DIY 3 phase converter. Build one and save.

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     A DIY 3 phase converter is a way to learn and save money. 

     You don’t have to be a rocket scientist or an electrical engineer. You just have to use common sense. These converters are not like modern day electronic stuff. No printed circuit boards with microscopic components.

     I would advise that if you know nothing about electricity build the converter and then have someone who does know, look it over before you apply power. My book that I sell on Amazon goes through quiet a bit of information on the design and construction of these converters.

It is available here (link to Amazon).

    Hopefully if you read and study this site and look at the videos I have on You Tube you will be better informed as to what you really need and what to expect when building your own 3 phase converter. 

    It is important to know exactly what you are hoping to accomplish before you begin. 

     The last thing you want to do is spend time and money building something that is not going to get the job done. A big shop filled with machines is a lot different then just running one or two motors. Hard to start motors are different then easy ones. Machines that you start when you are standing there are different then ones that come on and off automatically 24-7. The amount of electrical power you have available to you makes a difference.

I have covered the differences between the transformer converter and the rotary converter on another page on my site.

      There are two types of converters you can build yourself.

Phase perfect all digital phase converters
Phase Perfect all digital phase converter

Transformer converter or rotary converter. That’s it. You can not hope to build a Phase Perfect unit or a VFD.

     You need to understand the differences between the two types of converters, rotary and transformer

The transformer converter has fantastic starting power and uses the load motor as part of the converter.

The rotary converter has weak starting power and uses an idler motor.

     Because the transformer converter uses the load motor as part of the converter it can not just be connected up to any machine. It has to be connected directly to the motor itself. This means that you can not have speed controls, reversing switches, and other assorted machine controls in the circuit. At least not with out a lot of rewiring work. 

     The transformer converter works perfect for a larger air compressor, dust collectors, pumps, vacuums, hydraulic presses, etc. These are simple machines that have a motor that runs in one direction and at one speed.

     The transformer converter is also excellent for small motors. Something like a small pump or fan that you want to run with out having a large rotary running all the time to power it.

     Maybe a drill press, band saw, or vacuum where you want to control when the action happens. By action I mean you don’t have any idea when you are going to use the machine. You may open at 8 AM but don’t want to bother starting the rotary converter and hearing it for hours on end. You may only use the drill press at 11 and the band saw at 1 and 3.  One transformer could power those three machines at a cost savings. 

     We have machines that will start automatically when needed. Like a sump pump in the middle of the night. You don’t have to make sure the rotary converter is always on.  And of course there is silence  when the machine is off. 

    Now the rotary converter is very similar to the transformer converter except you leave out the transformer and add in an idler motor.

     That one difference changes the whole character of the three phase converter. Because you have this large three phase motor in the circuit you have, along with the capacitors, manufactured three phase power.

     That big motor acts to smooth out the power and allow it to be connected up to those complicate machines. Ones with speed controls, reversing switches, feed and coolant pump motors. We can actually see this in operation by taking a transformer converter and hooking it up to an unloaded or lightly loaded motor and presto we have a rotary converter. It is the exact same principle involved, the motor acts as a big buffer to even out the voltages.    

      For more about the differences between the transformer converter and the rotary converter see my transformer page here.

    Again I mention; know what your needs are, before making a move on a converter. 

Here is a point that I should mention: Converter size

     When you use a rotary converter you need to over size the idler motor you are going to use to give you starting power. The rotary is very weak on starting power compared to the transformer converter. 

     So what size should you use?  

     I have recently done a whole lot of testing of rotary converters and went so far as measuring the power draw with an electrical utility meter. I found out some interesting things.

    I have changed my opinion now as to what I would recommend to a person. Why? Here is what I found out. 

      A 10 horse idler motor was using 1300 watts of electricity that you were going to pay for idling. But a 30 horse motor was only using 1200 watts of electricity. So the electricity used for a larger idler motor can not be the excuse for not having a larger idler motor. The next thing I found was obvious but worthy to mention. That was that the bigger 30 horse idler balanced and started everything much better.

     This means less fiddling with the thing if you are after a perfect balance. So what is the big draw back for using a larger idler motor? It can not be starting it, as I show the 30 horse starting instantly from a 200 amp service. The only drawback I see is the price of the motor and the larger size of the contactors and more capacitors. All, well with in reason. 

Build a transformer converter 

     This can be done by either buying the suitable transformer new (about $600 for a 10hp motor) Here is link to what you would use   Or scrounge up a used transformer for anywhere from $50 to $200. I show you how to modify used transformers so you can use a wide variety of used models. I also show how to make your own transformer out of commonly available cores. This has been a boon to people in overseas countries where they just could not get used transformers. The beauty of making your own or modifying a commercial one is you have the ability to change the voltage ie; raise it up. This can be done with out having to buy another transformer. I also show you how to raise the voltage using a factory three phase transformer. I show a video of that here. if you have a big hard to start motor then you need the transformer converter.


Build a rotary converter

     Using a premade panel. Here is what could be a big game changer. I noticed on the American Rotary site that they sell premade panels. They just get done with extolling the benefits of their custom made rotary transformer. Then are willing to sell you just a panel for use with your own motor. But this is why I feel it is the game changer. It appears as if the panel they sell has their voltage balance circuit. Now if this works as good as they claim, then you want it. I have to be a bit skeptical for this reason. If you buy a 50 hp panel from them, will it handle starting your un-customized plain jane motor?? You would have to call them and find out.

     In addition to that concern, it appears that they have some extra design circuit to improve the starting of the load motor. This does not seem to be part of the micro smart controller for voltage balance. They would be two different things. So you may not get that with the panel. If you could buy their panel and get both features then that would be a real deal. In any event as of this writing in November 2016 the 20 hp panel is only $576 which sounds good. Saves you some time.

      If you can use the transformer method in your shop with your machines and you want to build something yourself and save money then that is a great way to go. If you have an extremely hard to start machine or other motors suitable for the transformer converter then that could be the best for you.

     One additional point is that if you have a transformer converter you can always start an unloaded motor with it and now you have a rotary converter. It smooth’s out the power and you can connect that up to welders and other machines needing a rotary converter. In my latest videos I used my test box setup and I could start the motors with the transformer and then switch it over to pure rotary.  

     So  again knowing what you want to run is vital. Here is a video that America Rotary posted with tips on selecting a converter. Naturally biased for them but you could watch it anyway here.


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