushes it through one extra full cycle and shortens its lifespan by that much: under normal, regular use it's not necessary to do this (see #3).

3) Invest in a good charger. No matter if you change guns or how often, a good charger can stay with you for years. A smart charger will detect if your battery is fully charged no matter what its initial charge level was. Furthermore a good charger will do more to control charging rates to maximize your pack's charge, rather than just dumping a large amount of amps into it (which sounds like is what's happening in your case if you need to calculate charge times).


Point #3 really addresses the crux of your problem, which is that your battery is dying mid-game because you couldn't charge it before the game due to having a shitty charger. Fix that and everything else goes away.

Or if you're really broke ass, use a slow/trickle charger and let it charge all night: you won't damage the pack with a 0.1-0.2A charge, even if it "over charges." (in fact it's usually recommended to let the pack trickle charge for a while after it's finished fast charging, in order to maximize the charge)

What he said.

As for your answer, you can go and buy a 12V automotive lamp and hook it to your battery. That is the best way to drain it properly, it will drain roughtly 1A per bulb you hook-up. We are using that to cycle our packs faster than with the charger when racing RC cars.

There is an other trick, but not a good idea with a full/quite full pack. You can wire a large gauge tin piece between the poles. That is usually done for storage, and since it is lead (the one used for plumbing soldering, usually around 12-10ga), it will melt if the pack is too charged and over drain (too fast).

If you had your battery for more than 4 years, it is most likely dead.
And if you have to calculate charge time, it means that you don't even have a charger, you have a power supply. A charger by defenition will stop by itself when done.

DON'T BUY the "Universal Smart Charger". They should be named "Universal Battery Killer". For airsoft use, a good choice is the Onyx 210. Cheap and works great.

I've got question or two if you guys don't mind...hopefully this isn't too off-topic from the thread.

I've got 2 PTW batteries...good factory matched Sanyo packs. One is 9.6v 1200mah and the other is 12v 1100mah (or the mahs might be reversed...can't recall at the moment). The batteries are working just fine at the moment.

I'm using a B6 xcharger. Set to NiCd, charging at 1.1A. The discharge setting is set to 0.6A

At most of the games I go to they are limited ammo, real cap games....so I've never shot my battery (either of them) until it's been dead at those games. Then it gets stored away for potentially a long while (month-8weeks) between games.

So...
Q. What would be your recommendations for charging/storage?
1. "Top them up" before a game and top them up afterwards for storage
2. Discharge+Charge before a game, leave them however they are afterwards
3. Shoot 'em until they're dead, charge them up fully for storage
4. Other combo of actions

If they're partially used...I'm 50/50 on running a discharge+charge before a game....I don't want to unduly shorten the lifespan of the batteries, but I definitely don't want to run out of juice in a game. So far...it's been infrequent enough (used my gas rifle all season) that I've run a discharge + charge before the games.

Q. Is there any "easy" way to see how much is left in a battery before I charge it?
- in the discharge + charge cycle it'll show me the results of what it did (i.e. D 500mah - C 1098mah)...but that's after the fact
- if I don't know where the battery is at (i.e. how used it is) and "top it up"...the charger will do its thing and stop when it detects the battery is full...but it only displays "how many mah it put into the battery".

According to my mom you actually can't tell how much "juice" (amperage) is left in a battery without some weird setup or something like that. You CAN however, get a *general idea* of how much juice there is left if you take a multimeter and test for voltage obviously this isn't really an accurate way of testing but that's what we do at home.

Really, how much is a battery worth for your time? Obviously $50 is a lot of money, I'm not saying it isn't but if you have a smart charger it will extend the life of the battery and instead of 100 charge/discharge cycles you might now get 200 charge/discharge cycles out of it.

Now IRT to the OP's question. According to my mom as well, NiCD, although it is more susceptible to the "memory effect" than a more "modern" battery chemistry (ie. NiMH) it's not really much to worry about (anymore). As well, the newer NiCD cells are actually supposed to be better at negating the memory effect and the real problem people have is actually *OVERCHARGING* the batteries (not a big deal if you have a smartcharger that cuts power after it tells the battery is fully charged up) so that's a better reason to toss out that dumb wallcharger. If you must use a wallcharger though do some math and set a timer (ie. charging rate and battery capacity to figure out how long it is until the battery is fully charged then you physically disconnect it).

PS: If you're doing a "fast charge" it's actually defined as charging at 1C or more. 1C will give you a charge time of 1 hour (and a bit to compensate for inefficiencies in the charger). It's best to charge a .5C or less ("slow charge") but 1C isn't really bad or anything.

5. Discharge the pack fully, plug a wire between the two sides to keep if fully drained. When you intend to use it, cycle 2-3 times and use it. You should discharge the pack a LOT higher than that... around 5A should be good for that type of pack. Because what you are doing does nothing, should as well just not cycle them.

You can tell by discharging the pack at about 1C and checking voltage. A no-load discharge (when plugging the meter at both ends) means nothing. You would need to have a graph or reference for your battery before that. I know my charger can trace it for me when it cycles, then I just need to read the values at each 10% to know it. You can get a good estimate when your charger gives you the cycles data. If your pack is 1100mAh, Discharge should be around 900-1000mAh and charge about 1200-1300mAh. The tighter they are, the better the shape of the pack is. When you charge it after a cycle and you get at or under the "theorical" value, it means that your pack is dead/dying. I have a 3800mAh that will cycle about 2900mAh charging... when I fire the gun, it shoots 3-4 BB before droping voltage under 4V...

Thank you, that's most helpful.

I will have to check my charger settings....I can't be sure at the moment what the discharge rate off hand. I understand what you mean though.

I see how a performance/spec graph would be helpful...I don't know if I'll ever get to that, but I'll look for that if I ever need a new charger. The charger I have might be able to do it...just haven't looked into it.

I have a different opinion on this than KosMos, personally I would store them with whatever charge they have left: rechargeable batteries will naturally shed their charge slowly over time and there's no real need or benefit from storing them 'empty' -- in fact, if their charge drops too low (i.e., fully discharged then stored for a long time) some of the cells might reverse polarity (which will potentially kill your pack unless you have a good charger and really know what you're doing).

Then just charge your pack up before the game. If its been stored for a long time (more than a few months) you might want to charge, discharge then re-charge it and let it trickle charge for a while after.

As for measuring how much juice is left in a pack, L473ncy is right (or L473ncy's mom, I guess): trying to measure the amps with a multimeter won't give you a usable result, but you can estimate charge from voltage. A 1.2v cell when fully charged will give off about 1.3v (so a 9.6v pack will usually read around 10.4v, sometimes even more if they're high capacity cells). "Discharged" cells show about 0.9v (you don't want to let cells drop below 0.9v, that's when bad things start happening), so your 9.6v pack will show something between 7.2 and 9.6v depending how drained it is.

If you had a "pretty empty" pack showing close to 7.2v and you knew you were going to store it for several months (like over winter), I'd actually charge it a bit before putting it away: just trickle charge it for a few hours, so that when it drains itself over time the cells don't drop below 0.9v.

Drake's system sounds easier....and that's a good thing...:)

I'll do some more poking around and see if I can't get a concensus from another source or two.

(essentially everything comes home from a game and gets pushed into the corner until it can be sorted out much later...so if there's a dummy proof method I'm up for that)

Tys

Me and my dad used to charge all our rc airplane battery packs on power supplies for years without a problem. I could use a voltometer and check it's remaining power then use math to charge it properly. At least till I get my car then I can buy a second batter so I can basically loop. (battery 1 runs out, throw in battery 2. Charge battery 1. Run 2 till it goes out and throw in 1. Charge 2. Repeat)

0.9v is for NiMh chemistry. NiCd work differently and fully discharging (to 0v) is preferable, otherwise it forces a "memory" effect into the pack. Always discharging to 0.9v would actually be bad in this case.

The reason for the shorting wire is that the cells will also recover over time, some cells will do faster than others. That means that it can cause a cell to reverse itself if the other cells gain enough juice before it. Shorting the pack makes sure that there is nothing, no positive or negative power in the pack.

You really should have a good charger if you consider using this method to store your packs, because the "wake-up" can be hard if you need to charge them with a crappy charger that will not work when voltage is too low (like most cheap "universal" chargers, they just don't detect a battery plugged and never start)