Had what appeared to be a great harvest day yesterday...ambient temps were about 60-62 with a bit of a brisk breeze to keep things cool, and bright clear sun. So I get home and check my Sunpower/Xantrex SPRx monitor and sure enough I have a record 31.6kW-h (System is 27 Sunpower 205BLK panels with a Sunpower SPR5000x inverter, previous best was about 30.5).

But, there is also a pie-shaped slice out of my output curve, right after what appears to be a 3-hour run of 90-100% rated output. The output seems to have dropped from about 4,900W-5,000W to about 2,500 in a blink, then gradually builds back up to about 4,500W over a 1.5-2hr period (its later in the day by now...)

this probably cut about 2-3 kW-h from my yield. I am assuming this was a thermal derate? My inverter is mounted in the garage, so there is no breeze cooling effect. Now, I'm thinking about some kind of fan cooling but I wonder if the cost of such a setup will ever be offset by occasional derating...any thoughts on this? If I let things go, do I risk any long term damage to the inverter from the overheat/derate?

Thinking back on the 4 or so months I have been online, I can recall 2 other instances where I had that same slice in the curve...I suspect now that these were derates, also.

Any thoughts on the pro/con of an external cooling system? Kind of defeats the purpose of a fanless design, but it seems that the heat sink may not be cutting it for my setup all the time.


Thanks for any info !

for starters, hookup a PC with SG-View and start logging data via the RS232 port. With the data you will know exactly the cause of the reduced power output and not guess.

Some have put a cheap desk fan on a timer to cool the unit, but a 5kW inverter is a poor design choice and you will need to address this before the summer heat

A poor design choice in which way? Too much generation for the unit?

I thought the Sunpower/Xantrex was the best choice around...

Guilty of cheap fan and cheap timer !
http://www.mike-burgess.org/images/WiredInverter_c.jpg

Sorry, I fogot a few words!.The poor choice is to confine a 5kW inverter in a garage with no ventilation. Mine are mounted on the outside wall of the garage and I have never seen any thermal issues. Again, using a PC you can log the invereter and understand exactly the cause of your power dips and then make a plan of attack.

Thanks for the replies.

My install would have placed the inverter in direct sun, so I figured the lesser of 2 evils was to mount it indoors. In retrospect I probably could have gotten the installer to use a spr4000x and a 3300x and split the load...but too late now...if only I knew then what I know now...


I have been meaning to get SG-View going, looks like now is a good time!

OK, so I dug an old Pentium II laptop running W98 out of the closet, loaded up SG-View (works fine on W98, BTW) and now I just have the RS232 cable to contend with. I have a couple of made up cables, but the ends are so large there is no way I could fit a proper cable bulkhead fitting in the inverter.

What are you guys doing about the cable? Making up a custom one, after threading the cable through?

Almost. I made a cable, (solder type, uses a thinner connector) and no backshell, just heatshrink on the data leads. Then that was easy enough to fold to fit thru the knockout. Other folks have used a ethernet or phone cable with DB9-RJx connectors

Yet another is the "Yost" style http://yost.com/computers/RJ45-serial/

I think my solution was much more simple. Take a Round file about the width of your serial cable, maybe 1/4 inch. Remove the wiring box cover.
Use file to create a small groove at the lower right side of the opening that wiring box cover fits in. Now simply connect your RS232 cable, run it through the new groove and replace the cover. If you made a large enough groove then the cover of your wiring box will hold the wire in place, but not so tightly as to pinch it. This way it will look like the manufacturer designed it that way, you hardly notice the small white rs232 wire comming out of my inverter and stapled to the plywood running up the wall right next to it. Worked great for me. I used a 100' pre-made RS-232 cable by the way, mine also would not fit through to 3/4 inch nockouts.

Found this controller:

http://www.rancoetc.com/ranco-etc111000000-prewired-digital-temperature-controller-p-87.html?osCsid=215ca014fd17e2f186d98dee7104e0

http://www.icca.invensys.com/uniline/d/d71.pdf