Battery condition?
 

Being new to this I hope that you can answer a question about batteries. How do you tell the condition of a nicad battery you plan to use. If it takes a full charge is it a good battery. I would hate to send my plane up only to get half way through a flight and have the battery go dead. I know that a wet cell can have a full charge, say 13 volts but fail a load test leaving you sitting. So how do you load test a nicad or similar reciever/servo battery.

RE: Battery condition?
 

You want to invest in something called an "Expanded Scale Voltmeter" Digitals are best but cost more than analog. It puts a load on the battery similar to a servo and will give you a reading of approximately how much power the battery has left. Or, invest in an $11 Voltwatch (mounted on the model or just plugged in temporarily in an open receiver jack) and load up the servos yourself while watching the LED's.

RE: Battery condition?
 

The only way to know for sure is to charge the battery for 12 -14 hours as a C/10 rate. Then discharge it with a battery cycler that can measure the amount of energy discharged. Someone you fly with should have one of these dischargers also called "cyclers".

As you pointed out, even if the battery shows a full charge on the voltmeter, this is no guarantee that it will last for long.

If you can't borrow a cycler or discharger, then do this: Charge the battery for 10 - 14 hours at C/10 rate. Then sit in front of the TV and fly your plane (keep moving the sticks to force the servos to move and burn up some battery) for an hour or so. If the servos stop moving or get slow before an hour, then get a new battery. A good battery should run your receiver and servos for at least one hour. In flight, the servos will use MORE battery than at home because of the air pressure against the surfaces when the plane is moving.

RE: Battery condition?
 

Even after all that you can't guarrantee that your battery is good. Last month I had a battery that I cycled several times, each time it discharged properly and then left it on my Alpha 4 charger on a trickle until I took it to the field. 10 seconds into my maiden flight the battery went dead and I lost the plane. After I recovered the pieces I checked the battery and it was complete dead.

RE: Battery condition?
 

Cycling a battery will tell you the battery was healthy but not the current charge . . . er, the present status. :)

It's still a great idea, though. An ESV can be used just before a flight to tell what's up. Mostly. A stalled digital servo can still drain even a fresh and healthy battery in seconds.

RE: Battery condition?
 

I recently received some 5g servos from HK. I locked the servo arms with my hand and measured the current while driving the servo with a servo tester. That little 5g servo was drawing a current of 0.5A while it was locked (stalled)!

After the test I performed, I also believe that a stalled servo is really, really bad news for any battery.

RE: Battery condition?
 

Right!

That's a 500mA draw on a single small 5g servo.

A regular size servo can draw 2A ( 2000mA ) at stall, yet many fly with 400mAh packs.

Now we usually never fly with our servos stalled, but the current drain is indicative of how much the servos COULD pull in the air under aerobatic loads.

After I saw what servos can draw under load, I took to upgrading ALL of my battery packs to well over 1600mAh even on my smaller planes.

RE: Battery condition?
 

New ARF $100 - 200 and up
New Engine $100 - 300 and up


New Battery $20 (or 5 Starbucks Mochas)
New ESV $69
New Cycler $69

:)

RE: Battery condition?
 

To all;
It just so happens that right nowI'm designing/developing a piece of lighting equipment using low self-discharge NiMH cells.
Charging is at 0.1C for 19 hours or a shorter time using dI/dT control.
I started off using an AA cell at 2100mAH as the primary source. The DC averaged load was 1.2A , but with a sawtooth type waveform that saw it peak at over 4A. At first the battery lasted 109 minutes (spec requirement 90), but after only 4 of such charge/discharge cycles, the impedance had doubled and the endurance was down to 54 minutes.
It's not just the current*time integral that matters, nor even the cell capacity, it's the actual can size. The high capacity AA cells do not like high discharge rates.
They also DO NOT put up with being discharged below 0.9V per cell. So if you are used to periodically discharging NiCads until they are flat to get rid of the dreaded dendrites, don't do it with NiMH cells.
My B model now uses a 4500mAH C cell (HR14). Although the ampere-hours are doubled, the endurance is now 3x the initial figure simply because the discharge is lower as a fraction of the AH rating. I haven't done multiple cycles yet to report on how it holds up.

RE: Battery condition?
 

Hi!
It's easy!
Use a "volt watch" in each plane!

RE: Battery condition?
 

Hmm, as an electric flyer, who uses rx packs in some planes, I use a similar method. I can use my charger as it has a discharge capability of up to 10 amps, and I hook up my Astro meter in series between the pack and servos. Last attempt was 7 high torque servos Y'd all together to plug into the meter. That way I can see the draw, and any voltage drop as I work all the servos.

Funny thing about packs that die even though they check ok. I had one rx pack I was using to set up a plane. Hooked up the pack, and flipped the retracts on.

This is a pair of heavy retracts with 10 inch wheels, each uses a separate JR 791 servo to run them.

Anyhow, nothing from the retracts, not even a whimper. Check and all the other servos worked fine for the control surfaces. What the Heck?

So what do I do, spend close to an hour pulling the harnesses for the retracts, checking for a bad lead or two. Not fun on a 110" ws bird. I even unhooked the retracts and plugged them straight into the rx. Nothing, Nada, on either one.

Double what the heck?

I know they worked a couple of days ago . Ok let's try something else. Grab a spare esc, and lipo. Plug the esc into the lipo, and then plug the esc into the rx, using the built in bec to power everything. Zip/Zip both retracts go up and down.

Hmmm. Finally dawns on me to check the rx pack's voltage..................yep bout 4 1/2 volts.

Dang it. Playing with the plane the last couple of days, I had run the pack down to the point where if I activated the retracts it would draw down the pack and not run the retracts, yet it had enough power to run the smaller draw servos on the controls one at a time.

DUH!!!!!!

RE: Battery condition?
 

Okay so now you have me worried so went out and bought a new 2700mah pack. Should be good for several flights before worrying. Only flying with 4 servos and futaba 2.4 system so should be plenty I would guess.

RE: Battery condition?
 

Now you have to worry about how to charge it. ;-)

RE: Battery condition?
 

Ummmm Are you telling me that the Futaba charger that came with the 7c set wont do it? It said to charge both the tx and rx for 24 hrs prior to use.

RE: Battery condition?
 

If it is a 4.8 volt pack, then the wall wart charger will charge it ok, but it will take some time.

If it charges at 200mah/hour... do the math. That's at LEAST 14 hours for a full charge (completely depleated to fully charged).

CGr.

RE: Battery condition?
 

If it is a Futaba charger like mine the Rx jack is 100 mAh - or 27 hours on the wall for a 2,700 mAh pack.

RE: Battery condition?
 

Yeah thats ok for the first charge on a NiMH or NiCAD pack. But these batteries should be cahrged at 1C thereafter on a charger that has a charge problem able to deliver the correct current over time.
NiMH and NiCAD should npt be slow charged if you want to keep them in good condition. Slow charge is good for storage but not for regular use.

RE: Battery condition?
 

That is backwards:D. Consistently slow charging at a C/10 ma's for 15 hours after using a NiCad or NiMh battery is the only way to assure long life. Charging at a 1C ma rate will cause the battery to deteriorate over a shorter time period. After a day of flying, I but both transmitter and receiver batteries on timed 15 hour charge at C/10. After 15 hours I switch to a trickle charge of C/50 ma's and leave the batteries on the tickle charge until the next time I go flying. My batteries last for many years. I have been doing it this way for 30+ years. Also I cycle the batteries at the beginning and end of the flying season to insure they have at least 80% of their rated capacity.

Bruce

RE: Battery condition?
 

Like Landeck, I plug all the flying battery's and the field box into the slow chargers after flying, except my timer turns on at 9:00 P.M. on Friday night and off at 09:00 Saturday Morning. So on Saturday Morning If, I go fly I just check the Voltage and go. I cycle every couple months when I remember. :D

The Main concern for batterys is heat. They are charged when they are warm, so stop charging. Fast charging produces more heat and can lead to keeping the battery warmer for longer[:@], which reduces battery life.

Ref: http://www.hangtimes.com/id30.html.
:)

RE: Battery condition?
 

Thanks Bruce, that makes more sense to me. I was always taught to slow charge all batteries to get the most life out of them, but that is dealing with a wet cell battery.
Herb

RE: Battery condition?
 

I completely agree with this. High capacity NiMH AA cells don't like high currents either in or out.
I was told by a manufacturer recently that their own charger, set to NiMH, is capable of damaging their own NiMH cells http://www.rcuniverse.com/forum/js/f...n/confused.gif. The charge rate was 0.75A for a 2100mAH cell, or only 0.36C.
Charge rates at 1C will require a charger with thermal managment and dV/dt end point control, and even then will degrade the cell life.

The optimum trickle current will depend upon the battery technology. I've been working with Low self-discharge types recently and trickle currents at about 5mA (2100mAH cell) seem suitable for those types.

RE: Battery condition?
 

well the battery manufacturers I use claim 1C charge current will not deteriorate the NiMH battery life and in my experience that works out.

I've batteries that are close on 10 years old and have now lost 20% capacity and ready for retirement.

leaving the NiMH on tricklecharge is also fine but theres nothing wrong with fast charge at 1C on the appropriate charger.

RE: Battery condition?
 

What is an "appropriate" charger? A peak charger? A timed charger? A tempure sensing charger? Consistent use of a peak charger on NiMh batteries has been shown to lower the life time of a battery because of the slight over charge they experience. A NiMh battery that gets warm during charge is also having its life time shortened. A NiMh battery that is slow charged (C/10 ma rate) for 15 hours neither gets warm nor over charged, both of which shorten the life of NiMh batteries.

Bruce

RE: Battery condition?
 

i can't be bothered to argue: took this from wiki.

<span id=".CE.94V_charging_method" class="mw-headline">ΔV charging method</span>

According to <font color="#0645ad">Panasonic</font> and other NiMH cell manufacturers, the ΔV method is one of the preferred charging methods for charging. The charger measures the rate of change (signified by the symbol Δ) of the voltage of the cell (signified by the letter V). This is illustrated in the "NiMH charge curve" figure. The cell or battery is rapidly charged at a <font color="#0645ad">constant current</font> of 1 C/h, where C is the capacity of the battery (the capacity is expressed in ampere hours, or more commonly milliampere hours (mA·h). After the cell is fully charged, and as it begins to overcharge, the voltage polarity of the electrodes inside the battery will begin to reverse, and this will cause the battery voltage to decrease slightly. A ΔV type battery charger ends the charge cycle by switching off the charging current when it senses this drop in voltage. In some cases, a very small "<font color="#0645ad">trickle charge</font>" may remain. The "charge curve" graph also shows that the charge voltage will change depending on the charge current (it also changes with temperature and battery age). This generally means that a constant-voltage charging method cannot be used automatically, because it will either be unsafe, or it will not charge batteries reliably and consistently. This is unlike a <font color="#0645ad">lead-acid cell</font> for example, which can, in theory, be more easily charged at a suitably chosen constant voltage.<sup id="cite_ref-Panasonic_6-1" class="reference"><font color="#0645ad"><span>[</span>7<span>]</span></font></sup></p><h3><span id=".CE.94T_temperature_charging_method" class="mw-headline">ΔT temperature charging method</span></h3>

The ΔT temperature change method is similar in principle to the ΔV method. Because the charging voltage is nearly constant, if constant-current charging is used, then a near constant power is entering the cell. When the cell is charging, most of this power will be converted to chemical energy. However, when the cell is fully charged, most of the charging power will then be converted to heat. This results in an increase in the rate of change of temperature, which can be detected by a sensor measuring the battery temperature.</p><h3><span id="Manual_charging" class="mw-headline">Manual charging</span></h3><div class="thumb tright"></div>

If a suitable battery charger is not available, constant-voltage or constant-current charging can be done manually, at a moderately high charging rate, if careful attention is given. For proper charging, the voltage and/or current must be set to a suitable charging rate for the particular battery, and a timer should be set. Periodic monitoring is strongly recommended to avoid overcharging (resulting in a voltage drop), or overheating (resulting in an excessive temperature rise and possibly an overpressure condition).<sup style="WHITE-SPACE: nowrap" title="This claim needs references to reliable sources from September 2008" class="Template-Fact">[<font color="#0645ad">citation needed</font>]</sup></p>

It is safer just to use a C/5 or C/10 charge-rate. <sup id="cite_ref-7" class="reference"><font color="#0645ad"><span>[</span>8<span>]</span></font></sup></p><h3><span id="Trickle_charging" class="mw-headline">rickle charging</span></h3>

Some equipment manufacturers consider that NiMH cells can be safely charged in simple fixed, low-current chargers with or without timers, and that permanent overcharging is permissible with currents up to 0.1 C (where C is the current equivalent to the capacity of the battery divided by one hour). According to the Panasonic NiMH charging manual, extensive <font color="#0645ad">trickle charging</font> can cause battery deterioration due to overcharging, and it is the least preferred charging method concerning battery performance. If it is used, the trickle charge rate should be limited to between 0.033 C and 0.05 C for a maximum of 20 hours to avoid damaging the batteries.<sup id="cite_ref-Panasonic_6-2" class="reference"><font color="#0645ad"><span>[</span>7<span>]</span></font></sup></p>

For a slow charge, or "trickle charge" process, <font color="#0645ad">Duracell</font> recommends "a maintenance charge of indefinite duration at 0.0033 C".<sup id="cite_ref-8" class="reference"><font color="#0645ad"><span>[</span>9<span>]</span></font></sup> Some chargers do this after the charge cycle, to offset the natural self-discharge rate of the battery. To maximize battery life, the preferred charge method of NiMH cells uses low <font color="#0645ad">duty cycle</font> pulses of high current rather than continuous low current.</p>

RE: Battery condition?
 

At least we agree on something can't be bothered to argue, :D But then I never considered wiki that reliable a source.:eek:

Bruce