Running a 12VDC inverter from a 3V source using DC-DC booster.

EdsimonEdsimon Registered Users Posts: 15 ✭✭
Please, what will be the effect of using a DC-DC booster to raise the voltage of a single 3.2V/180Ah cell to 12V and using it to run a 12V inverter? What will be the effect In terms of ability to carry loads?
Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,650 ✭✭✭✭✭
    What are you trying to run, that's a tiny battery, I would expect trouble...

    Think wattage, the battery stores 3.2x180= 576 Watt hours, a 20 watt 120 inverter load added to an 8 watt inverter use and some loss in the DC-DC conversion and you have over a 1/20th of your batteries capacity.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    +1 on the depends on loads. Also, the type of battery (high current capacity) and whether the DC/DC conversion is fixed or proportionate output.
    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
  • EdsimonEdsimon Registered Users Posts: 15 ✭✭
    Thanks, all. I was actually investigating the possibility of using a single CALB prismatic cell (CA180) to run a 500W inverter. The DC-DC converter I have in hand is proportionate output.
    Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Others here know a lot more about that battery than I do, but my understanding is they do okay with high discharge rates. A 500w inverter could draw > 1C (~130a+surge capacity of inverter). Obviously you couldn't run long at that rate, and you would want heavy cable and proper overcurrent protection.

    I think the battery has a fairly flat voltage curve between ~10-90% SOC so proportionate may be okay. Assuming the converter and/inverter has a reasonable low battery voltage cutoff, it just might work IMHO.
    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
  • mike95490mike95490 Solar Expert Posts: 9,358 ✭✭✭✭✭
    Here's some load figures.  I'll use 10 watts so you can scale it to any wattage easily   W = V*A

    120VAC @ 10 W = 0.0833A
    12VDC @ 10W = 0.833A
    3.2VDC @ 10W = 3.125A
     And now you need to add about 25% more to it, to allow for losses in both the 3.2V to 12V up-converter, and in the 12 - 120VAC inverter
    So, for every 10W you pull out of the inverter, you are sucking about 4A from the 3.2V battery.
     What's the battery safe limit?
    The Terminal amps limit (I've melted lead posts off of golf cart batteries in an EV conversion going up hills)

    A 50W load would be 20A from the battery.   Or else I've not understood the question.




    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • EdsimonEdsimon Registered Users Posts: 15 ✭✭
    You're correct Mike, though the system is 230VAC. That's quite a huge current draw! The whole experiment is to see if small portable inverters can use a single LiFePO4 cell and completely avoid the need for balancing that results if we're to put together the multiple cells that make up 12.8VDC.
    Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    What is the load ultimately intended to be powered by the inverter?
    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
  • EdsimonEdsimon Registered Users Posts: 15 ✭✭
    Considering 120W continuous at 230VAC
    Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    So ~3hr run time? [email protected] is about .5a. Is this for lighting? Maybe the loads could be dc and take the inverter out? A 500w inverter with a 120w load may not be very efficient.
    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
  • EdsimonEdsimon Registered Users Posts: 15 ✭✭
    Ok, if we establish the safe continuous wattage the system can run for 4hrs, the inverter will be sized as close to that as is safely possible for efficiency.
    Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.
  • EdsimonEdsimon Registered Users Posts: 15 ✭✭
    What would the figures look like if we use loads @ 12VDC and eliminate the inverter?
    Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Assuming you can use an inverter sized for about peak efficiency, the inverter is never running with little or no load, and a fairly efficient PSW inverter (or purely resistive loads) I'd expect roughly 15-20% better efficiency by using 12v. Could be higher if some of the above assumptions aren't true.

    This could be offset by wire losses at 12v vs 230v if the load is distant. It might make sense if the loads are close by, but the higher current at lower voltage could mean either heavy wire or unacceptable voltage drops if remote.
    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
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Edsimon said:
    Please, what will be the effect of using a DC-DC booster to raise the voltage of a single 3.2V/180Ah cell to 12V and using it to run a 12V inverter? What will be the effect In terms of ability to carry loads?
    This is doable but in general not a good idea. 

    At 500W (max inverter output) you would be seeing about 170 amps.  That's hard for wiring to carry but it's even harder for a switchmode boost converter to work with.  Power switches have "sweet spots" where resistance and standoff voltage are optimized, but I don't know of any power devices that are optimized to work below 12V, so you are going to have to use a lot of non-ideal FETs.  For example, I did a quick search and at 200+ amps, you're going to be stuck with 24V FET's, which are going to be high gate and D/S capacitance (and thus not that efficient.)

    You can also do a switched-capacitor boost converter, but you have a similar problem with FETs (although you save the inductor at least.)

    All the above means that the boost conversion step is going to be fairly lossy - and the converter itself will be both expensive and large.  You'd probably be better off designing an inverter to work directly off the 3V battery; you would save one stage of loss.
  • EdsimonEdsimon Registered Users Posts: 15 ✭✭

      You'd probably be better off designing an inverter to work directly off the 3V battery; you would save one stage of loss.
    Thanks bill. If this is doable then it is a route to consider with the advantage also of avoiding multiple points of failure that the boost converter introduces.
    Abuja, Central Nigeria: 5.8kWp, 63kWh Storage, DC Lighting, Grundfos SQFlex. Off-grid since 2013.
Sign In or Register to comment.