two Trace SW4048's in parallel [RE-wrenches]

[allan]

David,
    It helps me to remember that you are in Vermont, not New Mexico, so
generators are what carry folks through the winter when there's no sun.  A
few concerns come to mind: Each SW has an idle current of about 16 watts, so
you are adding the potential of a lotta wasted inefficiency if you split the
loads.  Each 5548 can supply 45A @120 VAC, so if you had no problems with
overcurrent shutoff with one, there is no benefit to balancing big loads
between two.  If you do split loads, you might put all large,
intermittent-duty motor-type loads on one inverter, and routine and
sensitive (computer-type) loads on the other.  This both reduces chance of
crashing computers, flickering lights, etc., when motors start, and also
lessens the occurrence of two small (one CF light) loads causing both
inverters to wake up and run at their least efficient.
    Your solution will work, but seems somehow inelegant, like using a
chainsaw to cut butter...  How big is the Kohler, and what's your elevation?
Could a cheaper, dedicated charger-only do the job, if the only job is using
more of the generator output to charge faster?  Remember, the Trace SW is
woefully inefficient (about 55%, I beleive).  All Kohlers thru 12 or 20kW or
so can be wired 120 VAC output, so you don't have to match a pair of
inverter/charger loads on each leg of 240 VAC output--you could use a
charger in parallel with the inverter.  IBE makes 48V models and would be
cheaper (818 767-7067).
    Hope this helps.
Allan at Positive E
-----Original Message-----
From: David Palumbo, Independent Power & Light <ipl at sover.net>
To: RE-wrenches at topica. com <RE-wrenches at topica.com>
Date: Saturday, August 19, 2000 1:57 PM
Subject: two Trace SW4048's in parallel [RE-wrenches]


>Wrenches,
>
>We are adding a second SW4048 onto a system for two reasons.
> 1) To increase the speed of battery charging (system has a large 120/240
>Kohler genset).
>
>      2) To provide backup inverter power in case one of the SW4048's
should
>fail.
>
>This is a 120 volt system only so we will not be series stacking the two
>SW4048's. The client
>also does not need any more power on one circuit than one SW will supply.
>
>Our idea is to keep the SW4048's independent of each other and simply wire
>each inverters
>output hot wire to a different leg in the AC load center. We have
>successfully done this with
>two Exeltech 1100's and I don't see why this should not work with SW4048's.
>It is relatively
>easy to balance the home's various circuits so that all of the big loads
>will not be fed from
>one inverter. For instance we will make sure that the water pump and
washing
>machine are fed from
>different inverters.
>
>By doing it this way we will save our client the $ 345 for the Trace
SWI/PAR
>paralleling kit.
>Plus the extra labor to install, and the added system complexity.
>
>We wanted to float this idea out to the list in case we are missing
>something.
>
>David Palumbo
>IP&L
>
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