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2.4 Receiver Batteries

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Old 12-19-2010, 07:03 AM
  #1  
yard-dart
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Default 2.4 Receiver Batteries

Over the past several years, I've gone copletely to Nimh batteries in all of my planes. I used to be copletely Nicd but it got to where I was constantly having to cycle batteries simply because I may go weeks not flying certain planes and I didn't want the batteries to develop "memory". Anyway, that was before I went to 2.4 Ghz. I"ve heard that it's better to use Nicd packs with the new 2.4 sytems rather than Nimh. Something about 2.4 has more constant draw and the Nimh's want stand up to it. I'm going completely off of hear-say. Is there any truth to this that you know of?
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Old 12-19-2010, 07:20 AM
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Default RE: 2.4 Receiver Batteries

Myself and many others in my club have gone to two cell LiPos, LithIons, or A123 cells instead of NiCad and NiMh. They charge faster and they hold their charge much longer. They are lighter. They do not False Peak the charger.

I have never experienced any problems with these types of cells. I do disconnect them from the Switch Harness, at the end of each flying day, just to avoid an accidental Switch On. There are more HV servos available now, so running without a Voltage Regulator becomes more common.

I use them in all my Transmitters, as well.

With chargers like the FMA 10S and the PowerLab 8, you can charge at 3S, 4S, 5S, and 6S, depending upon what Power Supply you use and the batteries you choose.

There is no problem with Current Draw, either.

I believe that with NiMh, you need to choose cells that have low Impedance in order to handle the higher Current Draw.
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Old 12-19-2010, 07:20 AM
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Default RE: 2.4 Receiver Batteries

You want batteries that won't drop voltage under heavy load (like 6 or 8 large digital servos all moving at once). The easiest way to accomplish this is to use 5-cell packs instead of 4-cell packs. Use 5-cell NiMh with enough capacity and you'll be fine.

The 2.4 receivers do not respond to the transmitter immediately upon power-up. In the old days of 72 mHz, if your receiver saw a voltage drop of 1/100 of a second (during a snap roll when all the servos are demanding power), the receiver would stop responding for 1/100 of a second. You would not notice it.

But if a 2.4 receiver sees a voltage drop for even 1/100 second, it might take a few seconds to get connected back up with the transmitted signal. That's what is different about 2.4.
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Old 12-19-2010, 07:34 AM
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Default RE: 2.4 Receiver Batteries

Thanks for the input guys. I don't plan on running Lipo's anytime in the near future. I'm aware of their advantages, it's just that I really don't require all of that. As for Nimh's, I think I'll stick with them. I run 5-cell packs in nearly everything I fly, and I've made it a habit of putting a volt meter on them before every flight. I run very few digitals, only where lots of torque is required. So, I think I'm safe. Thanks again for your input.
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Old 12-19-2010, 07:45 AM
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Default RE: 2.4 Receiver Batteries

I very much recommend this http://www.xtremepowersystems.net/pr...hp?prod=XPS-TT device with any 2.4 system...FWIW
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Old 12-19-2010, 08:01 AM
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Default RE: 2.4 Receiver Batteries

Looks like a very useful device, but the way I read the instructions, it says that the wire has to be plugged straight into an empty channel or harness. Seems pretty inconvenient if you want to check the battery before every flight. Can it be plugged into the switch like a regular load tester?

BuschBarber, I checked out the A123 batteries. I like what I see. I have a Triton Jr. D/C charger. Will my charger work on the A123's?
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Old 12-19-2010, 08:17 AM
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Default RE: 2.4 Receiver Batteries

Unless the charger specifically indicates support for A123 I would not use it. They are also referred to as LiFe cells since A123 is a Brand name.
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Old 12-19-2010, 09:38 AM
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Default RE: 2.4 Receiver Batteries

The reason to plug it in a receiver location is to read (monitor) the voltage at that location and avoid any voltage drops anywhere else.

A Y connector coud be used if no outlet is available at the receiver. The Y split should be right at the receiver.

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Old 12-19-2010, 09:42 AM
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Default RE: 2.4 Receiver Batteries

Looks like a very useful device, but the way I read the instructions, it says that the wire has to be plugged straight into an empty channel or harness. Seems pretty inconvenient if you want to check the battery before every flight. Can it be plugged into the switch like a regular load tester?
This device captures the lowest voltage "Dip" level seen during the flight & displays it via a multi/colored led....Simply have/a/look after landing & before you shut down the on/board power supply....Yes, it should be mounted so it can be seen at a glance....FWIW
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Old 12-23-2010, 09:21 PM
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Default RE: 2.4 Receiver Batteries

Hi All,

I see many references in this thread to voltage drops and high currents.

Can someone post some figures to these comments?

What is the instantaneous voltage below which the drop should not go ?

What is considered a high current in terms of miliamperes or amperes ?

It would be helpfull if we knew the limits.

Zor

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Old 12-27-2010, 08:00 PM
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Default RE: 2.4 Receiver Batteries


ORIGINAL: yard-dart



BuschBarber, I checked out the A123 batteries. I like what I see. I have a Triton Jr. D/C charger. Will my charger work on the A123's?

http://www.hangtimes.com/a123_batter...iants_faq.html Great info here.

I went to A123's for receiver power and will never go back. As my nimh die and they do after 2 years if I'm lucky they will get replaced with the A123. I have A123's that are going on 3 years and still discharge within 5 ma'h of new. 1000 cycles so they say and I'm starting to believe them. My 2000 ma/h Hobbico Hydrimax batteries discharged at 1800 ma/h when new and after the first year they are now hitting 1600 ma/h. They just don't last.

I guarantee you the money you will save and then some can purchase the FMA multi 4 charger. The bonus is the gravy.

A123's, charge them in the plane and no worries about fires, no regulator needed, store them 50%, 75% or 100% for 6 months (I do unfortunately) and take them out and charge and go flying. Give the info a read, take some time to search and do a little reading, they really are that good. I truly believe anybody that tells you they are not the cat's meow for receiver power has NEVER TRIED THEM.
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Old 12-27-2010, 09:01 PM
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Default RE: 2.4 Receiver Batteries

A123's for me also. Constant 6.6 volts means no need for regulators and your servos feel the same through all flights during the day.. You can charge them at 10 amps, that means a 10 to 15 minute charge. Very low self discharge, charge them and a month later you can go fly. Capable of 30 amp discharge rates, more than any plane will see, but you WILL NOT drop voltage during high amp draw manuvers. They are way safer than lipos, as stated above no need to remove from the plane when charging. I believe the advertised 1000 cycle life. I've got packs that are over 2 years old with LOTS of flights and still going strong.
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Old 12-27-2010, 09:22 PM
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Default RE: 2.4 Receiver Batteries

Anyone has some answers to post #10 ?

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Old 12-27-2010, 10:19 PM
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Default RE: 2.4 Receiver Batteries


ORIGINAL: Zor

Hi All,

I see many references in this thread to voltage drops and high currents.

Can someone post some figures to these comments ?

what comments

What is the instantaneous voltage below which the drop should not go ?

Depends on the manufacturer

What is considered a high current in terms of miliamperes or amperes ?

Over 1 amp is high current in my opinion.

It would be helpfull if we knew the limits.

Zor

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Old 12-27-2010, 11:21 PM
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Default RE: 2.4 Receiver Batteries



Hi dirtybird,

ORIGINAL: dirtybird


ORIGINAL: Zor

Hi All,

I see many references in this thread to voltage drops and high currents.

Can someone post some figures to these comments?

what comments


Comments such as these _ __withoout values.

in order to handle the higher Current Draw.



Something about 2.4 has more constant draw



running without a Voltage Regulator becomes more common.




What is the instantaneous voltage below which the drop should not go ?

Depends on the manufacturer

Value could have been given if known for the main manufacturers.

What is considered a high current in terms of miliamperes or amperes ?

Over 1 amp is high current in my opinion.


Are you referring to average or peak current ? If a brownout can occur with a few milisecond voltage drop then the instantaneous current is important. The peak currnt is many times the average current.

It would be helpfull if we knew the limits.

Zor
Thanks for responding and Best wishes for the coming New Year.

Zor

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Old 12-28-2010, 06:21 AM
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Default RE: 2.4 Receiver Batteries

A test that I do that costs me little time and no money is to use my digital multi meter to read the actual voltage at the receiver. I wired up a servo plug for the meter, and I plug it in to the receiver or into a Y harness if the RX is full. I then deflect two servos by hand (on a 4 channel plane) until they stall. That's as bad as it can get in flight, so that will tell me if my power system is up to par. While I'm at it, I also run my servos through their full range of motion and look for a voltage drop, which would indicate a binding servo. For the fussy types, you can even do the test with a 1/2 discharged battery to see where your real discharge limit is. Check the battery on a loaded voltmeter, then use the multimeter to see what it's giving your system in a worst case scenario.

In my testing, I've found that there are no worries in .40-.60 size planes as long as you're running a quality 5 cell pack that's in good shape.
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Old 12-28-2010, 11:59 AM
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Default RE: 2.4 Receiver Batteries

Hi jester_s1

I hope you do not hate me for this response but I suspect you might.
My comments inserted in red.

ORIGINAL: jester_s1

A test that I do that costs me little time and no money is to use my digital multi meter to read the actual voltage at the receiver.

That is fine to read the average voltage but it will not detect instantaneous voltage drop down spikes.
These drop down spikes is what the receiver does not like and it may gointo "brownouts" .


I wired up a servo plug for the meter, and I plug it in to the receiver or into a Y harness if the RX is full.

The Y in the harness should be right at the receiver connector so that the votlmeter wires do not carry any servo current or any other than the very tiny current actuating the voltmeter.

I then deflect two servos by hand (on a 4 channel plane) until they stall.

Deflecting two servos by hand ( I suppose you mean grabbing the servo horns with your fingers and forcing them to turn) does not cause any current to flow in the servo circuit.

That's as bad as it can get in flight, so that will tell me if my power system is up to par.

I do not see that it tells you anything.
NOTE: I read and interpret what you wrote more than a dozen times.
Ican guess what you meant to say but I do not wish to change nor should I change what you said. (wrote).


While I'm at it, I also run my servos through their full range of motion and look for a voltage drop, which would indicate a binding servo.

A bound (jammed) servo connected to a good battery would not drop the voltageenough to really notice it. A Spektrum DS821 digital servo held jammed draws just over 700 miliamps (0.7 amdp). A good battery would supply this current and much more without dropping voltage noticeably.

For the fussy types, you can even do the test

I have to suppose that you mean as "the test" ___the measurement of voltage with the digital voltmeter you are mentioning at the beginning ???

with a 1/2 discharged battery to see where your real discharge limit is.

Sorry I do not know how to tell how much charge is existing in a battery. Some elaborate methods of keeping track of how much charge has to go in to fully charge them are very crude and inaccurate.
Thus fully charge the batteries before any flying session.


Check the battery on a loaded voltmeter,

Perhaps you are thinking of a voltmeter that applies a small load to the battery when it is connected to it. A voltmeter with a shunt across its terminals. Some are sold to modelers with an expanded voltage scale. They are more useful to make money for the seller thant they are for the user. Anyone is always free to swear by them.

then use the multimeter to see what it's giving your system in a worst case scenario.

In my testing, I've found that there are no worries in .40-.60 size planes as long as you're running a quality 5 cell pack that's in good shape.

Quality 5 cells pack have low internal resistance and maintain their voltage nicely under load.
The use of5 cells raise the system voltage by about 1.2 volts (4.8 to 6.0 thus raising the power by a factor of 1.56 and simultaneously keeping the voltage that much higher above any minimums that could create a failure.

There is nothing wrong in measuring the voltage at the receiver pins ifwe keep in mind the limitations of our instruments and the conditons likely existing in the circuitry.

Those conditions have to include the voltage and current waveforms we are measuring and their effect on our instruments.

Wishing you a super enjoyable New Year for you and your loved ones.

Zor


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Old 12-28-2010, 02:54 PM
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Default RE: 2.4 Receiver Batteries


ORIGINAL: Zor

Hi jester_s1

I hope you do not hate me for this response but I suspect you might.
My comments inserted in red.

ORIGINAL: jester_s1

A test that I do that costs me little time and no money is to use my digital multi meter to read the actual voltage at the receiver.

That is fine to read the average voltage but it will not detect instantaneous voltage drop down spikes.
These drop down spikes is what the receiver does not like and it may go into ''brownouts'' .


You really need an oscilloscope in order to see what is a problem here.

I wired up a servo plug for the meter, and I plug it in to the receiver or into a Y harness if the RX is full.

The Y in the harness should be right at the receiver connector so that the votlmeter wires do not carry any servo current or any other than the very tiny current actuating the voltmeter.

The Y connection will not carry any servo current

I then deflect two servos by hand (on a 4 channel plane) until they stall.

Deflecting two servos by hand ( I suppose you mean grabbing the servo horns with your fingers and forcing them to turn) does not cause any current to flow in the servo circuit.

Not true. The torque produced by the servo is directly proportional to the current draw.

That's as bad as it can get in flight, so that will tell me if my power system is up to par.

I do not see that it tells you anything.
NOTE: I read and interpret what you wrote more than a dozen times.
I can guess what you meant to say but I do not wish to change nor should I change what you said. (wrote).


While I'm at it, I also run my servos through their full range of motion and look for a voltage drop, which would indicate a binding servo.

A bound (jammed) servo connected to a good battery would not drop the voltage enough to really notice it. A Spektrum DS821 digital servo held jammed draws just over 700 miliamps (0.7 amdp). A good battery would supply this current and much more without dropping voltage noticeably.

again you need an oscilloscope. Some digital servos can draw up to 3 amps. This will cause a noticeable drop in the voltage

For the fussy types, you can even do the test

I have to suppose that you mean as ''the test'' _ _ _ the measurement of voltage with the digital voltmeter you are mentioning at the beginning ? ? ?

with a 1/2 discharged battery to see where your real discharge limit is.

Sorry I do not know how to tell how much charge is existing in a battery. Some elaborate methods of keeping track of how much charge has to go in to fully charge them are very crude and inaccurate.
Thus fully charge the batteries before any flying session.


Check the battery on a loaded voltmeter,

Perhaps you are thinking of a voltmeter that applies a small load to the battery when it is connected to it. A voltmeter with a shunt across its terminals. Some are sold to modelers with an expanded voltage scale. They are more useful to make money for the seller thant they are for the user. Anyone is always free to swear by them.

A good expanded scale voltmeter is much more accurate and well worth the money.

then use the multimeter to see what it's giving your system in a worst case scenario.

In my testing, I've found that there are no worries in .40-.60 size planes as long as you're running a quality 5 cell pack that's in good shape.

Quality 5 cells pack have low internal resistance and maintain their voltage nicely under load.
The use of 5 cells raise the system voltage by about 1.2 volts (4.8 to 6.0 thus raising the power by a factor of 1.56 and simultaneously keeping the voltage that much higher above any minimums that could create a failure.

There is nothing wrong in measuring the voltage at the receiver pins if we keep in mind the limitations of our instruments and the conditons likely existing in the circuitry.

Those conditions have to include the voltage and current waveforms we are measuring and their effect on our instruments.

Wishing you a super enjoyable New Year for you and your loved ones.

Zor


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Old 12-28-2010, 04:21 PM
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Default RE: 2.4 Receiver Batteries

Hi dirtybird,

Some of your planes may become "dirtybirds" but I do not think you are one .

I wish I could find some claim to the accuracy of these expanded scale voltmeters.
I did some research but have not yet found any info.

If by any chance you have some technical information about these voltmeters, I would much appreciate whatever you can help with.

Personally I do not own one already having good quality voltmeters not only of good and known accuracy but also often verified.

I accept valuable information when comparing two readings in tems of their difference but I do not know their absolute value without a good calibration or a known accuracy figure.

The batteries we use have such a nearly flat voltage graphs during discharge that a voltage measurement has to be accurate within 0.05 volts to become significant. I cannot see that this is available in a $30.00 instrument or there about cost at retail level.

I am always open to learn more if the knowledge is available and reliable.

Happy New Year.

Zor

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Old 12-28-2010, 04:46 PM
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Default RE: 2.4 Receiver Batteries

I have been using Expanded Scale Voltmeters (ESV) for many years with my RC Batteries. Currently, I use a Hangar 9 Variable Load Digital ESV. I measure the voltage of my receiver batteries before each flight. I use a .5a load for NiCad and NiMh and a 1a load for LiPos. I have never lost an aircraft to a Low Voltage battery when using an ESV. Everyone in my RC club uses them and relies upon them.

For LiPos, LithIon, and A123 cells, I use an FMA 10S charger. I can easily tell the Percent of Charge left in my batteries if I am not sure.

I do not see anyone using a more expensive Multimeter execpt, perhaps, for checking Continuity and other issues.
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Old 12-28-2010, 04:49 PM
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Default RE: 2.4 Receiver Batteries

You really need an oscilloscope in order to see what is a problem here.
dirtybird is correct; the "Sampling/Rate" of a "Digital volt meter" is simply to slow to capture & display these L/V spikes....But as I understand it, you could use the "TattleTale" to make this test...FWIW
What is the instantaneous voltage below which the drop should not go ?
Not sure about other "Brands" but I think the latest "XPS" RX's (SS 2.4) will operate down to 2.0 or even 1.9 volts...Someone will correct me if wrong...
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Old 12-28-2010, 04:55 PM
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Default RE: 2.4 Receiver Batteries

The batteries we use have such a nearly flat voltage graphs during discharge that a voltage measurement has to be accurate within 0.05 volts to become significant. I cannot see that this is available in a $30.00 instrument or there about cost at retail level.
I have NO experience with this... http://electrodynam.com/rc/EDR-207/index.shtml
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Old 12-28-2010, 07:36 PM
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Default RE: 2.4 Receiver Batteries




BuschBrber,



I am in full agreement with you.



ORIGINAL: BuschBarber



I have been using Expanded Scale Voltmeters (ESV) for many years with my RC Batteries. Currently, I use a Hangar 9 Variable Load Digital ESV. I measure the voltage of my receiver batteries before each flight. I use a .5a load for NiCad and NiMh and a 1a load for LiPos. I have never lost an aircraft to a Low Voltage battery when using an ESV. Everyone in my RC club uses them and relies upon them.



It is not the ESV that gives you the security. It is the fact that you have enough pack voltage and capacity charge.
If every time you measure the voltage and read something higher than 4.8 volts on a so called 4.8 v pack or 6.0 or higher on a so called 6.0 pack, the system is certainly way above the voltgage at which it would fail due to low voltage if the system is installed properly.
I do not see any indications of the amount of charge in the pack from this measurement.



For LiPos, LithIon, and A123 cells, I use an FMA 10S charger. I can easily tell the Percent of Charge left in my batteries if I am not sure.



Please share your knowledge. How do you know; How can you tell before charging ? How do you know the charging current during the whole charge ?
I have made charging current measurements with charger saying on the label "output DC 12 volts 600 ma and the charging current was 340 ma and an hour later was 230 ma.
Another example output 9 v DC 280 ma and the measured current was 135 ma. at the time of measurement. These types of chargers are not "constant current" chargers. The current diminishes as the back EMF from the battery goes up with the charge.



I do not see anyone using a more expensive Multimeter execpt, perhaps, for checking Continuity and other issues.



Apparently there are chargers on the market that monitor the charging current and can tell how many mAh have been going into the battery and also show when the battery is full charge.
That does not mean that we can predict how much charge will go in to the full charge level so we would know how much charge was in the battery only after the charge has taken place.



I still do not know of anyway or any test that can tell me how much charge or % charge is in a battery pack. We cannot rely on a voltage measurement unless we have a very accurate voltmeter or have a calibration chart for that voltmeter. A calibraton shcrt could tell us that if the voltmeter reads 6.22 the real voltage is 6.31 then the chart might need to tell us at what temmperature the chart is accurate or have a calibration made at differnt temperature so we could interpolate.



Yes I know _ _ _ _ just fully charge your batteries before.heading to the flying field and you should be ok for a known time of flying (if you ever tested that).



So you crashed and the voltage was hih enough ? Rememeber how much a pack can gain voltage after resting for even just a few minutes. You can test for that as well.



Have a Happy New Year folks and lots of flying without voltage or charge problems.



Zor



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Old 12-28-2010, 08:19 PM
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Default RE: 2.4 Receiver Batteries

The Cell-Pro chargers tell you how many mah you put back into a battery. Not sure about other chargers as I just use the Cell_pro for my A123's. With the A123's you cannot use voltage as a measurement to tell how much you have left. They have a very flat discharge rate. When they start dropping off you are in trouble. The best way that I have found, and most people that use them is to charge the pack, make a flight or two then recharge. If you fly two flights and replace 240 mah that means you are useing 120 mah per flight. With a 2300 mah pack that means you can fly 10 flights and be plenty safe. I try to never use more than 50 or 60%.
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Old 12-28-2010, 08:28 PM
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dirtybird
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Default RE: 2.4 Receiver Batteries

You should read up on the Wheatstone bridge.
http://en.wikipedia.org/wiki/Wheatstone_bridge
John Fluke used a similar scheme to create a very accurate VM using a common ammeter
An expanded scale uses the scheme to enhance the accuracy of a VM.
The accuracy depends on the accuracy of the reference source and very little on the meter.
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