Dive lights and Battery Life March 29, 2009
Posted by Chris Sullivan in Equipment.Tags: Battery Life, CR123, Dive Light, Dive Torch, Diving, LED, LED Flashlight, Lithium Battery, SCUBA, Scuba Diving, Scuba Equipment, Scuba Light, Underwater Light
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Continuing on from my description of my new (to me) OMS Vega V191 dive light, I would be interested in figuring out when to replace the batteries. With new batteries, this light runs for 3 hours. So the first challenge is to determine how much life is left in a used set of batteries. I don’t know if this can be done reliably, but I am going to set out to find out.
Energizer provides a data sheet for their CR123 Lithium battery, which shows the change in voltage over time as the battery drains. I should point out that the term Lithium battery is somewhat colloquial in this respect because there are many types of Lithium battery, and this particular one (like all the other brands) is a Lithium Manganese Dioxide cell. This curve uses a load of 100Ω on the battery, a standard used for the purpose of testing batteries. Using the relationship between power (P), voltage (E) and resistance (R) of P=E²/R the power output of the battery starts at .09 watts, dropping to about .08 watts when the battery quickly declines to around 2.85V. I used this simple calculator to apply the formula to these examples.
Energizer 123
In the last 20 hours of the battery’s life, the voltage declines further reaching 2.5 volts after about 53 hours of continuous operation. At this point we’re seeing just over .06 watts output, down a third from the 3 volt level.
The voltage then drops precipitously in the final hours.
My dive light uses two batteries in series for an output of 3 watts, which is much greater than this test. The resistive load of the LED would be a mere 12Ω at this output with the full 6 volts. OMS documentation says that
A few questions come to mind…
- What is the minimum voltage that the light needs to operate? I’ll be able to answer this once I flatten a set of batteries to the point where the light stops operating. To do this, I’ll have to use the light as a primary light with a separate set of batteries for dives where I don’t need it as a standby. I measured the used ones that the light came with at 2.855 and 2.845 volts (under zero load), so I will use these. I have another set lying around that are at 3V, which I’ll use when I really need the light for a standby. According to Wikipedia, white LEDs start to emit light at 3.5 volts and above. The Marl LED Technical Library shows illumination starting at 5.5 volts, so it will be interesting to discover what the truth is.
- Is the discharge curve the same shape under the heavier load of the light. Instead of .06 to .09 watts, for 1.5 watts the resistance for a single battery is a mere 6Ω. At this level of output the voltage at the flat part of the curve (in the 100Ω example this is the first 30 hours) might be less than 2.85. That’s hard to tell without testing, and I don’t really want to burn up batteries just to do that.
- What is the relationship between light output and voltage? LEDs have a pretty linear relationship between voltage and output, although high power LED applications use voltage regulators to keep the voltage constant so that the LED does not draw to much current and overheat. I noticed on a UK lights LED underwater light that there was a fair bit of circuitry built into the head.
- Can the no-load voltage of the batteries be used to track where the battery lies on the discharge curve? I imagine I could test a battery with zero load, 6Ω and 100Ω separately and see how the readings vary (I own a very accurate & precise Fluke DMM).
Question #1 will be answered in time once my weaker set of batteries fails to produce light from the LED. I’ll simply have to measure the combined voltage of the two batteries to answer that question. With this information and measurements over time I can plot the decay of the voltage with time and use.
I might end up working on #2 after doing some of the other projects.
I’m thinking about checking #3 with using the lightmeter of my camera, an old Nikon FE. It would require that I construct a jig to ensure that I can reproduce the setup to test the light at different voltages.
The final test would be to see if the voltage of the battery is different under load. That would help calibrate the battery against the discharge curve. At 100Ω the power is low enough that a 1/2W or 1/4W resistor would be just fine for the test.
Should be interesting. I’ll keep you posted.
OMS Vega V191 Dive Light March 28, 2009
Posted by Chris Sullivan in Equipment.Tags: Dive Light, Diving, Diving Light, Diving Torch, Ocean Management Systems, OMS Vega, Outdoors, SCUBA, Scuba Diving, Scuba Equipment, Scuba Light, Sport, Underwater Light
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I was at the dive shop last night and one of the instructors who is now working as a paramedic was selling off some of his excess materials and gear. I got a good deal on a couple of lights, one of which was this nice little OMS backup light.
The construction is pretty much solid metal, except for the lens and the bulb, and a hard plastic insulator at the base of the head where the positive end of the top battery connects. I haven’t removed the lens which requires a special tool (which could easily enough be home-made) so whatever is between the reflector and base of the head hasn’t been looked at.
The light runs on CR123A photo batteries. For a primary light, I’d definitely consider this a negative as these batteries are quite expensive. As a backup light though, the long shelf life and good temperature characteristics mean that is probably a good thing. The burn time for the two batteries wired in series (like most lights) is only 3 hours. At $6 each retail that’s a fairly high price to pay, but the use by dates I just saw in the building supply store was 2017 – so great for standby applications. I saw these batteries for $1-1.50 from web retailers. They’re also the same batteries that the sensors use in my home alarm system, so I usually have some around. They last for years. I’ve had some for more than 10 years, although about half have been replaced once.
OMS recommends their own brand of battery, which is actually just a Power One battery. Their literature says that these batteries have 1550 mah (milliamp hours) rating and others you can buy have less. While they’re absolutely correct in the statement, you can get 1550 mah CR123 batteries from plenty of suppliers, like Panasonic and Duracell. I had to search around a bit to find the spec on the Energizer version, it was 1500 mah – not so much difference as you would notice but not something they’d want to advertise. Energizer has better spec sheets than Duracell, and I found the operating range of the battery was -40C (-40F) to +60C (+140F). Hopefully that will cover everyone’s diving needs!
The light is constructed similarly to most, with the head that screws into the handle. There are two o-rings that fit into slots on the head, just after the threads. The o-rings need to be lubricated occasionally as you would with any light, and kept free of debris.
The “manual” (1 page in length) says that an anti-seize compound must be used on the threads. While OMS says to order it from them or buy at your dive shop, there are plenty of suppliers. I think I might check out a marine supply store for something that is designed for marine (salt-water) use. Many of these compounds have very high (more than 1000C) temperature ratings which is not needed for this application.
To turn the light on, you twist the head somewhat less than 3/4 of a turn. You are warned against twisting more than 3/4 of a turn in case of leaks. The light is rated to 100 metres (330 feet). It’s interesting to compare that to my UK light (more on that another time) which is rated to 500 feet with a plastic case and a single o-ring.
Output of the light is 80 lumens. OMS introduced a new model of the Vega, the K2, in 2009 and claims its new LED technology has “graded high colour temperature” and is much brighter at 180 lumens. This with the same batteries and battery life. I actually sent them an email asking how they did it, but haven’t received a reply. It’s quite an advance if I’m reading the specs right. The V191 was also described as graded high colour temperature and reviews have said it has a stunning light output – so if the K2 has more than doubled it without drawing more current from the batteries it is an incredible achievement.
One review I read criticised the light because it can come on during a dive as a result of the increased pressure. I suppose that I will have to make sure that it is twisted a little further than necessary on the surface before descending with it.
I might get to try it in the pool next weekend but failing that, I’ll use it on the Oriskany when I’m down in Pensacola in a few weeks.
Chronicle of an older diver 