It strikes me that with these becoming so cheap these days that they may well have other cost effective hobby applications. I'm aware of the minimum loading that some have, presumably the regulation is relatively poor Do they have a DC output with any degree of smoothing or do they produce high fequency AC at the secondary? This would then be consistent with some references to maximum length secondary leads.
I need about 50v in steps and so was wondering of they were hf ac output I could use a voltage multiplier direct on the output with relatively small electrolytics and tap off the ladder to get my voltage steps. I might just buy one to play with - only £3 for 60VA at toolstation.
HF AC. They have no active regulation - they just rely on the native regulation of the HF transformer being much better than a LF mains transformer (which is also why they are dimmable), and a low power trip to prevent excess output voltage.
I tried using one a long time ago to drive a TV line output transformer and got frightening length stream of sparks from the EHT connector. One day, I'll see if it can drive a Jacob's Ladder
My curiosity got the better of me today and I bought a 60w model from Toolstation.
Externally it looks like this
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does what it says on the tin. Underload it and there is just a stream of narrow pulses, overload it and it shuts down. In between with loads in range (20w -60w) it provides a smooth envelope bursts of around 38kHz square wave with rounded tops at 100Hz repetition rate. Obviously efforts have been made to knock off any sharp corners for EMC/RFI emission reasons. At lower loads the duty cycle is about 20% at 100Hz and at max output the duty cycle rises to an maximum of 80%
I was amazed to find this model just has a couple of philips screws and inside reveals all.
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main power transformer has a potted primary but the secondary is loose wound. I need about 48 volts from it and had hoped to use two voltage doubler stages only needing small capacitors. However as it does not have a continuous output, I can imagine the final voltage will sag unless I use big capacitors. My idea now that I can open the device up, is to add extra turns to get my target voltage and then add a fw rectifier and single capacitor. I will possibly bring out some taps for a few different voltages. The transformer is about 1 turn per volt.
Neither of my two DVMs (one a mid range Fluke and the other a cheapy) work at all well with the output waveform so beware of any readings I used an oscilloscope to see what was going on.
Yebbut the point of my original post was that these newer devices are less than £3 for a 60w device and not much more for 105w and hence need investigating to provide genuine DIYers with fresh knowledge
Indeed... plus they're fanless aren't they? I remember my folks had some for their kitchen which were - although every once in a while one would cook itself...
I would hav thought anyone thinking of modding such a psu would take the BR and reservoir C from a junkbox, costing nothing.
I dont know what their feedback path is, but since the details posted indicate that they do actively regulate, some minor messing with the feedback should be able to stretch the V output range somewhat without messing about with a rewind.
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