Don
Tigo Modules basically MPPT the module. Now installing them on an
inverter that has MPPT sure does pose an interesting question. "Who is
going to win the fight". Tigo sweeps relatively fast so if you had a
really slow tracking inverter the Tigo's would likely win and life would
be ok. If you had an inverter that tracks real fast it could be a
battle. The fact the aurora failed in the early AM confirms my thinking
it is the battle of the MPPT.
Ryan
On 5/8/2013 1:38 AM, [email protected] 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 <[email protected]
<mailto:[email protected]>>
To: RE-wrenches <[email protected]
<mailto:[email protected]>>
Subject: [RE-wrenches] Dual Channel Inverters
Message-ID: <[email protected]
<mailto:[email protected]>>
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
[email protected] <mailto:[email protected]>
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