Author Topic: I need help solving an electronics problem  (Read 862 times)

bcalla

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I need help solving an electronics problem
« on: May 26, 2020, 11:16:58 AM »
A while ago I bought a couple inexpensive LED strips from Electronic Goldmine that I intended to use to build a light fixture over my workspace.  They are 22" long with 14 SMD LEDs and +/- terminal connectors at one end.  The catch was that the ran on 40v DC, but I figured I'd come up with a way to power them later.  Well, I just got lucky and picked up a 42v wall wart that was intended to power a battery recharger for power tools.

I tested the power supply with one of the LED strips and it worked great.  Too great.  The light is blinding.  I was thinking that I might add a toggle switch to select either or both strips; and either a resistor to set the correct level of brightness, or dimmer (either a trimmer or pot).

So I hooked up a 100k pot to see how much I could dim it.  While turning the pot, I heard it pop & saw it spark.  After tossing the pot in the trash, it occurred to me that the components I buy for building 9 - 18 volt pedals may not be able to handle 42v.

Since my electronics knowledge is pretty much limited to following a build doc, I'm reaching out to see if someone here can guide me.

Should pedal components - specifically pots, trimmers, resistors & toggle switches - be able to handle this?

If not, what do I need to look for?

Thanks!

m-Kresol

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Re: I need help solving an electronics problem
« Reply #1 on: May 26, 2020, 11:28:50 AM »
Hi,

look for the power rating. Your pot will have no resistance in one extreme position, meaning that a lot of current will run through. Even at a low voltage drop, it will likely exceed the power rating, which is 0.06-0.125 W for 16mm Alpha pots.
You'll have a chance with a 100k pot in the 100k extreme corner, you'd have P=U*I=U^2/R=42*42/100000=0.017W. Not sure if the current will be large enough, but you could start there and dial it down. I *think* that this way you have a chance of getting to a reasonable test result without blowing the pot.

I would have totally done the same btw.  ::)
I build pedals to hide my lousy playing.

My projects are labeled Quantum Effects. My shared OSH park projects: https://oshpark.com/profiles/m-Kresol
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jubal81

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« Last Edit: May 26, 2020, 12:05:12 PM by jubal81 »
"If you put all the knobs on your amplifier on 10 you can get a much higher reaction-to-effort ratio with an electric guitar than you can with an acoustic."
- David Fair

danfrank

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Re: I need help solving an electronics problem
« Reply #3 on: May 26, 2020, 02:02:50 PM »
Hey, next time provide a link to what you need help with so those here know what all the specs are.
From what you've described, make a simple voltage regulator with one of these. You can even use your recently bought transformer to power it. You will need to isolate and heatsink the regulator. Good luck.

https://www.jameco.com/z/LM317HVT-Texas-Instruments-Standard-Regulator-1-2-Volt-To-57-Volt-1-5-Amp-3-Pin-3-Tab-TO-220-Rail_192276.html?%20CID=GOOG&gclid=EAIaIQobChMIrPO8zajS6QIVD9bACh3PBgzKEAQYASABEgLFu_D_BwE
« Last Edit: May 26, 2020, 02:05:35 PM by danfrank »

bcalla

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Re: I need help solving an electronics problem
« Reply #4 on: May 27, 2020, 07:32:19 AM »
Thanks for all the suggestions, I'll check them out.

Regarding the link, I've searched the web & couldn't find one.  The LED strip has "Acuity Brands" printed on it, and various numbers.  I tried every combination and got nothing.  Electronic Goldmine sells a lot of electronic salvage / overstocks.  As far as I can tell, Acuity Brands sells only finished commercial lighting, not component parts, so this was likely an overstock.

BTW, Electronic Goldmine sells lots of cool things.  They send out emails 2-3 times a week with clearance deals and new inventory.  They're worth checking out & getting on their mailing list.

danfrank

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Re: I need help solving an electronics problem
« Reply #5 on: May 27, 2020, 11:27:31 AM »
Hi again,
My post was a little harsh. My apologies for that.
Since your LED array takes 40 volts, you could also probably use the standard version of the LM317 as it goes up to 37 volts output which may be enough brightness for your needs.
Yeah, EG has been around for a long time but I've forgotten about them. It was nice looking through their website again. Lots of stuff!
« Last Edit: May 27, 2020, 11:29:10 AM by danfrank »

bcalla

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Re: I need help solving an electronics problem
« Reply #6 on: May 28, 2020, 07:07:51 AM »
NP, I didn't take it as harsh.  I didn't mention that I scoured the web before making this post.