Auto Transformer Queries

Author	Message
Chopperp Guru Joined: 03/01/2018 Location: Australia Posts: 1110	Posted: 02:12pm 01 Dec 2024       Hi I have been on the lookout for a while now for a decent DC power supply & found this one the other dayHere The only thing is that it is rated at 220V +/-10% input. At my place, the AC mains is normally 240V+ & when the sun is really shining overhead, the voltage can go above 250V. (I have solar). Today it was about 244V with cloudy conditions which is above the rated input of the supply. I did buy a SMPS a few years ago & it didn't last long with an input filter capacitor going caput. I did get a refund. I was thinking that I could reduce the input voltage by using a normal transformer (toroidal) wired as an auto-transformer as per the diagram below. (one of a couple of spares I have laying around). The transformer is a 240V to 2 x 13V @ 7.7A toroid (The secondaries shown as a single winding in the diag). From my understanding, for an auto-transformer wired as shown, the "secondary" winding carries the load current for the load while the primary just supplies the magnetising current so the primary winding size & the core size can be considerably reduced. The 7A rating should be adequate for the SMPS. The voltage table shows my calculations for the input volts & the corresponding out put from the equation:-   Vout = Vin * 240/(26 + 240) = ~0.9 * Vin. This should give plenty of margin for voltage fluctuations. If the volts do drop too much, I can use just one of the 13V secondary windings. What I really want to know is that I am on the right track with with my thinking. Even better, if someone knows of a SMPS of similar capacity with a 240V rated input. Thanks Brian             Edit, Only one 'r' in Toroid Edited 2024-12-02 00:13 by Chopperp ChopperP