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Autotransformer to balance electric panel

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Posted by Glia on January 14, 2007, 3:00 pm
 
I have a manual Transfer Panel that has a 100A utility and a 30 Amp
(really only 23A) Generator feed. The Tranfer panel has a 60A circuit
that services a Trace SW4024 inverter which has about 6KV loads on a
subpanel. This is used as a backup power system and connected to 8
GC110 batteries. If power goes out, inverter kicks in, if it last
longer then a few hours, I turn the generator on and run everything
including the inverter harging runs via the generator. The problem is
that the inverter being 120V makes the panel which is 240V unbalanced
as it can draw up to 60A on a single leg.. Not much of an issue when on
utility power, may be not ideal, but when on the generator it is a big
problem as the generator cannot handle the load..
The plan was to put the autotransformer into the loop. I see two places
to do that.
1.) Permanently in front of the inverter in which instance all
circuites that the inverter switches use the transformer all the
time....down side power loss in the transformer
2.) In front of the transfer panel on the generator side so that the
transformer is only used when the generator is used. I am not sure if
that works as the Transfer panel would have to receive both 120V and
240V from the generator since I have a few items on it that are 240V.
The latter scenario is described on page 40 of the Xantrex TX6 manual
and seems to do just that in a balanced way. Could the Outback PSX-240
do that as well? How large will my power losses be and what would you
recommend?  
Let me know what your thoughts.


Posted by Bruce in Alaska on January 14, 2007, 6:21 pm
 


I have a 10Kw 240/120Vac transformer that is feed by my 240Vac Genset.
The Secondary then feeds the Non-Inverted 120Vac SubPanel which feeds
the SW4024.  The output of the SW4024, then feeds the Inverted SubPanel.

I also have a 3Kw 240/120Vac transformer that is feed from the 240Vac
Generator Panel. This then feeds the Input of my Trace 2624. The
output of the 2624 then feeds the Winter Shop Lights and Outlets.

Works good for "Me".....


Bruce in alaska
--
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Posted by sylvan butler on January 14, 2007, 6:52 pm
 
Why did you use the manual transfer panel ahead of the trace instead of
using the automatic transfer built into the SW4024?  About the only
reason I can see is to have 240v loads run by the generator and NOT by
the inverter...

I would recommend, if possible, to set up the generator for full output
at 120v, and wire it into the AC2 input on the SW4024.  This will let
the SW transfer switch handle everything and also eliminate the phase
balance problem at the generator.

Then the 240v loads can be powered by a transformer (preferably not
autotransformer) on the output of the trace.  I manually transfer the
240v loads and turn on the breakers to the transformer only when needed.
This gives me the option of running 240v stuff from battery.


Are they a true 240v (2-wire) loads or are they mixed 120v and 240v
(3-wire)?  I would hesitate to use an autotransformer if they are 3-wire
loads.  "Normal" 240v is 120v-neutral-120v but that relationship is not
well preserved thru most autotransformers.  Mine, the Trace product from
just before Xantrex, creates neutral-120v-240v.


A 5kw transformer will have idle losses typically between 20W to 50W and
operating losses typically at least as much as the idle loss and
typically capped between 5% and 15% of power in.  That's why my
transformer is normally off, and I turn it on (and transfer the load to
it) only when needed.

sdb
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Posted by Glia on January 15, 2007, 1:55 pm
 I am using the transfer panel at 240V because I have a 240V pool pump
on this panel. This runs off utility at 240 and really cannot be
rewired to 120V. My reason for having it hooked to the generator is to
alow me to power the pump in the rare event that we have a freezing
condition and I need to run it to prevent pipes from breaking. I rewire
the generator I can no longer handle my pool pump. Hence I am stuck
with a tranformer solution of some kind. Hearing the losses I assume
that running the Trace permanently downstream of a tranformer is not a
good idea as I will incur looses of 10% or more on all my power items
that are connected to the Trace.
Should I split the generator output? I could run parallel wires to the
transfer panel and the generator input on the Trace. I could then limit
the draw on the trace in case I need to run the pump at the same time.
Does that sound reasonable?

The most interesting solution I saw was from the manual for the new
Trace TX4K on page 40.

http://www.xantrex.com/web/id/159/p/docs/pt/5/product.asp

They simply connect the transformer as a balancing tranformer between
the genset and the panel seemingly achieving a balanced panel with 120
and 240V output. I don't understand how it works.


If I wired the generator to the input of the Trace I will need a
tranformer.
sylvan butler wrote:


Posted by Glia on January 15, 2007, 2:00 pm
 I am using the transfer panel at 240V because I have a 240V pool pump
on this panel. This runs off utility at 240 and really cannot be
rewired to 120V. My reason for having it hooked to the generator is to
alow me to power the pump in the rare event that we have a freezing
condition and I need to run it to prevent pipes from breaking. I rewire
the generator I can no longer handle my pool pump. Hence I am stuck
with a tranformer solution of some kind. Hearing the losses I assume
that running the Trace permanently downstream of a tranformer is not a
good idea as I will incur looses of 10% or more on all my power items
that are connected to the Trace.
Should I split the generator output? I could run parallel wires to the
transfer panel and the generator input on the Trace. I could then limit
the draw on the trace in case I need to run the pump at the same time.
Does that sound reasonable?

The most interesting solution I saw was from the manual for the new
Trace TX4K on page 40.

http://www.xantrex.com/web/id/159/p/docs/pt/5/product.asp

They simply connect the transformer as a balancing tranformer between
the genset and the panel seemingly achieving a balanced panel with 120
and 240V output. I don't understand how it works.


If I wired the generator to the input of the Trace I will need a
tranformer.
sylvan butler wrote:


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