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Author Topic: Load Balancing and how best to wire genset  (Read 2778 times)
Tenor
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« on: July 15, 2008, 03:45:56 PM »

I keep finding reference to load balancing in postings, but I also see it referred too when people wire their gensets for 220.  Does it apply if you are running 120?For an upcoming event, I will need the genset, so I plan to put on a 50 amp female socket and just plug my shore cord in.  Eventually I will install my sw4024 inverter, but not for a while.  This is a temporary job. 

Here's the list of equipment.
Kohler 7.5KW genset - 2 hot wires coming off of the head had been run to a 220 outlet.  Each leg is receiving 130 volts.
50 amp shore cord
100 amp panel - currently wired with 3 roof airs, fridge, microwave and 1 other outlet all on one hot leg - the two legs in the panel are not connected to each other.  They are all on one leg because I only had a 20 amp cord attached and I just switched to a 50 amp.  No problem to move these around if necessary.

Am I safe to run the two hot legs to a 50 amp outlet?  Do I need to shuffle my equipment at the breaker?  Will Batman and Robin escape from the evil clutches of Catwoman?

Thanks for the help!
Glenn



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Glenn Williams
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DrivingMissLazy
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« Reply #1 on: July 15, 2008, 03:55:29 PM »

I keep finding reference to load balancing in postings, but I also see it referred too when people wire their gensets for 220.  Does it apply if you are running 120?For an upcoming event, I will need the genset, so I plan to put on a 50 amp female socket and just plug my shore cord in.  Eventually I will install my sw4024 inverter, but not for a while.  This is a temporary job. 

Here's the list of equipment.
Kohler 7.5KW genset - 2 hot wires coming off of the head had been run to a 220 outlet.  Each leg is receiving 130 volts.
50 amp shore cord
100 amp panel - currently wired with 3 roof airs, fridge, microwave and 1 other outlet all on one hot leg - the two legs in the panel are not connected to each other.  They are all on one leg because I only had a 20 amp cord attached and I just switched to a 50 amp.  No problem to move these around if necessary.

Am I safe to run the two hot legs to a 50 amp outlet?  Do I need to shuffle my equipment at the breaker?  Will Batman and Robin escape from the evil clutches of Catwoman?

Thanks for the help!
Glenn
To do what you want to do, you will need to reconnect your genset for 120 volt output only. Based on your comments I do not think you have any requirement for 240 volts. If this is correct, then you absolutely need to reconnect for 120 only. Once you are connected this way, you no longer have a need to balance your loads like you would have to do it you were wired for 240/120 volts.

Richard

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« Reply #2 on: July 15, 2008, 04:07:05 PM »

    Running the 220 to your 50 amp plug is OK as long as you wire it properly. Each leg will get 120 volts. Load balancing means keeping the load on each leg within about 20% of the other leg (such as 1 AC on each leg or hater heater on one leg, AC on other, etc. Keeping the loads balanced help prevent excessive heat build up in the generator windings and helps insure better voltage regulation (per Powertech service manager).
   If you have a 10 KW generator with 220 volt output, you will have 5 KW on each 120 leg.  If the generator is wired 120 output, you will gave 10 KW on the one 120 leg.
   We wired our generator for 120 output (no need to worry about load balancing). At the transfer switch (or generator receptacle you plug your cord into), connect the generator "hot" wire to one of the "hot" terminals and run a jumper from this connection to the other "hot" terminal.  
    Jack
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« Reply #3 on: July 15, 2008, 04:30:41 PM »

Running 3 a/c units on a single #6 or #8 shore cord along with other loads
will let the smoke out of the wire and probably the generator.

A 7.5 kw would be running at its limit or potentially overload even if you wired it for 120 volts. More loads than generator in that example.

I have a 10kw Onan, Wired for standard 220 volts. My rear air and electric water heater live on the second 120 volt leg along with exterior plugs for stuff like air compressors and such.

My primary systems and living space occupy the primary leg. Front air and Inverter/Charger that supplies everything inside with a 3000 watt capacity.

With all my stuff on and running my load is fairly balanced...My way...
I also don't have problems with campground plugs because the 50 amp service is generally 220 volts and it keeps the shore cords from frying from overload.

Do it your way and if it doesn't work then you can fiddle with it until it does...

Dave...
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« Reply #4 on: July 15, 2008, 04:53:15 PM »

I wired my genset (10kw) for straight 120vac.  I have 3 roof airs, 2 water heaters, etc, with only my stove and furnace being run off propane.  On my 50 amp shore cord, I only use one side of the circuit so I have a straight 50amps at 120vac.  I love the convenience of not having to worry about "balancing" the load between two legs of 120vac, and having 50amps for shore service has never been a handicap-just have to be a little bit wise as to not overloading it.  When I do another conversion, I will do it exactly the same way.  Good Luck, TomC
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« Reply #5 on: July 15, 2008, 08:32:17 PM »

Let's clear up our definitions of 220 vs 120 here.  Assuming there are no 220 appliances in use, we are talking about 50 amp service (2 lines of 120) or just 120 (one hot wire)

Richard - (and anyone else who may know),  how do you wire a generator up for 120?  Do you just ignore one of the two hot wired? ( that really seems like the wrong answer).  You are right, I have no 220 appliances.

Jack - 3.75 KW per leg on the genset head makes 7.5KW right?  Or, if made to run 120, 7.5KW one leg only, then jumper in the recepticle to pick up the second hot wire in the shore line?

Dave - I don't really ever see me running more than two AC's at a time, and I will be moving them to seperate legs.  Probably 2 on my primary hot line, and then the other and maybe the microwave on the other..

Keep the feedback up here.  So far, it seems the easiest method is Jacks.  Wire it straight 120, and run a jumper in the outlet to pick up the second hot wire in the shore line.  I just need to know how to do this.

Thanks!
Glenn
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Glenn Williams
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« Reply #6 on: July 15, 2008, 08:46:22 PM »

Glenn, what Jack was saying was that when you wire the generator to produce single wire 120, you would then jumper it at the transfer switch to feed both hot legs of your distribution panel.

When the transfer switch is on shore power, both hot legs will come in and appropriatey feed the distribution panel.  When the transfer switch is on generator, the one hot wire from the genny will feed both hot legs of the distribution panel.

As for how to wire the generator to output single leg 120, I look forward to reading the detailed how to on that.  I've read that it can be done several times here, but not how it's done.
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« Reply #7 on: July 16, 2008, 05:24:07 AM »

Jack - 3.75 KW per leg on the genset head makes 7.5KW right?  Or, if made to run 120, 7.5KW one leg only, then jumper in the receptacle to pick up the second hot wire in the shore line?

YES.   There are 4 AC wires coming out of the generator head. These are usually labeled L1,L2,L3,L4 or T1,T2,T3,T4 or U1,U2,U3,U4, or some other combination. How you connect these wire determines if the output is 120 only, 240 only, or 240/120. Proper connection depends on your needs. If all needs are 120 (no 220 appliances), 120 only is your best choice.  What brand/model is your generator, I might have the wiring diagram showing the proper connections.  Jack
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« Reply #8 on: July 16, 2008, 05:42:24 AM »

On most gensets it is relatively easy to convert from 240/120 to 120 only.

For example,open up the electrical box and check the number of electrical leads. I suspect you will have four heavy leads (maybe #8 or #10) and two light duty leads, maybe (#14 or $16). The light duty leads are the input to the voltage regulator.

The heavy leads will be numbered H1, H2, H3 and H4 or something like that. Maybe L instead of H. The light duty leads will be numbered + and - or something similar.

In the current high voltage connection H2 and H3 will be connected together and that will be the neutral connection. H1 will be one of the hot leads and H4 will be the other. The + will be connected to H1 and the - will be connected to H2/H3.

The above configuration is the international standard for most all alternator manufacturers. If yours is connected as above, then it is a very simple matter to reconnect for 120 volts only as follows:

Disconnect the present connections and then connect H1, H3 and + together. Then connect H2, H4 and - together. One of these connections will be your hot lead and the other will be your neutral. It is as simple as that.

If your wiring is not as per the example I gave, let me know. Also, check on the alternator electrical box as there is generally a connection diagram there or on the actual alternator name plate.

Richard
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« Reply #9 on: July 16, 2008, 06:34:59 AM »

High Tech - Since for now I am not using a transfer switch, wouldn't running a jumper wire inside the 50 amp recepticle from the single hot wire from the head (hot 1) and taking it to the other terminal for hot 2 be the same thing?  I'd just then be able to plug my shore line into the recepticle and have both hot 1 and hot 2 in my shore line used?  I don't see the difference.

Jack,  My genset is a Kohler 7.5KW A26 10607A  Probably a former marine unit.  Gold paint.  I'd love to find a full set of manuals for this thing.  I haven't had much luck on the interntet.  Thanks guys!

Richard - I will check out your explanation this afternoon.  It seems quite straightforward.

thanks!
Glenn

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Glenn Williams
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« Reply #10 on: July 16, 2008, 07:18:17 AM »

High Tech - Since for now I am not using a transfer switch, wouldn't running a jumper wire inside the 50 amp recepticle from the single hot wire from the head (hot 1) and taking it to the other terminal for hot 2 be the same thing?  I'd just then be able to plug my shore line into the recepticle and have both hot 1 and hot 2 in my shore line used?  I don't see the difference.

Yup, that works just as well too. No difference at all.  Jack also referenced that too when he mentioned the genset plug.  In some ways I like the plug approach better myself.  Less cost and less parts to potentially develop problems (although I don't know that I've ever heard of a manual transfer switch failing).
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DrivingMissLazy
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« Reply #11 on: July 16, 2008, 08:24:53 AM »


Jack,  My genset is a Kohler 7.5KW A26 10607A  Probably a former marine unit.  Gold paint.  I'd love to find a full set of manuals for this thing.  I haven't had much luck on the internet.  Thanks guys!
Glenn

Since it is a Kohler, I am 99.9% sure that the wiring diagram I discussed will be correct for this alternator. BTW, all the Kohlers that I ever saw were gold colored.

The only connection that I am unsure of is the voltage regulator connections.

Richard
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« Reply #12 on: July 16, 2008, 09:42:33 AM »

I thought of starting this as a new thread, but since it deals with the same wiring issues with only a slight variation, I hope that it is seen as an augmentation rather than a hijack.  My system has a three prong, 240 plug that goes to the electrical panel.  One can plag it into an outlet to the generator or an outlet for the shore power.  I do not have any 240 volt appliances.  The hot wires from the panel plug go to the separate legs in the panel.  There is a jumper wire in the shore power outlet to energize both legs in the panel.  The generator, another 7.5 Kohler, though is wired for 240 and, of course, there is no jumper wire in its outlet, so each leg is energized as a separate 120.  This is the way the coach was wired when I got it, and I did not see any reason to change it.  However, this thread has started me thinking about it.  I have purchased a transfer switch to use for an inverter, both of which have not been installed yet, and am wondering if I would be better off wiring the generator at 120 and putting a jumper wire in that outlet also.  Would this make things simpler and avoid problems in hooking up the inverter and transfer switch?
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« Reply #13 on: July 16, 2008, 09:47:22 AM »

Richard, I think we are close.  Here is a picture of the 2 junction blocks.



The left junction block seems to be getting the two smaller lines from the head, labeled F1 and F2.

The right junction block we will label:

135
246

Terminals 1 and 2, 3 and 4, 5 and 6 are tied together.

Terminal 1,2 gets a hot line from a small transformer that is fed by what I think is a voltage regulator.

Terminal3,4 is the neutral, grounded to the genset case.

Terminal 5 gets a hot line from the head labeled A1.

Terminal 6 gets 2 lines from a large transformer underneath.

What do you think?

Thanks!
Glenn
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Glenn Williams
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« Reply #14 on: July 16, 2008, 12:47:29 PM »

Richard, I think we are close.  Here is a picture of the 2 junction blocks.



The left junction block seems to be getting the two smaller lines from the head, labeled F1 and F2.

The right junction block we will label:

135
246

Terminals 1 and 2, 3 and 4, 5 and 6 are tied together.

Terminal 1,2 gets a hot line from a small transformer that is fed by what I think is a voltage regulator.

Terminal3,4 is the neutral, grounded to the genset case.

Terminal 5 gets a hot line from the head labeled A1.

Terminal 6 gets 2 lines from a large transformer underneath.

What do you think?

Thanks!
Glenn

Glenn, call me. I think we can work out what you have. 304   927    4093

Richard
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