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Old 28th January 2013, 08:31 PM   #1
Atilla is offline Atilla  Norway
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Default Simplest way for low-VA 220V->110V ?

I need to get 5-10W worth of power, in order to use a Neon light bulb made for 110V. Is there anything simple I can do so I don't have to get a full-blown transformer? Or, at least, does anyone know of 10VA miniature transformer that I can easily hide in a small box?
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Old 28th January 2013, 08:37 PM   #2
Atilla is offline Atilla  Norway
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Actually, neon light bulbs would work perfectly fine on both AC and DC, right? I could use a simple low-power SMPS to power it, I suppose?
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Old 28th January 2013, 08:47 PM   #3
Elvee is offline Elvee  Belgium
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I think you mean fluorescent tube, not neon. They might light with DC, but their lifetime will be seriously reduced, I wouldn't recommend it.

Normally, these lamps are voltage-independent: their actual voltage is generally below 100V, and their outside operating voltage is set by the ballast, either conventional or electronic.
That is the part you should change to change the voltage.

If it is included in the lamp, it depends very much on its implementation: some will only tolerate the exact type of current and voltage, others will accept DC, and /or a wide of input voltages.

Can you provide additional details?
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Old 28th January 2013, 09:23 PM   #4
Atilla is offline Atilla  Norway
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Actually, yes, I've been a bit unclear. I'm pretty sure I mean neon, however not your usual neon pilot light. I mean Aerolux glow light bulb (or, more likely, a clone of that) like so: Aerolux Light Corporation - Wikipedia, the free encyclopedia. Given the age of their existence and manufacture, I am guessing they're working directly plugged into 110VAC. I suppose that like any other Neon bulb nothing is stopping me from using them with 110VDC, except that only one of the electrodes will glow, I'm not too sure if that'll have negative impact.
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Old 28th January 2013, 09:40 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Work our the approximate resistance for 7.5W
at 110VAC and apply that in series for 220VAC.

Clearly you'll need a 10W rated resistor.

You probably need higher a higher value if you
work out the conduction voltages and duty cycle.

rgds, sreten.
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Last edited by sreten; 28th January 2013 at 09:43 PM.
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Old 29th January 2013, 08:22 AM   #6
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Atilla View Post
I suppose that like any other Neon bulb nothing is stopping me from using them with 110VDC, except that only one of the electrodes will glow, I'm not too sure if that'll have negative impact.
I am pretty sure it will, better stick with AC. To avoid most of the useless dissipation of a resistor, you could use a capacitive dropper as a main ballast.

A small resistor would probably still be needed to avoid effects of negative resistance. You could try with two 1µF/250VAC X capacitors in parallel, and a 100 ohm/1W series resistor.
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Old 29th January 2013, 03:05 PM   #7
Atilla is offline Atilla  Norway
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Alright, thank you very much for the help! I'll get to it when the lamps show up.

Slightly-off-topic: I guess they come with a current-limiting resistor integrated, if they're made to directly go in a 110v socket?
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Old 29th January 2013, 03:20 PM   #8
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Atilla View Post
Slightly-off-topic: I guess they come with a current-limiting resistor integrated, if they're made to directly go in a 110v socket?
Not necessarily, it depends on the type of discharge. But you can check the presence/value of such a resistor, it will provide useful information for the 230V conversion
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Old 29th January 2013, 03:24 PM   #9
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Default Watt-less Power

Why use a transformer/resistor?
Use a 470nF 250Volt class Y capacitor in series with the lamp. That will give you approximately 5Watts of power at a reduced current.

This method is nicknamed 'Watt-less Power' as there is no loss and no heat given off, wasting power.
Television and audio equipment, over the years, used this method to produce a Standby voltage to run the microprocessor and basic memory.
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Old 29th January 2013, 10:34 PM   #10
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a safe way for experimenting:
if you have one 220v / 12v plus one 220v / 24v trafo, connect them back-to-back
220v / 12v -> 24v / 220v out comes 110v isolated from mains

another not so safe way:
if you have a 220v trafo which has a 110v+110v primary it could be used as auto-transformer not (!) isolated from mains though
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