A thread about voltage

[Accutronitis]

I see a lot of talk about amperage this and amperage that but what about voltage, can a few watt blue laser be ran off 3.6 volts ?

 

[Rivem]

Yes, but likely only for a moment before it fries as its resistance decreases.

You need a constant current source for most laser diodes since their voltage (through resistance) changes as they warm up, but they always need the current to lase.

Yes, you could use a constant voltage supply to power some diodes, but you usually won't ee it unless it's something really big and not very sensitive. Even then, current is still the key to lasing.

Edit: Then again, your question doesn't clarify if you're talking about diodes or modules with drivers.

 

[Accutronitis]

Let me rephrase my question, could the laser diode that is in a cheap Chinese host run on 3.6 volts with a driver change ?

The laser is now running on 7.4 volts.....

 

[Rivem]

Let me rephrase my question, could the laser diode that is in a cheap Chinese host run on 3.6 volts with a driver change ?

The laser is now running on 7.4 volts.....

With a boost driver, yes. Many lasers you see here run on a single 18650 for 445nm and 405nm. You just need something that can slightly increase the voltage the diode sees for ideal operation.

Cheaper linear and switching power regulators cut the voltage down from the battery, so there's not quite enough for a blue or violet diode.

 

[Crazlaser]

I'm not sure about a blue laser but the 800mw Oclaro laser I have uses 3.6 and the 800mw 980 uses the same.

 

[Rivem]

I'm not sure about a blue laser but the 800mw Oclaro laser I have uses 3.6 and the 800mw 980 uses the same.

The operating voltage of laser diodes generally depends upon their semiconductor bandgap.

For red-ir, this badgap is smaller and requires lower voltages.

Blue and violet have a larger bandgap and therefore require more voltage to operate. That's why they'll need a boost driver for a single battery.

 

[Accutronitis]

The reason I asked the question is I'm looking to power the most powerful blue laser diode/driver/boost I can get/afford and power it with a custom host that houses a battery which is rated at Ni-Cd 3.6V 1.8Ah, Is this possible ?

 

[Rivem]

The reason I asked the question is I'm looking to power the most powerful blue laser diode/driver/boost I can get/afford and power it with a custom host that houses a battery which is rated at Ni-Cd 3.6V 1.8Ah, Is this possible ?

Yeah. As long as you have a boost driver, it should work. Though, that Ni-Cd might not give you great performance compared to some of the li-ion batteries. A single good 18650 will have more capacity with better current characteristics.

 

[Accutronitis]

But it should be light years above 2 each 16340 3.7v 2800mAh batteries I would think ?

 

[Rivem]

But it should be light years above 2 each 16340 3.7v 2800mAh batteries I would think ?

Where are you getting that from? All Li-Ion batteries are going to perform a bit better than any Nickel Cells in both load performance and capacity. Nickel cells are mainly just safer and can be cheaper.

You said you were going to use a 1.8Ah battery. How is that supposed to be better than 2×2800mAh (5.6Ah)? Granted, you do need good cells to trust that rating, and it's probably a good bit lower.

 

[dden4012]

Yes, but likely only for a moment before it fries as its resistance decreases.

I had mentioned this not long ago and was told this is not correct. But I know I have read this before. I would definitely like our upper level members to clarify this.

 

[Rivem]

I had mentioned this not long ago and was told this is not correct. But I know I have read this before. I would definitely like our upper level members to clarify this.

It does depend upon the resistance vs temp curve of the diode itself. Basically, the diode has to maintain a resistance that won't let too much current through from the battery's supply voltage.

Over-current could happen with any diode that develops an operating voltage below what the battery could have and why CC drivers are important in our sort of laser.

I'll admit that you can probably get away with this in a few blue and violet high power diodes, but it's not a great idea if you want to keep the diode running. Either way, turned out to be inconsequential to what Accutronitis wants to know.

 

[Accutronitis]

Where are you getting that from? All Li-Ion batteries are going to perform a bit better than any Nickel Cells in both load performance and capacity. Nickel cells are mainly just safer and can be cheaper.

You said you were going to use a 1.8Ah battery. How is that supposed to be better than 2×2800mAh (5.6Ah)? Granted, you do need good cells to trust that rating, and it's probably a good bit lower.

I can believe that The very light Li-Ion batteries (2 cells) on the right have more capacity than the Ni-Cd battery (3 cells) on the left ? Is that correct ?!?



How can that be ?

If there is no mistake and the 2 batteries on the right are that much better than the 3 on the left i'll find Li-Ion cells that will fit in the same space as the Ni-Cd's did !

 

[Rivem]

No that would be 5600 mAh (mega Amp hours) with the Ni-Cd being 1.8 Amp hours

This kills me as an engineer. Especially as an EE.
Please read this: How to convert milliamps to amps (A)

Edit: Your edit makes no sense. You divide your 2800mAh by 1000 to get 2.8 Ah. Charge is inconsequential.

 

[WizardG]

If you look at the data sheet for any laser diode I've ever encountered it will show that the forward voltage of the diode falls as temperature increases. Higher temperatures also lower the efficiency of these diodes. So if you connect a laser diode to a voltage source it will draw more and more current as it heats up. It's called thermal runaway, and it's why we use CC drivers.

 

[Rivem]

I can believe that The very light Li-Ion batteries (2 cells) on the right have more capacity than the Ni-Cd battery (3 cells) on the left ? Is that correct ?!?



How can that be ?

Li- cells are the most energy dense battery chemistry that's widely available. They carry more energy per volume and mass than any other battery you can get. They're usually at least twice a Ni-Cd in energy density.

Google "energy density of batteries".