Battery Bank - AGM

[HARG Hunter]

I continue to build my system and make adjustments as I go.

Looking for advice on setting up my battery bank to fit best with the rest of my system.

Current Set-Up:
*300 watts of panels (3 - 100 Watt Renogy Panels in parallel) 21.6 VOC
*Renogy Rover Elite 20A MPPT Charge Controller
*Battery Bank: (1) Universal Power 100ah AGM, (3) Mighty Max 30ah AGM (Wired in parallel)
*Stanley 1000 watt Modified Inverter (I know I need to upgrade this for sure)
*The most we expect to use is approx 1200-1300 watts per day, so our system is a little short right now but close to being up to the task.

We are in a wooded area where the panels only get 3-4 hours of really solid sun. I've taken down most trees, but I do get small bits of shade across the array occasionally which is why I have them in parallel instead of series. I may buy a 4th panel and go 2p2s with them to send more to the charge controller.

I've read in a few places that wiring more than 3 batteries in parallel isn't good as there is some loss there. Thoughts?
If I decide to go with 2s2p (Bringing me to a 24v system), is it OK that I have 1 at 100ah and the others at 30ah each, or do I need to balance the battery bank out somehow?

If I do go that direction, I would most likely add 1 panel, add 1 battery (100ah), upgrade to a 30a or 40a controller and go to a 1000-1200 watt Pure Sine Inverter.

That would give me this system:
*400w in Panels (2s2p)
*30a MPPT Controller
*130 ah in Batteries (100ah+30ah in parallel wired in series with another 100ah+30ah in parallel) Gives me 24v/130ah correct?

I know I've posted a lot of stuff in different areas of the forum.
The reason I'm posting it here is my main concern that my current configuration of batteries is hurting my system.
I've got 100ah+30ah+30ah+30ah wired in parallel at the moment.
Idea was that if we need approx. 1200 watts per day, this bank would come to close to giving us that (190ah total, with 95ah usable giving us 1140 of usable wattage).

I do have a constrained budget. In the end, I'll spend what I have to, to get the system where it needs to be. Hoping for some advice on how to get this system to where it needs to be piece by piece. I can't buy what I need to upgrade everything right away.

OK - Tear it apart and give me your opinions!

 

[snoobler]

24V will not improve and may worsen any potential battery mixing issues.

Note that the resources you reference would also likely completely poo poo the concept of paralleling dissimilar capacity batteries as a "definitely do not do." But we're acknowledging the budget constraint - deliberately do less than optimal because money is an issue.

The 6-8awg wire you have connecting them is likely the bigger issue when your loads are high (coffee pot). Generally, parallel battery interconnects need to be pretty beefy to insure even current flow through each battery, and they need to be connected optimally (see "wiring" in link #2 below). However, given your typical low usage, they may not be a major concern.

Your issue appears to be very poor location for solar. 3-4 hours of unshaded production is not good. Numbers you see thrown around here are based on an entire day of unshaded production.

Get that $45 battery monitor from the other thread and start logging some data. Data will tell you what this system needs, or it will tell you that you're fine.

 

[Hedges]

Rover Li 20 Amp MPPT Solar Charge Controller

Check out Renogy's Rover 20 Amp MPPT Solar Charge Controller. With its advanced MPPT charging technology, your batteries will be protected from discharging and over-charging. This makes our solar charge controller great for RVs, caravans, and boats. Free Shipping!

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PV Input Voltage Range : 15V – 100V VOC
Hard to believe 15V for MPPT operation when battery need to charge up to 15V or so.

PV panels are probably 17Vmp under STC conditions, could be less on a hot day.
Possibly 1s3p is too low a voltage.
3s1p is within range. Shading is not an issue, that is what by pass diodes are for. All panels would need same orienation.

2s2p sounds good. 34Vmp, 43Voc. 400W in, 20A at 12 to 15V = 240 to 300W out.
Orient one string of 2 panels one direction (morning sun), the other afternoon sun. Peak is 0.7 as high, 280W STC, good fit with charge controller.

Looks good for 12V. No need for new charge controller.

If you go 24V, still no need for charge controller.
I think 2 panels in series is too low. Go 3s1p or 3s2p.
You have 3 panels. See if you can get one panel that is 65 Voc, a "36V" panel. Could be anything 250W to 500W. Put in parallel with the (3, 100W 12V panels that are in series.)
With 600W to 800W (STC) of panels, not so hard to generate 1500 Wh/day to make up for efficiency losses.

1000W to 1200W inverter - are those even 24V? If 12V, they draw about 100A.

Mixing new and old batteries can be a problem. Assuming existing aren't terribly old,
rather than (100 ah || 30 ah) connected in series with (100 ah || 30 ah), I would do:
(100 ah series with 100 ah) || (30 ah series with 30 ah)

Do your batteries get drained overnight? Even though they started out fully charged the previous day?
You say 1200 watts (watt hours) per day. Is that 600 Wh at night?
Just two, 12V 100 Ah batteries is 2400 Wh. 600 Wh is 25% DoD over night.
Two in parallel should be fine.

 

[HARG Hunter]

Your issue appears to be very poor location for solar. 3-4 hours of unshaded production is not good. Numbers you see thrown around here are based on an entire day of unshaded production.

I do believe this is my biggest issue.
Thinking that maybe adding more panels first to get the most out of the few hours we get would be good.
The "mix" of batteries as far as age isn't an issue. They are all within a few months of each other, and only about 5 months old.

 

[HARG Hunter]

Rover Li 20 Amp MPPT Solar Charge Controller

Check out Renogy's Rover 20 Amp MPPT Solar Charge Controller. With its advanced MPPT charging technology, your batteries will be protected from discharging and over-charging. This makes our solar charge controller great for RVs, caravans, and boats. Free Shipping!

www.renogy.com

Do your batteries get drained overnight? Even though they started out fully charged the previous day?
You say 1200 watts (watt hours) per day. Is that 600 Wh at night?
Just two, 12V 100 Ah batteries is 2400 Wh. 600 Wh is 25% DoD over night.
Two in parallel should be fine.

When I get to the cabin after not being there for a week or 2, the battery bank is usually sitting at 13.1 max, and there is no draw while we're gone at all. I even disconnect the inverter.

Wondering if the 4 batteries all being wired in parallel is hindering the charging somehow.

All of the batteries range from only being 3 to 5 months old, so they aren't really mixed that bad.

The 1200 watts I mentioned we use is rare. We typically are only running 3-4 LED lights (5-6wea) and charging a few phones.
At night we might watch the TV for a couple of hours (40 wh)

Seems the bank never really reaches is max to begin with, so when we start using it, it drains quickly.

 

[snoobler]

13.1-ish is normal. They should charge to 14.X and hold for a bit. Once current drops to a certain level, they enter "float" mode where the batteries are held at full charge. This varies, but is typically 13.2-13.6V.

Care to give your charge controller settings?

It doesn't take much to pull the voltage down into the mid-12s, which is pretty normal if you don't have much solar to keep them floated.

As a reference point, if you were to disconnect your batteries and just let them sit for 24 hours, they'd drop to about 12.8V.

Methinks you really need that battery monitor.

 

[HARG Hunter]

13.1-ish is normal. They should charge to 14.X and hold for a bit. Once current drops to a certain level, they enter "float" mode where the batteries are held at full charge. This varies, but is typically 13.2-13.6V.

Care to give your charge controller settings?

It doesn't take much to pull the voltage down into the mid-12s, which is pretty normal if you don't have much solar to keep them floated.

As a reference point, if you were to disconnect your batteries and just let them sit for 24 hours, they'd drop to about 12.8V.

Methinks you really need that battery monitor.

Methinks you're right so I can get a handle on the data. Tough to monitor it close when I am only there for a couple of days then leave for 2 weeks at a time.

The only setting I really had to worry about was the battery type.
I wasn't instructed to do any other programming on that charge controller.

Here's the link to the manual.

Maybe I'm missing something:

Also, it could be that my timing just sucks.
Last weekend when I got there, the bank was at 13.1, but it was cloudy pretty much all day, so even though we didn't use much of a load, it wouldn't take long to drain it without the panels sending anything to replenish.

The next morning before I left, when it was 10am, the sun was hitting the panels 100% and it jumped up pretty quick.
That's what started my questioning of the way my battery bank is set up.
Are 4 batteries in parallel too much? If so, I could disconnect one of the (3) 30ah batteries to reduce the bank down to only 3 batteries. Wouldn't hurt the overall storage that much.

 

[snoobler]

You should note your battery voltage first thing in the morning before solar charging to get a feel for the level of charge.

You should see it rise during the morning and peak at 14.6V (boost) followed by a drop to 13.8V (float). If you have sufficient solar, it should hold 13.8V and supply loads. If not, it will drop below 13.8V.

 

[HARG Hunter]

I think I may have found another variable that can improve my system.
I currently have everything hooked up to the same battery.
Meaning...Charge Controller, Inverter, and even the DC water pressure pump.

After doing more research, I feel I need to switch up the cabling for equalization.
Positives to 1 battery and negatives to another, with the other batteries in between.

Are there diagrams somewhere that show the best way to wire up the battery bank?

 

[snoobler]

"Wiring" link in link #2 of my signature. A portion of that document shows optimal ways to connect batteries. In the case of multiple parallel batteries, you'd attach one lead to the (+) on an end battery and the (-) lead to the (-) terminal of the battery at the other end.

In your case, it's unlikely to do anything meaningful that you can observe, but it will likely give a small improvement in the long term health of the batteries by more evenly distributing the load.

 

[Bob142]

I've often wondered about situations like this where the batteries are significantly dissimilar in capacity so I'm going to throw this out there because of who's on this thread.

Thoughts on arranging like this, with beefy short cables/busbars for the 30Ah parallel group?:


To make it look logically like these two batteries?:



Or is the resistance between the 30Ah batteries w/the interconnects too great and it's a waste of time etc.? I'm just wondering if treating the 3 30Ah batteries as a unit might even out some of the wear issues.

 

[HARG Hunter]

I've often wondered about situations like this where the batteries are significantly dissimilar in capacity so I'm going to throw this out there because of who's on this thread.

Thoughts on arranging like this, with beefy short cables/busbars for the 30Ah parallel group?:
View attachment 29864

To make it look logically like these two batteries?:

View attachment 29865

Or is the resistance between the 30Ah batteries w/the interconnects too great and it's a waste of time etc.? I'm just wondering if treating the 3 30Ah batteries as a unit might even out some of the wear issues.

I will be heading to the cabin Monday morning and the first thing I'll do is set it up like this. It was exactly what I was thinking, and this confirms it. We'll see how the performance changes.

 

[Bob142]

I will be heading to the cabin Monday morning and the first thing I'll do is set it up like this. It was exactly what I was thinking, and this confirms it. We'll see how the performance changes.

Not sure you can consider my input as confirmation, but it seemed logical to me. I'm interested to see if you notice any improvements.

@snoobler, @Hedges: thoughts on the arrangement above?

 

[Hedges]

How about loading the different capacity strings/battery independently, determine their internal resistance. Or at what voltage they deliver similar "C" rate, percentage of capacity.
Then design interconnect resistance to match them.

Or, just use two of the 100A batteries for this setup, and the 30A for a portable setup?

Likely the 3, 30AH in parallel are lower resistance than the one, 100 AH because all use lead as internal conductors.

 

[snoobler]

@Bob142 I don't hate it, and the concept is valid.

@Hedges presents the correct approach in analyzing the circuit and designing accordingly. He also makes a good point about the 3 30Ah in parallel having lower resisistance vs. the 100Ah, so they will naturally shift the load to the 100ah.

In retrospect this is probably a "picking fly turds out of pepper" situation due to the typical low draw. The only time it matters is when the coffee pot is running. Having both leads to the 100Ah battery in the current configuration probably doesn't have a measurable downside except for long term health... maybe knock 6 months of a 5 year life span (purely speculative).

I think it's more important to make sure the batteries are being charged correctly with sufficient solar before any changes are made.

 

[HARG Hunter]

Heading up in the morning tomorrow.
Going to try a few things, but unfortunately the forecast doesn't promise a lot of sun for me the next few days.

Going to try the different wiring options discussed above, and also may wire the panels in series to get a boost in current to the CC.

I also just bought some new cable for the batteries.
I think I under-gauged my cables. Got 2ga for battery-to-battery and will use the 4ga I have for battery-to-inverter.
I fell like I need to "clean up" my system a little bit.
All of this little things are adding up to a lot of inefficiency I think.

Thanks for everyone's input.
I'll let you guys know my results.

 

[snoobler]

We're at the ranch this weekend... 9°F this morning, but we have plenty of sun. 3kW array is pulling 2.2+ 2 hours before peak sun.

The beefy interconnects are a great idea. I would caution that you're probably not going to see much difference, but these steps should extend the life of your batteries. I would encourage you to try and pay attention to the charge cycle and confirm that you're getting to the 14.X voltage and dropping to float to confirm that you're getting fully charged (sun permitting).

 

[HARG Hunter]

Just arrived. 9 am CST
See photos of sun situation and SCC report.

Going to rewire the battery setup, then keep an eye on it. Might let it go as is until noon, then change the 3 panels to series instead of parallel.

 

[HARG Hunter]

Photos

 

[HARG Hunter]

I feel much better. I haven't touched anything yet, and the batteries are up to 14.5v

I think I was just impatient and had bad timing last time I was here. Stil going to rewire everything to balance the batteries, but I'm going to leave the panels in parallel so I can get power even in semi-shady conditions.