[RE-wrenches] Dual Channel Inverters

[Jesse Dahl]

I installed 2 10kW 208V powerone inverters this summer and both failed.
 The first one failed right out of the box and the second made it a few
months.  We were hired just to install the system by a local firm that
designed and sold the system and have had a bear of a time getting paid
from anyone.

Jesse


On Wed, May 8, 2013 at 12:38 AM, <don at energysolarnow.com> wrote:

> Hi all- While I have not had the failure problems noted with
> microinverters, PowerOne inverters have recently given me a big headache.
> Installed their 6kW model last November that failed in a month. They
> replaced it under warranty, no problem no reimbursement. Then the
> replacement failed in March. Again replaced, no problem. But that's the
> problem-- there was no indication from the inverter of why it failed. When
> the replacement inverter that was installed in March failed in April, they
> declared it out of warranty and made me pay nearly $900 for repairs. This
> is less than 6 months from initial installation.
> All the failures occurred after rainy weather. This time I bought megaohm
> meter and checked the wiring. There was a nick in the insulation where a
> negative DC home run pulled around a rail corner, with a small but
> noticable burn spot. This did not show up with a standard meter check, but
> it did with the megger and some watering from a hose. OK, so there is an
> intermittent ground fault. With a transformer inverter that would just be a
> blown fuse with a ground fault error message. But it seems this inverter
> will self destruct with a ground fault. No error message or any other
> indication that even PowerOne would or could relate before sending 3
> replacements.
> The Tigo monitors indicated that each inverter failure happened at morning
> power-up, with minimal solar current. Oh, and having Tigo monitors in the
> system but not on the one-line drawing was PowerOne's nominal excuse for
> canceling their warranty. They posted a document on their website dated
> March 10, right after the second failure, to the effect that when using
> Tigo monitors you must disable the inverter MPPT scan so they don't fight.
> But didn't tell me, or apparently their tech staff....
> The post-mortem on the last two inverters (performed well after the
> replacements were sent) indicated over-current in the IGBTs.  So where is
> this lethal current coming from? There are only two strings, one each into
> this dual channel inverter.  There is not enough solar current to kill it
> even in broad daylight. But a morning power-up failure can only mean some
> AC input surge current sneaks through the ground fault and into the DC
> inputs. Sounds like a design flaw to me... There should not be anything
> that can kill an inverter other than over-voltage or over-current; and that
> would kill it quick, not a month or months later after a rain.
>
> Can anyone suggest a possible failure mechanism? Surely not the dreaded
> electrolytic caps-- the inverter is mounted under a dry eve.
> In general, how are transformerless inverters protected internally from
> external ground faults?
> And the obvious question is: how could anyone trust a company with this
> kind of warranty service?
> Thanks
> Don Barch
> Energy Solar
>
>
> Message: 13
> Date: Tue, 7 May 2013 09:03:13 -0600
> From: Troy Harvey <taharvey at heliocentric.org>
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> Subject: [RE-wrenches] Dual Channel Inverters
> Message-ID: <1F568BAC-8D04-4E09-BC44-9090C147F0B5 at heliocentric.org>
> Content-Type: text/plain; charset="windows-1252"
>
> Since we stopped using micro-inverters due to the high failure rate,
> network problems, difficultly in replacement ? I've been using the
> power-one inverters a bunch because the dual channels solve most of tricky
> issues like different roof aspects, shading, and uneven strings.
>
> However, they are limited to 6kW, which is only mid sized in todays world.
> I'm constantly having to design 7-12k systems in residential applications
> all the time. Any other dual channel inverts of the market for 240VAC? I
> remember back a few years ago that sharp had a 3-channel inverter. Doesn't
> look like it is still around.
>
> thanks,
>
> Troy Harvey
> ---------------------
> Principal Engineer
> Heliocentric
> 801-453-9434
> taharvey at heliocentric.org
>
>
>
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