Power Supply question [bridge rectifier]

[ArcaneDreams]

Well here is the schematic:
**broken link removed**


I'm not sure what type bridge rectifier to use, there are so many to choose from. I want a reliable one.

 

[Sceadwian]

What's the turns ratio on the transformer? If it's 20 to 1 it's a 12 volt supply, and you're going to get a max of about 20amps on the secondary. So pick a full bridge rectifier that can handle 20 amps, if you want better reliability try a 40amp rectifier as it'll put less stress on the diodes, you pay more though. Not sure what you mean by types of bridge rectifier to use. They're pretty simple and standard, four diodes.

 

[ArcaneDreams]

Its made to be a 35v supply. The only thing it tells me about the transformer aside from the schematic is that it should be a rating of 150VA (3A) minimum.

The place I got this from also states to use a 35A rectifier.

Which is fine, however when I am looking to actually buy one, I need to specify three phase or single phase. I assume this is going to be single phase since its not being used on a huge power line. However, I was not aware there was a distinction. Why couldn't a single phase rectifier work on a 3 phase signal?


Anywho, what I was mainly looking for was a brand reccomendation.

Oh, and would a 200V rating on it be overkill?

 

[Nigel Goodwin]

Its made to be a 35v supply. The only thing it tells me about the transformer aside from the schematic is that it should be a rating of 150VA (3A) minimum.

The place I got this from also states to use a 35A rectifier.

Then why not follow Elliott Sound Products advise?.

Which is fine, however when I am looking to actually buy one, I need to specify three phase or single phase. I assume this is going to be single phase since its not being used on a huge power line. However, I was not aware there was a distinction. Why couldn't a single phase rectifier work on a 3 phase signal?

Three phase uses more diodes (six instead of four), but I've never heard of being asked that if you ask for a bridge rectifier.

Anywho, what I was mainly looking for was a brand reccomendation.

Oh, and would a 200V rating on it be overkill?

No, that's fine - and probably the value you should be looking at.

 

[ArcaneDreams]

Right here it askes for different phase types in a bridge rectifier:
https://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=24819&Site=US&Cat=32375488


Now that I got that down however, I just have to find a transformer that isnt too expensive.
What do you think about this one:
**broken link removed**

 

[Nigel Goodwin]

Well it might help if you had your location filled in! - as it is we've no idea where you might be, but here's a suitable source if you're in the UK!.
**broken link removed**

 

[Sceadwian]

You asume it's going to be single phase? You're building this circuit, if you don't know what phase power you're using something is drastically wrong here! You can't pick component values for a bridge rectifier if you don't know what the transformer output is going to be..

 

[ArcaneDreams]

Perhaps I mislead you with the use of the word "assume". I was using it in a sarcastic manner...jokingly. Replace "assume" with "know".


And I am from the US.


And I want to get this one off ebay
**broken link removed**

Because it is the cheapest I can find, and it appears to be everything I need. 160VA, A pair of 25V outputs, and 3.2amps.


I do have a question about the wiring though. I can't seem to find a good color code guide. Anyone know where I could find one? I only see 5 connections made in the schematic to the transformer, yet the one in the picture that I was going to buy has 6 leads.

 

[Sceadwian]

You're not going to find a standard colour code for transformers really, you can tell what lead leads to what section of what coil with an ohm meter.

 

[Sceadwian]

If it has 6 wires it sounds like 2 wires are for the primary, and it has two coils (in what configuration i don't know, and is winding dependant) If it's two halves of the same coil you can just tie the two ends closest to each other together and you end up with a 5 wire transformer like in the schematic. Which sounds like it's going to give you 50 volts out with a ground refrence at 25 volts relative the the rest of the power system. I'm not sure what will happen if you hook that kind of transformer up in paralell, as the voltage/power is going to be out of phase?

 

[ArcaneDreams]

hmm, it says it has 2X25v outputs with 0v ground. Grrr...why is it so hard to find a transformer?!

 

[Nigel Goodwin]

It's not, it's a VERY common and standard transformer - it could have three secondary wires (and be 25-0-25) but they are more commonly two seperate 25V windings and you simply connect them in series, and in phase - it's more versatile that way.

 

[ArcaneDreams]

Thats what I was thinking but Sceadwian said that would give me a 25v ground.

Thanks a ton for the help so far Nigel! I plan on ordering all the parts soon. I'll be sure to take pictures once I get started.

 

[Gaston]

i have never seen a schematic like that before. what is the second rectfier from the center tap going to earth ground?

 

[Nigel Goodwin]

i have never seen a schematic like that before. what is the second rectfier from the center tap going to earth ground?

If you notice my previous post?, I said it came from Elliott Sound Products, the article there explains why it's done like that!. It's from a guitar amplifier, and it's to prevent earth loops.

 

[Gaston]

but why the rectifier parallel to the 10 ohm resistor. wouldnt all of the current go through the resistor unless the current got high er than .7 volts to pass through the diode?

 

[Nigel Goodwin]

but why the rectifier parallel to the 10 ohm resistor. wouldnt all of the current go through the resistor unless the current got high er than .7 volts to pass through the diode?

Read the article, it explains it all!.

 

[RODALCO]

With an analogue insulation resistance tester, on the low ohms ranges, you can very accurately determine the dc resistance from the wiring from the transformer.
After that you can test the insulation resistance between the windings eg prim to secondary or sec1 to sec2 to check the insulation value of the actual windings in the TX.
As already said by our other members, get a standard 1Ø 35Amps 200 or 400 Volts block rectifier, which you can buy for less than 10$.

 

[em2006]

The equivalent schematic is like in attached BRIDGE.PNG.
I don't well understand why diodes are necessary, the voltage drop across them means power loses.
Diodes are antiparallel connected, so each diode conduct a half cycle,and 10/1W resistor become short circuited. (I think, effect of resistor is only active when diodes are blocked, around zero crossing of line voltage).
Efect of capacitor parallel is well known, bypass for high frequency.
What happen if a fault occur and a diode only become interrupted? A continuos component may be appear. This is not good for trafo.

 

[Nigel Goodwin]

The equivalent schematic is like in attached BRIDGE.PNG.
I don't well understand why diodes are necessary, the voltage drop across them means power loses.
Diodes are antiparallel connected, so each diode conduct a half cycle,and 10/1W resistor become short circuited. (I think, effect of resistor is only active when diodes are blocked, around zero crossing of line voltage).
Efect of capacitor parallel is well known, bypass for high frequency.
What happen if a fault occur and a diode only become interrupted? A continuos component may be appear. This is not good for trafo.

As my previous reply - READ THE ORIGINAL ARTICLE - it explains the reason for it. If you can't work google?, it's at **broken link removed**