Generator Output Question

Reply

  #1  
Old 08-30-07, 09:07 AM
Member
Thread Starter
Join Date: Feb 2005
Location: Frozen Tundra, WI
Posts: 304
Generator Output Question

I have a theory on this, but need to ask anyhow (please, feel free to correct the error in my thinking).

It all started while preparing a portable generator for input into the house. I made up a generator cord (proper ends, 5 feet long, 10 gauge) to plug into a 4 prong generator receptacle. Being very cautious and paranoid, I wanted to verify the wiring to be correct. Before I fired it up, I decided to take resistance measurements and noted that between “phases”, the resistance was nearly 0, so I checked the resistance between the hots on the 120V output and they were also 0 (which confirmed I had read the correct pin out on the cord). Just to double verify, I fired up the generator and measure voltage between the 2 hots on the cord (and the 120V outlets) and got 257 VAC (as espected).

It has been a long time since I have had any generator theory or saw a wiring diagram for a generator. I assumed there were 2 independent coils, each producing 120V (thus I would have assumed infinite resistance between “phases”. The way I read it, it appears as though it is a single coil, designed for 220, with a center tap (neutral) to produce 120 VAC with respect to the neutral, and 220 with respect to each other (note, 120 implies 110-130V, 220 implies 220-max output). If I am correct, my question as to why zero resistance between phases is answered, if I am not correct, can anyone explain? Geeky minds want to know.

Thanks

P.S. The 5KW generator works fine, requires a lot of load management, but even runs the well pump and the bathroom light at the same time (and nothing else).
 
Sponsored Links
  #2  
Old 08-30-07, 09:30 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,335
> The way I read it, it appears as though it is a single coil, designed for 220,
> with a center tap (neutral) to produce 120 VAC with respect to the neutral,
> and 220 with respect to each other

You got it. This is the same way that power company transformers out on the pole are wired also. To take it a bit further, you can see why an open or broken neutral on a service is a serious problem. Without the grounded, center-tapped neutral, the voltage on each leg of the transformer winding will float with the total voltage still equal to 240. Instead of 120-120, you may get 80-160 or 140-100.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'