The efficiency is close to 95% around 3.7V, reasonably good (probably in the 80's) around 4.5V and drops another 10-15% as you get to 6V.
With regards to the best way or settings to run the ProVari at;
The ProVari was designed from the ground up to be as reliable as possible considering the environment in which it is used. Wherever possible, design margins were selected that would allow it to perform with the best efficiency over the entire wattage use range. The posted Efficiency Chart shows actual lab data as measured during the product development cycle. The ProVari, by design, has to be as efficient as possible to keep its internal heat down as this insures long term reliability and allows the maximum battery run time.
Some have asked, "Why are High Drain Batteries recommended?" The answer to this is: High Drain Batteries have an internal resistance of 20 milliohms. All other batteries have an internal resistance of over 160 milliohms. This factor of 8 (or more) means the battery terminal voltage will be lower and internal battery heat will be 8 times higher during its use. That all translates to less runtime and less battery life. All DC/DC Converters work on a power in/power out principle.
For example, if you are running at 12 watts output, the current that is being taken from the battery when the battery terminal voltage is 3.7 volts is: ((12 watts) / (3.7 volts)) / .95 (converter efficiency) = 3.414 amps. During the condition when the power output is 6 volts and 2.5 amps (the maximum rated ProVari power output condition) the battery current can be ((15 watts) / (3.7 volts)) / .92 (converter efficiency) = 4.4 amps. Now let’s look what happens when the battery terminal voltage drops to 3.3 volts. ((15 watts) / ( 3.3 volts)) / .92 (converter efficiency) = 4.94 amps. OR when the battery terminal voltage drops to 3.0 volts. (15 watts / 3.0 volts) / .92 (converter efficiency) = 5.43 amps. It is important to note that this is just the average current drain, the peak currents from the battery can be double this number. Remember the converter works on a pulse principle.
So, what happens to the battery terminal voltage when these high currents are being drawn? With an internal resistance of 20 milliohms, the battery terminal voltage drop when 5 amps is being drawn is: (5 amps)x(.02 ohms) = .1 volts. But if the battery internal resistance is 160 milliohms then it becomes: (5 amps)x(.160 ohms) = .8 volts or 8 times worse. The ProVari internal components have to be selected to handle over 12 amps of pulsed currents to deal with these boundary conditions in order to meet the rated output of 6 volts and 2.5 amps (15 watts). Even if you don't choose to use it there, that is what it is rated for.
The other engineering factor to keep in mind is this: the battery internal resistance goes up with battery “end of charge” and battery “end of life”. So these calculations are for the best case condition of a new battery or a battery that is in it prime of its life. As the battery gets older the internal resistance goes up. There is not a lot of data on what it will actually degrade to and this degradation will vary a large amount from battery to battery. If you want to use the ProVari in a way that will make everything last longer, then the one thing we recommend is to recharge the battery when the low battery light starts to flash. It is when the battery terminal voltage drops low that these large currents get drawn. That is when the maximum stress is placed on everything.
So, for those that say: “It’s no big deal, we are only using 2 amps output”, remember it is not the output current that matters with regards to the battery current; it is the power taken from the battery with reference to the battery terminal voltage. That is an entirely different number, especially when taking the battery internal resistance into account.
As far as the ProVari electronics is concerned, it is as efficient as we could make it and still keep the size and cost reasonable. The lab data taken on an actual unit posted below:
