50V rated capacitors with a 29VAC transformer OK?

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PauloPT

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Joined 2010
Hi,

I'm using a 29VAC 800VA toroidal transformer ( 4 secondaries ) from Toroidy (not sure about regulation) to power a class AB amplifier. I'll built two separate PSUs in an almost dual mono configuration (channels only share the primary of the transformer.) Taking into account mains variation (don't now how much in my country - maybe 10%?) and a CRC with 0.22R between filter caps (33000uf + R + 33000uF), and perhaps any other factores I'm not ware about, is it safe to use 50VDC rated filter caps?

Thanks.
 
DUG

DUG

Member
Joined 2003
29 * 1.414 = 41.00 peak

41 * 1.1 = 45.1 10% high line

45.1 - 1 + 44.1 diode drop

Should be OK.

However.

Is the 29VAC at no load or fully loaded?

If it is at fully loaded then the output may be higher with light loads...might not be OK.

If 29VAC is unloaded then it should be OK...lower when loaded.

IMHO :)
 
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PauloPT

Member
Joined 2010
DUG said:
29 * 1.414 = 41.00 peak

41 * 1.1 = 45.1 10% high line

45.1 - 1 + 44.1 diode drop

Should be OK.

However.

Is the 29VAC at no load or fully loaded?

If it is at fully loaded then the output may be higher with light loads...might not be OK.

If 29VAC is unloaded then it should be OK...lower when loaded.

IMHO :)
Click to expand...

29VAC is printed on the trafo label. I custom order the transformer but I don't remember the regulation.
 

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AndrewT

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Joined 2004
Output voltage = input voltage / rated primary voltage * rated secondary voltage * {1+transformer regulation}
For a 253Vac maximum input to 230:29Vac transformer that has a regulation of 4% the maximum output voltage will be
253/230*29*{1+0.04} = 33.18Vac
Convert to peak of a sinewave and one arrives at 46.9Vpk.
The lowest diode voltage drop is likely to be ~0.5Vf leaving ~46.4V across the smoothing capacitors.
 
JMFahey

JMFahey

Member
Joined 2009
You speak of single 29VAC , then state you have 4 secondaries but do not say how are they connected; you *might* have all 4 in parallel, all 4 in series, or, as I guess, connected in series in pairs making 2 x 2x29VAC center tapped secondaries.
Just to keep things clear, please confirm.

IF you use 29+29VAC to create 2 roughly 40VDC secondaries, fine, and 50V caps are ample.
 
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PauloPT

Member
Joined 2010
JMFahey said:
You speak of single 29VAC , then state you have 4 secondaries but do not say how are they connected; you *might* have all 4 in parallel, all 4 in series, or, as I guess, connected in series in pairs making 2 x 2x29VAC center tapped secondaries.
Just to keep things clear, please confirm.

IF you use 29+29VAC to create 2 roughly 40VDC secondaries, fine, and 50V caps are ample.
Click to expand...
It's a dual mono setup except instead of using 2 transformers I use a single one with 4 secondaries. Each PSU receives 2 secondaries, not center tapped, each rail has it's own bridge, 2 rectifier bridges in each PSU.
 
Bibio

Bibio

Member
Joined 2009
i spoke to toroidy last year and asked how they rated their transformers. unless you specify each line rating then the VA figure they quote is the total figure. for instance if you get a 1x 12vac x50va then the rating is 50va but if you get 2x 12vac the rating is halved to 25va for each 12vac. so if you want 2x 12vac x 50va you must tell them or they will send 2x 25va.

i also asked what to do with the inter winding shield if you dont have an earth (PE) and they said to connect to COM (0V GND) of the board. so you can connect the shield (green/yellow wire) to earth or COM.
 
A

AndrewT

R.I.P.
Joined 2004
AndrewT said:
Output voltage = input voltage / rated primary voltage * rated secondary voltage * {1+transformer regulation}
For a 253Vac maximum input to 230:29Vac transformer that has a regulation of 4% the maximum output voltage will be
253/230*29*{1+0.04} = 33.18Vac
Convert to peak of a sinewave and one arrives at 46.9Vpk.
The lowest diode voltage drop is likely to be ~0.5Vf leaving ~46.4V across the smoothing capacitors.
Click to expand...

JMFahey said:
You speak of single 29VAC , then state you have 4 secondaries but do not say how are they connected; you *might* have all 4 in parallel, all 4 in series, or, as I guess, connected in series in pairs making 2 x 2x29VAC center tapped secondaries.
Just to keep things clear, please confirm.

IF you use 29+29VAC to create 2 roughly 40VDC secondaries, fine, and 50V caps are ample.
Click to expand...

PauloPT said:
I want to thank you guys for your kind answers.

Should I conclude using 50V caps is too close so I should use 63V instead?

Thanks!
Click to expand...
Myself and another have already confirmed that 50V rated capacitors are OK.
 
A

AndrewT

R.I.P.
Joined 2004
Bibio said:
i spoke to toroidy last year and asked how they rated their transformers. unless you specify each line rating then the VA figure they quote is the total figure. for instance if you get a 1x 12vac x50va then the rating is 50va but if you get 2x 12vac the rating is halved to 25va for each 12vac. so if you want 2x 12vac x 50va you must tell them or they will send 2x 25va.

i also asked what to do with the inter winding shield if you dont have an earth (PE) and they said to connect to COM (0V GND) of the board. so you can connect the shield (green/yellow wire) to earth or COM.
Click to expand...
The interwinding screen goes to Enclosure/Chassis, not to audio.
 
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