FLEXmax 100 Voc: 300 V or 250 V?

Discussion about the FM100, FM80, and FM60 Charge Controllers

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AllPawDrive
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FLEXmax 100 Voc: 300 V or 250 V?

Post by AllPawDrive » Sun Aug 02, 2020 5:31 am

From the FLEXmax 100 manual,

Open Circuit Voltage (Voc) Open-circuit voltage is the unloaded voltage generated by the PV array. The FLEXmax 100 controller can withstand Voc of up to 300 Vdc. However, if the Voc exceeds the following voltages, the controller will suspend operation to protect the system components.

48-volt system ≥ 290 V

However, from an outback webinar at 6:45 https://www.youtube.com/watch?v=dyQWLNNLHuY, it was stated that maximum input Voltage from the array is 250 V as the max voltage includes the battery voltage of 48 V for a total COMBINED voltage of 298 V.

Thanks,

Dave

raysun
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Re: FLEXmax 100 Voc: 300 V or 250 V?

Post by raysun » Sun Aug 02, 2020 6:13 am

I've not worked with the FM100, but if it behaves similarly to the other FM controllers, then 300V would be an absolute maximum input voltage. It appears the FM100 will protect itself from over voltage events with some form of shutdown mechanism, but I'd think it decidedly bad system design to drive it into protect mode.

Voc is measured at STC, however solar panels have a negative temperature coefficient, so a cold, clear morning, among other conditions, can drive VOC significantly higher.

I'm not sure about the comment relating PV string voltage to battery voltage, but it would seem prudent to keep the string voltage to no more than 250V.

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Re: FLEXmax 100 Voc: 300 V or 250 V?

Post by fcwlp » Sun Aug 02, 2020 10:58 am

AllPawDrive wrote:
Sun Aug 02, 2020 5:31 am
However, from an outback webinar at 6:45 https://www.youtube.com/watch?v=dyQWLNNLHuY, it was stated that maximum input Voltage from the array is 250 V as the max voltage includes the battery voltage of 48 V for a total COMBINED voltage of 298 V.
Hi Dave, I am not sure what Mark was trying to convey with that statement. The PV Voltage/Current/Power is on the input side of the CC and the Battery Voltage/Current/Power is on the output side of the CC. I ran a test with the OB string sizing tool for a 320W panel with a Voc of 42.2 and Voc temperature coefficient was -0.3%. At -18C and it gave a valid solution for a string of 6 with a Voc of 285.9. When I bumped up the Voc to 42.82 it gave a warning starting at 290.1V.

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