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Tech Tip Project ~ 18volt High Amp Power Supplies On The Cheap

Wire Weasel

Senior Moment
Dec 13, 2008
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Local tech just made one, learned project from another local. Cheap build on 18 volt high amp variable power supply for pill boxes. This is all the info I will have or will post here. If you're a tech and know electronics, you can take this info and figure everything out for do-it-yourself ;-)

The point is - it takes a step-up to 18 volts with sufficient amperage to really make pill boxes, like 2879's & similar, to really come alive and reach full capability …. like approaching 250 watts per pill. (This is a generalization). Yes, a few peeps like Fatboy are making these …. but have you seen their prices for such ??? Need to take out a 2nd mortgage to buy one.

Make one yourself from parts from a discarded microwave oven. Notably the transformer, diodes. He states you'll need to use a typical metal can type A/C motor run capacitor for the filtering. Use a heavy rheostat from a typical electric stove (burner eye controller) for the Variable. A smaller 800W microwave should give you a 100 amp supply. Use the transformer from a larger microwave to make a 150 amp supply. If you know electronics and are good with power supplies in general …. then you can figure all the construction and specs out. All the above parts are readily available and can even get from scrap appliance piles. Build into a typical PC Tower Box for convenience.

Typical application would be like for a 4 x 2879 or similar. They do around 450 on 15 volts but you'll see closer to 1,000W on 18 volts. This is for use a base amp of course. They'll be fine as long as you don't hammer on it to the max constantly and provide PROPER cooling across the heat sink with a good fan. Some amps, like a Texas Star, will need an easy modification of beefing up the solder trace coming off the output of the board going over to the SO239 center pin. This is carrying the final output out the back. Solder a good size piece of solid copper wire right onto the trace from end to end. Now that trace will carry the extra watts/amp without failing. All components in a Texas Star and other better-built amps are rated to take 25 volts.

Here ya go and good luck. Especially if you get these parts as scrap or used take-off …. you can make yourself a 150 amp variable 18 volt supply for under $50 or less. My friend only had to buy the electric stove controller, had everything else in his appliance scrap pile. So he made his first one for $20
 

A smaller 800W microwave should give you a 100 amp supply. Use the transformer from a larger microwave to make a 150 amp supply.

I'm going to urge CAUTION when mucking about with microwave oven transformers. I've got one here that I use for electrical wood burning (Lichtenberg figures).

110V in, 2KV out.

Be careful, or be dead.
 
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And they will store energy for long periods of time as well. So make sure like said to be very, very careful when messing with a microwave oven!!! You only get one shot or should I say shock, and it's over!!! Be safe and take your time!!JMHO's
 
So make sure like said to be very, very careful when messing with a microwave oven!!! You only get one shot or should I say shock, and it's over!!! Be safe and take your time!!JMHO's

Exactly right. There is no such thing as a "mild" shock from Mw oven supply.

The thing is, using mw supplies as a linear power source just won't work without modding the transformer. The wire in the secondary of an mw transformer is usually 20 - 24 ga., and output current seldom exceeds 250 ma. If you lower the output voltage to 18v, there is no way in hell that the stock transformer secondary will handle the current draw that a 1000w linear will need. Ditto the mw diodes which are rated (typically) at 500-600 ma continuous. Plus, one side of the transformer secondary is connected directly to the laminations. Not too good for safety. I could go on and on.

Saying that you can use a stock mw transformer to make a 18v- 150A supply is a pipe dream. 150 milliamp maybe.

- 399

BTW Wire ...

I would like to see a pic or a vid of the supply that your tech friend made.
 
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