Power wiring series and parallel

[Buffalo Tom]

Hi. I need to get 12VDC 1 amp from a G Lab PB-1 psu. There is four 9 volt 350mA outlets available. Can I use a switching regulator and wire inputs in both series and parallel like this?

[duck_arse]

antonis will be along to tell you about current sharing resistors, and he will also tell you that 350mA + 350mA does not equal 1000mA.

also, your bottom two supplies are not wired the same as the top two. in3 (-) to in4 (+), no other connection to this node. does the G lab allow these connections?

[Buffalo Tom]

antonis will be along to tell you about current sharing resistors, and he will also tell you that 350mA + 350mA does not equal 1000mA.

also, your bottom two supplies are not wired the same as the top two. in3 (-) to in4 (+), no other connection to this node. does the G lab allow these connections?

G Lab PB-1 has eight outputs and is full-galvanic separated (isolated from input and others outputs). Maximal current of each output is 0,35A under the condition of not passing 1A for each section. Im using section 1 with outputs 1+2+3+4 this should give me 1A.

In my schematic input 1 and 2 are wired is series to get 18V for the switching regulator. To get more current I'm adding two more inputs in parallel.

Input 1+2 = 350mA
Input 3 = 350mA
Input 4 = 350mA

Combined = 1050mA. But the current limitation on both the G-lab and the Switching regulator is 1A.. So Im expecting to get 12V 1A out of this.

Wrong?

[Ice-9]

No - it's not going to work that way. I would suggest buying a 12v DC 1-2amp PSU for the  purpose.

[duck_arse]

series current is the same - so in1 at 9V 350mA + in2 9V at 350mA = 18V at 350mA. now you have 18V, you can't add 9V to it in parallel. in3 at 9V 350mA // in4 at 9v 350mA gives 9V at 700mA.

from that supply you can have 18V at 700mA, or 9V at 1.4A. in theory.

[Buffalo Tom]

series current is the same - so in1 at 9V 350mA + in2 9V at 350mA = 18V at 350mA. now you have 18V, you can't add 9V to it in parallel. in3 at 9V 350mA // in4 at 9v 350mA gives 9V at 700mA.

from that supply you can have 18V at 700mA, or 9V at 1.4A. in theory.

Thanks for explaining! I understand now  Made a new version that should give me 700mA. And it might be enough.. Its for powering RJM Gizmo rack + RJM LT controller.

[antonis]

antonis will be along to tell you about current sharing resistors

You didn't shout enough, Stephen, so I'm a little bit late..

Tom, depending on your power supply design, you might need a couple of "balast" resistors for current sharing between INs 1 & 3..
In your case (6V difference between regulator In & Out ) it should be more than OK to "waste" 1V , or so, for current draw equalization..
(2 X 2.7R, 400mW resistors should be marginally OK, 600mW should be more than OK..)
I'm not aware of TSR 1-24120 switching regulator specs but, in case of it could work with even lower IN - OUT voltage difference, it should be a good idea to raise resistors values (toghether, if needed, with their wattage) to let regulator run cooler..

[duck_arse]

!  !   A  N  T  O  N  I  S    !  !

[thetragichero]

i understand wanting to pseudo diy but it seems like a lot of work when 1. it's likely you already have a suitable supply (maybe minus supply noise filtering) wherever you keep unused electronics  and/or 2. a 12v 1 or 2a switching supply costs less than a cup of coffee on ebay. heck, for less than the cost of the switching regulator you mentioned i got a 24v 5a supply delivered to my door about a month after ordering