Tractorsport Flowbench Forum Archive

Posted: **Tue Apr 20, 2004 3:23 am**

240 volt may have half the current going accross each leg (less stress on breakers), and 240 volt will provide less voltage drop in proportion to 120 volt, but just so those thinking of building a bench know... you pay for your electricity by kilowatt/hour and 240 volt is not cheaper to operate.

watts= voltage x current

120 volt times 10 amps =1200 watts = 1.2 kW

240 volt times 10 amps =2400 watts = 2.4 kW

I'm in the process of putting together a pitot style bench for myself, but I noticed while gathering ideas from the net that some old info, like the MSD orifice bench article, mentions 240v is cheaper to operate. It should be more common knowledge these days, but worth a mention in case people are 'replicating' that article. It's possible it's been mentioned on here, but if not... that's about the only thing I'll contribute now other than questions.

At least it's backwards from what I've been taught, and if it was cheaper, I'd like to know how.

Posted: **Tue Apr 20, 2004 8:43 am**

I'm no electrician for sure, but I think the amps drop in 1/2 when you double the volts. Correct??

Posted: **Tue Apr 20, 2004 1:12 pm**

When you double the voltage you cut the current in half so by your example;

120 v x 10 A= 1.2KWH
240V x 5 A =1.2KWH

You are right that we pay for energy by the KWH so you would think that in both cases the cost would be the same. I believe that the advantage of the higher voltage is that with the lower current you have LESS heat generated in the wires and motor due to the high current. This heat is generated by the energy you are paying for. Less heat means less energy means less cost. The high power lines that deliver the power to your city are at a very high voltage to keep the current lower so the wire is smaller and that less energy is lost to resistive heating of the wire. The voltage is stepped down only at substations and close to your home.

Just my $.02

Dan

Posted: **Tue Apr 20, 2004 1:48 pm**

From a power consumption point of view there's almost no difference to the end user between the two, a 240v system may be a bit more efficient but not enough to make much of a difference. Where a 240v flowbench may be somewhat cheaper is during construction. As already stated, the current in a 240v system is half that of a 120v and low current parts tend to be cheaper for example it's a lot easier to find an inexpensive switch or relay rated at 15A-240v than it is to find one rated at 30A-120v.

Posted: **Wed Apr 21, 2004 12:46 am**

I thought it was on Audie's flow-quik site where the recommended vac motors they had listed 240volt that drew nearly as much current as the reccomended 120 volt motors they had. Maybe I'm remembering their recommendations wrong... I went to go to the site but it was down the other day. Just thought I'd bring up the point..

Tractorsport Flowbench Forum Archive

Why do I read cheaper 240v? - I'm sure this myth has come up before..