arduino

[Chip Fetrow]

Do you need a center tap neutral?

If not, just buy a 240 to 120 Volt step down transformer and run it in  
reverse.  Cut the neutral lead on what is now the primary and put a  
small wire nut on it.  You really don't want it to find ground.  I  
have done this several times.

The first was when I used adjustable audio oscillators into Crown D-60  
amplifiers.  They will easily put out 70 Volts (for 70 Volt audio  
distribution).  Wired to a step down transformer in reverse, I was  
able to to have 120 Volts, with the actual Voltage set by the volume  
control.  These installations were used to vary the speed of broadcast  
turntables which had synchronous motors.

I also used a 480 Volt to 208 Volt three phase transformer in reverse  
to power nine high power strobes on a tall tower.  It worked well on  
mains power, but the strobes drove the Onan generator nuts.  I didn't  
need 277 Volt lighting on the tower, so the neutral was not needed  
(and never available on the primary side, so not available when the  
transformer is used in reverse).

When I called for the county electrical inspection, the inspector  
asked for the electricians seal.  I told him I did the wiring.  He  
said the electricians "self inspect."  I had to hire an electrician to  
"go over" my work and place his seal on the box.  Well, that didn't go  
well.

My work is always well above code, and this was no exception.  The  
electrician obviously was not familiar with three phase power.  He  
wanted the neutral connected.  I explained that if we did that any  
imbalance current would flow through that wire.  As much as I  
explained and even protested, he insisted.

Finally, I figured the worst that could happen is we burn the  
insulation off some 12 gauge wire, so I told him we will hook it up,  
then measure the current once the breaker was closed.  If it was  
unreasonably high, he would agree it didn't need to be connected.  So,  
I connected it and closed the breaker.  The current was about six  
times the total of the three legs.  He agreed that was wrong, and gave  
up.  He never did understand the issue/problem.  I learned something  
interesting though.  Out of 720 Amperes our unbalance current was only  
60 Amperes, or less than 10%.  I was proud of how I had balanced the  
loads on the three phases.  That isn't a proper way to measure  
imbalance though.

I really was scared as hell we would start a fire though.

Anyway, any decent electrical shop should be able to provide the small  
transformer you need.


One other thing; you might be able to rewire the motor to operate on  
120 Volts, then power it from one leg to neutral as opposed to two legs.

--chip


On Mar 23, 2013, at 10:22 AM, tacos-request at amrad.org wrote:

> Message: 4
> Date: Fri, 22 Mar 2013 19:15:35 -0400
> From: Richard O'Neill <richardoneill at earthlink.net>
> To: tacos at amrad.org
> Subject: Re: arduino
>
> On 3/22/2013 6:47 PM, Joseph Bento wrote:
>> Now why on earth would I want a 240 volt primary transformer?
>
>  Well, I've been looking for a 120 to 240 volt transformer to power my
> home's furnace fan from a 120 volt generator.
>
> Richard