I'm a bit confused...I'm planning on ordering a P3D RB100 in the near future so this is of great interest to me.
I was recently educated about digital regulation (which the P3D has), but how do protected/unprotected cells differ...I thought they were two sets of terms referring to the same thing. Originally I thought regulation was within cells, but it was pointed out to me that it is within the flashlight itself.
So...what are protected cells? Above, Wade says that running two unprotected lithium cells can be risky...I was told that Energizer E2 Lithium batteries were the best choice for the P3D...are these protected?
I am certainly not the expert on this... But I will take a chance...
First, you are correct, there is a regulator in the P3D (and other lights too--99.9% of them are LED--ignoring HID and others). More or less, the regulator provides a fixed voltage (or current) to the emitter for a constant output light (and many lights can also adjust the output).
Technically, a regulator has feedback to monitor the voltage or current of interest.
There are also converters that can boost the voltage up, or drop the voltage down. These may or may not have regulator function too (i.e., as the battery voltage falls, the light output falls).
There are also switch mode and PCM regulators which are pretty efficient at controlling the light output, and there are linear regulators that just burn off the excess voltage to control light levels (same thing as just adding a variable resistor in the circuit).
Now, to the batteries. Various Lithium (and others too) chemistries have issues that make them unsafe if used incorrectly.
Some protection is just placing the equvalent of a PTC resistor (positive temperature coefficient resistor) on the end of a Lithium **** cell to limit the maximum amount of current through the cell--in some cases, exceeding current limits of the cell can cause internal failures that will, basically, cause the internals of the cells to generate more current an heat)--basically thermal run-a-way and can cause fire and overpressure conditions.
As I understand it, a "Protected" Lithium cell is usually a rechargeable cell where there is literally an electronic circuit and FET (Transistor) switch that monitors a single cells voltage (and perhaps current?)--and if that voltage goes over a certain level, or drops below another level, the electronic circuit will "open" the FET and prevent the battery from further operation in out-of-spec territories. Used primarily in Laptop computer battery packs.
Without knowledge about the rechargeable Lithium cells you are using (and being very careful about using them), it is not hard at all to create fires/explosions (of some sort) by abusing an unprotected Lithium rechargeable cell. If you are in the parking lot and your flashlight or R/C battery catches fire--probably not a big deal. If you are on an airliner and if an unprotected battery fails (or it is in checked luggage)--you may be lucky if all you have to do is give explanations to a group of very unhappy people.
The rechargeable Lithiums, if over or under charged, some chemistries can create dangerous conditions (like plating out pure lithium) or other failures where batteries can catastrophically fail (with or without loads).
Lastly, as I understand, there are also some CR123A sized Lithium rechargeable batteries that have an internal regulator (probably linear?) that can take the output voltage of a nominal 3.6 volt chemistry, and drop it down to a 3.0 volt output that matches the "standard" primary CR123A cell voltages. Only use this as a "last resort" if the light (or camera/etc.) cannot tolerate the 3.6-4.2 VDC or so output voltage of the rechargeable lithium. These "regulated" cells are typically a bit larger in size than a standard CR123A battery (because of the extra components) and also probably don't have the current or energy capability of standard (unregulated rechargeable or primary) cells because of their design.
Does this help?
Try the Batteries Included forum here if you need more information (there is also a thread or two with pictures of the regulated/protected batteries disassembled too).
-Bill
PS: I should probably add that the P3D is perfectly able to use the non-regulated RCR123A cells. It is designed to operate from roughly 4.2 vdc to ~8.4 volts (and has been tested one time up to 16 VDC) and will perform just fine for you.
However, if you use a non-regulated CR123A in a P1D or P2D (single CR123A light), you may loose some modes (i.e., light may only turn on in high/turbo mode and flashing--low modes may not work until the battery has discharged (to near dead) down to ~3 volts or so).
