SW Efficiency/ PWM Angle Adjustment [RE-wrenches]

[Joel Davidson]

Bill,
I wish Xantrex was as interested in field testing and sharing knowledge as you
are. What affordable test equipment do you recommend so that the folks in this
group can share field test data?
Best regards,
Joel Davidson

Bill Brooks wrote:

> Wrenches,
>
> Just a quick word about what this about. I think many are completely
> misunderstanding what this setting change addresses. It would be easiest to
> show you on an oscilliscope, but since I can't do that in an email, let me
> try to explain.
>
> This problem was discovered when looking at the current waveform coming out
> of the SW inverter. At each zero crossing (when utility voltage goes to zero
> 120 per second), the Trace SW would inject a substantial amount of current
> (from the battery into the grid at zero volts). Since the current injection
> happens at nearly zero volts, no power is transferred to the grid. It was
> injecting current because it was not expecting to see zero volts so it tries
> to inject current to keep the voltage from going to zero (trying to fix the
> utility voltage). Well, the utility voltage ain't broke--it's trying to fix
> something that ain't broke (technically speaking).
>
> However, when an inverter flows current, there is heat lost in all the wire
> in the transformers in the inverter (a lot of wire). We often refer to these
> losses as I-squared-R losses (current squared times resistance in wire equal
> the power lost). These are the very same losses we have when we talk about
> voltage drop in wires on the DC and AC sides of the inverter. Heat is
> generated, as power is lost.
>
> It's a lot like jumping rope. If you get in sync with the rope, you can jump
> faster, better and more efficiently. If you are out of sync slightly, you
> have to jump too early and expend a lot of energy just staying up in the air
> longer than you need to. Try it sometime.
>
> There is nothing magic or mysterious about this in the least. It is simple
> physics. Joel and Don are simply testifying that their inverters cooled off
> (less heat loss due to unnecessary current flow). Most of the wrenches
> community is extremely cognisant of the slightest ineffeciencies in loads.
> We are simply talking about the efficient operation of the inverter.
>
> You can debate me offline if you like and I will be happy to enlighten those
> who enjoy learning. I learn new things every day. That's what makes life
> interesting. I learned volumes from this one incident.
>
> Bill.
>
> -----Original Message-----
> From: Don Loweburg, Offline [mailto:i2p at aol.com]
> Sent: Wednesday, September 19, 2001 2:06 PM
> To: RE-wrenches at topica.com
> Subject: Re: SW Efficiency/ PWM Angle Adjustment [RE-wrenches]
>
> In a message dated 09/19/2001 8:47:15 AM Pacific Daylight Time,
> joeldavidson at earthlink.net writes:
>
> I changed the PWM on my SW4048 from 129 to 126 the day after Bill Brooks'
> post.
>
> Joel and Bill,
> I just happened to be at one of my grid sites last week and did notice the
> inverters fan running in sel mode with only about 900w input. Since this
> procedure was fresh in my mind I made the change. Within 2 minutes the fan
> turned off.
>
> Seems like a good thing to me. As I have occasion I plan to change the
> setting on all ETL grid SW systems I maintain.
>
> Don
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