All that Power
|In the last decade the
batteries we use in our hobby have taken a giant leap forward. When
I started in the hobby over 30 years ago NiCd (or Nickel Cadmium)
batteries where all we could hope for. Almost all higher end radios
came with the best Japanese NiCd batteries available. Well maybe one
of the best anyway. The cold war and the space race had given us
this great technology of rechargeable batteries and we bought the
radios with them and at the same time we received the charging
system to maintain them, or at least keep them charged. But we did
not need anything more and as long as we treated the batteries with
a little respect and did not leave them in the hot garage all summer
or over charge them, they gave us hundreds hours of use. The little NiCd battery had it's quirks, like a discharge curve we had to get
used to and something referred to as memory? Then came the NiMh
(Nickel Metal hydride) battery. This cell promised more capacity and
longer use time between charges, a flatter discharge curve and no
memory. Some of the claims rang true but maybe a little exaggerated.
The standard way of charging had not changed as the wall wart was
still the most common charging mechanism. Peak detection chargers
and automatic trickle chargers start to come on the market and our
batteries love it. Battery cyclers and fast field chargers come soon
after from companies like Ace and Litco that give a way to test and
keep tabs on our batteries performance.
These batteries have done well to power the transmitters, receivers and servos on our glow and gas powered aircraft up to this point and still do today in many cases. However power cell technology has not stood still and with the telecommunications industry pushing the envelope of battery power and miniaturization we have seen a surge of high power light weight batteries available to us. Lithium Ion has been the boom of energy cell technology and an off-shoot the Lithium Polymer (or LiPo) has flooded the hobby market. These light weight high energy cells along with new more powerful brushless motors with their small but high performance controllers (ESCs) have made electric power a viable alternative to the internal combustion engine for today's models. there are even electric helicopters that out perform their alcohol burning brethren. Large 90/700 class helicopter that have power systems pushing peeks of over 8000 watts, that is nearly 9Bhp. The average .90 Helicopter motor barely pushes 4hp.
Now with this new found power comes great responsibility my padiwhan! The Lipo batteries we are using pack a lot more energy and weigh a fair bit less than our old NiCd and NiMh Batteries of the past but, we have to treat them better than we ever did with the old packs. Lipos need to be charged and balanced and most include special connections for this purpose. In addition these new batteries come in two distinct types, Smart and dumb. The smart battery has a special circuit board that reads the charge condition and balance of the pack and even regulate the input for each cell. The dumb battery pack has only a terminal board connecting the cells to form the pack and a balance cord isolating each cell. For this dumb battery you need a smart charger. Smart chargers have flooded the market with all types and output configurations. From single circuit units that can charge from 1 to 12 cells all the way up to multi battery chargers that can charge 4 different batteries at the same time. Some are better than others and some are a better solution than others. I will not try to offer which is which here just to say that if you do your homework you will find the right choice. Just keep in mind two rules of thumb, first if you have dumb batteries you need a smart charger and second, you get what you pay for! The latter may not be as true today as it was years ago, but to an extent if it sounds too good to be true it usually is.
Finally remember the use of the battery will dictate the type. If you are powering your model via electric you will need more power (ie. volts), but our radio systems have limits to the voltage they can endure reliably. That voltage is 6 volts give or take 10% for most of the electronics on the market. Although our modern receivers can handle a bit more the servos, gyros and some other electronics are designed around lower voltage sources. the 6 volt limit will guarantee more life and reliability. I have recently witnessed this first hand when my son ran servos for cyclic off the high side of a Spektrum 7100R with a 2S lipo battery. Thinking the receiver regulated both the high and low side of the outputs. Not, the receivers high side is the battery voltage and he had a servo failure that may have been the higher than recommended voltage. I will be running the LiFe battery that is a 6.6 volt pack and closer to the recommended voltage for the servos I am running. Of coarse there are HV or High Voltage servos that are designed for the higher voltage of today's LiPo driven systems. Remember to take all considerations into account when planning out your electronics on your plane or helicopter and how you will power them. Personally, for my planes I still use NiMh batteries in the 1650+mah cappacity in 5 cell 6 volt configuration. As many pilots are using 2.4Ghz radio systems, the tiny micro processor controlled receivers are more complex than our older FM 72Mhz models. All receivers have a threshold voltage of about 3.7 volts. If the voltage drops below that the receiver will reboot. On the old 72Mhz that was about 1/250 second on a 2.4Ghz it could be over 2 seconds. That is a long time to not have control, so a 6 volt 5 cell NiMh is recommended. And since most modern servos and receivers can take the 6 volts it makes sense to use the 5 cell pack on 72Mhz receivers as well.
Well I hope this answered any basic battery questions out there. For more Lithium battery info you can read this article on RC Groups