Transformer for power supply.

[iceburg47]

I am working on building a DC power supply for use with my charger. I found what seems like it might be a good transformer to use. It is a 115-120 VAC primary coil, with 5 amp output, but rather than VAC or VDC output it lists it as 12 VCT.

How is VCT different from DC voltage? If i were to put it through a full rectifier after the transformer would it meet my needs?

Thanks for the help.

Ben

[iceburg47]

Okay, I actually found the answer, so I'll post it here just to help anyone else who may wonder.

VCT means Volts Center Tapped. What this does is it has an extra tap half way through the secondaty coil which allows you to use ither the full output by connecting the two outer taps, or half the output voltage by connecting to the center tap and either outer tap.

BTW, here is a link to the transformer if anyone else might want one for a power supply or something.

http://www.allelectronics.com/cgi-bin/category.cgi?item=TX-125

[Dan Baldwin]

A 12 VCT at 5 amp transformer means that you could get 12 volts at 5 amps,6 volts at 10 amps, or +-6 volts at 5 amps depending on how you wire it.

Dan

[Miami Mike]

...which allows you to use ither the full output by connecting the two outer taps...Don't connect the two outer taps, or you'll get lots of terrible smelling smoke! :eek:

If you want, we'll help you design the power supply here.

And no, Dan is wrong. You won't get 10 amps from that transformer at any voltage.

[Dan Baldwin]

Don't connect the two outer taps, or you'll get lots of terrible smelling smoke! :eek:

If you want, we'll help you design the power supply here.

I was hoping he meant connect TO the outer two taps.

Dan

[iceburg47]

Sorry, I did mean connect to the outer taps, not connect the two taps. I was thinking correctly, just not typing correctly.

Thanks for the help. In a little bit I'll uplead my schematic that I have designed and I would be very appreciative of any pointers.

BTW, I am intending for a 12 VDC 5 Amp output from the supply.

Thanks again,

Ben

[Miami Mike]

Sounds good!

You won't want to use the center tap. You'll need a full-wave bridge rectifier across the end taps, followed by a capacitor filter, which will raise your no-load voltage to about 17 volts, and then some sort of voltage regulator. That's the basic circuit, but then you'll want some extras for safety and convenience, like a fuse, switch, pilot light, and so on.

There are lots of ways to do the regulator, so that's where you'll probably get a variety of suggestions here.

[iceburg47]

Yeah, I've already got a full wave rectifier, a switch, and light. I could definitely use some tips for the regulator.

As far as a capacitor filter goes, I know that the formula for capacitance in farads is F = V*s/A where s is charge time in seconds. What value should I assume for s? I also am assuming that I want the cappacitance to be about balanced with the VA going through it so that it will smothe out any surges and dips, is that right?

Thanks again,

Ben

[Dan Baldwin]

Yeah, I've already got a full wave rectifier, a switch, and light. I could definitely use some tips for the regulator.

As far as a capacitor filter goes, I know that the formula for capacitance in farads is F = V*s/A where s is charge time in seconds. What value should I assume for s? I also am assuming that I want the cappacitance to be about balanced with the VA going through it so that it will smothe out any surges and dips, is that right?

Thanks again,

Ben

What voltage range are you looking for? Do you need current limiting as well?

Dan

[iceburg47]

I am looking for an output voltage range of as close to 12 vdc as possible, but the charger I am building it for says it can hande 10.5 - 14.5 vdc. It requires a minimum of 1.2 amps, but does not specify a maximum. I am thinking that I will use either a 3 amp or 5 amp transfirmer. The charger has it's own built-in current regulator, so I am not anticipating this being a problem.

I will upload a schematic for what I am planning once I get to work and can use a scanner there.

Ben

[iceburg47]

Hi again.

Thanks for the help everyone, but I am thinking that I will put this project off for a while due to the fact that I don;t think I will have enough time to do it properly ( I am attending University full time and working part time). Thank you so much for all the advice. I'll be putting it too good use, probably after midterms though.

Thanks again.

[arx_n_sparx]

$5 more bux and get one of these: http://www.allelectronics.com/cgi-bin/item/PS-1231/search/12_VDC_3.5_AMP_POWER_SUPPLY_.html
Only $9.00 for this one - there are threads in here on how to convert it. http://www.allelectronics.com/cgi-bin/item/PS-4151/search/150_W_SWITCHING_POWER_SUPPLY_.html
Brad

[olmod]

old cb radio power supplies often found at garage sales are the best as they are fully regulated and kind to your gear. ;) and cheap. :)