yard-dart

My Feedback: (35)

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?

BuschBarber

My Feedback: (2)

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.

DMcQuinn

My Feedback: (13)

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.

yard-dart

My Feedback: (35)

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.

tande

My Feedback: (48)

I very much recommend this http://www.xtremepowersystems.net/pr...hp?prod=XPS-TT device with any 2.4 system...FWIW

yard-dart

My Feedback: (35)

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?

BuschBarber

My Feedback: (2)

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.

Zor

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.

Zor

tande

My Feedback: (48)

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

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 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

Mikecam

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.

flatspinjim

My Feedback: (3)

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.

Zor

Anyone has some answers to post #10 ?

Zor

dirtybird

My Feedback: (5)

Zor

Hi dirtybird,

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

Zor

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. 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.

Zor

Hi jester_s1

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

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

dirtybird

My Feedback: (5)

Zor

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

BuschBarber

My Feedback: (2)

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.

tande

My Feedback: (48)

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
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...

tande

My Feedback: (48)

I have NO experience with this... http://electrodynam.com/rc/EDR-207/index.shtml

Zor

BuschBrber,

I am in full agreement with you.

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

flatspinjim

My Feedback: (3)

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%.

dirtybird

My Feedback: (5)

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.