Outback FM100-afci and Tigo ts4-a-O nuisance afci tripping?

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fswank
fswank Registered Users Posts: 3 ✭
in Advanced Solar Electric Technical Forum #1
I’ve got a 2kw off-grid system, 2-strings of 3x 340w Panasonic panels each with their own Tigo ts4-a-O optimizers, those combine in a combiner box then run through conduit fully enclosed to an outback fm100-afci. System has been running fine for a few months with solid sun, but now we are getting quite a bit more mid-day shading of some of the modules and we are also now getting intermittent arc fault shutdowns. Have recently got them on the last 2 sundays about mid-day and two today (Saturday), one just before noon, and one just after 1pm (I had reset the system after verifying all connections were tight in combiner, no insulation pinched in terminals or otherwise, all mc4’s, breakers, crimps, in controller, grounds,etc and no damaged wires in the array or inside the junction boxes or panels.) both times today the panels were partially shaded. The shutdowns have occurred on days where the max array voltages were as low as 150vdc and as high as 201vdc (based on max volt readings in the mate3 datalog)

I read the sandia report on unwanted tripping and optimizers and shading are listed as causes of unwanted tripping of afci’s. Tigo support site says that their “ts4-a-o’s) are compatible with most INVERTERS on the market”,  but are mute on charge controllers, and they have compliance letters from outback for their fm100-afci and Tigo ts4-a-F but not the -O (which makes sense since the -F has no voltage adjusting circuitry). 

I finally found an obscure Outback 2019 application note indicating way down in the q&a section that the Tigo-O and other optimizers may cause nuisance tripping https://www.outbackpower.com/downloads/documents/appnotes/fm100_afci_nec_app_note.pdf

I also have a small dc-dc switching power supply running the Tigo cca (since we turn off the inverter and thus AC power when we are away) which is probably generating some noise on the dc system.  We have also had an afci trip when we were away and had the inverter off (aims 4kw power inverter) so don’t think it’s an issue with the inverter feeding back noise into the dc system. 

Has anyone had any similar issues like this and can confirm the incompatibility with the fm100-afci and the Tigo optimizers?  If so, have you identified any solution other than disabling the afci detection? I’m reluctant to do that and only want to do that as a last resort since we are in a fire prone area and I really don’t want to be the cause of one. 


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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,749 ✭✭✭✭✭✭
    #2
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    An old problem that is easily solved by not using the roof for offgrid, not using AFCI, RSD, and any other device that replaces wires with headaches, offgrid!    Keep it simple and DC couple solar!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • fswank
    fswank Registered Users Posts: 3 ✭
    #3
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    The system is DC coupled. Unless. I’m misunderstanding what you’re saying. The tigo optimizers are basically dc-dc converters that adjust for panel output differences when encountering partial shading. DC all the way from the panel through the tigo to the charge controller (which has the afci circuit) and dc output from the controller direct to the batteries
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  • MJSullivan56
    MJSullivan56 Registered Users Posts: 42 ✭✭
    #4
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    I will be installing a very similar system this spring and will report back if it works or not. I too have shading issues so that’s a concern.
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