• The second disadvantage is that NIMH cells have what I call a "shelf life". What I mean by that is that NIMH cells seem to discharge more than NICD's while they are just sitting there with nothing turned on! Therefore, since I do not use a "trickle" charger, I ALWAYS start charging my batteries the day before I plan to fly, figuring the necessary "time on charge" and plan it so that they come off charge no more than two hours before I leave for the field. This may not be necessary, but it's just what I do.

I have learned to accept the disadvantages, and I believe the advantages far outweigh the disadvantages!

Should you choose to step up from the "standard" 600 mah batteries to higher capacity NICD or NIMH battery, there is one consideration you must plan for: If you continue to use the "standard" charger that came with your radio, you must leave them on charge longer!

Let me explain why:

The charger that came with your radio system is probably designed to produce a 50 or 75 mah charge output because the NICD's that came with your system like to be charged at a rate of one-tenth (1/10th) of their rated capacity. Most "off the shelf" radio systems come with either 600 mah or 700 mah NICD cells. In a perfect world that would translate to a 10 to 12 hour charge time. (75 ma times 10 hrs = 750 mah to charge a 700 mah pack) or (50 ma times 12 hrs = 600 mah to charge the 600 mah pack)

Actually, you need to keep them on charge longer than the above example because the chargers that usually come with radio systems are not "constant current" chargers and therefore, as the cell voltage rises closer to the charger's output voltage, there is less "differential" to "push" the electrons into the cells, and the charge rate decreases. Most manufacturers will tell you to charge the NICD's for 14 to 16 hours to reach a full charge.

But if you use the same 50 ma charger with NIMH cells, rated at 1500 mah, you can easily see that they will need to be left "on charge" much longer than the NICD's. (1500 mah divided by 50 ma = 30 hours!) Again, because the charger is not a "constant current" charger, (see paragraph above) it is more likely you will need to be "on charge" for 36 to 48 hours.

If you have a 75 ma charger the time will be less, but still more than you would expect: 1500 mah divided by 75 ma = 20 hours! Again, you would more likely leave them on charge for 24 to 36 hours to reach a full charge.

NOTE:The above example depict charge times that assume the cells are totally discharged before the charge cycle begins.

Naturally, if the cells are at half capacity when the charge cycle begins, it will not be necessary to charge for the full times shown above. But remember, unless you have a "constant current" charger, the last half of the charge time will be at a lesser current than the first half.

I like to use the "timer" function in the RDS8000 to keep track of the "on time" of the radio which gives me a rough indicator of necessary charge times to bring the cells back to peak charge.

Well -- enough about batteries.   As I have stated, I like to use 5 Cell (6 Volt) airborne packs and have done so for years.   All Airtronics receivers thus far have been able to handle this voltage and I naturally assumed that the RDS8000 receiver would also. Maybe it will, but I am worried about it.

There is a long story here, but let me "boil it down" some:

When I received my RDS8000 system, and while I was charging the transmitter batteries, I read the manual from cover to cover.  (Yes, I do that.)  The ONLY reference to receiver battery pack voltage was listed as 4.8 volts!   So, I called the technical department and was told that the receiver would operate satisfactorily down to less than 3 volts and up to 5.7 volts.   I searched the Internet and found in the Airtronics "FAQ" (Frequently Asked Questions) section the same information.   I was concerned about exceeding that 5.7 volts so I removed one cell from my 5 cell pack and went to the field.

Several others pilots were there and were impressed with the system and now at least three other pilots own RDS8000 systems!   One of those pilots was Hardie Jefferies who emailed the technical department about the 5.7 volt limit.

In the reply to his email he was advised, "it was perfectly fine to use a 5 cell pack"!   I, then, emailed the same people quoting what I was told on the telephone and in the reply to my email the technical expert said it "depended upon the capacity of the battery pack and the number and type of servos I was using", and asked me to send him a list of the "hardware" in my airplane.