External low voltage disconnect> anyone use one ?

sunbunny
sunbunny Solar Expert Posts: 59 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
Hello all.
I'm reading a lot and collecting components for an off grid system.
Someone gave me 10 slightly used AGM batteries;100 amp and I've bought 8 Renogy 250 watt panels.
The array will be 48 volts, the batteries 24 volts. Next purchase: Flexmax80.

Now, I'm studying inverters. What I don't like about any of them is the built in low voltage disconnect is too low. I realize I should be monitoring everything closely but an external low voltage disconnect seems like cheap insurance for my batteries.
Any opinions ?
Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: External low voltage disconnect> anyone use one ?

    Welcome to the forum.

    You are correct that many an inverter's LVD is set too low. Most inexpensive 12 Volt inverters will go on down to 10.5 Volts, for example.

    The best solution is to buy a better inverter that has a programmable LVD. You are going for a 24 Volt system, which opens up the possibilities of using perhaps an Outback 3524. Setting the LVD to nominal system Voltage pretty much precludes drawing batteries too low.

    Adding such a safety afterwards is not easy. Yes, you can get programmable Voltage controlled relay drivers: http://www.solar-electric.com/moredr.html The thing is, for controlling an inverter you need a relay capable of handling substantial current. And of course the extra circuitry uses extra power.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #3
    Re: External low voltage disconnect> anyone use one ?
    sunbunny wrote: »
    Hello all.
    I'm reading a lot and collecting components for an off grid system.
    Someone gave me 10 slightly used AGM batteries;100 amp and I've bought 8 Renogy 250 watt panels.
    The array will be 48 volts, the batteries 24 volts. Next purchase: Flexmax80.

    Now, I'm studying inverters. What I don't like about any of them is the built in low voltage disconnect is too low. I realize I should be monitoring everything closely but an external low voltage disconnect seems like cheap insurance for my batteries.
    Any opinions ?
    Thanks
    Don't know what Inverters that your looking at , but all the big 3 and many others are adjustable. You may be confusing the default settings with the high and low perimeters. The only drawback is you have to have the remote to re-program them, couldn't imagine buying a Inverter without one.
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  • sunbunny
    sunbunny Solar Expert Posts: 59 ✭✭✭✭
    #4
    Re: External low voltage disconnect> anyone use one ?

    Thanks for the welcome and the link. I hadn't found many programable disconnects searching for them... didn't realize they had another name.

    I'm hoping to buy an inverter that is just an inverter. I dislike 'combination' things because when one part dies, you still have to replace the whole ( expensive) thing. The combination unit would simplify wiring so I'll study some more.

    Blackcherry: I just read the Samlex manual linked to in another thread and that and the others around $700-$1000 haven't mentioned a remote. Is an inverter really going to cost more than the panels just to be able to control the LVD ? !
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
    Re: External low voltage disconnect> anyone use one ?
    sunbunny wrote: »
    Thanks for the welcome and the link. I hadn't found many programable disconnects searching for them... didn't realize they had another name.

    I'm hoping to buy an inverter that is just an inverter. I dislike 'combination' things because when one part dies, you still have to replace the whole ( expensive) thing. The combination unit would simplify wiring so I'll study some more.

    Blackcherry: I just read the Samlex manual linked to in another thread and that and the others around $700-$1000 haven't mentioned a remote. Is an inverter really going to cost more than the panels just to be able to control the LVD ? !
    Samlex probably wouldn't be one that would have a programmable remote, maybe a on & off switch. Xantrex, Outback, Magnum, SMA and some others would. A Voltage Controlled Switch with a relay as Coot said would do it, i'll take good sized relay if your going to cut the DC to it. The difference in a Samlex and other low end Inverters is that the are all on one circuit boards. Most all the Inverter / Chargers are modular with 3 boards controlling the different functions, one board goes out, you change it, not the whole Inverter.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    Re: External low voltage disconnect> anyone use one ?
    sunbunny wrote: »
    I'm hoping to buy an inverter that is just an inverter. I dislike 'combination' things because when one part dies, you still have to replace the whole ( expensive) thing. The combination unit would simplify wiring so I'll study some more.

    I tend to agree with your sentiment about 'combination' things, but I don't think that applies to inverter/chargers. The inverter/chargers use bidirectional circuitry... the same circuit that inverts also charges. If you do decide to buy just a pure inverter, take a look at the Exeltech line.

    You are correct that the combo unit would simplify wiring. I suggest that you also consider the Midnite ePanel... They sell a box with all breakers, busses, lightning arresters, bypass switch, shunt, etc. You can also buy them with inverter and charge controller all pre-wired... just screw it to the wall, hook up the battery, the solar input, the ground rod, the generator, and connect the output to your electrical distribution box.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • sunbunny
    sunbunny Solar Expert Posts: 59 ✭✭✭✭
    #7
    Re: External low voltage disconnect> anyone use one ?

    Thanks VTmaps. Yes, Exeltech is one of my top picks because it's made in America among other reasons.
    I'll look at the ePanel.

    I'm trying to start small and when I sell my house (ie have $) upgrade. I've lived on a boat for several years so I have a good idea how to manage loads or do without.
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  • sunbunny
    sunbunny Solar Expert Posts: 59 ✭✭✭✭
    #8
    Re: External low voltage disconnect> anyone use one ?

    The ePanels are brand specific and Exeltech is not one of the brands.

    I like one of the Outback inverter/chargers but it's just not in my budget right now. Guess I'll get a small (250-600 watt TSW) inverter for now and refigure it when I can afford better.
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