(1) AC to DC Voltage calcualtion (2) Connecting to bridge rectirier

[r77]

Hi everyone

(1) I found this formula for calculating the DC value of an AC Voltage and am wondering if it is correct.
For example, if I have a 230 volt ac source and rectify it, what will the resulting DC voltage be,
the example online used 230 x 0.636 to calculate the above, which resulted in 146.28 vots DC.
If this is correct, then do I simply deduct 0.7 volt per line, ie single phase 230 volts, or 1.4 volts to cover
the round trip losses through the bridge rectifier.

(2) Can I take two 230 feeds from a three phase 400/230 volt alternator, one live from each phase and use the common neutral / centre of the y
and put both lives through a bridge rectifier and from there take the DC out to feed an inverter, or can I go as far as take a  230 volt line from all three phases
and the common centre of the y and rectify them to feed the inverter.

Bottom line I have a three phase alternator, and do not want to buy a single phase of the correct kva rating, and am hoping I can harness either 2/3 of 3/3 of
the power my 3ph alternator already has, it is 10kva three phase.

Any help would be much appreciated

Thank you kindly, john

[mike90045]

NO !  Wrong Calc.

AC sinewave is measured at an RMS AVERAGE of the PEAK voltage of the waveform. 

Example 230VAC (RMS) = 326V  peak   So your DC circuits have to be rated for at LEAST 326VDC.  Capacitors, Diodes, charge controllers

Adding more phases gives you more amps, when converted to DC.  Measuring between AC phases, you can get some wild voltages.

see  http://www.daycounter.com/Calculators/RMS-Calculator.phtml  for more info.   

To compute the RMS voltage from the peak voltage, the peak voltage is multiplied by 0.7071.
To compute the RMS voltage from the peak-to-peak voltage, the peak-to-peak voltage is multiplied by 0.35355.
To compute the RMS voltage from the average voltage, the average voltage is multiplied by 1.1107.
   RMS voltage is a method of representing an AC voltage waveform in which the RMS value specifies the amount of DC voltage that will produce the same heating effect, or power dissipation, in a circuit, that the AC signal would over its entire cycle.
   Thus, the RMS value is a very important value when comparing AC signals to DC signals, in that they both produce the same amount of heating in a circuit and cause the same amount of dissipation of power.

[r77]

Thangk you mike90045

Now I understand the corect way to calculate the DC value of an RMS AC voltage.

In the graphic below perhaps you could tell me what I propose is going to work or not.
I have a 3ph alternato that produces 230 / 400 volts AC, what I want to do is rectify
the three 230 volt terminals, I need the common in the center of the Y in order to get
this 230 prior to rectification, so am I right in thinking I also need to rectify this common,
and if so, how do I do this in order to make the common available to the three legs I am
rectifying, I know I do not need the common rectified if I were using the 400 volt three ph
side of things, but am not sure if the same principle applies to the 230 side, though I can not
see how it does.

[mike90045]

Here's a couple links to better 3 phase bridge rectifiers.
If you are looking at 350 VDC, you want diodes rated for at least 600 V so if a spike comes along, or some inductive kickback, you don't fry the diodes. 800V or 1,000V would be better. Over 1,000v not needed generally, unless nearby lightning may be expected to induce voltage from nearby strikes.  putting some 500V MOV's would not hurt.   https://en.wikipedia.org/wiki/Surge_protector#Metal_oxide_varistor_.28MOV.29

Article:
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/rectifier-circuits/
3 phase about half way down

and
single ph vs 3 phase rectified:


Reasons for MOV's
http://www.electronics-tutorials.ws/resistor/varistor.html
here's a beefy $2 item  http://www.mouser.com/ProductDetail/EPCOS-TDK/B72220P3461K101/?qs=sGAEpiMZZMuQmL5N8IqpX1rD2Ma733J7WojpNDDqQWw%3d

[r77]

Thanks mike90045

I have learned much from your answers, and will consider whether or not to go ahead with my idea, given the high voltage I will only do so for testing and education purposes.

I am now questioning the fesability of using a transformer based AC Welder rectified to supply a charge controler / inverter, below is a link to this post, I hope someone will once again take on my many questions, and in return hopefully help a lot of others who are consideing exiting the controlled sanctioned taxed to the hilt existance our so called governments are pushing down our throats.

Below is a link to my new idea, an 80 volt 180amp output welding transformer, which will keep the voltages quite low.
http://www.microcogen.info/index.php?topic=3460.0

Many Thanks to all