Gast Pump and Transformer

[Ed Scolforo]

Hi guys. Maybe someone can answer this: I have a 1/4 hp Gast vacuum pump coming from Surplus Supply. Since I don't have 220 wiring in the house, I thought it would be easier and cheaper to buy their step down transformer (item#15-1069) to convert the pump to 115VAC. Now that I ordered that also, I saw a thread on AAW in which 2 elect. engineers don't recommend using that transformer in this application. They said the proper transformer has to be for an "inductive load" and that the typical isolation/step down transformer, like this one, is intended for "restrictive" loads, ie. lighting, and not for highly reactive loads. I have no clue what that means. So, has anyone used this transformer with the pump, and if so, have there been any problems? If there are valid concerns as to using the transformer, I'll send it back and run a 220 line instead. Thanks for your help.
Ed

[Bill Boehme]

I have not seen the transformer that they supply, but as I recall, it is little dinky thing that probably would not hold up very long. I am also an electrical engineer and the information that you got on the AAW forum is correct. There is one error, however, the term "restrictive" that you mentioned should be "resistive".

A simplified explanation of what the term "resistive" load means is that all of the energy supplied to the load is being dissipated in some way so that none of gets returned back to the source. In general, this means that the energy gets converted to heat or some other form of energy that can't get back into the line as electric energy. Examples of this are resistive heaters such as toasters, ovens, ranges, and incandescent light bulbs. The preponderance of energy in these devices gets converted to infrared energy, but part of the energy becomes visible electromagnetic energy. You will notice that the heating elements in the oven and range glow red which is the closest color to the infrared part of the electromagnetic spectrum. The toaster element may glow yellow which is even further into the visible spectrum and incandescent lights glow white which means that most of the visible spectrum is being radiated. (The visible light being generated is a secondary effect of how hot the heating element is getting and not a direct conversion of electricity into visible light. Other resistive loads such as fluorescent lights and LED's are closer to direct conversion.)

Reactive loads are things that can absorb energy from the supply line, store it, and return part of it back at al later time (by later time, I mean a tiny fraction of a second later). Motors are about the best example of reactive loads that you will encounter in your home. A motor is basically a large rotating magnet. Some of the energy supplied to it is converted to mechanical energy to move a load, some of it gets converted to heat to warm the motor, and the rest is stored in the constantly changing magnetic field of the motor. As this magnetic field changes, some of the stored energy in the magnetic field goes back into the supply line. If you are connected directly to the supply line, this is no problem as it has the capacity to absorb what is known as "out-of-phase" power. But, if you are connected through a transformer designed for resistive loads, the returned energy gets summed with the supplied power to create a distorted waveform. This can cause the transformer to be less efficient and possibly overheat.

Bill

[Kurt Rosenzweig]

Yea! What Bill said! LOL!!!! When I did my system I ran the 220. I just used 12/2 wire on a 20A breaker. I believe the pump only pulls 1.5 amps and my lathe pulls 6.2 so the load isn't that much. In fact my mustard monster and the vacuum pump share the same 220 circuit. If you already have 220 to your lathe can't you just jump off that outlet. I'm not an engineer like Bill but I haven't had any problems. Bill' Is this OK the way I have my system wired. I'd love to hear the opinion of a pro.

[Bill Boehme]

Kurt,
I would have to check what the code book says, but I don't believe that it allows you to daisy-chain outlets on a 240 VAC branch circuit. I believe that you must have a separate breaker for each outlet. The best way to do this is to install a subpanel in your shop and then install as many branch circuits as you will need.
Bill

[Ed Scolforo]

Bill, I want to thank you for your informative answer to my question. Things are less fuzzy now. I'm going to send back the transformer and wire 220. I assume 12/2 wire with a double pole 20 amp breaker will be sufficient? My Nova DVR is also 220 capable, I don't know if it would be worth converting that at the same time, altho it sounds like I'll need to keep that on a separate circuit. Thanks again, Bill.
Ed