12VDC fan driven by 120VAC...

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Externet
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12VDC fan driven by 120VAC...

Post by Externet » Mon Oct 22, 2012 9:09 am

How would you do it/calculate, directly from 120VAC, the same capacitive series circuit as leds are driven fron mains? -No transformer-, -no zener-

Say the fan is from a PC supply ~4" square, 12VDC, ~0.2A type.

120VACLine-----------||-----------4Diodebridge-----------Fan

Capacitor >240VAC duty
1 Ampere 1KV diodes,
a 1M resistor in parallel to series capacitor
A smoothing electrolytic capacitor in parallel to the fan leads ?

Any particular considerations / additions you would suggest in the circuit ?


Reason: The 120VAC fans are 10-20 times the price as those 12VDC.
Miguel
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Re: 12VDC fan driven by 120VAC...

Post by gerty » Mon Oct 22, 2012 10:37 am

There are a few types listed here, personally I have no experience with them.
http://www.daycounter.com/Circuits/Tran ... lies.phtml

And another..http://ww1.microchip.com/downloads/en/a ... 00954A.pdf

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Re: 12VDC fan driven by 120VAC...

Post by Externet » Mon Oct 22, 2012 3:56 pm

Thanks, Gerty. All those use zeners.
The test set I have running for a while on 120VAC uses a 3uF/250VAC series capacitor, and a 10uF electrolytic in parallel to the 12VDC / 0.13A load fan. Raising the value of the electrolytic decreases the voltage from 11.7 Vdc about 0.5 Vdc.
Nothing gets warn, seems veeeery happy. Perhaps a 3.3uF AC capacitor with a 25 uF electrolytic at load will bring the voltage to 12.0Vdc.

Am concerned with reliability, and if further smoothing/filtering the output would be convenient.

The calculations show for 120VAC/60Hz into 3.3uF ; Xc = 804 Ohms + 92 Ohms for the fan = 896 Ohms ----> 0.13 Amperes, which matches the observed above.

Miguel
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Re: 12VDC fan driven by 120VAC...

Post by gerty » Mon Oct 22, 2012 7:55 pm

Whoops! I missed the 'no zener' part of your post.

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Bob Scott
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Re: 12VDC fan driven by 120VAC...

Post by Bob Scott » Wed Oct 24, 2012 8:53 am

gerty wrote:There are a few types listed here, personally I have no experience with them.
http://www.daycounter.com/Circuits/Tran ... lies.phtml

And another..http://ww1.microchip.com/downloads/en/a ... 00954A.pdf
Perhaps the authors of the schematics in those links don't know that Neutral and ground are connected to each other in the electrical panel.
If you build those circuits as shown, be prepared stand back and see smoke, fire, dead parts and tripped breakers, especially GFCI breakers.

Externet: You have a good idea. I'd use a capacitive divider using two caps. A capacitive bridge to get the voltage down and a diode bridge after to make the fan current DC. Don't connect any part of the circuit to ground
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Re: 12VDC fan driven by 120VAC...

Post by Externet » Wed Oct 24, 2012 1:25 pm

Hi Bob.

Yes, the thingy is working great for several days with a single 3uF/250VAC capacitor, and about the neutral to ground in the panel always bothered me a lot; waste of a conductor in all installations. What was the original intention, having two rails at the breaker box, one for each? Which was never implemented; or what happened ?
Is it related to non-polarized plugs applying phase to non-insulated metal cabinets ?

Miguel
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Re: 12VDC fan driven by 120VAC...

Post by Bob Scott » Wed Oct 24, 2012 5:00 pm

Externet wrote:What was the original intention, having two rails at the breaker box, one for each? Which was never implemented; or what happened ?
Is it related to non-polarized plugs applying phase to non-insulated metal cabinets?
Miguel
I'm waiting for Dean. He's so much better at explaining these things in detail. :shock:

In the meantime, take a look at this:
http://en.wikipedia.org/wiki/Ground_and_neutral

At the bottom of that page, there is a reference to another link "Neutral wire facts and mythology" Beside it, it says "dead link", but it's not! It is a very interesting article from the company "American Power Conversion":
http://www.apcmedia.com/salestools/SADE ... _R0_EN.pdf
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Re: 12VDC fan driven by 120VAC...

Post by Robert Reed » Wed Oct 24, 2012 5:58 pm

Bob & Exter
I think the circuit intended to be - the "ground" symbol really being a "common" for the DC output only and not a power line ground. This way it will work. But I agree that this is a very dangerous and misleading print for someone not well versed on standard residential wiring.

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Re: 12VDC fan driven by 120VAC...

Post by Ed446 » Thu Nov 15, 2012 1:06 pm

Here in Tennessee, new construction the neutral and ground are not connected. Old constructions are as you stated. I know a swimming pool builder that says this is causing a lot of problems.
Edwin

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Re: 12VDC fan driven by 120VAC...

Post by Robert Reed » Fri Nov 16, 2012 9:05 pm

Edd
"Here in Tennessee, new construction the neutral and ground are not connected."

Don't understand that, as the neutral and ground have to be connected by rule of the NEC for years. Usually at the service entry point.

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