24v to 48v boost converter to power a 48v inverter

Fabian
Fabian Registered Users Posts: 131 ✭✭
in Off Grid Solar & Battery Systems #1
I am planning to buy a 24v to 48v  step up converter boost supply rated at 40ah 1920watt to power my 48v 3000watt pure sinewave inverter. 

I have a 24v 150ah battery bank and I want to connect the circuit to it which would allow a input voltage of 18-32v and produce 48v at the output which would then connect to the 48v inverter to power it.

I want to know what are the pros and cons with this step up.

Here is a link with the boost converter stating the specs:

I can't find any reviews on the converter so I am not sure if it will handle the full wattage has it stated and how it operates under heavy load. But assuming it works good there are some questions i would love to get answers for.

Using it with my battery bank rated at 24v 150ah during operation in theory I would only get a total of half of my battery bank(75ah) to use due to the fact that it is doubling the 24v input to 48v? Or what is the estimated total useable amps out of the battery bank i would be able to use?

Also would this be far more efficient comparing to if i was using a battery bank rated at 48v 75ah to power the inverter?

What is the estimated efficiency lost I would accumulated going through this process? and would it be the same even if i was powering the inverter with a 48v battery bank instead of the boost converter?

Do you think I could double 2 of these units to get a total output of 80ah and would this decrease or increase efficiency?
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited February 2017 #2
    For various reasons the proposal of using a boost converter to drive an inverter is the wrong approach to achieving your goals, a battery is better suited to satisfying the needs of an inverter, a battery can support high current demands with less effect on voltage. The 3000W inverter is also way too large for the current  battery. Building a 48v system would be the best solution, the battery would be determined by load requirements, and charging/array would be sized according to battery requiments and geographic location. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    You will lose efficiency using the boost converter compared to running the inverter directly off a 48v bank.

    Your 24v 150ah bank is likely rated at a 20hr rate. Drawing 1920/24=80a will reduce apparent capacity a lot. Available run time at that rate would be minutes not hours.

    A 75ah 48v bank has the same total power (watts) as a 150ah 24v bank. Note that amp-hours is *capacity* at a given voltage, whereas amps is a *rate* at that voltage. Your 1920 watt load is 40a at 48v or 80a at 24v or 160a at 12v. Total power is the same in all 3 cases. The current (amps) though, is much higher at 12v, which requires much bigger wire to handle.

    As mvas said, the load at 3000w is way too big for the battery for most applications.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited February 2017 #4
    Fabian said:
    I am planning to buy a 24v to 48v  step up converter boost supply rated at 40ah 1920watt to power my 48v 3000watt pure sinewave inverter. 

    I have a 24v 150ah battery bank and I want to connect the circuit to it which would allow a input voltage of 18-32v and produce 48v at the output which would then connect to the 48v inverter to power it.

    Using it with my battery bank rated at 24v 150ah during operation in theory I would only get a total of half of my battery bank(75ah) to use due to the fact that it is doubling the 24v input to 48v? Or what is the estimated total useable amps out of the battery bank i would be able to use?
    The 24v-to-48v DC step-up converter is rated at only 1,920 watts, not at 3,000 watts.
    This will now limit your 3,000 watt inverter to just 1,920 watts or 60% load MAX.
    And with just a 1,920 watt load, the battery bank must supply 80 amps, but in 1 hour it will be 50% DOD.
    You battery bank is way too small (AH's) and/or you inverter is way too large (Watts).
    I would, at minimum, build a 600AH 48 Volt battery bank to run a 3,000 watts inverter (100% load) for 5 hours.
    Fabian said:
    Also would this be far more efficient comparing to if i was using a battery bank rated at 48v 75ah to power the inverter?
    They claim (up to) 96% efficiency, which really good (if true).
    But ...
    A 48 volt 150AH battery bank at 1,920 watts load = 40 amps
    A 24 volt 150AH battery bank at 1,920 watts load = 80 amps
    The 48 volt battery bank will run more efficiently given the same 1,920 watt load on the inverter.

    What you want to do will work, but you should not exceed 400 watts for 4.5 hours maximum.
    Two good things about the 24v-to-48v inverter ...
    1) It allows you to fully charge your 24 volt battery bank without disconnecting anything.
    2) It allows you to use your existing 24 volt charger 
    Do you have any other devices that currently use 24 volts?

    I would use a 48 volt battery bank vs 24 volt battery bank ...
    a) To significantly reduce the amps at the battery bank
    b) To reduce the size of the wires
    c) To allow full use of the 3,000 watt inverter
    d) To increase the battery run-time before 50% DOD.
    But now you need to buy a 48 volt battery charger.

    Fabian said:

    Do you think I could double 2 of these units to get a total output of 80ah and would this decrease or increase efficiency?
    No, I would not "double 2 of these units".

    Fabian said:
    I can't find any reviews on the converter so I am not sure if it will handle the full wattage has it stated and how it operates under heavy load. 
    It ships from China - it may be high quality or poor quality, that is an unkown risk.
    30 day Warranty.
    Support?
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited February 2017 #5
    To elaborate a little on why my thoughts that using a step up, or boost converter, is not the best approach is based on the following theories.

    An inverter is designed to be used with a battery as it's power source, viewed on an ossiliscope the voltage would be represented as a straight flat line, the output of a converter would most likely not, having ripples or spikes. The rational behind this is that, in order to increase the voltage a switching circuit would be utilized and capacitors used to smooth the output, depending on the quality of the unit, these would either be a of small or large amplitude, but would never be as smooth as a battery.

    The inverter which too is a switching device, is designed to receive a smooth DC input, these ripples and or spikes may well generate harmonic resonance, something you can't see without elaborate equipment, these harmonics can result in premature failure due to capisitor resonance. An example of this is the failure is in switching transformers used with modified sine wave AC, although not exactly the same as the proposed application, it demonstrates the effect undesirable noise can manifest in certain components which were not designed to process them, which is why a 48v  battery would be the best solution. 

    The method you propose  may work, but the question of how long is open ended.

     Please understand these are only my thoughts and opinions based on previous experience and offered for what it's worth.


    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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