question regarding power inverter

prince_77
prince_77 Solar Expert Posts: 31 ✭
in Solar Beginners Corner #1
Hello all

i have a question regarding a power inverter .
im not sure what model of power inverter to buy or use, i found this power inverter
from china
http://www.aliexpress.com/fm-store/503261/211250904-499138768/1500w-3000w-pure-sine-wave-power-inverter-24V-DC-to-AC-100V-60Hz-solar-wind-power.html

do i connect the inverter to the battery and leave it on all the time ?

thanks
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: question regarding power inverter

    Leaving an inverter on 24x7 or not is really based on how much solar panel you currently have...

    An inverter like this may take 30-40 watts just turned on with no AC load:
    • 24 hours * 40 watts = 960 WH per day
    The amount of solar panel to power than 9 months of the year (assuming 4 hours minimum sun per day):
    • 960 WH * 1/0.52 system derating * 1/4 hours of sun per day = 462 watts of solar panel
    So--you would need ~500 watts of solar panel just to power the unloaded inverter 24x7 for roughly 9 months of the year... If you have enough panel/excess power to do that--go ahead.

    If this is a smaller system, you really should look at a MorningStar 300 watt TSW 12 volt inverter which only has ~6 watts draw when on, and much less draw in Standby and Search Modes.

    Since the inverter you listed did not provide the minimum input power requirement--The above are just guesstimates (probably worst case--it might be down to 20 watts tare loading too--just don't know).

    In any case, to have a "happy off grid system"--You need to pay attention to your battery bank and its state of charge. It is very easy to leave relatively small loads on 24x7, such as an inverter, and kill a battery bank (especially during bad weather and/or winter time).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: question regarding power inverter

    I would not trust that inverter to be what it claims to be nor to be reliable. You probably would just be throwing money away.
    Quality inverters: http://www.solar-electric.com/inverters.html
    Yes, more money. But at least they actually are what they claim to be and you don't have to deal with a foreign country on any warranty issue that might arise.

    As to leaving your inverter on all the time, it depends on your needs. You can turn them on and off if your AC use is intermittent. Some have a "standby" mode which allows them to power down to low consumption until they sense a load present and then "wake up" to full power. Depending on the size, an inverter can use up to 60 Watts on its own - and that has to be figured in to battery capacity.
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #4
    Re: question regarding power inverter

    Thank u for the answer
    according to the data provide from seller the inverter
    "No Load Current Draw < 1.4A "

    i have 2 solar panel - 190W- 40V-9A total

    4 batteries (24V system - 160ah total )

    so 1.4 A is alot no?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #5
    Re: question regarding power inverter

    1.4 amps is:
    • 24 volts * 1.4 amps = 34 watts [oops-24 volt system]
    About for a TSW/PSW inverter. You would still need ~500 watts of solar panel to keep it running 24x7 9 months of the year (using my above assumptions).

    Basically your solar panels would be supplying power for your inverter with no energy left over to do actual useful work.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: question regarding power inverter

    If it's really 1.4 Amps @ 24 VDC, it's worse than my 3500 Watt Outback.

    Your 380 Watts of panel will probably produce about 12 Amps @ 24 Volts, or a 7.5% peak charge rate for the 160 Amp hours of battery. That's good. But you need to know the fine details of those panels, specifically Vmp; it may be too low to charge a 24 Volt system unless the panels are wired in series and fed through an MPPT controller. I suspect the 40 Volt rating is Voc, which is meaningless for that question.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: question regarding power inverter

    Note, I fixed my previous post...

    And battery wise:
    • 24 hours * 1.4 volts / 160 AH battery bank = 0.21 = 21% of battery bank capacity
    You are using ~21% of your battery bank capacity to operate the inverter 24x7--Again, just about 100% of the recommended load for your sized battery bank for ALL LOADS.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #8
    Re: question regarding power inverter

    somebody offer me this kind of power inverter
    http://www.cotek.com.tw/pro34450.html

    ST model 1000W - with noload 0/75A - standby mode - 0.15A

    what do u think about that model ?

    thanks again
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #9
    Re: question regarding power inverter

    Before you buy an inverter, it is probably wise, to define the loads that you are likely to have, and their daily duration. For example, a 1200 watt inverter, powering a 50 watt load is very inefficient. Most cheap MSW inverters are notoriously inefficient.


    To do anything else is, as we say, " redy, fire, aim"!

    Icarus
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #10
    Re: question regarding power inverter
    Cariboocoot wrote: »
    I would not trust that inverter to be what it claims to be nor to be reliable. You probably would just be throwing money away.
    Quality inverters: http://www.solar-electric.com/inverters.html
    Yes, more money. But at least they actually are what they claim to be and you don't have to deal with a foreign country on any warranty issue that might arise.

    As to leaving your inverter on all the time, it depends on your needs. You can turn them on and off if your AC use is intermittent. Some have a "standby" mode which allows them to power down to low consumption until they sense a load present and then "wake up" to full power. Depending on the size, an inverter can use up to 60 Watts on its own - and that has to be figured in to battery capacity.


    what kind of intermittent i can use, cam i find something that remotly can be triggered
    like a contactor for 24V ?

    thanks again
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #11
    Re: question regarding power inverter
    icarus wrote: »
    Before you buy an inverter, it is probably wise, to define the loads that you are likely to have, and their daily duration. For example, a 1200 watt inverter, powering a 50 watt load is very inefficient. Most cheap MSW inverters are notoriously inefficient.


    To do anything else is, as we say, " redy, fire, aim"!

    Icarus

    Im not talking about high loads, more of lights, low power 20W PL lights, some LED garden light and a laptop, and most of the time it for emergency use when we have power issue because of bad weather.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #12
    Re: question regarding power inverter

    Like I said, define the loads, then choose the inverter. Personally, I would suggest the Suresine 300 for a light load application.

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #13
    Re: question regarding power inverter

    But that would require rewiring your battery bank to 12 VDC and probably purchasing a smaller MPPT charge controller if they are >>Vmp~17.5 volts each.

    Is the change over from 24 volts possible?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #14
    Re: question regarding power inverter
    BB. wrote: »
    But that would require rewiring your battery bank to 12 VDC and probably purchasing a smaller MPPT charge controller if they are >>Vmp~17.5 volts each.

    Is the change over from 24 volts possible?

    -Bill

    No, i cant change it and the controller is PWM and not MPPT
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #15
    Re: question regarding power inverter

    Yea, that is the problem. There are very few smaller inverters (under several kW) that have search function and/or remote on/off.

    That is one of the reasons the MorningStar 300 watt 12 volt TSW is recommended so many times here...

    Otherwise, the Exeltech 600 watt TSW 24 volt draws around 8 watts input power with no load. Also, it appears to have a remote on/off switch function too (double check, also higher output models may not have remote on/off).

    If it is a cost issue--It may be cheaper to rewire to 12 volts and get a $325 Rogue MPPT 30 amo charge controller or the $220 Morningstar SunSaver 15 Amp MPPT Solar Charge Controller + the MorningStar 300 watt inverter.

    The Rogue will allow for future solar panel expansion (the 15 amp controller pretty much is cost effective to ~265 watts maximum @ 12 volts) and both charge controllers support 12 or 24 volt battery banks.

    If you can live with the remote On/Off (possibly timer controlled) on the Exeltech--And you need 24 VDC direct power for other loads--perhaps that will be enough.

    Off grid solar power is a game of conservation and finding the right parts for the job (if they even exist:roll:).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #16
    Re: question regarding power inverter

    thank u for the answer

    when u say remote, u mean something like :
    http://www.carymart.com/index.php?main_page=product_info&cPath=243_166&products_id=160
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #17
    Re: question regarding power inverter

    Sorry, missed the 24 vdc info.

    T
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #18
    Re: question regarding power inverter

    Remote meaning you can connect a simple relay (or possibly a transistor) across the two terminals. Close and Open the switch will turn the supply on and off using low voltage/low current control voltage. You can certainly use a remote wireless control if that makes sense for your installation.

    Without a switch on the inverter, you need an external switch/relay that can switch 100 amps or more (for a 600+ watt 12 volt inverter).

    It can be done, just more painful (more parts, more expense, if using a relay, more power loss, etc.).

    There are large "latching" relays that won't waste power--but they are not cheap either (>$140?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • timtak
    timtak Registered Users Posts: 1
    #19
    Re: question regarding power inverter

    I don't like to start another thread regarding the same supplier because these forums are associated with a reputable retailer that provides a mine of information, unlike the supplier-conglomerate mentioned that provides almost no information, but, at the same time, recently there are so many cheap solar goods available from over there often with free shipping (to where I am in Japan at least). For example even if as stated above a full time inverter uses 500W of solar panel, that can be purchased now for only $1 per watt. 50A 24v contollers are about $100. I have at most $2500 to spend but for that one might be able to get a 2KW system (8 panels, a controller, an inverter) and then hunt for batteries. I guess this might pay for itself in quite a short time.

    Perhaps someone knows of a forum where I might ask for a system purchase recommendation (from over there) that will not adversely affect a US business.

    Timothy Takemoto
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