# What power supply (amps) would run this plasma globe optimally?

1. Apr 7, 2013

### Kidphysics

It says DC in 12volts but I'm not sure how many amps this thing can handle... I don't want to plasma myself so I was looking for helpful answers, thanks guys pic of globe (paid \$8 not bad) http://postimg.org/image/462gwlj5v/

2. Apr 7, 2013

### Staff: Mentor

It's not how many amps it "can handle", it is what the current demand is at the 12V input. There is a power supply inside the device that converts the 12Vdc input to some high voltage that causes the plasma arcs. The product will have a specification in its datasheet or user manual that will tell you what size 12Vdc power supply you need to use. The maximum input current at 12Vdc input will be specified for you.

3. Apr 7, 2013

### Kidphysics

yes I should have stated in my original post that I bought just the top from a thrift store so I do not know the specs on the machine

4. Apr 7, 2013

### Drakkith

Staff Emeritus
Shouldn't it just be the voltage that matters unless the power supply cannot put out enough current at 12 volts to operate the device? Have I misunderstood something?

5. Apr 7, 2013

### Kidphysics

Well I have the option of having a power supply at that voltage but with an amp range of .5amps to possibly 6 amps and one would think the effect would be more pronounced with a larger current no? The question is could this thing blow at 3 amps or what I'm not really sure on this one..

6. Apr 7, 2013

### Drakkith

Staff Emeritus
I don't have any practical hands on experience, just a basic electronics course and my own reading under my belt, but I was under the impression that the applied voltage to the device determined the amount of current through it. As long as the power supply can handle the required current of course. Some can apply the right voltage, but if you reduce the resistance of the circuit too far, the power supply literally cannot supply enough current, so it 'stalls out' and the voltage fluctuates. So what's it matter if your power supply can handle 100x as much current as your device needs as long as the applied voltage is right?

7. Apr 7, 2013

### Kidphysics

Ah well I thought that the power supply wasn't handling that current but feeding it into my device.. so if my device could only handle 5amps and it was being fed 6 bad things could happen.. I am asking around though

8. Apr 7, 2013

### Staff: Mentor

No, you are misunderstanding this. You do not "feed" current into a device. You present a voltage, and the current drawn is determined by the device. Just like with a resistor: I = V/R, so the current drawn is determined by the voltage and the resistance.

So you need to find out what the maximum current drawn by that device is, when presented with the 12Vdc input that it needs. Does it have any vendor info on it, like a model number or something that you can use to look up the power supply requirements? It is strange that it specifies the 12Vdc input, but does not specify what input current is drawn from that 12Vdc power supply.

9. Apr 7, 2013

### Kidphysics

I don't think it does but thank you berkeman seems like Drakkith was correct! With this information though I could always go higher, like 6 amps and then let device just take what it needs... I have a 30 volt dc adapter but I don't believe voltage works the same way does it?

10. Apr 7, 2013

### Staff: Mentor

Odds are that it doesn't require a special power supply so just pick up a mid-sized one at an electronics store (or if you're like me, grab one from the box of power supplies for things you no longer own in your basement). 0.5A would probably do it, but if they sell one that's 1A I'd get that.

And no, voltage does not work the same way. Supply too much and you'll destroy it.

11. Apr 7, 2013

### Kidphysics

thanks russ I figured that would be the case, I think I'm going to purchase a 4 amp from amazon
https://www.amazon.com/LEDwholesale...r=8-11&keywords=12+volt+dc+6+amp+power+supply

in case the plasma globe is ambitious with current since I want to optimize it's effects- thanks everyone in this thread!

Last edited by a moderator: May 6, 2017
12. Apr 7, 2013

### Drakkith

Staff Emeritus
You aren't understanding the relationship between voltage, current, and resistance.

Take Ohm's law. Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points divided by the resistance. In math terms this comes out to: I=V/R (I is current)

Now, we cannot apply current. What we do is we apply a VOLTAGE. Voltage is the potential difference between two points, and it is the force that causes charges to move in a circuit. This makes sense if you realize that the charges require a force to move just like anything else. So we apply this force, the voltage, and depending on how much resistance the circuit has we have some amount of current that flows.

So, if your power supply applies 12 volts and can handle up to 6 amps, it pretty much doesn't matter if the device you're powering requires 1 amp or 5. It will only draw however much it needs. (Note that this is only a very basic summary and the real world is always more complicated)

13. Apr 7, 2013

### Kidphysics

I see, thanks Drakkith!

14. Apr 7, 2013

### Staff: Mentor

That should be plenty. Good price too - I may have to pick one up. I'm running my telescope from a benchtop PSU and it is a little cumbersome.

Last edited by a moderator: May 6, 2017