The Lithimon 234 covers batteries of 2, 3 or 4 series cells (7.2, 10.8 or 14.4 Volts nominal),

The Lithium Battery Problem Solver

Lithium-Ion (LiIon) and Lithium Polymer (LiPo) batteries are set to revolutionize the world of electric-powered models. They offer an unprecedented power-to-weight ratio, offering greatly extended flight times compared with NiCd or NiMH batteries.

However, Lithium batteries can be temperamental and have limitations that must be understood.

There are two principal sources of trouble: firstly, there's what is known as the Peak Pulse Effect. This is a result of the way that electronic speed controllers (ESCs) work. Instead of presenting a constant load to the battery, an ESC switches very rapidly between full-on and full-off, varying the motor speed by changing the ratio of on-time and off-time. This presents a pulsating load to the battery, and Lithium batteries object to this much more than other types. The result, if the problem is left uncorrected, is that the battery appears to go flat prematurely, but if rested for a minute or two will start providing power once again, just as if the battery were overloaded. The reason is that the battery is sensitive to the peak , not average, load. For example, Lithium Ion batteries are typically rated for 3.5-4.0 C , implying that a 1.4 Ah battery could drive a load of 5 Amps --- but the Peak Pulse Effect means that an ESC drawing 5 Amps (average) will actually be drawing peaks of typically 10 Amps, and these peaks overload the battery.

The second limitation of Lithium batteries is that they are easily damaged by over-discharging, and must never be discharged below a specified value (usually 3 Volts per cell, off load). Excessive discharge will permanently ruin the battery.

Dawnmist Studio's best-selling Lithimon product family solves these problems and transforms the Lithium battery from a technical curiosity into a trusty workhorse.

The compact, lightweight Lithimon unit is simply connected in parallel with the speed controller, and has two functions. Firstly it uses a pair of energy-storage capacitors to 'smooth out' the peaks of the ESC's energy demand --- thus presenting an average, rather than peaked, load to the battery (these are purpose-designed capacitors, since regular 'over-the-counter' types cannot meet the demands of Lithium batteries). Lithimon supplies an extra burst of current to the ESC during the peaks to assist the battery, while recharging in between the peaks. This happens automatically, thousands of times per second. As well as curing the Peak Pulse Effect and allowing the battery to work right up to its full rated current without going flat prematurely, Lithimon also greatly extends the service life of the battery by avoiding overload conditions during every peak, and furthermore, reduces the heat generated in the battery (wasted power).

Tests in real models have shown reductions of over 50% in the wasted power, 50% less heat generated in the battery, and up to a doubling of flight duration.

Without the Lithimon's energy-smoothing function, the only way to deal with the Peak Pulse Effect would be to use a much bigger battery, negating the principal advantage of Lithium technology --- its light weight. The Lithimon's special energy-storage capacitors yield a pulse impedance below 0.04 Ohms, which means that the Lithimon can provide the battery with assistance at an impressive 25 Amps per volt dropped, making the Lithimon family easily powerful enough for large models while still small and light enough for use on indoor helicopters.

The second function of the Lithimon is a sophisticated battery monitor which helps prevent over-discharging of the battery and consequent battery damage.

Three ultra-bright LEDs, visible at a distance even in daylight, show the battery status, and an 85 decibel audible 'Land Now!' alarm activates when the battery reaches its limit. The Lithimon 234 covers batteries of 2, 3 or 4 series cells (7.2, 10.8 or 14.4 Volts nominal), while the Lithimon 5678 covers 5, 6, 7 or 8 series cells (18, 21.6, 25.2 or 28.8 Volts nominal) and the Lithimon 9012 covers 9, 10, 11 or 12 series cells (32.4, 36, 39.6 or 43.2 Volts nominal). All versions offer three selectable discharge responses for moderate, heavy or very heavy current drain applications. An on-board microprocessor uses a sophisticated measurement technique (10-bit ADC with 64x oversampling and a specially-developed DSP algorithm) to obtain an accurate, stable battery level measurement --- despite the peaks and surges from the ESC and motors, which would defeat a simple voltage monitor.

The Lithimon 234, 5678 and 9012 can pay for themselves many times over by preventing damaged batteries and by allowing Lithium batteries to be used to their full capacity without the ravages of the Peak Pulse Effect.