[RE-wrenches] Dual radian system stopping selling on sunny days

scot.arey at solarcentex.com scot.arey at solarcentex.com
Fri Sep 26 14:25:12 PDT 2025


I don't have but two paralleled Radian systems but I removed the FNDC in those. While I REALLY want to love and use the FNDC, I feel like that gives unintended issues in more complex systems.

Howard "Scot" Arey
Owner, Solar CenTex
254-300-1228

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From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf of Steve Higgins via RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Friday, September 26, 2025 4:01 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: Steve Higgins <steve at surrette.com>
Subject: Re: [RE-wrenches] Dual radian system stopping selling on sunny days

Dave,  I've had the same thing happen with a couple of systems...

Do you have the FNDC installed?

Outback wont admit it but I think that there is a software conflict between the FNDC and the radian firmware.

The only way I could get it to stay in sell mode was to remove the FNDC.

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On Fri, Sep 26, 2025, 10:53 AM Dave Tedeyan via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
To the Outback extraordinaires,

I've got a dual radian, grid tied system that has been in service for about 9 years. Recently, it has started this behavior where it will stop selling to the grid on sunny days. Looking back at the data, this has happened intermittently and very infrequently a couple years ago. But now we are at the point where it happens every sunny day. Once the batteries get up to fully 100% charged (not 99%), the selling stops and the system only harvests enough solar to cover the backed up loads.

I got a hold of the USB card data. It appears that the inverter goes from "Sell Enabled" to "Offset" when this happens. I cannot tell whether the inverter randomly decides to switch mode and then stop selling, or whether it is the stopping selling that puts it in "Offset" mode. The sell voltage is set at 52V, and float is set to 54.4V. It looks like the batteries are generally sitting around 54V when this happens. Once the inverter enters "offset" mode, then the battery voltage stays steady at 54.0V

Does anyone have any idea what can be causing this to happen?
Cheers,
Dave

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