# 110 VAC to 20VDC Question

• posted

Terry, If you really need DC for your application, you must determine the following: . 1) Load Current . 2) Maximum Ripple that you can tolerate . 3) What load regulation is required? (What change in voltage can be tolerated . as the load varies from 0 to full load?) . . 4) Do you need line regulation? (Must the voltage remain constant . with varying line voltage . If the answer to 4 is "Yes", then you need a regulated supply, which may put you beyond your price point. . If the answer to 3 is something "reasonable, like 5 - 10 %, then a transformer - bridge rectifier - capacitor filter type design will probably work. . As a staring point, the following (rough) rule of thumb applies: Let R = Load resistance = Vout/Iload let F = line frequency

2*PI*R*C = 10 gives 10% ripple and 10% load regulation. The peak diode current will be 10 times the load current. Scaling the value of C up or down will get you close to your requirements for ripple and load regulation. If the value of C becomes too high to be practical, then you will need a regulator, which may put you outside your price point. Don't ignore the peak diode current. This will probably be more important in selecting your diode than the average current. Regards, Jon
• posted

I'd say so.

Here's a nice 0 to 45V 0.5A HP power supply going for \$10.

```--
Thanks,
- Win```
• posted

You don't say what your power requirements are, but there's a 20V, 6A unit on ebay right now, and the bidding as of 7:51 AM PST Wednesday is at \$149.89:

Mind the word wrap.

Just shop around. You can buy something for much much cheaper than it would end up costing you if you're not experienced at building stuff and designing stuff and specifying components, albeit, if you only want an educational exercise, you should shop around surplus places and ham fests and that sort of thing. If you can get a surplus transformer then building a supply with some diodes and filter caps and a regulator could be a reasonable beginner's exercise, depending no how much work you want to do. :-)

Good Luck! Rich

• posted

A question. I have 110VAC coming in, and need to (cheaply) be able to provide 20VDC out. What is the quickest and cheapest method? A transformer? Are there other means that might be a bit more expensive?

Thank you!

• posted

Thanks Phil, but can you point me in the right direction? What are some other means that might cost as much or slightly more?

Terry

• posted

Sorry, I suppose that would help. I have a coil that will heat up some fluid. I am trying to keep this as inexepensive as possible, all the parts and pieces totaling no more that \$7 or \$8 dollars. The transformer, while it sounds like it is the cheapest, might also be the most cumbersome and heavy, that is why I was looking for alternatives.

Does this help?

Thanks

• posted

you also need a rectifier if you want DC, but it is not clear that is needed for a heater application. If you only need heat, consider a large wattage resistor and eliminate the transformer entirely.

• posted

Why does it have to be DC?. Heaters are equally happy with AC, and this reduces the parts needed, to just the transformer. Basically, if isolation is required, a transformer will have to be involved (it is the only economic way of providing isolation of this sort). Smaller transformers can be used, by increasing the operating frequency, bu this adds the complexity of converting the incoming power to DC, then chopping this at a higher frequency. If DC is required, then rectification will have to be added, and if the voltage needs to be smooth/stable, smoothing, and possibly regulation. Normally if you look at things like low voltage halogen lighting, and fish tank heaters, a simple transformer is used. Assuming there is some reasonable current involved, except in very large production, you will not get any other solution, down to the desired 'price point'. However the key 'missing data', is how many amps are involved...

Best Wishes

• posted

Not much. I can't see why you need DC though.

How much power do you need man ?

Graham

• posted

"Terry Dennis" schreef in bericht news:l57xf.35188\$ snipped-for-privacy@tornado.rdc-kc.rr.com...

Not enough. What's the power rating of that coil or what's its resistance? Why do you ask for DC, is the inductance of the coil really that high? Do you need insulation between 110Vac and the coil?

petrus bitbyter

• posted

"Terry Dennis"

** Yes and yes.

Boy, that was as easy one ;-) .

.......... Phil

• posted

"Terry Dennis"

** Please do NOT top post !

Explain what your application is and give us a few numbers eliminate the mysteries.

....... Phil

• posted

"Terry Dennis"

** Err - you say 20 volts DC.

How many amps would that be ??

BTW

Your price limit exclude low weight solutions.

....... Phil

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.