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How much do good batteries matter?

Joe Mo

Joe Mo

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Just curious, I searched this and didn't find much. Can someone put in perspective how much good batteries matter when it comes to straight power output? I know I have 2 18650's that have almost double the power difference in some lasers I have. What 18650's/chargers are recommended? And are there examples of LPM results with bad/good cells?

thanks guys, still learning :)
 
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Cyparagon

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Laser diodes use a constant current driver. Crappy batteries will give you the same power as $50 batteries although they won't last as long.
 
BShanahan14rulz

BShanahan14rulz

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Power sags from bad batteries because when you pull current from a battery, its voltage sags a little as it is worked. The more current you pull, the lower the voltage sags. When you stop pulling current, the voltage slowly rises back up to a settling point. Good batteries do this too, but older ones will sag more.

The older a cell is, the higher its internal resistance will get. This means that it is harder and harder to pull the amount of current you need from the cell. What can happen is that the driver will try to pull more current from the cell, and the cell's voltage will drop dramatically, to a point where it isn't enough voltage for the driver.
Sometimes, damage that has been done over the years will create surface imperfections that can also negatively affect the performance of the cell.

The main lesson to take from all of this is old cells are generally bad.
The lesson that is harder to learn is that cheap cells are generally old cells that have a new outer wrapper on them to display the fake made-up capacity and company name.
 
jayrob

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Also, for high current 445 builds using a single 18650 with a FlexDrive. (common)

You need a quality battery that can handle high current draw... (like AW)

A FlexDrive will use current to boost diode voltage demand as your battery drains and drops in voltage.

So that means your battery must give more and more current as it drains!

Cheap batteries just don't cut it...
 
bobhaha

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They matter quite a lot. A good battery will not sag as much as lower quality brands at higher currents/voltage draws. Here I LPM my Firedragon III. Check out the difference in power peak AND stability with different batteries.

This it the output power with a GTL brand battery...
Lasersman%20300mW%20532nm%20GTL.bmp


This is the output power with the included ultrafire battery...

FireDragon_LPM.jpg


This is the output power with a used battery that I pulled out of a laptop...

Lasersman%20300mW%20532nm%20LB.bmp
 
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Cyparagon

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Try those graphs on a non-DPSS pointer next time. I'm sure you'll see the variation is much less, if not zero.
 
InfinitusEquitas

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Cyparagon said:
Try those graphs on a non-DPSS pointer next time. I'm sure you'll see the variation is much less, if not zero.
Click to expand...

They are still very much there though... the same laser that does 1.2-1.3W with an AW IMR for example, does only ~1.1W with a cheap ultrafire. The ultrafires don't seem to last nearly as long either.
 
BShanahan14rulz

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Cy was just commenting on the graphs posted by Bobhaha, talking about the choppiness of the graphs.

Personally, I find the graphs very misleading. According to his graphs, ultrafires are the best. I think, though, that bobhaha might just not have any better cells, and that is understandable. For many things, an old, used 18650 does the job just fine. For most lasers, old 18650s should be fine. It is when you start having to pull a lot of current that they start falling flat on their face.

Also keep in mind that many companies rip off of ultrafire's name, which is itself a modified version of an American company's name. Some of these clone companies don't even change the name, leaving us to wonder if it is the real ultrafire or one of the fakes. Don't even get me started about names like fandyfire and spiderfire. What's next, StartaFire?
 
justinjja

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fully charged it will rarely make a difference, unless you have terrible batteries.
The time the battery can maintain output @ fully charged level is where you will notice a difference.

If you are you are using a linear driver, quailty of the batteries is less important
with a boost driver, it starts to matter more.

None if this aplies to... say an overspec pen laser that runs on Alkaline AAA's in which case, good batteries will generaly make a big difference.
 
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rhd

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This question is a lot more about understanding your laser build, than it is about understanding your batteries. You need to think about what your driver needs as an input, and what your chosen battery combination provides as an output. Then, you need to think critically about what the limiting condition will be. For example:

- If your build is using a boost driver, and thus you're relying on increased current to create voltage, and perhaps you also have a small cell (like a 14500), then your limiting condition will be the current supply capabilities of a 14500. In that scenario, you'll want a good high-drain cell like an AW IMR.

- If your build is using a buck driver, but your cell's voltage surplus (above Vf) is really small, then you might want decent cells that won't sag in voltage quickly.

- If your build is using a linear driver, but maybe it's using 2 cells with a total Vin that (even when fairly depleted) will exceed Vf + VDropout, then maybe you don't care about voltage sag at all. Since it's a linear setup, high drain might not be important either. In that scenario, you might be looking for sheer highest capacity per cell, in which case something like a good AW IMR is actually poor choice.

You get the point. The question isn't "Are good cells important?".
The question is "What will be the first power-limiting condition for my build, and what's the best cell to use use to avoid this for as long as possible?"
 
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LarryDFW

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In my opinion . . .

internal resistance is the most important battery spec.

It is the amount voltage will sag under a given load.

It will determine how long a given laser will run, before the power starts dropping.

Newer cells with higher voltage will help in "boost designs",

or direct drives for for 445nm lasers.

All battery protection circuits add some internal resistance.

Larry
 
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Joe Mo

Joe Mo

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rhd said:
This question is a lot more about understanding your laser build, than it is about understanding your batteries. You need to think about what your driver needs as an input, and what your chosen battery combination provides as an output. Then, you need to think critically about what the limiting condition will be. For example:

- If your build is using a boost driver, and thus you're relying on increased current to create voltage, and perhaps you also have a small cell (like a 14500), then your limiting condition will be the current supply capabilities of a 14500. In that scenario, you'll want a good high-drain cell like an AW IMR.

- If your build is using a buck driver, but your cell's voltage surplus (above Vf) is really small, then you might want decent cells that won't sag in voltage quickly.

- If your build is using a linear driver, but maybe it's using 2 cells with a total Vin that (even when fairly depleted) will exceed Vf + VDropout, then maybe you don't care about voltage sag at all. Since it's a linear setup, high drain might not be important either. In that scenario, you might be looking for sheer highest capacity per cell, in which case something like a good AW IMR is actually poor choice.

You get the point. The question isn't "Are good cells important?".
The question is "What will be the first power-limiting condition for my build, and what's the best cell to use use to avoid this for as long as possible?"
Click to expand...

this is very helpful, thanks rhd and everyone else here, I feel lost sometimes trying to find correct info :can:
 
Cyparagon

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InfinitusEquitas said:
The same laser that does 1.2-1.3W with an AW IMR for example, does only ~1.1W with a cheap ultrafire.
Click to expand...

That means your driver isn't regulating properly. Don't get me wrong though, I hate ultrafires as much as the next guy. ;) But I really doubt the internal resistance is high enough to drop the terminal voltage down to <insert minimum driver voltage here>.
 
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rhd

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Cyparagon said:
That means your driver isn't regulating properly. Don't get me wrong though, I hate ultrafires as much as the next guy. ;) But I really doubt the internal resistance is high enough to drop the terminal voltage down to <insert minimum driver voltage here>.
Click to expand...

Well, if it's a boost driver, his observation might have been a reasonable one. A TrustFire and an AW IMR might not be THAT substantially different in terminal voltage, but they could certainly show a large difference in current delivery ability.

In a boost, if you need to draw like 2.5A @ 3.7V to supply 1.5A of output at the boosted output voltage, then I can see a TrustFire not cutting in. The symptom would be lower output voltage, because technically your boost driver wouldn't be hitting its regulated output target. Put in an AW IMR with the ability to supply the required 2.5A, and your driver would work as intended.
 
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Cyparagon

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Well, the minimum voltage for a flexdrive looks to be 2V. With a 3.6V battery terminal voltage, you'd need an internal resistance of 640mΩ for the voltage to sag that much. I just measured 95mΩ on one ultrafire, and 120mΩ on another. Even the 10-year-old laptop battery pulls I have are only around 400-500mΩ.
 
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