D cell run test: datiLED 3v Volt Vamp on a 10 year old D cell

[sbslider]

I recently purchased three Volt Vamps from datiLED, one of which is a 3V version for CR123s or other 3v primaries. I've noticed that it seems to run longer on my alkaline batteries that the 1.5V versions I purchased. I realized today why. The 3V board draws less current than the 1.5V board. I suspect it was designed for 3V cells (duh) and is out of regulation down at 1.5V. I don't have a good current meter for the current being drawn, as when I do try to measure the LED is dimmer than when directly connected to the battery. Edit: I connected the circuit using banana plugs directly to my meter, and this helped a lot. I suspect the measurement is affecting the result some, but it's not nearly as much as with the long leads. I was measuring about 20mA with the long leads.

Anyway, I started the test at 7am today. I think the battery is supplying about 70mA on my meter. If so, and if the D cell can provide 20,000 mAhr, it would be about 320 hours, or about 2 weeks. I think this is what datiLED told me for the 1.5V version of the Volt Vamp goes about 3 weeks. We'll see what the 3V version does. I imagine as the battery voltage decays the current will drop also, so it is not easy to predict the run time based on the initial measurements.

For the first few minutes I used a 1.5V version, which appeared to be drawing 95mA on my meter. I wanted to draw this out for as long as possible, so in the first 15 minutes I switched to the 3V version.

After running for 1/2 hr the battery measures 1.533V. I'll take data every day or so and eventually post the battery voltage vs time.

I checked the voltage again after making the current measurements, and it's down to 1.455V. That suggests this test may be over sooner than I imagined . . .

Images left to right, measured current, measured voltage 5 hours into test, Volt Vamp 3V on D cell, ISO 100, 1.250 sec shot for comparing intensity of the light.

 

[dc38]

I recently purchased three Volt Vamps from datiLED, one of which is a 3V version for CR123s or other 3v primaries. I've noticed that it seems to run longer on my alkaline batteries that the 1.5V versions I purchased. I realized today why. The 3V board draws less current than the 1.5V board. I suspect it was designed for 3V cells (duh) and is out of regulation down at 1.5V. I don't have a good current meter for the current being drawn, as when I do try to measure the LED is dimmer than when directly connected to the battery. Edit: I connected the circuit using banana plugs directly to my meter, and this helped a lot. I suspect the measurement is affecting the result some, but it's not nearly as much as with the long leads. I was measuring about 20mA with the long leads.

Anyway, I started the test at 7am today. I think the battery is supplying about 70mA on my meter. If so, and if the D cell can provide 20,000 mAhr, it would be about 320 hours, or about 2 weeks. I think this is what datiLED told me for the 1.5V version of the Volt Vamp goes about 3 weeks. We'll see what the 3V version does. I imagine as the battery voltage decays the current will drop also, so it is not easy to predict the run time based on the initial measurements.

For the first few minutes I used a 1.5V version, which appeared to be drawing 95mA on my meter. I wanted to draw this out for as long as possible, so in the first 15 minutes I switched to the 3V version.

After running for 1/2 hr the battery measures 1.533V. I'll take data every day or so and eventually post the battery voltage vs time.

I checked the voltage again after making the current measurements, and it's down to 1.455V. That suggests this test may be over sooner than I imagined . . .

Images left to right, measured current, measured voltage 5 hours into test, Volt Vamp 3V on D cell, ISO 100, 1.250 sec shot for comparing intensity of the light.

At 320h, that would realistically translate to about -
80-90 days worth of light? (3-4 hours a night, anyway...)stick a resistor in it and quintuple the runtime, lol

 

[sbslider]

At 320h, that would realistically translate to about -
80-90 days worth of light? (3-4 hours a night, anyway...)stick a resistor in it and quintuple the runtime, lol

I've thought about adding a resistor to reduce the current and increase the run time. But these are so clean looking, I didn't want to mess with them.

Also, my 20,000 mAhrs is likely way too high, but current will go down so I'm going to stick with my guess for now anyway.

 

[lampeDépêche]

Thanks for running these tests, sb!
Like I said, I'm a fan of these datiLED Volt Vamps, but I have never run actual test runs with them, so I'll be learning from you.

 

[sbslider]

stick a resistor in it and quintuple the runtime, lol

Actually, I have done something can add significant resistance in the path, but is hard to duplicate. I was running some of the Volt Vamps with aluminum foil between the cell and the magnet/contact. I did this to measure the voltage of the cell without disconnecting the contact to the cell. If the foil isn't adjusted just so, then I can see the light output decrease. I know that aluminum is conductive, but there must be something with the lack of flatness, or oxidation, dissimilar metals or ? It doesn't take much resistance to knock the voltage down, which reduces the intensity at some point. The 1.5V lights will draw 100mA from a cell it only takes an ohm or so to make a significant affect.

 

[sbslider]

Paint's not dry yet. Thought I would take a look 24 hours in. looks like the Volt Vamp is still regulating as the battery voltage is down 0.2V from the start of the test and the current is up to 95mA. I don't have a good current data point from the test start. I also know the current measurements are a bit flaky, and often lower than what is actually happening due to my setup. but the previous pictures yielded power of 1.455 * 0.07 = 0.102W. Now the power is 1.377 * 0.095 = 0.131W. I don't trust my initial current measurements, or the efficiency of the Volt Vamp really starts to go down as the battery voltage goes down.

 

[dc38]

Actually, I have done something can add significant resistance in the path, but is hard to duplicate. I was running some of the Volt Vamps with aluminum foil between the cell and the magnet/contact. I did this to measure the voltage of the cell without disconnecting the contact to the cell. If the foil isn't adjusted just so, then I can see the light output decrease. I know that aluminum is conductive, but there must be something with the lack of flatness, or oxidation, dissimilar metals or ? It doesn't take much resistance to knock the voltage down, which reduces the intensity at some point. The 1.5V lights will draw 100mA from a cell it only takes an ohm or so to make a significant affect.

ALong with the possible oxidation, the sheer mass of a piece of folded aluminum (plus an inefficient path from folding) might cause a drop in current. That's purely speculative, but if you stick enough material between two points in a circuit, it will eventually hit a point where electrons don't flow so well, or if they're forced to flow, will transfer their energy as heat.

 

[thermal guy]

I think I ran mine off of a D cell for almost a month.

 

[sbslider]

I think I ran mine off of a D cell for almost a month.

I'm probably half way there? It's been a couple days short of 2 weeks. The cell voltage has settled at 0.8x for the past few days. How low will it go before the light is out? It's about a lumen or so right now of light.

 

[sbslider]

The test started April 25, lights out on May 9. 2 weeks on a never used D cell with an expiration date of 2025. Perhaps the 1.5V Volt Vamp would have run longer? We'll never know . . .

 

[Beacon of Light]

@sbslider, when you added the foil did the lumens drop? One of my pet peeves with any of the volt vamps was it was way too bright. I was hoping it was going to be a very low output like the PakLights 9v light.

 

[sbslider]

@sbslider, when you added the foil did the lumens drop? One of my pet peeves with any of the volt vamps was it was way too bright. I was hoping it was going to be a very low output like the PakLights 9v light.

I could get the lumens to drop with added foil, but I can also get them to drop by adjusting how the magnets sit on the cell.

I also sort of wish the volt Vamp was a bit dimmer. I do think I get the longest run times with the 3V version, but I haven't done any qualitative testing.

 

[Bimmerboy]

Very cool post. I have three of this type item from datiLED, one of them is a 3V version. Love these things, and though I don't wish for a power outage, they are an integral part of my SHTF lighting plan.