Does the Inverter cut-off point of 10.5v safe?

JakachiraJakachira Solar Expert Posts: 47
My inverter cuts off at 10.5v.

Is this a safe cut-off level for my batteries. It seems as if 10.5v cut-off point is when the inverter is on load. So practically, the battery's actual voltage will be more than this. But this may depend on the type of a load on the inverter. Small load may drain the battery to the last drop. Isn't it?

My inverter is not programmable.. so i would like to control the battery discharge by the Inverter loads. 12v loads are controlled by my solar regulator. What can I use? Btw, i need something that disconnects the battery as this system is operated by people who are not clued up. I will then lock up this together with the batteries in a cabinet. Only the battery monitor, inverter and the regulator will be mounted on the cabinet surface. My problem is when they run a small load on the inverter for long periods, that might drain the battery beyond the 50% mark.

I'm going to buy a Battery monitor ( Victron BWV 602S). And if i have some extra cash will buy the Victron Global remote to monitor the system remotely.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Does the Inverter cut-off point of 10.5v safe?

    Probably 11.0 volts would be a better setpoint for turning off the loads--but as you say, the voltage varies with loads and temperature.

    Both a couple models of the Xantrex and Victron battery monitors have a programmable output that you could connect to an alarm or inverter inhibit/relay of some sort. You could program the alarm to turn on at 50% and turn off at 80%--or whatever setpoints you choose.

    I have not used either one--but I believe that is how they work. The Victron instructions I read were a bit less clear (as I remember).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Does the Inverter cut-off point of 10.5v safe?

    You are correct to assume that allowing your "12 Volt" bank to drop to 10.5 Volts is hard on the batteries. And you are right that sometimes loads will draw so much current that the Voltage will "appear" to be low at the inverter causing it to shut down.

    The latter problem is usually cause by one or two things: 1). insufficiently sized DC wiring which "chokes" Voltage; 2). loads that are too heavy for a 12 Volt system. Normally you wouldn't want more than 1 kW on a 12 Volt system. Sometimes start-up surges will exceed this, causing a sudden shut-down of the inverter. Sometimes it's the cumulative loads that do it.

    To protect against the batteries getting too low without a programmable inverter you have to use something like one of these:
    http://www.solar-electric.com/volconswit.html
    http://www.solar-electric.com/moredr.html

    Depending on your particular set-up, they can be programmed to operate a relay which would turn off AC loads, turn off the inverter, or shut down the DC supply to the inverter. But it will require a hefty relay and some advanced wiring.
  • JakachiraJakachira Solar Expert Posts: 47
    Re: Does the Inverter cut-off point of 10.5v safe?

    Thanks a lot for the information. I have done a lot of research about low voltage diconnection of my inverter. Since I do not like it to disconnect at 10.5v but 11.0v I have found something which may be easier to connect.

    Motormate battery protector 12V 60A

    My inverter is a 300watt one and the maximum load will be 25amps. I have no idea if Surge currents will permit that but the maximum it can hold its 60amps. I would like to believe my inverter can stand up to 700 or 800Watts during surge currents which amount to 66amps just above the mark.

    I will connect this protector between the inverter and the battery monitor and see what happens. LOL
  • JakachiraJakachira Solar Expert Posts: 47
    Re: Does the Inverter cut-off point of 10.5v safe?

    @BB : I'm having a problem to decide a recommended cut-off voltage. I have decided to buy a Victron Battery Protect 40i -40amps continuous (120a maximum surge) because it consists of about 10 programmable settings

    (disconnect voltage: re-connect voltage)
    1) 10.5v: 12v
    2) 10v : 11.5v
    3) 9.5v : 11.5v
    4) 11.25v : 13.25v
    5) 11.5v : 13.8v
    6) 10.5v : 12.8v
    7) 11.5v :12.8v
    8) 11.8v : 12.8v
    9) 12v : 13v
    10) 10v : 13.2v

    What i would like to do is to have a 50% discharge and anything lower the BP will disconnect and only re-connect when the battery soc reachs 80%. The battery capacity is 200ah. Which setting do you think will correspond to this? The item is mearnt to control my 300w inverter.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Does the Inverter cut-off point of 10.5v safe?

    None of those selections actually correspond to your criteria.
    There are a few factors at work here. Battery Voltage isn't exactly related to state of charge, especially under load. Your cut-off Voltage will be under load, so it will to be a bit lower than what the resting Voltage of the battery would be at the desired SOC. How much difference depends on the amount of load.
    The other thing is that whoever picked those Voltages clearly did not want the loads coming back on until the battery was recharged enough to handle them. This means the Voltage without load has to go slightly higher than what it would be with load.

    It's a balancing act. Without a fully programmable selection (found only is expensive charge controllers) I'd pick 11.8 : 12.8

    If you find you're losing power too quickly or it isn't coming back on when you want you can change it.
  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Does the Inverter cut-off point of 10.5v safe?

    I actually like #4 of 11.25/13.25 volts the best of all those options...

    If you are serious about 80% charge (running a genset for backup charging), if the unit was programmable, I would choose ~11.x/14.0 volts (just below your "bulk/absorb" battery charging voltage setting of the solar/AC genset charger). Basically, you know the battery has substantially recharged (in theory around 80-90% recharged when absorb voltage has been reached).

    Also, if using a backup AC genset for recharging, you could install a semi-automatic AC Transfer Switch...

    Iota ITS-30R Automatic AC Transfer Switch 30 Amp

    Basically, the AC transfer switch falls over to the generator AC power when the genset is running. Allowing them AC power while the battery bank is charging--At least giving them AC power for their needs while the battery bank is being recharged. Of course, the genset needs to be sized to supply both the AC charger and their AC loads at the same time.

    Because generator fuel is expensive, picking the "right" generator/AC Charger for the battery bank can be very helpful at reducing fuel usage...

    This thread on Stevek's research on choosing the "best" generator/AC charger for his setup goes into the details of his search.

    Question about battery charger selection with EU2000 generator

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JakachiraJakachira Solar Expert Posts: 47
    Re: Does the Inverter cut-off point of 10.5v safe?

    @Cariboocoot: Thanks for the reply. As you said i will have to run tests to see how it performs. All I want is to restrict family members from misusing the battery whilst I'm away.

    @BB: Thanks for the reply i think i will go with 11.25-13.25 setting because this will force the guys to recharge the battery once they hit the low level. I doubt i will ever use a generator. What i'm going to do now is to put up a lockable cabinet. I will put the battery in there, the Battery protector (BP) will hide between the Inverter and the battery. The inverter will be put outside of course. So basically if they run down the battery to 50% which will be ~100ah of 200ah battery, the BP will disconnect the inverter and leaves the regulator still connected and with 3 x 12v 1.5watts lamps.The lambs are connected to the load terminal of the regulator. This allows them to have lights and restricts them on using the inverter if the battery is low. So they will have to wait until the battery is 80-90% full to use the big load. The wait won't be long, I guess, because I have put more Solar Panels now with maximum current output of ~26.8amps to a 200ah deep cycle battery. I will put a battery monitor as well. Their maximum load is 120watts AC.

    Thanks for the help. i think i'm safe for now..
  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Does the Inverter cut-off point of 10.5v safe?

    You might also try 5) 11.5v : 13.8v ... That would give you a better chance of getting more charge into the batteries. Just watch that the 11.5 volts does not "shut down early" or starting surge causing issues.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.