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JR Servo operating voltages

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JR Servo operating voltages. Author Dave Wilshere
On many of the JR Propo servos, the operating voltage is stated as 4.8v. This is very misleading as there is no energy source (Battery) that actually gives out 4.8v and most popular power management devices are generally set between 5.5-6.0v for standard non HV (High Voltage servos)
The 4.8 voltage term comes from the four cell (4N NiCad/NiMH ) style cell packs which nominally each have an individual cell voltage of 1.2v (x 4 = 4.8v) This voltage is really only applicable when the packs are near flat.
The Ni type of cell reaches 1.5-1.57v per cell towards the end of a charge, so 6-6.3v pack voltage before the voltage settles. In use a good pack will deliver 5.7v, so as you can see, even on a 4 cell Ni battery none of these servos actually operate at 4.8v, even though JR say they are 4.8v servos!
Electric flight speed controllers that feature a BEC (a feature that supplies your Receiver its power down the throttle lead) will normally be set to give between 5.5 and 5.6v, again also above 4.8v.
The popular PowerBox products have been used by thousands of modellers and feature in all my jets and more than 50% of my personal fleet of models. These devices mostly produce an output voltage of 5.9v and many thousands of flights have given me zero servo or radio failures, all with JR servos stated as 4.8v servos.
The reason JR say that 6.0v should not be used on these servos is because people would think of a five cell (5N) pack as 6.0v. Again as above, this is a near flat voltage based on 1.2v per cell. The reason this pack is not suitable for JR servos is that 5 x 1.5 volts is 7.5v and that’s HV territory!
2s Li-Po batteries are marked as 7.4v, but actually reach 8.4v fully charged. Connecting this directly to a Receiver means the servos also receive 8.4v initially. The voltage will reduce in use, so the servo speed and ultimately power will reduce with voltage. Powerbox chose to regulate Li-Po batteries to 7.4v as an HV output, this would be maintained until the pack is almost exhausted.
Lithium cells will usually deliver their stated capacity even under load, so a 2200mAh pack can have 2000-2100mAh used at the load we develop through our radio systems. A 2000mAh Ni Rx pack will not deliver much more than 1300mAh before it would struggle to deliver its nominal voltage under load.

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