Is it normal for the Classic to pull the array (Classic's displayed input) voltage down to a couple of volts above the battery voltage? The picture below caused some concern over at the NAWS forum with one of the moderators there by causing me some concern.
http://i1000.photobucket.com/albums/af125/verdigo59/IMAG0469.jpg
Depends on what your VMPP on the array feeding the Classic is...
Looks to me like you might have two 60 cell PV modules feeding it, the VMP for those are around 30VDC with a VOC of 40 plus VDC each...
The Classic will find the MPP where it generates the most Watts.
Don't see what the issue is, it's charging with a lot of watts coming in... unless something does not fit with the PV specs etc...
I believe the concern about the array voltage being just above battery voltage is that if the array drops any further there will not be sufficient voltage to push the charge into the battery. When the weather is hot with sun shining brightly the panels get hot. Hot panels have reduced voltage output. If the total rating of the strings Vmp is not much higher than the battery bank voltage the system could stop charging even though the sun is shining brightly.
Don, I agree but without the PV specs it may just be the MPPT algorithm doing its thing as long as he has enough head space ( voltage) between bat V and MPP V to run the CC and cover line loss....
I saw 25.4 PV Volts at less than 1 amp on mine last week and the CC outputting 25.5 V into the battery at .1amp, it happens a lot right around Batt V and afternoon sun. the Classics will sure squeeze it out if its there. BTW inverter was on but no loads, other than tare...
Yes; we have a Kid and it too is amazing at what it can squeeze out of a few early morning or late evening sun rays. Panel and environmental specs would help settle the theory.
Elsewhere, Dennis has said, "The panels are in strings of two 37 volt vmp". (74 Vmp strings. This appears to be on a fairly modest Hybrid GT system.
We have always run relatively high String Vmps on systems here -- one at 106 V and another at 93 Vmp nominal, all on 48 V battery banks.
BUT, I was quite surprised to see that the 2320 Watt STC array (from memory) could deliver that amount of power at such a low Vin, and at that close to Vbat.
Have always tried to give the MPPT CC a bit more room to operate, at a bit of a hit on efficiency.
All FWIW, Vic
Sure looks like these panels are getting a lot of shading on them.
Quote from: Westbranch on September 23, 2014, 03:51:24 PM
I saw 25.4 PV Volts at less than 1 amp on mine last week and the CC outputting 25.5 V into the battery at .1amp,
Eric,
Althought its only 0.1volt the Classic does not have voltage boost so 25.4v making 25.5v is likely a little inaccuracy in the voltage readings. The tweaks options may need applied to get the voltages correct using a decent voltmeter (fluke).
Then again, boB said some time ago he was looking at boost so he may have quietly sneaked it in the code ::)
dgd
Quote from: Vic on September 23, 2014, 07:04:22 PM
Elsewhere, Dennis has said, "The panels are in strings of two 37 volt vmp". (74 Vmp strings. This appears to be on a fairly modest Hybrid GT system.
We have always run relatively high String Vmps on systems here -- one at 106 V and another at 93 Vmp nominal, all on 48 V battery banks.
BUT, I was quite surprised to see that the 2320 Watt STC array (from memory) could deliver that amount of power at such a low Vin, and at that close to Vbat.
Have always tried to give the MPPT CC a bit more room to operate, at a bit of a hit on efficiency.
All FWIW, Vic
Viv at one point I have seen 2500 watts and you are correct "out of a 2320 watt array". I didn't and still don't have the experience to have been concerned about the low input voltage.
I thought the classic was just doing it's thing. My plan is to buy four more panels and the advice I was seeking was whether I need four more or perhaps just two more of the same panels in strings of two.
The Classic sizing tool indicated I was getting close having a hyper VOC issue in colder weather with strings of three.
I guess I will go ahead with my original plan for 4 more panels, and try them out in strings of three and see what is best.
What I gather is if I can make the same or more power in strings of two it would be more efficient than having the CC work harder down converting higher voltages from strings of three?
Thanks for the advice
Hi Dennis,
The system with 106 Vmp strings was on the hairy edge using the venerable OB MX-60 CC. Highest recorded Voc on this system is now at 141 V. This in a very moderate CA climate. The PVs in this system are 35.4 Vmp, in strings of three. This really IS a bit too high, but wanted to play with harvesting PV DC for an electric Water Heater, so higher V is a bit better. Probably would not want to run any higher string Vs than these (here at least).
In theory, strings of two of your 37 Vmp PVs should be fine, but on hot days, doing an EQ might not work out so well (if you use FLAs).
But you seem to be able to make good power at about Vbat + 2V, so on most days you may not have an issue.
David, recall that boB did say that he saw a slight Boost function on a Classic at one point, with low output currents, but with the Classic charging a battery, which was showing a voltage a bit above the Vin to the Classic ... just from memory.
OK, Good Luck, Vic
Dgd,
The equipment label on my Classic says:
Midnite Solar Classic 150
MPPT Solar Wind Hydro Buck Boost Charge Controller
I take that literally that it can buck or boost.........that is what a buck boost controller does
David
<edit>. Ok that was a memory fart......that was not on my Classic but in the not too up to date online manual which I downloaded. td
Quote from: tecnodave on September 23, 2014, 10:41:59 PM
The equipment label on my Classic says:
Midnite Solar Classic 150
MPPT Solar Wind Hydro Buck Boost Charge Controller
I take that literally that it can buck or boost.........that is what a buck boost controller does
Thats interesting. Have you tried charging, say a 24v battery bank, with pv input of maybe 18v mpv (single 12v nominal solar panel) on a bright sunny day?
I'm pretty sure its a no-go but I would be very pleasantly surprised if in fact it did charge the battery bank - then the label would be spot on :o
dgd
Quote from: Vic on September 23, 2014, 10:39:36 PM
David, recall that boB did say that he saw a slight Boost function on a Classic at one point, with low output currents, but with the Classic charging a battery, which was showing a voltage a bit above the Vin to the Classic ... just from memory.
Vic,
I must have missed that. A slight boost, I guess, caused by some chance arrangement of oscillating charging caps adding an ac component to the PV voltage which maybe a diode bridge later boosting rectified DC output voltage OR maybe just the caps and diodes being a voltage pump ;)
dgd
Tecnodave, Where and what label was this that said the Classic was a buck-boost ? I don't remember that but maybe
a real old one had something like that on it ?
The Classic does not boost. At least, not in normal operation. What you probably saw was where the input voltage
appeared to be less than battery voltage. Not exactly sure why but I have a couple of ideas why.
Dgd,
I have never pushed it that far but my old stacks of Siemens SM-55 are wired switchable 35.4/70.8 volt or 35.4/105 volt so I have the option of throwing a few switches so I can swap out Classic with Trace PWM controller for servicing of if there is a controller failure. I have run the Classic with a 34 volt in and it does have trouble on equalize on 24 volt system. My main systems are now all 72 cell panels as they are easier to handle than bunches of small panels.
David
Verdigo,
I could not see the picture you linked to.
What is your PV Voc (open circuit) voltage and your battery voltage. VERY important.
Do you have any "partial" shading on your PV array ? Is your PV array hot ?
These 2 things can make the MPP (Max Power Point) voltage low.
Try this sanity check, change the "mode" from SOLAR to Legacy P&O. This will
drag the PV voltage from Voc down to battery and then it will stay close to what
it found as MPP V but will periodically walk above and below this point. It will do this
slow enough that you can watch it do its thing.
Maybe "SOLAR" mode isn't the best for your array and Legacy will do better ?
I will see if I can find the NAWS thread.
boB
PS... Just found this on the NAWS forum... AND I saw the picture !
The panels are in strings of two 37 volt vmp. The Classic's display input voltage has always dropped when the current has some place to go and without selling with charged batteries will typically show around 80 volts
2320 watts of PV
464ah GC2 battery bank @ 48 volts
Not too bad actually ! Probably just some partial shading and/or a hot day or something.
If your batteries are full and noplace for power to go, then 80V Voc would give you about
64 volts MPP so you're real close to that. I would still try Legacy P&O anyway.
Will continue reading the NAWS thread.
http://forum.solar-electric.com/showthread.php?24707-Questions-on-over-paneling-with-Grid-Interactive-Inverter
boB,
Memory failure.....does not say that on my Classic. CL11137..... It's in the online manual dated 1/7/13 page 77. I have never documented a boost condition. I have temporarily run with two Arco SM-45's in series.....30 cell self regulating panels.........barely works
David
Td,
I had thought about those low cost voltage boosters from China, seen on Ebay.
Specs look good enough to use 150 watt 18volt mpv panel to boost to about 35v for input to Classic/Kid charging a 24v battery.
But it would be nicer if the Classic/Kid did this boosting
dgd
Dgd,
Volume of production is making 125 mm and 156 mm cells the best price points, I am buying new last years model 72 cell panels at 80-90 cents a watt. Doesn't make sense to use the smaller panels anymore. I have phased out my CdTe panels due to real estate concerns. They did 9.5 watts/SQ.ft verses 13 watts/SQ.ft for my new Suntech and Sharp panels. I just bought 6 Top point 125 mm 72 cell 190 watt panels at 33 cents/watt. Siemens SM-55 are being traded away along with the dreaded Tracers, finally done with them.
td
Quote from: tecnodave on September 24, 2014, 02:22:30 AM
Siemens SM-55 are being traded away along with the dreaded Tracers, finally done with them.
What didn't you like about the Tracers ? I had heard that they were at least, kind of "OK".
We have one but I haven't hooked it up yet. Aren't they like, really inexpensive ?
boB
boB
They are kind of ok......and cheap @ $190 with remote control for a 30 amp unit but they do not properly charge FLA's. The charge profile cannot be changed. They leave my GC-2's and L-16's at 1.220 s.g. And shut off. Even when on a group 27 deep cycle RV battery I need to run generator to top off the batteries.
I currently have one on system 3:
One EP Solar Tracer 3215RN MPPT with 220 watts ,34.8 volts string 12 volt GC-2.
and a backup controller Trace C-40 PWM with 220 watts , 17.4 volt parallel, same battery set
All panels Siemens SM-55 55 watt 36 cell monocrystalline,
By 10:00 am the Tracer is done and the Trace is still charging at full tilt......?
The Tracer does put out 25-30% more power at bulk but total power for the day the Trace C-40 has done the bulk of the work........a MPPT controller outdone by a PWM controller....?
The one on a D-8 gel does much better, that charge profile works
EP Solar is a street light company and bundles up the 3215RN with two gel batteries at 24 volts, a LED controller for the light, and two CdTe panels at VMP 68 volts. This works very well but is not my use.
Service or technical help from EP Solar is non existant ...they rely on their dealers who know very little and will give you another unit to not post a bad review on Amazon about their units....yes I did take one to remove my scathing review on one of the units.
Bottom line......my gasoline use on the generator had been much lower when using good controllers to top the batteries off.......the Tracers forced me to top off the batteries with the generator due to their poor charge profile.
After that lesson of nearly ruining a new set of Interstate L-16's I bought the Classic 150 and very soon the first of the Kids and have never had that undercharging issues again.
Nobody beats MidNite service or technical help! I get awesome service from Schnieder Electric' Square D unit as I am a stocking installer of Squard D QO and Homeline products but this support has not filtered down to the Xantrex/Schnieder Solar division. Too bad....that knocked them out of the running when I was making my decision to go with big controllers. MidNite and Outback were the finalists. It was a hard choice there but the support I found with MidNite sealed the deal....no regrets
I have 3 MidNite controllers now and will be buying a third kid soon.
David
<edit>. Spelling and clarity......I am a much better speller than my iPad is!