Adding a low voltage disconnect device to a 12 volt wet cell system.

TellGRBill

We have a new solar system with a Renogy 60 amp MPPT controller and a Renogy 3000 watt inverter.  I have read that my controller has a 11 volt disconnect, and have read that such a low voltage disconnect is too low for wet cell, deep cycle truck batteries.  I am wondering if it would be advisable to add a low voltage disconnect device that allows me to set a higher voltage disconnect

BB.

Is this your controller?

https://www.renogy.com/rover-60-amp-mppt-solar-charge-controller/

On Page 24 of the manual, the LVD (low voltage disconnect) is programmable (I think):

https://www.renogy.com/content/RNG-CTRL-RVR60/RVR60-Manual.pdf

So you can set your LVD from 9.0 to 17.0 volts...

Now gets into the reason why I have a difficult time answering a simple question with less than a "wall of text"...

If you want a different LVD voltage, this controller will allow you to pick any voltage you want, and a 0-60 second time delay... So that is "doable".

Other questions, this controller only supports a maximum of 21 Amps on the LVD terminals. You cannot attach any "high current" loads (such as AC inverters and such) to this terminal. Plus, it appears, you need to manually reset the controller if Over Current Load is exceeded (page 29 of manual):

So, you may have to be there to reset the controller if Over Current is tripped. Would you get a large DC relay to cut loads if over discharged (upwards of 100's of Amperes of DC current)?

For your setup, you may want to set LVD to 11.5 volts, and 30 second delay to allow for heavy starting loads. If you have larger current circuits, then you would have to use something else to disconnect >21 amp circuits (larger 12 VDC loads). Especially Lead Acid batteries, they will sag under heavy loads (such as starting/surge current), so the time delay is helpful. But many (?) AC inverters are either not programmable voltage, or have programmable delays. Like 11.5 volts for 20 minutes (low load current LVD). And 10.5 Volts for 5 seconds LVD (surge current droop in voltage).

AC inverters will usually have their own LVD settings... Many are set at 10.5 volts and may not have any "fine programmable" time/voltage ranges.

Or, would you want a Red Light or Warning Buzzer? There are simpler meters with warning contacts:

https://www.solar-electric.com/mnbcm.html

Just a voltage based State of Charge estimating meter. One neat function, it will warn you if the battery bank has not reached "full charge" in the last week... Kind of nice to know.

There are also the more complex state of charge meters. They use a current shunt (precision resistor) to measure the Amp*Hours in and out of the battery bank. So these meters can give you actual (better estimate) of state of charge capacity (not simple voltage based estimate).

https://www.solar-electric.com/victron-energy-bmv-712-smart-battery-monitor.html

The above meter also has an alarm output... You can "trip" at 30% SoC, and "reset" at 75% SoC. Also has Bluetooth and other networking equipment options.

I am a big believer in "alarms" vs automated shutdown (and startup?) of equipment. But, there is always the time you are on vacation, nobody on site, and the choice of ruining the battery bank, or cutting power to the fridge/freezer/alarms/networking/security cameras during a snow storm (that covered the solar panels or other hardware fault).

-Bill