Electroplating Setup from Microwave Transformer

Discussion in 'The Projects Forum' started by ajhalls, May 19, 2016.

  1. ajhalls

    Thread Starter New Member

    May 12, 2016
    I am prototyping a trailer tie down strap and when done making it, I wanted to do some electropolishing (http://www.electropolishingsystems.com/bulk1.htm) and then plate it with nickel or zinc. While trolling the forums at Finishing.com and reading some of the electroplating books, I need to get about 0.5V, but high amps. This reminded me of a King of Random video where he made a welder out of a microwave transformer which got me watching a bunch of those types of videos.

    Now that I have a little knowledge, it is a bad thing :) Here come the stupid questions.

    First, I got the microwave transformer and cut out one of the secondary loops. I plugged the transformer in with just the small secondary (the shielded one that goes around 4 times. I had it on a volt meter to find how many volts I got from 4 wraps, but I tripped the breaker. I have read up a little about inductive resistance and understood this was why it didn't trip the breaker, but does it depend on there being a substantial secondary coil? I thought it was simply because it was wrapping around the iron core so many times that it was making an electromagnet that created that resistance.

    If the answer to that is that it depends on there being a secondary coil, why didn't it work with the 4 loops? I realize it was thin gauge, so does it depend on me filling up the entire space with as much copper as I can? What do I do if the "right" number of wraps ends up being 2, but it isn't full, do I need to swap it out with a thicker gauge, or can I just make a second loop set and tie them together (so I have two sets going around 2 times) to fill up the remaining space.

    Silly question, what is it that actually controls the amps? So lets say I want 1V. Coming from a 110V socket, what is the difference between going with a 110 wraps on the primary, and one on the secondary, vs say 550 wraps on the primary, and 5 on the secondary? On the microwave, they are using much heavier gauge wire on the primary than the secondary, does that supply more amps, or is it simply to prevent it from burning out the wire. I assumed that I could plug it in without a secondary at all since there was no "load", it would get it's inductive resistance - stabilize and sit there doing nothing for all intents and purposes, which of course it did - with the exception that it tripped the breaker before sitting there doing nothing.

    Let's say we go back to the other question about the ratio of loops, if I am using battery cable wire and can only get 2 loops in and it ends up being the wrong voltage, can I just cut the primary a little shorter to reduce how many loops I am utilizing?

    Sorry for so many beginner questions, trying to take it slow and safe - so I didn't play with it at all before cutting out the HV secondary.
  2. #12


    Nov 30, 2010
    Microwave oven transformers are strange birds. They have a magnetic shunt which limits current.
    Still, the primary should be able to stand there running forever with no secondary.
    Try it with no secondary to find out if you broke something while disassembling it.
    After that, it's volts per turn, and be careful not to try to get a lot of amps out of a skinny wire.

    ps, try to keep your questions under 500 words or nobody reads them.
    Last edited: May 19, 2016
  3. Marley


    Apr 4, 2016
    A little knowledge is a dangerous thing!

    Microwave transformers are high voltage step-up. And produce LETHAL voltages. DON'T TOUCH!
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Unless you have a plating bath the size of a large bath tub you will not need the amount of current a MOT can deliver.
    The current should be calculated on the Sq ft of surface the object being plated presents.
    Get a battery charger that can do 6 volts and 10 to 20 amps.

    You CAN set up two or more baths and run them in series to plate more than one identical item. The benefit is that you can use higher voltage. 6 volts across 3 baths in series is 2 volts per.

    Use an ohm meter on your MOT and check for shorts between the wire and the iron core, and between primary and secondary. No power applied for ohms check.
  5. ajhalls

    Thread Starter New Member

    May 12, 2016
    Thanks #12, I was thinking that was true about being able to run without a secondary - I wasn't sure what the difference would be between that and a secondary with an open circuit. Kermit I have continuity of course with the primary circuit on both ends, but I couldn't seem to get much of a measurement on the ohms, it just seemed like it was basic closed circuit, but wasn't shorted to the core. I guess it is possible that it shorted to itself after 10 wraps and so wasn't using the whole thing. I picked up another microwave from the thrift store to start again.

    As far as being overkill, you are certainly right about it supplying more than required, but I figured I could limit it's output by limiting the dissolved salts and limiting the continuity of the solution. Then when we did step up to a bathtub sized setup I won't have to rebuild it. I am hoping to deliver the setup to the machine shop so the guy manning the CNC lathe can dunk them in without needing to send them out for another process, which would increase costs from shipping and involving another company :)

    ps I always have trouble keeping my posts short :)
  6. #12


    Nov 30, 2010
    From a transformer's point of view,
    An open secondary is the same thing as no secondary.
    A single shorted turn is as good as a hundred shorted turns.
  7. ian field

    Distinguished Member

    Oct 27, 2012
    MO transformers are actually not as robust as they look.

    It doesn't take much to cause shorted turns in the primary.

    A momentary short even on the filament winding can be enough!