Simple bridge rectifier question. - Page 2

JoeBob · 13th February 2002, 07:20 PM

Well, I've only got 2 caps and two transformers. And if I wanted to use multple power suplies less power would go to some channels then others, which I'd rather avoid. I'll just try using a bridge for the positive and one for the negative and see how it goes. When only using either the positive or the negative poles of the bridge, the opposite pole is sent to ground, correct?

paulb · 13th February 2002, 07:29 PM

JoeBob, could you let us know what your transformer voltages are and what DC voltage you expect to get? I'm a bit confused. The arrangement you mentioned doesn't use the centre-tap of the transformer, but I was talking about using it as ground. Your way will get twice the DC voltage.

arnach · 13th February 2002, 08:06 PM

People seem to be saying that it's ok..

If you pull 30A amps out of a 35A bridge recitfier it will BURN UP. I've seen it happen many times.

Also, why don't you at least spec a 50A amp part or use individual diodes? Using individual 60A diodes you'd be fine..

-- Aaron

blmn · 13th February 2002, 09:23 PM

Arnach,

If you use correct sized heatsink the bridge will not blow up considering 85% of their continuous nominal capacity. I had some in my bench power supplies with this problem when I was testing some class B amps. I solved it increasing the heatsink. However, there are some manufacturers wich use peak, or not continuous, current value information for their devices as a basic information, and, in these these devices have much less continuous current capacity.

regards

JoeBob · 14th February 2002, 02:17 AM

Well, I checked and the peak for my bridge is alot higher then 35A, in the hundreds, although I can't remember exactly what.

paulb, sorry, I don't really understand how you mean to connect it. Each transformer is a 750VA +/- 24VAC toroidal with dual primaries and dual secondaries. The DC voltage I'm gathering I'd get is probably around 28VDC or 30VDC, it doesn't really matter exactly, it's for some LM3886's. I hope that clarifies some things, sorry for my ignorance by the way, I just don't see how I can use one transformer for the + and one for the -, if using them the center-tapped way, wouldn't that produce twice the DC voltage, compared to using them in parallel?

AudioFreak · 14th February 2002, 02:32 AM

Joebob,

i'd wire the primaries as per your mains voltage then wire the same secondaries of each transformer together and use 2 bridges to form the rails .... the + of 1 bridge goes 2 +ve rail, -ve goes to gnd, +ve of other bridge goes to gnd, -ve of same bridge goes to -ve rail.....

i'll post a pick of how this looks later if you want. you've just got to make sure all the AC phasing is correct.

blmn · 14th February 2002, 03:32 AM

JoeBob,

Maybe something like this was the idea of PaulB. Don't worry about the polarities of the transformers.

regards

blmn · 14th February 2002, 03:34 AM

OOOPS, the capacitor at the negative side is inverted. Sorry...

JoeBob · 14th February 2002, 04:05 AM

Oh, now I understand. Thanks, I'll give that a shot. Thanks for all the help guys.

AudioFreak · 14th February 2002, 04:21 AM

or you could try this.......

13th February 2002, 08:06 PM	#13
arnach diyAudio Member Join Date: Apr 2001 Location: USA	Hello People seem to be saying that it's ok.. If you pull 30A amps out of a 35A bridge recitfier it will BURN UP. I've seen it happen many times. Also, why don't you at least spec a 50A amp part or use individual diodes? Using individual 60A diodes you'd be fine.. -- Aaron

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13th February 2002, 07:20 PM	#11
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	Well, I've only got 2 caps and two transformers. And if I wanted to use multple power suplies less power would go to some channels then others, which I'd rather avoid. I'll just try using a bridge for the positive and one for the negative and see how it goes. When only using either the positive or the negative poles of the bridge, the opposite pole is sent to ground, correct?

13th February 2002, 07:29 PM	#12
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	JoeBob, could you let us know what your transformer voltages are and what DC voltage you expect to get? I'm a bit confused. The arrangement you mentioned doesn't use the centre-tap of the transformer, but I was talking about using it as ground. Your way will get twice the DC voltage.

13th February 2002, 09:23 PM	#14
blmn diyAudio Member Join Date: Feb 2001 Location: .	Arnach, If you use correct sized heatsink the bridge will not blow up considering 85% of their continuous nominal capacity. I had some in my bench power supplies with this problem when I was testing some class B amps. I solved it increasing the heatsink. However, there are some manufacturers wich use peak, or not continuous, current value information for their devices as a basic information, and, in these these devices have much less continuous current capacity. regards

14th February 2002, 02:17 AM	#15
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	Well, I checked and the peak for my bridge is alot higher then 35A, in the hundreds, although I can't remember exactly what. paulb, sorry, I don't really understand how you mean to connect it. Each transformer is a 750VA +/- 24VAC toroidal with dual primaries and dual secondaries. The DC voltage I'm gathering I'd get is probably around 28VDC or 30VDC, it doesn't really matter exactly, it's for some LM3886's. I hope that clarifies some things, sorry for my ignorance by the way, I just don't see how I can use one transformer for the + and one for the -, if using them the center-tapped way, wouldn't that produce twice the DC voltage, compared to using them in parallel?

14th February 2002, 02:32 AM	#16
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	Joebob, i'd wire the primaries as per your mains voltage then wire the same secondaries of each transformer together and use 2 bridges to form the rails .... the + of 1 bridge goes 2 +ve rail, -ve goes to gnd, +ve of other bridge goes to gnd, -ve of same bridge goes to -ve rail..... i'll post a pick of how this looks later if you want. you've just got to make sure all the AC phasing is correct.

14th February 2002, 03:34 AM	#18
blmn diyAudio Member Join Date: Feb 2001 Location: .	OOOPS, the capacitor at the negative side is inverted. Sorry...

14th February 2002, 04:05 AM	#19
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	Oh, now I understand. Thanks, I'll give that a shot. Thanks for all the help guys.

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