# Midnite Classic question

Solar Expert Posts: 143 ✭✭

OK, my tiny 'lil 900w (3 panel), 4x golf cart battery system has been running for a few months and I have a good feel for how much it generates and how much I can take from it.  My next plan is to jump into a larger system, probably 9 panels (close to 2700w) and a Midnite Classic 150.  If the system's PV puts out (on a sunny day at high noon) around 84A (24v) and the Classic can handle 96A, I'm fine.  But if I install a 4th string of 3 more PV panels to yield something like 3600w, the max output will be near 111A (24v) and the Classic will be over its 96A (rated max output)... but only by 15A, and it should rarely see this condition.  My question is, will the excess amps simply be lost? or will the Classic shut down until the amperage from the PV panels drops below its 96A capacity?  I get the above figures from my current system, which uses a Midnight Kid, and the 3 panels I have maxes out at 1pm at 27A and change, I have never seen 28A to the batteries.

thanks,

walt

• Solar Expert Posts: 5,183 ✭✭✭✭

I don't know if it's self regulating, but you can set the max output...

I think your math is wrong though. 112 amps should be about normal out put with 3600 watt array, 3600 ÷ 24 = 150 amps {} 150 amps at 75% normal panel rating 150 X .75 = 112.5Amps or at near Absorb 3600 ÷ 28volts = 128 Amps {} 128 x .75 = 96 Amps...

Max output would be based on a cold day when a panel would put out close or above panel rating.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 3,738 ✭✭✭✭
I don't follow your numbers... where does the 84 amps come from?
"the system's PV puts out (on a sunny day at high noon) around 84A (24v)"
You might be mistaken about the Classic's 96 amp capacity.  The capacity of the classic depends upon the battery voltage and the input voltage (from the array) to the classic.   A Classic 150 is rated to output a maximum of 94 amps (in a 24 volt system) if the input voltage is 90 volts or less.   If your string voltage is 120 volts, the maximum output of the Classic is 82 amps (in a 24 volt system).

You asked about overpaneling a Classic.  Yes, it will clip the power it can't handle but will otherwise work.  I think it is a poor design to overpanel like that.  The reason is that the output amp limits of the Classic are limits... it's like operating your gas engine with the tachometer in the red.  The Classic limits are heat limits... when you reach the limits the Classic throttles back the power to protect itself from melting.   It's not good to operate the controller for extended periods every day when it's on the verge of melting.

As the input voltage gets higher, the Classic becomes less efficient (makes more heat) and that is why the limits are lower with an input voltage of 120, than with an input voltage of 90.

You haven't mentioned your panel specs or string voltage.  Nor have you mentioned your battery.... is it large enough to handle the increased output of your proposed array expansion?  I presume it is a 24 volt system.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 1,218 ✭✭✭✭
9 panels (close to 2700w) and a Midnite Classic 150.  If the system's PV puts out (on a sunny day at high noon) around 84A (24v) and the Classic can handle 96A, I'm fine.  But if I install a 4th string of 3 more PV panels to yield something like 3600w, the max output will be near 111A (24v) and the Classic will be over its 96A (rated max output)...

For a 3kW system, a 48V battery bank is pretty much not negotiable. Therefore:

Peak charge rate is 2700W/48V*0.77=  43A, thus you still have room to double that array if you desire.

Array would be best configured as (assuming 60cells) 3S3P, in that case. If you use 72cell panels, 2S5P.

1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Solar Expert Posts: 5,183 ✭✭✭✭
zoneblue said:  For a 3kW system, a 48V battery bank is pretty much not negotiable. Therefore:

While a 48 volt system would be nice, I think to say "not negotiable" is silly. I would say planning a 24 volt system would be reasonable up to the capacity of 2 charge controllers. 4-5KW array.

I personally would much rather have a 48 volt system, but I had the battery and inverters from my previous system where I had intended to stay for 20+ years. But things change and having a 24 volt battery with a long life left it was reasonable to plan my system around it.

That said, a 'system' is the combined total of the parts, not just an array and batteries. Power requirements and life style need to be taken into account. He may already have an inverter that will work for his life style and requirements. Which brings me to why I came back to this discussion. He has a charge controller now that he could use in parallel to the classic. Maintaining a range that would work for a single classic...

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 1,218 ✭✭✭✭
Perhaps not negotiable is a little strong, but if youre starting out, dont have much or any of the components, its most definitely the way to go.
1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Solar Expert Posts: 143 ✭✭
Thanks, guys. You're all a great help, as usual. I am getting my numbers from my current system, which is 3x 285w panels, and at high noon in the summer I see no more than 27.x amps to the Kid at roughly 112v, give or take. But my main gripe is that although that is a maximum, I rarely see that much... there are far too many partially cloudy days or slight cloud cover rolling past, I think a much more reasonable number is more like 17 or 20A for maybe the 4 hours from 10am to 2pm. After that, it drops considerably... it does not help that I have neighbors with large trees everywhere, so shading is an issue... and this system was put into place on the very handiest surface available, namely my back yard, on the ground (:  ...it was only supposed to be in place roughly a year to gather data for me, in order to plan how feasible a larger system would be.  I have since thought with the partial output I see much of the time, I should probably add 1 more panel to go 4x 285w to keep the Kid busier and only occasionally max out its 30A capacity... but I guess the consensus is that is probably a bad idea. But similar to the question asked in the subject line, with the 150 Classic.

The main things I have learned in the past 10 months is that I am VERY disenchanted with LA batteries.  My 6v GC2 Interstates from costco have been a bear to live with.  I lucked out with 3 good performers but 1 was not so good.... so I exchanged it, and got another not so good performer; I just exchanged that one yesterday due to the excellent costco warranty, got in under the 1 yr mark easily. It's in the system now and seeing daylight for the first time inside my tiny system. For the past 10 months the bad battery in the bunch has dragged down system performance steadily... I could initially run (during the summer) both a 14.7cu ft fridge and a 7 cu ft chest freezer off the 208ah Interstates (just barely, with lots of sunny days); then during this winter it was down to only running the freezer .... then running the freezer for most of the time during the days but having to revert back to the grid latenight.... so I just replaced the bad battery and hoping to get back to mostly running both appliances again full time during the day and then watching it at night to make sure they don't discharge the batts too far.

While I would like a 48v system, the batteries are probably going to be more expensive to the point of unobtainium; and, as I don't plan a very large system and plan to keep the grid as backup, I would like to keep the 24v inverter (cotek) and Kid as they have peformed very well, so I have been fudging and hoping the median of 24v would be a good compromise. I realize that 48v and 72v would be preferable for a  larger system, but this is mostly a growing small system with plans to re-use some parts.  I plan on picking up a 500ah NiFe battery but still kicking that one around. The cost would be roughly 7x over a used forklift LA battery... and I'll need to get an Outback inverter and since I have been happy with the Kid, probably a Classic.

Note that my system has been completely DIY, the system is not tied into the house's electrical at all.  The system is supplemental to the existing wiring and is comprised mostly of extension cords to the 2 appliances I run off the current system.  But, since I have not yet actually purchased the new components, its not too late to change my mind.... have at it gents! I am open to persuasive arguments to swing my away from the 24v I am currently planning.

aloha,
walt
• Solar Expert Posts: 2,993 ✭✭✭✭
edited March 2016 #8

Hi walt,

Do not know exactly what PVs you are running,  but at 285 watts,  they might be 72 cell or 60s.   And assume  that you  are running a Kid CC (?).

If you added a fourth PV in series,  you may well be running at the very high end of acceptable Vin to either a Classic or Kid.

Guess that you are in HI,  so Cold Voc may not be a huge concern ...  dunno.

You might be planning on going to two strings of two PVs,  if you added a fourth module,  and that would seen to be the best,  from a Vin to the CC standpoint.

FWIW,   Vic

Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
• Solar Expert Posts: 143 ✭✭
edited March 2016 #9
Hi Vic, yes, I'm in Hawaii. The panels are Trina Solar TSM-280 and Voc is 44.7v, Vmp = 35.6, Imp = 8.02A.   Under use, the Vmp is close, and the Imp is slightly higher at something over 9A. But as stated earlier, I rarely see this condition; and that was new, with sparkling clean, brand new panels. I have found that I need to wash them off about every other week (mostly red dirt, but occassionally stupid cat tracks are found)... the rinsings seem to increase Imp over half an amp per panel.  The controller is a 1 year old Midnite Kid. The temperature never drops below 58F here at night, during the days 75F-95F is normal.
• Solar Expert Posts: 1,218 ✭✭✭✭
I am getting my numbers from my current system, which is 3x 285w panels, and at high noon in the summer I see no more than 27.x amps to the Kid at roughly 112v
3*285W/24v*0.77 = 27.4A
3*285W/28.8V*0.77= 22.9A

Depending on the SOC it sounds like you are in the right place. I dont think thats you issue.

My 6v GC2 Interstates from costco have been a bear to live with.  I lucked out with 3 good performers but 1 was not so good.... so I exchanged it, and got another not so good performer; I just exchanged that one yesterday due to the excellent costco warranty, got in under the 1 yr mark easily....I could initially run (during the summer) both a 14.7cu ft fridge and a 7 cu ft chest freezer off the 208ah Interstates (just barely, with lots of sunny days); then during this winter it was down to only running the freezer .... then running the freezer for most of the time during the days but having to revert back to the grid latenight..
How you absolutely sure, those batterys are being charged properly? Thats a much more likely explanation than two consequitive failures, isnt it?

The charge rate is fine at 0.13C, so that leaves setpoints, shading, and loads.
For the latter, two 1200Wh/d fridges is 2400Wh /0.85 + 24h*30W= 3500Wh/d
At a peak production level of 650Wh, that implies the need of 3500/650= 5.4 sun hours.

Ive made some pretty aggressive assumptions there, but if thats at all whats going on there, then you can see how marginal that is to being sustainable. Around here i budget on a year round base load of about 1/2 of "average" daily production.

While I would like a 48v system, the batteries are probably going to be more expensive to the point of unobtainium; and, as I don't plan a very large system

Im lost , i thought you said you were planning on a upgrade to 3000Wp. That is a big system when it comes to lead acid. You  cant ramp up the PV without also scaling up the battery. Unless you go to lithium (which does allow smaller batteries in this type of system). Either way , do or do not, bigger system = bigger budget.

1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Solar Expert Posts: 143 ✭✭
edited March 2016 #11
Thanks, zoneblue.  My 14.7cu ft fridge uses .500kwh/day, measured by watt meter. I have not measured the freezer, but its a standard 7 cu ft frigidaire and the watt draw while on is slightly less than the fridge, but I've noticed the cycles are longer so it probably uses more than the fridge does, feels like twice as much. The setpoints on the Kid are:  29.6v absorb, 270 min (which I do reach if I have a sunny day and only 1 of the appliances connected... almost never reach float if both are on though), float 26.8v.

The manufacturer says SG of my batteries should be near 1.290, the 3 good cells have always been near 1.280 at full charge, the bad cell was down near 1.240 or 1.1xx or even lower, sometimes. I use a refractometer, much more accurate than hydrometer.  I have tried breaking the batteries up and running an EQ on only the bad cell, and it would come up, but only to near 1.240 or so.  I cannot keep the array fully charged all the time, they seem to spend most of their time near 70-80% SOC.  I have never let them go below 50%, ever, although I've come close to 50% a couple times.  I make the absorb voltage most days and make the float only once every other week, probably. I partially disconnect the loads to do so, though.
• Solar Expert Posts: 143 ✭✭
I do not believe the 2 bad cells were a result of misuse.  The SG's were pretty low, those particular batteries were much more thirsty and used lots of water... the costco I am at here doesn't seem to move their stock of the GC2 batteries very much. I see the batteries on the rack and the lead terminals are flat colored and there are acid tracks on the top of the case and a little corrosion sometimes on the terminals... i think the distributor has been taking them back and having to 'recondition' them due to long sitting on the shelf, as the old looking terminals have shiny, newly scrubbed parts as well as being old and slightly corroded in places. I try to pick the best looking ones, but doesn't seem to have worked.
• Solar Expert Posts: 1,218 ✭✭✭✭
My 14.7cu ft fridge uses .500kwh/day, measured by watt meter. I have not measured the freezer, but its a standard 7 cu ft frigidaire and the watt draw while on is slightly less than the fridge, but I've noticed the cycles are longer so it probably uses more than the fridge does, feels like twice as much. The setpoints on the Kid are:  29.6v absorb, 270 min (which I do reach if I have a sunny day and only 1 of the appliances connected... almost never reach float if both are on though), float 26.8v.
Exactly. So you are are a) deep cycling those batteries, and b) not that often reaching float. Do you have WBJr? If not you should and you should reach end amps and float for at least a couple hours at least one or twice a week. A fixed abosrb time only works on "average". Your system is working hard.

The manufacturer says SG of my batteries should be near 1.290, the 3 good cells have always been near 1.280 at full charge, the bad cell was down near 1.240 or 1.1xx or even lower, sometimes. I use a refractometer, much more accurate than hydrometer.
Thats my point, a series bank of batteries implies that the whole set must be overcharged to hit the lowest cells. Thats what a full absorb, and float achieves.

I have tried breaking the batteries up and running an EQ on only the bad cell, and it would come up, but only to near 1.240 or so.
Well, ok thats does sound bad. You did this with a 6V charger, for a decent period? If the cell wont reach full SG then its cooked, and a liability to the rest of the bank.
I cannot keep the array fully charged all the time, they seem to spend most of their time near 70-80% SOC.

Im still gona need more convincing. Your load profile is excessive for that bank, weve already established that. But to rerun the numbers:

Peak wattage= 3*285W*0.77 = 855W
Assumed east coast US sun hours for this time of year: 2.5hrs
Production = 855W * 2.5h = 2130Wh/d

AC Consumption: 500Wh/day + 800Wh/day = 1200Wh
DC consumption= 1200Wh/.85 +24*30W = 1920Wh

Thats why you arent making float, and if youve had the batteries any period most likely why they are failing. With lead 70% isnt enough. All cells must reach full SG regularly.

I have never let them go below 50%, ever, although I've come close to 50% a couple times.  I make the absorb voltage most days and make the float only once every other week, probably. I partially disconnect the loads to do so, though.

What do you judge your SOC numbers on? I might be barking up a tree, but they dont appear to tally with your other data.

1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar