New member questions.

TomHTomH Registered Users Posts: 6 ✭✭
I am looking to set up a small off grid system.  I have a few questions I'm hoping someone can help me with.  They are probably all answered somewhere in the forum so forgive my redundancy. 

This is to be used in an emergency shelter.  I am interested in using a battery bank to power a 2000 W inverter to run mostly 120V LED lighting and occasionally a few appliances such as a Ninja Blender for instance.  No long term daily draw as with a fridge or freezer.  I am going to maintain the batteries with a generator powered by a wood gas generator which I'll run for a short while daily.  The wood gas and generator set up are already in place.  Unless there is a good reason not to, I'd prefer to run everything on 120v through the inverter rather than 12v. lights and incidentals.   From what little research I've been able to do  a 600 amp hr battery bank is  the minimum for a 2000W inverter.  Is that about right?  Is there a big advantage to going 24V in a minimal system like this?
To charge the batteries from a generator will a good battery charger work OK or do I need some sort of charge controller.  The charging can be monitored.
I am retired on the usual fixed income.  Money is a concern.   I am considering a Energizer 2000W inverter based on reviews I've read however the Jupiter inverter Harbor freight sells  seems equivalent and is a hundred cheaper.  I'd also go at least $50 over the cost of the Energizer is there was a significant improvement in quality.

I saw recommended in one of the forums here that the cheapest batteries are recommended  due to the probability that you will screw them up learning to run the system.   The cheapest I can find that have equivalent specs to the Trojan T-105 is the Duracell sold by Batteries Plus.  Next in line is the Exide sold by Napa Auto parts  model 8146.  Any opinions on this or is it better to just go with the Trojan's.  Thanks for any help you can provide.


  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    Running 12vdc lighting directly would be more efficient, but keeping everything 120vac works too.

    Using a 2000w inverter may have a couple of issues.  The first is tare losses.  A big inverter can use significant amounts of power just being on or with light loads relative to capacity.  The second is that cheap inverters are almost always modified sine wave (MSW), which can be a problem with some loads.  In some cases, the load will run hot, some not at all, and others will run okay.  Purely resistive loads (like heaters and incandescent light bulbs) should run okay.  Others (like LED lights, or anything with a motor) may not.  

    Something like a Morningstar 300w pure sine wave ($252 from our hosts) would likely work well for lighting and other small loads.  For short, occasional use, a larger MSW inverter may work.  I use one on my boat, and it runs a small microwave, for example, at about 60% of the output power as it would using grid power.  As the rest of the power ends up as heat, I wouldn't want to run it on inverter power for long, but it seems to be okay for the couple of minutes the microwave is on.  Some wall warts get notably warmer when powered by the MSW inverter.  If possible, it would be best to time large loads to run while the generator is charging the batteries.

    There is probably no advantage to 24v.  You would go up in voltage if you had larger loads to keep wire size down.

    Golf cart (GC2) 6v deep cycle batteries would likely be a good choice.  The size of the bank is determined more by loads than the size of the inverter.  You need to estimate or measure the wattage of each load, and the length of time the load is expected to run daily.  If you have any pump-type loads with high starting current requirements, that needs to be considered also.  Multiplying the wattage of loads times the daily time used gives you a total watt-hours required daily.  If you're going to run the generator daily, you would want a minimum bank size of twice the daily watt-hours, to keep the depth of discharge to 50% or less for reasonable battery life.  

    GC batteries tend to be a commodity type item.  Often buying what's cheapest locally is best as shipping is a big factor in price.  Walmart and Costco seem to be places to check as well.
    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
  • TomHTomH Registered Users Posts: 6 ✭✭
    Thanks for the information.   I'm finding it surprising difficult to get some of these questions answered  and the information seems to be all over the map  especially about sizing the battery bank and inverter.  I know that a pure sine wave inverter is necessary for most electronics to work correctly but I am wondering about lap top computers if they are run off their batteries.  The the power would not be coming from an outside source and the battery should charge all right off the MSW source.  Is that right?  
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    You're welcome.  This is a pretty good forum in terms of people helping, but sizing batteries starts with loads.  Everything flows from there, so it's important to get a good handle on exactly what you need to run and for how long in order to end up with a system that meets your needs without going overboard.

    You may find the brick that converts from AC to DC for charging gets warm with a MSW inverter.  I will likely charge ok, but keep an eye on the temperature of the brick.
    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
  • myocardiamyocardia Solar Expert Posts: 118 ✭✭✭
    Wait, so you're wanting to power 12V LED lights (there is no such thing as 120V LEDs), and charge your and your wife's cell phones, even though both of you are very, very likely to own 12V chargers for them, but want to buy a 2000 watt inverter to do so, instead of using the 12V battery power directly? Why such a small inverter? Couldn't you find a 10,000 or 20,000 watt inverter? I mean, you're planning on using an absolute maximum of 75-100 watts at any one time, so I fail to see how a 2,000 watt inverter will be anywhere near enough...

    Seriously, you aren't planning on using more than 100ish watts, therefore you buy a 150 watt inverter. This is how it's done in this business. You want this inverter, specifically:
    DoD= depth of discharge= amount removed from that battery   SoC= state of charge= amount remaining in that battery
    So, 0% DoD= 100% SoC, 25% DoD= 75% SoC, 50% DoD= 50% SoC, 75% DoD= 25% SoC, 100% DoD= 0% SoC
    A/C= air conditioning AC= alternating current (what comes from the outlets in your home) DC= direct current (what batteries & solar panels use)
  • mcgivormcgivor Solar Expert Posts: 3,502 ✭✭✭✭✭
    @myocardia This is the beginners corner, so no need for ridicule, you are correct with regards to using such a large inverter for small loads, the larger inverter would consume more and operate Inefficiently.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,547 ✭✭✭✭
    edited October 2017 #7
    myocardia said:
    Wait, so you're wanting to power 12V LED lights (there is no such thing as 120V LEDs

    I have a whole house full of 120 volt LED ceiling fixtures. The voltage may be converted internally but the fixture connects to conventional AC voltage

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    All the ones I've seen are 12v. Most have 120vac external connection stepped down with a transformer sized for the number of lights powered. Some specifically say they can be used directly off 12vdc for marine/rv applications, but most don't. I'd be a bit concerned that the ones that don't say may not play well with the voltage range involved between low battery cutoff and equalization.
    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
  • TomHTomH Registered Users Posts: 6 ✭✭
    I didn't give enough information about my needs.   I haven't had the time to explore this site to get an idea about what the folks here are interested in other than the obvious.  I am a prepper.  I'm fine with staying on the grid as long as possible but I see a definite end to that ability.  My knowledge of alternate energy is minimal and my experience with 12V is strictly automotive. 

    I don't expect to live in the days ahead as we do now but I will need to use certain food processing equipment on an intermittent basis which may have a 1500W start-up load and I will be continuing to running the rows of LED grow lights  I am using now.  I joined here because the people whose posts I read seemed knowledgeable and not to judgemental so any advice I can get I will appreciate.  Perhaps I am completely wrong about what I want or need a system to do.  That's why I have sought out people with some expertise.  I don't know much about off-grid electrics but I have 52 years of experience as a builder  if that is of any use to anyone here.   Yes, I'm older than dirt.
  • BB.BB. Super Moderators, Administrators Posts: 30,961 admin
    Can you tell us a bit more about the off grid system (where/when it will be used, reason--no local power, out in a shed/out building and just want some lighting, save money, etc.).?

    In general, if you have AC power to the property, it is almost always cheaper, more reliable, and less costly to trench a 120 VAC cable from the main home.

    Using 120 VAC for lighting (yes, almost all screw in bulbs these days are LEDs--And just about as efficient as 12 VDC or other LED lamps).

    Using a 12 volt battery bank and 12 VDC LEDs--If that is the only need, and the lighting is local (within a few tens of feet of the battery bank), 12 VDC can work OK. However, if your lighting (and other off grid power usage) goes for longer distances and more than a few watts (typical for LED lighting--low power)--Then 120 VAC can make more sense--Sending lots of current at 12 VDC requires heavy cables. And many devices have issues with voltage drops (long cable runs of too small of diameter copper wiring, the wide range of deep cycle battery voltage--From 10.5 volts - 16.0+ volts is pretty common--Many "12 volt" adapters for laptops/etc. do not like that wide of range).

    Define your loads and power needs first--Then we can be a bit more helpful. But, in general, Off Grid solar power is not cheap--It can run $1-$2+ per kWH, whereas utility power is $0.10 to $0.30 per kWH typically).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TomHTomH Registered Users Posts: 6 ✭✭
    Thanks Bill.    What I am trying to power is a 650 sq ft  underground  survival shelter.  The main thing is lighting  and it is currently wired in 12 ga  romex connected to my house power.  I am currently using about 200 watts of LED bulbs for lights but not all of them are in use all the time.  I live in a heavily wooded site and  PV or wind is not an option due to the trees.  I have multiple generators I used when I was in business as a builder.  One of them is hooked up to a Wood Gas producer and runs fine on wood gas fuel.   My intention was to run it each day for as long as it takes to maintain a charged battery bank  and at the same time for tools and heavy loads  and to run my well pump to top off my water storage tank.   I have a  small pump, to circulate water.  Not sure of the amps on that my not many.  I'd also like to be able to run small tools like a chain saw sharpener and bench grinder without waiting to run the generator.    The grow lights currently draw 200 watts for 8 hrs a day but I'll be at least doubling them.  As far as I can see, that would be my total load.  As far as charging electronics, we could go with a individual battery with a small PSW inverter for that if it would be better.
  • PhotowhitPhotowhit Solar Expert Posts: 5,328 ✭✭✭✭✭
    Tom the grow lights will be a huge load for you, 200 watts x 8 hours = 1600 watts and doubling that would be 3200 watts hours. 

    If your intent is to run a generator for a short time each day, You should look at batteries that will accept a high charging rate. Since this will be a generator based system, and prepper system. I think I would look into the newer lithium batteries. Touted as having a long life, and it appears they do, they can accept a very high rate of charge and can be at a lower state of charge without damage and can use most of their capacity without damage.

    Standard flooded lead acid batteries can only accept a 13-15% rate of charge. Some AGM's can accept a higher rate, not sure if that will reduce their useful life. To meet the same standards as a lithium battery bank, you might have to have4x the battery bank size.

    Thangs to think about...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • TomHTomH Registered Users Posts: 6 ✭✭
    Thank you.   very good information.  The grow lights are the main thing I want to run on this system.  Is there a formula to determine how many t-105 type batteries  at that rate of charge it would take to carry that particular load  and still provide decent battery life, using the 1600 watt hours for a base line? 
  • PhotowhitPhotowhit Solar Expert Posts: 5,328 ✭✭✭✭✭
    You generally want to stay in the top 20% of capacity, since you would be recharging after each discharge, you could push that a bit.

    But with without more info on load, will you run a fridge? I'll give a bit generous addition of 800 watt hours for personal lighting, radio, pump (this could be a large load!) I'll use 4000 watts of AC. A fridge would add about 1000 watt hours. 

    For 4000 watt hours of AC load, you would first need to figure out what the DC load would be... Inverters are roughly 85% efficient.
    So 4000 x (100/85)= 4706 watt hours of DC

    watts = amps x volts

    4706/12= 392 amps

    392 amps should be 20% of your capacity, so x5 for 100% of capacity
    392x5=1960 amps at 12 volts for a battery bank size. T105's have about 230 amps each at 6 volts. If we divide by 230

    1960/230= 8.5  --  x2 for 12 volts we get 19, call it 18, natural voltage will start at 12.7 volts and fall to around 12 volts under load over 24 hours. Several things here, your loads will be handled by the generator when the generator is running so your actual time discharging will be less, and the load on the battery bank for less time.

    As I stated above the battery bank will accept the current at 15% or less of it's capacity, So While you need to push 392 amps back into the battery bank, it will take some time. With  8 strings at 12 v x 230 amp= 1840 amp bank maximum charging capacity would be 1840x1.5= 276 amps per hour, but you will also run up against another characteristic of Flooded Lead acid batteries as they approach full charge they will accept less current. 2 hours of charging should get you close to full capacity.

    Please note Trojan uses 13% as the max charge rate, you can run the numbers using that as well. Also understand that the input voltage will be 15-20% higher than the resting battery voltage. Think of it as the generator being  cup of water/current and the voltage as being the height, you have to have the height higher than the battery to facilitate the water/current to flow to the battery. So 276 amps at 14.4 volts = about 4000 watt generator. I don't know how efficient inverter/chargers are at making DC current, but suspect you would need around a 5000 watt generator.

    I hope others will check over this, I don't use generators, just having tried to help people here.

    As I said earlier, a Lithium battery bank might be = in cost. and take the energy at a faster rate saving you generator run time if you have a larger generator. Lithium would be able to use 80% of it's capable. So you would need about a 500 amp 12 volt battery bank... 

    In general I would suggest higher system voltage for a few reasons, 8 strings of flooded batteries are hard to keep in balance. 2 strings of 8 at 48 volts would be less likely to get out of balance.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • TomHTomH Registered Users Posts: 6 ✭✭
    Thanks.  A  lot to digest.  I am currently using an 8000 watt generator with the wood gas set up.   I never paid attention before because they are running on grid but the grow lights are 12V with a power adapter.   If anyone is interested in this, these are the lights I'm currently using.  They are cheap and work fine. I may upgrade them later.  I'll spend some time on the information you provided.

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