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Reepicheep
| | Posted on Sunday, December 29, 2013 - 08:50 am: | 
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If you are "close", a forward biased diode (non light emitting) will drop .6 volts or so. Cheap, easy to source, and reliable. |
Hughlysses
| | Posted on Friday, January 10, 2014 - 03:45 pm: |
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Bill- any progress to report with your LED experiments? |
Reepicheep
| | Posted on Friday, January 10, 2014 - 04:15 pm: |
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No, I got distracted by the heated grip controller thing (which is coming along extremely well right now!)
For LED's, I think the trick will be to find some cheap metal flashlights with zoom lenses and cannabilize those to make headlights out of (maybe 4 or 8 of them). The prices are getting close.
The obstacle now isn't the light source, it is the lens and enclosure. I tried to find some cheap 9sx headlight assemblies on ebay to hack, but they were all $$. |
Reepicheep
| | Posted on Friday, January 10, 2014 - 04:15 pm: |
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Oh, and I think those LED's I got are now $4 each! |
Hughlysses
| | Posted on Friday, January 10, 2014 - 04:26 pm: |
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Thanks for the update. I was thinking they might be worth trying in my cheap ~$15 auxiliary driving lights on my Uly. |
Reepicheep
| | Posted on Saturday, January 11, 2014 - 02:01 pm: |
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If you don't mind cutting up the lights, and could come up with an appropriate heat sink (not a lot, but might need something) they would likely work really well. You might end up needing voltage protection though (which you could do in a pinch with a series of forward biased power diodes cheaply). They get pretty hot above 12.0V. I didn't try and see if the would survive at 13.8 or whatever. |
Cataract2
| | Posted on Saturday, January 11, 2014 - 04:49 pm: |
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What about using Zener Diodes for voltage control? |
Iamike
| | Posted on Saturday, January 11, 2014 - 07:31 pm: |
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I believe using a zener @ 12V would blow the fuse. Our radios have had them @ 18V & 24V to protect the radios from overvoltage.
Our mechanics loved to use the battery charger boost that would put about 26V when they jump started the vehicles. That was until they started killing my radios and vehicle electronics when they did it.
There are 12V regulator modules that could handle that current easily. |
Cataract2
| | Posted on Saturday, January 11, 2014 - 07:43 pm: |
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Zener's can be made to a various amount of voltages that you might require. They are typically used in voltage regulators to provide a stable voltage yet, allowing greater current. This is achieved by running them in reverse bias. I figure if you are needing a stable voltage they might be the ticket. |
Reepicheep
| | Posted on Sunday, January 12, 2014 - 01:10 pm: |
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A zeener diode is just a diode fabricated to deliberately have a low reverse breakdown voltage. So instead of blocking reverse flow of current, it just settles to X volts and lets current flow.
The problem is that they typically can't handle much current (at least not economically). So they are OK for establishing and holding a reference voltage, but you can't use them directly as a regulator for anything but the most low power applications.
Power is heat, and the amount of heat a device can handle before the magic smoke comes out is what usually matters. Power (watts) is Volts times Amps, and most zeener diodes are likely around .25 or .75 watts... so that would be 1 volt across them at 750 milliamps. Which is next to nothing.
So you use the zeener with a high impedance resistor in series, like 1k or 10k, and just use that as a reference voltage to control a device that can more economically manage power, like a MOSFET or a power transistor.
I recommended a power diode forward biased, as they are "easy". Each one will drop about .6 volts, so you just stack them like legos until you get the drop you want.
So if you go to Radio Shack, you can get some 1 amp rated diodes for about 35 cents each (and you are paying about 10x what they should cost because you got them from radio shack, but hey, its only 35 cents). 3 amp rated diodes are a bit more. So slap 4 of those things in series (-->|--, where the line on the diode represents the tip of the arrow which is the direction current can flow), and for under $2 bucks you have dropped 2.4 volts on a 12 watt or so load and they will run for-freaking-ever. The 3 amp diodes would do the same thing for a 36 watt load. 10 amp diodes would do for 120 watts. And you can add or remove them to get the result you want.
The regulation won't be that precise, but it's a good easy way to drop voltage without having to resort to a low ohm power diode, or a pricey high power zeener.
Thinking about it as I type this, they would also make a nice simple "high/low" option. Have 6 diodes forward biased. Run a simple switch to bypass 3 of the 6 with a wire when the switch is closed, but when the switch is open the power has to go through the diodes. Bingo, a high / low power selector.
Zeeners are also fairly current and temperature sensitive as well, so while they are better than nothing, there is a reason there are custom voltage regulator semiconductors out there to do voltage regulation (they internally compensate for things like temperature changes and current changes to keep the right voltage).
(Message edited by reepicheep on January 12, 2014) |
Reepicheep
| | Posted on Sunday, January 12, 2014 - 01:14 pm: |
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Oh, and if you do want to mail order, this place does retail.
3 amp, $10 for 100 of them:
http://www.parts-express.com/1n5408-rectifier-diod e-3a-1000v--1n5408
6 amp, around 45 cents each:
http://www.parts-express.com/power-supply-diode-6a -1000v--6a-1kv |
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