Battery capacities & wall charger outputs for NICDs

[Myron Beaumont]

Using wattmeter "Wattage" to analyse discharge parameters they are nowhere near the figures printed on the batteries in my experience. After many charge & discharge cycles of my NICDs (yes I know they will soon be extinct) the figures just don't make any real sense but I have made some  progress.

1) For two years I have given my Rx batteries a discharge load of 250 mA i.e. a bulb and a charge at 70mA on a variety of chargers i.e. Futaba, Ripmax for 10 -12 hours with poor results

2) Recently given them a 17.5 hour charge for the first time. The first astounding result was 4 hours on my Futaba Tx  T6EX before it beeped.

3) My (what I thought were no good ) NICDs lasted 1.5 hours after 17.5 hours charge as well.

4) The "Wattage" meter measured max 370 - 400 mAH for so-called 600 mAH Rx batteries. All pretty much the same

N.B. Very awkward to ascertain what the capacity consumption is on an RX battery whilst flying e.g. 4 servo 60" span model aerobatic. Does anyone know the duration/lasting power to within a quarter hour or so many milliamps?

Assuming that the throttle and rudder servos don't work as hard as the aileron and elevator servos!

P.S. After 3 years my Hitec batteries are the best I have ever owned and still perform as new but even they don't live up to the spec according to my  data.

Comments welcome. Does this mean that allcharging system manufacturers claims are over-rated?

[Peter Beeney]

  Myron,
     I thought that as you had invited comments on your post I’d have a little bash at trying to answer. Particularly as this morning (Sunday) I was given 4 battery packs to test and report on. I’ve been testing batteries for about the last many, many years!
    Taking your points one at the time:         

1)    Unfortunately your information is a bit sparse. Is it a 4 or 5 cell pack?  Is the 250mA a guess or a measured current? What is the capacity on the label? Is it  the 600mAh that you mention later? Regarding the 70mA charger output, this can vary. I’ve tested a few in the past, but they are becoming a bit out of vogue now. The earlier ones, 50mA, always seemed to be fairly accurate but the later ones can be unreliable. They are supposed to be constant current devices, when the battery is flat they will supply better than 70mA but as soon as the battery voltage comes up, which it does very quickly, the current can drop off to as low as 40 or even 30mA. Can I suggest the only way to determine this is to measure it carefully.           

2)    Here you seemed to have flipped to the transmitter pack. However, it does appear from the figures you may have been undercharging. 4 hours sounds a nice likely number. Just to recap, lithium batteries apart, if you charge at 0.1C for 10 hours plus 40%, another 4 hours, (the telecoms outfit that I worked for insisted on a 60% overcharge), then you will have guaranteed to have put the requisite charge in but of course that doesn't mean you will get 1C out. If you do, within some well defined parameters, then the battery is in good nick. You certainly would not do any harm to try 24 hours at that low rate.         

3)    1.5 hours discharge time sounds slightly iffy. BUT, if you are discharging at 400mA, using a constant power, (constant current), discharge load, on a 600mAh pack then you are spot on. We need more info. please.           

4)     I’m not familiar with the ‘Wattage meter’ or even watt meters (for modellers) in general. I am tempted to buy one though, I have some vague questions about these. In particular, the inline impedance interests me                                                                                                                                                                                                           
        The figures, as you say, don’t add up, but without more information on the terms of discharge any other comment would be just speculation.  To try and establish the in-flight current drain, why not give the model a fair number of flights, using a good, known capacity pack, clock everything so that you know the total time elapsed, then discharge the battery, noting the remaining number of milliampere hours. Don’t recharge, that could give you a false reading. Subtract this number from the full capacity, and divide that figure by the time. That will give you a basic average drain.                                                      
          An example. You have a 1000mAh battery. You fly for a total of 30 minutes, or 0.5 hour. Then your subsequent discharge is 500mAh measured, so 500mAh used. 500 divided by 0.5 equals 1000mAh, or 1Ah. Thus your average discharge rate is 1 Amp per hour. In reality, I think it would be a lot less than this, rx packs in ordinary fixed-wing models generally have the Life of Old Riley! Permanent holiday!

 

          Regarding the 3y old Hitec packs, I have a colleague with a JR transmitter that still uses the original Yuasa pack, 27 years on. It still passes my rigid test. Also once upon a time I bought a scrap string of 20 4Ah D size Saft NiCads at a boot fair. For 50 pence. The lot. They were ex. security use. I gave most away, keeping 4. I used those for around 15 years as glow drivers, it’s only just very recently that I’ve finally pensioned the last one off. At one point I was getting seriously worried they would see me off!

[Peter Beeney]

  

   Part Two.       The Last Paragraph.

 

      The reason for the 4 packs today? A cautionary tale. Last Sunday my mate Steve had just started the engine on his Pitts when Henrie, a friendly Dutchman, just happened to notice that the VoltsSpy in the cockpit was hard in the red.  An independent check confirmed a flat battery, despite being charged all night. I’ve just tested the pack and one cell is totally banjaxed. Beyond all hope. I’m sure you will agree that that model got to within a gnat’s whisker of being a total disaster. I constantly cajole fellow modellers to check everything, batteries most of all, with some justification it seems. Steve certainly will, at least for the next half hour!

    In very general terms, with regard to batteries, I’m frequently very suspicious of what it says on the label. There are many tales to tell here. But the short answer is, stick a plain label on, and write your own..  .. But keep this within fine limits. 

    Hope some of this is of use.                             Pete.    

[Myron Beaumont]

Peter

Thank you so much for your reply and interest .Sorry I havn't replied sooner .I'm a bit tied up at the moment so will give a proper reply tomorrow .Much appreciated ! Catch you later

All the best   Myron