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Old Jan 24, 2015, 08:24 PM
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Question
disharging nimh

I have a jr 1500mah 4.8v 4c nimh pack which is brand new. I charged it with a trickle charger about 30 hours for the initial charge and got a peak of 5.6v. I am currently just leaving the rx on to discharge it and I need to know at what point should I stop the discharge. I have a map that reads the voltage that plugs into my rx so I am going off of that. I was also reading about a 12v light bulb that I could wire to a battery connector that would discharge the battery at a quicker rate, has anyone tried this? If I had the money to get a nice charger and discharger I would already have it, but I don't so I'm trying to work with what I have here.
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Old Jan 24, 2015, 08:52 PM
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Originally Posted by osman1986 View Post
I have a jr 1500mah 4.8v 4c nimh pack which is brand new. I charged it with a trickle charger about 30 hours for the initial charge and got a peak of 5.6v. I am currently just leaving the rx on to discharge it and I need to know at what point should I stop the discharge. I have a map that reads the voltage that plugs into my rx so I am going off of that. I was also reading about a 12v light bulb that I could wire to a battery connector that would discharge the battery at a quicker rate, has anyone tried this? If I had the money to get a nice charger and discharger I would already have it, but I don't so I'm trying to work with what I have here.
If you're trying to discharge your battery with only the receiver, that could take several days.

Another option is to take a run to your local Radio Shack, and pick up a 10 Ohm, 10 Watt power resistor.
http://www.radioshack.com/10-ohm-10w...l#.VMRak_7F90Y

With around 5 Volts DC, your current will be I=E/R, or 5 Volts/10 Ohms which equals 0.5 Amps.

With a 1500 Mah (1.5 Ampere Hour) battery, your battery should last 1.5/0.5 or around 3 hours.

You can discharge your battery down to around 1.0 Volts per cell, or 4 Volts DC with no problems. At 4 Volts DC, your batteries voltage will be dropping like a rock, you need to keep a close eye on it.

Or, just run it for two hours, and if the battery is still holding around 4.4 Volts DC, call it "good"
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Old Jan 24, 2015, 10:01 PM
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So here is what I did with the materials I could find around the house. I found a igniter from a old rocket launcher and soldered a battery lead to it that would plug in to the charge hookup. I taped the safety key in place so the light would stay on. Now all I have to do is flip the power switch on the plane and I can get a current volt reading from my maping device that is plugged into my rx. I have heard mixed opinions on weather or not to cycle the nimh batteries, what is your opinion on that? So you are saying that I should discharge the battery down to 4.4v before I put a charge on it? Pics coming momentarily.
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Old Jan 24, 2015, 10:07 PM
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Old Jan 24, 2015, 10:19 PM
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First question :

Why are you discharging your NiMh ?

Second :

What do you hope to achieve by doing this ?

Nigel
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Old Jan 24, 2015, 10:32 PM
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It is a new battery and the guy at the hobby store said I should cycle it a few times before I use it.
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Old Jan 24, 2015, 10:33 PM
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Or am I good to go after the initial charge?
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Old Jan 24, 2015, 10:35 PM
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If you want to discharge the battery hook up a LED light it a light build and let it sit there.
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Old Jan 24, 2015, 10:47 PM
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I tried a led light and it wouldn't work for some reason.
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Old Jan 24, 2015, 10:50 PM
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Cycling new Nixx battery packs, usually about 3 to 5 cycles, will bring them up to full potential. Having a charger that is programed to do cycles is the best way to go but I see you are having to do without a charger having that feature. Just be careful that you don't discharge them too far nor overcharge them to where the pack becomes hot. Discharge down to 1 volt per cell should be fine and expect about 5.6 volts for a full pack. Once a pack is full, excess charging is given off as heat. Therefore you will feel the pack warming up once it is full. A few degrees above room temperature is okay but don't let them get hot.
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Old Jan 24, 2015, 11:16 PM
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Quote:
Originally Posted by osman1986 View Post
I tried a led light and it wouldn't work for some reason.
Could have been a 12V LED, it wont come on if you power less....unlike an incandescent where it will but dim
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Old Jan 24, 2015, 11:39 PM
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It is a new battery and the guy at the hobby store said I should cycle it a few times before I use it.
Fair enough ....

But usually a good charge up initially and then use is good enough ...

Very few people actually use full capacity of batterys and I assume you will charge up model after a sessions flying ...

I use 2300mAh NiMH in my models / Tx's - never do cycle charges except to check periodically. Many of mine are over 2 yrs old - some 3yrs. They are all delivering same as when new and near enough stated capacity.

As example : My Tx's use 8 cells ... all 2300mAh AA's. None have been cycled, but I get over 9hrs use of Tx before Low Volt alarm sounds - even with my old 2 - 3yr olds. Average Tx uses 250 - 300mA .... simple maths ... 9 x 250 = 2250mAh .... and that's at LVA meaning there is still life left in the cells. QED.

To be honest all you do with cycling is use up lives of the batterys.

Others will disagree I know - but that's life.

Nigel
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Old Jan 24, 2015, 11:41 PM
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Or am I good to go after the initial charge?
As a standard Rx pack - yes I would. But then again I'm like that.

Nigel
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Old Jan 24, 2015, 11:50 PM
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Ok, well thanks for the advice! I discharged it down to 4.8v but I'm not staying up waiting for it any longer so I took it off and put the charger on it so it will be ready for tomorrow. I have flown it prob 8-10 times on the initial charge and it only went down to 5v so I'm guessing at that rate I should be ok without cycling it a few times. I may try to do it on the next rainy day!
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Old Jan 24, 2015, 11:59 PM
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Originally Posted by osman1986 View Post
Ok, well thanks for the advice! I discharged it down to 4.8v but I'm not staying up waiting for it any longer so I took it off and put the charger on it so it will be ready for tomorrow. I have flown it prob 8-10 times on the initial charge and it only went down to 5v so I'm guessing at that rate I should be ok without cycling it a few times. I may try to do it on the next rainy day!
All three of these are flown on 4.8v NiMH 2300mAh packs. None are cycled - except occasionally to check capacity is still good. The model in centre is over 3 yrs old ...



Never had any brown-outs - I fly FrSky anyway which I've never heard it happen with ... never had any problems.
The Pitts to the left has an LED power indicator on the side of fuselage next to Rx switch. Even after a days flying .. maybe 3 ~ 4 x 10 min flights - it's still in green.

Nigel
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