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Electronics Stuff Locally

ozzy702

ozzy702

Well-Known Member
Location
Sandy, UT
Anyone have a preferred place for electronics locally? I need some 3 ohm resistors that can handle at least 3 watts. I couldn't find anything at Radio Shack that is heavy duty enough.

Edit: Also looking for some thermal adhesive that's fairly strong if you have any recommendations I'd appreciate it!
 
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jackjoh

jackjoh

Jack - KC6NAR
Supporting Member
Location
Riverton, UT
Sounds like you are making an old Capacitive Discharge system. I might have some in my old stuff. Let me know and I will check tomorrow.
 
MikeGyver

MikeGyver

UtahWeld.com
Location
Arem
Sounds like you're driving 1amp worth of LED(s). You could use a LM317 voltage regulator configured as a current regulator. This will give you the added benefit of actual current regulation and still only requires 1 (smaller wattage) resistor. 12v 3w led drivers are very cheap on ebay BTW.
 
ozzy702

ozzy702

Well-Known Member
Location
Sandy, UT
MikeGyver said:
Sounds like you're driving 1amp worth of LED(s). You could use a LM317 voltage regulator configured as a current regulator. This will give you the added benefit of actual current regulation and still only requires 1 (smaller wattage) resistor. 12v 3w led drivers are very cheap on ebay BTW.
Click to expand...

Yep, I'm shooting for right about 1amp to the LED. I'm not very well versed in this whole electrical thing. I've made a 600 lumen 3D mag lite but that's the extent of my experience (and I had instructions for that :D).

In an automotive system what would the benefit be to using a current regulator? Am I to assume that the amount of voltage and current my 12V system will provide to my LED's will constantly fluctuate making my lights change brightness or would a current regulator be safer than using resistors?

I ran all my calculations off of a max of 14.4V and the LED's max amp rating of 1500ma's just to have a safety buffer. That comes out to a 3ohm resistor. Then when running at normal 12.6v the 3 ohm resistor should allow roughly 850ma to 900ma.
 
MikeGyver

MikeGyver

UtahWeld.com
Location
Arem
LEDs are current controlled devices and they have a very non-linear voltage vs current graph, so even a small increase in voltage could double the current through the diode. Since automotive voltages could be from 10-16v a regulator would be good practice and will hold it at 1000mA all the time, so it would be brighter with the engine off or at idle. If you got a buck mode switching regulator from ebay the efficiency would go from <50% to ~90%, which isn't a big deal since this isn't a flashlight, but there would be less heat removal to deal with which is always a plus.
The LM317 circuit is really simple and u can get them at radioschmuck.
Current output is determined by Vref(1.25v)/R. so a 1.25ohm will give you 1 amp out.
http://www.gpsy.com/ev/images/9Watt/LM317LEDDriver.gif
Regulation isn't necissary, but the only drawback is the small extra cost and complexity.
 
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ozzy702

ozzy702

Well-Known Member
Location
Sandy, UT
MikeGyver said:
LEDs are current controlled devices and they have a very non-linear voltage vs current graph, so even a small increase in voltage could double the current through the diode. Since automotive voltages could be from 10-16v a regulator would be good practice and will hold it at 1000mA all the time, so it would be brighter with the engine off or at idle. If you got a buck mode switching regulator from ebay the efficiency would go from <50% to ~90%, which isn't a big deal since this isn't a flashlight, but there would be less heat removal to deal with which is always a plus.
The LM317 circuit is really simple and u can get them at radioschmuck.
Current output is determined by Vref(1.25v)/R. so a 1.25ohm will give you 1 amp out.
http://www.gpsy.com/ev/images/9Watt/LM317LEDDriver.gif
Regulation isn't necissary, but the only drawback is the small extra cost and complexity.
Click to expand...

Ok, so since my LED's are roughly 10V and I want to drive them anywhere from 800ma to 1amp you think the LM317 is the best bet in an automotive system? So correct me if I'm wrong but the LM317 will provide a constant current regardless of the voltage? That sounds like it would work great. Now I just need to figure out how to wire it all up. This electrical stuff is new to me. :D

When you say the LM317 is adjustable how do you adjust it? From the sounds of it this is the route I'll need to take.

The reason I didn't want to run a buck driver is the cost and lack of drivers that will work with the LED's I want to run. They just have too high current and voltage requirements so I'd end up spending a ton of money just on the silly drivers.
 
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