Newb confused about series cells.

I was reading through the FAQ and stumbled across this:

"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. "

I thought I understood the difference between series and parallel. Series increases voltage, parallel increases capacity without increasing voltage. But series doesn't increase capacity at all? 100 D cells in series would still have only 1000 mAh?

So, why do 3rd gen 3D maglites get about twice the cell life as 2Ds? Would an older 2D with Nite Ize drop in get the same battery life as a 6D with the same drop in? Or would the voltage limiter (which I assume those bulbs have) compensate and allow for better capacity as well?

As I said in my intro, I'm technologically illiterate. If someone could explain what I'm missing I'd appreciate it. My whole world has been turned upside-down!

The capacity is defined as the amount of energy the batteries can supply. The unit is Joule or Wh (Watt-hour). Watt-hour is calculated by multiplying the average voltage with the Ah (Ampere-hour). Therefore 6 batteries always have the same amount of capacity (energy). It is either 6 x (1.2V x 1 Ah) = 6 x 1.2 Wh = 7.2 Wh or then (6 x 1.2V) x 1 Ah = 7.2 V X 1 Ah = 7.2 Wh.
It is important to realize that Ah or mAh is not really the capacity.

Now, why different flashlights last longer is a complete different story. Kind of why different cars have different mileage with the same fuel.

One step further. Different leds and different drivers have their own efficiencies or inefficiencies.

The example of the NiteIze, theoretically they should last the same time. However my guess is it would likely result in the 2 D lasting longer. Here is my logic. The 6 D batteries would likely supply too much voltage to the led, so the driver will help regulate that. And that excess voltage would be converted to wasted energy via heat.

So: It may be brighter? It may be exactly the same output, It may not work it at all, it may fry something. It all depends on the NiteIze driver. FYI: I don't know anything about the NiteIze you are talking about.

Does that help any?

Additional rough math:
2 D cell system in Series: Each cell in the system is 1.5 volts with 15000 mAh capacity in series = system total = 3.0 volts with 15000 mAh
2 D cell system in Parallel: Each cell in the system is 1.5 volts with 15000 mAh capacity in parallel = system total = 1.5 volts with 30000 mAh

There are some more tiny variations in the system to calculate losses and such. That was just to give you a basic example. Hope I didn't jumble that up, kids yelling and screaming in background. lol

Just wanted to say you're not completely tech illiterate if you're asking intelligent questions like that. As you can see, it's actually a somewhat complicated subject. You already had the basic idea.

mag is correct. At least you asked. Some folks are literally and figuratively in the dark when it comes to flashlights and battery voltages. We were ALL there at one time or another. I had to learn the series and parallel years ago when I was wiring up my first solar system.

drmaxx said:

The capacity is defined as the amount of energy the batteries can supply. The unit is Joule or Wh (Watt-hour). Watt-hour is calculated by multiplying the average voltage with the Ah (Ampere-hour). Therefore 6 batteries always have the same amount of capacity (energy). It is either 6 x (1.2V x 1 Ah) = 6 x 1.2 Wh = 7.2 Wh or then (6 x 1.2V) x 1 Ah = 7.2 V X 1 Ah = 7.2 Wh.

Click to expand...

Okay, now I'm even more confused. If watt hour is capacity, and 6 cells would equal 7.2 Wh, then 1 cell would be 1.2 Wh. So wouldn't 6 cells have more capacity?

Also, was the 1Ah chosen arbitrarily to make the explanation easier? or do different cells have different Ah?

It is important to realize that Ah or mAh is not really the capacity.

Click to expand...

But according to http://whatis.techtarget.com/definition/watt-hour-Wh

"mAh A unit for measuring electric power over time. mAh is commonly used to describe the total amount of energy a battery can store at one time."

???

In regards tot he Nite Ize drop in hypothetical, I was referring to the 2-6 cell 55 lumen drop in pills. They're so ubiquitous I figured everyone here would know all about them by now. I'm curious as to what happens from the energy from all the extra cells when one goes beyond 2. If it's just turned into heat that's very disappointing. If they figured out a way to keep, say, a 6 cell at only 3/2.4 volts (depending on cell type) and saving the rest of the voltage as extra capacity, that would rock. But like I said, I'm technologically illiterate, so I don't even know if that's possible.

I know the older Nite ize drop in with the big bulb on the LED had diffrent ratings for different cell combinations. Each additional cell would add run quite a bit of time. The newer version doesn't have the same chart on the back. I emailed Nit Ize so hopefully we'll find out.

magellan said:

Just wanted to say you're not completely tech illiterate if you're asking intelligent questions like that.

Click to expand...

Thanks. I'm trying!

There are reasons that a 2 cell light lasts longer than a 3 cell light.
1) a 3 cell light is direct drive so the current needed to drive the LED is less and there is 50% more power because of the additional battery.
2) a 2 cell light has to have a boost circuit to raise the voltage up to drive the LED, this voltage is raised from 3v to about 4v or about 33% and the boost circuit is usually not totally efficient so that 33% more power needed turns into closer to 50% more power needed or perhaps even more. With 50% more power on the 3 cell side and 50% loss in power on the 2 cell side we can sort of see the double run time difference between the two.

Lynx_Arc said:

There are reasons that a 2 cell light lasts longer than a 3 cell light.
1) a 3 cell light is direct drive so the current needed to drive the LED is less and there is 50% more power because of the additional battery.
2) a 2 cell light has to have a boost circuit to raise the voltage up to drive the LED, this voltage is raised from 3v to about 4v or about 33% and the boost circuit is usually not totally efficient so that 33% more power needed turns into closer to 50% more power needed or perhaps even more. With 50% more power on the 3 cell side and 50% loss in power on the 2 cell side we can sort of see the double run time difference between the two.

Click to expand...

Now that makes a lot of sense. Except for this:

There are reasons that a 2 cell light lasts longer than a 3 cell light.

Click to expand...

Either I'm really not getting it or that's backwards!

I was thinking of this whole thing backwards- the 6 cell setup using a voltage limiter instead of the two cell setup using a booster (sounds more likely). This is all new to me. Thanks for the... wait for it.... ENLIGHTENMENT.

BTW, when funds permit I plan on doing some head to head testing of 2, 3, 4, 5, and 6 D cell maglites with the Nite Ize drop in to see how cell life compares. I'll be using Tenergy Ds so in the spirit of the scientific method I will also need a smart charger to eliminate the variable of possible different charges. And since Mag won't front me the 2, 5, and 6 cell lights (I asked very, very nicely) I'll have to buy them myself, so, it's going to be a while before I get that undertaken.

London666 said:

Okay, now I'm even more confused. If watt hour is capacity, and 6 cells would equal 7.2 Wh, then 1 cell would be 1.2 Wh. So wouldn't 6 cells have more capacity?

Click to expand...

As I tried to outline above, 6 cells always have 6 times more capacity. This doesn't always translate into more or longer light.

London666 said:

Also, was the 1Ah chosen arbitrarily to make the explanation easier? or do different cells have different Ah?

Click to expand...

Yes, I just chosen your example in the first post. Different cells have different capacity. E.g. eneloop 'classic' have 2000 mAh and the new eneloop pro have 2550 mAh - which is a 27.5% increase in capacity (and you also pay for that).

London666 said:

But according to http://whatis.techtarget.com/definition/watt-hour-Wh

"mAh A unit for measuring electric power over time. mAh is commonly used to describe the total amount of energy a battery can store at one time."

???

Click to expand...

This is correct for one specific battery type, where the average voltage is more or less the same. However, compare two different batteries with each other - e.g. an eneloop with 2000 mAh and a 18650 with 2000 mAh: The eneloop has an average voltage of 1.2 V and the 18650 has 3.7 V - this means that the 18650 has considerably more (3 times more) energy stored then the eneloop.

You could say mAh is capacity and V is the pressure it can release.

dc38 said:

You could say mAh is capacity and V is the pressure it can release.

Click to expand...

Or if you want to have a metaphor: The mAh is the number of tennis balls (electrons) and the V is the height this balls fall from.

drmaxx said:

Or if you want to have a metaphor: The mAh is the number of tennis balls (electrons) and the V is the height this balls fall from.

Click to expand...

I like the waterfall metaphor. The V is the height of the waterfall, and the mAh is how much water is flowing/how big the river is.

richbuff said:

I like the waterfall metaphor. The V is the height of the waterfall, and the mAh is how much water is flowing/how big the river is.

Click to expand...

Not quite: A or mA is the size of the river; mAh is the size of the pond on top of the waterfall.

London666 said:

Now that makes a lot of sense. Except for this:



Either I'm really not getting it or that's backwards!

Click to expand...

I got it backwards.... "oops". My explanation sorts it out though.

I was thinking of this whole thing backwards- the 6 cell setup using a voltage limiter instead of the two cell setup using a booster (sounds more likely). This is all new to me. Thanks for the... wait for it.... ENLIGHTENMENT.

BTW, when funds permit I plan on doing some head to head testing of 2, 3, 4, 5, and 6 D cell maglites with the Nite Ize drop in to see how cell life compares. I'll be using Tenergy Ds so in the spirit of the scientific method I will also need a smart charger to eliminate the variable of possible different charges. And since Mag won't front me the 2, 5, and 6 cell lights (I asked very, very nicely) I'll have to buy them myself, so, it's going to be a while before I get that undertaken.[/QUOTE]

drmaxx said:

Not quite: A or mA is the size of the river; mAh is the size of the pond on top of the waterfall.

Click to expand...

Or mah is the size of the water tank, V is the water pressure due to the height of the tank above "ground" and A is the size of the pipe coming out of the water tank.

For the same output current seen by the LED, a setup that bucks voltage/current slightly on fresh batteries and boosts them afterwards can last longer than a setup that must always boost. When boosting, the battery is drained harder and faster, giving less total energy output.

For batteries in series:
3x NiMH: Good output and runtimes. The battery voltage is roughly that required to drive the LED already. Good efficiency.
2x NiMH: So-so output and then runtimes can be okay.
1x NiMH: For good runtimes, output must be moderate to minimal. 1 battery must always be boosted to drive the led, so runtimes are worst for high output. Example: The Zebralight SC5 only gets a few minutes at max on a single battery.

We can approach this the other way around.

6x NiMH: Output can be whatever you want, basically. You'll take a major efficiency hit because rather a lot of voltage must be bucked and some energy is going to be turned into waste heat. The energy won't be used as effectively as NiMHx3.

Less than 6 but more than 3: Efficiency can improve as the battery voltage approaches that of what's needed to drive the LED. This is the range of "buck only" driving.

With respect to runtimes, we must also consider drive strength aka brightness.

For the same brightness, the number of batteries used directly affects efficiency.

Also, this is why lithium ion is so nice. With 4.2v on tap, we can mostly buck but only slightly. It's a pretty good setup for most LED Vf.

Nice post MV!
+1

drmaxx said:

an eneloop with 2000 mAh and a 18650 with 2000 mAh: The eneloop has an average voltage of 1.2 V and the 18650 has 3.7 V - this means that the 18650 has considerably more (3 times more) energy stored then the eneloop.

Click to expand...

Interesting. I would have assumed the 3.7 would have less life since 3.7 would drain 2000 mAh faster than 1.2, but I get what you are saying. Looks like a lot of my presumptions are backwards!