A140 Diode ~8V, on LM317 Driver?

[itsmei]

I am building a A140 laser with a DIY LM317 driver. I am using 2x 18650 batteries so when fully charged it is 8V+. Is this enough voltage? I am running this diode to 1.5A but is this enough voltage?

It would be a HUGE pain if it was not the required voltage and i have done the set up..

I just need your help

Thanks

 

[itsmei]

Bump :d

 

[chipdouglas]

that is plenty of voltage. the diode only needs like 4.5 and the driver needs like 2.5. 2 18650s is a good choice for this set up.


michael.

 

[itsmei]

Yes, that what i thought but i have had lots of people disagreeing with that statement. Can anyone else just say yes or no? Is the voltage find?

 

[itsmei]

Sorry for being so inpatient but i really need the go ahead before i actually put the laser together, i am so excited for building it!:drool:. Will ~8V be enough for a LM317 based driver with a A140 running at 1.5A?

Sorry again!

:bumpit:

 

[budabob07]

LM317 voltage drop: ~3V
A140 voltage drop: ~4.5V
Add them up and you get 7.5 volts. 8 would be fine

 

[itsmei]

ok thanks a lot

 

[rhd]

In practice though - at 1.5A, the math notwithstanding, it just doesn't quite work as perfectly as it seems like it should.

1.5A is right at the LM317's limits, and that voltage doesn't leave much wiggle room as the cells sag. I don't think you're going to get much over 1W of optical output

 

[anselm]

It works fine with freshly charged batteries, but not for a long time.
As soon as the batteries start discharging somewhat the drivers output will slowly decline from those initial 1.5Ampere....

The better your batteries are (capacity and internal resistance) the longer they can keep
up those 1.5A....

Besides, be sure to heatsink that LM317 real good, for that much amperage going through...

 

[LaZeRz]

why not use a lm1117? it has a lower dropout so it "should" be more stable

 

[itsmei]

How long do you think i could keep 1.5A with 2x 18650 batteries then? I have an inbuilt charger so it won't be hard to charge it.

Thanks

 

[laserman55]

I had a quick question and I didnt feel like it was worth starting a new post:

So i recently purchased an A130 and I am using a LM317 driver running at about 900 ma. So my question is if the diode can share the same heat sink as the LM317t. I know according to the data sheet the tab of the LM317t is connected to the 1.25 adjustable voltage. However the pins used on the diode are not case pins so can they touch????

Thanks,
Keith

 

[rhd]

Nope, because the 317 will short with the battery (-) through the case. In other words, it's not the diode that creates the problem, it's the case charge.

You can heatsink to the main heatsink, but you need to electrically isolate it.

 

[laserman55]

Alright that is good to know!

Thank you!