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PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please sub

CynicalBrad

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

5mW 520nm Green Portable Laser Pointer Point Pen Laser Diode Pointer Osram LD in | eBay

Interesting to see these 520nm diodes in cheap feebay pointers now.
Don't even think I could build anything with one that cheap when the cheapest ~520 diode from DTR is $19 bare diode.
Might be decent for someone that wants a low power 520 and doesn't mind waiting on the rowboat from china.
 



Cyparagon

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

"520nm Green Portable Laser
Laser Color: blue
Power: 5mW
Output:<5mW
Working Current: 500ma"

What a mess. They couldn't even be bothered to use a boost converter. Not sure I would gamble on this, personally.
 

Alaskan

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

7.4 VDC is close to the voltage you would have with two completely drained batteries. I built a pointer with a 520nm Osram laser diode and thought two batteries were fine with it, as long as they were fully charged. However, if they are using a constant current driver, as they should, there will be some amount of voltage drop, or drop out. Because of this you will probably be unable to use the full milliampere rating of your batteries before they run too low to drive the diode. Not that this would be a huge issue, with such a relatively low power laser diode, but something to consider.
 

Cyparagon

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

7.4 VDC is close to the voltage you would have with two completely drained batteries.





I hope you're just having a brain fart. For two lithium cells, 7.4V is nominal, not empty. 4.2V is not the nominal voltage of a lithium cell, 3.6-3.7V is. Here's a chart from google images in case you actually believe otherwise.





Medium-low quality 16340s are 500mAh. If the 500mA current spec is accurate, that's 1C discharge. Therefore, 500mAh/1900mAh would be used in the above discharge curve. It's still ~3/4 full at 3.7V.
 
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Alaskan

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

You most like to answer or post to threads where you can help fix misconceptions, such a teacher! Better you do that then let them fly, that is a great help, thank you.

I better explain my reasons: I never let my Li-ion cells go very far below 3.7 each with this diode (if the 50mw diode) when I am using two batteries without a boost, it just doesn't have enough voltage to drive it if much lower, there is more capacity there, but you just can't use as much of it with that diode, except at reduced output so I call them drained much below 3.7 VDC each with that driver.

I'm basing this on about a half volt drop from the regulator which is the maximum acceptable to me, if you have a regulator with extremely low drop-out, it isn't so bad at 2 X 3.7 VDC or 7.4 volts, if so you can probably do fine at 7.4 VDC with at least 7.150 VDC to the diode if only a quarter volt dropout from the driver, but few are that low. I know, you guys like talking constant current, not voltage, but the typical voltage required at the typical 125 mA of current needed to drive the 50mw diode to that rated output is what I'm referring to.

The nominal voltage for this diode is 6.9 volts at full rated output, but all down hill below that, even then not a lot of capacity remains until you get down to 6.9 V. This is if using the B1 or 50mw, if the pointer has been designed for 30 mw (PL 520_B1_2), you have an extra half volt to work with before you go below the rated voltage for that power output.

Also, depends on the make of the battery, I don't want to spend the time to find curves for the particular battery this unit uses, but here is an idea of the remaining capacity at voltage for the 18650, but this is moot if the voltage is too low to fully drive that diode (after losses) anyway:



If using Panasonic batteries you will have a lot more remaining capacity at 3.7 VDC (if you can get to it, depending upon the driver dropout loss and laser diode), but if using crapFire batteries, probably 10-12% or less which to me is too far drained. Of course, the time to discharge would be different for a lower current draw, but as a general example.
 
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Cyparagon

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

I think I've found the problem here. You're making the classic mistake of assuming the open-circuit voltage reflects the voltage under load. The open-circuit voltage doesn't tell you what the voltage is under load, and is often substantially higher. Dave Jones from the EEVBlog has made several videos explaining this. The search term "probes the monkey" will probably get you there if you're curious.

It might tell you how much charge is remaining, but only if you're familiar with that particular cell, and obviously varies a lot between cells. 3.7V doesn't do you any good if it drops to 1V under load. The device being powered doesn't care what the open-circuit battery voltage is, it only cares if the cell can supply the operating voltage while under load.

I've found a review for the 18650 black. If we look at the 1C curve (~3A) to compare apples and apples, this cell has used 600/3200mAh at 3.7V. It's still 80% full.



The complex subject of electrochemistry isn't as simple as poking the cell with a voltmeter.
 

Alaskan

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

No mistake, why assume an open circuit battery voltage measurement on either my part, or those of the individual who came up with that test data?

I don't want to migrate too far away from my main point in the earlier post that using two Li-ion batteries with the 50mw PL520 laser diode will not allow the full capacity of the batteries to be utilized, due to the higher voltage this diode needs and are not well matched in such a configuration, even worse if a constant current regulator with a relatively high drop out voltage is used. Better to use a boost driver with a single battery, which is what I thought you were saying earlier too. I think we find ourselves in general agreement regardless if the 30 or 50mw diode is used in that pointer..

I don't know, who uses their pointer that long in a single use to drain it down so far it quits anyway and after all, they can be recharged. I'd buy that pointer whether it used the 30 or 50 milliwatt diode except I don't want to have it mailed to me here in Iraq. I'd be happier if it used a single 18650 battery with a boost CC regulator, but the price is great as well as far lower divergence than the higher power 520nm green lasers.

One question though, we are assuming this pointer has a CC regulator, it might not at that price, these specific diodes can run without them when using two Li-ion batteries, I've proven that myself and not had a failure yet with mine. I'm not saying it is right or good practice, it is NOT a good thing to do, just that I have done so without failure, knock on wood. This is the ONLY diode I have ever used which can survive that, when it overheats due to high current it dims and recovers after letting it cool. DTR observed this on his own tests too when pushing the current too far. This is one tough little diode, your own milage may vary, so please don't hold me to it if someone here tries that, yours might behave differently or get hotter quicker which might cause failure, depending upon the heat sink used. Regardless, I believe the life would be reduced running this diode without a CC regulator, just that mine has not reached end of life yet, you can't know until observing it, but there is a high probability it will.

 
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CynicalBrad

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

Once I get some funds aside (hopefully next paycheck) I might order one and tear it apart carefully to see how they are driving the diode. Who knows, might even actually be close to 5mW unlike the 532 pointers.

The description seems to suggest that it would actually be lower power as it states no visible beam etc and the only green that runs that low decently is the PLT5-510 which is also lower wavelength than the rest of the green diodes.
At least to my younger eyes, a few nm in that range makes a HUGE difference that would make it worthwhile to have one.
 

Alaskan

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

I believe it is likely the 30mw diode and that you can see a beam, if using in the dark, just that it will be a fairly dim beam. My guess is if you put it on a laser power meter it will probably measure 20-25mw.
 

Cyparagon

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

I've got one of the really early ones that also runs at 7.4V, and it was ~25mW if memory serves. That's my wild guess as well.

No mistake, why assume an open circuit battery voltage measurement on either my part, or those of the individual who came up with that test data?

Because that's the only measurement that makes sense with the table you've posted. Every discharge curve of lithium you'll ever see puts lithium dead at somewhere around 2.8-3.0V, not 3.7V.
 

Alaskan

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

Damn, you are trolling tonight aren't you... go back and re-read.

If you would do so with your eyes open, you will see I agree with that, I am simply referring to the battery for all intensive purposes being DEAD when used with the PL520 50mw laser diode driven by common CC regulators because the voltage is too low for it to produce much power when they discharge too far down, even though they have remaining capacity otherwise for other uses, or other diodes.

You are being obtuse, right? How many times must I say so without your coming back with the same statement disregarding what I am talking about? At this point I am starting to wonder who is behind some of the trolls here, you seem to enjoy it so much.... Of course, I'm kidding, but really bro.
 
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ricktrent4

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

You most like to answer or post to threads where you can help fix misconceptions, such a teacher! Better you do that then let them fly, that is a great help, thank you.

I better explain my reasons: I never let my Li-ion cells go very far below 3.7 each with this diode (if the 50mw diode) when I am using two batteries without a boost, it just doesn't have enough voltage to drive it if much lower, there is more capacity there, but you just can't use as much of it with that diode, except at reduced output so I call them drained much below 3.7 VDC each with that driver.

I'm basing this on about a half volt drop from the regulator which is the maximum acceptable to me, if you have a regulator with extremely low drop-out, it isn't so bad at 2 X 3.7 VDC or 7.4 volts, if so you can probably do fine at 7.4 VDC with at least 7.150 VDC to the diode if only a quarter volt dropout from the driver, but few are that low. I know, you guys like talking constant current, not voltage, but the typical voltage required at the typical 125 mA of current needed to drive the 50mw diode to that rated output is what I'm referring to.

The nominal voltage for this diode is 6.9 volts at full rated output, but all down hill below that, even then not a lot of capacity remains until you get down to 6.9 V. This is if using the B1 or 50mw, if the pointer has been designed for 30 mw (PL 520_B1_2), you have an extra half volt to work with before you go below the rated voltage for that power output.

Also, depends on the make of the battery, I don't want to spend the time to find curves for the particular battery this unit uses, but here is an idea of the remaining capacity at voltage for the 18650, but this is moot if the voltage is too low to fully drive that diode (after losses) anyway:



If using Panasonic batteries you will have a lot more remaining capacity at 3.7 VDC (if you can get to it, depending upon the driver dropout loss and laser diode), but if using crapFire batteries, probably 10-12% or less which to me is too far drained. Of course, the time to discharge would be different for a lower current draw, but as a general example.
keep up the good work and "nice chart" if you made it and ignore rude people :D
 
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Cyparagon

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

Yes, I may have misread something. If you're correcting yourself when you said "7.4 VDC is close to the voltage you would have with two completely drained batteries."... to saying "3.7V per cell is the minimum voltage for a direct drive for a particular diode", then I have no disagreement with that.

Just as long as we agree: 3.7V doesn't mean an empty lithium cell. :beer:

ignore rude people :D

If you think I'm being rude NOW, you and I are not gonna get along :na:
 
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CynicalBrad

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

Can we take the battery chemistry voltage/capacity chart debate to it's own forum? This is spamming my email with all this craziness on the internet finds thread and I am sure I do not happen to be the only one.

Some interesting data has come to light but this does not feel to be the place for it.
 
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Alaskan

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

This ought to help, some good information instead of useless public banter: The seller responded to a question on this pointer, they said it produces 10mw, that they use a 10mw diode. They also stated they put it on a LPM to confirm the output at 10mw.



5mW 520nm Green Portable Laser Pointer Point Pen Laser Diode Pointer Osram LD in | eBay

If the 10mw Osram laser diode, it normally produces rated output at 5.4 VDC. The concern I had regarding the batteries draining below the operating voltage of the diode too early (if typical) is now pushed to the side and probably not a factor, unless you get an odd diode. This explains the low price, these diodes can be purchased fairly cheaply. Still a good price for the unit regardless.

http://www.osram-os.com/Graphics/XPic9/00206515_0.pdf/PLT5 510.pdf


Model NO.: PLT5 510
Material: Element Semiconductor
Package: To18 5.6mm
Application: Light Sources
Lasing Wavelength: 510nm~530nm (515nm typical).
Life Time: 20000 Hours
Pd Reverse Voltage: 30V
Operating Voltage: 5.4V typical, 7.0 max.
 
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Laserbuilder

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Re: PERMANENT THREAD: Ebay& other internet FINDS of interest- read all the OP please

A set of CO2 laser optics is on sale at e-bay. A BIG (1.75" dia) ZnSe lens and a set of total reflecting mirrors. And only for 150$. I think, this is a great bargain. I have already bought a couple of lenses so I don't going to buy this lot.


Huge ZnSe lens + HR total reflectors set for high power big CO2 laser | eBay
 
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