NiMH charging question

[GMTII]

1

[ILLusion]

ni-mh batteries should never get warm or hot. if it does, damage is setting in.

ni-mh batteries also do not have memory effect, which is why some ppl choose to use them. don't worry about unplugging.

[GMTII]

1

[666]

Originally Posted by ILLusion

ni-mh batteries should never get warm or hot. if it does, damage is setting in.

Really? I didn't know that. I have ni-mh battery which was only charged twice with high end changer, both times it got a bit worm in the last minute or two, right before it finished charging.

[ILLusion]

Originally Posted by Erik_james

Oh ok, glad you told me that. So, if the charger puts out 300 mah a hour and the battery is 1100 mah I should charge it for approximently 3.6 hours regaurdless of how the battery feels? Right now the battery is slightly warm, but I have unplugged it, do you think any serious damage would be done because of that?

Erik

Well... 3.6 hours is a very basic calculation. You (as well as many other ppl who follow this calculation) do not take into consideration charging deficiencies due to lost energy through heat transfer. The heat you get off the packs is due to excess energy. It's not taken in by the cell fast enough, so it gets emitted off as heat.

To compensate for the lost energy, you need to charge longer - a constant needs to be multiplied into your B/C=T equation (where B = battery capacity, C = The charge rate and T = Time required).
This constant ranges from 1.2 to 1.6 and is dependant on how hard you're charging your cell, and how you feel your charger's accuracy is.
General rule I would use is 1.3 for NiMH batteries and 1.4 for Ni-Cad. This constant goes up as your charging rate goes up.

So your equation would be something along the lines of:
B/C*1.3=T
OR
1100/300*1.3 :: 4 hours, 45 minutes

Keep in mind that these are general rules of thumb. EACH individual cell and each individual battery pack and each individual charger and each individual power outlet, and each individual room's ambient temperature will have variances which will ultimately affect the charging time of your battery. Going by these primitive calculations will 99.9999% of the time undercharge or overcharge your battery to some degree.

Hooking up a multimeter to your battery and closely monitoring it can aid in seeing how each individual battery pack's charge characteristics perform, but it requires constant and close monitoring.

Of course... I don't bother with these calculations and crazy electronic contraptions, because I just use a smart charger that takes care of all that for me and gets it accurate. I plug it in, push "charge", walk away, eat some food, take a shower, take a dump, clean the pipes, take a nap, watch 24, do some work, (not necessarily in that order,) come back and my battery is all charged, good to go and healthier than if I were to manually calculate a charge time.

Originally Posted by 666

Really? I didn't know that. I have ni-mh battery which was only charged twice with high end changer, both times it got a bit worm in the last minute or two, right before it finished charging.

A "little bit" warm for a brief period of time is okay. It's only when the heat is excessive or for prolonged periods of time, that's when Ni-MH batteries will start to cry.

[Psycho]

hmm.. a quick quistion.. what is the battery memory?[and what ist for?]

Edit: thanks for the link

[ILLusion]

Google:
Battery Memory

[Mantelope]

www.batteryuniversity.com

[wey ferro]

also pm JohhnyDo he knows everything about everything about battery packs.

[Greylocks]

If you dont want problems with expensive batteries for your expensive airsoft (no power is a bitch), simply invest in a battery charger that is worth it.

It makes no sense to me to see folks spend $600 for a gun, $50 for battery packs, and then $10-50 for the cheapest charger they can find. Invest wisely, those chargers repay themselves in less than one year in saved batteries and no headaches.

[JohnnyDo]

Originally Posted by Greylocks

If you dont want problems with expensive batteries for your expensive airsoft (no power is a bitch), simply invest in a battery charger that is worth it.

It makes no sense to me to see folks spend $600 for a gun, $50 for battery packs, and then $10-50 for the cheapest charger they can find. Invest wisely, those chargers repay themselves in less than one year in saved batteries and no headaches.

I could not agree more. I've seen it time and time again where people cheap out on the wrong thing and pay for it in the end. Then ask why did this happen or that happen.

Erik:
One thing to note about NiMh batteries is they perform better if you charge them after only useing up say half it's capasity. NiCads on the other hand need to be discharged before charging them back up. This is another reason people prefer NiMh packs.

I am curious to know if your charger is even ment to charge NiMh batteries. Alot of those cheap wall wort chargers that I have seen are only ment to NiCad. You may want to double check as charging with the wrong charger may/will cause damage to your packs.

[firemachine69]

Depends how often you play, as is my case.

My pulse charger I got from Scarecrow has served me well.

[Gryphon]

Alright, there is a lot of bad information in this thread that needs to be corrected.

First of all, for all practical purposes there is no such thing as memory. What everyone likes to call memory is actually voltage depression and is NOT from failing to discharge your batteries fully before recharging. If anything, discharging your battery is a needless task that in fact harms your cells by reducing their remaining cycle count. Furthermore, discharging your batteries past 0.9V/cell will cause them to go into reversal which REALLY destroys them, and is probably the cause of most nickel-based battery failure.

Also bad, contrary to Illusion's post, leaving your pack connected after it's charged IS harmful to your cells and you definitely SHOULD worry about unplugging your charger at the proper time. A wall wart is simply a transformer that supplies a fixed amount of current and voltage and has no peak detection circuitry to tell it when the battery is full. What happens is, as explained by the following link, the chemistry of the nickelic hydroxide changes from the beta to the gamma form on the positive plate which has a potential of some 40-50 mV less than the beta form. That means in an 8.4V pack, you are losing some 300-400 mV total from your pack. Charging with a trickle charger encourages this.

http://www.wppltd.demon.co.uk/WPP/Ba...ry/memory.html

Solutions:

1. Get a reliable, linear, peak detection charger that can monitor your battery's progress as it charges.

2. Don't discharge your pack unless you need to, and make sure it doesn't discharge past 0.9V/cell (the link says 1.0V but it seems 0.9V is the accepted standard).

3. Don't overcharge your battery.

[ILLusion]

Originally Posted by W.K.Shuridys

Also bad, contrary to Illusion's post, leaving your pack connected after it's charged IS harmful to your cells and you definitely SHOULD worry about unplugging your charger at the proper time. A wall wart is simply a transformer that supplies a fixed amount of current and voltage and has no peak detection circuitry to tell it when the battery is full. What happens is, as explained by the following link, the chemistry of the nickelic hydroxide changes from the beta to the gamma form on the positive plate which has a potential of some 40-50 mV less than the beta form. That means in an 8.4V pack, you are losing some 300-400 mV total from your pack. Charging with a trickle charger encourages this.

http://www.wppltd.demon.co.uk/WPP/Ba...ry/memory.html

Not sure how that contrasts my post... I clearly indicated that using a wall wart with primitive calculations will 99.999% of the time undercharge or overcharge the battery. I never said leaving it in was okay.

Also, most smart chargers now automatically cut off the discharge when it reaches the 0.9v mark.

For example, the one I'm selling right now will do it, complete with fuzzy logic charge functions!

http://www.airsoftcanada.com/showthread.php?t=511

[Gryphon]

Originally Posted by Illusion

ni-mh batteries also do not have memory effect, which is why some ppl choose to use them. don't worry about unplugging.

I took that to mean you were saying it's alright to leave it plugged in and not have to wory about disconnecting it on time. I apologize if I was mistaken but that seems to be how it's worded.