low amp output from panels

elesaver · August 2016

I'm trying to determine if there is a problem with the new panel set up at the barn or if it is just my expectations.

I have 4 panels total with 2 ea in series and those two strings into a combiner box. The specs on the 4 panels are:
310 wp
45.2 VOC
35.8 Vmp
8.68 Imp

My "calculations" were that each string would have double the amps (17.36) but the same watts (310). Then, with those two strings
going into the combiner box, I would have (in a perfect world), I could have a maximum of 34.72 amps and 620 watts.

The battery bank is 24V and 440 aH using 8 Trojan T-125. I put my Classic 200 Charge controller with a mini-dc disconnect in also. I've been watching this system and have never seen the amps above 13+. I am not getting enough charging to get the cc to go into absorb on a regular basis, let alone an EQ. It does hit the Vabs of 28.5 once in a while. It has gone into float once in a while. (Sorry I don't have accurate amount of time on any of these.)

When winter comes, I will need to run chicken water heaters (25 watts each) and once in a while a couple of infrared Sweeter Heaters (100 watts each) for the "girls" to keep warm. I thought I would be well within being able to power these with this set up.

Using 250 watts/hour @ 24V = 10 amps/hour. At 10 hours, that's only 100 aH...only 25% of the battery bank DOD.

Have I made more errors again?

vtmaps · August 2016

elesaver said:
Have I made more errors again?

Quite a few. You have 1240 watts of solar panel. You can harvest about 77% of that on a hot day. (less on a very hot day).

1240 X 77% = 954.8 watts
954.8 watts ÷ 29 volts (charging voltage) = 32.9 amps coming out of the controller.

That's a 7.5% charge rate into a 440 ah battery bank.

elesaver said:
My "calculations" were that each string would have double the amps (17.36) but the same watts (310). Then, with those two strings going into the combiner box, I would have (in a perfect world), I could have a maximum of 34.72 amps and 620 watts.

You are very confused about what's going into the controller. When you put two panels in series the voltage doubles, but the current stays the same. So one string is 620 watts (8.68 amps X 71.6 volts)

When you combine (= put in parallel) two strings, you have 17.36 amps at 71.6 volts = 1240 watts.

elesaver said:
Using 250 watts/hour @ 24V = 10 amps/hour.

you mean "Using 250 watts @ 24V = 10.4 amps"

--vtMaps

elesaver · August 2016

OK. Thank you Vtmaps. Several things are not clicking for me:

I see the calculation for 954.8 watts. How did you determine 29 volts "charging voltage?"

When I have measured at the combiner box with a voltmeter, I have measured 70 volts but the amps are very low. I have used a clamp meter on the PV wires...3.3 A on one, 1.9 A on the other (just remembering some of the readings; I will have to write down some of the measurements as I go forward.)

Apparently, with wire losses, the 17+ amp potential would end up being far less.
So, if that's the case, would I be better served to put all 4 panels in parallel rather than 2 strings of 2? Or does this create
other issues?

I sure appreciate the help.

westbranch · August 2016

The configuration you have now 2S x 2P is the best for your system , 4 P will barely give you enough volts to charge before heat losses..., find the point of loss , a poor connection, too small a wire etc. you know which side it is on already... start with re-torquing all connections on both strings.... copper 'flows' under pressure.

vtmaps · August 2016

elesaver said:

I see the calculation for 954.8 watts. How did you determine 29 volts "charging voltage?"

That is approximately your absorb voltage. 954.8 watts = volts X amps. When you start bulk charging the voltage may be at 24 volts, in which case you could (with full mid day sun) have 39.7 amps coming out of the controller. As the voltage rises towards absorb voltage the current (amps) must decrease.

Of course, on many days when you begin bulk charging in the morning, the watts will be less than 954.8. You might start at 400 watts ÷ 24 volts, and work your way up to 954.8 watts ÷ 29 volts by mid day.

As Westbranch pointed out, your panels are configured properly.

--vtMaps

elesaver · August 2016

OK, gentlemen. I've been checking everything and haven't come up with anything that was "loose." I rarely get above 27V, even in the mid-day with HUGE sun. Today, I'm going to try to check the panels. I disconnected them last night without sun.

I've re-installed the CL 150 into my other system and it is working BEAUTIFULLY. When I see this one now and its performance, I wonder if the other cc is not functioning correctly either. It was originally with the larger system and it was not going into absorb or eq very easily. Hmmm. Maybe something to think about. I have 2X the panels in the larger system.

Thanks again. I'm staying on it. :-)

Vic · August 2016

Hi elesaver,

Regarding this new PV array, is there any shading at all, during midday sun? Any shading whatsoever can really kill production, as will even moderate cloudiness.

What is the elevation and the Azimuth (direction) of the new PV array?

YES, it looks like this new array as a Combiner, so open the breaker for all strings, and measure the voltage that is coming from the PVs. Place the positive meter lead on the breaker's input terminal, and the meter negative lead on the PV common negative buss. In good sun, what are these readings fro each string, please record these for future reference.

In good sun, during Bulk mode, what is the Combiner PV output voltage with the string breakers switched on? Soon after taking this measurement, what does the Classic read as its input voltage? Under these conditions, what does your DC Clamp meter read for current of each string? What is the clamp meter reading on the cable that is positive PV output current reading for the array (total current). Does this agree fairly closely with the sum of the individual PV string currents?

Please measure and record the SG readings of each cell in this battery bank, and record these readings in your new battery Log book for this new system.

It might be a good idea to remove loads on this system, until you get on top of any issues, and get this battery bank fully-charged, and then EQed.

Thanks for the info. Good Luck, Vic

elesaver · August 2016

Vic, I see your questions and will need to take the readings to post later. No, there is no midday shade at all. Today is a great day
for full sun although heat apparently can cause reduction in panel output.

Meanwhile, I have been watching the MGNP screen to monitor what's going on. I'm happy to report that the amps in value is up. There is no load at this time. I have put the cc into EQ mode. The voltage is not getting high enough to accomplish that.

What I see is that the watts are not what they should be. Watts on MGNP has not eclipsed 600 yet. Because the watts are low, EQ cannot be met even though the amp in is great. I turned off one breaker in the combiner box at a time to see how the levels changed. The right side breaker dropped the watts dramatically (I left the paper in the barn so I don't have exact right now) but the amps in only dropped from 18.4 to 13.5.

The battery bank is not good, so perhaps that is a greater contributing factor? These are Trojan 125 that I purchased used 2 years ago! After reading different things, I figured it would be better to start out with used batteries so I wouldn't ruin brand new ones. :-) I've measured the SG in each cell and there are at least 3 batteries with one cell that is 1.10 or below. That's why I would like to work on equalizing these to see if I can bring them back for a bit longer. Funny thing is, the string still works. It was holding at 25.6. It's only the barn! To sink $600 in new batts. is something to put off until it's absolutely necessary. And, maybe that time is now?

I'll work on getting the info you could use to perhaps find something. I just don't know why the watts coming in are so low. I have measured the voltage on each string with the breakers off. Both strings measure 72.6, I believe (paper in the barn) The combiner output wires also measure 72.6.

Once again, I thank you. It's a mystery...at least to me.

Vic · August 2016

Hi elesaver,

Thanks for the additional info.

With no shading of any kind, at all, whatsoever, the string currents should be very close to each other.

About shading, even the slightest shade, caused by a small diameter wire, or almost anything else, can reduce PV production by a large amount. SO, there could possibly be a poor connection. Check that the connectors on the PVs are fully-seated, and tight. How do you make the transition from the connectors that came on each PV, to cables that feed the Combiner?

What brand/model number are the PVs? Are they Grade A PVs?

But, in any case, any standard FLA, with any cells having SG readings of 1.100, or below would seem to be well beyond end-of-life. Agree that trying to EQ the batteries is a good idea. You should separate the two strings of batteries, and try charging one string at a time, then try to do an EQ on that string. Then switch strings and try to do the same thing. An EQ of a battery bank in this apparent state can require many, many hours. And, with SG readings this low, am personally not too optimistic that this bank can be brought back, without continuing heroic efforts, on your part ... but, worth a try. The longer period of time that the low SGs have remained this low, generally, the more difficult it will be to return any useful Capacity, IMO.

Heavily Sulfated batteries may appear to charge quickly, but this seems to not be the case with your batteries, from what you have said previously. It is possible that one, or more cells have some type of shorting (like a "partial" short). You mentioned that the battery bank "holds" about 25.6 volts, is this with the battery Rested (no charge or discharge of any kind for six or more hours)?

More Later, Good luck, Vic

vtmaps · August 2016

Vic said:

You should separate the two strings of batteries, and try charging one string at a time, then try to do an EQ on that string. Then switch strings and try to do the same thing.

Totally agree. Another approach is pick the good batteries from each string and operate with one good string. A battery bank is only as good as its weakest cell. If you can't fix (eq) a bad cell, cull it.

--vtMaps

elesaver · August 2016

Thanks for the suggestions above. I have already tried "selecting" 4 good batteries for a string of 240 aH. And, that's what brought me to the quest for answers. I am unable to get the system into EQ. On Saturday, I did see 20+ amps but the watts were 530. Volts in was high 60's.

So, I have a new plan although today it may not materialize as it is raining. I have recently received my CL 150 back from Midnite Solar. It has a new control board. When I put it into the system at the house, it ran like a champ and I could easily do an EQ on my forklift battery. I had not been able to do that before with the CL 200 installed there. This is leading me to believe that the CL 200 may have a problem.

So, I'm going to put the CL 150 that I know is functioning correctly into the system at the barn and see if I get a different result. That info will allow me to more forward one way or another.

It may be a day or two, but I'll report back when I have that answer about the CL 200. Thanks again. You guys are great!

vtmaps · August 2016

elesaver said:

Thanks for the suggestions above. I have already tried "selecting" 4 good batteries for a string of 240 aH. And, that's what brought me to the quest for answers. I am unable to get the system into EQ. On Saturday, I did see 20+ amps but the watts were 530. Volts in was high 60's.

Huh? If your voltage is in the high 60's, you are equalizing. Watts and Amps are secondary, and subject to what the battery will accept. Maybe it's time for new batteries.

--vtMaps

elesaver · August 2016

"Huh? If your voltage is in the high 60's, you are equalizing. Watts and Amps are secondary, and subject to what the battery will accept. Maybe it's time for new batteries."

If you don't mind, explain this to me. A = Watts/Volts So, if I have (just for a number) 20 amps and 60 volts, I should have 1200 watts. I don't much above 600 watts. This cc does not go into EQ. It is set at 31.5. Battery voltage doesn't get high enough to EQ.

It may be time for new batteries, that's for sure. Before rushing off to spend, I'm still working at eliminating any other possibility. This
evening I've gotten the CL 150 installed at the barn. Looks like we've got some rainy days ahead but as soon as I get some good sun, I'll be able to see a little clearer as to what's going on.

Don't pull your hair out...just yet anyway. I'm still working on this.

vtmaps · August 2016

vtmaps said:

Huh? If your voltage is in the high 60's, you are equalizing. Watts and Amps are secondary, and subject to what the battery will accept. Maybe it's time for new batteries.

elesaver said:
If you don't mind, explain this to me. A = Watts/Volts So, if I have (just for a number) 20 amps and 60 volts, I should have 1200 watts. I don't much above 600 watts. This cc does not go into EQ. It is set at 31.5. Battery voltage doesn't get high enough to EQ.

I lost track of your system (hint: describe your system in your signature). When you said your voltage was in the high 60's, I thought you had a 48 volt system and were equalizing with an EQ voltage in the 60's.

Are you equalizing just one string? 1200 watts should get you through absorb and into equalization. By the way, when/if you do get to equalization voltage, it's not a high wattage situation. The batteries push back and limit the current that they will accept.

--vtMaps

Vic · August 2016

elesaver said, " ... Volts in was high 60's ... ".

Believe that elesaver is saying that the INPUT voltage to the Classic was in the high 60s.

Good luck with those batteries ... earlier in this Discussion, I had referred to;esaver's "new" battery bank, a bad assumption based on another discussion about a conversation with a battery dealer, looking for some new batteries.

Good Luck with the batteries, if can often take considerable time to try to get beaten batteries back up to snuff. Sometimes a lot of time for not a lot of Capacity. FWIW, VIc

elesaver · August 2016

Sorry that my signature doesn't hold all the info needed. I am just getting started with the small system at the barn. I'll correct the signature before I post again.

elesaver · August 2016

OK, winding this thread down. What a journey! There's no need to go back to read all of the posts as I have come to the conclusion that it's the batteries that are causing my angst. Somewhere in this grouping of posts, I mentioned that these batteries were the first ones I bought so that I could learn on something that wasn't going to cost too much if I ruined it!

I had moved the CL 150 cc to the barn where the 2nd system is. I wanted to verify that the CL 200 cc did not have problems.   After determining that the CL 200 is functioning OK, and after checking all the connections, etc., my final thinking is: "It's the batteries, Stupid." :-)

Here's my only missing piece now. I'm going to have to get some new batteries. I had saved the formula that Cariboocoot had shown me a while ago to figure the battery bank and panel array sizes. My calculations show that 4 each Trojan 105's @ 225 aH each would be the correct amount. But since it's not good to mix old and new batteries, I've got to get all that I want right now.   And, it doesn't appear that my PV array could handle much more than that anyway. Am I correct in the thinking and calculations?

Battery bank:

500 WH/day X 1.176 AC inverter efficiency X 1/24 volt battery bank X 2 days without sun X 40% maximum discharge = 122 aH.
(I do not know the Cotek inverter efficiency)

Panel sizing:

26.5V charging X 225 aH battery bank X .13 rate of charge = 775W array

My array is 1200W so it appears that I could keep 4 of the Trojan 105's happy. ( I am not certain of the charging voltage or the 13% rate of charge in this formula.)

Johann · August 2016

Vic said:

elesaver said,   "   ...    Volts in was high 60's   ...   ".
Believe that elesaver is saying that the INPUT voltage to the Classic was in the high 60s.
Good luck with those batteries ...   earlier in this Discussion, I had referred to;esaver's "new" battery bank,   a bad assumption based on another discussion about a conversation with a battery dealer, looking for some new batteries.
Good Luck with the batteries, if can often take considerable time to try to get beaten batteries back up to snuff.   Sometimes a lot of time for not a lot of Capacity.     FWIW,   VIc

You are so right, it may take weeks or even month's to get some capacity out of old bad batteries. A few years ago I tried to revive 2 ''good/bad'' batteries that where sitting to long uncharged. One battery took 2 month before I got some low capacity, while the second battery never made a comeback after 2 month of trying.

vtmaps · August 2016

elesaver said:
Battery bank:

500 WH/day X 1.176 AC inverter efficiency X 1/24 volt battery bank X 2 days without sun X 40% maximum discharge = 122 aH.

What are you trying to calculate? I don't understand this formula. If you have 225 ah of battery and want to discharge 40% of the capacity, 40% of 225 ah is 90 ah. So you can draw 90 ah to take you down to 60% SOC.

elesaver said:
Panel sizing:

26.5V charging X 225 aH battery bank X .13 rate of charge = 775W array

a 13% charge rate of a 225 ah battery is 13% X 225 ah = 29.25 amps.
29.25 amps X 29 volts (charging voltage) = 848 watts.
typically you get 77% of an array's wattage, so 848 watts ÷ 77% = 1101.6 watts

Therefore, a 1101.6 watt array will yield a 13% charge rate for your batteries (assuming there are no daytime loads).

--vtMaps

elesaver · August 2016

Thanks for the numbers, VtMaps. The missing piece is that there would probably be daytime loads, depending on the weather.

low amp output from panels

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