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Old 10-11-2009, 05:07 AM #1
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Default 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?


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Old 10-11-2009, 05:20 AM #2
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Default Re: Diode voltage drop?

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?
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Old 10-11-2009, 05:34 AM #3
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Default Re: Diode voltage drop?

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...
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Old 10-11-2009, 07:24 AM #4
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Default Re: Diode voltage drop?

Quote:
Originally Posted by PlasmaCube View Post
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?
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.
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Old 10-11-2009, 03:30 PM #5
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Default Re: Diode voltage drop?

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.
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Old 10-11-2009, 07:23 PM #6
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Default Re: Diode voltage drop?

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.
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Old 10-11-2009, 07:29 PM #7
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Default Re: Diode voltage drop?

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?
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Old 10-11-2009, 07:55 PM #8
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Default Re: Diode voltage drop?

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
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Old 10-11-2009, 08:02 PM #9
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Default Re: Diode voltage drop?

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?
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Old 10-11-2009, 10:00 PM #10
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Default Re: Diode voltage drop?

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: 8X Diode Murder fund
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