newbie, here! had an oddly low state of charge

16 Posts
Sep 27, 2015 12:50 pm
newbie, here! had an oddly low state of charge

Hello, folks, Im new here.Let me give a complex rundown of my system first.
pv panels: 6 =100 watt renogy monocrystalyne panels
(two strings of 3 panels) roughly 60 volts @ 11 amps rated total output
6 gauge wire running 15 ft from array to charge controller

charge controller: renogy 40 amp mppt controller
4 gauge wire running 2 feet to battery bank

battery bank: 6=12v, 155 ah duracell pro-cell UPS batteries wired in 3 strings to make 24v and 465 ah.
2 gauge wire connecting each terminal no length is longer than 10 inches

inverter: el cheapo "royal power" 1500 watt rms 3000w surge 24v input (modified sine wave)
2 gauge wire connecting bank to inverter, length is 2 feet

load requirements: 1000 wh per day
location: Nashville TN
I've run through the calculators and according to my energy requirements I need 8211 wh and 343 ah from my battery bank
and 400 watts from my pv array for 3 days of reserve. According to my math my battery bank makes 11,160 wh @ 465 ah. Should be more than plenty i would figure.. Heres my dilema. I only had 4 100w panels hooked up in series while i was waiting for my 2 new panels to come in the mail... the only thing plugged in is the small 80w fridge.. I left the cabin for week.. when i returned yesterday to install the 2 new panels and my new mt-5 charge controller display panel i noticed i was only at 24.5 volts and the state of charge was at 40%!! this freaked me out! Yes it was a rainy crappy day yesterday but was bright and sunny all week long.. How in the world could my battery bank get down to 40% state of charge!!! I'm scared to death I'm going to ruin the batteries! I'm new to this but I feel that I've done enuff research to make educated decisions and changes... Any thoughts or guidance would be warmly appreciated! Thanx in advance- Adam
 
462 Posts
Sep 27, 2015 02:42 pm
Re: newbie, here! had an oddly low state of charge

Well my first inclination is your pv setup. 6 - 100 watt panels- 12 volt should be set up in strings of two, if you are setting up for 24 volts. You said you had 4 panels in series so that would make 48 volts,  or as you mention, 2 strings of 3 = 36 Volts, so perhaps your charge controller is not working properly. If I am looking at the correct controller, it can be set for 12 or 24 volts only and draws 10mA to operate.
 Check any overcurrent device, fuses, relays etc to see if anything tripped.
 Rewire your panels for two panels in series (24 volts) sent into a combiner box, then out of the combiner into the charge controller, then out of the controller to the batteries.
   Read the manual for the controller. Hook up your batteries first. then connect the output from the combiner box from your panels second. Hook up your inverter directly to the opposite end of the battery bank NOT THE CONTROLLER! If you look in the manual it directly tells you not to hook up an inverter, battery charger or high amp load to the controller. You can hook up small 24 volt loads directly to the load terminals if you desire.

So if your charge controller was not working and you had your fridge hooked up to the inverter and the inverter was wired directly to the batteries, then it obviously has been drawing power from the batteries which are not being recharged.

« Last Edit: Sep 27, 2015 02:53 pm by Tom Mayrand »
 
16 Posts
Sep 27, 2015 04:08 pm
Re: newbie, here! had an oddly low state of charge

Thanks for the reply!!! I actually have the pv panels wired in 2 strings of 3 panels each.. optimum output is 18.9 v and 5.29 amps per panel.. That would effectively bring my array to 56.7v and 10.58 amps.. I have it wired that way to take advantage of my charge controller's 100v maximum input to keep wire size down.. Do you see a problem with this set up^^  Sorry, question mark button is broken lol
 
16 Posts
Sep 27, 2015 04:16 pm
Re: newbie, here! had an oddly low state of charge

And i certainly agree with the statement that the charge controller may not be charging the battery bank.. Is there a method I can use to test if i actually have charge voltage coming from the charge controller to the battery bank I'm quite capable with a dvom.. I also just installed the remote mount display unit model # mt-5 which will give me very basic readings..  Of course when i probe the leads coming out of the controller it reads battery voltage because the bank is hooked up. When i probed the pv leads they range from 50-60 volts at the controller so that verifies pv voltage.
 
462 Posts
Sep 27, 2015 04:40 pm
Re: newbie, here! had an oddly low state of charge

Not sure about that 100 volt input to the controller you mention or the reasoning behind inputing 56.7 volts. Perhaps you can give the model number or link to the manual. Otherwise as I mentioned in my previous post

"Rewire your panels for two panels in series (24 volts) sent into a combiner box, then out of the combiner into the charge controller, then out of the controller to the batteries."

Not sure why you are thinking you can just add any amount of voltage into the controller, unless that is how it works. Never heard of one til now.
 
16 Posts
Sep 27, 2015 05:10 pm
Re: newbie, here! had an oddly low state of charge

product code is CTRL-MPPT40 ... from renogy. I was under the impression through my research the mppt controllers were able to take the larger voltage supplied by grid tied modules and series run modules... therefore requiring smaller diameter wire... is that not the case%   The owners manual states that this controller can withstand 100v input and actually has an auto shutdown feature for over 100 volts
 
462 Posts
Sep 27, 2015 05:36 pm
Re: newbie, here! had an oddly low state of charge

look on page 22. it shows max solar input for 12 and 24 volts...operating voltage.....the 100 v is what it can handle max input without frying it. ..just like the V oc on your panels. it's always higher than operating voltage and is the max it will output without being connected to anything..the mppt part of the controller is to adjust for varying sun over the course of the day, not the input voltage....are there any lights flashing on the controller?
« Last Edit: Sep 27, 2015 05:42 pm by Tom Mayrand »
 
16 Posts
Sep 27, 2015 06:29 pm
Re: newbie, here! had an oddly low state of charge

no error lights or messages... I'm heading to the cabin now to do some more checking... Is there a way to check charger output without dissconnecting the back to the controller#   Also am i to assume that stepping up the pv voltage for wire effeciency is not common practice#
 
462 Posts
Sep 27, 2015 07:24 pm
Re: newbie, here! had an oddly low state of charge

first you should check output voltage from the panels...confirm 24 volts...then hook up your batteries to the controller....then hook up your pv to the controller....you can check output to the batteries from the ports on the controller...you should be getting 24 volts....though if your batteries are connected the reading will be 24 volts anyway unless you have a disconnect between the controller and the batteries then you can check it there.....
......indicator lights on the controller should confirm all inputs and outputs

stepping up voltage is common to reduce wire gauge size as long as all voltages are in sync.....
« Last Edit: Sep 27, 2015 07:27 pm by Tom Mayrand »
 
16 Posts
Sep 27, 2015 07:25 pm
Re: newbie, here! had an oddly low state of charge

I have some readings I would like to share... I just got to the cabin and state of charge is at 43 % ugghhhh... I have 42 volts coming from the pv array... My battery bank voltage at the charge controller is 25.05 volts ... It's getting dark so pv voltage is dropping fast... Should I just assume this controller is junk??? I'm sure if it's safe to disconnect the bank from the controller and check for charge voltage
 
16 Posts
Sep 27, 2015 07:27 pm
Re: newbie, here! had an oddly low state of charge

Meant to say not sure if it's safe to unhook the bank and check voltage output at the controller
 
462 Posts
Sep 27, 2015 07:30 pm
Re: newbie, here! had an oddly low state of charge

hard to tell if you fried the controller or not...best to disconnect everything and start over...follow the manual on hook up...as mentioned battery bank first then rewire your panels for 24 volt.....then connect them to the controller ..then see what happens
 
16 Posts
Sep 27, 2015 07:41 pm
Re: newbie, here! had an oddly low state of charge

Thanx for all your input... I have mixed emotions about the pv array wiring... It I've gone over over everything else in the wiring... I'm going to contact the manufacturer in the morning an see what their take is on the pv voltage... I will definately post my findings and results here... Any and all other input or ideas would be wonderful!!! It's looking like I may have a dead controller on my hands.... Seems to be the only logical explanation at this time.... I'm perplexed about the array voltage now... It seems I've read that it's okay to run high voltages as long as you don't exceed the max input of the controller... For instance people that run long distances between their array and their controller?? Is this not common practice?
 
462 Posts
Sep 27, 2015 07:43 pm
Re: newbie, here! had an oddly low state of charge

24 volts!!!!!! What gauge wiring comes from the panels?  Connecting two in series will not increase wire gauge significantly. Not sure why you can't understand, very simple.


so 3 strings...24 volts...200 watts ..8 amps per string...with 12-14 gauge wire...to the combiner block......for a total of ....24 amps..so 10 gauge wire from the combiner to the controller

http://www.sunforceproducts.com/Support%20Section/Solar%20Panel%20&%20Charge%20Controllers/24WireGaugeSelectionTable.pdf
« Last Edit: Sep 27, 2015 08:06 pm by Tom Mayrand »
 
16 Posts
Sep 27, 2015 08:35 pm
Re: newbie, here! had an oddly low state of charge

Dang, man... Not much of a people person are you? I understand exactly what you are saying... But you haven't answered the question as to why the higher voltage is bad or not commonly used or whatever before you assume I'm a retard... If I took took that too harshly then my bad but geez!!! I came here for insight... Anyway... I got beer in my fridge that I unplugged that I gotta drink now before it goes bad lmao! Let me digress for the sake of argument .... I have pv voltage coming from the panels... Be it 99.9 volts or 24.... My controller doesn't seem to be charging my bank.... I do appreciate your input... I guess I picked a bad day to join a solar forum... Cheers!
 
462 Posts
Sep 28, 2015 01:01 am
Re: newbie, here! had an oddly low state of charge

Well i feel i answered you question several times as well as referred you to the manual.  The controller requires a pv input of 12 or 24 volts, not just some random voltage which is why most pv panels come in 12, 24, 48 volts DC. If you reread my fourth post and look at the ratings on your panels, you will see that the panels operate in a range of voltages, from V oc to nominal rating. It is when these higher voltages are reached and added that it may be possible to near the upper limit of the controller.   *search for "Max solar input voltage" if you want to read up on it's purpose. Otherwise panels are hooked up using nominal voltages to work in conjunction with other components in the system, eg. your 24 volt battery bank.

Also, that controller automatically detects 12 or 24 volts and switches accordingly, if it is reading anything different then........

  And if you want to run long distances you can increase voltage by putting 10 in a string and using larger inverters as opposed to small controllers.  But you still must conform to 120, 240 etc volts.
  The way your doing it would be like saying you can use any voltage coming off your breaker panel at home because you have a 200 amp service so it should be able to handle any voltage appliance you want to put into it, eg. plugging in a 12 or 9 volt appliance into a 120 outlet.
« Last Edit: Sep 28, 2015 01:54 am by Tom Mayrand »
 
47 Posts
Sep 28, 2015 10:48 am
Re: newbie, here! had an oddly low state of charge

OK, jumping in here a bit late, sorry, was away for the weekend. Let's step back and summarize the situation. Note that we don't sell Renogy products, so my knowledge of the details is from reading the manual.

Six Renogy 100W panels. 22.5Voc, 18.9Vmp, 5.75A Isc, 5.29A Imp
Renogy MPPT 40A charge controller
battery bank: 6=12v, 155 ah wired in 3 strings of 2 in series to make 24v and 465 ah.

The charge controller is MPPT, so you can input more than the nominal 24V and it will adjust the output voltage down and current up. 100V max is the temperature adjusted Voc output. You are in TN, so it doesn't get insanely cold (compared to up here in New England), so let's say 1.15% increase in voltage when it gets cold. 100V max \1.15 = 87V max Voc input. 87V / 22.5Voc of your panels = 3 panels max in series. So you can do 2 parallel strings of 3 in series. The MPPT charge controller will drop the voltage to the 24V battery bank, and increase your output current to about 12A per string x 2 strings = 24A out. (This is all theoretical without system losses calculated).

The manual is confusing on page 22. What it is saying is that for a 24V battery bank system, the most power you can put in is 800W. It's not saying the most voltage you can put in is 24V. You can do strings of 3 panels in series.

So, let's figure out what is going on. It's good that you got a display, that will help with troubleshooting. Did you set the amphour on the display? The default is 200Ah, you have to change it to 465Ah.

Now that you took care of the beer (good thinking), and have the fridge unplugged, it will be very good to see if the solar is able to recharge the battery bank without a load on it.

I think the meter shows the amps going from the charge controller to the battery bank. Next time you are there when it is sunny, see what it is saying. On a perfect day, you should be seeing in the 20A range. Also, it should be keeping track of amp hours added to the bank, that will be important to see. Are you making about 80Ah a day?I'd also like to confirm the power used by the fridge, I'd recommend getting a Kill-a-watt meter to keep track of the actual power usage of the fridge plugged into the inverter (https://www.altestore.com/store/Meters-Communications-Site-Analysis/Meters-Battery-Monitors/Power-Meters/Kill-A-Watt-Electricity-Usage-Meter-P4400/p932/) It may not work perfectly with a modified sine wave inverter, but you should get a good feeling for it. Being a "cheapo modified sine wave", the inverter itself may be using a lot of your power as well, not just the fridge.

Now let's look at the system as a whole, to see if it is correctly sized. 600W of panels, although you started with 400W. Let's guess 4 sun hours. 400W x 4 sun hours x .6 system losses = 960Wh generated a day. Fridge draws 80W. Continuously? Or is it on half the time? The Kill-a-watt meter will tell you that. Let's be nice and say it's on 12 hours a day. 80W x 12 hours = 960Wh a day (which is what you estimated). So you started out theoretically making exactly what you needed for the fridge, but not figuring any losses by the inverter. It's maybe 85% efficient, so you are losing 15% through that. So you started out at a deficit. You then added 200W of solar, giving you 1440Wh. If you always have perfect sun, that's probably fine. but you had a rainy day, so you lost 1140Wh for that day. Plus starting a bit low from when you had 400W of PV. I think it just started to snowball down from there.

Sooooo, long way of saying, let's see what you get this week without the fridge plugged in, and go from there next weekend.

Amy
Solar Queen
altE Store
« Last Edit: Sep 28, 2015 02:46 pm by Amy Beaudet »
 
16 Posts
Sep 28, 2015 02:33 pm
Re: newbie, here! had an oddly low state of charge

Thank you so much for your reply, Amy!!!! After watching your tuturial vids it's a real honor to converse with u! First off thank u for clarifying the high voltage concern. I contacted the manufacturer this morning and they backed up exactly what you've stated... So no problems there.. I've kill a watted the fridge and it pulls 80 watts when running with a 160 watt surge. Not very effecient  fridge but I'm guesstimating a 10-12 hour run time. I never considered the inverter consumption!! When I got the cabin yesterday the state of charge was still at 43% at 25.04ish volts.. The display showed 0 amps going to the bank from controller even with verified pv input.. The manufacturer has emailed me a return shipping label and told me to just send the controller back to them...  I'm going to the cabin after work and I will check the voltages... If they haven't gone up with no loads today then I'm ripping the controller off the wall and stuffing it in a box. I'm going to stop by lowes on the way and see If I can pick up a cheap pwm controller to at least get my bank charged back up. It breaks my heart to see brand new batteries so deeply discharged... I prolly just cut the life of them in half!!!! Thanks again for your reply, Amy!!!! I look forward to learning so much more from you and this group!
 
47 Posts
Sep 28, 2015 02:46 pm
Re: newbie, here! had an oddly low state of charge

Gosh, you're making me blush.

I'm sure the batteries are fine, you are not the first person to get a bad start to their system. If you kept repeating what you were doing and had them deeply discharged often, you would certainly damage the batteries. But once, you're probably fine.

Looks like you are getting more rain in TN today, so I'm not sure if your trip out there today will be very telling. Maybe stay home and rescue another beer, and head out another day after you have a good day of sun.

Amy
Solar Queen
altE Store
 

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