New to Pv, looking for advice

[kf4hzu]

Hello all,

About a year ago I purchased my first Pv setup. It consisted of a Renogy 100W Monocrystalline panel and their "30A" PWM charge controller (which I found out later only handles ~300W @ 12V). I also bought one Power Patrol (Interstate Batteries) SLA1165 12V 55AH AGM battery. I had a few small inverters already so I used one of them to run a laptop or two off the system. I mounted the panel on my back patio roof and bought some 8AWG Pv cable (50ft) to connect it up to the charge controller inside. I was trying to spread out the cost of the system I wanted to build by buying this setup first. I eventually bought more of the SLA1165 batteries for a total of 4. I found out after noticing some problems and doing some research that this was not a good idea. At first the system worked fine, but the 4 batteries in parallel eventually got unbalanced.

Today I have a MidNite Classic 150 with 3 of the Renogy 100W panels in series. I've purchased a Samlex 2KW pure sine wave inverter (SSW200012A) for large temporary loads, and a Go Power 175W modified sine wave inverter (GP-175) for small continuous loads. The 2KW inverter doesn't get a lot of use, just short duration loads just to get some time out of it. It is intended for power outages only. The 175W is always on and usually has laptops or other small electronics connected to it. I actually just bought a 2nd one since they are very efficient and have a surprisingly low idle power utilization. I've made several other improvements and started putting in more safety equipment as I've learned what is needed.

Before I get to my questions, this is what the system looks like now, starting from the roof:
Renogy 100W panel, 22.5Voc, 5.75Isc - 3 in series
50ft, 8AWG Cu, Pv cable
1000V 20A in-line fuses (one on each Pv conductor)
MidNite Classic 150
2ft, 6AWG Cu, welding cable with PP75 connector
2ft, 6AWG Cu, welding cable with PP75 connector and 32V 80A in-line AGU fuses (one on each conductor)
Wire combining blocks (7 screw-down connections)
1ft, 4AWG Cu, welding cable to each battery with crimped-on rings
-------------------(Also connected to wire combining blocks)--------------
2ft, 1/0AWG Cu, welding cable with SB350 connector and 32V 250A in-line ANL fuses (one on each conductor)
1ft, 1/0AWG Cu, welding cable with SB350 connector, connected with rings to 2KW Inverter
-----
3ft, 6AWG Cu, welding cable with PP75 connector and 32V 100A in-line AGU fuses (one on each conductor)
PP75(1) to PP45(4) adapter, PP45 and PP30 can connect.
(several devices connected using PP30 connectors, including 175W inverter, with their own fuses)
-----

I've already learned that my 4 parallel-connected 12V 55AH batteries are going to have problems based on balance. When they finally die, I plan to replace them with 6V or 4V batteries in series, one string. However, I'd like to get at least a few more years out of these batteries. I've read using the equalize function on the charge controller is a bad idea with AGM batteries. How would I equalize the batteries? I know they are off because they used to charge and discharge showing the same amperage flow to/from each battery using a clamp meter. Now they are off by about 15% after a year. This is my biggest issue right now and the main reason I wanted to post on this forum. The batteries used to settle out at night around 12.9V after a full charge with light load, but now they settle around 12.7 and continue down to 12.4 with only light load overnight. This change in voltage is when I first realized something was wrong.

For my 2nd question, which may be irrelevant depending on the answer to the first one above, what would be the recommended settings on the Classic for my current battery bank? The spec sheet only has the following (per battery):
Charge Voltage (constant)
(float) 13.5V ~ 13.8V
(cycle) 14.4V ~ 14.7V
Max Charge Current 16.5A

So I setup the classic with Bulk and Float at 13.8V max (I think), and Absorb at 14.7V (1hr max). Equalize is disabled. Re-bulk is set to 12.5V.
Any suggestions?

For my 3rd question, any comments on the wiring? My maximum expected continuous amps is 200A from the batteries and the wiring to the 2KW inverter matches the manufacturer's suggestion. Obviously if I change the battery bank I will change out to 2/0 or better wiring for the battery connections.

Edit: 4th question. I eventually want to have 1200W of Pv on the roof, but I want to keep the 12V battery system. It will be all the same panels that I have now. I planned two strings of 6 panels, but I've read on here that can cause stress on the Classic. Suggestions?

This is all off-grid, obviously, and I have no intention to ever connect it to the grid. The system final design is to take the place of a 2KW portable emergency generator. I intend it to operate my refrigerator and small electronics during an extended power outage. I realize right now I will likely have an 80% DOD and kill the batteries if I put the refrigerator on it, but that is an acceptable risk right now. Let's hope the power doesn't go out for very long anytime soon! Day-to-day operation will be just small electronics to keep the DOD at 30% or better.

As a side note, I am in West Central Florida, so plenty of sun. However, my panels are facing North so I don't get the most optimum power generation that I could. I also have some shading issues at the beginning and end of the day due to trees.

[kf4hzu]

Thought I would attach some of the graphs for my setup from MyMidNite. The lowest voltage on the graph is 12.4V.

[Westbranch]

I am sure you know what that graph is telling you...  you are deficit charging, as the Voltage line is ever so slightly decreasing as time advances, if the hard numbers don't tell the same story, it will just be a matter of time.
300W (17.5A) of poorly located is marginal to recharge 220Ah @ 12 v , normally you would need 22A from ~ 4 well placed panels to give you a 10% charge rate...  see what I am getting at?
you would be much better off with 4 6V GC2 batteries
hth

[kf4hzu]

Thanks for the reply Westbranch!

I think the graph may look like deficit charging since I have been progressively putting more load on the system over the last few weeks since it seemed like I was hardly utilizing the power generated by the panels. You may notice the first day on the graph I put a little too much load on it during the day and it never reached float charge. On the 7th day I put load on the system late in the day after it was already float charging, so the float charge amps increased as seen by the increased wattage from the Pv array.

You are right, I don't have enough solar panels yet. I plan to add 3 more this year as money allows. I'm just not sure I am deficit charging since the load on the system is very small. My worse issue currently (I think) is the batteries are unbalanced causing the voltage to drop off quickly after the sun goes down, even with only 200mA of load. I know a newly designed battery system is in my future, but I can't do that this year.

What do you think?

[Westbranch]

You have a Classic, did you get the WhizBang jr?  If not it is a recommended powerful little piece of electronics as it allows you to log the actual power going into the battery, measured at the battery (well as close as you can get almost).
It will also let you know if you have to raise/or lower the Absorb voltage based on those crude specs you posted... as well as the amount of Absorb time you set in the classic..

hth

[kf4hzu]

I keep forgetting to mail in the postcard for that! I'm also not sure how best to hook it up given the way my batteries are connected. I also don't have a shunt, does it come with one?

I tried to wire everything to minimize loss due to cable/connections. It will be interesting to figure out how to rewire to include the shunt.

[Resthome]

I keep forgetting to mail in the postcard for that! I'm also not sure how best to hook it up given the way my batteries are connected. I also don't have a shunt, does it come with one?

I tried to wire everything to minimize loss due to cable/connections. It will be interesting to figure out how to rewire to include the shunt.

You will have to purchase a shunt, the WBjr does not come with a shunt.  It is pretty simple to connect it up. Just remember this rule. One end of the shunt goes to the negative of  your battery bank and that is the only connection on that side of the shunt. All other negative loads including the Classic Battery negative, inventor negative connect to the other side of the shunt.

[Westbranch]

here is a good pic of the WBJR mounted,
http://www.midnitesolar.com/productPhoto.php?product_ID=519&productCatName=Charge%20Controllers%20-%20Classics&productCat_ID=21&sortOrder=9&act=pc

not knowing how your wiring goes, here is a pic of my Epanel with shunt in middle, taken in progress...

[kf4hzu]

http://www.altestore.com/store/Meters-Communications-Site-Analysis/Shunts/500A-50mV-DC-Shunt-for-Current-Monitoring-Meters/p4638/

Will this shunt work fine, or is there a better resource for one? I usually shop on Amazon but can't find the MidNite Solar shunt on there. I'd prefer to use known good components.

Also I have attached a picture showing how my batteries are connected to everything else (also reference my first post on this thread). This is just the negative connection in the picture, but the positive one is identical.

The orange circle indicates where the 4 batteries are connected. The blue circle is the charge controller negative, green is 2KW inverter, red is 75A "general" feed where the 175W inverter is, among other things.

So inserting a shunt is going to require some new hardware and rewiring. Suggestions welcome!

Also I had a few other questions in the original post, including how/when/if to equalize the batteries. Any ideas on those?

[dgd]

Inserting a shunt into your existing wiring would not be trivial.
You could tidy up all this wiring and improve control and safety with a Midnite  Epanel or an MNDC box. These can simplify your wiring and they come with a detailed wiring diagram, spaces for circuit breakers and mountings for the shunt. Epanels include a shunt but you need to get one for the MNDC

Dgd

[kf4hzu]

dgd,

I think the MNDC is the way to go for me, I don't have a lot of space. It may be a little while before I can drop the money on it, along with the money for all of the new wiring, breakers, etc I would need to connect everything. If I am going to up my game to a box like that, I would want to move to 2/0 or better cable for the batteries and main inverter connections.

So I read in the manual that it is not acceptable to use welding cable for residential wiring. Does that mean my current system violates code? That may expedite changing out the cabling and moving to a wiring box like the MNDC.

[Vic]

Hi Jesse(?),

Know that you want to run a 12 V system;  a 2 KW Inverter is fairly large on a 12 V system,  this could hammer your smallish AGM batteries,  especially if each battery is not equally sharing the current demands.

In my opinion,  strings of five of those PVs would better than six,  especially on a 12 volt system.     Believe that strings of six,  with 1200 watts STC may well push things  too much,  but have not run that through the MidNite Classic String Sizer. Even five 12 V nominal PVs might push the Classic  a bit on a 12 V system.

The Linked Shunt looks fine to me.   Deltec is the standard Shunt for our types of systems,  and that Shunt looks just like the Deltec.  This IS the most common shunt used around here.

You should only EQ your AGM batteries if it is recommended by the manufacturer.  Often EQ on AGMs is really a L-O-N-G Absorb,  and the customary Vabs.

Regarding using Welding Cable in your system.   It would probably be OK,  but might not pass an Inspection ...  but your system may not even need to be inspected.   Often welding cable does not meet some specs,  especially for use in residential applications.   AND,  you would generally need to use lugs that are rated for use on finely stranded cable,  and you might want to use breakers or fuses that have terminal connections that either have studs for lugs,  or are rated for clamping fine stranded cable,  etc.

FWIW,   Vic

[kf4hzu]

Hi Jesse(?),

Know that you want to run a 12 V system;  a 2 KW Inverter is fairly large on a 12 V system,  this could hammer your smallish AGM batteries,  especially if each battery is not equally sharing the current demands.

Yep I'm Jesse!

I want to stick with a 12V system because I have so many 12V devices, cables, fuses, etc with Anderson PowerPole connectors, that I hardly need to use inverters with the system for most of the things I would need in an emergency situation. I've been in to ham radio for many years, and I've built out much smaller portable emergency power configurations so I could work in a disaster area if needed (Helped out after Charlie hit). I used "Field Day" events to test everything, using small generators to charge small AGM batteries. I also want the power system (minus batteries and CC) to be portable so I can move it to my car (running the alternator) if I'm somehow in dire need of power and the solar power is non-functional.

The 2KW inverter is over-built for my needs. I only planned 1.5KW max (microwave), and only about 600W semi-continuous (fridge/freezer), so I bought an inverter that is slightly over what I need so I don't run it at 100% duty cycle for any length of time. (Yes, that is 2.1KW, I would unplug the fridge before running microwave) I think it may hurt efficiency, but I don't run the 2KW inverter 24/7 because it is very noisy, especially under load. It only runs when I would have normally turned on a generator in an extended power outage (or brief periods just to test it and get some time out of it).

In my opinion,  strings of five of those PVs would better than six,  especially on a 12 volt system.     Believe that strings of six,  with 1200 watts STC may well push things  too much,  but have not run that through the MidNite Classic String Sizer. Even five 12 V nominal PVs might push the Classic  a bit on a 12 V system.

I did use the string sizer setting up 12 of my panels in 2 strings and it said it was ok on the Classic 150 down to (IIRC) -8F which is unlikely in this part of Florida. But "ok" and "optimum" I know are different things. 5+5 may be fine for me, I'll need to re-do some math to figure it out.

The Linked Shunt looks fine to me.   Deltec is the standard Shunt for our types of systems,  and that Shunt looks just like the Deltec.  This IS the most common shunt used around here.

Cool, I'll order it after I get the WBJr, thanks!

You should only EQ your AGM batteries if it is recommended by the manufacturer.  Often EQ on AGMs is really a L-O-N-G Absorb,  and the customary Vabs.

Long absorb sounds safe, the guys at Interstate Battery didn't really have an answer for me. I increased my normal Absorb to 2 hours to help. How about I setup the Equalize for 14.7V for ~5 hours every 30 days (if I can even do that with the Classic)? Also, they are unbalanced right now, badly. I have a "smart" charger that runs off the wall. Any suggestions on bringing them back in to balance soon-ish, or just let the CC do it over time?

Regarding using Welding Cable in your system.   It would probably be OK,  but might not pass an Inspection ...  but your system may not even need to be inspected.   Often welding cable does not meet some specs,  especially for use in residential applications.   AND,  you would generally need to use lugs that are rated for use on finely stranded cable,  and you might want to use breakers or fuses that have terminal connections that either have studs for lugs,  or are rated for clamping fine stranded cable,  etc.

FWIW,   Vic

I purchased all the major artery cables (6GA to 1/0GA currently), excluding the orange 4GA cables, from powerwerx.com because I didn't have the right tools to properly crimp connectors on cable that large. I believe they would have given me the correct connectors for the assembled cables. I didn't want to skimp and risk issues when messing around with this much DC potential. I think before I rebuild the wiring as discussed earlier in this thread I'll purchase the proper tools to make my own connections. I didn't even know there were different ratings for clamping different strand types. I've only been aware of differences between solid and stranded connectors.

I am less concerned about random inspection, and more concerned about doing it wrong, causing a fire, and THEN an inspection finds out I did something wrong (like selecting the wrong cables/connectors) which caused the fire and therefore I don't get insurance coverage for my house. Worse would be if someone gets hurt by a bad decision on design or components. This is in a closet that I close when I have visitors, but there isn't a lock on the door. I've had thoughts about building a new small closet dedicated to the Pv system, but that is not going to happen anytime soon.

I appreciate your input and advice. Definitely learning a lot of things in the few days I have been on this forum. I've also been browsing around old posts, but I have some unique issues that I haven't seen on here.

Looking forward to more discussion!

[mike90045]

Please, do not try to use any Equalize settings on your AGM batteries.   Go to the Mfg's website and look up the maintenance charge voltages.
When charging AGM, once you exceed the internal gas recombiner, it Vents gas, and therefor you loose electrolyte that can not be put back.

[vtmaps]

How would I equalize the batteries? I know they are off because they used to charge and discharge showing the same amperage flow to/from each battery using a clamp meter. Now they are off by about 15% after a year. This is my biggest issue right now and the main reason I wanted to post on this forum. The batteries used to settle out at night around 12.9V after a full charge with light load, but now they settle around 12.7 and continue down to 12.4 with only light load overnight. This change in voltage is when I first realized something was wrong.

For most folks, by the time they realize something is wrong with their parallel batteries, serious damage has been done.  You seem to be more on top of it than most folks.... you have a clamp meter and use it, and you are sensitive to tenth-of-a-volt differences.  You might be able to rescue your bank.

What you MUST do is separate those batteries and charge them and evaluate them one at a time. 

Some AGM manufacturers do recommend an "equalization" when needed... but it's usually just an extra long absorb, or its very few tenths of a volt higher than a routine absorb.  I think you mentioned that you have interstate batteries... they're OK batteries (in my opinion) but you must understand that Interstate's tech support folks are clueless, and have no clue that they're clueless.  If you can find out who made those particular batteries for interstate, you can look up that manufacturer's recommendations for the battery.

For safety reasons it is a good idea to put a fuse or circuit breaker in each string of a parallel battery bank.  If you had done that it would be very easy to switch in or out any particular battery in your bank.  Of course, all the extra connections involved in fusing each string add connections (which are points of failure) to the battery wiring.  You seem to understand some of the issues with parallel batteries.  Do you know that the problems are exacerbated with AGM batteries?  This is because their lower internal resistance makes the resistance in the wiring relatively greater.

--vtMaps