How long do I charge?

[Kingpin665]

I went through the Battery FAQ and there is a lot of great info, along with a few other threads. But I just have not found anything that flat out says how long a battery should be charged so its full. This was posted http://www.greenbatteries.com/batterycalc.html but the only thing I know what to enter is the battery capacity, so I'm at a loss with this apparently useful site. I have Ni-mh 8.4 minis both 1200 and 1400mAh... I don't get it, I know not to let them get hot but is thats all you do, sit there until its warm and pull the plug?

I have a BOL Basic-01 charger I bought from ASCA a few years back but if someone could help me out with this it would be greatly appreciated. Call me an idiot or tell me google 40 times, post a thread I over looked... w/e as long as I can get an answer I'm happy.

Thanks in advance guys,

Noobie out :P

[ujiro]

Read on the charger. It should give a current rating (how many amps/milliamps it outputs). Take the number of mAh your battery is, divide it by that current from the charger, and that tells you how many hours you need.

[incrediboy729]

Well i as i remember you can find the charge time by divideing the battery mah by the charger output mah. But since your charger is adjustable i don't think you can use this method.
Sorry to state the obvious but shouldn't a light come on or off when it's done?
Also the cooling fan might speed up or slow down (probably the latter) or turn off when it's done at least on my astroflight charger.

[kalnaren]

Ok, basically, a Ni-Mah battery is about 80% efficient. That means about 80% of the energy you put into charging it will be stored.

So, for example, charging at 1 amp for an hour will store roughly 800 milliaps in the battery.

You need to know your charge rate before you can calculate it.

[Kingpin665]

Yeah, there are a few settings. 0.5A, 1.5, 2.0 2.5 3.0, 3.5, 4.0.

[kalnaren]

Well, since you don't have a 1 amp setting (odd..), and you never want to charge a battery at more amps then the battery itself, you're forced to use the 0.5 amp setting.

All of the below is assumed you are using the 0.5 amp (500 mah) setting.

Every hour, your charger will charge about 400 mah. (500 * 0.8; 80% of 500, since ni-mh batteries only retain about 80% of the power you put into them).

1200 / 400 = 3. The 1200 mah battery will take 3 hours to charge.

1400 / 400 = 3.5. The 1400 mah battery will take 3.5 hours to charge.

[Kingpin665]

Thank you guys.

[incrediboy729]

No problem

[Kingpin665]

What differance would it make time wise to do a fast charge instead of a slow? Speed.. yes, but if I put it on the 0.5 or just eye balled 1.0a on the dial would that work? Although I know its best to always charge as slow as possible to help keep your battery in good standing a long time but just curious.

[m102404]

There was a really good write up about the chemistry of rechargeable batteries...and I'm sure some of these guys know the specifics way better than myself...

But I seem to recall that as a battery discharges it forms crystals. The faster it discharges, the larger the crystals. Charging a battery reverses (not fully) this process. A slow charge more fully breaks down the crystals, a fast charge does not so much (NOTE....that's horrible grammar...). A deep cycle discharge/charge breaks the crystals up as much as possible (or at least that's how my simplistic brain remembers the article)

Again...I can't find the article off hand and I may be completely wrong in this.

[kalnaren]

Originally Posted by Kingpin665

What differance would it make time wise to do a fast charge instead of a slow? Speed.. yes, but if I put it on the 0.5 or just eye balled 1.0a on the dial would that work? Although I know its best to always charge as slow as possible to help keep your battery in good standing a long time but just curious.

Rapid charging builds up heat. Heat is the enemy of batteries. Charging a battery too rapidly will wreak it. I usually charge my 1500 mah packs at 1 amp without issue.

www.batteryuniversity.com

Check that site out. Everything you ever wanted to know about batteries. Well written, explains a lot.