Power supplys

[alin_im]

Hi guys, quick question when it is safe to serie or paralel 2power supplies (floating ground point) If they share the same transformer Need some tips

[JacquesBBB]

 If they are floating, with respect to ground, its ok. Its like you were putting batteries in series or parallel.

[Rerouter]

When you say they share the same transformer, grab something like a 10K resistor and put it between one supplies negative and the others positive with it running, if the voltage across the resistor is 0V or very close to, the supplies are both floating, if you get the supply voltage across it, they are not,

as for putting the 2 in parrellel, measure the voltage of the 2 supplies, if there is a gap more than a few hundred mV, then likely not something to attempt, if very close then you may just need something like a 0.2 ohm resistor on both outputs before connecting them in parrellel to balance any loads used,

[Ice-Tea]

In parallel? Doesn't seem like the best idea. Might work albeit with poor load balancing with a simple trafo but will probably go (horribly) wrong with a SMPS.

[jeroen79]

Exactly how do they share the transformer?
That they float relative to ground doesn't mean that they will float relative to eachother.
Is this an existing powersupply or one that you are building?
How are the transformer's windings wound?

[alin_im]

Exactly how do they share the transformer?
That they float relative to ground doesn't mean that they will float relative to eachother.
Is this an existing powersupply or one that you are building?
How are the transformer's windings wound?

i am building my own and i am trying to figure it out which is the best method.
i am using a transformer like this http://uk.farnell.com/block/rkd-160-2x24/transformer-2-x-24v-160va/dp/2362171 and it has an output of 2x42v DC
and i want to build something like this http://uk.farnell.com/tenma/72-10500/power-supply-2ch-30v-3a-adjustable/dp/2251948
any ideas   so far i am thinking of using a lt1074 IC

[Shock]

Probably best at this point to draw what your suggesting out and label it.

[jeroen79]

i am using a transformer like this http://uk.farnell.com/block/rkd-160-2x24/transformer-2-x-24v-160va/dp/2362171 and it has an output of 2x42v DC

The transformer in your link has separate secondary windings that will float relative to eachother.
Wether your transformer has this too can be checked with a multimeter.