Flexnet DC Keeps Showing Lower and Lower Battery SOC

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Flexnet DC Keeps Showing Lower and Lower Battery SOC

Postby bpad on Tue Dec 19, 2017 2:33 pm

My grid tied system is just about 1 year old. The Flexnet DC always displayed a voltage about 1.1V higher than actual on a good DVM. I had already calibrated the Radian inverter and 2 Flexmax charge controllers to agree with the DVM. The battery SOC (State of Charge) readings never seemed accurate, but the SOC displayed was reasonably high.

After reading another post I found that I could calibrate the FlexnetDC and battery voltage displayed on the Mate3 by adding a small potentiometer in series with the FlexnetDC + (black) battery wire. I used good quality 10 turn 1 K ohm PC board potentiometer. Displayed battery voltage is now correct and agrees with the charge controllers and inverter.

However since this calibration the displayed SOC has slowly and continually gone down. It now displays less than 50% and the red warning LEDs are displayed on the Mate3. The new Trojan wet cell batteries are close to full charge. The grid tie sell voltage is close to the specified float voltage, and there have been no outages requiring battery power. Once a month I run an equalizing / stirring charge at the recommended absorption voltage; for 1 hour. The current starts at about 4 amps and tapers to below 1 amp before the end of the hour. (This to me tends to indicate that the batteries are fully charged.)

I am worried that this low SOC will shut down my system. I have already acknowledged the "low SOC event" on my Mate3.
bpad
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Re: Flexnet DC Keeps Showing Lower and Lower Battery SOC

Postby blackswan555 on Tue Dec 19, 2017 9:33 pm

It does sound like your batteries are fully charged, But Please check that with a hydrometer first, If indeed so, Unplug FNDC and replug, It defaults to 100% SOC, Which is where batteries should be when first installed anyway, You will then need to look at the calibration of the FNDC and adjust accordingly to match SGs as your batteries run in and age ( they take about 70 cycles to reach full capacity)

Tim

To add, EQ is not a timed operation & should be done properly on install, & thereafter about every 6 months or 100 cycles, By properly I mean charge at normal absorb untill all SGs stop rising, switch to EQ voltage and charge again untill SGs stop rising, The below manual is very good reading,
https://www.rollsbattery.com/wp-content ... Manual.pdf
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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Re: Flexnet DC Keeps Showing Lower and Lower Battery SOC

Postby bpad on Wed Dec 20, 2017 11:47 am

Thank you for your suggestion on resetting the FLEXnet DC to 100% SOC. It is easy to unplug and re-plug the Cat 5 cable to the FLEXnet DC. Will put this in my "knowledge base".

Some other comments on FLEXnet DC -

1. Some time ago I saw some other posts on calibrating the displayed battery voltage from FLEXnet DC. I found that this is easy to do as long as the displayed voltage is higher than the actual. The Flexnet DC voltage sensing has an input impedance of approximately 25K ohms, or 500 ohms per volt. Mine was about 1.1V high; so it was easy to insert a 1K ohm 10T PC board trim pot in series with the + (black) lead. If it reads low it would probably be necessary to add a voltage in series with this sensing lead.

2. As far as Equalizing batteries; recommendations depend on the specific battery manufacturer. My batteries are Trojan brand. Trojan recommends equalizing only if the specific gravity varies by a certain amount from cell to cell.
bpad
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Posts: 23
Joined: Thu Oct 05, 2017 6:58 am
My RE system: Outback 8048A Radian inverter, (2) FM80-150VDC charge controllers, MATE3 operator interface, 8KW solar panels, 370AH 48V Trojan wet cell batteries


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