Inverter/Charge Controller

RoySalisburyRoySalisbury New UserPosts: 80Solar Expert ✭✭✭
I'm looking for recommendations on an inverter and charge controller that will let me convert the power from a 24v battery bank (8 T-105 6v @ 225 ah) to AC (110/120) and allow me to both charge from and use power from a generator.

Basically I want to use the power form the bank when the generator is not working, but when the generator IS running it should charge the battery bank and also provide the AC load (3000/5000 watt). At some point I would also like to start adding in solar or wind to charge the battery bank as well.

I'm not wanting to spend a lot of $$ (say around $800) if possible.

Any ideas or suggestions?



  • BB.BB. Just some guy Posts: 23,902Super Moderators admin
    Re: Inverter/Charge Controller

    Unless you build it yourself from components (inexpensive MSW inverter, Battery Charger, and Transfer Switch)--you probably would be in the $2k-$4k range for a good quality setup (just for the major hardware inverter/charger/transfer switch).

    What are the loads you are powering? A washer/drier, TV, lights, A/C, Fridge type items or are you looking at needed clean switch overs (desktop computers, etc.).

    The simple side is just to get a simple AC relay transfer switch or two and then connect your needed hardware (mains, genset, charger, inverter). Use one transfer switch to source power from AC Mains or Generator to charger. Use second relay to source AC loads from Mains or Generator.

    If you want sophisticated, just a large automated transfer switch / generator controller (with weekly exercising, etc.) is around $1k itself.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RoySalisburyRoySalisbury New User Posts: 80Solar Expert ✭✭✭
    Re: Inverter/Charge Controller

    Yes, it would need to be something that does a clean switchover. Most of the equipment is computer controlled hardware such as cameras and telescopes, so cutting of power too switch over is not an option.

    Mainly the idea is to have enough battery power to run everything for about 3 or 4 days at a time without needing a charge, and to have the generator available to charge the battery bank when it gets to a certain level or to power larger items such as AC units or refrigerators.

    I initially looked at just getting an inverter/battery Charger combo unit (about $600), but it just did not seem like the right thing to do. Right now I just plug my generator into the building like it was coming form the power company and that works, but I want to use the battery bank so I can leave it unattended for days/weeks at a time.

    So something simple is all that I am looking for.
  • BB.BB. Just some guy Posts: 23,902Super Moderators admin
    Re: Inverter/Charge Controller


    To be honest, cheap and reliable, low maintenance--you are looking at a propane or diesel powered genset running an APC or Tripp Lite UPS...

    And if you are looking for "Really Clean Power" I would look at the continuous conversion type UPS's. AC power to battery to inverter--with no AC switch over--less power efficient but less chance of "glitching"--a standard failover type UPS--even to "small 1-2kW computer room types" I found would glitch/reboot an industrial PC when hit with a "real power failure"--as opposed to a "lab test" failure. I think that a real power failure is so ugly they can confuse the UPS switchover to be delayed.

    You can do a "continuous conversion" type UPS out of solar RE equipment... Just a backup genset with AC mains transfer switch always charging/floating a battery bank, and a good quality inverter (TSW preferred, MSW can be OK).

    The genset itself can be a used RV unit running your fuel of choice setup with autostart (either based on AC mains fail or battery <50% capacity, etc.)...

    In the end, really need to know your loads to make a suggestion. A 1,000 lbs of batteries may hold the equivalent of a few gallons of gasoline.

    And sizing the battery bank and genset to the loads (peak and average) can really help prevent you from overspending.

    A genset should run around 50% rated capacity or a bit more (especially if diesel) for efficient fuel flow (below 50% rated electrical capacity, fuel flow usually remains at 50% in gallons per hour).

    You could probably set up a pretty nice system with a used genset (RV type if smaller genset needed), a good battery charger like an Iota running from AC mains with fail-over to generator, a used fork lift battery bank, and a good quality inverter.

    Depending on your exact loads--such a system would be around (80% AC to DC conversion; 85% DC to AC inverter =) 68% end to end conversion efficiency (picking numbers from a hat)... Or, increasing your utility bill by 1/0.68=147%

    Your thoughts Roy?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RoySalisburyRoySalisbury New User Posts: 80Solar Expert ✭✭✭
    Re: Inverter/Charge Controller


    Ok.. Here is what I have. Some equipment needs to run 24/7 .. That would include a computer, satellite internet and weather station. About 150 watts to run that stuff. Then there are times when the main equipment is used that I could be pulling another 250 watts for another computer, lights, telescopes, camera equipment, ect.. I had already planned on putting smaller UPS backups on the major equipment (mainly to get cleaner power, but also for minor brown-outs).

    So, basically I have about 400 watts that could be pulled during normal use. Then there are the instances that I may need to run say an AC unit (I have a low power RV unit that I can use .. but it still pulls about 2500 watt). That is what the generator would be used for.

    Originally I was looking at getting a 1000 watt complete solar power system (off grid). That would supply me with all the power I currently need, plus have a bit of room for expansion. The system I looked at was about $4000. That is about what I wanted to spend total, but then started looking at just getting the batteries and a generator (because I think I will need a generator anyway). And on top of that, I have no clue on how to install a solar power system, but the batteries and a generator I could handle.

    Perhaps I just need to go back to the total solar power solution and then have a separate circuit just for the generator and the AC unit (which I can add later). But I would still like to have a backup way to charge the batteries off the generator.

  • BB.BB. Just some guy Posts: 23,902Super Moderators admin
    Re: Inverter/Charge Controller


    I am still not quite sure I understand what your "ideal" requirement is... 400 watts of 24x7 electronics? If so, that is:
    • 400 watts * 24 hours * 30 days = 288,000 WH or 288 kWhrs per month
    Using the PV Watts program, for Las Vegas NV, assuming you wanted to use solar panels to power your loads for at least 9 months of the year--Assume 1kW of panels (just an even number), 0.52 derating (including battery and inverter losses), fixed panels, we get:
    "Station Identification"
    "Lat (deg N):", 36.08
    "Long (deg W):", 115.17
    "Elev (m): ", 664
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 36.1"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.7 cents/kWh"

    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 5.19, 79, 7.66
    2, 5.98, 80, 7.76
    3, 6.57, 98, 9.51
    4, 7.32, 103, 9.99
    5, 7.42, 105, 10.19
    6, 7.35, 96, 9.31
    7, 7.37, 98, 9.51
    8, 7.29, 97, 9.41
    9, 7.31, 96, 9.31
    10, 6.56, 94, 9.12
    11, 5.75, 83, 8.05
    12, 5.05, 77, 7.47
    "Year", 6.60, 1106, 107.28

    That gives you November at 83 kWhrs per 1kW of solar panels (120/240 VAC 60 Hz equivalent power)... For your 400 watt need--288 kWhrs per month (that is a fair amount power):
    • 288kWhrs per month/83kWHrs per month per 1kW of panels = 3.5 kWatts of solar panel
    Even at $2.50 per watt or so for solar panels (prices are really low right now), that is around $9,000 just for the solar panels.

    Batteries, assume 3 days of no-sun and 50% maximum discharge to support your 400 watt load:
    • 400 watts * 24 hours * 1/0.85 invtr eff * 3 days * 1/0.50 * 1/24 volt bank = 2,824 AH battery bank at 24 volts
    Get some Trojan L16RE-2V 1110 AH 2-Volt Deep Cycle Battery at ~$300 each (3 strings * 12 batteries per string for a 3,330AH bank) = $10,800 worth of batteries.

    We are pretty near $20,000 just for solar panels and battery bank (enough solar panels to run your loads 24x7 9 months of the year and a battery bank for 3 days of no sun/power with 50% maximum discharge for long life).

    I can go farther--But I am pretty sure that this is not where you really want to go...

    A battery bank large enough to handle 5 hours of 400 watts (50% discharge):
    • 400 watts * 5 hours * 1/0.50 * 1/0.85 inverter eff * 1/24 volts = 196 AH bank @ 24 volts
    Four x Trojan T105-RE 6 Volt, 225 AH Deep Cycle Battery at $560 for the set...

    Run a Iota Iota DLS-27-25: 24 volt 25 amp regulated battery charger for $250 (will run 600 watts of load). You could go one size larger if your genset supports a larger converter. You might want the IQ-4 multi-stage charge option ($30 extra).

    Although, to allow for >400 watt loads, you probably should consider the Iota DLS-27-40: 24 volt 40 amp regulated battery charger for $450 (all depends on how firm the 400 watt load number is -- and you have to assume some inverter losses too).

    Put a simple AC transfer switch Iota ITS-30R Automatic AC Transfer Switch 30 Amp for $60 (optional 20-30 second delay to allow generator warm-up) on the front of the IOTA. Runs from AC mains, Genset will power battery charger/converter while AC mains down.

    You wire up your genset to power up when AC mains fail (you could setup for up to a 5 hour delay--but then I would suggest a larger battery charger to power loads and charge bank at the same time--more load for genset too).

    Last--the Inverter--400 watts is not very large--I would humbly suggest that you only get a TSW (true sine wave) type inverter for your installation. A MSW (modified sine wave) may work for most of your hardware--but some items (like wall warts, non-Power Factor Corrected laptop computer power supplies, cell phone chargers, etc.) really don't like MSW wave forms (may overheat/die early deaths).

    Exeltech XP1100 24-volt 1100 watt sine wave inverter for $612 or so... (there is a 600 watt model for a $100 less).

    There are some inverter/charger combinations--but they will glitch on switch over--I am guessing that glitching your instruments is not worth the savings on power (120 vac to 24 vdc to 120 vac double conversion losses) to have an absolutely stable 120 VAC output no matter what the input power does...

    You can size the battery bank to supply as much or as little power needed (just time to crank up the genset to 5-10 hours to allow somebody to drive to the site when the get a page the power went out).

    Also, you might want to look at a Sanyo Mini-Spilt AC system... If you can run it on low power (3,000 BTU) it only takes around 300 watts (has heat pump option for heating too--if needed).

    Sanyo mini split AC (inverter/variable speed)
    smallest, most efficient A/C ?

    I will stop here for now...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RoySalisburyRoySalisbury New User Posts: 80Solar Expert ✭✭✭
    Re: Inverter/Charge Controller

    OK then.. I guess I will once again scrap the idea of creating a battery bank with a generator. There is no way I will be paying 2-4K for a charge controller and inverter, and no way at all that I will be getting 20k worth of solar panels.

    Thanks for all the info..

  • BB.BB. Just some guy Posts: 23,902Super Moderators admin
    Re: Inverter/Charge Controller


    I just linked to new components as examples of what to look for... You can use others (MSW vs TSW), used forklift battery and charger, etc... Nothing magic about the components I linked to.

    My intent was to show how I got the min/recommended/maximum range of values for the various components and allow you to modify the calculation / components to fit your needs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: Inverter/Charge Controller

    i am not sure if that $2-$4k for the inverter and controller is including any batteries or not. a large battery bank can also go into the thousands. no way you're doing this at around $800.
  • RoySalisburyRoySalisbury New User Posts: 80Solar Expert ✭✭✭
    Re: Inverter/Charge Controller

    I completely understand that the batter bank will cost a lot. I had already figured that into the other price (battery and generator costs). I was just looking for something to tie the battery and generator together for around $800.

  • AntronXAntronX New User Posts: 462Solar Expert ✭✭✭✭✭
    Re: Inverter/Charge Controller
    Ok.. Here is what I have. Some equipment needs to run 24/7 .. That would include a computer, satellite internet and weather station. About 150 watts to run that stuff.

    What computers are those? Laptops or desktops? Don't give up on solar option yet. If you manage to reduce your continuous loads and eliminate the need for DC to AC conversion, I think we could pull something off.

    Computers can be easily powered directly from DC battery bank using DC-DC converter power supplies. If your cameras and weather station use AC-DC adapters, then that equipment can be powered using DC-DC converter as well.

    If you eliminate DC-AC inverter, then you save anywhere between 40 - 15% of your system losses, which means battery and solar panels can be that much smaller. The range is so large because DC-AC inverter conversion efficiency depends on load power to maximum rated power ratio. For example, if you have 150W of continuous load powered by 2000W rated inverter, then your DC to AC conversion efficiency will be very poor, around 70%. That means 30% of your battery and solar and generator will be wasted to conversion losses. If you use smaller 600W inverter (like Exeltech inverter i have) then your efficiency will be higher, around 85%. But still you will lose 15% of your energy to losses. So it makes sense to try and eliminate your AC power requirement.

    Added benefit of going DC is that by being continuously connected to your battery bank, there is no need for AC transfer switch, so no worrying about transfer delay time. That's like being connected to free UPS system.

    So, if you are interested, go ahead and list every piece of gear you need to run and what DC voltage and current each one uses. You can find that info either written on the power adapters or on your device itself. Also, what is the purpose of your computers? What are they used for? There may be a chance to switch them over for a lot less powerful custom computers or laptops. If your loads can be smartly engineered, then you may get away with only 4 solar panels or so, well within your budget and waaay under the worst case scenario cost of $20K you got.
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