General > General Technical Chat
120VAC input to variable 3 phase output PSU?
<< < (3/4) > >>
neverendingstudent:
Picture attached.  Transformer is a Daykin model DKN200A, part number TF501, wired as shown.  I have standard US wall voltage (120VAC) wired to the secondary (labeled as 120V) and was checking... well, all output combinations really.  I have also tried with and without the H3/H2 bridge bar seen screwed in (transformer came with that bridge wired in) - I saw no change in output H1/H3 or H2/H4.  I also checked H1/H4 with and without but, although I don't remember the voltage offhand, it wasn't 240 or 480.  I specifically remember 46VAC being the highest measured voltage.  Checked with 2 different meters to make sure I wasn't reading scale wrong or something simple like that.

Hmm.  I suppose one thing I didn't try was swapping the connector legs on the 120VAC side.
WattsThat:
With no power: confirm low ohmic values (2-5 ohms likely) between:
X1-X2
H1-H2
H3-H4

If any of the three windings are open, it’s shot and will not work for the intended use.

Always verify meter function first. Don’t use auto-ranging (if your meter has it), select lowest ohm range manually, usually 200 ohms and shorting probes together to verify zero ohms. If all three windings are good, you’ve probably got a measurement error.
neverendingstudent:
Yep, that was it - H1-H2 is shot, 97 Meg-ohms.

Well, I do have a second one and that one is showing good - ~5 ohms on each winding.  I'll try it next.

Edit: sweet, the other one works, I have my 240/480VAC test source!
NiHaoMike:
There's usually a thermal fuse on the primary side, if that's the problem it would be an easy fix.
dmills:
Just a note that this works for powering up most control circuits, but will NOT (Without extra help) run a three phase motor load.

I run a three phase motor on my lathe by combining a 1.5KVA control transformer wired backwards (Gets me 400V single phase give or take) and a smallish three phase input VFD (Only two phases connected) to get three phase delta for the lathe. Turns out it is a bit on the small side, and that switching to high speed makes the VFD frequency sag until the thing gets to about half speed, looks like I really need about a 5kVA inverter to handle the starting surge.

The earth connections take a little thinking about, particularly if you don't have a centre tap on the 400V winding. 
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod