7.2 Volt Battery for Airsoft Gun

This guide deals with a lot of the maths behind charging NiMH, then if that's non for you, switch off now. It doesn't deal with NiCad, Li-Ion or anything else.

EDIT: Crikey, at that place's a lot here isn't in that location. Before yous start reading, have the post-obit information to hand.

i) Your bombardment'due south voltage (V).

ii) Your bombardment'due south output rating (mA/h). It could be 1100mA/h, 2200mA/due south, yourbattery'southward#mA/h but expect to run into a number in the chiliad'south for an airsoft bombardment.

3) Your charger's output in milliamps (mA) for the voltage of the battery yous are charging. WARNING: Your charger may not quote an output current for the verbal voltage you lot wish to charge. If information technology's a cheap charger, lookout man out. Output current goes down every bit voltage goes up and up as voltage goes downwardly in low quality chargers.

Your battery's rating is information technology'due south capacity. The nomenclature for this is C. For case, my battery has a 3300mA/h rating, (theoretically it can discharge 3300milliamps in an 60 minutes), so 3300 is to me, C. My friend has an 1150 mA/h battery, her "C" is 1150.

IMPORTANT FACT: This mA/h figure relates to a unmarried cell of your bombardment. NiMh battery cells give out approx 1.2 volts. You can't purchase a single 8.iv volt NiMh battery cell. What you have to do (and commonly the manufacturers exercise this for us airsofters) is to is link them together in series and add the voltages up. So...

i cell = 1.2v

2 cells = 2.4v

iii cells = 3.6v

4 cells = 4.8v

v cells = 6v

half dozen cells = seven.2v

7 cells = 8.4v

8 cells = 9.6v

9 cells = 10.8v

10 cells = 12v

etc..

This is my original battery. Each cell is 1.2v 3300mA/h and there are seven of them. It's an viii.4 volt battery.

This is my new battery. Each cell is ane.2v 3300mA/h and there are eight of them. It's an 9.six volt battery.

You get the thought? The college the voltage, the more cells you lot need. And high voltage doesn't hateful high capacity. Y'all can have a 9.6v 1500mA/h battery and a beefier 6v 5000mA/H battery.

Okay, there are several means you can accuse a NiMh battery: Trickle, slow, rapid, fast and ultra-fast.

(Retrieve that rating "C", I'thou going to refer to it a lot!)

TRICKLE CHARGING

NiMh batteries lose their accuse with time. Typically a good one will lose 1% a day. A poor-quality or poor status bombardment may well lose more. (Really there are some which DON'T lose their charge at one% a 24-hour interval, which complicates things a chip, but they are not the norm.) Trickle charge is basically used to counteract this loss and keep the battery fully charged, NOT to accuse a bombardment that is depleted. The charging rate for trickle charging is around C/xl. So for my battery that's 3300/40 which is a charging rate of 82.5mA (at eight.4 volts).

Important FACT: You need to match your charger to your battery!!!

If I use my battery's 82.5mA trickle charge rate on my friend'southward 1150mA/h battery, I'll be charging hers at C/14, which is not trickle-charging. Information technology is pretty much.....

Boring CHARGING

Tiresome charging is how NiMh batteries beloved to exist charged, but as its name suggests information technology is tiresome. The charge charge per unit for slow charging is C/10, or 10% of the battery's capacity. So for me, that's 3300/ten=330mA. But for how long? Batteries are not like a drinking glass of water. You can't put some in and get out everything y'all put in. Due to losses you have to put in 150% of what y'all expect leave of a NiMh battery. (At present you know why people say "You have to times it by i.5). So as well as the 10 hours I need to charge simply to match the output (330mA * 10 hours = 3300mA/h) I also demand to charge for another five hours to bring me upwardly to the 150%. So that's 15 hours given a perfect C/10 charge rate.

Simply in the real world, you get a charger with a rating. This is the info I got with my charger.

So permit's interpret that into use. Information technology'due south 200mA at 8.4v. So that's information technology's output for my battery. (the higher the voltage, the lower the mA in inexpensive chargers). Equally I explained earlier, I need 330mA/h for a 10% slow charge, and then I just have a accuse rate of 6% or 0.06C with this 200mA/h charger. This means I have to accuse for 3300mA/h / 200mA = 16.5 hours PLUS the extra 50% to annul the losses, which ends up at 24 hours 45 minutes.

Why the hell would anyone want to slow accuse? Well there'due south at least one good reason. Every bit batteries finish their charge and start to overcharge, they start releasing gasses internally. Almost NiMh cells have an inbuilt ability to reabsorb these gasses and then long equally they exercise not overwhelm that ability either by also loftier a accuse current or overcharging for too long. Judge what their ability is designed to exist able to deal with? You got it! A charge rate of well-nigh 10%. More than than that and they overheat and start to get damaged. This is why almost OEM chargers are slow chargers. It ways the batteries can be moderately overcharged without much risk of battery damage and subsequent customer anger with the shouting and biting etc. It too explains why you get pretty vague charging advice with your irksome charger. "Until it gets too hot!" seems to exist a common theme, and it's pretty much the truth. Now you know why. But I am former and haven't got the time to slow charge, which brings me on to…..

RAPID CHARGING

Rapid charging is seen as typically 0.3C – 0.5C., or thirty% to l% of the battery'southward chapters. Maybe 60% too. The aforementioned maths applies, but at present things are getting more manageable. If I charge at 0.5C, that's 3300/2=1650mA for 2 hours plus the 50% actress for losses is 3 hours.

USEFUL FACT: Accept you noticed how the charge fourth dimension is only the charge rate denominator *1.5? Just a thought….

Well I tin live with 3 hours charge fourth dimension, so I've ordered a rapid charger which is switchable between 1000/2000mA.

The bad news is that the nice circular theoretical 1C and 0.1C numbers have to go out of the window and I deal with the chiliad/2000mA rates what I've got. The good news is that this is a quality charger and can deliver m/2000mA at 6-12v, so that's nice.

To work out the accuse rate of my charger, I divide the charger's outputs by my bombardment rating. Which is m/3300=0.3C and 2000/3300=0.61C. Okay, those are squeamish rapid accuse rates so I've got the correct charger for my bombardment if I desire to rapid-charge.

To work out my charge TIMES, I carve up my battery rating by the charger ratings and multiply the number by 1.5 to add in the l% losses accuse.

Then that'south (3300/1000)*one.5=4h57m and (3300/2000)*1.five=2h28m. I tin live with that.

At this charge rate, I'll need to make sure I accuse for no longer than I'm supposed to or I'll cook my bombardment. I'll would have needed a timer plug prepare to the correct time, but I've ordered a smart charger which detects the little electrical twitch in the NiMh cell when it's fully charged and changes from RAPID to TRICKLE charge. (Incidentally, it would exist nice if my "smart" charger too had a temperature probe to forbid overheating, but it doesn't. If you're buying a smart charger, one with a temperature probe is a very safe bet, as just sometimes, the lilliputian electrical twitch in the battery is not detected at the lower finish of the range. With that in heed, I'll always be charging mine at 2000mA. This forces a larger voltage "twitch" when fully charged and should make sure the detection circuitry works reliably and the charger switches to trickle accuse when it should.)

But, maybe y'all want your battery fully charged as fast as possible without risking damage to your bombardment?! Which brings me to….

FAST CHARGING

Fast charging is basically charging at 1C. So my 3300mA/H battery will take a accuse of 3300mA for 1 hr, plus the 50% which takes information technology up to 1h30m. Likewise my friend'south 1150mA/H battery volition take a 1C charge of 1150mA for 1.v hours.

USEFUL FACT: See how that charge charge per unit *i.five is still working at 1C?

IMPORTANT FACT: Note how with my charger, the RAPID charge rate of 0.3C on my 1000mA output for my 3300mA/H battery becomes a FAST charge rate of 0.87C on my friend's 1150mA/h bombardment. And too note how the RAPID charge rate of 0.61C on the 2000mA charger output for my 3300mA/h battery becomes a ane.74C accuse rate on her 1150mA/H battery? Which brings me to….

ULTRA FAST CHARGING

Ultra fast charging is a charge rate of 1C-10C. At this charge rate, you are putting quite some stress on your battery, and then you'll need to give it some TLC in the class of a dull charge every now and and so. It can be done but do I desire to put around thirty amps into my battery to charge it at 10C? I'll laissez passer thank you.

Decision

Remember, a NiMh is not for life. Yous will probably get well nether 1000 accuse cycles, so don't think that you'll get to keep your batteries in perfect condition forever if you but ever slow charge. It won't happen. Like us, batteries all go sometime and die, sooner or afterward.

In that location are other problems, such as crystalisation, but it'southward not a big event. The bottom line is to deadening charge now and and so, but rapid or fast charging every bit the norm is perfectly fine, and ultra-fast charging is possible with intendance. Merely to charge your battery properly, Yous MUST KNOW THE RATING OF BOTH YOUR Bombardment AND CHARGER.

That'due south all folks.