I found this how to, by Brain James, on heliproz’s website, and thought it was a great article, and would like to post it for everyone to read about.
Powering the receiver, servos, and gyro can be accomplished a couple different ways. The most common way traditionally was to use a NiCad or NiMh 4.8v battery. It is simple, easy to install and the least expensive route you can choose. Recently the use of a lithium regulated system has become popular. Typically a 2 cell lithium polymer or lithium ion battery rated at 7.4v or 7.2v respectively is used with a regulator to provide power to the receiver, gyro, and servos.
What system should you choose?
Well, that depends on a couple things. Are you just starting out, or are you a more advanced pilot? Are you constrained by a limited budget? Which servos are you using? These are questions you really should consider before making a decision. Both systems will usually work, but a regulated system may be more suited to a more advanced pilot needing the very most performance. A NiCad or NiMh 4.8V battery just like any other battery provides voltage that as the battery is depleted lowers, which means that as the battery gets current drained from it, the voltage drops resulting in servos that run slower and weaker than they did when the battery was fully charged. If you’re just starting out, you probably will not notice this, and a simple nicad or NiMh battery is a good option to save some money when starting out. With the 4.8v option, you simply plug the battery into a switch and then the switch plugs into the receiver’s battery port. There are many different size 4.8v battery packs to choose from and it can be tough trying to figure out which one to buy. Again, this depends on which servos you’re using and how you fly your model, If you’re really banging around the sticks obviously the servos are going to draw more current, which depletes the battery faster. So again, which size battery to choose? I usually recommend a battery with about 2000 Mah for most beginners and sport fliers. However a smaller capacity pack can be used on 30 size helicopters with standard analog or “sport” grade digital servos. I usually don’t recommend using the 600Mah battery packs that used to come with most transmitters. They’re fine for some airplanes using “standard” servos, but helicopters use 5 servos (for a nitro model) and a gyro. How do you know how many flights you can get on your Nicad or NiMh battery? If you don’t have a charger that shows how much current goes into a battery pack, the best way is to use a load tester. Futaba and Hangar 9 make good ones. They plug into your battery, and when a button is pushed apply a load (simulating the servos) and display the voltage. The manufacturers of these load testers will have their recommended “no fly” voltage included in the instructions.
When should I think about a lithium/regulated system?
If you are getting to be a more advanced pilot, and want the most performance out of your servos and gyro. If you are running any of the higher end digital servos, they will drain the receiver battery faster, placing a greater load on the battery. In some cases when using a NiMh battery the large current load on a fully charged battery will drop the voltage down to a near unacceptable level. You may have heard of the “brown outs” with Spektrum receivers? This is what was happening with the brown outs. The Battery’s voltage was dropped below the operating threshold of the receiver causing it to “reboot” often leading to a crash! If the people experiencing the “brown outs” would have been using a regulated lithium system, the crash would have been avoided! There are several regulators on the market that are very good. Duralite makes a simple regulator which has been available for years, Fromeco makes the “Arizona” which is a dual output regulator, providing an adjustable 5-6 volts to the swashplate and throttle servo, and a fixed 5 volts to the gyro and rudder. The Scott Gray “Reactor” is dual output as well and very easy to use. The Duralite Gemini system is a dual output and it can also be run with redundancy with two separate battery packs. Align also makes several regulators one of which actually contains the glow igniter built in and a bank of colored LED’s to indicate voltage! Exactly what the regulator does is pretty simple. It takes a input voltage from the 2 cell lithium battery and reduces the voltage to something usable by the receiver and servos. Servos are typically rated for a certain voltage. Most servos on the market can safely be run from between 4.8 and 6 volts. Some servos warn 4.8v only, but experience has shown them to work fine on a regulated 6 volts. Here’s why: A fully charged 4.8v nicad style battery is actually closer to 6 volts! Many airplane guys use a 6v nicad pack which contains 5 cells, and when they’re fully charged they are around 7 volts! I feel what the manufacturer is trying to say is that the servos were not intended for use with a 6v Nicad or NiMh battery. There are some exceptions to this, the servos that are specifically designed for use with a gyro controlling the rudder are special high frame rate servos. They seem to not tolerate the higher voltage, and their operating voltage should be kept around 5 volts. With the Align regulators and others that do not have a 5 volt output for the gyro and rudder, a step-down is commonly used. A step-down is a simple diode that drops the voltage from 6 volts, down to around 5 volts.
The two types of lithium batteries that are most popular are Lithium Polymer and Lithium ION. They are pretty similar, but do have some differences. The Lithium Ion have a hard shell similar to a NiCad battery, Lithium Polymer batteries have a “soft” shell that you have to be careful not to damage, but they are lighter which is always a concern!. Also, the voltage of the batteries are slightly different. A Lithium Polymer 2 cell battery is 7.4V while a Lithium ion is 7.2v. These kinds of batteries are different in the way that you charge, store, and use a NiCad or NiMh. Lithium batteries must be charged with a charger specifically designed for lithium batteries. When they are to be stored for any length of time, they should be at half charge. Using the battery is different as well, whereas with a NiCad battery it should be fully discharged before it is charged back up, Lithium batteries cannot be fully discharged. If they do get over discharged they are ruined!
You can see more of Brians articles in the Tech Articles and Revew part of his biography on Heliproz’s website.