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Forum Index : Electronics : Varible Power Supply
| Author | Message | ||||
Bryan1 Guru  Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
G'day Guy's, I scored this at a garage sale for $2 and thought if this works it can become a new variable power supply. When it got home well it was time to plug it in and with my Fluke 865 lets see if this thing works. As the pic shows only one wire is coming from the rectifier I used that as one lead and put the other one on of the heatsinks as one leg of the transfer is on each isolated heatsink. Got a reading of 32 volts DC and then I put the positive probe on the left diode and got 47 volts. Now one would assume the second leg of the 4 diodes is the negative and the first one is the positive. Knowing full well the magic smoke can come out in 1 metre arc's with a blue flame after my 5KVA genset and trusty 140 amp Lincoln welder bit the dust while welding a base for my 16 HP Listeriod. Well it has been quite a few years since I played with electronics and the grey matter is showing here I want to be sure if hooking this thing up correctly.  Heres a pic of the variable transformer and I do have a bigger one on a 75 volt power supply a guy made back in the 90's. The capacitor on that one is the size of a coke can and the variable transformer is about 6" diameter. Now heres a pic of the transformer  Here is a close up of the variable tranformer  I do have a 400 volt 1500uf capacitor to add to the project to smooth out the DC but didn't take a pic of that. Regards Bryan |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The label on that varic says its for 120 American volts. It is not going to like 240 Aussie volts very much, so BEWARE. Cheers, Tony. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah that 120v input rating is a worry. It might work ok at 230, or it might cook. Also, its basically a variable auto transformer, meaning the output isn't isolated from the input, and electricity is one of those things that really hurts as it kills you! When measuring DC from a rectifier using a digital meter, put a cap and bleed resistor across the output. I find digital meters and unfiltered DC straight out of a rectifier gives weird results. The sampling rate and 100Hz DC dont play ball, needs a little smoothing. I have a big variac out of a Telecom power supply rack, its good for 10 amps and had multiple taps, so I wired it to give a output of 0 to 280VAC. I also have a 1000W isolation transformer, heavy! Found it in a metal recycling bin. The both of them are handy when repairing power supplies. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Beware that the big transformer may be a 120V unit as well and even though may appear to cope with short bursts of 240V, with prolonged use it could catch fire!! I agree the diodes appear to be a mix of common cathode and common anode making a full bridge rectifier. As you surmised, the second output should be from the outer diodes black wire. It appears to be a fairly agricultural 110V - 12V batter charger and the Variac set the charge & float voltage (if there was any electrolyte left........) I would return it and get my money back lol (hope you have a sense of humour) If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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