Wanting clarity on how these charge controllers would handle battery disconnect situation

[Lorax]

I have several small systems and a few I have helped friends with. I use a Magnum PT100, EPEver 100a, EPEver 80a, EPEver 50a, EPEver 30a, Victron SmartSolar 100v | 50a, Victron SmartSolar 75v | 15a

I have recently installed a few lithium systems and am worried about temperature, since I live at a high elevation where temps get below 32F. I have heating pads installed, but say they fail. I have installed temperature sensor modules that will disconnect the batteries from the charge controller and any loads. If any of these controllers start getting PV while the charge controllers are disconnected from the batteries, will the charge controllers get damaged by the incoming power from the panels?

Will all, some or none of these charge controllers be okay in a battery disconnect situation?

If they do indeed risk damage, should I install a relay on the PV circuit that turns the PV off as well?

 

[snoobler]

Welcome to the forum.

This has been discussed several times. While most or all SCC strongly state that "batteries must be connected before panels," it's the general consensus that this is not a significant issue, and the main purpose of the recommendation is to ensure that the SCC properly senses the battery voltage BEFORE the panels are attached.

I can speak specifically to a FM80, Victron 150/100 and Victron 250/100 that cutting battery with active or inactive panels does not damage them.

 

[Steve_S]

I can say that my Midnite can handle the Battery Bank being completely disconnected while the panels are connected.
As long as the Battery System is available WHEN the SCC starts up so it can recognize the Voltage Profile and load it's settings prior to it enabling the incoming solar it's fine. There is a delay with the midnites during start cycle, check & recognize battery then enable solar on.

The majority of SCC's do start up in such a manner. I have not encountered any that are "hard" preset to a specific battery voltage, for the most part they all support 12,24,48 volts. Some also do 36 & 72V.

IF the batteries are NOT online when an SCC starts, it likely will may not even powerup at all.
IF something forces the SCC off while the batteries are disconnected, it will require manual intervention.

 

[RStone13]

I inadvertently disconnected my Epever 60a from battery 1st once & it still works

 

[HRTKD]

The Victron 100/50 that I'm using has settings to not charge the battery when the temperature is below a user configurable temperature.

The temperature will be come from the solar charge controller itself unless an external temperature sensor is used. I have the Victron BMV-712 with an external temperature sensor (on the battery) and it communicates that temperature to the solar charge controller. My batteries have warming pads so it is often the case that the battery is warmer than the solar charge controller. This configuration works well.

Victron also sells a product called the Smart Battery Sense that can also transmit the battery voltage and temperature to the solar charge controller.

 

[pollenface]

You can set up a relay so that if the connection to your batteries is lost, the solar panels are immediately disconnected.

 

[snoobler]

The Victron 100/50 that I'm using has settings to not charge the battery when the temperature is below a user configurable temperature.

The temperature will be come from the solar charge controller itself unless an external temperature sensor is used. I have the Victron BMV-712 with an external temperature sensor (on the battery) and it communicates that temperature to the solar charge controller. My batteries have warming pads so it is often the case that the battery is warmer than the solar charge controller. This configuration works well.

Victron also sells a product called the Smart Battery Sense that can also transmit the battery voltage and temperature to the solar charge controller.

The MPPT's internal temperature sensor function leaves much to be desired. For lead-acid, it's better than nothing, but I do not trust it to appropriately protect LFP or conduct temperature compensation for lead-acid. It takes a "snapshot" of the MPPT temperature when the unit first activates with PV input. It then operates as though that is the temperature for the entire day - even if it changes. I do not trust that if the temperature were to drop below freezing, the unit would recognize it and appropriately stop charging.

I'm vigorously seconding the recommendation for a BMV and smart battery sense.

 

[HRTKD]

The MPPT's internal temperature sensor function leaves much to be desired. For lead-acid, it's better than nothing, but I do not trust it to appropriately protect LFP or conduct temperature compensation for lead-acid. It takes a "snapshot" of the MPPT temperature when the unit first activates with PV input. It then operates as though that is the temperature for the entire day - even if it changes. I do not trust that if the temperature were to drop below freezing, the unit would recognize it and appropriately stop charging.

Good to know. My Victron MPPT units have never been active without the BMV-712 also in the mix. So I had no idea that the internal temperature of the MPPT acted that way. At one point, I tried to find the internal temp of the MPPT through the Victron Connect app, but the only temp I could find appeared to be coming from the BMV-712.

 

[snoobler]

Good to know. My Victron MPPT units have never been active without the BMV-712 also in the mix. So I had no idea that the internal temperature of the MPPT acted that way. At one point, I tried to find the internal temp of the MPPT through the Victron Connect app, but the only temp I could find appeared to be coming from the BMV-712.

If you break the bluetooth network between the two, you'll see it on the MPPT VC screen. There have been a few times where my smart battery sense lost contact with the MPPT. I noticed it in the absorption/float voltages when they were constant rather than tapering off as temperature increased.

The few times this has happened, it lasted all day, so I assume there was a communication failure when the MPPT went active. I should probably switch to the BMV-702 via the GX, but for some reason I really like the smart battery sense stuck to the side of a battery vs. the BMV attached to the terminal.

 

[HRTKD]

I have three temperature sensors on one of my batteries.

Thermostat sensor (taped to top of battery, in the center)
BMS sensor (taped to top of battery, in the center)
BMS-712 sensor (on battery terminal)

So far, they are all giving me a temperature reading that is within ~1° F.

The other battery has only two sensors. The battery closest to the wall is the one with three sensors. My thinking was that it would be the battery most likely to have a lower temperature.