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atraildreamer
2008-11-28, 20:54
My wife asked me to check the batteries in her LED headlamp as it was starting to dim out in use. The battery pack is the cylindrical type common to LED lights and uses 3 AAA batteries.

I tested the batteries and found that 2 were near full charge, while the third battery was totally dead. This seems to be a common problem with this type of light.

The obvious way to maximize battery life would be to periodically rotate the position of the batteries in the battery pack and allow the draw down of each battery to be equalized thru the life of the battery(s).

Just my 2 cents worth.

Rick
2008-11-28, 22:47
....Or could it have been that one battery was much weaker than the other 2 to start with?

kayak karl
2008-11-29, 07:19
....Or could it have been that one battery was much weaker than the other 2 to start with?
since batteries are normally in series , not parallel circuits, does ONE go bad before the others?? who has a good volt meter to test this theory?

AMPEX799
2008-11-29, 10:34
They aren't batteries untill 2 or more cells are connected electrically. Most likely the dead cell was defective.

atraildreamer
2008-11-29, 20:16
This has happened to me at least 3 times with LED lights and headlamps that use the cylindrical battery holder that holds 3 AAA batteries. Same result each time. Three, tested, new batteries installed...one dead battery and 2 usable batteries with high charge remaining upon removal and retesting.

As all units seem to be similar in design, I wonder if a design flaw could be causing the problem with unequal battery discharge?

GGS
2008-11-29, 21:59
This has happened to me at least 3 times with LED lights and headlamps that use the cylindrical battery holder that holds 3 AAA batteries. Same result each time. Three, tested, new batteries installed...one dead battery and 2 usable batteries with high charge remaining upon removal and retesting.

As all units seem to be similar in design, I wonder if a design flaw could be causing the problem with unequal battery discharge?

What type of batteries?

Lithium batteries, for example, hold their voltage until they are almost dead. So a close to dead cell wouldn't show as such on a voltmeter. It could be that one is crapping out just a little early, with the other two shortly to follow.

JewDuh
2008-11-29, 22:01
Never much liked that battery layout. It's awfully hard to replace batteries in the dark, and it's prone to shorting out... With as bright and long lived as LEDs have gotten I don't see any point to have more than a 1 AA cell LED headlamp. Mine is bright enough to walk (or even run) with in the dark. and it has a lower setting that is great for reading with. One AA lasts about 13 hours.

atraildreamer
2008-11-30, 20:16
What type of batteries?

Alkaline. No particular brand preference, but all were new out of the package.

GGS
2008-12-01, 02:11
Alkaline. No particular brand preference, but all were new out of the package.

Did a little research. Alkaline batteries also do not have a linear discharge curve. The voltage output remains relatively flat for the life of the battery, then nosedives near the end of its life.

Here's a site that compares different brands of AA alkaline batteries and shows the discharge curve for different current drains: http://www.powerstream.com/AA-tests.htm

Look at it this way. It's like having light bulbs rated 1,000 hours. That's an average rating; some light bulbs will expire before 1000 hours, some will burn well after 1,000 hours. So if you took three new light bulbs from the same package and put them in lamps they wouldn't all die at the same time, they would die at different times, the average being after 1,000 hours of use.

I would expect batteries to have the same behavior.

taildragger
2008-12-01, 02:15
Could be something with your connection causing charge leakage.

GGS
2008-12-01, 02:29
Never much liked that battery layout. It's awfully hard to replace batteries in the dark, and it's prone to shorting out... With as bright and long lived as LEDs have gotten I don't see any point to have more than a 1 AA cell LED headlamp. Mine is bright enough to walk (or even run) with in the dark. and it has a lower setting that is great for reading with. One AA lasts about 13 hours.

Most high intensity LEDs requires around 3.5 volts for full illumination, some near 4 volts. 1 AA only generates 1.5 volts; it takes at least three cells to fully illuminate the LEDs, adding in some margin for partly discharged batteries and all. This would be the simplest design, you just need a battery case, switch, and LEDs.

One can use electronics to create a voltage multiplier circuit to use a single cell to drive the LEDs. Of course now cost and complexity increase, and you would drain a single cell 3x as fast.

Technobabble aside, what single-cell headlamp do you use?

Jim Henderson
2008-12-01, 14:32
I have several of these LED lights with the little 3 cell cylindrical carrier. If I recall they are series connected so there is a higher voltage available.

When cells are connected in series, eventually the weakest cell will be fully discharged and then the other two cells will "Reverse Charge" that cell. Since there are manufacturing differences between cells from the same line, there will always be a "weakest" cell

This is also the reason why most manufacturers recommend not mixing brands or new and used cells, since this creates a weak cell from the start.

Since the cells are in series, it doen't matter much which position the cell is in so rotating location won't help. I have not looked in detail at all my carriers in the flashlights but if some maker got clever and designed the carrier with multiple taps that make 1, 2 or all 3 cells available for varying brightness, then this would explain always having one cell(the number 1 position) die quickly. Most good flashes use a chip to control brightness so I would not expect a multi tap carrier.

Just my observations,

Jim Henderson

atraildreamer
2008-12-22, 15:50
I have several of these LED lights with the little 3 cell cylindrical carrier. If I recall they are series connected so there is a higher voltage available.

When cells are connected in series, eventually the weakest cell will be fully discharged and then the other two cells will "Reverse Charge" that cell. Since there are manufacturing differences between cells from the same line, there will always be a "weakest" cell

This is also the reason why most manufacturers recommend not mixing brands or new and used cells, since this creates a weak cell from the start.

Since the cells are in series, it doen't matter much which position the cell is in so rotating location won't help. I have not looked in detail at all my carriers in the flashlights but if some maker got clever and designed the carrier with multiple taps that make 1, 2 or all 3 cells available for varying brightness, then this would explain always having one cell(the number 1 position) die quickly. Most good flashes use a chip to control brightness so I would not expect a multi tap carrier.

Just my observations,

Jim Henderson


Best explanation that I've heard, so far.

GGS
2008-12-22, 23:10
Best explanation that I've heard, so far.

I was getting there... ;-)

Jim Henderson
2008-12-23, 15:19
Well, I am a collector of VOMs, VTVMs(bet ya haven't seen one of these in a long time) and multimeters, so yes I do have a good meter or two and I have measured the voltage and current of far too many batteries to count. This kind of stuff happens when the wife is snowed in at Portland airport, leaving me and the boys to entertain ourselves.

Just thought I would mention it since it gives me a bit more credibility than saying I are an Enjuneer. I is or wuz too.

Just this weekend I measured a triple A cell that was used in series with 3 others and it was truly reverse charged. It had a negative voltage reading and essentially no current capacity. This comes from the current flowing the right way thru the other cells, being forced thru the dead cell the "wrong" way which causes it to go negative or more than dead.

So if the cells are in series, one will fail before the others. Position in the series will have no effect except for random effects like dirty contacts.

So, FWIW,

Jim Henderson

atraildreamer
2008-12-25, 11:52
Well, I am a collector of VOMs, VTVMs(bet ya haven't seen one of these in a long time) and multimeters, so yes I do have a good meter or two and I have measured the voltage and current of far too many batteries to count. This kind of stuff happens when the wife is snowed in at Portland airport, leaving me and the boys to entertain ourselves.

Just thought I would mention it since it gives me a bit more credibility than saying I are an Enjuneer. I is or wuz too.

Just this weekend I measured a triple A cell that was used in series with 3 others and it was truly reverse charged. It had a negative voltage reading and essentially no current capacity. This comes from the current flowing the right way thru the other cells, being forced thru the dead cell the "wrong" way which causes it to go negative or more than dead.

So if the cells are in series, one will fail before the others. Position in the series will have no effect except for random effects like dirty contacts.

So, FWIW,

Jim Henderson

So, does this mean throwing out (I mean...recycling :ahhhhh: ) all 3 batteries, or can the 2 partially discharged batteries be used with another battey with a similar charge level and save some $$$.?

What train did you run? :biggrin:

Jim Henderson
2008-12-30, 15:35
So, does this mean throwing out (I mean...recycling :ahhhhh: ) all 3 batteries, or can the 2 partially discharged batteries be used with another battey with a similar charge level and save some $$$.?

What train did you run? :biggrin:

I reuse hundreds of batteries all the time. A good thing too, when you have two boys who seem to think batteries are free, they are at least to them.

If you have a meter, you can measure the voltage of the cells and get an approximate idea of the relative energy left in the cell. Not an exact science but "close enuf". It works better with the same brand batteries. Measure the cell voltage and group the same brand, similar voltage cells together. You can use these as a set. I often used "worn out" cells in my radios to listen to space alien and ghost hunting reports on late late late night radio. I get several weeks of all night radio from partially depleted cells. In general a battery is usable for various drain levels when they are between 1.0volt and upto full charge, often above 1.5v. The higher the voltage the more powerful the equipment you can run.

A better measure is to check the current output of the cell with an amp meter, but this has certain perils if you don't know what you are doing. Such as damage to the meter or quick draining of the cell, and sometimes sparks, do this only if you know what you are doing. Or, just go to Radio Shack and buy a battery tester, they are pretty foolproof and OK for cell matching.

You can also recharge worn cells but you need a special charger to do it safely, ie no exploded batteries or leaky battery "acid" all over your flashlight, radio etc. Recharging is a game of diminishing returns, ie a full recharge is nowhere near as good as a fresh battery but still useful. They may no longer power your kids RC car, but they will work in radios and small flashlights just fine. Don't use them for critical things like emergency lights etc.

I forget the brand but the They are HO trains made in Czechoslovakia in the 60s. I think the engine was a Burlington and Northern. My forte is electrical enjuneering, ie I plugged car keys into the wall socket as my early start in the profession.

Jim Henderson

Gaiter
2009-01-01, 20:08
rotating battery's works not just in headlamps.... many electronics will pull from one battery more than the other: expample: that remote that has gone dead but you are fresh out of battery's then rotate them... works for many things

atraildreamer
2009-01-12, 17:29
I often used "worn out" cells in my radios to listen to space alien and ghost hunting reports on late late late night radio.
Jim Henderson

Obviously an Art Bell devotee. I have something for you in the way of a "Thank You" for your input. Checkout post #25, 26 & 27.

http://www.whiteblaze.net/forum/showthread.php?t=16970&page=2

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BTW, if you can find a Rayovac Renewal battery charger (no longer made) you can recharge just about any alkaline cell (not just the Rayovac special alkalines made for the charger) by putting a piece of foil over the positive end of the battery. This allows the connection to be made and the recharging to start.

texas hiker
2009-04-22, 10:41
Personally, I no longer buy non-rechargeable batteries. The day before I go on a hike or a camping trip - I will go through all of my gear. That also means that I put the batteries on to charge. I use one of those 15 minute quick chargers - so the batteries are ready in just a few minutes.