Whats wrong with this wiring?

I finally added the 3 LEDs i needed to. And once i turned the laser on, everything was fine, until about 8 seconds later when my laser just totally stopped working. I didnt think it had blown out because the heatsink wasnt hot at all and the glue holding the wires didnt melt a little (which is what is always does when it gets a little hot).

The diode is a 445nm diode. I am using a LM317T driver, with only LM317T and a 1ohm resistor.

Also, i wired the LEDs with resistors the way i did because if i connected them in series with 1 33ohm resistor, then it would have been extremely dim.

So here is my really crappy drawing of the wiring........Sorry haha



And yes, there is no switch because i still need to find the right switch, so i just stuck the batteries in and wanted to see how it worked.

Thank you again so much for the help. :thanks:

Matt

I'm going to have to assume a few things:
A peak charged voltage of 8.4V
A set of typical 5mm LEDs.
LED forward voltage drop of 3.4V (typical of green blue and white LEDs)

That means the resistor has 5V across it. Each of the LEDs could be getting as much as 150mA. They're only rated for 20mA. You'd need something more like >200 ohms to properly limit these. I'm not sure how this would affect the laser, but it's something to look in to.

The first thing I check when something electrical goes wrong is voltage. Check voltages everywhere and go from there.

-how do you know what the peak voltage is?
-the LEDs are 3mm(if it matters)

Thanks again! ill buy some new LEDs to limit these.

Anyone else have an idea why the diode died?

Because lithium ion batteries are 4.2V when fully charged. 3mm LEDs have similar characteristics to their 5mm counterparts.

Also, what rating is the 1 ohm resistor on your LM317 driver? I hope you are using one rated to at least 5 watts, anything less and the resistor will burn out VERY (8 seconds is possible) quickly.

Cyparagon said:

Because lithium ion batteries are 4.2V when fully charged. 3mm LEDs have similar characteristics to their 5mm counterparts.

Click to expand...

Oh, got it. =] Thank you

Things said:

Also, what rating is the 1 ohm resistor on your LM317 driver? I hope you are using one rated to at least 5 watts, anything less and the resistor will burn out VERY (8 seconds is possible) quickly.

Click to expand...

I think im using a 2 watt ohm resistor? But before i soldered on the LEDs, i could turn the laser on without a problem. And it would run for a pretty long time until i turned it off...

2 watts will be fine. Mine runs fine with a 1W, even (albeit a slightly lower current) Where do you see that 5W is needed?

My source

So i would be able to use a 2W 1ohm resistor, i just need to use different resistors for the LEDs?

How come you would need a 5W? Im just wondering.

You don't need a 5W resistor. If there is doubt, check out this calculator, as it makes wattage rating suggestions:
LM317 Current Calculator - Electric Circuit
You really can't make the required resistor wattage peak above 2W without exceeding the current an LM317 can handle (1.5A) anyway.

I think the problem is more basic:
- You're trying to power a 445nm diode at 1250mA, with an LM317 driver, using only two li-ion 14500 cells, that are also powering a bunch of other stuff.

You may not have enough CURRENT:

Those are 14500s, not 18650s. They might only be able to SUPPLY 1250mA, yet you've got your LM317 setup to try and provide 1250mA current OUTPUT. This challenge is then compounded by the fact that you are also diverting a bunch (perhaps up to 450mA?) of current to the LEDs.

You probably don't have enough VOLTAGE:

An LM317 can take as much as a 3V bite out of your voltage. If the batteries are only supplying ~7.5V, then you could have as little as 4.5V for the diode, which might not be enough. It's borderline territory, but usually the common wisdom seems to be that an LM317 doesn't work too well for 445nm diodes using just 2 li-ion cells. I would think this to be even more true given the relatively smaller (than 18650) batteries you're using, and the generally high demand you're placing on those batteries.

So if i bought 2 18650 batteries, it'll increase my current and voltage and still keep my diode at a safe current?

Not quite -

If you use 18650s, it will increase the CURRENT available to the driver. If you add a 3rd cell, that will increase the available VOLTAGE.

Of course you'll also need to adjust the resistors used on those LEDs.

Good luck!

rhd said:

Not quite -

If you use 18650s, it will increase the CURRENT available to the driver. If you add a 3rd cell, that will increase the available VOLTAGE.

Of course you'll also need to adjust the resistors used on those LEDs.

Good luck!

Click to expand...

Add another 14500 battery?!?! Thatll be a challenge

Thanks a lot for the help everyone!! I really appreciate it!! :bowdown::bowdown::bowdown:

Matt :beer:

If you can't add another battery because of space limitations - you might want to consider:

1) Getting a pre-made laser driver like the Microboost, or Flexdrive, because they can certainly power the laser off two cells (one cell even)

2) Replacing the LM317 with an LM1117. I'm yet to test this, as I've only just become aware of the option recently, but apparently it uses half the Voltage of the LM317, and thus has enough remaining voltage to power 445nm diodes from 2 cells.

Good luck!

rhd said:

If you can't add another battery because of space limitations - you might want to consider:

1) Getting a pre-made laser driver like the Microboost, or Flexdrive, because they can certainly power the laser off two cells (one cell even)

2) Replacing the LM317 with an LM1117. I'm yet to test this, as I've only just become aware of the option recently, but apparently it uses half the Voltage of the LM317, and thus has enough remaining voltage to power 445nm diodes from 2 cells.

Good luck!

Click to expand...

Ya, i had already taken the Flexdrive into consideration. And think i might take that route. And if not, then a LM1117 will be my second option, just because i prefer to try and save enough money as i can

Thanks again for your help and everyone elses help! =D :wave: