# Ni-Mh battery sort usetime

Discussion in 'General Electronics Chat' started by astral, Feb 18, 2009.

1. ### astral Thread Starter New Member

Feb 18, 2009
3
0
Hey there folks,

I have a Ni-Mh battery which lasts for a very short time even if fully charged.
It is RC Plane's battery with following specifications:

Voltage: 4.8 V
Amps: 180 mah
4 x 1 /3AAA.

Here is a shot of it:

The Plane comes with no external charger, but the control board has an internal charger for battery. control board is not connected to external power sources and only has 8 Alkaline type batteries standard 1.5V. It's kind of strange to use Alkaline batteries to charge that Ni-Mh but anyway, if i'm correct 8 alkaline battery 1.5V x 8 = 12V. So 12 volts are required to charge my battery?

Also I haven't charged it for almost a year... is that a case?

Any help is aprecciated,

Last edited: Feb 18, 2009
2. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Compared to the age of the planet, "80 years" is a very short time. Can you give us a number to put your own "very short time" in context? Is it six minutes? Thirty seconds?

And do you know how much current your circuit draws from the NiMH?

Your 8 alkalines are probably two parallel strings of four in series. This would give 6V at increased current capacity, which could then be current-regulated for charging voltage needed by the NiMH.

3. ### Audioguru New Member

Dec 20, 2007
9,411
896
The battery uses cells that are 1/3rd the size of normal AAA cells. So their current capacitty is very low at only 180mAh. It has 4 cells that charge to 5.6V to 6.0V when they are fully charged.
If the alkaline cells are not name brand and brand new then the rechargeable battery will not fully charge.

Modern electric airplanes use lightweight and higher capacity Lithium-Polymer cells.

4. ### astral Thread Starter New Member

Feb 18, 2009
3
0
thanks for replies,

Yeah sorry I had to mention a time of usage;
it is around 1-2 minutes; I mean the rotors of plane work for that time, but in air it lasts 40 seconds or so.. then goes down.

No, all 8 of them are in Series circuit to each other.

Not sure but I'll find it out.

I dont much care about those batteries, I can provide that current to control board from external energy source.

The thing is, that charging lasts for only 3-4 minutes. It's kind of strange. When I plug the Nimh battery to ControlBoard to charge it, then I need to push a button which has labeled on it "Timer" for charging to begin; I think that timer turns charging off after 3-4 minutes as it thinks that it's enough.

And one more, I tried to charge battery with my own extreran power source with following specifications:

Voltage: 12 V
Amps: 1.2 Amp

And after 15 minutes of charging it keeped flying for around 5-7 minutes.
Can that timer be a problem?

Thanks,
I much aprecciate it.

Apr 5, 2008
15,806
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6. ### Audioguru New Member

Dec 20, 2007
9,411
896
We don't know the charging current of the charge control circuit.
The 180mAh battery needs about 234mA for 1h which is 1.4A for 10 minutes.
I think the timer should be set for 10 minutes and the current should be set to 1.4A.

If you use the timer 3 times then does the airplane fly for 5 minutes?

7. ### astral Thread Starter New Member

Feb 18, 2009
3
0
Well I think charging currrent is equal to alkaline battery current, I dont think that control board is converting it to some other numbers.

The "Timer" button has a little bulb above it; when I push timer it starts flashing; and when the flashing is over [in 3-4 mins] - charge is over. If I push again timer button the bulb won't flash anymore. until I discharge battery to some level. So I think Control Board also has some indicator with whitch it understands the weather battery is charged or not. Eventually I can't charge it more than one time.

Also how do you calculate the time and amps which are needed to charge the battery to full? eg. if
1.4A = 10 mins, then 2.8 = 5 mins ?

Thanks,