Where do I get a low voltage disconnect for my Solar Powered Pool Pump?

st4rgut
st4rgut Registered Users Posts: 36 ✭✭
edited May 2021 in Off Grid Solar & Battery Systems #1
Hi all, I'm running a pool pump off solar, and when the voltage from the inverter dips below 115V the pool pump will shut off. It's a major problem for me because the pump will re-enter priming mode, which consumes too much power for the BMS and Inverter (~2500W Peak) too handle. This has happened on several occasions and resulted in popping circuit breaker connected to the BMS which was toasty to the touch. Luckily, the BMS wasn't toasted, though I had to reconnect the balance ledes to the BMS to output the correct battery bank voltage (~48V). However, I would like to prevent this from happening, and am trying to find some kind of low voltage AC disconnect. Even better would be a DPDT switch that automatically switches to grid power when the voltage is too low. I'm not sure if anything of this sort exists and would really appreciate any guidance on the matter. 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    edited May 2021 #2
    How far is the voltage dipping? I would expect "normal" load/motor operation down to ~102 VAC on a 120 VAC nominal USA Utility line...

    Yes, there are voltage sensitive/adjustable relays... Here are a few (you will have to look at the details--I have to do some other stuff now):

    https://www.grainger.com/category/electrical/industrial-controls-automation-and-machine-safety/relays-and-accessories/voltage-sensor-relays?attrs=Item+-+Relay|Voltage+Sensing+Relay&filters=attrs

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • st4rgut
    st4rgut Registered Users Posts: 36 ✭✭
    #3
    Thanks for the link. The voltage dipped below 115V which I think is the cutoff for the pump. It must be very sensitive to electricity. The power is carried over essentially an extension cord, so I think voltage drop factors in here too.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #4
    You can find (nice/not cheap) transformers to boost the line voltage a bit:

    https://www.mouser.com/datasheet/2/643/ds-st-m4l-series-1633501.pdf

    This does cause some additional transformer losses.

    To experiment (figure out is the power supply is having problems), a cheap Variac type transformers can go upwards of 130 VAC with a 110 VAC or so input:

    https://www.amazon.com/Mophorn-Transformer-Voltage-Automatic-Regulator/dp/B07ZH95TGN

    Anyway--Some options (besides checking the voltage drop on the AC line and looking for bad/overheated/corroded connections in your wiring).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    st4rgut said:
    Thanks for the link. The voltage dipped below 115V which I think is the cutoff for the pump. It must be very sensitive to electricity. The power is carried over essentially an extension cord, so I think voltage drop factors in here too.
    Beef up the ext cord.   Horrible Fright has some good prices on serviceable cords that don't need to be extra flexible
    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 ||
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