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potiometer specs????

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TyRex

Member
Joined
Sep 12, 2002
Location
Indiana
potentiometer specs????

Could you guys give me run down on pots......I need to know how big of a pot to get....I'm gonna need one that can handle 12volts at 2.5 amps, so right around 30 watts....
 
I'll never understand the obsession with potentiometers - or rheostats - that people on here seem to have. From an electronics engineers point of view, it's an extremely inneficient way of doing a simple job, as all you need is a small switching regulator - I can make one and post the circuit diagram if you like. This way, you don't have to deal with 30watts of heat in you case, degrading nearby drives / components through it's heat emmision, especially if it's in a baybus of some kind. I'm not trying to have a go at you personally TyRex, but wouldn't it be much nicer if you used less electricity, produced less heat, and could control more devices more reliably as well?
 
pots and rheostats are nice, quick and dirty solution. The concept is very easy for advertisers to work with.

Electronics is just a little hobby for me, but I'm def. a beginner. And since your here, frostmeister....say I wanted a 3.5V power lead for an LED, but my power source varies from 12-14V, is it possible and somewhat easy to give an LED a constant power voltage?
 
Sure, I understand that it's a quick and easy solution - sorry if I stepped on any toes :) Yes cryogen97, you can give an LED a constant power solution from that voltage. Two ways.
1. If you can get an LM7805 voltage regulator, put that in line, then use a 75 ohm resistor in series - that'll give you 20mA for your LED, as long as it's only one LED.
2. Quick and more simple, use a 680 ohm resistor. As the voltage is only varying from 12 to 14 volts, it won't matter very much and shouldn't vary the brightness on the LED noticeably.
Happy soldering :)
 
yeah, I'm very familiar with the resistor method, I use that all the time...I just didn't know if there was a better way to go about it.
 
frostmeister said:
I'll never understand the obsession with potentiometers - or rheostats - that people on here seem to have. From an electronics engineers point of view, it's an extremely inneficient way of doing a simple job, as all you need is a small switching regulator - I can make one and post the circuit diagram if you like. This way, you don't have to deal with 30watts of heat in you case, degrading nearby drives / components through it's heat emmision, especially if it's in a baybus of some kind. I'm not trying to have a go at you personally TyRex, but wouldn't it be much nicer if you used less electricity, produced less heat, and could control more devices more reliably as well?

I would love it if you could do that.....I really never liked the idea of 30 watts of extra heat, but figured it might be to complicated to make a switching regualtor. It would help me out a lot because my 300w PSU is already starting to show it's limits, and if i dont have to use that much power, i'd rather not......thanx a bunch!
 
Sure, I'll get on a circuit diagram for one right away. It should only use one IC. Are your soldering skills up to making a circuit with an IC and a dozen or so external components? I'll try and make it as simple as possible, and thinking about it, there's several ways of doing it, so finding a fairly small circuit shouldn't be too much of a problem. I'll post again soon :)
 
that would be sweeeeeeeeeeeeeeeet frostmeister! since ur v. brainy you couldnt by any chance be able to integrate it into some kind of dimming led (5v)? i hear that the best way to do it is by some kind of pulsing voltage thing although im not sure i understand that fully yet...
 
How do you mean seal? You want an LED to dim and brighten with the voltage change? If so, you can just put a resistor on for the maximum voltage, say 680 ohms at 12 volts on a standard LED, and when the voltage goes down, the LED will fade as the voltage drops. I'm nearly done on that switching regulator now as well.... :)
 
Well, here's the circuit. Build it and test the output with a voltmeter first, so you can verify you're getting the correct output. This thing is 80% efficient - translates to 1 watt of heat for every 5 watts it supplies. The output current depends on the inductor and resistor. Inductors will usually come with a current rating, and check the diode you're using as well. I can't find a 1N5820 in my electronics catalogue, but you could use a 1N5822 which has a 3A current rating, and will be good for an output of up to 40 volts. 3 amps is the max the LM2577 can supply by the way, which should be ok for about 4 standard 12volt fans quite safely.
Have fun :)
switchreg.jpg

Let me know if there's anything you're unclear on by the way :)
 
sweet, frostmeister you're the man......I'll run buy the local electronics place sometime today or tommorow and get the parts.......thanx man
 
could anything else be used in place of the LM2577??? I couldnt find it anywhere in town or on the web.....
 
wow, thats great, the only thing is that the regulator is quite expenvie! (£6.50 in uk), it might even be cheaper to just buy a pre built one with 4 rheostats on.

Also, i cant get a 1N5820 but i can get a 1N5819 or a 1N5821, which would you go for?
 
OK stupid question coming - how on earth do you guys have the equipment to make this stuff?

My college has a tech department, so I guess I could make on there, but what do you guys do for equipment?

I mean like, etch tanks, UV box thingys, stuff like that.
 
all you need to do is build it on a "perf" board. This is basically a thin piece of fiberglass or non conductive composite that has holes in it on a 0.10" x 0.10" grid. Just pop your components through and solder them together with a small gage wire. I would typically use a 22 to 24 gauge "bus" wire - uninsulated. Just gotta be careful how you run it and use small pieces of insulatin whre required., and remember to connect all your grounds to a common point as frostmeister pointed out.
Nice job btw frostmeister from another EE.

LA
 
frostmeister said:
a 1n5821 would do fine, seal. And TyRex, the LM2577 is pretty much non-subsitutable. Hope this helps.

is there any particular place i could order the lm2577 online? i'll try some local stores tomorrow... but i'm kind of doubtful i'll find any.. and looking online i can find where i can order them in quantities of 500 or 1000...

if i wasn't on a work term i'd try the school's crib... i really wanna get this working, fun little project for a sophomore EE student :)
 
frostmeister said:
Well, here's the circuit. Build it and test the output with a voltmeter first, so you can verify you're getting the correct output. This thing is 80% efficient - translates to 1 watt of heat for every 5 watts it supplies. The output current depends on the inductor and resistor. Inductors will usually come with a current rating, and check the diode you're using as well. I can't find a 1N5820 in my electronics catalogue, but you could use a 1N5822 which has a 3A current rating, and will be good for an output of up to 40 volts. 3 amps is the max the LM2577 can supply by the way, which should be ok for about 4 standard 12volt fans quite safely.
Have fun :)
switchreg.jpg

Let me know if there's anything you're unclear on by the way :)

say wahaaat?
 
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