# tuning wall warts and amperage question



## Devils Chariot (May 23, 2007)

Hey Smarties. I have some simple questions, and some might overlap with the batteries to plugs thread, but I didn't want to 1. hijack his thread, and 2. have it turn into a clusterf*ck with answers and questions all over the place.

Question Setup:

Here is what I want to do. I want to wire a whole stack of skulls, each with two leds in it for eyes. I want to use one LED tealight as a flickr circuit (if possible) to run 20+ leds.

The tealight uses 3v batteries (let us assume it does in case I remember wrong, might be 5v) and has a circuit board that flickers. I have tried hooking it up to a 9v battery, and used a resistor to knock down the voltage, because at 9v it kinda just blinks. So I know I can tune the voltage to make it work right from another power source.

Question 1: Can I get a walwart, that is say 5v, 3.7 amps. and use resistor to bring it down? ( I dont know if that will cause over heating) or even a 12v and bring it down to say 3.2v (what most of my leds run at) or would that heat up?

Question 2: If the amperage rating is 3.7 amps, that like 3700 ma right? So could I theoretically run 148 LEDs (at 25ma draw each) from this if I wired them in parallel?

Question 3: Does anyone think amperage would affect the flicker function of the tealight circuit as long as the voltage is adjusted to match it normal battery operated voltage?

Thanks everyone for the help, I don't know much about electronics.


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## fritz42_male (May 5, 2009)

Each LED ought to have it's own resistor wired in UNLESS you specifically buy 5V LEDs which usually have the resistor soldered in for you.

Yes, a wall wart which puts out 3.7A (good power by the way) can theoretically drive 148 LEDs.

HOWEVER, if you want to use a flicker candle to drive a number of LEDs, the only way is to hook up a decent transistor (actually 2 in a single package - called a Darlington Pair) to the LED on the candle and use this to drive your LEDs. You then have to replace the batteries on the candle with a wall wart of exactly the same voltage as the original batteries.

http://www.kpsec.freeuk.com/trancirc.htm - Darlington Pair info.

The transistor pair will pass higher currents than the candle flicker circuit and this in turn will allow you to drive more LEDs

Otaku, have you tried this? I wouldn't mind doing this as well but I need to find some flicker candles - they aren't easily available in Oz without going the mail order route.


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## 4nntt (Nov 28, 2006)

I suspect drawing that much current through the little tea light flicker board would actually cause it to catch fire.

I think a better approach might be to leave the tea light circuit powered by the batteries, but hook the output to a power transistor that then powers your string of LEDs from the wall wart. 

Unfortunately, I don't know how to actually do this specifically. Hopefully one of the electronics gurus here can whip up a quick circuit for you.


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## Otaku (Dec 3, 2004)

Those little boards probably aren't able to handle big current (relatively speaking) like you're proposing. I've run up to 6VDC through those flicker circuits with no issues, but above that the flicker kinda craps out, as you noticed. However, that was still with just one LED. Since the tea lights have just one low-power LED, I imagine that they're built for low amperage. They're cheap, though - I'd go ahead and test it out with some loose LEDs wired in parallel to the board.


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## Devils Chariot (May 23, 2007)

fritz42_male said:


> Each LED ought to have it's own resistor wired in UNLESS you specifically buy 5V LEDs which usually have the resistor soldered in for you.
> 
> Yes, a wall wart which puts out 3.7A (good power by the way) can theoretically drive 148 LEDs.
> 
> ...


I was thinking that if I put the resistor between the wallwart and the circuit then the circuit could only pass on what it was getting from the resisotred wallwart..


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## Otaku (Dec 3, 2004)

4nntt said:


> I suspect drawing that much current through the little tea light flicker board would actually cause it to catch fire.
> 
> I think a better approach might be to leave the tea light circuit powered by the batteries, but hook the output to a power transistor that then powers your string of LEDs from the wall wart.
> 
> Unfortunately, I don't know how to actually do this specifically. Hopefully one of the electronics gurus here can whip up a quick circuit for you.


Yes, this would be a good way to go, better than directly wiring the board to a mess of LEDs. You could use an IRF510 MOSFET to switch the wart, using the 6VDC battery pack to keep the gate open. I don't know how the MOSFET will behave with an intermittent voltage input, though.
A Darlington will work, but will have problems at higher current loads. There's also a significant voltage drop with a Darlington that the MOSFET doesn't have. I have a cannibalized flicker circuit board laying around somewhere, along with an IRF510. Let me try this out with a handful of LEDs. More to come...


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## Devils Chariot (May 23, 2007)

I guess I'll try it and see what happens, just building it a little at a time. I'll se how many i can get on one circuit, and then see if I can get enough to make it feasable to then just wire a few more candles in parallel from the wallwart (which I will trim down with a resistor).

The darlington circuit sounds like an easy solution if I understood how to make what I needed. I'll make that plan B. Unless someone can just tell me what parts I need.


Hey i got a question, and this explains my thinking on this, the GOE guys said volts is what make stuff catch fire, so you have to get tht right, what about amperage. The way i understoof it is that if you ( and I am trying to illustrate this simplay) had a LED that runs at 3v, and you had a 3v powersupply, that was 250ma, then you could wire 10 LEDs that run on 3v and have a current draw of 25ma. (ok probably only nine would run, but in a perfect world). or even simple a 3v ps with 10000000000000ma would run led just fine, since the voltage is matched, the map mean nothing, as log as there is enough.

Am i getting it all wrong?

oops didnt see your last post otaku, it came up while i was writing this. I will try at least two leds in parellel, that will cover individual skulls.


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## pshort (May 6, 2008)

Here's a related thread from some time back.

http://hauntforum.com/showthread.php?t=10038


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## fritz42_male (May 5, 2009)

Otaku is probably right in saying a MOSFET would be a better bet. They are cheap now and available from Radio Shack.

Another option would be to go out and buy a solid state relay (SSR) designed for DC work. I've got some DC SSR boards on order that are normally used for controlling large amounts of Xmas LED lights.

You should be able to pick up a DC SSR for about $10-20. All you would do is wire the original LED connections to the SSR (probably leaving the LED in place and then use the output from the DC SSR as your flicker 'switch'

As for a power source, for 500mA (20 x 25mA LEDs) you could just use a 3xAA battery pack and not bother with the resistors - the LEDs will be overdriven and shorter life but hey, it's only in use for a limited period.


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## Devils Chariot (May 23, 2007)

pshort said:


> Here's a related thread from some time back.
> 
> http://hauntforum.com/showthread.php?t=10038


That was a good thread. Too bad Rev didn't make a how-to for people who can't read diagrams. Maybe I should buckle down and try to learn them this year...(((sigh)))


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## fritz42_male (May 5, 2009)

Diagrams aren't that hard to read and make ONCE you start learning about the components. In this case you are only talking about 2-4 components (apart from the LEDs)

The simplest way to learn is to use whats called a protoboard - this allows you to make the circuit pretty much EXACTLY as the schematic.

If this is a temporary rig then you could use a small breadboard, use the components and then pull it all down to use with something else. Again, breadboards are easy to understand and there is little or no soldering involved. A small breadboard will cost $3-$5

If I can pick up a flicker candle soon, I'll make something up and take pics.


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## Devils Chariot (May 23, 2007)

well i know battery, ground (earth), resistor, diode, switch, but i cant alway figure out the line into a real circuit.


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## hpropman (Jul 27, 2008)

Yes you can use the flicker circuit to drive the mosfet which will supply the power to you leds. Make sure that each led has the correct resistor value for the voltage that you use (just google resistor calculator). You can also use a single resistor for two leds if you wire them in series.


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## Devils Chariot (May 23, 2007)

hpropman said:


> Yes you can use the flicker circuit to drive the mosfet which will supply the power to you leds. Make sure that each led has the correct resistor value for the voltage that you use (just google resistor calculator). You can also use a single resistor for two leds if you wire them in series.


What mosfet do I need? a P or an N? And then are there any other specs I need to know when I go to allelectronics? I see on allelectronics that the have power ratings, so do I just want one to match my power source?

So the circuit is like a signal the that tells the the mosfet to open and close the the gate to let voltage thru. To connect the the leds to the mosfet, do I need some kind of distribution block of some sort? (one of those things with all the screw like terminals).


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## Otaku (Dec 3, 2004)

I whomped up a little circuit this morning that accepts the input from a flicker board, runs it through a Darlington (couldn't find a IRF510 MOSFET on the bench) and switches wall wart power to a LED array. I'll have a drawing of the circuit later for those interested. It's only three parts, a 1N4148 diode, a 470K resistor and the Darlington. If you wanted to simplify the LED array/wall wart attachment, you'd want to include some terminal blocks on the board. I'll add those to the drawing.


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## Otaku (Dec 3, 2004)

OK, here's the circuit drawing. I used callouts rather than symbols for the components. All of the parts will fit on one of those small PC boards from Radio Shack. It's assumed that the flicker board will be powered by the stock batteries. I recommend just hacking the tea light open, cut off the LED and solder wires to the LED legs. Attach those wires to the input T-block. Check polarity on the legs first.


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## Devils Chariot (May 23, 2007)

Ok otakeu i think I got 90% of it. Just some symbol failure. There are two block i am unsure of as to what they are, if they are terminal or batteries. I drew a picture of how i understand it should look. Tell me if you think I am getting it. I drew it for mosfet, in my drawing the mosfet is rotated 180 degrees.

I think I'll go with mosfet since i want to drive alot of leds, thought I think I will make 2-3 of these so that they all don't flicker in unison.

Question on the darlington, if i go to the store and say hey give me a darlington, are they all the same or do i need to spec it out?

Thank for tutoring me Otaku and everyone!


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## Otaku (Dec 3, 2004)

Those are two-pin terminal blocks. It'll make it easier to attach input and output wires if you use them. All parts are available at R-S. Regarding the terminal strip, since you'll be wiring the LEDs in parallel, you really only need a two-position strip. Here's a parts list:

IRF510 MOSFET - 276-2072 - 1 each
Dual miniboard - 276-148 - 1 each
1N4148 diode - 276-1122 - 10 per pack
470K resistor, 1/2W - 271-1133 - 5 per pack
PC terminal block - 276-1388 - 4 per pack
Barrier strip, 2-pos. - 274-656 - 1 each


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## Otaku (Dec 3, 2004)

Devils Chariot said:


> Tell me if you think I am getting it. I drew it for mosfet, in my drawing the mosfet is rotated 180 degrees.
> 
> Question on the darlington, if i go to the store and say hey give me a darlington, are they all the same or do i need to spec it out?


You definitely got it. If you want to drive more than about 20 LEDs per circuit, go with the MOSFET.

I've had some issues in the past with Darlingtons. I prefer to use the MPSA13 from Motorola. They seem to be more predictable in their behavior. You can get Darlingtons at R-S and Fry's, but they're not MPSA13's and I've had a number of failures. It's not an issue if you use the MOSFET.


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## hpropman (Jul 27, 2008)

Sorry DC I have been tied up all day and am just getting back to this. It looks like Otaku has you well in hand. I was thinking of the same circuit more or less.


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## Devils Chariot (May 23, 2007)

Thanks for thinking of me Hprop. I went to allelectronics and got half the parts, I'll go to Radio Shack tomorrow and get the rest. Hope I can finish this by the weekend (going on vacation). I'll post pics/video when I finish.


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## Otaku (Dec 3, 2004)

Devils Chariot said:


> I went to allelectronics and got...the parts.


Man, I wish I could say that - I don't have anything like A-E nearby. The only surplus electronics supply place within 20 mi. sells third-hand junk and factory rejects.


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## pshort (May 6, 2008)

Otaku said:


> OK, here's the circuit drawing. I used callouts rather than symbols for the components. All of the parts will fit on one of those small PC boards from Radio Shack. It's assumed that the flicker board will be powered by the stock batteries. I recommend just hacking the tea light open, cut off the LED and solder wires to the LED legs. Attach those wires to the input T-block. Check polarity on the legs first.


For this circuit I assume that the tea-light board is powered with the original battery setup, and that the wall-wart is used just for powering the add-on LEDs.


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## Devils Chariot (May 23, 2007)

allelectronics is a mixed bag. but they have great prices for a walk in store. They didnt have the mosfet, and some stuff is poorly labeled so its hard to find.


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## Otaku (Dec 3, 2004)

pshort said:


> For this circuit I assume that the tea-light board is powered with the original battery setup, and that the wall-wart is used just for powering the add-on LEDs.


Correct. I figure those tea lights can last for hours on their batteries, and you may even be removing the LED as well, which will help.


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