Best inverter for water pumping [RE-wrenches]

[Michael Welch]

Hello Wrenches. Roy is out of town, and the folks at Xantrex asked me to post this response on his behalf.

Christopher Freitas  -  OutBack Power wrote at 03:05 PM 10/31/2003:
  
>Roy - 
>
>I think what you are talking about when you say 134 "peak" amps is on a 
>meter set to 1 millisecond sample - so it is not the maximum RMS current 
>- but is the maximum current during the peak of the sinewave.  So this 
>134 amps of peak current should probably be described as 95 amps RMS 
>instead (134 x 0.707) ... no?   

Roy's post clearly states that we are talking about observed peak...not RMS.
The 134 amps was indeed the peak value our Fluke 39 power meter saw and we
don't know how many cycles it took to start the air compressors.

We at Xantrex specify peak current (listed as "over-current trip point"),
simply to inform the customer the max amount of current draw before the
inverter shuts down.  However, if RMS is desired as a means to make an
inverter selection for water pumps...this is also in our published
specifications.

>Most peak recording meters used by electricians in the field will record 
>the peak current in the 100 millisecond range - which means its the 
>maximum RMS current - not the peak during a single cycle. The ones 
>engineers like to use (or an oscilloscope) will display the current at 
>the peak of a single cycle - not the maximum RMS current.   
>
>We at OutBack advertise the maximum RMS current our inverters produce - 
>not the single cycle peak current - because this is what motor 
>manufacturers provide when you ask them what they require and is what 
>most installers can measure.  
>
>Also - the SW inverter's design requires more maximum current capability 
>(either in peak or RMS terms) to start a motor because it cannot control 
>the waveform on the fly to limit the current during motor start-ups. 
>High frequency switched inverters (like the OutBack FX) are able to 
>limit the current being delivered to the motor while it is starting - 
>and so, can start larger motors with less "peak" amps.   

While possibly true (Xantrex manufactures high frequency sine wave inverters
too), this may confuse the issue.  High frequency switched topologies have
advantages, but surge overhead is not one of them.  The characteristic
described above may help mitigate this deficiency, but it's not a
comparative benefit to base a selection on.  For water pumping applications,
the SWPLUS' huge surge overhead should be considered.  

>So comparing the peak amps of the SW to an OutBack or talking about peak 
>amps to someone who is used to RMS amps is like comparing candied 
>oranges to carmelled apples...

The point of the thread was "Best inverter for water pumping"...so a
comparison is inevitable.  Below is a spec to spec comparison.

VFX3648 = 50 amps RMS (100 milliseconds) *From the Outback web site
SWPLUS4048 = 124 Amps RMS (100 milliseconds to 1 second)   

More usable surge...No?

Lloyd Gomm  
  
Michael Welch
  
------------------------
"I'm hopeful. I know there is a lot of ambition in Washington, obviously. But I hope the ambitious realize that they are more likely to succeed with success as opposed to failure."
			Resident George "Dubya" Bush
        
Michael Welch, michael.welch at homepower.com
     Home Power magazine
     www.homepower.com
     To reach me: 707-822-7884
     To reach Home Power: 800-707-6585

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: re-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
--^----------------------------------------------------------------