Power supply grounding

[Mosaic]

Hi all:

I have a 120VAC transformer with secondary 2 coils...
Individually the secondaries give 13VAC and 25.5VAC or so.

By joining each secondary I am able to get 38.5VAC which gives 51.7VDC after a FWB and 7500UF smoothing cap.


Ok...Now I want to make a lower voltage DC as well, so I run the 13VAC segment of the joined secondaries into another FWB and smoothing cap. This gives 17.7VDC. BUT the negatives from each FWB (circuit ground) have a potential difference of 11.7VDC!!

How can I get a common ground for each of the DC volts, 51.7VDC & 17.7VDC?

 

[BeerBelly]

Use one end of the transformer grounded with the center and the other end of the transformer having a single rectifier.

 

[Mosaic]

Seems like a fwb can't do this
https://electronics.stackexchange.com/questions/61270/common-dc-ground-with-two-bridge-rectifiers

 

[BeerBelly]

Maybe I wasn't clear

 

[Mosaic]

yes thx, i got that....just a lot more ripple

 

[BeerBelly]

You could do it with 2 FWBs but it will require another capacitor.
Maybe 2
The more I think about it the harder it seems to isolate the 2.

If it is a transformer where you can see the windings tied together, break the connection between them. Then you could add their DC voltages and have a common ground.

 

[alec_t]

As BeerBelly suggests....