DIY driver problem

[Gata]

Problem solved. I feel as dumb as I did after watching kipkay's video.

 

[hugo999999]

use the rule V= I * R
where r is ohms and I amperes, and voltage the constant of 1.25 for the LM317

so, 1.25/0.8= 1.56 ohms needed

there is also the other equation (R1*R2) / (R1+R2) = total resistance (this is for 2 resistors soldered in parallel).

 

[Gata]

So only 1.56 ohms is needed to get .8A?

 

[hugo999999]

yes a 1.5 ohm resistor would work fine. note it will need to be about 3W

 

[Gata]

The only ones I got on hand are 1/4W. What is the 3W needed for?

 

[hugo999999]

3W of electricity are going through it... if you try with a 1/4W its gonna end up in flames lol

 

[Gata]

I ran the driver with a test load for about 3 minutes just to see how hot the LM317 got and the resistors seemed fine. But I will replace them when I get the chance to a higher wattage just to be safe.

 

[Toaster]

So the watt rating on a resistance is only the upper limit of the resistor? The watt rating has always confused me.

 

[Gata]

I have never professionally worked with electronics such as these, only in hobby projects and such, and I have never had a problem with different watt resistors. But with lasers things need to be precise and you have to do things a bit more carefully, so to be on the safe side I am not gonna plug in my 445 diode until I get some tougher resistors.

 

[hugo999999]

i once used a 1/4W resistor in a build using even less current then this. a few seconds later it got so hot it desoldered itself from the bread board lol

 

[Rafa]

For .8A you will need 1.6Ohm with a rating of 1W or more.

Resistor rating is how much the resistor can dissipate itself, if too much power is passing thru it, it will ovearheat, and eventually burn, just like laser diodes.

 

[hugo999999]

For .8A you will need 1.6Ohm with a rating of 1W or more.

Resistor rating is how much the resistor can dissipate itself, if too much power is passing thru it, it will ovearheat, and eventually burn, just like laser diodes.

1W is still not enough.
about 3W of electricity will be going through the resistor (4Vx0.8A=3.2W).
to be safe i would go with a 3W resistor, using anything less is asking for trouble (even a 1W, it would work for a while but eventually burn out).

 

[jaycey]

Just upgraded the resistor on my 445nm driver to a 1 watt 0.5 ohm resistor.

Anyone tell me the max output, because thats what it is running at now:eg:


Just tested it on the Mrs (she didnt know LOL) and at 15metres she thought a wasp had stung her...after about 3 seconds Double LOL!

 

[jib77]

I thought it was [Voltage drop across the resistor X Current = W] in the case of LM317 the regulator will always maintain a 1.25 voltage drop across the resistor so that is 1.25 x .8 = 1 Watt.

 

[Rafa]

I thought it was [Voltage drop across the resistor X Current = W] in the case of LM317 the regulator will always maintain a 1.25 voltage drop across the resistor so that is 1.25 x .08 = 1 Watt.

Thats right.

 

[Gata]

Just upgraded the resistor on my 445nm driver to a 1 watt 0.5 ohm resistor.

Anyone tell me the max output, because thats what it is running at now:eg:


Just tested it on the Mrs (she didnt know LOL) and at 15metres she thought a wasp had stung her...after about 3 seconds Double LOL!

What regulator are you using? LM317? If so then your max out put would be around 1.5A, the max that the LM317 can put out.

When I lived at home I did that to my brother all the time on the back of the neck, he always though something was stinging him.