Battery testing for dive lights? (specifically non-rechargeable CR123)

[elgoog]

Hi all -

While doing some research on backup dive lights and battery types, I came across some articles about explosive CR123 batteries.
The specific use case is when 2 batteries are used and one is at a significantly higher charge than the other, 1 battery starts charging the other (technically, I think, reverse charging) which results in heat build-up and hydrogen gas being released. In flashlights that are sealed, like dive lights, this is more problematic as the hydrogen doesn't slowly leak out but accumulates to the point where it could go kaboom. A precaution is to check the charge levels of batteries before use and make sure there isn't a huge disparity in the pair put into a light. This could happen with alkalines or any other battery types as well, but CR123s seem more susceptible to this kind of failure due to the higher rate at which they release the energy (??)
I've been looking at getting a couple of LightMonkey 2W LED lights which use the CR123s as they seem very well reviewed for that form factor. Do users of this light (or any others that use CR123s) do any additional checks on the batteries before using them? Maybe use a battery tester on them before each dive? I've read a bunch about these tests on other forums but nothing on any of the SCUBA ones. Just curious to see if this has come up in the diving community.

Thanks in advance,
elgoog

 

[Kharon]

Instead of using 2 CR123's I use a single 18650 (Best 18650 li-ion battery 3400mAh (Panasonic inside) Protected Li-ion Orbtronic). They have a built in protection circuit for over charge and under charge. IMO they can't be beat. You di need a special charger but I suspect that's true of CR123's.

 

[elgoog]

For backup lights, I'm specifically looking for ones that use disposable batteries and have narrowed down to those that will eat alkaline Cs or the Li CR123s. This is with the intention of also being able to use them as backups for GUE/tech courses in the future. Regardless of course requirements, I like the idea of using primary cells for backup lights and rechargeables for primary lights. Hence the question about care/precautions before use of disposable batteries.

Instead of using 2 CR123's I use a single 18650 (Best 18650 li-ion battery 3400mAh (Panasonic inside) Protected Li-ion Orbtronic). They have a built in protection circuit for over charge and under charge. IMO they can't be beat.

Yeah, love the 18650s - our primary handheld lights (DGX600) use these (don't have/need can lights at the moment) and I already have a bunch of good quality batteries and charger.

You di need a special charger but I suspect that's true of CR123's.

The CR123s I'm looking at are the disposable kind. I think the rechargeable variant in this format is called RCR123 (not sure)

I looked pretty closely at using 1x18650 or 2xCR123 interchangeably in the lights (depending on the dive requirements) and found that this usually works but, in theory, the following could cause it to not work -
1. Inside diameter of the light may not hold the 18650 - 19mm for this vs 17mm for CR123. I've read that you can bore out the receiver but that seems like a major hassle and beyond my skill.
2. LED driver circuit may not work with the lower voltage of the 18650 - 3.7V vs the nominal 6V of 2xCR123
I'm actually calling Light Monkey and DGX today to get the above specs on their handheld lights to see if 18650 and CR123 can be safely swapped.

Thanks for the reply,
elgoog

 

[Kharon]

Got a question. With the cells in serries (end to end) I thought they would output 3V. I thought they had to be parallel to get 6V. Wasn't great at E&M in physics so I'm confused.

 

[lowviz]

Quick and slightly inexact:

Power in Watts = Volts x Current.

Batteries end to end: Same current as one cell, voltages add.

Batteries in parallel: Same voltage as one cell, currents add.

Same power capability either way. A combination of series and parallel cells allows you to get a needed voltage at a needed current.

 

[Kharon]

Thanks for the lesson. Not sure I'll remember (but I will try). But it did generate another question (sorry).

Using 2 CR123 I would get 6V at ≈ 1000-1400mA. My 18650 gives me 3V at 3400mA. How does that affect brightness of my 700 lumen light and how does it affect how long the batteries last?

 

[lowviz]

First you need to know the current draw of your light at rated brightness. Manufacturer picks this.

If you slowly increase the voltage on the LED with something like a variable voltage source (that can supply as much current as required) the LED will turn on and increase in brightness with increasing voltage until it burns out due to excessive current resulting from overvoltage.

So the manufacturer makes a compromise between lifetime and brightness and picks a working current for that particular LED. Next they design a circuit that delivers the desired current constantly to the LED under varying supply voltage conditions (your batteries dying).

So your brightness probably won't change much with increasing voltage, your voltage control circuitry just has to work harder. How long will your light last with any given batteries? Need to know the dropout voltage (when it quits working) for the control circuit.

Look on your batteries for an mAH rating. That is milliamps times hours. 1,000 milliamps is one amp. So a good GUESS in hours can be had by dividing the effective mAH rating of your entire battery pack by the current (in milliamps) that your light requires. If you can remove the light assembly or base and reconnect it with a jumper and a volt*ohm*meter (VOM) set to amps or milliamps you can turn your light on and directly measure your light's current requirement. Next do the division and you are left with how long in hours.

 

[Kharon]

lowvis - Thanks for the lesson. The manufacturer says one rechargable 18650 or two non-rechargable CR123's. Guess I'll stick with my 18650's. I can recharge them and they have high & low protection circuits. Doesn't sound like I would gain anything by going higher voltage but lower mAH.

 

[lowviz]

Correct, think of mAH as your total energy rating. (not entirely exact either, but close enough)

 

[Kharon]

Thanks again.