Battery backup power

roksroks Solar Expert Posts: 28
Recently I was on holiday with my family in Bangladesh, very hot muggy, temperature was 27-32 c. Utility power is herendus, power outages several times a day, outages last from 30min to several hours (day or night). The house is of concrete roof, the upper floor is baking oven, ground floor is just bareable.

I bought a 1000VA, 12V modified sine wave inverter (they call it IPS) and a 200AH battery that gave me about 2-3 hours backup power for 30,000Taka (£230 sterling). The electrician run a single live wire from the IPS to all the lights and fans that will have back-up power and used the existing neutral wire. In the UK, I'm used to seeing separate Live, Neutral, and Earh cables but over there they seem to have the Earth and Neutral to terminal on the distribution board.

Main loads:
6x Ceiling Fans @ 78watts (no more that 4 used simultaniously)
6x Energy Bulbs @ 11watts
4x Energy Bulbs @ 26watts

I found that on prolonged outages, the IPS cannot supply that long, even with 2 fans and 4 or 5 lights. The battery does not have enough time to charge between the outages.

The retailer told me that maximum I could have was 300Ah battery connected to the IPS, but could not tell me what the maximum charge current it can provide. I was thinking of adding another 200AH battery and a separate charger but I was told it cant be done……that cant be right, can it?

I am thinking of selling this IPS thing and get a better system. Ideally I would like to have a 24v pure sine wave inverter, as with the current one, the fans are nosier, most likely due to the fact that its modified sine wave and also 24v would have less line loss.

I was thinking of adding couple of solar panels to help charge the battery during the day, lots of sun, at least 7 hours. They seem to be quite expensive here, 28,000Taka for a 80watts pannel.

I am wondering if two panels will be enough to charge 400Ah battery bank…..or just get extra charger to charge the batteries quickly?

Is it worth spending the extra money on PV panels? What do you guys suggest, the house is used for about 4-6weeks couple of times a year. I was thinking of storing the PV panels away when I'm done and pull them out when I'm there again.

Thanks in advance.

Comments

  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: Battery backup power
    roks wrote: »
    I am wondering if two panels will be enough to charge 400Ah battery bank…..or just get extra charger to charge the batteries quickly?

    Is it worth spending the extra money on PV panels? What do you guys suggest, the house is used for about 4-6weeks couple of times a year. I was thinking of storing the PV panels away when I'm done and pull them out when I'm there again.

    Thanks in advance.

    I'm not sure what you edited/changed, or what the question is. But, Solar PV is Very expensive, here in the states, a 120W panel is $600 (22V, 7A) You would also need a charge controller.

    Recharge rate for batteries mostly depends on the type of battery, but for your rough guess, use 10% of the battery capacity, if your battery is a 130AH battery, charge it at 13Amps.

    I think you will need a larger battery bank, AND a charger to go with it.

    Flooded cell batteries (removable caps to add distilled water) can take a bit higher rate, and you just add more water afterwards.

    AGM batteries are sealed, and you can very quickly charge to 80%, but you must have a fancy charger to put the last 20% in, or else they boil, and loose water that you cannot replace.

    Gel batteries (often in portable gadgets) cannot take any overcharge either, or they loose water too.

    This is just a rough pass at what I think you were asking. Ask again, till we get it right.
    Mike
    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 ,

  • roksroks Solar Expert Posts: 28
    Re: Battery backup power

    Hi Mike,

    I edited some spelling errors and duplicate words.

    I will be using the flooded type of batteries, so a 400Ah will need 40A? How long will that take to charge?

    What are the difference beween the 12v and 24v system other than low line loss?

    Also, what happens if there is sun and the utility power on at the same time, does the battery over charge or will the charger or CC know when to stop?

    Thanks
  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: Battery backup power
    roks wrote: »
    I will be using the flooded type of batteries, so a 400Ah will need 40A? How long will that take to charge?

    What are the difference beween the 12v and 24v system other than low line loss?

    Also, what happens if there is sun and the utility power on at the same time, does the battery over charge or will the charger or CC know when to stop?

    Thanks

    1) Since you should only deplete your battery to 50%, you will have 200AH to replace
    At 40A, that would take at least 5 hours, because, the last 20% of charging goes very slowly.

    2) lower line losses are 1 difference, the other is the advantage of series connections, vs parallel connections. Here's some reading about battery size and parallel connections:
    Here for battery sizing: (javascript required)
    http://www.freesunpower.com/battery_designer.php

    Here to read about wiring schemes: (diagonally)
    http://www.smartgauge.co.uk/batt_con.html

    3) Solar and Utility chargers, the good ones are smart enough to see that the battery is coming close to full charge from the other one, and both will start throttling back, to prevent overcharge.

    Hope this helps. Mike
    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 ,

  • roksroks Solar Expert Posts: 28
    Re: Battery backup power

    Thanks Mike, that was a good read too. I will continue reading/searching and maybe then I can try to setup on paper
  • roksroks Solar Expert Posts: 28
    Re: Battery backup power

    Hi Guys,

    Been busy other stuff so didnt have time to bother you guys...:)

    I am still looking to do this setup, but been looking at the inverter/chargers, quite expensive some of them....after a pure sine wave version.

    I was thinking of getting a APC smart-up 1500va, that puts out about 1000watts, just enough for my needs.

    I plan to strip out the internal batteries and connect 2x200Ah batteries(flooded truck type, in series, 24v). I am aware that it will take long time to charge the batteries so I am planning to use couple of 100watt solar panels to assist the charging.

    Will this work?

    This is just as a small experiment, so dont want to shell out...

    TA
  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: Battery backup power
    roks wrote: »
    I plan to strip out the internal batteries and connect 2x200Ah batteries(flooded truck type, in series, 24v). I am aware that it will take long time to charge the batteries so I am planning to use couple of 100watt solar panels to assist the charging.

    Will this work?

    Don't bother.
    100W solar panels will not affect your charge time by more than a few minutes.

    Price a 48V (4, 12V batteries) system & inverter/charger. That will give you capacity for repeated blackouts in one day, and will recharge fairly quickly when power is back on. Should have an internal, automatic transfer switch, so it happens automatically. It will run lights and fan, but not air conditioning or fridge. (fridge maybe if you had more batteries, but the contents of the fridge will stay cold for many hours if you keep the door closed.)

    Here's a suggestion Outback FX3048T 3000W, 48V Inverter/Charger, and sales ad:
    http://www.simpleray.com/Outback-FX-3000W-48V-Inverter-Charger-FX3048T-p/31001-07.htm
    (I could not find this at wind-sun)
    or the Outback 2300W FX2348
    http://www.altestore.com/store/Inverters/Export-Inverters-230V-50Hz/Outback-2300W-FX2348ET-48V-Inverter/p847/
    This might depend on the AC voltage you need.
    They are expensive, but with 4 batteries, you will last through longer, repeated blackouts. Just don't hook more loads on them, or you will drain the batteries too fast.
    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 ,

  • roksroks Solar Expert Posts: 28
    Re: Battery backup power

    Hi Mike,

    Thanks for the reply, I just cant figure out how a 48v system will last longer?

    With 4 batteries in series, the Ah is still 200Ah, I thought to last longer one needed to increase the Amps stored in battery...or have I got the wrong end of the stick?

    Also, just realised 2x100w panels will only give out ~5Amps. How about 4x100w panels, that will put out ~11Amps?

    Thanks.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Battery backup power

    When the panels or batteries are installed in series (say 12 vs 48 volts) the voltage adds, but the current remains the same. The power remains the same:

    4x panels in series:

    5 amp * 17 volts = 75 watts

    4 panels in parallel x 5 amps * 17 volts = 300 (four panels in parallel @ 17 volt output)
    5 amps * 4 panels in series x 17 volts = 300 watts (four panels in series @ 68 volt output)

    Same thing with batteries. If you have four batteries in parallel, the Amp output will increase but voltage remains the same.

    Four batteries in series, the voltage will increase, but the amperage wil remain the same.

    In either case the stored energy will be the same:

    P=V*I (does not matter if 4xIxV or 4xVxI --- the answer is still the same)

    What 48 volts vs 12 volts will buy you is lower current in your DC battery bus. For example, assume 10.5 volt minimum (or 42 volt minimum for 48 volt bank), 3,000 watt inverter, 85% efficiency:

    3,000 watts * 1/10.5 volts * 1/0.85 = 336 amps maximum
    3,000 watts * 1/42.0 volts * 1/0.85 = 84 amps maximum

    So the advantage is you can use smaller (cheaper) wire and fuses/breakers on the DC bus with higher voltages.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: Battery backup power

    2, 12V 200AH batteries, will store 2,400Watts

    4, 12V batteries, will store 4,800watts (volts x amps =watts)

    The watts are the same, either series or parallel. Batteries in SERIES (48V) are easier to manage, because parallel batteries do not share currents evenly. And you can use thinner wires.
    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 ,

  • roksroks Solar Expert Posts: 28
    Re: Battery backup power

    Thanks for clearing that up guys......

    I dont know why I am so enthsiastic about seting up solar panels.....all that free sun not being used i guess.

    I'd still like to use the APC ups (24v) as cheaper solution to a pure sinewave inverter (for the time being). Use a seperate charger + the solar panels to assist the charging during power cuts during the day.

    As for buying the solar panels, I can get these from within Bangladesh for $4/watt.
    Or
    get them shipped from China for $2.01 including shipping, what should I be looking out for in this case.

    Thanks
  • seagullseagull Registered Users Posts: 3
    Re: Battery backup power
    mike90045 wrote: »
    ..........It will run lights and fan, but not air conditioning or fridge. (fridge maybe if you had more batteries, but the contents of the fridge will stay cold for many hours if you keep the door closed.)...........

    I have 8- 6v golf cart batteries (4 pairs in parallel for abt 880AHr of juice. I was experimenting yesterday trying to run my 26CuFt fridge ( mfg'd 2008 ). I was using a Trace DR2412 inverter. The fridge was objecting sending out beeps every few minutes. I also noticed the temp went from 37 deg to 40 deg inside. I have a Sperry DigiSnap DSA-400 which should be able to measure current in the line cord plugged into the wall. It measures about .6 Amps when running on commercial juice. The start up current is probably higher when the compressor kicks on.

    I don't know what to do. Should I switch to Trojan T105??? in order to increase AmpHrs?

    I has been a few months since I have neutralized the batteries....perhaps this is the cause of them not performing too well. The batteries are almost 3 yrs old and have been neutralized twice.

    All suggestions would be welcomed. Thanks.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Battery backup power

    The first problem may be the DR Inverter... I believe that is a Modified Square (Sine) Wave (MSW) inverter. Many motors, fridges, electronics do not like MSW inverters:

    1. Many motors draw too much current (square wave) and can overheat/die.
    2. Many electronic timers that use line frequency for timing--do not like square wave edges--may cause them to run very fast and not time correctly.

    "Neutralize" Battery--Do you mean "Equalize"? You should follow the battery mfg. instruction but that usually means equalizing every month or so.

    Measure the battery voltage (both at the bank, and at the input to the inverter). If the voltage is above the inverter's minimum requirements (typically around 10.5 volts) and the AC inverter output is the correct voltage--there is probably nothing wrong with your setup (other than the batteries may have lost storage capacity because of age, the way you charge them, and/or lack of equalization--and remember to check the electrolyte levels and keep up with distilled water--read the Battery FAQ here for more information).

    You probably need a True Sine Wave (TSW) type inverter to run this fridge. And it would be recommended anyway to avoid long term issues with your fridge (such as an early death running on MSW)--if you have the cash to spend for a new TSW inverter (not cheap).

    Also, you may wish to look at getting a Kill-A-Watt meter. You can leave it plugged in for a week to measure your average kWhr usage of the fridge and make sure that you have sufficient batteries/solar panels/etc. to power it (very handy for use around the whole home to aid in conservation decisions). You will probably find there are times the fridge uses >500 watts (such as during the defrost cycle). Your fridge probably uses ~1-2kWhrs per day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • seagullseagull Registered Users Posts: 3
    Re: Battery backup power

    Thanks, Bill.

    I now intend to upgrade to a XW4024.

    I have a 12v PV array (pretty small--160 watts). It appears I'll need to upgrade this to a 24v system w/ probably more panels......maybe 400 watts total????

    Lastly....or maybe 2nd priority would be to replace the golf cart batteries w/ Trojans.

    Any comments?
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Battery backup power

    A 4kW inverter is still a pretty big inverter (I do like the XW Hybrids) to run with 160-400 watts of solar panels...

    You can use >4,000 watts of solar panels with the 4kW inverter--400 watts would hardly seem to make sense as a grid tied inverter unless you have some very special requirements.

    You will have to check with the manual and/or Solar Guppy, but a 4kW 24 volt hybrid inverter should have around 533 amp*hour minimum battery bank (at 24 volts--assuming the standard recommendation to run 400 amp*hour minimum for the XW 6048 inverter system).

    If your loads are much less than 4kW, then you may be able to scale back the battery bank--but then that gets into the whole question of why such a large inverter in the first place...

    In Covington Ky (PV Watts website), a 1kW array (minimum for this program) you will generate around 50-120 kWhrs per month (depending on the particular month).

    400 watts would be 2/5ths of that level--plus the losses (relatively small) of needing to keep the batteries charged (and watered, etc.).

    That is like $1-$4 per month of electric bill reduction for a 400 watt Grid Tied system...

    I am not understanding your needs.

    -Bill

    PS: If you really need a 4kW inverter--also check the out the XW 6048 inverter/system--not that much more cost for the 6kW inverter and it runs at 48 volts--less DC current than the 4kW 24 volt version.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • seagullseagull Registered Users Posts: 3
    Re: Battery backup power
    BB. wrote: »
    A 4kW inverter is still a pretty big inverter (I do like the XW Hybrids) to run with 160-400 watts of solar panels...

    You can use >4,000 watts of solar panels with the 4kW inverter--400 watts would hardly seem to make sense as a grid tied inverter unless you have some very special requirements.

    You will have to check with the manual and/or Solar Guppy, but a 4kW 24 volt hybrid inverter should have around 533 amp*hour minimum battery bank (at 24 volts--assuming the standard recommendation to run 400 amp*hour minimum for the XW 6048 inverter system).

    If your loads are much less than 4kW, then you may be able to scale back the battery bank--but then that gets into the whole question of why such a large inverter in the first place...

    In Covington Ky (PV Watts website), a 1kW array (minimum for this program) you will generate around 50-120 kWhrs per month (depending on the particular month).

    400 watts would be 2/5ths of that level--plus the losses (relatively small) of needing to keep the batteries charged (and watered, etc.).

    That is like $1-$4 per month of electric bill reduction for a 400 watt Grid Tied system...

    I am not understanding your needs.

    -Bill

    PS: If you really need a 4kW inverter--also check the out the XW 6048 inverter/system--not that much more cost for the 6kW inverter and it runs at 48 volts--less DC current than the 4kW 24 volt version.

    I essentially agreed that a True Sine Wave inverter is the way to go and I didn't see anything less than 4K watts. I probably can get by well w/ a 2k inverter. Is there anything that is TSW & ~ 2k watts?

    I'm going off grid-- no grid tie. It's for emergency back-up and possibly to run a few circuits on a regular basis. I have a sub panel I can make changes to.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Battery backup power

    Our host (Northern Arizona Wind & Sun) has a page of different off-grid TSW Inverter vendors that run from 125-6kW+ devices.

    For North American Homes--we have the split phase 120/240 VAC 60 Hz issue... Few residential sized inverters output split phase power without adding a second inverter (synchronized with first inverter) or adding external transformers. The XW series does this without added components--but they are not small inverters.

    For generator back up--you have a couple options... 100% of the Generator output goes to a battery charger that charges the bank and supports the inverter loads...

    Or, you can buy/build a DPDT transfer switch/relay which switches your loads back to the Generator Output (or AC mains) when the batteries are discharged and you need backup power.

    NAWS Transfer Switch products

    Using a transfer switch is much safer and less confusing vs switching plugs around as you transfer power sources around. And easier for a spouse/child/friend to use if you are not there.

    Again, depends on your needs.

    And Seagull (and everyone else)--please feel free to start a new thread to discuss your system questions... Do not feel you have to ask your questions in an earlier thread. May help keep your Q&A sessions a bit more clear.

    Also, feel free to discuss multiple aspects of your system in one thread--usually it saves us hunting around or asking questions that you have probably already answered elsewhere (and help keep me from looking dumb :roll: ).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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