Rectifier circuit fails when capped.

[jvdbossc]

I am a bit confused, made this a while back to test and it worked 100%.








Now I thougt let's make it more clean, and in this circuit my caps blow, although it's fed the same 2x24V lines...

I am getting a feeling the diodes aren not fit for the job? Without cap they rectify, with cap the cap draws all the power and explode

 

[(*steve*)]

My guess is either that you have the caps around backward, or they're getting substantially more than 35V, or they're not 35V capacitors. I'd probably use 50V caps in this circuit.

Did you measure the voltage across them before they blew?

How long did it take before they blew?

How did they "blow" (explosively?)

 

[GreenGiant]

The caps are labelled at 35V, and it looks like 4700uF?

so capacitance should be fine, but like steve said you want at least 50V caps (I would probably go a little higher than that if you could)

 

[jvdbossc]

My guess is either that you have the caps around backward, or they're getting substantially more than 35V, or they're not 35V capacitors. I'd probably use 50V caps in this circuit.

Did you measure the voltage across them before they blew?

How long did it take before they blew?

How did they "blow" (explosively?)

Well without cap I get 33 V, with one cap as shown in the last picture, I get 6V

Please note the first 3 images are a working config, it's the last pic.. MM the last two were 25V but they were in series so should go 50V ?

I think I blew them, (20 secs) the wiring is not correct I get -33 without the cap.. Sorry, will re-report so stupid mistake to hook it up wrongly

 

[jvdbossc]

The caps are labelled at 35V, and it looks like 4700uF?

so capacitance should be fine, but like steve said you want at least 50V caps (I would probably go a little higher than that if you could)

All my caps are blewn, can I use the series trick to use the 25 V ones?

 

[jvdbossc]

Thanks right orientation - have one 50V 4700 uf left.



Uploaded with ImageShack.us

 

[CDRIVE]

I'd prefer caps rated >=50V but when wiring the caps in series you must provide a voltage divider by placing a resistor in parallel with each cap. A 10KΩ to should do it.

Chris

Edit: After re-thinking this the resistors may have to be lower than this. The larger the caps are the lower the resistors will have to be. Opinions welcome..

 

[duke37]

Show us the circuit, I cannot think how 9 diodes can be involved.

 

[CDRIVE]

Show us the circuit, I cannot think how 9 diodes can be involved.

Good point. The bottom view of the board seems to show groups of three diodes in parallel per leg but that makes no sense either because then I would expect a total of twelve.

Chris

 

[BobK]

I'd prefer caps rated >=50V but when wiring the caps in series you must provide a voltage divider by placing a resistor in parallel with each cap. A 10KΩ to should do it.

Chris

Edit: After re-thinking this the resistors may have to be lower than this. The larger the caps are the lower the resistors will have to be. Opinions welcome..

Actually, I don't think is it necessary. The two capacitors will divide the voltage equally as long as they are the same capacitance.

Bob

 

[CocaCola]

Good point. The bottom view of the board seems to show groups of three diodes in parallel per leg but that makes no sense either because then I would expect a total of twelve.

From what I gather...

+ 24 -> diodes ->
+ 24 -> diodes ->
GND <- diodes <-

That isn't to say I fully understand why it's done like I assume it is above...

 

[jvdbossc]

There is no circuit, I had a broken amp, and I was planning to convert it as labo psu.

The circuit I've got was using a 2x15V psu hooked up to have 30V.

my amp psu ended up to be 2x24 or 1x48. (if I hooked it up that way)

Since I really do not need to get as as high, I was hoping to use the 2x24 AC and convert it to DC wich will be higher then and then build the "labo part". I have a lower specced labo psu that gives 30V at 2 amps, wich should be enough at that voltage

I already switched the unit to 220V to get some more out of it instead the 240V to fool the coil.

As far as I know one two diodes out to be enough

--------
NC (output 48V AC)
--------

--->--- plus (output 24V AC)
wired ---- (as minus)
--->--- plus (hooked up with other plus)

I was not sure so I just thought let's be sure and have this

-->--- plus (plus hooked up with other plus at DC )

---<-- min
--->plus.

Then my ratings in my first circuit where 3 amp diodes, and although I probably never get there I wanted to have 9 amps.

Anyhow I have used two diodes to make sure now.

I hope this make scense.

Anyhow this circuit is the one (with one cap missing) I was hoping to use finally and continue work on another separte board to build the labo psu.

It's the same but it uses two diodes per wire instead of 3.

[Images removed -- causing problems]

It is overdimensioned, but I want to build robust. The module should be able, if I get my hands on an heavier coil to be used again.

 

[duke37]

You must have decided on a circuit, you did not just throw components on to a board.

If you have connected diodes in parallel, that is not a good thing since the hottest diode will take the most current and become even hotter.

Running a transformer above its rated voltage is not good, you may get away with running at 240V on a 220V tap but it will be a close run thing. Get the power supply working before doing fancy modifications.

Series capacitors will only share the voltage equally if they have the same leakage, I would always use balancing resistors. At this voltage, capacitors are easy to get so series connection is not needed. It is different if trying to smooth 1000V.

 

[jvdbossc]

You must have decided on a circuit, you did not just throw components on to a board.

If you have connected diodes in parallel, that is not a good thing since the hottest diode will take the most current and become even hotter.

Running a transformer above its rated voltage is not good, you may get away with running at 240V on a 220V tap but it will be a close run thing. Get the power supply working before doing fancy modifications.

I do understand the part about the diodes, but they are now 2x15A so, it does not matter to get 9A ?

I don't get the transformer part, I just put the switch to 220V, I was told a transformer using copper coils can be used at any voltage. The windings should do there job at any voltage? And end up at a certain ratio anyhow.

 

[CDRIVE]

I do understand the part about the diodes, but they are now 2x15A so, it does not matter to get 9A ?

I don't get the transformer part, I just put the switch to 220V, I was told a transformer using copper coils can be used at any voltage. The windings should do there job at any voltage? And end up at a certain ratio anyhow.

Please stop with the photos and post a schematic. Draw it if you have too.

 

[(*steve*)]

I don't get the transformer part, I just put the switch to 220V, I was told a transformer using copper coils can be used at any voltage. The windings should do there job at any voltage? And end up at a certain ratio anyhow.

As long as you are selecting a voltage appropriate to your local mains voltage (and that sounds like what you're doing) then you should be OK.

I presume that this part has all been "factory" wired.

 

[CDRIVE]

Actually, I don't think is it necessary. The two capacitors will divide the voltage equally as long as they are the same capacitance.

Bob

Electro caps can be +- 20%, have variant leakage and ESR. It's good practice.

Chris

 

[duke37]

I don't get the transformer part, I just put the switch to 220V, I was told a transformer using copper coils can be used at any voltage. The windings should do there job at any voltage? And end up at a certain ratio anyhow.

A transformer is rated for a certain voltage, you can use it at a lower voltage but can overstress it at a higher voltage.
There are two limitations.
1.The insulation between turns and the case. This restriction will be important in high voltage equipment.
2.The limitation of the magnetic flux, this is the limit which you will have. If the voltage is too high, the iron core will 'saturate' and the transformer will allow excessive current to pass through the primary winding. The transformers with rectangular cores are fairly tolerant to some over voltage but torroidal transformers are designed with more fussy materials and closer to the limit so that they are smaller and weigh less.

Your original amplifier had a power supply to drive the audio amps. Can you use this directly?