Battery rating question

[degarb]

I've a question. I see at sears that Dorcy has a 1 watt lux rated at 20 hours 3xAAA. While Brinkman 3xAAA was rated at 15 hr.

I assume, correct me if wrong, that the Watt is juice used not watt of light. (1 watt should give 45 to 90 lumens with today technology) So, 1 watt 3xAAA should always have same battery life with all manufactures. Or not?


Also (for those good in electronics), why does more batteries in series yield a better hours per battery ratio? This true, at least according to package rating and my experience.

 

[divine]

From what I've read here, what the packaging says for watts doesn't always mean a whole lot.

Maglites list a 3 watt LED, but they can run however much power into a 3 watt LED they want to and get a wide range of light out of that LED.

Also if it has a high and low selection, you could have a 3 watt light that puts out 200+ lumens but will list 55 hours as the run time because it also has a lower power mode.

I'm sure someone can give you some better numbers on those lights.

 

[divine]

I just saw your other question.

The voltage is added when you run the batteries in series. If you put 3 1.5 volt batteries in series, you essentially have a 4.5 volt battery... so, one battery versus the three if they needed the same power out of each one, will require 1/3 of the current (amps) from the three batteries compared to the one.

Does that make sense?

 

[degarb]

I assume a 3 cell series uses a resistor v. 1 or 2 cell. And logically 3 cell in series would be same as 3 cell on parallel. Perhaps, it is regulators that are killing battery life, knocking back the latesst lines of led usefulness to near halogen batterylife numbers.

I wish to mod my 3 aaa to a rear 4 AA. Without a resistor, will this cook my unit or kill battery life with too high voltage overrunning the resistance? Can I buy a reostat that I can put inline with batter pack. Or, What resistor will I need to cut 1.2x4=4.8 volt back to 4.5 or 4 volt range?

 

[TigerhawkT3]

A "1 watt lux" is a Luxeon I emitter from Lumileds. These are speced to run at about 1 watt. That's all that means.

I'd like to correct some apparent misconceptions about voltage and current. From the Welcome Mat:

Q: Please explain volts, amps, watts, and C.
A: That's not a question, but okay. Volts are electrical potential, amps are electrical current, watts are total power equal to volts*amps, and C is electrical current as a function of battery capacity. Think of volts as the width of a pipe: In general, a wider pipe has more punch than a narrower one. Think of amps as the water flowing through a pipe: Some pipes can only handle little trickles of water, and others can handle lots of water pushing through with great force. Think of watts as a combination of volts (pipe width) and amps (flow of water): A large pipe with water flowing through really slowly has the same output as a small pipe with water blasting through it. This is why high-voltage applications are preferred over high-current applications, as a stream of water zooming at 200mph through a 1"-diameter pipe is much more dangerous and difficult to maintain than a calm, 3mph flow of water through a 4'-diameter pipe. As for C rates, that's just a function of current draw and battery capacity. Any power source discharged at a 1C rate will be depleted in 1 hour, any power source discharged at a .25C (or C/4) rate will be depleted in 4 hours, and so on. As an example, a 1.8Ah AA NiMH capable of an excellent 10C discharge rate can manage 1.8*10=18 amps.

Q: What are series and parallel?
A: Series connections have a device's positive terminal connected to the next device's negative terminal. This is what you get when you line up some ordinary C-cell alkalines (for example) end-to-end, like in a Maglite or other flashlight. This arrangment adds up the voltages of the cells. Such a battery neither handles more current nor contains more mAh capacity than a single cell. This is the opposite of a parallel configuration, which has positive terminals joining together and negative terminals joining together. An example is those 3AA>1D adapters where all three AA cells' positive terminals meet at the top, and all their negative terminals meet at the bottom. Such a configuration has the same voltage as a single cell, but can handle more current draw (or contains more capacity). For example, 1AA alk can push about 500mA at around 1.5V for about four hours. 2AA alks in series can push 500mA at around 3V for about four hours. 2AA alks in parallel can push 1000mA at around 1.5V for about four hours (or 500mA for eight hours, and so on).

Actually, I think you both would benefit from reading it. It should answer most if not all of your questions, as it was made for this exact situation. It's available here and here.

 

[GaryF]

Actually, I think you both would benefit from reading it.

I think that's a little harsh.


The responses from devine and degarb were technically correct. 3aaa cells in series will service a 1 watt demand as 4.5 volt * .22 amp = 1 watt or 3aaa cells in parallel as 1.5volt * .67amp = 1 watt. Either way, the load on each cell is around .22 amp, with any difference coming from differences in regulation efficiency. Typically we would see better regulation efficiency at the higher voltage – 3 cells in series – than we would with the cells in parallel.

 

[TigerhawkT3]

I think that's a little harsh.


The responses from devine and degarb were technically correct. 3aaa cells in series will service a 1 watt demand as 4.5 volt * .22 amp = 1 watt or 3aaa cells in parallel as 1.5volt * .67amp = 1 watt. Either way, the load on each cell is around .22 amp, with any difference coming from differences in regulation efficiency. Typically we would see better regulation efficiency at the higher voltage – 3 cells in series – than we would with the cells in parallel.

How was that harsh?

Technically, yes, three cells in series contains the same power as the same three cells in parallel, but the two configurations aren't interchangeable. Your explanation doesn't address whether the driver in the flashlight in question has the same efficiency at 1.5V as it does at 4.5V, or that it would even work at such a low voltage. It really only applies to buck circuit flashlights, and it's not clear whether this light uses a circuit at all.

You have to be very careful giving such loose responses to statements such as "logically 3 cell in series would be same as 3 cell on parallel".


I apologize in advance if any of this offends anyone.

 

[GaryF]

How was that harsh?

I think your intent was good, but I would have been left feeling like I had been corrected by somebody who didn't read what I had typed.

By saying

I'd like to correct some apparent misconceptions about voltage and current

and citing sections of the FAQ relevant to that topic, then finishing with

Actually, I think you both would benefit from reading it. It should answer most if not all of your questions, as it was made for this exact situation. It's available here and here.

would lead one to think that there were some errors in their statements, when at most there was an ambiguity in one of the posts. It looked to me like they had a pretty good handle on it.

 

[mdocod]

going to pull this in another direction for a moment, and at the same time clear up some of the runtime confusion..

MOST 3xAAA lights are, by CPF standards, junk, for the following reasons:

manufactures use 3xAAA configurations on LED lights because the voltage requirements of an LED can be met with little to no current control at all. In most cases it's a simple resistor and nothing more. So the LED will steadily dim as the batteries drain, in the case of alkaline cells, that means a ton of runtime below 50% initial output. The 1W ratings is basically meaningless on a light like this, because most of the run is below 1W anyways. In reality, because as the voltage drops, the current across the LED continues to drop as well, these 3xAAA direct drive configurations will probably continue to make noticeable light at the emitter for days, where the company decides to call the output "useful" pretty much determine how they calculate runtime. One company might think that 1 lumen is still "running" and count every minute down to where it falls below 1 lumen useful runtime, that's how we get super inflated runtime ratings. And why one manufacture could say 15 hours while the other says 20, in reality they both probably could have said 100 if a fraction of a lumen were considered by them to be acceptable output.

3xAAA cells are a very poor source of power as far as volume/watt/hour is concerned. 2.7watt/hours is about typical for a stack of 3AAA cells. Surprisingly, a similar sized light could be made that uses 1 C cell instead, it would require a boost regulator, (which would make it more expensive to manufacture), but it would have more than double the available watt/hours, and would run the LED at the full 1W for a much larger chunk of the total runtime, making better use of the cell. Even a single CR123 cell has more juice than 3 AAA cells and takes up substantially less space.

Now, if you do the math on it, you would realize, that if what I said before is true, that a stack of 3 AAA cells has about 2.7W/H capacity, then obviously the light shouldn't run for any more than 2.7 hours at 1 watt output, so it becomes very apparent that the light is NOT using 1 watt of power through the run. over 15 hours, it would actually be averaging something like 0.2W, pretty misleading eh?

 

[drmaxx]

@mdocod: Now that's a good explanation! I actually knew the math already - still enjoyed your text. Well said.:twothumbs

 

[TigerhawkT3]

I think your intent was good, but I would have been left feeling like I had been corrected by somebody who didn't read what I had typed.

By saying and citing sections of the FAQ relevant to that topic, then finishing with would lead one to think that there were some errors in their statements, when at most there was an ambiguity in one of the posts. It looked to me like they had a pretty good handle on it.

Gotcha. I just wanted to make sure no one broke their light by using series where parallel was required, or vice versa. Sometimes it's easier to start fresh than to tweak an existing understanding.

As for recommending a read of the Welcome Mat, I think it's just a great resource, especially for those new to the hobby (now THAT was a shameless plug! ).

 

[degarb]

What modifications have others made to increase run times without decreasing light?

Are there thermal mods that can help? Lens mod? What battery pack mods have others done? (I drilled two screws into the brinkman 1watt and use banana clips and a 3 AA pack glued to headband. The good light seems to last 9 hours, instead of the 4.5 hours with AAA.)

 

[GaryF]

It's usually easier to increase brightness with a higher efficiency led. Increasing runtime on an existing light requires a change in the circuit, which is a little more difficult in most lights.

Using different batteries is of course another way to do it, I've been contemplating something similar. I want to take the head of a light that runs off of a CR123 battery and put it in a headlamp with a 2AA power source. The result should be almost double runtime with the correct AA battery choice.

 

[degarb]

going
Now, if you do the math on it, you would realize, that if what I said before is true, that a stack of 3 AAA cells has about 2.7W/H capacity, then obviously the light shouldn't run for any more than 2.7 hours at 1 watt output, so it becomes very apparent that the light is NOT using 1 watt of power through the run. over 15 hours, it would actually be averaging something like 0.2W, pretty misleading eh?

Sounds about right: 3aaa 1watt lux at 3 hours has noticeable drop, I swap at 4 to 4.5 hours. With AA at 9 hours, might as well finish a 10 or 11 hour day. But I am often amazed at how well the Garrity does at 11 hour mark, probably better than some since it has several lesser levels I can switch to when not needing the whole beam.

But my gripe is this entire day performance would never be possible with a regulated light.

 

[LukeA]

Sounds about right: 3aaa 1watt lux at 3 hours has noticeable drop, I swap at 4 to 4.5 hours. With AA at 9 hours, might as well finish a 10 or 11 hour day. But I am often amazed at how well the Garrity does at 11 hour mark, probably better than some since it has several lesser levels I can switch to when not needing the whole beam.

But my gripe is this entire day performance would never be possible with a regulated light.

Not on 3AAA, maybe on 3D.

 

[mdocod]

But my gripe is this entire day performance would never be possible with a regulated light.

actually if it were a 1C light, rather than 3AAA, and you ran it on a 6000mAH NIMH, and the regulator were set to run at 200mA at the LED (~2/3W), assuming 80% regulator efficiency, it would run for over 8 hours in full regulation and on a decent LED would still deliver over 50 solid torch lumens. A 1D variant could do the same for 16+ hours.