Undervoltage Controller needed

Hi,

I have a Norcold Refrigerator that draws about 5 amps with about a 25% duty cycle - powered off several solar cells and a 200 Ah battery (12V), charged by 195 watts of solar cells and a Blue Sky 2000E solar controller.

We had several cloudy days and the bank dropped below the start voltage of the refrigerator. The refrigerator kept running without cooling and drained the battery, eventually dropping the bank voltage to 0.

When the sun came out, the Blue Sky controller didn't restart charging because there was no battery voltage. Even though there was lots of solar power, the 2000E needs battery power to charge.

I'm looking for a 12V spst relay that will drop out (open) at about 11.85 volts and reclose at about 13 volts.

I'm also looking for help modifying the 2000E so it can draw its power from either the battery or the solar bank.

Please recommend a source of a low voltage disconnect relay that will protect my system.

Thank you. /Stu

Comments

  • mike95490mike95490 Solar Expert Posts: 9,393 ✭✭✭✭✭
    Re: Undervoltage Controller needed

    This relay may be something that you need to make from parts. I don't know if you can buy one.

    However, some charge controllers, have a "Load Control" output, that is intended to function as you describe. They have a "Low Voltage Disconnect" built in.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: Undervoltage Controller needed

    The MorningStar Sunsaver Mppt has what you want built in. It has a load output ( seperate from the battery output ) that is Low Voltage Disconnect capable

    You could also get one of the MorningStar relay units or pwm controllers with the LVD, but its not much more to just have the last in Mppt technology
  • SolarJohnSolarJohn Solar Expert Posts: 202 ✭✭✭✭✭
    Re: Undervoltage Controller needed

    I use the Morningstar Relay Driver for my disconnect and reconnect automation. You can program it for any upper and lower threshold voltage you want. You can also add a delay so that a momentary surge (or sag due to the compressor kicking in) doesn't cause the relay to trigger prematurely. I wrote more about my setup on my blog:

    http://solarjohn.blogspot.com

    Check my February 25th post.

    You can also check the NAWS store for a Voltage Controlled Relay. This would be a somewhat less expensive solution.

    John
  • System2System2 Posts: 6,290 admin
    Re: Undervoltage Controller needed

    Thank you - I looked around at prices and ordered a ELK-912 for about $15 from SafeMart. I'll add a resister in series with the coil to adjust the cut-out voltage - and at 0.035 amps draw, I can afford the extra load.

    Thanks for the many pieces of advice. /Stu
  • SolarJohnSolarJohn Solar Expert Posts: 202 ✭✭✭✭✭
    Re: Undervoltage Controller needed
    captstu wrote: »
    Thank you - I looked around at prices and ordered a ELK-912 for about $15 from SafeMart. I'll add a resister in series with the coil to adjust the cut-out voltage - and at 0.035 amps draw, I can afford the extra load.

    Thanks for the many pieces of advice. /Stu

    I had to look up the ELK-912 to understand what you're planning to do. I'm not sure you're going to be happy with the results. As I pointed out; it would be best to have individually adjustable upper and lower setpoints, and a way to compensate for the momentary voltage sag you'll get when a compressor kicks on.

    John
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