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300VA DC power supply

1645 Views 7 Replies 4 Participants Last post by  Richard Johnson
Was looking at the 300VA Power supply description. I have a 15 volt torridial transformer but it is actually giving me over 18 volts out. I have tried loading it to near it's rated output and the voltage only drops very slightly. Have never used a torrodial transformer before so am unsure of myself.
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***More data needed for a helpful answer - whats supplied so far is a little cryptic. What 300vA power supply description? Exactly what is the question? ....and what is the application you want to use it on?

a 300VA transforemer with an 18 volt output will deliver 16.6 amps - that is a very, VERY high current.

The toroidal transformer in the article above had a dual 16V output. This is the final voltage it supplies to the DCC equipment. If your DCC equipment can handle 18 volts then that's fine, but 18 volts is quite high and perhaps a bit much for most systems.

You must never connect a toroidal transformer from both sides of the 'doughnut' otherwise it will create an induced current in the box. Only attach it on one side with insulated pads.
Besides Doug's comment re the need to mount the toroidal transformer with insulated fixings, the only thing you need to know is that toroidal transformers do have better 'regulation', that is the output voltage varies less with changes in load than the more common rectangular cored type, as you have found out. If your transformer has tappings on the mains side for different input voltages, then connecting the supply to a higher-voltage tap will result in a slightly lower output voltage.

Welcome to the forum as well!

John Webb
The 300VA DCC Power supply is the one mentioned on this site. The transformer I have has two 80 VA windings and was purchased from RS some time ago. Any 'ordinary' transformer that I have used in the past will give a higher voltage off load but this will drop once you add a load, which the torridial doesn't seem to do this. The manufacturers spec on no load voltage doesn't appear to match up with real world figures, approx 2 volts of difference. The transformer will be used to supply everything on my DCC layout except the track voltage. I was planning to regulate at least part of it down to 12 volts dc.
*** Where on MRF?

Id suggest that a toroid is a good choice as its stability is as John said, quite good compared to an iron core transformer.

With that high potential current, its worth considering the potential for damage and arranging several outputs and on each, add a 5 amp circuit breaker or similar... that will limit any current on an accidetal short circuit to below "welding levels"


QUOTE (Richard Johnson @ 8 Mar 2009, 12:37) <{POST_SNAPBACK}>*** Where on MRF?....
Richard - see "DCC quick links" "300VA DCC Power Supply" - was posted quite a while back. Sorry - uncertain how one links to such items.

*ahhh - thank you John

Doug - that is very nicely done and well set up.... well presented too!

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