# I need 3 VDC filtered about 50 amps.

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#### gary350

##### Well-Known Member
I am trying to find a way to get 3 VDC about 50 amps. I know I can rewind a transformer and build a power supply with capacitors but I was hoping to find an easier way?

I need 2.121 volts transformer.

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#### ronv

##### Well-Known Member
how about a single cell battery?
What are you trying to do?

#### ronsimpson

##### Well-Known Member
Like this?

I can find new from $200 to$50 with 40, 50, 60A.

Another option is to use any 200 watt power supply. Example: 24V 7A and then add a DC to DC module that will buck the voltage down to 3.3V.

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#### Pommie

You can get 5V 60A supplies of ebay that are adjustable (around US$30). Whether they'll go down as low as 3V is anyone's guess but might be worth a try. What are you using it for? Mike. #### gary350 ##### Well-Known Member This is an electrolysis project using a 1960 industrial engineering book that tells how this is done. I need to make several spring steel valves that are no long available. Machine shops want$85 to $120 per hour labor. I can buy .010" spring steel in 6"x24" sheets$15 enough to make 50 spring steel valves. If I use paint to paint the shape of the valve I can eat away all the unpainted metal then remove the paint with paint stripper and have a valve which would have cost $10 about 25 years ago when you could still buy them. I need to buy a titanium plate, anything thin will work, 1/16" thick x 8" x 12" is$20. The titanium plate is connected to the power supply, the spring steel is connected to the power supply, both are put in a salt water bath and 20 minutes later the metal that is not painted is gone.

With out looking at the book again I don't recall which plate is + or -.

The book says, best results is 3 volts. It also say best results is .5 amps per square inch of the titanium plate. Titanium has to be used to not contaminate the salt water mix with other metals. The water has to contain 4% salt.

Back in the days when this process was used, laser cutters had not been invented yet, no water jet cutters and no plasma cutters either, they had to find other ways to do things.

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#### Pommie

##### Well-Known Member
Would something like ammonium persulfate work?

If not, I'd go the 5V 60A ebay supplies with 3 series diodes.

Mike.

#### gary350

##### Well-Known Member
Would something like ammonium persulfate work?
Mike.
Ammonium Persulfate to do what?

An how much does that stuff cost compared to 5 gallons of water and 1 pint of salt?

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#### schmitt trigger

##### Well-Known Member
Would something like ammonium persulfate work?

If not, I'd go the 5V 60A ebay supplies with 3 series diodes.

Mike.
This sounds like a very straightforward option.

Very interesting chemical etching process, BTW.

I read somewhere that the Apollo lunar lander module's walls were chemically etched to reduce their thickness at certain selected areas (and of course its weight).

#### dr pepper

##### Well-Known Member
I made a adjustable power supply for the wifes pyrography pen, its 0.5 to 3v at around 30a, but it can give over 100a.
I used a 1.8v processor reg off a scrap server motherboard, the reg is a plug in module, the control ic is a sg3525, so it was simple to add a pot on the feedback to make its adjustable.
Main power comes from a standard pc power supply with the usual bench power supply mod.

#### vanan

##### New Member
Hi,
The Mean well PSU Model SE-350-3.3 is the right one VOLTAGE ADJ. RANGE: 2.97 ~ 3.7V, 60A, 198W

#### mvs sarma

##### Well-Known Member
It is great that Mr.Vanan has indicated the RIGHT and ready to use item. For those who have access, they could salvage spot welding transformer. These transformers are big and dam very powerful to deliver higher loads. Of course balance circuitry have to be built.
I noticed use of power mosFETs as rectifying elements with a tap on transformer for gate triggering.

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#### Mosaic

##### Well-Known Member
I have found you need about 1.8 x the stock Primary turns for better efficiency.

#### dr pepper

##### Well-Known Member
the reason why a mot runs at high current off load is the fact its not designed to be off load, for more than a couple of seconds.
The magnetic flux in a transformer core is lower at full load than idle, and to save iron mots have just enough iron to run at full load for 20 mins or so, as soon as you remove the load the core will saturate.
Also why mots are not a good idea for long term running.
Another not so good thing for general constant voltage power supply use is mots are high leakage, thats why all the e's and i's are at the same end, this does make them good for being shorted out as in a spotter.

#### vanan

##### New Member
Hi,
The PSU avaiable with mouser for about USD 95 to 147 see the attachment

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#### gary350

##### Well-Known Member
I have found a correctly would high voltage transformer is not under full load until it is loaded. The magnatron in a microwave does not load a high voltage transformer so a correctly wound HV transformer is very slow to power up the magantron if it ever powers up at all. MOTs are designed to come on at high power this fires up the magnatron very quick.

There is a formula to calculate the correct number of turns on a transformer primary winding for a 120v 60Hz transformers and a MOT always has 1/2 the number of turns a transformer needs for the E I core. Most transformers come on and idle with no load at a low power of about 10% but MOTs come on at about 95% power load or not.

I collect old microwaves. It is a good source of sheet metal, wire, switches, and transformers. I have never found a bad MOT or bad Magnatron. The circuit board is usually what keep the unit from working. If you wire a toggle switch in series with the door safety switch you can close the door, turn on the switch and the microwave oven works good, but no timer.

MOTs make great spot welder transformers. Hammer a short piece of 1.5" diameter copper pipe flat, bend it into a U shape then slide it into the core. Output is about .75v at 1850a.

#### dr pepper

##### Well-Known Member
Mots have magnetic shunts, to increase their impedance to better match them to the magnetron, if thats what you mean.

I'd like to say to anyone else reading this playing with magnetrons is exceptionally dangerous.

#### gary350

##### Well-Known Member
I have taken many MOTs apart and have never found shuts in any of them. Neon transformers have current limiting shunts. You are right about magnetrons being dangerous I don't remember the toxic stuff in them but it is very dangerous never take them apart.

1970 right after college I worked for a company that made transformers. There is a formula engineers use to calculate the correct number of turns for the primary coil according to the core size. Transformer are designed to run at a certain safe power rating none stop but can pull peak current 3 times their rating for a short time with no damage to the transformer. Now days all power transformers have a built in safety fuse wound right into the transformer soldered in series with the primary winding. If the transformer shorts out the safety fuse blows and it does not burn your house down. MOTs are an interesting new idea in transformer technology they use 1/2 as many turns on the primary this caused the transformer to come on at almost full amp load just like an electric motor with a locked rotor. The magnetron will not pull a high amp load on its own so the high amps and high voltage both need to be there for the magnetron to come on in about 1/4 second. MOTs are designed to have 12 to 14 amps on the primary winding with no load the secondary winding is about .7 to .8 amps 2000 v without the MOT design it would be about .08a on the secondary, the magnetron would probably never come on.

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#### dr pepper

##### Well-Known Member
Mot's have 2 spacers between the pri and sec, usually a few plates of silicon steel about 30 x 15mm wrapped in tape, also the e's and i's are all aligned, this is done deliberately to increase leakage flux.

Magnetrons are dangerous powered and unpowered, the liquid stuff in your eyes will boil in less than a second with a blast of rf from a magnetron, and the pink ceramic insulators are loaded with beryllium which isnt very friendly.

Your correct with the universal transformer equation, used it many times, and some transformers have a thermal fuse, however I fail to see any relevance in your other comments.

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