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Screw this, I'm going direct drive!

ryansoh3

ryansoh3

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After discovering that my cheapie buck driver was overheating and causing the current to drop below 1.3A (originally set for 1.66A) I just figured I would go direct drive with a single li-ion cell.

I was using a East-092 direct drive driver (not technically a driver) with the 5 usual modes in a flashlight, high, medium, low, strobe, and SOS.

It was a very straight forward setup, as I didn't have to worry about heatsinking the driver or making sure that the output had no current spikes or ripples, as the max voltage of a fully charged li-ion is well below the forward voltage of M140's at 1.8A.

After some soldiering, I measured the tailcap current at a mere 0.655A, but it was still bright enough. All the 5 modes worked flawlessly as well.

The main reason I don't use the recommended drivers at LPF is because I really like the flexibility of choosing low, medium, and high outputs by simply changing the modes.

Thanks for listening to this quick report, but I'm sure this is nothing new. :D
 
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jander6442

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You rebel you! let us know how that works out. I'm betting that the spike is going to kill that poor diode.
 
Leodahsan

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@jander
Actually not. The blue diodes are pretty strong... and unless ryan is shorting the battery/diode during operation, there should be no problem...
The only problem is the voltage dropping and the laser going weaker. I've built one DD and have seen members overcharging their batteries to 4.35V, for more powah. :crackup:

@ryan
Soldering a 10/100nF ceramic cap on the diode would be wise ;)
Or a lasorb.
 
jander6442

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DD and overcharging batteries are not at all what I would call best practices unless you like living on the wildside I could link dozens of well written post on why not to so I would say your throwing caution to the wind.
 
ryansoh3

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Thanks for your replies.

I'm actually pretty confidant that the direct drive will not kill the LD because the current, even at 4.2V fully charged for a li-ion battery, will not go over the 1.8A max recommended current. I have tested the diode with a regulated power supply, and its Vf at 1.8A is about 5.5V, IIRC.

The driver however comes into question, especially when using PWM for med and low modes, but I've tested it with my scope and there are no current spikes, thankfully.

I agree that overcharging a li-ion to 4.35V is very dangerous and not recommended at all. However, there are special 18650's that are designed to be charged to 4.30V or even 4.35V, as rated by the manufacturer. The LG 3000mAh D1 18650 is an example.

I'm using Samsung ICR18650-28A 2800mAh cells that can be charged to 4.30V, but I'm only charging them to 4.20V for longevity's sake.

The Lasorb device is pretty cool, I wonder if it can be used in hand held builds?
 
Leodahsan

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ryansoh3 said:
Thanks for your replies.

I'm actually pretty confidant that the direct drive will not kill the LD because the current, even at 4.2V fully charged for a li-ion battery, will not go over the 1.8A max recommended current. I have tested the diode with a regulated power supply, and its Vf at 1.8A is about 5.5V, IIRC.

The driver however comes into question, especially when using PWM for med and low modes, but I've tested it with my scope and there are no current spikes, thankfully.

I agree that overcharging a li-ion to 4.35V is very dangerous and not recommended at all. However, there are special 18650's that are designed to be charged to 4.30V or even 4.35V, as rated by the manufacturer. The LG 3000mAh D1 18650 is an example.

I'm using Samsung ICR18650-28A 2800mAh cells that can be charged to 4.30V, but I'm only charging them to 4.20V for longevity's sake.

The Lasorb device is pretty cool, I wonder if it can be used in hand held builds?
Click to expand...

Yeah maybe that person overcharged a battery thats designed for that.
IIRC (I may be wrong) it was LarryDFW who did that, using some quality cells (he seems to be a source for batteries)

edit:
You're asking if the lasorb fits inside a portable? I don't think there should be any problems with using it when driving the diode using batteries.
 
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BShanahan14rulz

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I've not ever had a driver hooked up to my A140. It's direct drive, with not even a mode change board.

My cells are 4.2V cells, so there is no way for a spike >4.2V to occur other than static from outside the system. A lasorb would protect from that. I'm sure if you searched, you might could find a set of components that, when used together, might closely match the protection of a lasorb. But then again, lasorbs aren't that expensive either, and someone's already done the work of finding, buying, assembling into a sturdy package, etc.
 
Zom-B

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Today I was just thinking about making a laser driver that has low and high modes selectable by toggling the switch. Then I realized i barely have time for anything lately, let alone a micrococntroller-driven adjustable driver.
 
Leodahsan

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BShanahan14rulz said:
I've not ever had a driver hooked up to my A140. It's direct drive, with not even a mode change board.

My cells are 4.2V cells, so there is no way for a spike >4.2V to occur other than static from outside the system. A lasorb would protect from that. I'm sure if you searched, you might could find a set of components that, when used together, might closely match the protection of a lasorb. But then again, lasorbs aren't that expensive either, and someone's already done the work of finding, buying, assembling into a sturdy package, etc.
Click to expand...

Yeah agreed. Anyways a spike would happen should one short the battery during operation. If everything is well insulated, there should be no worries imo.
 
LarryDFW

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Leodahsan said:
@jander
Actually not. The blue diodes are pretty strong... and unless ryan is shorting the battery/diode during operation, there should be no problem...
The only problem is the voltage dropping and the laser going weaker. I've built one DD and have seen members overcharging their batteries to 4.35V, for more powah. :crackup:
Click to expand...

There are several 18650 cells that are rated @ 4.35 VDC +or- .05 VDC.

The Sanyo 3000 mah cells have the lowest Internal Resistance. :D

I use them in my Direct Drive 445 lasers.

Never had a driver or laser diode failure . . .

LarryDFW
 
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jayrob

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ryansoh3 said:
After discovering that my cheapie buck driver was overheating and causing the current to drop below 1.3A (originally set for 1.66A) I just figured I would go direct drive with a single li-ion cell.

I was using a East-092 direct drive driver (not technically a driver) with the 5 usual modes in a flashlight, high, medium, low, strobe, and SOS.

It was a very straight forward setup, as I didn't have to worry about heatsinking the driver or making sure that the output had no current spikes or ripples, as the max voltage of a fully charged li-ion is well below the forward voltage of M140's at 1.8A.

After some soldiering, I measured the tailcap current at a mere 0.655A, but it was still bright enough. All the 5 modes worked flawlessly as well.

The main reason I don't use the recommended drivers at LPF is because I really like the flexibility of choosing low, medium, and high outputs by simply changing the modes.

Thanks for listening to this quick report, but I'm sure this is nothing new. :D
Click to expand...

If you have modes, then it's not direct drive from the battery to the diode...

Sounds like your using the stock flashlight driver.

These 445 diodes are very sturdy, and for that reason some are using cheap flashlight drivers with no problem.

Especially if it's only about an Amp, which it sounds like you have there...
 
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ryansoh3

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On high mode it's direct drive, and on med and low modes, the MOSFET is switched via PWM at about 4 and 6KHz, respectively.

At about 0.655A current, I'm fairly sure I can run even run the diode 24/7. :D

Like LarryDFW said, if I wanted to increase the current, I can charge my 18650's to 4.30V, which is their rated charge voltage.
 
jayrob

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Wonder how long it will even lase as the voltage drops??
 
ryansoh3

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Good question, I'll do some testing and report back in a few hours...
 
BShanahan14rulz

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A PWM "driver" is generally considered direct drive. Not to be confused with drivers that are modulated with PWM. A PWM "driver" is simply a fet inline with the supply or ground, and controlled by a microcontroller. So, the fet does introduce a tiny bit of resistance, but negligibly so.

Since DD means diode determines current, best way would be to just test it. The diode will see the most current when the battery is fully charged, and as the battery discharges, so the current will decrease.

I use some old-ish cells, wouldn't be surprised if their IR was starting to creep up. Still lases for quite some time on DD. Can't say I've ever seen it not lase, but I also don't let my cells get discharged too much.

Edit: one last thing to note, DD is more efficient than using a linear driver, but linear driver may be able to regulate output longer if you set it lower.
 
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Leodahsan

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Not a direct drive since the current is limited by the mosfet "Rds(on)". :beer:
 
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