I'm designing an AC to DC distro build to replace multiple ac adapters for a rig of about 13 x 12v devices, 1 x 15v and 1 x 19.5v device - very basic schematic below.

I think i'm ok with 12v devices but i'm a bit unsure about specing a 15v converter and getting to 19.5v. 12v to 15v converters look fairly common place but not 19.5v. Though I understand that if voltage sources are connected in series I can achieve 19.5v with the 15v converter and a 5v (trimmed to 4.5v) in series?

What I don't know is what the 15v and 5v converters should be rated for. The 19.5v device pulls 170w - should the converters be rated proportionally to the voltage sum? 15v 131W is 77% of 19.5v 170W, 4.5v 39W is 23%.

any advice is greatly appreciated

 

Well for a start, your 15V 131W converter is magically supplying 200W to the two dc-dc converters hung off it.

The method shown of obtaining the 19.5V at 170W will not work – you can buy dc-dc converters that allow you to trim the output voltage, I suggest you buy three mains units to 12V, 15V and 19.5V each able to supply the required current.

I would also recommend you consider fusing the dc distribution at strategic locations given the potential fault currents available.

 

thanks @Hymie I would fuse the dc distribution, the schematic was more to illustrate the voltage combination to get to 19.5v and how to spec correctly powered converters. Thanks for pointing out the issue - if they were 154W and 46W would that be theoretical ok. I would of course slightly over spec them in reality but was I right about the power proportion on each converter?

Unfortunately I wasn't able to find any 12-20v 200W converters at RS, Mouser, Digikey. I did find some generic boost converters on ebay, amazon etc like this but I wasn't confident that these would be reliable components? I was also told by a electrical engineer friend that it would be more efficient to combine a smaller voltage with the previously converted 12v to get to 15v and 19.5v. Is that right? rather than 3 lots of similar converters?

or did you mean just use 3 ac dc converters for each group?

 

This unit has more than twice the output current you require at 19.5V (which is a standard laptop PSU voltage).

You could search for one having an output just over the 8.8A you require that might be cheaper – but it is always good to have spare capacity to avoid output voltage dips that might occur due to transient loads.

https://www.ebay.co.uk/itm/14399605...Jygi1Uy1A15pfNCZ5hs501PqQj|tkp:Bk9SR76T47CgYQ

 

In my opinion, you should look at the highest wattage supply first and the lowest last.
170 W 19.5V should be simple. Here we have power line-12-15-19.5. Three supplies in a string sometimes oscillates.
I could get a 200 to 250W power line to 19.5V supply first. Add a buck from 19.5 down to 15.
The 72W 12V supply could be separate from the power line or could be bucked down from 19.5V.

If everything comes from the 19.5V you will need 300 watts.

 

I think it would be better to keep the original power bricks for the 19.5V and 15V devices. Those drastically increase the size of the 12V supply, and then you're adding more converters to get 19.5 and 15V. Unless you intend this to run from a 12V battery, it seems pointless. I'd also be a bit concerned about possible ground loops for sharing power supply common if this is audio gear.