Battery Bank Sizing

[tr0y]

Hi All -

While currently not a full timer, I will be in a few months for anywhere from 6 to 10 months while my new home is being built.

I am just looking for some thoughts from people that do this on a daily basis.

So I have a fairly large solar array on my TT 1400 watts of PV panels, that produce close to 100 amps for 5 to 6 hours a day year round so I have quite a bit of charging capability and then also generator power, but don't love to run it as it is in frame and loud.

For those that ask the solar system is as follows:

4-275 Watt PV Panels
1-290 Watt PV Panel
1- Midnite Solar MPPT Classic 150 Charge Controller
1- AIMS 2000w Inverter Charger (Yes I know some people hate these but mine works well)

3 or 4 200 Ah AGM batteries

And a whole bunch of other interconnect and wiring stuff but you get the gist of it.


What I am wondering is how big are most battery banks ? I am waffling between 600Ah @ 12v and 800Ah @12v. I have the batteries and room to do either. I am just wondering if 800Ah is overkill.

Thoughts are appreciated.

[tr0y]

Thanks all for the answers. Some clarification in no particular order.

• - Yes home being built is in NV, just outside of Las Vegas.

• - I have external power for tool use 'till grid power is finished.

• - Panel voltage, not really an issue here as I am using an MPPT charge controller. It does the voltage matching. i am pulling about 96v from the PV panels.

• - Weight is an issue but not that much, still way under capacity and have F350 + Airbags as tow rig. I plan to travel as the home is being built, when I have subs swinging hammers, I will be building some of the house myself.

• - DC voltage - in this application I am married to 12v rather not have to add in DC to DC converter. I know higher voltage is easier to deal with in many instances, but not here.

• - Deep cycle batteries, yes these are true deep cycle Lifeline / SunXtender made in the US. I have used before in off grid solar applications.

I would like to say thanks for the thoughts and the input !

I ended up going with 600Ah as I was able to sell some of the batteries I had at a profit to make the 600Ah bank end up costing me $100.00 ( yes one hundred dollars for brand new batteries ) installed.

[theoldwizard1]

First, MOST (not all) 12V batteries (flooded or AGM) are NOT true deep discharge batteries. What brand and model number are your 200 Ah AGM batteries ?

For best performance and life you really want TRUE deep discharge batteries. Trojan makes a true deep discharge 12V battery, in flooded (T1275) and AGM (T1275-AGM). They will be hard to locate (probably only available at a solar/wind energy store) and will be VERY EXPENSIVE.

[Optimistic_Para]

You identify yourself as being in NV, but didn't mention whether your new home is also being built in NV.

If we are talking about the Pacific Northwest, where rain and clouds are frequent, I would say the biggest battery bank you could fit, there's no telling how many days you'd need to live off that before the panels could recharge it.

In a desert environment, with sun nearly every day, that becomes much less important.

Also, while battery weight can be significant in a rig that does a lot of driving, if you're just going to park it at your building site, weight becomes much less important.

Finally, if you're building your home yourself, and need to power saws and drills and a compressor to run an air nailer, then obviously you need the biggest bank you can find. And maybe a generator.

[Lwiddis]

“What I am wondering is how big are most battery banks ?”

IMO battery banks should be commensurate with your average daily use times 1.5. Of course if you want to play around...

[time2roll]

600 or 800 is fine. Go with 600 and if you need more then add it.

[pianotuna]

Since you have the batteries, I would go with two banks of 400 amp-hours each. Install the banks opposite each other to help with weight distribution.

Two banks will simplify doing equalization charging. Be sure to wire each bank in a balanced manner.

If I were starting over, I'd jump right to a 48 volt bank--but that may not work with the existing solar panel array. For panels in series it is needful to have the amperage the same on each and every panel.

I'm glad your Aims is hanging in there and meeting your needs.

[GordonThree]

Are you married to 12v? It gets rather hard to manage large kWh battery banks at such a low voltage.

Off the cuff, install the largest bank you can afford and have room for. No such thing as overkill when it comes to capacity, as long as weight is not an issue. All this lead will have a big impact on your CCC.