[RE-wrenches] Dual Channel Inverters

Ryan ryan at kb1uas.com
Wed May 8 02:30:51 PDT 2013


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, 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
>     <mailto:taharvey at heliocentric.org>>
>     To: RE-wrenches <re-wrenches at lists.re-wrenches.org
>     <mailto:re-wrenches at lists.re-wrenches.org>>
>     Subject: [RE-wrenches] Dual Channel Inverters
>     Message-ID: <1F568BAC-8D04-4E09-BC44-9090C147F0B5 at heliocentric.org
>     <mailto: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 <mailto:taharvey at heliocentric.org>
>
>
>
>
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