How to build a LVD to interrupt inverter output?

Rybren
Rybren Solar Expert Posts: 351 ✭✭
in Solar Beginners Corner #1
I have a Samlex PST-1500-24 inverter. The Low Voltage Disconnect is factory set at 20V and is not adjustable.

Samlex sells an adjustable LVD add-on for this inverter for a couple of hundred dollars. Being the cheap guy that I am, I would like to build my own LVD that would be triggered by the Classic through the Aux port.

In my simple mind, I was thinking that it might be cheaper and easier to interrupt the AC output of the inverter rather than the DC input. Yes, the inverter would still be running, but it would only be drawing ~0.5A. The inverter has a hardwire output that runs into the epanel, so I was thinking that I could run the hot wire through a normally closed (?) relay and use the Aux from the Classic to open the relay when the bat voltage reaches a particular setpoint.

The trouble is... I have no idea whether this is feasible or even where to begin to make it work.

Your collective thoughts and advice would be greatly appreciated.

Thanks, Jerry
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: How to build a LVD to interrupt inverter output?

    It looks like there is a Toggle On/Off input on pin 1 of the RJ Jack on the back on the inverter:

    http://www.samlexamerica.com/documents/manuals/11001-RC-200-1212.pdf

    Another option may be to do some surgery on the Inverter's On/Off switch and connect your signal relay there.

    In general, you really don't want to get into installing a high current relay on the DC Power input A 100 Amp mechanical relay takes at least 6 Watts to hold on, and a DC electronic switch can have a fair amount of voltage drop.

    BlueSea makes latching relays (I guess there is a motor inside that drives the switch open/closed)... But those are not cheap either (something like $160+???).

    https://www.bluesea.com/products/category/Remote_Battery_Switches/ML-Remote_Battery_Switches


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #3
    Re: How to build a LVD to interrupt inverter output?

    Thanks Bill.

    I agree, I really don't want to be messing with the high current DC side.

    I guess that what I was thinking of was something more along the lines of the aquarium automatic water top-off controller as described in this link...

    http://www.aquahub.com/store/media/TopitOffKitDeluxeInstruxCompDec07.pdf

    The Aux output from the Classic would replace the Float switch and the Hot line out of the inverter would replace the extension cord.

    In the linked description, the AC power is off unless the water level is low, then the float switch turns it on. In my case, I'd like the power to be on except when the Classic detects a low battery voltage, then the signal from the Aux would interrupt the AC output.

    I THINK that this basic idea would work, but I'm not smart enough to figure everything out.
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #4
    Re: How to build a LVD to interrupt inverter output?

    Just a gentle nudge
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: How to build a LVD to interrupt inverter output?

    Well you're thinking right.

    AUX controls relay, relay controls AC.
    The AUX should probably be used to keep the relay ON above a certain Voltage and turn it OFF when batteries are below that Voltage so that the relay draw doesn't further drain the batteries.

    Relay coil needs to meet AUX specs for Voltage and current.
    Relay key needs to handle AC Voltage and current.
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #6
    Re: How to build a LVD to interrupt inverter output?

    Thanks Coot.

    So. in theory it should work. I just have to figure out what relay and terminal to buy, how to wire it up, and how to program the Classic. Piece of cake! :D
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