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Rectifier and parallel ac sources

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abdo799
#1
Dec5-13, 03:39 PM
P: 103
I am new to engineering so i might not understand the concept well , but i want an ac source to provide current only in one way , so i can connect them in parallel.
I have 2 AC sources one with a 100 V output and one with a 120 V output , i need to connect them in parallel so i can get a 220 V dc ( i can not use a transformer, i need to connect them in parallel), so will the rectifier make it possible to connect them in parallel (YES or NO )
the thing is i have a very very tight space, very tight i cant even fit a bridge rectifier, i dont really care about the parameters or ripple now, i just need to know is it possible to make a rectifier just from a simple wire-thin diode?
I read about the ripple , and this can be fixed later in the main wire ( the 2 sources are connected to in parallel ) where we have a lot of space. Right now, I just need to have a 220 V in the main wire
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darkxponent
#2
Dec5-13, 03:50 PM
P: 383
Design of a rectifier is a complex procedure. You need to know the input side and the output side parameters first. Also the type of component you going to connect to the rectifier. The type of DC required etc.

I can't understand exactly what you are asking but rectifiers certainly dont come within semiconductor packages. You have to design a rectifier with capacitors and semiconductor devices.
berkeman
#3
Dec5-13, 04:06 PM
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Quote Quote by darkxponent View Post
Design of a rectifier is a complex procedure.
Not necessarily. In its simplest form, a rectifier can be just a diode, like a 1N4148 signal diode.

Quote Quote by abdo799 View Post
I am new to engineering so i might not understand the concept well , but i want an ac source to provide current only in one way , so i can connect them in parallel.
so question number 1) i know i cant connect ac sources in parallel , what if i used a single phase rectifier on each one turning it to a dc ?
2)i 've searched everywhere and still didnt find a conclusive answer, How small or thin a single phase rectifier can be ?, if it's made of a certain semi conductor material can i get it and make it as thin as a copper wire and weld it like it's a sector of the wire ?
If you could describe what you want to do in more detail, we can outline some of the diode parameters you will need to take into account (like forward current, reverse withstand voltage, etc.). What input and output voltages are we talking about here? And how much ripple can you tolerate on our output "DC"?

darkxponent
#4
Dec5-13, 04:31 PM
P: 383
Rectifier and parallel ac sources

I don't know about this 1N4148 but i have never seen a practical rectifier with single diode. The simplest one i have made was of 2 diodes(centre tapped) and 2 capacitors.

And in most cases i have used additional ICs
omega_minus
#5
Dec5-13, 07:35 PM
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P: 46
Why do you say you can't connect AC in parallel? If they both come from the AC mains you certainly can. If they are from different sources that could be out of phase (like 2 generators) then they in general cannot. A full wave rectifier can be made from 4 diodes. If you need to step up or down the voltage you'd need a transformer on the front end.
berkeman
#6
Dec5-13, 07:51 PM
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Quote Quote by omega_minus View Post
Why do you say you can't connect AC in parallel? If they both come from the AC mains you certainly can. If they are from different sources that could be out of phase (like 2 generators) then they in general cannot. A full wave rectifier can be made from 4 diodes. If you need to step up or down the voltage you'd need a transformer on the front end.
I believe the part of your quote that I bolded is why he cannot.
Bobbywhy
#7
Dec5-13, 09:20 PM
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P: 1,909
abdo 799, Mentor berkeman is exactly correct: with such a vague description it’s not useful to try to advise or help you.

Observations:

Yes, AC sources can be connected in parallel; it is done all the time. I myself once installed, tested, and delivered an Uninterrupted Power Supply (UPS) consisting of five separate three-phase, 60 Hz power converters, each one providing 450 KVA, for a total of 2.25 MVA. All that is required is to first ensure their voltages and phases are exactly the same. Connected in this manner they all share the load equally.

If you have multiple AC sources (you have not actually described exactly what you have, or what you would like to do) yes, you can rectify their outputs and then combine them. But it is absolutely imperative they are exactly the same voltage before connecting them together. Once that was done, you could apply that DC source to an inverter which converts DC to AC.

Comment:

AC generators can be connected in parallel. The same requirements as above apply: their voltages and phases must be the same. This is done routinely in some installations for automatic (uninterrupted) redundancy.
abdo799
#8
Dec5-13, 11:55 PM
P: 103
Quote Quote by Bobbywhy View Post
abdo 799, Mentor berkeman is exactly correct: with such a vague description itís not useful to try to advise or help you.

Observations:

Yes, AC sources can be connected in parallel; it is done all the time. I myself once installed, tested, and delivered an Uninterrupted Power Supply (UPS) consisting of five separate three-phase, 60 Hz power converters, each one providing 450 KVA, for a total of 2.25 MVA. All that is required is to first ensure their voltages and phases are exactly the same. Connected in this manner they all share the load equally.

If you have multiple AC sources (you have not actually described exactly what you have, or what you would like to do) yes, you can rectify their outputs and then combine them. But it is absolutely imperative they are exactly the same voltage before connecting them together. Once that was done, you could apply that DC source to an inverter which converts DC to AC.

Comment:

AC generators can be connected in parallel. The same requirements as above apply: their voltages and phases must be the same. This is done routinely in some installations for automatic (uninterrupted) redundancy.
i edited my question and tried to be more clear , thanks
Bobbywhy
#9
Dec6-13, 03:57 AM
PF Gold
P: 1,909
abdo799,

Here on Physics Forums we have a rule about responding to inquiries regarding dangerous activities. YOU seem to be the danger here. I hesitate to encourage you to take any action at all. Please DO NOT tamper with any electrical equipment without some competent assistance. You are clearly not competent to do this alone.

CAUTION! We CANNOT connect a 100 VAC source in parallel with a 120 VAC source. If you tried it there would be a huge current inrush from the higher voltage unit and the setup would generate maximum smoke!

What gives you the idea you could parallel two AC sources and expect the algebraic sum of their voltages? This is wrong: even if they would not burn from over current, when one wants to add voltages they are connected in series, and NOT in parallel.

You clearly have no idea of how a rectifier functions, or how it can be utilized. Do you really desire 220 V dc as your output, or was that a typographic error and you meant 220 VAC?

Where is your competent electrician? Who is in charge where these units are located? Have you consulted with the manager or supervisor? You risk fire, equipment damage, and even bodily injuries if you proceed without professional guidance. Please hire some qualified electrician or engineer to help you.

WARNING! Electric currents can injure or kill humans, damage equipment, and start fires! Remain safe and please remember, this kind of electric power can kill!
berkeman
#10
Dec6-13, 11:32 AM
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Quote Quote by abdo799 View Post
i edited my question and tried to be more clear , thanks
First of all, please do not go back and edit earlier posts. That makes the thread very confusing. You should have just posted a follow-up post that explained the extra details.

And as Bobbywhy points out, your new details make it apparent that you should NOT be working with high voltages. You have very little understanding of electricity so far (as evidenced by your belief that you can put AC voltage sources in parallel to increase the resulting voltage), and the voltage levels you describe are definitely a shock and fire hazard.

Thread is closed. Please seek out a competent local electrician to help you with your project.


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