Help with understanding a new setup

Need information...

I have a new 400w system with an MPPT40CC controller (KIT-COMPLETE400D-40MPPT), 1000w inverter, and a MT-5 meter hooked up to four brand new Trojan T-105RE 6v batteries (2 in series, then 2 parallel strings) in a 12 volt configuration. I have the four 100w panels all connected in series and then to the MPPT.

All the cabling came with the kit except for four new one foot 2/0 AWG battery cables used to interconnect the batteries.

I connected everything following the instructions that came with the kit (MPPT to batteries, then to panels, then meter) and everything seems/seemed to be working as expected. I also set the MPPT up for flooded batteries and set the AH to 450 (225 x 2 based on the 20hr rating of the two parallel 12v strings).

I have not connect up the 1000w inverter that came with the kit. Nothing is connected to the load terminals of the MPPT.

I did this at home prior to taking it all to my remote cabin for installation, just to make sure it all works...

I did this at about 2pm in the greater Sacramento area (still plenty of sun for many hours). Right after hook up the meter showed a SOC of about 70%. I watched it for awhile and it bounced around from between 62%-70% so I figured I'd head inside and let it do its thing (checking on it once or twice over the next hour or so).

At 7:30-7:45 (sunset) I went back outside to check on the charge state and low and behold the meter showed a SOC of 48%. WTH?

The meter currently (8:30pm) shows 12.7v and 47% SOC and -03 m/V when set to show battery information. I also thought 12.7v was a fully charged battery?

So I disconnected the solar panels as I am concerned they're drawing down power (they shouldn't but maybe a diode has failed?).

With that background information can someone help me understand what's going on? I'm a noob with this stuff so maybe this is normal when a MPPT controller is first connected to a set of new batteries (it's "learning" about the batteries?).

Is it likely that I have damaged batteries (they're new and from a reputable dealer).

Do they come with a low initial charge and the initial reading of 70% was misleading information on the high side (it actually seemed low to me).

Is it because I have the four panels wired in series and that high voltage input is confusing the SOC calc on the MPPT?

Help! I'm freaking out a bit and not being experienced (yet) with off grid solar systems I really don't know if this is "normal" or if I should be concerned...

Thanks in advance for any helpful feedback.

I've read from various sources around the Internet (Amazon questions/reviews for the product, for example) that the SOC reading is often inaccurate and should not be relied upon as an accurate measure of battery state. Personally, I'd go by the bank resting voltage level with no load/charge applied. Anything else (besides performing a specific gravity test on the cells) is inherently an estimate at best.

One thought comes to mind as to what might be going on: Your batteries needed a period of time to equalize amongst themselves. Even two identical batteries manufactured at exactly the same time have slightly different characteristics, state of charge, etc. Connecting any two batteries in parallel will cause one battery at a greater state of charge to empty into the one of lesser charge level until the two reach equilibrium. Perhaps the controller saw the initial state and then settled on a lower number after this occurred?

it was explained to me that the SOC "State of Charge" is what the panels are currently giving to the charger, when you look at it. This reading will differ through the day but should not be taken as battery level.

Thanks for the feedback. I've sent a question to tech support to hopefully get info on how to force an equalizing charge using the controller. From the items I researched I agree that the SOC shown is a SWAG more or less, but I've also seen info that suggests an equalizing charge cycle will let the controller "get to a 100% state" so it can recalibrate the SOC reading. I'll post what info I find, and if anyone else has additional info feel free to post it here.

One thing I must say is that the doco provided with the equipment I purchased in very minimal (so is the download version). It basically identifies things that are displayed but has no info on why an indicated reading is good or bad or why a configuration parameter should be set to accomplish a purpose. I like what I purchased, but it seems that there's a gap in describing how to configure and/or understand the information that is displayed (or configuration settings).

The feedback from Tech Support is that there is no way to force an equalizing charge on their MPPT controllers.

I can't say that I'm particularly happy about the fact that the SOC indicator is basically completely useless.

The SOC numbers I'm getting day to day on my set up are showing changes from the low 40% SOC to the mid 90% SOC in a single day. And, this is on a set of brand new Trojan T105RE's with no load on them at all. During the day the controller shows a blinking green light indicating an overcharged state (my volt meter shows 13.35v at the battery terminal), and by mid evening it's back to a solid green light (volt meter shows 12.75v at the battery terminal), and an SOC showing 40%-50%.

I've sent an additional note to Tech Support asking if this is considered "normal" as I would expect the controller to limit the voltage being sent to the batteries if they are fully charged. I believe a resting voltage on these new batteries of 12.75v is considered fully charged, so I don't get why the controller is continuing to pump in volts creating the overcharge condition. If my batteries get cooked I'll be a very unhappy customer.

I just hope it turns out it's the idiot end user (me) and not a fault with the MPPT controller. Or, if it is the controller, and it's faulty, Renogy replaces it ASAP before my batteries are affected. So far I've heard nothing back from the Tech Support folks on my second set of questions.

Madmacks, which exact light on the controller is flashing green during the day?

If it's the charging indicator light (flashing green), that indicates a battery-over-voltage condition according to the manual.  That's a problem and should be looked into.

But if it's the battery indicator light (flashing green), that indicates a full battery and is perfectly normal.

So, why apply voltage/current to a full battery you ask? Because even when a battery is full and no load is being drawn from it, it will self-discharge. From the manual:

"After the Boost voltage stage, MPPT40CC will reduce the battery voltage to float
voltage set point. When the battery is fully recharged, there will be no more
chemical reactions and all the charge current transforms into heat and gas at this
point. The controller reduces the voltage to the floating stage, charging with a
smaller voltage and current. It will reduce the temperature of battery and prevent
gassing, but charging the battery slightly at the same time. The purpose of Float
stage is to offset the power consumption caused by self-consumption and small
loads in the whole system, while maintaining full battery storage capacity."

Naturally, the battery voltage will be higher then the 12.7V resting voltage whenever any kind of charging is occurring. Hope that puts your mind at ease.

I have a blue sea battery switch: 1 and 2 and all, and off. Can I switch the battery switch on my boat, or should I put an inline switch to shut the s.panel power off when switching between 1 and 2, battery banks.

Thanks

Hello Dean,
I would recommend doing just that to safely switch between battery banks.
O.C

I wanted to revive this thread in case is helps anyone else. I experience the same fluctuation that madmacks describes above, and it appears that the SOC fluctuates depending on the charge phase, which still makes it inaccurate. My guess is that when the CC is charging in bulk or boost, it can get the SOC to show 100% relatively quickly, but when it switches to a float charge, that's when the SOC drops down to around 50%-60%, then slowly climbs back up again while in float to where the battery is actually full. I've read that voltage at rest is really the best measure of current capacity as stated above, so maybe reading the SOC on the meter when not charging is a better practice.

What wires do I need to buy for my Renogy Cabin kit? (12 v)

hi Suzette, what's missing? what kit?

best to start a new thread and ask in the new thread including details.