How to disconnect loads at low SOC, but keep inverter on so that charging can occur?

[whatismouse]

I have an mpp solar 48volt, 3000 watt inverter/charger (3048lv-mk), installed in an RV. It is my first inverter so I don't know what features differ from other models on the market. But in any case, I want to replicate the super user-friendliness of something that most of us experience every day: take for example the experience of a phone, you can run it down to 0%, and then just plug it in wherever and whenever to charge it back up.

If my battery bank runs down to 0%, the experience is much less convenient. Currently I have a non-adjustable low-voltage disconnect of 42 Volts at the BMS, and an adjustable low-voltage cut-off at the inverter. If either of these events occur, I believe the inverter shuts off. If the inverter shuts off, afaik, the charger is also off. In which case it doesn't matter if I connect AC power, or if I'm bringing in Solar, its too late. My only recourse at this point is to introduce an external charger, connected to AC, to charge the battery enough that the inverter will turn on again?

Ok I partially understand why these settings are like this, they are meant to protect the battery from damage. The inverter must shut off so that there are no further loads on the battery.

But shouldn't the inverter be able to turn itself back on when it senses an AC or DC input, so that it can charge my battery? It seems crazy that I could literally have my pick of charging inputs: plentiful sun, AC power, a generator, and nothing will re-charge my battery because the inverter won't turn on.

OR

Is there a way to create another event, that occurs at a specified SOC, that would put my inverter in charge-only mode. With only the inverter on, I could hang out in this mode for quite a while before the battery discharges to the LVC, and during that time, the inverter is on and available for whenever a source of charging input makes itself available?

Basically I'd like to have it set up so that its stupid easy and doesn't need to be monitored. Things will just turn off when the battery gets too low, but charging can still occur. When SOC again increases to a set threshold, loads turn back on.

 

[snoobler]

Priority one is to stop running your battery to 0%. If you're doing this on a regular basis, you're using too much power for the system and hammering your battery. Really no reason to go to below 46V. There's almost nothing left below that level.

When the BMS cuts the battery, it cuts the battery. Period. Open circuit. You've disconnected the battery from the unit. It MUST have battery voltage as that's where it draws its power. You need to avoid this at all costs. Raise your inverter cut off voltage to 46V so the battery never goes open circuit. If the BMS ever trips the battery, then there's a problem with the battery, or you're doing something wrong. Upper and lower voltage limits should be established by the chargers/inverters, not the BMS. BMS is there to protect before stuff goes sideways. Stay away from those limits.

If you change program 29 to 46V, it will go into standby mode with AC output disabled, but it can still charge from solar or utility/genny.

 

[Craig]

I have solved this problem by shutting off inverter loads with about 15% of battery capacity by using a DC-AC Solid State relay on the AC out of the inverter. This way loads will be shut off and the all in one will still be powered on allowing the solar to charge the battery when it hits 20% capacity the inverter turns back on.

The SSR is controlled by my Chargery BMS no problem.

 

[new off grid]

You can install this ,

Amazon.com: MOES Dual Power Controller 50A 5500 Watt Automatic Transfer Switch for Off Grid Solar Wind System ATS DC 12V 24V 48V AC 110V 220V: Garden & Outdoor

Amazon.com: MOES Dual Power Controller 50A 5500 Watt Automatic Transfer Switch for Off Grid Solar Wind System ATS DC 12V 24V 48V AC 110V 220V: Garden & Outdoor

www.amazon.com

 

[whatismouse]

You can install this ,

Amazon.com: MOES Dual Power Controller 50A 5500 Watt Automatic Transfer Switch for Off Grid Solar Wind System ATS DC 12V 24V 48V AC 110V 220V: Garden & Outdoor

Amazon.com: MOES Dual Power Controller 50A 5500 Watt Automatic Transfer Switch for Off Grid Solar Wind System ATS DC 12V 24V 48V AC 110V 220V: Garden & Outdoor

www.amazon.com

If this turns off DC output, my inverter would shut off, and then no charging could occur?

 

[Supervstech]

AFIK, MPP inverters will happily charge from AC power if you shut off the unit.

 

[snoobler]

AFIK, MPP inverters will happily charge from AC power if you shut off the unit.

They will do so if in standby mode. If they shut off due to fault, they won't.

 

[new off grid]

This thing works like this :
Let the unit monitor the batt voltage by connecting it @ the Inverter + & -
Connect AC out from inverter into this unit, and then out to load
Then you set the cut off and reconnect voltage values as you want
when the SOC goes down, so does the batt voltage
At the point when the Batt voltage hit the cut off value you set, this unit will shut down the load from the batt source ( by switching to the other source , if you have a connection for it ), BUT the Inverter is still running.
( assume that your inverter still OK with this low voltage )
The whole system is at idle now ( only the inverter is running without load )
When the Sun rise, the batt is charged, SOC is up, so does the voltage
And at the point when the Batt voltage hit the reconnect value, this unit will switch back to Batt source.......
And the cycle of life will repeat.......,

Hope this help,

 

[whatismouse]

interesting. i think that would work fine. frustrating that the same exact thing could be accomplished at the inverter with a simple feature to disable ac outputs at a given battery voltage (without shutting off).

 

[Supervstech]

I was under the impression that the inverter could be set to discharge to a cut off voltage, then switch to ac charging mode... no?

 

[Craig]

I was under the impression that the inverter could be set to discharge to a cut off voltage, then switch to ac charging mode... no?

Yez this is true but what if you have a grid down situation. Or your genny has no fuel. So AC backup is not present. I know this could be a rare scenario but definitely not outrageous either

 

[whatismouse]

Yez this is true

How is this true? This is a setting I've been trying to find...

 

[snoobler]

How is this true? This is a setting I've been trying to find...

Did you read the first response?

How to disconnect loads at low SOC, but keep inverter on so that charging can occur?

I have an mpp solar 48volt, 3000 watt inverter/charger (3048lv-mk), installed in an RV. It is my first inverter so I don't know what features differ from other models on the market. But in any case, I want to replicate the super user-friendliness of something that most of us experience every...

diysolarforum.com

 

[whatismouse]

Did you read the first response?

How to disconnect loads at low SOC, but keep inverter on so that charging can occur?

I have an mpp solar 48volt, 3000 watt inverter/charger (3048lv-mk), installed in an RV. It is my first inverter so I don't know what features differ from other models on the market. But in any case, I want to replicate the super user-friendliness of something that most of us experience every...

diysolarforum.com

I tried to find a program 29 but failed. I thought maybe you were talking about a different make/model of inverter. But looking now through the watchpower manual I see a "back to grid voltage" that appears to be the function that you are describing.

It's been slow troubleshooting because I've been without a battery for three weeks now on warranty repair.

In any case, it looks like this feature solves my problem. I now can set a voltage higher than the LVC that permits the inverter to remain on, and I can charge the battery in my RV via shore power, generator, or PV.

Also with regards to your point in the first post, running my battery down to 0 is not something I intend on doing often, if ever. BUT, I wanted to be sure that I was prepared for what occurs when that happens. Worst case scenario, if I was out boondocking, and reached the LVC, I'm stuck completely without power until I find an external power source and a charger that can charge a 48V battery.

 

[snoobler]

Per post #2, you should NEVER hit the BMS LVC. You should prevent that via the inverter LVC. The BMS LVC removes the battery from the circuit in most cases. You can't charge a battery that's not connected.

 

[whatismouse]

Per post #2, you should NEVER hit the BMS LVC. You should prevent that via the inverter LVC. The BMS LVC removes the battery from the circuit in most cases. You can't charge a battery that's not connected.

yes, hitting the BMS LVC would necessitate hooking up another charger directly to the battery.

but, hitting the inverter LVC turns off the inverter. Which means no possibility of charging from the AC or solar...? So actually the inconvenience is identical afaik

my goal is to have both, with the inverter LVC higher than the BMS LVC, and never hit either of them.

 

[LB3]

I separated the charging and discharging functions in my RV build. It meant going with stand alone chargers and inverters instead of using an inverter/charger.

 

[snoobler]

yes, hitting the BMS LVC would necessitate hooking up another charger directly to the battery.

but, hitting the inverter LVC turns off the inverter. Which means no possibility of charging from the AC or solar...? So actually the inconvenience is identical afaik

my goal is to have both, with the inverter LVC higher than the BMS LVC, and never hit either of them.

The unit you say you have may "turn off" the inverter, but it is still in standby mode and allows solar or grid/genny charging. If it doesn't, then you don't have the model you listed, or it is not functioning properly or is not configured properly.

 

[whatismouse]

The unit you say you have may "turn off" the inverter, but it is still in standby mode and allows solar or grid/genny charging. If it doesn't, then you don't have the model you listed, or it is not functioning properly or is not configured properly.

Well then I guess it was an imagined problem all along. In this case I don't need to set any additional parameters, I can safely discharge to the inverter LVC without interfering with the charging functionalities at all.

I'll have to check that this does in fact work if I ever receive a battery in the mail.

 

[Akb]

Hi everyone just a question i have 3k inverter with 4 x agm 12v 170Ah battery in parallel. Now you don't want agm battery to go down below 10.5v as it gets difficult to charge when drops this far and inverter cuts off at 10v now just to be safe side i want to stop inverter when battery drops to around 11v.
What shell i install in between to achieve this.
Thanks