Off the grid Island camp - 12v vs. 120v

shortfatguyshortfatguy Solar Expert Posts: 42
Hello all,

I own a one room un-insulated post & beam 16x32 camp with loft and a small bunkhouse on a island in NW Maine. I know what I have to do to insulated and take care of the heating and cooling of the camp & bunkhouse.

Current setup:
The place is wired for 120v generator power and wood stove for heat. I use propane for the refrigerator, stove and lights. There is no toilet, hot water or shower and we have a outhouse. I use a 5000w generator to pump water out of the lake 150' up to a holding tank for gravity fed water system, we can not use wind power.

We do not like using the generator as we're in the middle of nowhere and enjoy the solitude and watching the wildlife. We do not allow TV's. We are at camp 2-3 weeks a year and every other weekend.

Here is what we desire at this time:
Is to change the use of generator and propane to backup for the lighting and possibly refrigerator
Have enough power for 2 laptops and satellite internet access 12 hrs a day
Charging station for our flashlights, 2 way radios, cells, vacuum
12v water pump to increase the water pressure
Not sure about what type of direct vent "on demand" water heater propane or electric to install
We require lighting bright enough for reading

Here's my question.
What would be the most efficient solar powered system to install - 12v or 120v

Thank you in advance,

Mark
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Comments

  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    For your water pressure, can you pump to a higher location ? I've always preferred gravity fed water instead of a pressure pump that cycles off and on.

    as to 12V vs 120V
    1) You don't really have 12V, you have 12V - 15V, depending on what the battery charger is doing. Noontime, you have 15V feeding the battery and appliances. Early AM, before sunrise, you have 12.5V That's hard on LED reading lights.

    2) do you want to use "ordinary" appliances ? Then it's 120VAC

    3) computers and TV boxes - do they run with 12-15v or do they need adapters for 12V? You may save more in having the loss in 1 big inverter, than lots of little ones all over.

    4) there are some very bright 10 & 20 watt, 12V halogen reading lights, and LED lights are coming along pretty well too. Don't leave one on days, while charging batteries, or if the generator kicks in automatically.

    5) will you be there in the winter time too, alternate weekends ?
    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 ,

  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v
    Hello all,

    I own a one room un-insulated post & beam 16x32 camp with loft and a small bunkhouse on a island in NW Maine. I know what I have to do to insulated and take care of the heating and cooling of the camp & bunkhouse.

    Current setup:
    The place is wired for 120v generator power and wood stove for heat. I use propane for the refrigerator, stove and lights. There is no toilet, hot water or shower and we have a outhouse. I use a 5000w generator to pump water out of the lake 150' up to a holding tank for gravity fed water system, we can not use wind power.

    We do not like using the generator as we're in the middle of nowhere and enjoy the solitude and watching the wildlife. We do not allow TV's. We are at camp 2-3 weeks a year and every other weekend.

    Here is what we desire at this time:
    Is to change the use of generator and propane to backup for the lighting and possibly refrigerator
    Have enough power for 2 laptops and satellite internet access 12 hrs a day
    Charging station for our flashlights, 2 way radios, cells, vacuum
    12v water pump to increase the water pressure
    Not sure about what type of direct vent "on demand" water heater propane or electric to install
    We require lighting bright enough for reading

    Here's my question.
    What would be the most efficient solar powered system to install - 12v or 120v

    Thank you in advance,

    Mark

    You have an identical set up that we have, except we are in Northern Canada, and we are there 12 months: An Island in the middle of a big lake, frozen for ~7 months a year. (our ice just broke up a week ago today!)

    We run 220 watts of panels, into 4 l-16 batteries. We invert to 120 vac with a 300 watt prosine inverter. For fridge we use propane. All lighting is cfl, satelite internet, two lap tops, satelite phone etc. (No tv, but satelite radio)

    We are very happy with this set up but we are VERY frugal with our usage. If I were building it for someone else I would increase the panel capacity a bit. We almost never drop below 90% s.o.c on a daily basis if there is any sun. We go three days without getting to 80% with no sun. I have a collection of generators, (left from pre-solar days) so I charge when needed with a honda eu 1000 that is quiet and fuel efficient. For shop tools I run either a 2.5 kw mitsubishi, or when I really need something I have a 5 kw lister diesel.

    My water is interesting. Our original system was gravity, pumped from the lake once every few days with honda powered pump to a 100 gallon tank up the hill. After the 1st of September until late April we carried water in buckets after draining the gravity system to prevent freezing. This system is very simple and very reliable, as well as being very cheap.

    This winter I bit the bullet, and built a 12 vdc pressure water system using a shurflo submersible, a conventional pressure tank system. The system is detailed in the "water pumping" threads of this forum. If you wish more details I will either repost them or send you an e-mail. (My system was complicated by the desire to keep it un frozen year 'round, without using any power. I think I succeeded.

    Water heat is via a Paloma PH-6 demand water heater. Standing pilot that can be turned off when not used, b-vented with no power requirement, and very reliable, easy to repair in the unlikely need for repair. This little heater will take frozen lake water out of the lake (34f) and give us all the hot shower we need. In fact, after the ice went out, we have to turn it down even though the water temp is still below 40f. The pressure tank is in the house so that it warms up through the day so it works even better. (I do have voltage doubler on the pump so that it runs at 24vdc. Pumps a 50 gal tank in ~12minutes to 60 psi.

    Our key, is to use as much of our electrical usage when the sun is out. We charge the lap tops and run the modem and the router during the day for the most part. Our system can charge the laptops, and run the modem/router as well as charge portable tool batteries and still have some left over for the main battery bank. We get sun very early in the morning. I let the house batteries go on their own until the controller begins to taper the charge (usually around 11:00 am) then begin to plug in the other stuff, and turn on the water pump. (I often turn the pump breaker off at night during the last shower to save the power for the sunny morning)


    I would in all events invert rather than run just 12vdc. The losses from inverting are more than made up by the quality and selection of cfl lights, plus you are going to run 120vac stuff anyway. (Modems etc)

    The biggest thing you can do is control consumption. As I said we are very frugal. For most normal people I would consider a system with perhaps twice the capacity for charging. Our system has evolved from Kerosene lamps, so this is a huge step into the 20th century. You can build for the 21st.

    Good luck,

    Icarus

    PS My wife is from Peaks Island ME. We are off tomorrow to work on the house!
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    mike90045,

    1) You don't really have 12V, you have 12V - 15V, depending on what the battery charger is doing. Noontime, you have 15V feeding the battery and appliances. Early AM, before sunrise, you have 12.5V That's hard on LED reading lights.

    >>Thanks for the clarification

    2) do you want to use "ordinary" appliances ? Then it's 120VAC

    >>Leaning 80% in a direction. Would like expert opinions to justify my direction

    3) computers and TV boxes - do they run with 12-15v or do they need adapters for 12V? You may save more in having the loss in 1 big inverter, than lots of little ones all over.

    >> I agree

    4) there are some very bright 10 & 20 watt, 12V halogen reading lights, and LED lights are coming along pretty well too. Don't leave one on days, while charging batteries, or if the generator kicks in automatically.

    >>thanks

    5) will you be there in the winter time too, alternate weekends ?

    >>oh yeah hope to be sledding and some ice fishing too
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    5) will you be there in the winter time too, alternate weekends ?

    >>oh yeah hope to be sledding and some ice fishing too

    If your panels are vertical enough, they will self-shed snow, and when the sun is out, you WILL get much more power from them,
    A) reflection off the snow, 1.5X (roughly)
    B) cold temperatures = higher voltage output.

    remember to size your charge controller accordingly, use the sizer charts the mfg. have
    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 ,

  • catkincatkin Registered Users Posts: 19
    Re: Off the grid Island camp - 12v vs. 120v
    2) do you want to use "ordinary" appliances ? Then it's 120VAC

    >>Leaning 80% in a direction. Would like expert opinions to justify my direction
    Not really "expert" but one of the main benefits we found switching from 12 V DC to 220 V AC (in South India) was being able to buy ordinary appliances - ~25% of the cost, lots of retailers, lots of choice. Pump motor control, previously impracticable, became available off the shelf.
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    Thanks to all for your help.

    Since I've picked up these 4 6v deep cycle batteries with the following specs: 170 min discharge @ 75A, 335 20A hour rating, 745 RC at 25A. I'm thinking I'm going to wire them in parallel and add a off-the-shelve pep boys inverter as the camp is pre-wired. As my electrical requirements are for 12v shurflo water pump, 4-6 120v/14watt lights at night and 95w laptop during the day. Will expand to a point of use tankless water heater (30 amps) for my sinks as there is no shower yet.

    Q: What is a fast battery charger I can get to run off my 5000w generator to charge the battery bank until I pickup a few panels?
    Q: Thoughts on a cheap meters I need
    Q: Missing anything

    Please remember this is a low-end system so any suggestions would be appreciated.

    Cheers,

    Mark
  • System2System2 Posts: 6,290 admin
    Re: Off the grid Island camp - 12v vs. 120v

    Sounds like my first encounters with 12v vs 120v. I transitioned by buying a Sears charger 10/2/60a automatic 6/12v. I later went to the Prosine 2000 that had a charger built into the inverter.

    If you say 30a for the water heater may I suggest you get a LP tankless. They make one with a standing pilot. Then you wouldn't have to leap into the inverter/charger mode until later.;)
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Off the grid Island camp - 12v vs. 120v

    Hmmmm... You want to run a 12 volt or 24 volt system?

    Assuming 12 volt (2x2 series/parallel) with 335 AH batteries at 20 hour rate...

    That would be 670 AH at 12 volts, 5-13% charging rate would be ~33.5-87 amps...

    Assuming 15 volt output and 80% efficiency, a battery charger would be rated at:

    P=I*V/eff=33.5a*15v/0.80=628 watts
    P=I*V/eff=87.0a*15v/0.80=1,630 watts

    Your 5kW generator should be able to drive any 1,600 watt capable battery charger... Any larger/smaller charger will give you problems (overheat batteries / not enough current to properly equalize).

    However, you should also want to look at fuel consumption and noise.

    Generally, the average gasoline powered 5kW inexpensive genset is noisy... And fuel hungry.

    Getting a little Honda eu2000i (1,600 watt continuous--eu1000i and eu3000i also available) may be a good option. Generally, much quieter (you can talk while standing next to one) and for 1/4 powered loads (400 watts on a eu2000i in this example) the 4 hours @ 1,600 watts drops to 15 hours @ 400 watts on 1.1 gallons of gas. I would guess that a 5kW generator is going to use several times than amount of fuel.

    The other issue to look at is the Power Factor of the average battery charger... Most of them have very low power factors, and require a larger genset to keep the alternator's wiring from overheating (a 2kW charger may need a 5kW generator to operate correctly).

    A Power Factor Corrected battery charger can run with a much smaller generator (lower current requirements).

    Unfortunately, it is not easy to find power factor corrected battery chargers... Xantrex makes some. The Iota Engineering DLS series (another very good vendor) look like they should have power factor correction--but you need to ask to be sure.

    The new Xantrex inverter/charger looks like a very nice system--but is probably much larger than you will need (small one is 4kW?).

    Anyway, there are some folks here that run small generators and battery chargers that can give you real world solutions.

    Regarding inverters... You might want to try and swing a 24 volt pure sine wave inverter... Pure sine is really much better in the long run for reliable operation of appliances (motors) and receivers (TV/Radio). And 24 volts system allows much smaller wiring.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v
    Sounds like my first encounters with 12v vs 120v. I transitioned by buying a Sears charger 10/2/60a automatic 6/12v. I later went to the Prosine 2000 that had a charger built into the inverter.

    If you say 30a for the water heater may I suggest you get a LP tankless. They make one with a standing pilot. Then you wouldn't have to leap into the inverter/charger mode until later.;)

    I was leaning to the propane tankless. But for the time I'm at camp it doesn't make sense. A simple RV point of use hot water heater is where I'm leaning. Found a ton with less then 30a requirements. Remember it is a island camp and a lake bath with ivory soap (floats) does the job.

    Thanks and I was looking at the Sears charger.

    Cheers
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    The Honda generators are great. I have two a 5000w+/- and 1800w+/-. My camp is wired for 120v and I just picked up 4 6V deep cell batteries. I'm thinking the series / parallel is the way to go as my requirements are low and part time. Will add some panels next year (2 kids in college $$ issue) in the meantime just looking for a practical way to keep the bank charged and provide some lights beyond my gas lights.

    Thanks for the math

    Cheers
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    I highly recommend the Xantrex True charge series of chargers. The are almost the only charger that will put out full output off a small floating neutral generator set. http://store.solar-electric.com/xaprbach.html

    I run a TC 20 just fine off my honda Eu 1000i generator, and a TC 40 off a 1600 watt floating neutral honda. The have good battery type selection and temp compensation.

    Beware of homeowners and automotive type chargers.

    As for hot water, as I have stated elsewhere, demand Propane hot water is the only way to go. I have used both Boschs and Palomas for your identical situation. (Paloma legacy series use not electricity, can't remeber the Bosch series that uses no electricity. You could also consider a RV tank type Propane heater. They are quite cheap, and will do a batch of hot water (~5 gal) pretty quickly)

    If all you are doing is using the generator for charging the batteries, I would shy away from propane. While Propane is clean, on an island environment it can be hard to transport. We use 100# 20 (gallons) tanks, and it is getting to be all I can do to horse them around. 60# (15 gallons) are still pretty heavy.

    If you are using a Honda eu 1000 or 2000 type generator just to charge the batteries, you would only go through 10-15 gallons/ season. I don't know of any propane generator smaller than about 2.5kw.

    Good luck.

    Icarus
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v
    Thanks to all for your help.

    Since I've picked up these 4 6v deep cycle batteries with the following specs: 170 min discharge @ 75A, 335 20A hour rating, 745 RC at 25A. I'm thinking I'm going to wire them in parallel and add a off-the-shelve pep boys inverter as the camp is pre-wired.

    Q: What is a fast battery charger I can get to run off my 5000w generator to charge the battery bank until I pickup a few panels?
    Q: Thoughts on a cheap meters I need
    Q: Missing anything

    Please remember this is a low-end system so any suggestions would be appreciated.

    4, 6V batteries in parallel, gives you : 6V !!

    Cheap charger - look at Pep Boys again, look for the ~$100 Vector/BlackDecker 4/20/40A charger 1093D. Has selection for deep cycle, and it's a switchmode type of supply, so I think it's new enough to have a good power factor. (700W @ 40A setting)
    http://www.amazon.com/review/product/B00009RB0T?showViewpoints=1
    Also has equalize and desulphate settings too, truly shuts down with "FULL" reading on display, and fan idles back when done, so it won't boil cells dry.
    No battery temperature adjustment or sensor, but it's a $100 unit.
    12V system only, won't do 6V, so you have to have some batteries in series.

    look here to see how to best connect batteries, and why:
    http://www.smartgauge.co.uk/batt_con.html

    You will want 2, 6V batteries in series to get a 12V unit
    place 2, 12V units in parallel, and you have
    a 12V battery bank, made of 4, 6V batteries.
    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 ,

  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    Thanks all.

    I omitted the series in original post, series-parallel is what I need to do. Here is a quick link for a bunch of battery bank setups http://www.solarseller.com/battery_bank_wiring_diagram.htm

    Mark
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    Icarus,

    Propane hot water is the way to go for a shower. But our demand is not there yet, maybe when we retire in 20 years. Check this out http://www.campingworld.com/browse/skus/index.cfm?skunum=37786&src=SRQB kinda cool or hot. Humping the 100 gal tanks around is a pain. My propane lighting really puts a drain on my system.

    Mw
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    Probably not a bad alternative for a simple cabin. You have to mount it outside or figure a vent system. Another simple water heater we used for years in the winter is from Zodi Ouback gear :http://www.zodi.com/web-content/Consumer/zodihotstovetopshower.html Cheap to buy, cheap to run.

    Put one end in a pail of water, the heater on the stove, and presto, hot shower. Only uses a couple of "D" batteries. We used to use one all winter before we built our new system. We would heat the water on the woodstove to almost hot enough and then add just a bit of controlled heat with the stove burner. It wasn't a 5 star spa shower, but beat the hell out of anything else we tried. (We used to be 6 months without running water, so any improvement was a big one! We now have 12 month water and it's pretty luxurious!

    Icarus
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    Just got back from camp and installed my 4-6v (12v) series-parallel battery bank and 800w inverter with a on/off switch from my camp to the DC side of the inverter. I was able to use my 95w laptop and two 14w lamps with a 20w radio to test the system total time of 20 hours and used only .5 volts.

    SWEET!

    Any suggestions to size and type of panel(s) and controller to charge the batteries? Panels would be mounted on a east side of my generator shed with a 14/12 pitch.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    .5 volts doesn't mean very much. What counts is what was the cumulative amp/hour load relative to the battery size? How much (as a percentage) of the total battery capacity was that? Would this be a "normal" load on your system? How much recharge capacity do you (will you have)? What kind of buffer do you need (want) for no sunny days or additional loads?

    Assuming a fully charged battery bank starting at ~12.6 vdc, "using" .5vdc would leave the battery at ~12.1vdc. Assuming no surface charge on either end, that would leave you with a battery with ~50% of capacity used up. This is the absolute upper limit of depth of discharge for a lead/acid battery, and only if it is recharged to 100% within a day or two.

    As for sizing your system you have to "Do the math" Figure out your loads and then figure out your battery bank, and your panel needs.

    Icarus
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    Well my batteries ar rated 335 = 20a hour rate, which I assume 335 is time in minutes, correct?
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Off the grid Island camp - 12v vs. 120v

    The 20 hour rate is the capacity of the battery (in Amp*Hours) if it was to be 100% discharged in a 20 hour period...

    The 335 Amp*Hours @ 20 hour rate is the capacity of the battery... So, the current at a 20 hour rate would be:

    335 AH / 20 H = 16.75 amps for 20 hours will draw 100% of your battery's capacity (to 0% State Of Charge--SOC).

    And--because you don't want to discharge your batteries to lower than 50% SOC--you should draw no more than 16.75 amps for 10 hours (or ~8 amps for 20 hours, etc.)...

    Now--we need to be sure that your 335 amp*hour is correct... You have a series/parallel bank? Guessing that these are 6 volt batteries? So--when you put two 6v batteries in Series for 12 volts--the Amp*Hour is the same as the rating of one battery.

    When you take the 2 series 6 volt batteries and put them in series with another set of 2x 6 volt batteries (of equal rating), the battery bank A*H rating doubles (add the AH rating of each string of batteries when put together in parallel).

    Your load of:
    Just got back from camp and installed my 4-6v (12v) series-parallel battery bank and 800w inverter with a on/off switch from my camp to the DC side of the inverter. I was able to use my 95w laptop and two 14w lamps with a 20w radio to test the system total time of 20 hours and used only .5 volts.
    Works out like:

    (95watt + 2*14 Watt + 20 watt) * 20 Hours * 1/80% invrt eff * 1/12 volt battery bank = 298 Amp*hours

    You have used almost all of your battery bank's capacity and left ( 335-298 ) / 335 = 11% state of charge... You do not want to go blow 50% ever (assuming non-AGM batteries), and ideally not below 75%, for long battery life.

    Assuming all of my assumptions are correct... You should recharge your bank back to 100% SOC right away--you are running a real risk of shortening the life of your batteries to months if this keeps up.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v

    [(95watt + 2*14 Watt + 20 watt) * 20 Hours * 1/80% invrt eff * 1/12 volt battery bank = 298 Amp*hours

    You have used almost all of your battery bank's capacity and left (335-298)/335=11% state of charge... You do not want to go blow 50% ever (assuming non-AGM batteries), and ideally not below 75%, for long battery life.

    I'm catching on slowly, so bear with me. I understand most of all the numbers and math. Just need to put into practice.

    Q: Would it be ((335 aH *2)-298)/335?
    Q: So keeping an eye on the voltage drop is not as important as the amps?

    I've already recharged them

    Thanks
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    Bill, you're too fast, I was going to say just about what you did. You say it better however.

    Shortfatguy.

    May I suggest that you post your battery info, make model size and configuration so that we can see what you are dealing with?

    I also suggest that you read as much of the following links as you can. We all here have spent years using and destroying battery banks as we have learned how to care and feed them. No point in you having to reinvent the wheel!

    http://www.batteryfaq.org/

    http://www.rpc.com.au/products/batteries/car-deepcycle/carfaq4.htm#charge

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    You will learn the relationships between bolts and amps, state of charge, surface charge, specific gravity etc.

    One of the great misconceptions of batteries is that they are boxes into which you "pour" electricity, to be "poured out" when you need it. The truth is that batteries are chemical factories that "make" electricity by chemical reaction. Overtax the factory and it will significantly shorten it's life.

    Good luck,

    Icarus
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v

    I don't understand you question quite

    "Q: Would it be ((335 aH *2)-29/335?

    I don't get this please explain

    Q: So keeping an eye on the voltage drop is not as important as the amps?

    What really matters is the specific gravity of the electolite (acid)in the battery. Can only be tested with a hydrometer that compensates for temp.

    A voltage test is only marginally useful. Testing the voltage after the battery has been charged from any source, the voltage will be artificially high. Checking voltage while under load will give you a similarly low reading. (That may be why your inverter beebed and shut down on you). Checking voltage soon after charging will also give too high a reading.

    To properly check voltage, it should be done at least 2 hours AFTER the battery has sat with no load and no charge. Hard to do in most off grid situations. That is why a full battery of test instruments is needed, AND, the knowledge as to how to use them.

    Icarus
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Off the grid Island camp - 12v vs. 120v
    I'm catching on slowly, so bear with me. I understand most of all the numbers and math. Just need to put into practice.

    Q: Would it be ((335 aH *2)-298 / 335?
    Q: So keeping an eye on the voltage drop is not as important as the amps?

    I've already recharged them

    If you have 4 x six volt batteries, two in series and the two strings in parallel , then yes, you would have 2x 335 AH = 670 AH at 12 volts (assuming each battery is rated for 335 amp*hours @ 20 hour rate). So you would have run them to:

    ((335 AH *2)-298 AH) / (335 AH * 2) = 56% State of Charge

    --Better, but still something you would not like to do on a daily basis.

    Voltage can work OK--but you have to wait several hours after load (or charging) to get an accurate voltage reading. It is impossible to get a meaningful State of Charge reading with a voltmeter while the battery is under load (or charging).

    A better way to check bank capacity is to measure the electrolyte density with a hydrometer. But that has its own issues too--messy, loss of electrolyte, and possible contamination of cells... Also, you cannot use a hydrometer with a sealed battery. In the end, you usually only check your batteries once in a while with a hydrometer--not daily.

    The "holy grail" of measuring battery capacity (in my humble opinion) is the Battery Monitor. It is as close as you can get to a "gas gauge" for your battery system. Well worth the money in saved batteries and frustration if you have any larger sized system.

    Look at the Xantrex XBM--has been recommended by others here before.

    And Xantrex is coming out with a new line in the month +/- which includes programmable contact that you can use to shut down loads or start a generator...

    orange_arrow.gifwhitepixel.jpgBattery Monitor - LinkLITEorange_arrow.gifwhitepixel.jpgBattery Monitor - LinkPRO

    Remember that batteries are very temperature sensitive animals--so measuring voltage or electrolyte density all needs to be done with a thermometer and chart handy.

    Also, any charger (solar, generator, etc.) really needs to be temperature compensated too--if the batteries are not in a temperature controlled environment (or if you have high currents which can heat batteries too).

    -Bill

    PS: And, yes, voltage is also important. Especially during charging. If you meter is off by just a few hundred milli-volts--your estimate of charge state and settings for your charge controllers will be way off.

    So make sure your volt meter is calibrated and functioning correctly. We have had more than a few problems diagnosing problems when it turned out to be a "partially" functioning DVM... I remember one thread, at certain voltages/amps/settings the "Bad DVM" gave reasonable readings, and at other settings it was out to lunch. Made diagnosing Solar Panel/Charger problems impossible (could not tell if everything was working or not).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shastaronshastaron Registered Users Posts: 24
    Re: Off the grid Island camp - 12v vs. 120v

    Thanks to ShortFatGuy for starting this thread. And a thank you to the ongoing discussion by everybody. I have learned more from reading this thread than I did from the last book I read. You guys are great and please keep up the thread.

    Ron
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v
    shastaron wrote: »
    Thanks to ShortFatGuy for starting this thread. And a thank you to the ongoing discussion by everybody. I have learned more from reading this thread than I did from the last book I read. You guys are great and please keep up the thread.

    Ron

    Thank you,

    My story is I picked up 4-6v deep cycle batteries (12 months old) for free and bought a unused 800w inverter from a friend for $35 and he let me use his automatic 4/10/20/40A charger. Chatted with a local battery person and he recommended charging with 10A as it is slower but more consistent.

    What I found out with my weekend experiment at camp is the following items and list of questions:

    Need to do:
    Place is wired for 120v with 12/2 wiring which will allow me 20A or 2400W, need to wire my outhouse.
    Lower my lighting requirements and go with more direct lighting with 9W CFL's. Get a radio with lowest wattage requirements possible.
    My 95W laptop has chewed up my battery bank power faster than I expected and has given me a new perspective on what I need to do.

    Q's:
    When I add panels could the controller handle battery monitoring or do I need a separate battery monitor?
    When running the generator do I need a transfer switch to put power directly into the camp and bypass the battery bank or can I run the generator to charge batteries with the inverter powering the camp at the same time?

    As you can see I'm still very new to this, but can state - I have the bug now as all I've spent is $35 bucks and a bunch of personal time from the great folks on this forum.

    Mark
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v
    BB. wrote: »
    If you have 4 x six volt batteries, two in series and the two strings in parallel , then yes, you would have 2x 335 AH = 670 AH at 12 volts (assuming each battery is rated for 335 amp*hours @ 20 hour rate). So you would have run them to:

    ((335 AH *2)-298 AH) / (335 AH * 2) = 56% State of Charge

    OOPS! Forgot the *2 for /335. So would this double my per hour amps?

    >>335 AH / 20 H = 16.75 amps for 20 hours will draw 100% of your battery's capacity (to 0% State Of Charge--SOC).<<
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v
    icarus wrote: »
    I don't understand you question quite

    "Q: Would it be ((335 aH *2)-29/335?

    I don't get this please explain

    Q: So keeping an eye on the voltage drop is not as important as the amps?


    BB answered it below. thanks for all your help and links. I need to read 5-6 times before it sinks in.

    Cheers,

    Mw
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Off the grid Island camp - 12v vs. 120v
    Thank you,

    My story is I picked up 4-6v deep cycle batteries (12 months old) for free and bought a unused 800w inverter from a friend for $35 and he let me use his automatic 4/10/20/40A charger. Chatted with a local battery person and he recommended charging with 10A as it is slower but more consistent.

    What I found out with my weekend experiment at camp is the following items and list of questions:

    Need to do:
    Place is wired for 120v with 12/2 wiring which will allow me 20A or 2400W, need to wire my outhouse.
    Lower my lighting requirements and go with more direct lighting with 9W CFL's. Get a radio with lowest wattage requirements possible.
    My 95W laptop has chewed up my battery bank power faster than I expected and has given me a new perspective on what I need to do.

    Q's:
    When I add panels could the controller handle battery monitoring or do I need a separate battery monitor?
    When running the generator do I need a transfer switch to put power directly into the camp and bypass the battery bank or can I run the generator to charge batteries with the inverter powering the camp at the same time?

    As you can see I'm still very new to this, but can state - I have the bug now as all I've spent is $35 bucks and a bunch of personal time from the great folks on this forum.

    Mark
    I am still not clear what size our batteries are.

    Your first question,, it depends on the controller you buy
    Question 2,,, you can do it either way, but charging the batteries while using loads makes it hard for a good charger to know what is really going on with the batteries. Iota makes a real nice automatic transfer switch.

    Also, Most batteries don't like to live on automotive type chargers. They don't do a real 3 stage charge, (bulk, absorb, float)and they are ot temp compensated. Look into Xantrex TC chargers, or Iota. The Xantrex work well with small generators.

    Icarus
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v
    icarus wrote: »
    I am still not clear what size our batteries are.

    Your first question,, it depends on the controller you buy
    Question 2,,, you can do it either way, but charging the batteries while using loads makes it hard for a good charger to know what is really going on with the batteries. Iota makes a real nice automatic transfer switch.

    Also, Most batteries don't like to live on automotive type chargers. They don't do a real 3 stage charge, (bulk, absorb, float)and they are ot temp compensated. Look into Xantrex TC chargers, or Iota. The Xantrex work well with small generators.

    Icarus


    Right now I'm using a Vector 109d 3 stage smart charger and it appears to handle everything well.

    Would a Xantrex be a fast charger? Is a faster charger good for a system?
  • shortfatguyshortfatguy Solar Expert Posts: 42
    Re: Off the grid Island camp - 12v vs. 120v
    icarus wrote: »
    I am still not clear what size our batteries are.QUOTE]

    Battery specs: 8C6V 4-6v deep cycle batteries, 170 min discharge @ 75A, 335 20A hour rating, 745 RC at 25A. http://www.midstatebattery.com/deep.htm
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