Inverter Monitoring & Canceling Meter Legs [RE-wrenches]

[Christopher Freitas --- OutBack Power]

Travis Creswell wrote:
> If one inverter of a stacked pair was sleeping would a 240 VAC meter
> installed to measure output of them not be accurate?

With tht OutBack stacking system it would still work - since we use a 
autotransformer to keep the L2 leg powered even though the L2 
inverter(s) are "sleeping" to reduce power consumption.  

Using an external CT (current sense transformer) type meter is probably 
the best option as only one KWH meter with two external CTs could 
measure both legs simultaneously - the input and output wires for each 
inverter simply pass through the CT in opposite directions - cancelling 
out the pass through current.  This is what I did with the datalogging 
system that I installed and is operating on Doug Pratt's system.  

I talked with the guys who make the electronic KWH metering system 
listed as a approved monitor on the CEC rebate - their monitoring system 
is not capable of measuring current in both directions.  They are 
suppose to work on one and sample it to me for testing.  Since they 
always use external CTs they would be very useful.  

With the OutBack inverters the internal battery charger can be 
completely turned off - which eliminates the reverse power flow issue - 
so, therefore, could be used with one-way meters...  but if you ever did 
run the battery charger the data would be corrupted (some one-way meters 
will spin forward regardless of the power's direction).  

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  

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