Espritmodel.com Telemetry Radio
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Old Mar 02, 2011, 06:08 PM
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Canada, BC, Penticton
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So am I doing more harm than good?

Ok I'm no expert when it comes to elecronics but I would like you folks to read the following and tell me if what he is saying is true then what is the use of buying these 2700 mah packs for my planes if they are not going to offer me any advantages. I should add that I want to use a couple packs in my giant Corsair because of all the equipment on board.
Thank you, here is the Quote from this fellow.

"Right now, NiMH batteries are about the best choice for transmitter packs and receiver packs in many models.

Caution must be observed when using hi-capacity NiMH cells (over 1650mAH in AA size) because these are more easily damaged by over-charging or charging at too high a current. I prefer to stick with a good quality 1650mAH transmitter pack and top them up at the field if needed (charging at up to 1.0A).

While the higher capacity NiMH cells (up to 2700mAH in AA size) might seem to be better, they will self-discharge more quickly when the gear is turned off and can only be charged at currents of about 250mAH -- making field-top-ups impractical.

And don't be tempted to use the hi-capacity AA cells for receiver packs on anything larger than a .40-sized sports model. The price you pay for this higher capacity is a decided tendency for the voltage to drop under load. There's always a risk that if the voltage drops enough, your receiver will stop working and you could lose control of the model (particularly true with 2.4GHz radio systems).

A favorite NiMH receiver pack of mine is the 2/3A-sized Intellect cells with 1400 mAH capacity. These cells can deliver up to 20A continuously and I've flown my 30% Extra using two of these packs without problems. They weigh about the same as an AA-sized pack but are much better."
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Old Mar 02, 2011, 06:36 PM
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So. Cal.
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In my experience, 2700mAh NiMH are awful. High internal resistance and high self-discharge. I have been using low self-discharge 2000mAh AA Eneloops in all of my transmitters for nearly 5 years and they're absolutely amazing and by far the best option for transmitter usage, IMO.

AA Eneloops also make wonderful receiver packs. 2/3A cells as quoted above are fantastic for receiver packs.

The advice you've been provided is spot-on in my view.

Mark
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Old Mar 02, 2011, 06:42 PM
You can call me FANBOY!
Goodlettsville, TN
Joined Sep 2006
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Speaking specifically about nimh in AA then yes he is correct. Read the FAQ at NOBS, lots of good information there that explains in more detail what is being referred to. They are also a good place to buy Rx packs as they quote specs for all of their cells including resistance, which is probably the most important spec for a large or giant scale Rx pack. If you are able to run 6v on all your electronics personally I think A123 are a much better choice. And like Mark said Eneloops are the best for Tx's, even better than lipo/life as they have an even lower self discharge. Either way its never a good idea to use AA nimh packs as RX for anything bigger than a 40 size model.
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Old Mar 02, 2011, 07:22 PM
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ok thanks guys. I am strictly speaking of reciever packs and yes I'd be using 6 volts for most of the onboard equipment but it is good to know about the transmitter packs also. What sort of flight time would a person have in general running a smaller pack at 6 volts? I know it's hard to say depending on my eqipment but is there any sort of number? The other thing I'd like to know is what kind of charger could I use for a field charger on these or would I just usee the same charger that comes with the radio?
I'd like to try my hand at making a few if it's any cheaper than just buying them made.
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Old Mar 02, 2011, 07:37 PM
You can call me FANBOY!
Goodlettsville, TN
Joined Sep 2006
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Hard to say without knowing every piece of equipment that will be on board. Setup will also play a big part, any servo that doesnt move as freely as it could or binds will significantly decrease usable flight time. For a field charger look at the FMA Cellpro multi4. There are cheaper chargers to be had but none with the quality and reliability of it. The wall wart charger, am assuming thats what you are referring to charges way to slowly for that. I have always built all my own packs but as cheap as nimh are now I would just buy them. If you want to try your hand at making them look into the A123. You can build packs of those much cheaper than you can buy them. I can build an 1100mah A123 pack for ~$7. I buy the cells from ebay and use Radical RC for all of the hardware.
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Old Mar 02, 2011, 09:01 PM
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Ok thanks, this is some great information. Now I have a better idea of which direction to take.
What a great forum.
Randy
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Old Mar 02, 2011, 09:57 PM
BVH
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United States, CA, Pismo Beach
Joined Dec 2006
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+1 for Eneloops. They have worked out fantastically for us over at the flashlight forums. Very, very little self-discharge and capable of delivering high current with little voltage sag.
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Old Mar 03, 2011, 12:25 AM
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San Fernando Valley, California, United States
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eneloops for my transmitter and a123 for my rx packs.
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Old Mar 03, 2011, 09:13 AM
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Thanks again folks.
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Old Mar 03, 2011, 12:09 PM
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United States, GA, Gray
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I do see some sag on my eneloops on my RX. I am using two packs and 5 8711 servos on one plane and I get a low voltage alarm about halfway through my first flight. It is just a quick beep, but it is happening. I am going to change all my larger birds over to A123's as i can afford it.
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