LPF Donations
Links below open in new window
ArcticMyst Security by Avery
Direct driving nubm44 with 1 or 2 18650 ?
- Thread starter sddrummer
- Start date
- Joined
- Nov 28, 2017
- Messages
- 65
- Points
- 0
You know wrong.
- Joined
- Sep 12, 2007
- Messages
- 9,399
- Points
- 113
According to the tests I did on this diode several years ago, you can actually direct-drive them. The voltage of a single lithium cell will not push enough current to damage these.
Of course, the downside is that the laser is never in regulation. It will never be at full power, and the power will drop continually as the battery drains.
No, two lithium cells in series will pop it for sure.
Of course, the downside is that the laser is never in regulation. It will never be at full power, and the power will drop continually as the battery drains.
No, two lithium cells in series will pop it for sure.
Benm
0
- Joined
- Aug 16, 2007
- Messages
- 7,896
- Points
- 113
A bigger downside is that a laser diode's forward voltage drops with temperature, or the current it pulls off an unregulated supply increases as it gets hotter.
The forward voltage of a NUMB44 is attractively close to attempt direct drive from a lithium cell.
At least one of two things will be a problem though: Either diode doesn't get to full power leaving you with a dimmer beam, or it will heat up, draw more current, heat up more etc and go into thermal runaway until it is destroyed.
And if those curves are correct either could happen, really. If you have a freshly charged cell at 4.2 volts it will draw 4 amps or so, heating it up and going for thermal runaway. If the cell is at 3.8 volts or so it'll start outputting a watt or so and then die off slowly as the battery discharges further.
Which scenario unfolds also depends on cooling and ambient temperature - you could get the 'fizzle and go out' scenario on a cold day and the thermal runaway on a warm one.
You should really use a driver, or -perhaps- use a PTC/polyfuse between battery and laser to prevent the runaway problem to some degree - it might work, i guess they might do this in china, but you'll get an E or F from any electrical engineering class
The forward voltage of a NUMB44 is attractively close to attempt direct drive from a lithium cell.
At least one of two things will be a problem though: Either diode doesn't get to full power leaving you with a dimmer beam, or it will heat up, draw more current, heat up more etc and go into thermal runaway until it is destroyed.
And if those curves are correct either could happen, really. If you have a freshly charged cell at 4.2 volts it will draw 4 amps or so, heating it up and going for thermal runaway. If the cell is at 3.8 volts or so it'll start outputting a watt or so and then die off slowly as the battery discharges further.
Which scenario unfolds also depends on cooling and ambient temperature - you could get the 'fizzle and go out' scenario on a cold day and the thermal runaway on a warm one.
You should really use a driver, or -perhaps- use a PTC/polyfuse between battery and laser to prevent the runaway problem to some degree - it might work, i guess they might do this in china, but you'll get an E or F from any electrical engineering class
- Joined
- Sep 20, 2013
- Messages
- 17,726
- Points
- 113
Considering how much power this diode dissipates, you would be much better off using a driver and two large Li-ion cells to power it. At close to 5 amps this diode puts out much more waste heat than it does optical power. You will also need a large heat sink to deal with all that waste heat.
- Joined
- Mar 5, 2015
- Messages
- 1,336
- Points
- 113
I believe since you are asking you intend on trying, make sure you video the first few minutes and post here!
Last edited:
- Joined
- Sep 20, 2013
- Messages
- 17,726
- Points
- 113
I doubt you would get minutes of video if you use two high capacity 18650s in series. The only way it could not destroy the diode is if there was enough sag from the batteries to pull the total voltage down to the Vf of the diode. Maybe some cheap xxxfire batteries.
- Joined
- Sep 20, 2008
- Messages
- 17,639
- Points
- 113
- Joined
- Mar 5, 2015
- Messages
- 1,336
- Points
- 113
Could be crapp fire you never know, Anyway he won’t be back!
Benm
0
- Joined
- Aug 16, 2007
- Messages
- 7,896
- Points
- 113
Yeah, 2 cells in series would just make a very brief bright flash and destroy the diode, unless the cells are -so bad- that their internal resistance actually limits the current to an acceptable level.
I don't see that happening with proper quality cells at all, but if you get them for $0.99 shipped off ebay and the are labeled 'randomfire' it just could work briefly. Or you'll have a random fire - guess it says that on the label, right?
I don't see that happening with proper quality cells at all, but if you get them for $0.99 shipped off ebay and the are labeled 'randomfire' it just could work briefly. Or you'll have a random fire - guess it says that on the label, right?
- Joined
- Sep 12, 2007
- Messages
- 9,399
- Points
- 113
You're wrong about the latter (for this particular diode) for three main reasons:
1) Yes, the forward voltage will drop slightly, but it isn't going to drop the 0.5-1V needed to cause problems.
2) lithium cells are often quoted at 4.2V on this forum, but that's an edge case. A lithium cell cannot maintain 4.2V for very long. At high drain they INSTANTLY drop to the high threes because of internal/lead resistances.
3) The nubm44 can handle rather severe overcurrent.
Obviously direct-driving is dumb, but I can just about promise you a single lithium cell won't damage it.
Benm
0
- Joined
- Aug 16, 2007
- Messages
- 7,896
- Points
- 113
I'd agree on this thermal runaway not being likely (though not impossible).
It's more likely that the battery voltage would sag under the load to the point where you get less them optimum output power, but everything survives the ordeal.
This is, sort of, depending on the concept that poor batteries and thin wiring will serve as a current limiting mechanism. It's like testing LED's by putting them directly over a button cell will be fine due to internal resistances, which works out 99% of attempts.
But if you do have a cell with a very low internal resistance, and case/switch/etc with very low electrical connection you can get this runaway effect... I'm not sure how much overcurrent this diode can tolerate, but i guess i'd be dead if the shoved 20 amps down it
It's more likely that the battery voltage would sag under the load to the point where you get less them optimum output power, but everything survives the ordeal.
This is, sort of, depending on the concept that poor batteries and thin wiring will serve as a current limiting mechanism. It's like testing LED's by putting them directly over a button cell will be fine due to internal resistances, which works out 99% of attempts.
But if you do have a cell with a very low internal resistance, and case/switch/etc with very low electrical connection you can get this runaway effect... I'm not sure how much overcurrent this diode can tolerate, but i guess i'd be dead if the shoved 20 amps down it
hakzaw1
0
- Joined
- Apr 2, 2009
- Messages
- 10,662
- Points
- 113
why take the risk ??
too lazy or too cheap?... drivers are not expensive ..
best wishes AND GOOD LUCK!!
too lazy or too cheap?... drivers are not expensive ..
best wishes AND GOOD LUCK!!
Benm
0
- Joined
- Aug 16, 2007
- Messages
- 7,896
- Points
- 113
I don't do that to laser diodes, but i guess one reason would also be 'too complicated'.
The drivers are inexpensive, the host most likely has enough space for one, but if you have no idea what you're doing you may just connect it up directly as the forward voltage of the laser diode is so close to the battery voltage.
And to be honest, that's how they used to do it any good old flashlight: just put a 6 volt bulb over 4 alkaline cells in series and hope for the best. Or a 3 volt bulb across 3 cells, overdriving it a bit when the batteries are fresh etc.
Downside is that the I/U curve of laser diodes is a lot sharper than that of incandescent lamps and this doesn't reliably work.
You still see a lot of this shoddy work in cheap LED flashlights where they may just do something like 3 AAA cells directly to the LED or only with a small resistor in series. For such flashlights that works out reasonably well as it will not break the thing, the brightness will just drop off quickly.
The drivers are inexpensive, the host most likely has enough space for one, but if you have no idea what you're doing you may just connect it up directly as the forward voltage of the laser diode is so close to the battery voltage.
And to be honest, that's how they used to do it any good old flashlight: just put a 6 volt bulb over 4 alkaline cells in series and hope for the best. Or a 3 volt bulb across 3 cells, overdriving it a bit when the batteries are fresh etc.
Downside is that the I/U curve of laser diodes is a lot sharper than that of incandescent lamps and this doesn't reliably work.
You still see a lot of this shoddy work in cheap LED flashlights where they may just do something like 3 AAA cells directly to the LED or only with a small resistor in series. For such flashlights that works out reasonably well as it will not break the thing, the brightness will just drop off quickly.
