440v(AC) to 5v(DC) Using Resistor Network

It would be easier and more efficient to use a transformer and some rectifiers!

In short, no. It cannot be done with resistors alone.

You need to reduce the voltage (resistors can be used, but an isolation transformer would be safer), then rectify and smooth the resulting low-voltage AC.

Your post is confusing - the title states 5Vdc, while the body of the text states 5Vac. Which do you mean?

sorry for confusion,

its 440v(ac) to 5v(ac)

regards

rimpul

You cannot convert any AC signal to a DC signal without a non-linear device. Resistors are linear devices. (Well they are until one releases the internal smoke.) Diodes functioning as rectifiers are non-linear devices. Now converting 440 VAC to 5 VAC is possible with just a resistor network but your question brings many safety concerns to me.

The most readily available source of 440 VAC is a dangerous power distribution voltage that a novice should not ever directly use. There are many safety concerns beyond the understanding of a novice that must be considered for safe application of 440 VAC. Your question is such a basic question that you are clearly a novice.

440 VAC to 5 VAC is possible with resistors only, but would be VERY dangerous if no transformer isolation is provided. MORE data is needed. Without current(Amps) specifications on the 5 VAC side, any further calculation is pointless.

thanks for reply,

input= 440v(ac)

output=5v(ac) with 1A current

regards

rimpul

You could do it with a simple voltage divider about a false neutral, but I wouldn't as;

A. the ratios are a bit high for common 5 W plus resistor tolerances.

B. it needs a highly stable spike free supply and must be a constant uniform I amp current draw to not fluctuate in voltage widely

C. meaning, people may die.

D. and it's a waste of power

Use a transformer.

As I and others have already stated, working directly off of 440 VAC can be VERY dangerous without transformer isolation.

In addition, your goal of a 5 VAC @ 1 A (5 VA) load is just NOT practical. It would require large resistors rated for 1000 Volt operation. One resistor would need to be rated for 50 Watts and the other for 3000 Watts continuous power dissipation. This will provide an additional burn and/or fire hazard. Dissipating almost 3050 Watts to obtain 5 Watts is also extremely inefficient.

I strongly advise you to use a step-down (isolated winding) transformer in your application.

Sigh.

Stepping down from 440VAC (RMS) to 5VAC (RMS) while drawing one ampere of current with just a resistor, must dissipate 435 watts in the dropping resistor and 5 watts into your load. You don't understand what you are asking to do. Without going into the significant added hazards that a typically three phase 440VAC power line provides, I can immediately say that you are not qualified to work on this. If the only person you could injure was yourself I'd be willing to offer some help. The problem is that improper usage of 440VAC can cause building fires, electrocution and even significant X-ray exposure depending on how things fail.

The correct approach is to use a transformer with an appropriate fault interruption device (fuse, circuit breaker, etc.) to much more efficiently change the power level. Since you've started this with the completely wrong approach and with a power distribution voltage that only a qualified electrician should be using, I do not think you should even do this.

OP, AC or DC. Make up your mind!

I'm replying to this because I don't want you to fry yourself.

Many of the other contributers have pointed out how dangerous your proposal is. I can only agree - its madness.

Connect 2 identical resistors in series. The voltage at the mid point will be exactly half. (your proposal was 435 + 5)

A system like this - voltage dividing can be used on high impedance circuits (amplifier front end) etc quite usefully but not the way you want to operate.

Where it all goes very wrong is when you try and take the voltage from the resistor. You effectively put another resistance (your load) in parallel with it. This reduces the resistance and your voltage changes.

You must use a step down transformer or at 5V charge your USB appliance somewhere else.

Hi

In our site, we have a GE make Attenuator Card which converts 11kV (AC) to 4.4 V (AC). The card consists only of 1M Ohm resistors in series, with fuses along the path of the resistors and the final 4.4 V AC is taken across the last 1M Ohm resistance. Hope this will give you an idea of how many resistors to be used. What are the value of the resistors to be used depends on the heat dissipating arrangement provided. In our case, we have dedicated fans for heat dissipation purpose.

Thank you for ur feedback...

considering my case i need to convert from 440v ,so it could be fine to use 560k ohms for each of the phases ...

regards

rimpul

You won't get the 1 ampere of current you asked for though. You won't even get 1 milliampere of current. You will be able to safely use 1/2 watt resistors though.

Hi

There are a couple of points you are not grasping.

Danger - immediately before you connect your load the phase voltage will be present. Without knowing the earth system this could be 415V or 230V - each would prove fatal.

The load you put on the circuit will affect the circuit resistance and thus the voltage dropped over your load - in this case if you really got it wrong you could get a lot of volts.

As others have pointed out - the inefficiency of the system

You haven't grasped the concept of the isolating transformer. Its there to isolate you from the source, reduce the fault level, give you a steady and efficient supply and strangely its why everyone does it this way.

Have you considered plumbing ???

Hi

I am not connecting to the earth, its 440v ac input from the 3 phase line,I need to step down to atleast 5 v ac with only resistive network and not by using any transformers.

regards

rimpul

Is your 1A load guaranteed to be constant?

It should be less than 2A.

Now we're up to 2 amperes. You just do not understand.

A purely resistive attenuator is the simplest but most inefficient way to linearly reduce a voltage. All that one needs to know is how to apply Ohm's law. You obviously do not know how to apply Ohm's law. To safely work on 440 VAC you must know how to apply Ohm's law. You should not work on 440 VAC. If you were the only life you could harm by working on 440 VAC then I would not care if you achieved a Darwin award. 440 VAC if miswired can lead to disaster. This video link is actually of 480 VAC, the extra 40 volts are not much of a difference.

If you are not connecting to earth where is the other end of your wire going .......