Plasma Globe power supply change from AC to DC

[LordVader88]

Hi I have a cheap ebay plasma globe, and it never worked from day 1 but it was too late/expensive to complain. Later I opened it up and added a 470uF that was written on the PCB but missing from near the HV transformer.

Its meant to run off a 12V-AC transformer, and it has the bridge rectifier on the PG PCB. I can't find the wall transformer and so just tried 12V-DC right onto the main 220uF filter cap and it worked (there is no XY caps or any such things or a fuse I should add a fuse). I never did find its PCB schematic or for another for that matter

So today I took out the 4 diodes, and I'm just running it of a proper AC-DC wall trans with 12V 2A DC output (from a quality fibreOP modem) that fits the plug right


If 12V rms goes into a 4x 1n4001 rectifier, what DC voltage comes out ? I skimmed through this

So if I follow,

Vmax = 12rms / 0.707 = 17V and then Vdc = 0.637 * 17V = 10.8V
and then I'm supposed to take of another 1.4V for 2 diodes
=9.4V at the 1st filter cap ? (there is no XY caps or any such things) it was just the 4way and then a 220uF filter cap.


Does that sound right ? If so straight up 12V is way too high right ?

I never owed a PG before and don't remember so much the heat on the plastic, this seemed pretty hot, and something whines a bit . So I only ran it for a minute, but with it all closed up, no idea if anything inside is overheating and what not. (and its bedtime)

 

[cjdelphi]

After ac is passed through the rectifier, it might be seeing closer to 16v there's a possibility the whine comes from lack of voltage..

 

[Harald Kapp]

Vmax = 12rms / 0.707 = 17V

Right.

Vdc = 0.637 * 17V = 10.8V

Wrong.
Why? You didn't take into account the effect of the smoothing capacitor. The equation you used is for the rms value of the rectified DC without smoothing capacitor. With a suitable capacitor (rule of thumb: 1000µF per 1A of output current) the rectified DC is at about 17V - 2*0.7V = 15.6 V. The 2*0.7 V accounts for the voltage drop across the rectifier diodes (you got that part already).

Does that sound right ? If so straight up 12V is way too high right ?

Impossible to sy without knowledge of the circuit. Many a circuit can operate from a supply within a wide range.Others need a well defined voltage. If the latter were teh case, I'd expect the circuit to have an internal voltage regulator as the setup you describe (rectifier, capacitor not assembled) doesn't lend itself to a well defined operating voltage.

this seemed pretty hot

This doesn't sound too good. Warm yes, but hot? Never.

something whines a bit

Not unexpected. The plasma globe internally uses a high voltage to create the electric filed required for the operation. This high voltage is created by a transformer and a generator which generates the high frequency voltage for the transformer from teh DC operating voltage. If the high freqeuncy/high voltage circuit is not assembled quite well, the high frequency voltage/current can lead to mechanical vibrations which you hear as 'whining'.

 

[shrtrnd]

It's so hard to troubleshoot something without looking at the circuit itself.
Did you try looking at the globe in total darkness to see if you're seeing even weak lightning bolts inside that
globe?
Is there a trim-pot attached to the circuit to adjust the voltage?
Is it possible the globe experienced atmosphere leakage, and the argon or whatever gas they used may have
leaked-out?
Like Harald said, if you've got HOT heat, something is wrong with the electronics circuit.
I would THINK that whoever made the unit would test it to make sure it worked before they sent it out of the factory.
Whatever modifications you made to the electronics would complicate the original design.
My guess would be, maybe the globe gas wasn't sealed well enough and leaked out, or all the shipping jostling
from the factory, through the vendor, to you, may have caused a gas leak.
I'd be real careful about whatever modifications you make to the original circuit.

 

[LordVader88]

I don't ever remember owning an AC-AC wall pack until this year, so for all I know it probably never came with 1 so I plugged 12VDC itno its plug and nothing.

The schematic is probably near as basic an 80s or 90s EE would come up with, and it still ROCKS.

Yeah I've never studied EE or QED enough, but nevermind that, this is FUUNNNNN

I have an 8v AC-AC wall rig from a phone, I might try that back through a 4wayBR and see what thats like.


I know the basics of coil/cap whine, what typical noise should the actual plastic gas ball full of gas actually, do they make ???

The "high temperature" I'm talking about is when I'm touching globe and most of the (whatever a magnetohydrodynamists might call it) centers on that place.

It puts out a lot of jets? and works great that way and looks great, I never tried counting them but it looks normal that way. An when stuff touches it.

Perhaps in time I shall finish tracing out it small PCB, ages ago I got hungup on the hexINVERTER chip and how that all works for the HV transformer, and I still don't know

Also photos, we shall see !?2@!

Also perhaps I shall take it to THE UNIVERSITY, and ask EE girls

 

[LordVader88]

Nope no trimpots

It does have a little mic that makes it flash on/off when the case/whole thing it tapped, and I wonder what setups the freq/energy reponse for that and what it actually "hears", and what filters it

There's no inductors, after its reticified its just a bunch of resistors, caps, 1-2 diodoes, some 8 or 12 or 16??? DIP-hexinveter ....................................fun fun IDK ( I have to find it later)

this is not a telephone call , I find it and try a photogragh (in color)