low voltage disconnect

czyhorse
czyhorse Solar Expert Posts: 42 ✭✭
I was wondering if anyone knows of any devices that would be able to shut an off-grid PV system down when the battery voltage dropped below a certain level. I see this feature in a lot of charge controllers, but was wondering if any inverters have this function as well.

I would like to find a user programmable LVD to set at a certain voltage (say 30 to 50% charge of your battery bank voltage) to prevent accidental discharge.

I found a device here:
http://www.newmartelecom.com/LVD-Wall-Mount/LVD-Wall-Mount.html
could this be installed between a battery bank and an inverter to provide an automatic shut down of the inverter once the set voltage is reached by the battery bank?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: low voltage disconnect

    I like the Xantrex Battery Monitors... They have a programmable output that can be setup to turn "off" at 50% and turn "on" at 80% state of charge. It is a digital signal output--so you will may need some sort of signal level converter depending on what it is controlling.

    The voltage controlled battery monitors are just approximations (based on voltage) and generally do not include the load, temperature, and such. Mostly, they are set to "turn off" when the battery is dead (10.5 volts for 12 volt bank or 0% state of charge).

    A battery meter measures the net current flow over time (amp*hours in/out) and has a much better estimate of instantaneous state of charge for the battery bank than a pure voltage or compensated voltage would. If I where doing an unattended off-grid system--I would go with the Battery Monitor Inverter/Generator control. I would highly suggest a Battery Monitor also for vacation homes where kids and guests may be running the system while you are not there. Much easier to read XX%--and the output can be setup for a warning alarm (light/bell) to alert when power is getting low.

    A battery monitor can be programed to whatever levels you like (either to turn off an inverter or to cycle a genset, etc. There may be other brands/models of battery monitors with programmable outputs--but I do not remember seeing any...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: low voltage disconnect

    I think the Suresine 300 inverter has an adjustable LVD. http://store.solar-electric.com/mosu300wasiw.html

    I'm sure others do as well.

    Tony
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: low voltage disconnect

    unfortunately, I just bought a trimetric TM 2025A battery monitor a few weeks ago. Reading through the Xantrex LinkPro literature, I don't see a very detailed explanation on how it would function as a low voltage disconnect.

    Any ideas on how I would go about achieving my goals with a trimetric battery monitor and an Exeltech inverter on a 24V system? The inverter does shut down under low voltage conditions (21v), but that is for all practical purposes, a completely dead battery. :cry:
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: low voltage disconnect
    czyhorse wrote: »
    unfortunately, I just bought a trimetric TM 2025A battery monitor a few weeks ago. Reading through the Xantrex LinkPro literature, I don't see a very detailed explanation on how it would function as a low voltage disconnect.

    Any ideas on how I would go about achieving my goals with a trimetric battery monitor and an Exeltech inverter on a 24V system? The inverter does shut down under low voltage conditions (21v), but that is for all practical purposes, a completely dead battery. :cry:

    Whether or not it is a dead battery or not is determined to a great extent on the load.
    So the LVD is not related in the real world battery condition. I don't think you can configure the Tri-metric to trigger a LVD since it doesn't have any out put capability except data.

    Tony
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: low voltage disconnect

    Nobody seemed to comment on the NewMar LVD that I posted a link to earlier.

    It looks like it is designed for the telecom industry, but does anyone think it could work configured between a battery bank and inverter? If my system is 24V and I have a 1100W inverter, the amperage through the inverter input should be 1100/24 = 45.8A, correct?

    They make a 24-50 version of this product that operates at 24V and 50amp max.

    Any ideas?
  • GreenPowerManiac
    GreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: low voltage disconnect

    The Exeltech inverter shouldn't need an LVD since it's built in:

    http://www.infinigi.com/exeltech-xp110024-sinewave-inverter-1100w-24v-p-269.html?ref=100

    Whew ! Pricey. I paid $900 for 4500 watt PSW version 12v D/C to A/C 110-120v. Those 24v jobs must work more efficiently....

    About 3/4 the way down states:

    "Under Voltage*:Shutoff at minimum input voltage, per input conditions"

    My inverter shuts down at about 10.5 to 11 volts. 0% SOC, which in this case too late to save the batteries if they're in cold weather.

    That inverter should do the job, unless you're looking to shut the batteries down at a higher SOC, which would be favorable to adjust.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: low voltage disconnect

    It turns off at 10.4 volts DC (12 volt model)--pretty much a dead battery.

    The LVD is really designed to protect the loads that don't have their own low voltage shutdown circuitry--which pretty much all inverters have.

    If you have "dumb" loads (radios, TV, motors, lighting, etc.)--it appears to be an OK device. 30 amp maximum load (most of the other small solar charge controllers in the MorningStar line--the LVD is only 8 amps maximum.

    But, it will not protect your batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset