Inverter protection [RE-wrenches]

[Travis Creswell, Ozark Solar]

Doug,

If you remove the DC250 you will see a 1/4-20 (?) bolt the back that holds
the lug to the breaker.  Switch the feed from the top to the bottom.  Yes,
you can slide the wire under the lug with the 4/0 from the batteries but
this doesn't meet code and if I did I would only do it on 2/0 wire.  We do
this on all the power panels we install just to avoid the problem you speak
of.  According to Trace the inverter can take the OCV of the Array. What
I've seen happen is enough loads are on to keep the array from being totally
unloaded and staying within a voltage that the inverter won't go into a
safety shut down mode.  Eventually the loads get turned off and the array
goes to OCV then the inverter shuts down.  Sounds like the Whisper went to a
very high voltage pretty quickly before the 5548 could shut down.  

Also you still need to provide over current protection on the source
circuit.  The only draw back I have seen in doing it this way is the the 250
AMP breaker sees the total current coming from the batteries and the DC
charging sources.  You need to calculate the typical loads on the inverter
and add all the charging source inputs amps and see if that is going to
exceed the 250 amps and cause you some nuisance trips.  We do it this way
pretty much all the time and have never had any nuisance trips.

The benefit of this is that you can turn the 250 amp breaker off and still
charge batteries if you have to remove the inverter for service.  You are
going to have remove both breakers from the box and start over.  Take your
band aids with you and do some sort of relaxing exercise before you start.

Travis
----------
>From: "John Blittersdorf, Cent. VT Solar & Wind" <cvsolar at aol.com>
>To: RE-wrenches at topica.com
>Subject: Re: Inverter protection [RE-wrenches]
>Date: Mon, Dec 4, 2000, 7:32 AM
>

>Doug,
>   I,m not sure of the solution as I have had the same problem trying to tie 
>a large wind input into a DC250 with dual inverters.  We really need a 
>disconnect box which can hold 3 large breakers , two for the inverters and 1 
>for the large source input.  With one inverter it is simple, use the second 
>switch for the wind.  Unfortunately when the large sources are used, they are 
>often with dual inverters.  I can only recommend a 2nd DC disconnect box for 
>the wind and solar inputs but it would complicate metering as you would have 
>to have all the grounds routed thru one of the boxes and thru the shunt.   
>Anyone else have a better idea?
>
>John CVSolar

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