Help with Test Loads

Hello, I'm new to both the laser building hobby and the forum, and I don't want to risk breaking my first diode ever, so I would like to make a proper test load for it. It is a red diode 650nm I think, and I wanted to know if instead of 1n400x's I could use these: 1N5408 's

1N5408-T Diodes Inc. Rectifiers

The Info says that the forward voltage drop is only 1V versus the 1N4001's .7V. Could I use three of these and set my LM-317 driver to 3V and still have it safely drop to the red diode's 2.8V? Or is the forward voltage drop even the right thing to be looking for in the specs? Thanks in advance for any help, :bowdown:

Try this one It has everything you need and it's selectable so you'll only need one for all different diodes http://laserpointerforums.com/f39/fs-selectable-test-load-up-3a-assembled-diy-kit-stock-63450.html
You can get it assembled or in the DIY
Hope I could help

-Anthony

The rectifiers will work. Take three of them in series to make a testload for the red diode.

AnthoT said:

Try this one It has everything you need and it's selectable so you'll only need one for all different diodes http://laserpointerforums.com/f39/fs-selectable-test-load-up-3a-assembled-diy-kit-stock-63450.html
You can get it assembled or in the DIY
Hope I could help

-Anthony

Click to expand...

Thank you very much! :beer: This is a great test load and I now plan on getting one. But, seeing as this is my first build and I am too excited to wait, the original questions still stand, would these 1N5408 diodes work in a test load, and is the Forward voltage drop what i should be looking at? Because I looked at the specs for 1N400x series and it says it has the same forward 1V drop, but forums all say that it drops .7V. Am I looking at the right number? Sorry for all the question overload, but I'm new and need to learn the basics.:bowdown:

EDIT: Nevermind! Thank you very much Blord! I just found it damn near impossible for me to guess something correctly reguarding electrical cicruits. Many thanks!

I made this picture/schematic drawing for someone else, but maybe it hs use for you.

Thank you very much FretWrecker! I truly appreciate the diagram, it helps alot with the creation of my test load's circuit. I am honestly blown away at the wealth of information and the willingness of the forum community to provide it to a new guy like me. I suppose I should have expected such kindness after reading the thread to support Rob during his time of need. Thank you all who have helped answer my questions and provided me with useful information!:bowdown::bowdown::bowdown:

Fretwrecker94 said:

I made this picture/schematic drawing for someone else, but maybe it hs use for you.

Click to expand...

Your drawing isn't correct. The last three diodes on the lower drawing should be reversed. Now it is 3 diodes against 3 diodes.

Use this practical solution,

Blord said:

Your drawing isn't correct. The last three diodes on the lower drawing should be reversed. Now it is 3 diodes against 3 diodes.

Use this practical solution,

Click to expand...

Yes if you're building one yourself then you just reverse the last three diodes. Otherwise it won't work properly...

Argh!!! In a cruel twist of fate, I misread the third rectifier. This is a list of what I have immediate access to and their stats:

1N5844 (one of them) LTC6946 - Ultralow Noise and Spurious 0.37GHz to 5.7GHz Integer-N Synthesizer with Integrated VCO - Linear Technology

1N5408 (two of them) 1N5408-T Diodes Inc. Rectifiers

FR-103 (six of them) FR103 Rectron Rectifiers

FR-107 (four of them) FR107 Rectron Rectifiers

FR-157 (one of them) FR157 Rectron Rectifiers

RL-207 (two of them) RL207 Rectron Rectifiers

Is there a possible combination of these that would give me close to the desired 2.8V for a red diode? I do apologize for the rag-tag assembly of misc. parts, I'm trying not to spend to much, and disassembled a broken PSU for these parts. Any combinations you see that would work here? Again, I must bow down to the awesome help you guys continue to give me! :worthy:

*EDIT* I also have two of these buggers:
http://www.makershed.com/product_p/jm330772.htm

I don't plan on using them because I'm using an old computer PSU to power my diode and not batteries (i get the impression that only batteries have that higher-voltage when first plugged in issue, and even if it does happen with my PSU, I have a switch between it and the driver, so it shouldn't matter anyway) but IF I wanted to, how would I add them in? Also, is the 1 ohm resistor required or can it be any ohms. I don't mind buying some things (like one more 1N5408 or the resistor) but I DO prefer to know what I have to buy before driving out and getting it. Any suggestions?

Blord said:

Your drawing isn't correct. The last three diodes on the lower drawing should be reversed. Now it is 3 diodes against 3 diodes.

Click to expand...

Wow! I didn't even catch that! Thanks guys haha my bad! I should probably fix that. That's what you get for being braindead and bored in class with nothing to do but doodle.

Blord said:

The rectifiers will work. Take three of them in series to make a testload for the red diode.

Click to expand...

Looking at my previous reply's specs, Would using two 1N5408's with a forward voltage drop of 1V plus a RL-207 with a forward voltage drop of 1.1V (Total of 3.1V) work for a red diode (2.8V as I'm sure you know, but just so you don't get red and blue mixed up )?

Or would it be even better to use two FR-10X's to set the voltage to 2.6V and have it rise just slightly to the diodes 2.8V and not risk overshooting the voltage?

Use the 1N5408 diodes and assume a voltage drop of 0.7 Volts for EACH diode (at 1 amp load).

I would use 4 diodes for 2.8 VDC.

LarryDFW

LarryDFW said:

Use the 1N5408 diodes and assume a voltage drop of 0.7 Volts for EACH diode (at 1 amp load).

I would use 4 diodes for 2.8 VDC.

LarryDFW

Click to expand...

Thank you very much Larry. I will do so and test with a multimeter. Just to me sure though, what do you mean a 1A load? Use a 1ohm resistor before the diodes?

*EDIT* Never mind, I successfully completed building the test load and yesterday (3/17/21) my first laser. It's a cool little 650nm diode that I'm running at about 425mA, but the old computer power supply unit I'm using is on the fritz and is making it pulse. It's all well and good though, for a first laser build, lighting matches and popping balloons is a blast! Thanks everyone for the help you provided!

Blord said:

Your drawing isn't correct. The last three diodes on the lower drawing should be reversed. Now it is 3 diodes against 3 diodes.

Use this practical solution,

Click to expand...

hey! can you give a brief explanation on how testloads function. I mean I know that these testloads are used so people dont kill their diodes in setting the current and voltage but I dont understand how exactly these work and how are they used(the prosedure)so please explain in terms of voltage drops across the load and how this resembles he laser diode. also why are there different positive terminals for different color diodes. I would really appreciate it if you or anyone else for that matter can clarify this for me.

Please READ HERE about making a test-load, Remember A test-load simulates the Laser-Diode, It is used to measure the driver current, diagrams and description are in the link..