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

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.

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.

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.