Newbie with some questions (bank wiring, ebay meter, maintenance)

Dan_
Dan_ Solar Expert Posts: 61 ✭✭✭✭
Hi all, I'm setting up my first off-grid system to feed a small home where grid connection is prohibitively expensive. I've done a good deal of research and am feeling more and more comfortable but still definitely in the newbie phase so do forgive my questions if they seem elementary

I'm planning to purchase cheapy 6v Costco batteries. My calculations for daily household usage is about 6kwhr so Ive decided on 12 batteries (24v bank). Batteries will be charged from an Outback FM60 and 2000W of PV. Ive purchased a 2500W Sterling Power Pro Combi pure sine wave charger/inverter so I can charge from generator if needed.


Questions:
  1. I've heard advice to not go over 2 battery strings paralleled. Mine would be 3. Is this problematic?

    This is my proposed diagram with all interconnects the same cable length and all leads from the strings the same cable length (2/0)
    Dx6uQKP.png
    If necessary, I could go down to 8 batteries (2 strings) and reduce our household daily consumption (or run the genny more often)
  2. Does anyone have experience with Chinese Ebay battery monitors like this one? Would be a big savings compared to the 300 dollar Outback unit
    http://www.ebay.com/itm/DC-120V-400A-Volt-Amp-Combo-Meter-Battery-Charge-Discharge-Remaining-Capacity-/181152604367?pt=LH_DefaultDomain_0&hash=item2a2d8960cf
  3. Are circuit breakers safe to use? Ive read that they can fail to act as quick as a fuse and can cause damage to components.
  4. When I first purchase my batteries, should I bother checking voltage reading in store? Is there a process to balance the batteries initially?
  5. Finally, I'd like to get as many years as possible out of these batteries (despite them being relatively cheap). What can I do (or not do) to prolong their life?


Thanks in advance for your advice

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    Welcome to the forum Dan.

    Let's check some numbers. The first being 6 kW hours per day. Really that's 48 Volt system territory. On 24 Volts that will be using 250 Amp hours per day, meaning 500+ Amp hour battery bank. Three parallel strings of GC2's would be roughly 660 Amp hours, so technically it works but .... Two parallel strings will reduce the connection problems and decrease the Depth Of Discharge to give the needed power.

    In other words 440 Amp hours @ 48 Volts discharge 25% is about 5280 Watt hours DC, whereas 660 Amp hours @ 24 Volts discharged 33% is the same. Both come up a bit shy of you 6 kW hours goal, but the 48 Volt system will be discharged less even so. (Besides which some of your power may come directly from panels during the day.)

    Now about that 2000 Watt array. On 24 Volts that would supply about 64 Amps peak charge current. Only not through a 60 Amp charge controller. Go up to 48 Volts and you get 32 Amps of current which will go through a 60 Amp controller. In reality you should have a bit larger array than that for the 440 Amp hours @ 48 Volts though; about 2743 Watts +/- a bit.

    Cheap Chinese battery monitor? How much do you enjoy throwing away money? If you're in this for the long haul don't skimp on equipment or you'll be buying it twice. I have no experience with Sterling inverters. Seems to be European spec, so maybe some of our members overseas can advise. If you're not in a Euro standard market (you mention Costco) maybe I'm looking at the wrong inverter. Got a link to it?

    It is perfectly safe to use circuit breakers for over-current protection. They work fine. Provided they are rated for the current type, current, and Voltage involved. Do not use AC breakers on a DC circuit! If there's no rating for DC, avoid it.

    Buying batteries: look for recent and identical dating on each one. You don't want any that have been sitting on the shelf for six months already. Checking Voltage in the store probably won't tell you much. Yes, they should have a commission charge before being put into use: bring them all up to maximum Specific Gravity and the same SG for all cells. Write it down. A hydrometer is essential to proper battery monitoring. Much better than any electronic gadget.

    Perhaps you should revisit your load calculations. Measurement is better than trying to figure out how much power is required based on equipment ratings and estimated times (both of which tend to be inaccurate). Getting that right will be the biggest thing you can do to ensure success of the system.
  • Dan_
    Dan_ Solar Expert Posts: 61 ✭✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    Very much appreciate the thorough reply!!

    The inverter can ben seen here http://sterling-power-usa.com/Procombi-S-puresinewavecombiinverter-24v-2500w-120vac.aspx Very little talk about it online but I was happy with the specs and talking with sales and felt confident enough to give it a go.

    Our daily power consumption is a little back of the napkin and erring on the liberal side. Unfortunately I can't get a reading off of a meter on the actual devices as we're living out of a trailer (building a house). When we were on the grid, we used 3-5kwhr average per day. My wife and I are frugal people though and if needed we could cut our electric usage. We're planning for a chest fridge convert, propane cook stove and water heater and wood heat.

    So if this were still 24v, would you recommend then going to 2 strings (8 batteries)? I could cut usage and run the generator as needed
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    One thing I don't like about that inverter: the charger seems to have a choice of 4 settings only, and that by battery type. This means no adjustments for Absorb Voltage, time, current limits, Float Voltage, et cetera. The chances of that lining up with the batteries you pick are not good. Even inverters with really good chargers have too many limitations.

    If you go with a 24 Volt system an two strings of GC2's you'll have a maximum of around 2.6 kW hours @ 50% DOD. That's less than half your expected loads, so I would not recommend it; you'd probably be running the generator a lot.

    You're looking at a cheap inverter and it is limiting your system. I can't help but think you will find it inadequate and end up having to toss it and buy a better one later. Let me just stick a link in here to a quality 48 Volt inverter and see if you don't think it's worth the extra money (it will require a MATE programming interface which is another $300 just so you know): http://www.solar-electric.com/inverters-controllers-accessories/inverters/ouin/oupooffgrand/outback-power-pure-sinewave-inverter-fx3048t.html

    And no I do not work for NAWS or Outback and I don't sell anything. I've just had to fix a lot of systems that were wrong for one reason or another, and a poor inverter is in the top 5 mistakes people make.
  • Dan_
    Dan_ Solar Expert Posts: 61 ✭✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    Appreciate the candor and advice, that's why I came here. My thought though now is that even with a device that has adjustable voltage, time and current limit settings...I'd frankly have no clue what they should be. I was ready to trust the inverters baked in setting for FLA. So the inverters settings are incorrect?

    Regarding the 2.6kwhr figure: With 8 200ah 6v batteries, you'd have two strings of four, totaling 400ah@24v. The usable capacity, half, is 200ah@24v - 4.8kwh. Am I making an error somewhere?
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    For a full time house RE system to my mind you have two and only choices:
    A. buy decent name brand gear, and get your loads as low as you can, ie below 4kW/day, and spent not too much
    b. buy decent name brand gear, use as much power as you want and spent lots.

    While i dont recognise the brand, the case does look a whole lot like a chinese inverter sold here. For another few hunbred you could have got the most robust inverter in the industry.

    Dont despair, i also did what you did, bought first, came to NAWs second. In my case i sent the cheap chinese inverter back! Then took the forums advice and got a Midnite classic plus whizbang junior, which is an unbeatable combination.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Dan_
    Dan_ Solar Expert Posts: 61 ✭✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    Fortunately my 24v inverter was going to ship out today so I called in to cancel. Got the 48v Outback as recommended. The 700 extra is worth it for a trusted name and better voltage for planned system as well as future.
    Still planning to do 8 6v 200Ah batteries but now its simply one string. I'll try to get several years out of these cheap batteries and learn the ropes then get bigger capacity better quality batteries
  • Cathalsiew
    Cathalsiew Registered Users Posts: 13
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    Hi there,

    Im a newbie too. I have a question in terms of the NAWS charger linked on this page....So the kit charges the battery from the RE source(in my case will be a micro hydro scheme) and also inverts the DC from the battery bank to the household mains?



    Thanks
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)
    Cathalsiew wrote: »
    Hi there,

    Im a newbie too. I have a question in terms of the NAWS charger linked on this page....So the kit charges the battery from the RE source(in my case will be a micro hydro scheme) and also inverts the DC from the battery bank to the household mains?



    Thanks

    You're misreading it.
    The link is to an inverter which has a built-in AC powered charger. It does not regulate charge from an RE source such as solar panels. That requires a separate charge controller.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    Things can get very complex with modern Solar Hardware...

    There are Off Grid Inverters that can share their AC output with GT inverters too... The Off Grid inverter sets the 120 VAC and 60 Hz, and will output power (normal operation) to loads, but can all accept power from a GT Solar Inverter (or wind, etc.) and take the excess power on the AC "bus" and use it to recharge the battery bank.

    I tried to layout the available options here:

    battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dan_
    Dan_ Solar Expert Posts: 61 ✭✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    So what are the proper values for charging GC2 flooded lead acid batteries? (It was previously mentioned that the Sterlings values were not correct)

    These are the default values for Outbacks inverter/charger
    Attachment not found.

    And heres what Trojan says http://www.trojanbattery.com/tech-support/battery-maintenance/
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie with some questions (bank wiring, ebay meter, maintenance)

    It's one of those "it all depends" answers. In this case it depends on the particular batteries (not every maker recommends the same Voltage or maximum current) and how they are used.

    For example Absorb time varies with DOD. It takes longer to 'refill' a battery that has been drained more. This is why fixed Absorb times are a pain in the anatomy and the best way to do it is with a system that can use End Amps if not an actual SOC calculation.

    There is some trade-off between Absorb Voltage, Absorb time, and water use. I doubt anyone could set a system up from new and just walk away knowing it will work perfectly. Not everyone's DMM or hydrometer reads the same for one thing. So it is very important to try and start with the manufacturer's recommendations and then gently adjust one thing at a time until you get the best performance for your particular system. This is not easy, and is even more difficult with a sealed battery that you can't dip into and actually read the SG.