there is a wide variety of talent on here

[buzzinduzzin]

I can't find a step down 3 phase transformer specs : 250 V 3 phase input - 14 volt 3 phase output - 400 watts give or take / this will feed a rectifier with three diode pairs . maybe too far off topic for this forum , if so guide me to a forum please TIA

 

[Watthour]

That's pretty specific. Still, lets get even more specific. Do you need 400W total, or 400W per phase? Roughly, that would be either a 0.5kVA three phase transformer or 1.5kVA. What is the design DC voltage you require?

12/24V secondary is a lot more common. Since you are indicating DC output via a 3-phase bridge, and the DC could be regulated more easily, could you use a 16V secondary with the bridge and a 25A regulator trimmed to 14V? If so, you solution becomes a lot easier.

 

[Watthour]

FWIW, a 14VAC secondary and 3Φ bridge would result in just about 18 VDC unfiltered, and 25 VDC with proper filtration caps/inductors.

 

[buzzinduzzin]

my lack of education on this subject is showing ! not looking for any specific DC out put numbers , I was just saying I don't need big capacity .
Maybe this next question will simplify things . I can salvage ( from a HVAC friend ) 3 singlephase transformers - 230 v primary & 24 v secondary ; if I interconnect them in Y or delta will that produce 3 phase or do they have to have a common laminated core ? TIA again

 

[joeysmith]

What are you trying to accomplish?

Maybe there is a different way to get there if we know what the end goal is