What am I missing ... ? Correct classic?

[Riverwind]

I'm trying to figure out the best size Classic. Panels are 230w, I'm thinking of putting them in 4 panel strings, two strings for a total of 8 panels.
So I've got 36.8 VOC x 4 panels in series =147.2v x 1.25 because lowest temps can be -40 so = 184v. Each panel outputs 7.67a Imp so that's times 2 strings = 15.34 amps. When I look at the Classic power graph http://midnitesolar.com/images/classicFrontPage/graphs.php I can't see anything near 15.34 amps. Should I be running a smaller controller? 

[ibeweagle]

your missing the mppt of the controlller here is some math 184 volts *15.34amps  = watts 2822.56 max ok now buck into 48 volt bank watts devide by volts 2822.56/48 = 58.8 amps into 48 volt battery bank arox or 2822.56/24 volt bank =117.6 amps would go with personnaly classic 200

[Riverwind]

Still don't think I understand this. Doing the math you suggest - 2822.56 for a 24v system at 117.6 amps?? ... the Classic power graph doesn't go over 100 amps. Is this correct?

[laszlo]

A solar panel will typically output only 70-80% of its rated in normal operating conditions.  Look for specs for your panels that quote the  "NOC" - normal operating condition - values.

The CC will regulate the power  if it exceeds the rated amps. You should be OK on a 24V system, but I highly recommend a 48V battery bank -- they are so much more efficient at power transfer.

Still don't think I understand this. Doing the math you suggest - 2822.56 for a 24v system at 117.6 amps?? ... the Classic power graph doesn't go over 100 amps. Is this correct?

[Riverwind]

I'll try once more as there don't seem to be any replies to my question. If there are then I'm s t i l l missing the answer, chalk it up to senility. I have 8 230 watt panels and I'm considering two strings of 4 on a 24v battery, array located 100' from controller, . Can't go to 48v because of cost, I'm using a 1200 a/h battery bank and doubling it to 48 would kill the budget.
The question is: WHICH CLASSIC SHOULD I USE? I don't see my configuration fitting any of the scenarios shown on the Classic Power Chart. Should I be using a smaller controller or a different configuration for my panels?
36.8 VOC x 4 panels in series =147.2v x 1.25 because lowest temps can (rarely) be -40 so = 184v.

If ibeweagle is correct then I've got too many amps as the controller chart doesn't show anything around 117a. Surely this should be easier or there's a standard calculation I can use to make the decision. Appreciate any help!!

[Halfcrazy]

The Classic 200 would be required to run with the array configuration you specked. Now the Classic 200 is good for about 72 amps or 2066 watts according to the charts. So unless I am missing something the 200 should be just fine. 8 panels at 230 watts is 1840 watts and on a fairly dead battery say 24 volts this would be 76 amps with no losses or anything so this will be just fine.

I must confess to not reading the whole thread so I am unclear where the 117 amps comes from but from your last post this is what I come up with.

Ryan

Ok I went back and found the 117 amps they where multiplying IMP times temperature corrected VOC to get wattage. These 2 numbers will never be together if the array is at VOC the current will be 0 amps to get max amps you need to be at VMP.

The easiest way to figure any of these Classics is simply add up the wattage of the array and compare it to the battery voltage of the Classic you have in mind. Or to figure absolute max amps take the array wattage and divide by the nominal battery voltage this number will always be higher than what you will get in the real world unless it is super cold or there is some reflecting going on into the panels.

[Riverwind]

Thank you Ryan, that makes some sense. I have a neighbour who wants to replace his MX60 with a Classic and he has 6x215w panels at 48v, wired two in series, Vpm of 42.7v, so that would be about 27 amps according to your suggested calculation.

Once again I don't see which Classic would be appropriate for a 27 amp output. The 250 looks like the one he should use but he was told to use the 150 by his dealer!? Maybe I'm just not reading the Power Graph correctly. Some simple interpretive instruction would help on that page.

Martin

[Halfcrazy]

Yes the 150 would be his best deal. One thing to keep in mind is to use the higher voltage Classics when long wire runs come into play. Remember the 150 is the most powerful and least expensive.

Ryan

[ibeweagle]

Sorry for the confusion have to use the figures on the panels for array sizing VMP Voltage Max Power gessing 29.6v and IMP AMPS MAX POWER 7.67 = 227.032WATTS PER PANEL AND IF COLD VMP*1.25  AT  4 PER STRING YOU SHOULD NOT SEE OVER 148VOLTS IF EVER BECAUSE OF DIRT ON PANELS AND TEMP  Max wattage in cold weather should never be over 283.7watts  VMP*1.25*IMP 7.67 =283.7watts
watts per panel 4*283.7=1134.8 watts per string 2 strings =2269.6 watts    hope this clears some of it up cheers Mike p.s. if your 100 feet away you will have voltage drop so the wattage will be lower at 200 feet of wire drop and if it goes over 2123 watts would like to see it the classic will go into hyper or raise the voltage I think halfcrazy can chime in hear but would go with classic 200 if I was my set up.  Too get 2269.6watt you have to have spotless panels  -40 temp 10 feet of wire run! direct line with sun? and if It does go to hyper because of over current you safe as the 200 can handle the voc of the pannels of 183 volts VOC pluse the battery voltage 200volts +24 VOLT BATTERY BANK! THE CLASSIC 150 WOULD NOT HANDLE THE VOC OF THE STRINGS. ps this example is in one of an earlyer text book on solar will try to find