Teach me about battery placement(and why 2AA is brighter than 1AA)?

[coldlocus]

It was ages since I read any electronics, and wondered how the placement of the batteries affects the light.

1. For example, the L2D is much brighter than the L1D AND has longer runtime. I'm guessing that the 2AA-light is serial connected (right word?), does that mean you add the voltage (1,5+1,5 =3,0V) and that makes the light brighter?

2. Doesnt the current(or voltage if I was wrong before and it's the other way around) have anything to do with how bright the light is?

3. And how does runtime get effected by adding a second battery?

4. What happens if you would connect the batteries side by side (parallell connection?)? You add the current of the two batteries, or was I wrong before and it's the other way around (voltage)? And how is runtime and brightness effected by this?

5. And I noticed that 3 of my 3AAA lights has a carrier with one battery turned opposite the others, does that mean that 2 of them are serial connected and 1 parallell to the others?

Appreciate any help shedding a light over this.

And thanks for a great forum!

EDIT:Sorry, just realised that this thread might be better suited for the electronicsforum...

 

[RCatR]

1. For example, the L2D is much brighter than the L1D AND has longer runtime. I'm guessing that the 2AA-light is serial connected (right word?), does that mean you add the voltage (1,5+1,5 =3,0V) and that makes the light brighter?

The batteries are connected in series, yes this generally makes a light brighter(unless it uses a step-down regulation circuit)

2. Doesnt the current(or voltage if I was wrong before and it's the other way around) have anything to do with how bright the light is?

The basic idea is that voltage is the size of the pipe, and current is the amount of water that flows through it. Voltage X Current=Watts, a better comparison term

3. And how does runtime get effected by adding a second battery?

Runtime generally becomes longer, depending on regulation circuits(if any)

4. What happens if you would connect the batteries side by side (parallell connection?)? You add the current of the two batteries, or was I wrong before and it's the other way around (voltage)? And how is runtime and brightness effected by this?

In pararallel the voltage will stay the same, and the maximum current flow will increase

5. And I noticed that 3 of my 3AAA lights has a carrier with one battery turned opposite the others, does that mean that 2 of them are serial connected and 1 parallell to the others?

3AAA battery holders are usually wired in series for a total of 4.5V (1.5+1.5+1.5)

 

[powernoodle]

www.batteryuniversity.com

cheers

 

[flashy bazook]

I am not a specialist, but basically the runtime on the L2D against the L1D (CE's) is about twice, which is what'd you get for the L1D CE if you use a second battery after the first one expires!

there is a bit of a difference, probably related to the efficiency of the emitter and the LED, but it's second order compared with the first effect.

 

[amanichen]

The basic idea is that voltage is the size of the pipe, and current is the amount of water that flows through it. Voltage X Current=Watts, a better comparison term

Actually, resistance is more analogous to the size of the pipe. Voltage is analogous to the pressure difference between one point in the pipe and another point. A difference in pressure (or voltage) causes a fluid (or current) flow. A pump (or battery) creates a difference in pressure (or voltage.)

 

[TORCH_BOY]

Welcome, usually the more cells the greater the power or greater the runtime or
a combination of both, think of it like having a long range fuel tank fitted to your car

 

[mdocod]

the reason the L2D is both brighter and longer running than the L1D is because the voltage supply of 2 AAs in series is CLOSER to the voltage that the electronics need to boost the voltage to to run the LED (~3.5V).... so the boost regulator runs more efficiently off 2xAA (3V) than it does off 1 AA.

(and of cource the obvious, 2AA has ~double the watt/hours available as 1 AA...)

another factor is that the 2AAs don't have to work as hard when they are together supplying the same driver. So they deliver a better overall performance. The single AA has to supply higher current to makeup for the lower input voltage, As a result it doesn't deliver as much capacity.

 

[2xTrinity]

One limitation is battery internal resistance -- the more current you pull from a battery, the more the voltage starts to "sag" because some of the energy is used up overcoming the internal resistance. With a constant-power driver like the ones in the Fenix light, it is necessary for the circuit to draw twice as much current from one cell at 1.5 volts than it would have to do from 2 cells as 3 volts combined. This will cause more losses due to battery internal resistance. This resistance increases as the battery is used up, this is why direct drive incandescent flashlighst drop in intensity throughout the runtime. With a constant power driver they make up for this by drawing more and more current as the battery voltage sags -- until eventually the battery just can't sustain the current and you get rapidly diminishing brightness. This happens much sooner on one cell than on two.

Also, the driver is more efficient if the input voltage is closer to the output voltage, so having two cells is another advantage, as the 3.0V input is closer to the 3.6V used at the LED than 1.5V input.

Flashlights with two batteries will generally provide more light than a flashlight run off a single battery plus a spare. The advantage of the single cell light + spare is that it smaller overall. I'd recommend running NiMH rechargeable or 1.5V Lithium Primary batteries -- these have much less resistance than alkaline cells and will perform much better, especially in the one cell lights.

 

[coldlocus]

Thanks for all the answeres, you guys are really fast!

Just one thing I still dont get. For example, let's take a 2AA light, would it be any difference if it was parallell connected(higher current?) or serial connected(higher voltage)?
Or wont this mather, only watt matters (will still remain the same if you switch the connections?)? Are there any multibattery lights with parallell connection?
Thanks again.

 

[cratz2]

I think most points have been well covered, esp Trinity's mention of voltage sag. This is why a lot of times on a perfectly well current regulated light that can operate on a wide variety of voltages, runtime will be much longer than twice on a 2xAA config than on a 1xAA cell config. Few stock lights will be in this category though. I'm talking specifically about Mag mods using aftermarket boards.

Just one thing I still dont get. For example, let's take a 2AA light, would it be any difference if it was parallell connected(higher current?) or serial connected(higher voltage)?
Or wont this mather, only watt matters (will still remain the same if you switch the connections?)? Are there any multibattery lights with parallell connection?

Lets use CR123 cells as an example to make for easier real world comparisons. Again, a lot of factors going on here including regulator design and effective wattage of the light, but for example, if you have a Lux III light with a quality regulator, say the Flupic, and you run it on a single CR123 cell, it will be a certain brightness. If you run it on 2 CR123 cells, it should be the exact same brightness plus or minus a VERY small amount, but it will probably run 2.2 to 2.5 times as long as the 1x123 version because the demand put on the cells is considerably less.

Don't mean to sound offensive, but from your example, I get the feeling you don't fully understand booster circuit design. Most of the cheap ones in cheaper lighs work for a certain application and a lot of times they won't work at all (at least not more than a couple seconds) if used with a different combination of batteries. In your example, you ask if you change 2AA cells in series to 2AA cells in parallel, what will change. In most actual, 2AA LED lights, if you hooked them to 2 AA cells in parallel, nothing would happen. You might not have enough voltage for the circuit to realize it even has a power source, or it might only work properly up to 1.9V and it might kill the LED before you realize it even came on.

Good thread though... I'd imagine a lot of folks will get something out of it whether they post here or not.

 

[coldlocus]

Don't mean to sound offensive, but from your example, I get the feeling you don't fully understand booster circuit design. Most of the cheap ones in cheaper lighs work for a certain application and a lot of times they won't work at all (at least not more than a couple seconds) if used with a different combination of batteries. In your example, you ask if you change 2AA cells in series to 2AA cells in parallel, what will change. In most actual, 2AA LED lights, if you hooked them to 2 AA cells in parallel, nothing would happen. You might not have enough voltage for the circuit to realize it even has a power source, or it might only work properly up to 1.9V and it might kill the LED before you realize it even came on.

No offense taken what so ever at all, I REALLY DONT KNOW anything about booster circuit design, or a matter of fact, electronics, until now maybe.

You're saying that the booster circuit needs a minimum amount of voltage to drive it, so if I drop the voltage by parallell connect the batteries, it probably wont even start the light at all (unless the circuit can work on lower voltage, like Fenix L2P)?

I think I did wrong by using LEDs as examples. Another question(hopefully the last), if we go back to basic. Let's say that I connect 2AAs in serie to a incandescent bulb, no boost circuitry etc, direct drive. Would there be any difference if I connected the 2AAs parallell to the incandescent VS serial connection? Brighter or same? Longer runtime? Or nothing at all?

And I keep hearing that Crees can be driven at 1A, how many ampere is a regular AA? CR123?

Sorry for the maybe stupid questions, but I really want to learn what makes a light bright. :candle:

 

[mdocod]

more depends...
I'll give you some examples to explain this:
a 1.2V bulb, ~1W, ~0.8Amp: 3 configurations below:
1. 1 AA alkaline cell. bright and white at first, Runs for many hours of continually dimming light. Somewhere around the 1 hours mark it reach 50% output and from there it is downhill for a few hours longer.
2. 2 AA alkaline cells wired in parallel. voltage is still 1.5V, but with double the capacity(amp hours) Runs slightly brighter than the above example because the 2 cells in parallel have a lower total resistance under the load of the bulb. The result is each cell works about half as hard, and the voltage stays higher longer. The initial "bright white" output will last more than twice as long, and the trail of diminishing light will also last slightly longer than double the number 1 example. This is because you have twice as much power stored- but it is being released at about half the rate by each cell, the cells deliver a better overall performance when they aren't worked as hard.
3. 2 AA alkalines in series: the cells are now in series, the voltage is now 3V. The bulb simply blows immediately because the filament can not withstand the higher input voltage. As you increase voltage across a filament, more current *tries* to flow. A filament designed to to tolerate a watt of power doesn't do so well when you try to shove 2W through it- gets too hot.


Ok.. now lets step up to a 2.4V bulb, but cut the current in half, 0.416Amp. This is still a 1W bulb like the examples above, but it needs a higher input voltage to run at 1W because the filament has been designed differently.
1. 1 AA alkaline cell: the input voltage is only half the ideal voltage for this bulb with 1 cell. The result is a very dim light that puts out of most it's energy in the form of IR heat energy rather than light. This is because the filament doesn't get hot enough at this voltage to make much light.
2. 2 AA alkalines in parallel: The output would be about the same as above(slightly better), but since twice as much energy is stored, it would continue to be a very inefficient bulb for about twice as long. It's now, a longer lasting space heater. lol...
3. 2xAA alkalines in series: now we're up to the appropriate input voltage for the bulb. The bulb burns nice and bright. The output and runtime charts for this setup would look identical to the setup in example 2 under the 1.2V bulb.


ok... now lets look at some more examples:
the 2.4V bulb described above: but now we are going to run it on a single CR123 instead of 2 AA alkalines in series. The CR123 is a 3V lithium cell with 1300mah capacity. a AA alkaline is about 1.5V with about 2800mah capacity. However. The performance of these cells is heavily effected by the load they are under...

When we combine the 2 AA cells in series, the capacity remains the same, it's still 2800mah capacity. but the voltage is 3V instead of the 1.5V of a single cell.

(When we combine the 2 AA cells in parallel the capacity adds up, it's 5600mah at 1.5V)

now there is more to be considered.... back to our example of the 2 AA cells in series compared to the CR123...
if you have a look here
http://www.candlepowerforums.com/vb/showthread.php?t=64660
you see that alkaline cells do not perform anywhere near their rated power when delivering a 0.5A load.. which is pretty close to the load of our bulb here. Most of the cells only delivered about 1500mah capacity. Also notice the discharge curves drop very rapidly, the voltage keeps going down and down and down... this would result in a light that would just keep getting dimmer and dimmer and dimmer.. This is how most flashlights behave.
now take a look at this
http://www.candlepowerforums.com/vb/showthread.php?t=67078
The discharge graphs there show that at 0.5Amp... most CR123s deliver about 1500mah. also compare the voltage over time on these charts.. notice how the lithium cell (CR123) stays nice and flat throughout most of the discharge compared to the alkalines... Since it takes 2 AA cells in series to get the same 3V that the CR123 cell already has, and since the 2800mah alkaline cell only actually delivers about 1500mah into a 0.5A load, You can actually get the SAME AMOUNT of POWER out of a single little dinky CR123 cell, as you can out of 2AA cells.

Now... at very low power demands(like a clock), 2 alkaline AAs will have more energy than a single CR123, but when you get into flashlight power territory, lithium cells are much better.

And I keep hearing that Crees can be driven at 1A, how many ampere is a regular AA? CR123?

cells are not rated in amps.... maybe by reading the above you will get a better feel for this. The current that flows through an LED is determined by the input voltage. a CR123 or AA would barely move any current at all through an LED because it's not enough voltage to get things moving. Diodes have bizarre characteristics, they operate in a tight voltage range. Too little and practically nothing happens, but slightly too much and TOO MUCH happens, "pop."

Batteries are rated in Volts, and Amp/Hours.
if I have a cell that is rated 1.5V, and 2 Amp/Hours. Then I could say that I have a cell that can deliver 2 amps for 1 hour at 1.5V before "dieing"... however, this is rarely the case. A more appropriate way to describe a cell is this:
I have a cell that is rated for 1.5V, and 2.8 Amp/Hours. But the only way I can get 2.8 amp hours worth of capacity out of it is to stretch the test out to MANY hours to reduce the current demands on my cell, because at 2.8amps, my cell falls on it's face and performs very poorly. So I test my cell at a 280ma for 10 hours instead, Which is happily delivers. This is how I arrive at calling it a 2.8Amp/Hour cell.

Some cells can deliver more current than others as well. CR123s can deliver about 2.5amps. They run about 20 minutes at this output, sometimes going into thermal runaway. Alkaline cells could probably never achieve 2.5 amps. SilverFox Tested some D size alkalines at 3 amps... the result was about the same capacity delivered as a AA at 0.5A, pretty bad.

What makes lights bright is more power, more efficiency, or both. Battery configurations don't always decide this. The battery chemistry chosen for the light has a much larger impact on brightness because some chemistries like lithium can deliver much high power without falling on their face.