View Full Version : Power Supplies and Transformers on 240V

06-30-2009, 05:18 AM
Just in the process of sorting out my power requirements this year and looking at what im going to need. I will be running 2x 24VDC 9A power supplies, 1 x 48VDC 5A power supply , 1 x 5VDC 25A power supply, 2 x 24VAC toroidals and 2 X 36VAC toroidals.Im wondering how i would go running all this from 1 240VAC 15A power point (external) or should i switch between that and an internal 10A power point.They will all be enclosed in a single box with one power lead, or is the intention,otherwise 2 or 3 power leads.
Ta Synnie

06-30-2009, 07:14 AM

Assuming 300w Toroids the total equals 2kW or 8.3A at 240v before we include efficiency ratings.

A single 15A supply will carry the load with the only concern being turn-on current draw if all turned on at the same time.

Also it would be rare to fully load any one of those to max rating anyway.


07-01-2009, 03:44 AM
Thanks Phil, i forgot to mention they were 300VA toroidals.Everything will be running at 50% of total with all lights on, at present anyway.The power supplies are running my LEDS with the 5V supply running the SSR's and Olsens.

07-01-2009, 08:52 AM
Synnie I think Phil is talking about the initial 'turn on' of your transformer primaries when you intially power them up.

You don't seem to have a problem with the operational load on your mains when its working. But when you first turn it on and those toroidals aren't 'transforming' yet they look for a moment from the primary to be just long lengths of copper wire... shorting out the active and the neutral! This doesn't last long... but while it does there will be a momentary 'inrush' current that will be much higher than usual.

So if you hook them all up to one circuit you might need to think about an arrangement that energises the primaries one by one (ie so they dont all kick in with that inrush current at the same time)... It could be as simple as a couple of switches that you turn on one at a time?....

This is not about switching the lights... its about how you initially power up the transformers.


07-03-2009, 08:16 AM
thanks Tim, was something i did think of at first but i assumed since there wouldnt be output then it wouldnt matter, and was thinking of power draws with the lights running instead.Throw a couple of 20A hockey pucks to switch them on with Vixen and save a walk around the house to the power point..lol