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Old 26th September 2011, 02:34 AM   #1
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Join Date: Apr 2011
Location: Anchorage AK
Default home-made power supply

so, i went ahead and tackled the little project of building my own power supply for my bench testing. first, i started with a vintage powermite charger to house it. of course, being old, and the abuse i put it through years ago left the transformer a tad cooked, lol. anyways, for the 2nd donor, i had an auto-sensing "10a" charger that one day stoped sensing the battery connection, so i opened it up and found that it housed a 25a+ transformer in like new condition. the setup was 2-part secondary (12+12) each, with a single diode. i didn't really like this, so when i set it up, i went with a pair of full bridge rectifiers and ran in series. after hooking it up, i found a faulty switch in the powermite, so bypassed that to take readings, then a bad 25a cb that came with the transformer (probably why it stopped sensing, in hind-site, lol), abd aside form that, it wanted to go 28v, which i thought might happen. so, my thought, is to run the primary side from a standard 125v lightswitch dimmer. just trying to get some thoughts on how this will work, or problems. all i can see from the dimmer is a pot/switch, and a transistor "1400"or "14000" the last 2 "0" s overlap. my first thought is that this is just s quick fix, and the nature of how i'm cutting it down is going to lead to too much voltage drop as current demand increases. also, i don't want to run the voltage too high when current demand drops. now, i do plan on running the outputs through a choke and 1farad capacitor to smooth things out, but i don't want the cap to build too high of voltage..... perhaps, i'll just go get a spare 24/12v step from work, but that would take me a month to get, and i would like to use it before then....... i know the correct answer i would tell someone is to just get6 the proper transformer, or deal with the linear rectifier setup, but i just want to make this work as a challenge.......
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Old 26th September 2011, 05:12 AM   #2
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Join Date: Apr 2011
Location: Anchorage AK
pooo, it did just what i thought. ran dropped to half dc voltage under load on a halogen, and popped it at15v, then jumped to 28 unloaded.... i can't have the voltage creeping that high... on to the next plan...
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Old 27th September 2011, 11:33 PM   #3
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Join Date: Apr 2011
Location: Anchorage AK
ok, i was being a dummy. it was a phasing issue having the common in the middle of the secondary windings, so i split it into to separate windings and cot the desired voltage. however, the rectified voltage now seems to be running with 5vac on top of that. i plan on smoothing it out with the choke i built on a transformer core, but i'm worried about just how much current it runs with the ac being absorbed by the cap. i used a 15000uf 50wv cap to take readings, and it held fine, and the dc sag dropped, also, it allowed the current to nearly doubble back to where i wanted it to be. the setup is going to be using the 1farad cap i had laying around, but i'm just not 100% sure on the safety of it
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