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> wall warts, backwards?
NEVjr
Posted: February 07, 2006 06:01 am
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i got a transformer out of a wall wart, would there be anything wrong with hooking it up as a step up transformer for very low current apps? like 2-3mA


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HOTDROCKS
Posted: February 07, 2006 07:29 am
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No problem... You can get some pretty high voltage pretty quick...
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awright
Posted: February 07, 2006 08:44 am
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Yeah, definitely a problem if you are talking about applying line voltage to the secondary in an effort to get high voltage out of the original primary. Current isn't the only issue. Sorry, I can't remember the proper terminology and my books are not available at the moment, but any particular transformer core can only support a specific number of volts per turn of a winding at any particular frequency before the core saturates. At the point of saturation, the inductance collapses and the only thing left to limit current is the resistance of the wire in the winding - a very low value.

Depending upon how conservative the design of your transformer was, applying 115 VAC to a winding designed for 6, 12, or 24 volts could easily lead to saturation, very high currents in the new primary, and burnout. On the other hand, if the design was very conservative, the transformer may support significant overvoltage.

It's easy to test your transformer. Put a low-wattage (25 watts or so) light bulb in series with the new primary and gradually turn up the voltage on the new primary using a VARIAC (variable autotransformer). The lamp should glow dimly or not a at all below the saturation point. At some overvoltage, the bulb will suddenly glow much more brightly. Back off the voltage a few percent. That is the highest voltage that can be applied to that winding.

awright


This post has been edited by awright on February 07, 2006 08:59 am
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draget
Posted: February 07, 2006 01:57 pm
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You could say step down to 12V then apply 12V to a 6V winding.....less of a severe step.
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NEVjr
Posted: February 08, 2006 02:02 am
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hmm, anyone got a better solution to get say 1000v or so at a very low current? it will output to a bunch of voltage multipliers, but i dont have enough to get up to where i need it, im building an ion genrator


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awright
Posted: February 08, 2006 09:07 am
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Well,I hate to admit it after my first post, but about 35 years ago I used an audio output transformer (probably < 1 watt, based upon the physical size of the transformer) connected backward to generate about 900 volts for an electrostatic actuator for calibrating condenser microphones. (I was much more naive and ignorant in those days.) Current drain was extremely low, being purely surface leakage across glass insulators and a low-value, high voltage capacitor.

Despite the apparent success of that endeavor (nothing ever smoked), I'm not sure I would recommend that approach today. One thing to bear in mind is that an audio output transformer in those days would have been designed for a few hundred volts B+ voltage on an output tube, even for a low power amp, rather than the low voltage primaries of audio amp transformers today. I doubt you can get such a transformer today unless you gut an old low-power tube amplifier.

Consider HV DC-DC converter from PICO or ULTRAVOLT, ERG, EMCO, and others. Google HVPS for a listing of suppliers.

A surplus electronics dealer in the Olympia, Washington region had low-priced ($15 or $20, I think), small assemblies several years ago with a 900V and a 5500V DC-DC converter at a few ma. The main problem for my application was that they were MIL devices designed for about 28 VDC in. The store is Electronic Dimensions in Puyallup, WA. www.el-dim.com. Owner Glen Galati (a nice guy).

Good luck.

awright
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Ice-Tea
Posted: February 08, 2006 09:09 am
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Hav eyou considered recycling a backlight inverter?
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hal
Posted: February 08, 2006 04:37 pm
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what are the outputs of flybacks? No idea how to use them, but they are relatively available...
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NEVjr
Posted: February 09, 2006 07:04 am
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QUOTE (Ice-Tea @ Feb 8 2006, 09:09 AM)
Hav eyou considered recycling a backlight inverter?

um, im thinking this is out of an lcd or something?

what about the ballast for those flourscent spiral bulbs? i got one of those, the bulb broke, never used. how would i get it out of there? what will the connections look like? what kind of out put do they have?


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