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Author Topic: Question for the generator guru's (wiring the head)  (Read 2129 times)
thomasinnv
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« on: December 08, 2011, 09:12:45 AM »

This question is directed toward those that actually "know" or have intimate knowledge of generator heads and wiring configurations. I am capable of making guesses and assumptions on my own.

I have a 75QP gas Generac generator. When I installed it I wired it as 240 into a 50amp transfer, going to a 50amp panel. Many generator heads I have worked with or seen in the past have something in the neighborhood of 12 wires, and a few different wiring configurations to give you either 120 or 240 output, and a few possible of putting out 3 phase. This generator head is different from those that I have seen, it only has 4 wire output. L1, L2, N1, N2. (I believe that is correct, going off memory here. Basically 2 hots and 2 neutrals). The installation manual and service manuals make no mention of a single 120 output configuration, only 2 legs of 120 or single 240 configuration. I searched the net high and low, and came across a few posts from people that mention having tied the L1 and L2 together for a single 120 output, essentially balancing the loads across both windings of the head.( this is what I'm after, I am concerned about prolonged use of the head in a highly unbalanced load configuration) In one of the posts I read, the fellow seemed pretty knowledgeable about generator heads, and mentioned something about measuring voltage between L1 and L2. He also said that if there was no voltage present between the two that they could be tied together and the load between the 2 windings would balance themselves. (When I checked for voltage between the 2, it was fractional. In other words, less than a whole volt) I contacted Generac service department and the reply that I got basically said that they have not tested in that configuration, and they could not say as to the long term effects one way or the other. Basically no help there.

I went ahead and tied L1 and L2 at the transfer switch (on the generator input side, obviously), and ran some tests. Generator ran and put out power just fine. No voltage problems. No popped breakers. I ran one leg of the panel pretty heavily loaded and the other not. The amperage pulling from L1 and L2 (measured right at the generator) was within about 1 amp of each other, and the voltage drop was negligible. There seems to be no ill effects from doing this, but I can't speak for what may be going on inside the head or the control boards.

Which brings me to the point of this post. Does anyone have any real knowledge as to whether this may or may not be a viable configuration? Is there anything I should be looking at? Does anyone have knowledge as to what may be damaged from wiring this way?

I know there are a few electrical genius type guys on here, (Sean??) and I hope to hear from them.
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Geoff
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« Reply #1 on: December 08, 2011, 11:17:37 AM »

On my Newage generator head to go to a single 120v output I had to connect TF2 and TF4 together, and U5 and U1 together That made L2 N and L1 U (hot).  I have a diagram but the file is to big to post.

--Geoff
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« Reply #2 on: December 08, 2011, 04:03:46 PM »

I wouldn't even hazard a guess what the right answer is but there's a lot of really sharp generator guys hang out here in the various generator forums.
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« Reply #3 on: December 08, 2011, 06:14:53 PM »

If you  give me the model and serial numbers for your Generac, I will look it up and have a look see, let you know.  Please restate your desire, 120 volt only or 120/240 volt ?
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thomasinnv
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« Reply #4 on: December 08, 2011, 07:36:41 PM »

It is a QP75 7500 watt gasoline. I will have to look for the serial number I don't have it written down. I am wanting a 120 volt only configuration with both legs combined for a single output source. I have contacted Generac and they say they have not tested it in this configuration so they have nothing to offer.
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« Reply #5 on: December 09, 2011, 08:17:37 AM »

To go from 120/240 to straight 120, be sure to run 4 wires-or 2 wires of sufficient gauge to carry the total amperage output since it is a straight single phase (don't quite understand why 120/240 three wire isn't called 2 phase).  Good Luck, TomC
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thomasinnv
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« Reply #6 on: December 09, 2011, 10:09:32 AM »

I originally wired the system for 50 amp 240 service, 2 hots one neutral and one ground. L1 and L2 from the generator are bridged together at the 50 amp transfer switch, so each leg from the generator to the switch and each leg from the switch to the panel still has the same potential as far as possible load.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

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TedsBUSted
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« Reply #7 on: December 09, 2011, 05:20:16 PM »

...This generator head is different from those that I have seen, it only has 4 wire output. L1, L2, N1, N2. (I believe that is correct, going off memory here. Basically 2 hots and 2 neutrals). The installation manual and service manuals make no mention of a single 120 output configuration, only 2 legs of 120 or single 240 configuration.

I went ahead and tied L1 and L2 at the transfer switch (on the generator input side, obviously), and ran some tests. Generator ran and put out power just fine. No voltage problems. No popped breakers. I ran one leg of the panel pretty heavily loaded and the other not. The amperage pulling from L1 and L2 (measured right at the generator) was within about 1 amp of each other, and the voltage drop was negligible. There seems to be no ill effects from doing this, but I can't speak for what may be going on inside the head or the control boards.


So were N1? and N2? previously connected together as a 240/120 panel's neutral?  Huh

I'm not putting myself out as a generator guru, but since none spoke up with the same hunch I have about the new connection, I'll put it out here for Thomasinnv to investigate further.

I'm guessing that this generator has two stator windings, two leads each, which windings are (unauthorized) reconnectable in series or in parallel, with a Neutral tap in between, when series connected.

Previously, for 240/120 output, the windings were probably connected in series with Legs at T1 and  T4 and a neutral tap at the joined T2/T3:
L---------T1wwwwwwwT2---N---T3wwwwwwwT4----------L

To parallel connect the windings for 120 only, I think they should be connected:
           T1wwwwwwwT2
L -------|                  |-----------L
           T3wwwwwwwT4

However, since Thomasinnv did not mention splitting or swapping the N1/N2 (T2/T3?) Connection, I wonder if the windings now may be connected:
           T2wwwwwwwT1
L -------|                  |-----------L
           T3wwwwwwwT4

If so, that would cause an internal fight when the rotor's spinning  N and S poles pass stator windings wired out of sync.

I'm actually surprised that it works. Maybe something that I assUme is wrong? There must be a technical manual for the head, no? Anyway, Thomasinnv, lacking technical details from the manufacturer, I think you should at least  "ohm" the windings to try to figure out what sort of configuration it is. See if readings at T1/T2 and T3/T4 (N1/N2?) indeed indicate separate windings, joined at N.

Ted
« Last Edit: December 09, 2011, 05:38:54 PM by TedsBUSted » Logged

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thomasinnv
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« Reply #8 on: December 09, 2011, 10:25:58 PM »

Ok, I'll try and clarify what I've got here. Most generator heads have a cover plate on them , under which resides a certain number of terminals with which to connect certain wires and jumpers in certain places in order to achieve a desired output. Mine is not so. There are no terminals, only 4 wires coming out of the head. 2 are black and 2 are white. The black ones are the common, or hot; and the white ones are the neutrals. They are not labelled in any way, but a simple test with a volt meter confirms this. I have not ohmed the two whites to see if they are seperate or not, but my assumption would be that they are since they took the time to run 2 of them out of the head. There is no voltage present between the two black or hot wires. Tomorrow I can dig in a little further and verify whether or not the two white wires are isolated, if it will be useful information. Anything else I should check out while I am in there?
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
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robertglines1
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« Reply #9 on: December 10, 2011, 05:14:40 AM »

Look close one of the black will prob have a green stripe on it. But you understanding is correct about bridge to balance load. We removed bridge to get 220 outlet. Bob
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thomasinnv
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« Reply #10 on: December 10, 2011, 07:12:23 AM »

Bob, if memory serves me there was no stripe or number or any other identifying object on either of the white or black wires, aside from the listing identification of the wire itself.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

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TedsBUSted
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« Reply #11 on: December 10, 2011, 07:48:21 AM »

...When I installed it I wired it as 240 into a 50amp transfer, going to a 50amp panel...

Okay, from the above, and since leads were being reconnected,  I had assumed the system was originally series connected as 240/120 and was now being reconnected parallel, for 120 only. Thus my previous surprise that it worked with just one lead change. But now, I think that I understand that just the transfer and panel were connected per 240/120, with the generator configured as 120 only.

Now, thinking that the generator was, and still is,  connected for 120 only,  my new speculation is that the generator is parallel connected internally, and so externally connecting the two black leads together did not change anything.

I would suggest  "ohming" the Leads to check for internal connection of both black and both white leads, connected as pairs. I'm fairly certain that you'll find the leads are connected that way internally. In which case, the windings were (and still are) parallel connected, with the black leads connected together internally. So with that hunch, I'd say that also connecting the black leads together externally  did not change anything.

Ted
« Last Edit: December 10, 2011, 08:03:45 AM by TedsBUSted » Logged

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« Reply #12 on: December 10, 2011, 08:25:20 AM »

It looks like you might find the manual here:

http://www.generac.com/Service/ManualSearch/

QP75 was not enough information for me to find it.
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« Reply #13 on: December 10, 2011, 10:38:37 AM »

Wow!

Thanks BOTN!

That is one fine link to the smokstak site!

http://www.smokstak.com/forum/index.php

happy coaching!
buswarrior
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