Diode voltage drop?

Sorry for this noob question.
I understand that normal rectifier diodes (i.e. 1N4001) have a forward voltage drop of about 0.7 V. And when connected in series, the drops in voltage should just add up, correct?
Well, I've got two 3.0 V Soshine CR123A's (which are incredibly overcharged... together, they're 7.5 V measured from the terminals on the host's top piece), and I've got a FlexDrive. Obviously, I can't hook up 7.5 V, so I wanted to drop the voltage using some rectifier diodes.
I decided to try using 2 at first. So I connected them in series with each other and with the batteries, then measured the voltage. 7.1 V. I was slightly confused, so I tried adding another diode. 6.9 V. HUH???

What am I doing wrong?

Why not just use one CR123A? If you need two for your host you can use a spacer.

Anyways, different diodes have different voltage drops.. Do you know what kind of diodes you have?

Yeah they're standard 1N4001 rectifier diodes. And I have thought of using just one battery... but I can't find a suitable spacer at the moment, and I kinda wanted to finish it today... But I guess that's not going to happen...

PlasmaCube said:

I decided to try using 2 at first. So I connected them in series with each other and with the batteries, then measured the voltage. 7.1 V. I was slightly confused, so I tried adding another diode. 6.9 V. HUH???

What am I doing wrong?

Click to expand...

Diodes have different voltage drop at different current. Basically, more current flowing through the diode results in higher voltage drop. In your measurement setup you have only a multimeter as a load (very small current).
It will be different when you have the Flexdrive connected. Just assume ~0.8V drop across each 1N400x diode.

Oh, I see! That makes sense! Okay, so I'll just work with it after I connect the FlexDrive.
Except now I have to wait for another diode...
BDR-S03 LED'd at 250mA... So much for being an 8x.

There have been some bad SO3 sleds going around. I bought two a while back, one diode went LED at 140 mA, the other at 180mA. The only sure way of getting a good 8x diode is to remove it from a known good 8x bluray burner.

Should be able to make a spacer from simple materials like wood or plastic wrapped with some aluminum foil. I switched a greenie pen from 2 x AAA to 1 x 10440 by making a spacer from part of a pencil wrapped in foil and shoved in as a fake battery.

Yeah, I've seen it done before. Although, I think I'll just go with using diodes.
Is aluminum foil good enough of a conductor? The spacers that I've seen just had a wire going from top to bottom.

Also, I decided to get a SF-AW210 diode to replace the dead one. What current should I drive it at for optimal burning? I know ~200mA is recommended for long life, but I just want power (without it LEDing on me). Would 250mA be unsafe?

250mA is unsafe, I had one at 190mA that LEDed after about 2 weeks of normal use with a 405-G-1 lens (chunky heat-sink, no real duty cycle though). For that time it was putting out around 250mW though, so I wasn't too disappointed when it went

Well, I plan to use a decent duty cycle, and I also have a 405-G-1. Plus, I won't really use it that often.
So the mW per mA ratio is fairly similar to other Blu-rays, right? I saw some graphs that were showing like 150mW at 200mA, although that might've been through Aixiz acrylic.
So do you recommend around 200mA, then?

The BDR-S03 is lousy, not much better than a 6x. A real 8x will take 300mA just fine.

As for mA to mW ratio, IgorT is currently testing a bunch of 8x diodes in this thread: http://laserpointerforums.com/f38/8x-diode-murder-fund-43993.html