Rationale behind wide voltage acceptance and low voltage variation.

This is a little bit more of a technical question, but what is the rationale behind some lights being able to accept a very large variation of voltages, while others are confined to a very small range? I know this has to do with the driver, but wouldn't it make more sense to be able to accept a wider range of voltages to allow for the use of different battery chemistries?

Good question! Let's get this started!

Firstly, I'm a "battery vampire."
http://www.candlepowerforums.com/vb/showthread.php?405759-Battery-Vampires-2015
When you become a battery vampire, you simply MUST know this stuff or you risk yourself and your electronics.

Ok.

1. Why is low voltage variation good in a driver?
Simple. For there to be "overdischarge protection" in the flashlight electronics, the driver MUST cutoff before a certain value is reached. This value isn't really cut-and-dry. Some protections cutoff at 2.9v, 2.8v, 2.7v, but by 2.6v the protection really should have kicked in by then in a single battery lithium ion light or device. 2.5v is an overdischarge, you damage the battery and increase the chance of problems. Charging such a battery (below 2.5) is risky and should be done OUTSIDE, imho. So say we cut off a single battery at 2.9v to be on the safe side. A 2 battery in series light then should cut off at 5.8v.

For this to work, we CANNOT use battery extenders or else the light will now overdischarge the two or three batteries if our cutoff is only 2.9v. You see?

2. Why is wide voltage acceptance good?
Wide voltage acceptance allows you to use multiple chemistries (but not at the same time, you could run alkaline OR lion for example,) varying numbers of batteries, or even hack the light or device to another battery type that it wasn't really meant to use. You must know what you're doing if you play these games. Hook it up backwards even once, even for just a second, and you've now trashed your light, possibly your battery(ies) and maybe hurt yourself or lit a fire.

My favorite wide driver is 3v-18v. It is safe with one lithium ion as it will cut off at 3v, which is a little high but definitely safe to charge after that. It gives me the freedom to run 4 series if I want, but now I am the guardian of my safety. If I overdischarge, I can check with a multimeter before charging so I can no whether or not to proceed.. I can hook to power tool batteries and active automotive electrical systems for power. Though auto elecs are nominally 12v, when the charging system kicks in the electrics must tolerate up to 15ish some odd volts. Having the overhead of 18v rated max allows you to vampire active vehicle electrics and 12 volt standalone auto batteries no sweat.

3. Why is wide voltage acceptance bad?
You now lost one layer of protection that's there to protect you. You will trash your lithiums if you run four batteries down to 3v combined. You, the end user, must know this stuff. Never recharge lithium ion that you've overdischarged (2.5v and less.) The chance of smoke and fire during charging just became a real possibility.

4. Why is narrow voltage acceptance bad?
You just lost all of your flexibility. You might be stuck with just alkalines and NiMH. You might be stuck with just lithium ion only, and a set number of batteries at that. You might have a light that only works with 3v CR123ax1, but not 4.2v RCR123.

Good luck, Prepped. Stay safe!

Any more thoughts? Questions?

Very complete answer.

Some lights are smart. HDS knows the difference between a CR123 and a li-ion RCR123. Oveready's know the difference between 1 li-ion cell and 2. This gives you wide voltage flexibility and safe cutoff.

Are there questions of efficiency with wide voltage acceptance? Do certain driver electronics and/or emitters do better with more specific voltages?

Good explanation from more_vampires.

One thing he did not mention is efficiency. I will guess that drivers that accept only a small range of input voltages can be designed to be more efficient. Zebralight, for instance, is known for the efficient buck/boost drivers it uses in many of its 1x18650 models. Most (or all) of those do not allow use of 2xCR123A, i.e., their input voltage ranges are too narrow to accommodate 2xCR123A. I do not know the fact, but my guess is that these designs are both simpler and more efficient.

That was an awesome and detailed answer. Are there any lights that can be user programmed to tell them what voltage to cut off at?

the best answer - and the most useful one because it is easy understandable - was the one from KeepIlLight:

the nearer the battery voltage is to the led voltage, the higher the efficiency of the driver can be made

KeepingItLight said:

Good explanation from more_vampires.

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Thank you, guys!

KITROBASKIN said:

Are there questions of efficiency with wide voltage acceptance? Do certain driver electronics and/or emitters do better with more specific voltages?

Click to expand...

KeepingItLight said:

One thing he did not mention is efficiency. I will guess that drivers that accept only a small range of input voltages can be designed to be more efficient. Zebralight, for instance, is known for the efficient buck/boost drivers it uses in many of its 1x18650 models. Most (or all) of those do not allow use of 2xCR123A, i.e., their input voltage ranges are too narrow to accommodate 2xCR123A. I do not know the fact, but my guess is that these designs are both simpler and more efficient.

Click to expand...

yellow said:

the best answer - and the most useful one because it is easy understandable - was the one from KeepIlLight: the nearer the battery voltage is to the led voltage, the higher the efficiency of the driver can be made

Click to expand...

Efficiency isn't my forte, but I've seen a bunch of data that seems to imply that wide voltage input drivers are less efficient than a narrow voltage input. Another thing I've noticed is that pretty much all of the small format wide voltage input drivers I've seen have only moderate drive strength. It might only be 1-1.5 amps! So, that's another drawback. Reduced efficiency and weaker output. Bigger size drivers can push harder with wide voltage input afaik, but these aren't the coin-size ones that would be in a pocket light.

Some of the current boost modders I've seen are only tuning for single battery lithium ion because of this, except for those emitters with the monster currents and voltages in a big light.

This is based only on what I've seen. I've not seen data sheets on 100% of all drivers, so we always have more to learn (especially me.)

Cool link on buck-boost:
https://en.wikipedia.org/wiki/Buck–boost_converter

They mention "parasitic resistances," an enemy of efficiency I'm sure.

In the analysis above, no dissipative elements (resistors) have been considered. That means that the power is transmitted without losses from the input voltage source to the load. However, parasitic resistances exist in all circuits, due to the resistivity of the materials they are made from. Therefore, a fraction of the power managed by the converter is dissipated by these parasitic resistances.
For the sake of simplicity, we consider here that the inductor is the only non-ideal component, and that it is equivalent to an inductor and a resistor in series. This assumption is acceptable because an inductor is made of one long wound piece of wire, so it is likely to exhibit a non-negligible parasitic resistance (RL​). Furthermore, current flows through the inductor both in the on and the off states.

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more_vampires said:

Good question! Let's get this started!
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Wow, EXCELLENT post, m_v!!

Thanks, Gri. This is one of my favorite topics. Though I'm sure I don't have the most efficient drivers, they'll most certainly drain batteries dead, dead, dead.

Something about that appeals to me.