Help choosing the right MPPT Charge controller ....

**sensij** · 10-19-2017, 11:58 PM

Would you be willing to consider a hybrid grid-tie inverter? If your power company offers net metering, you could actually get some financial benefit from this backup system.

**AngliaUSA** · 10-20-2017, 12:12 AM

I looked into it .. but my power company won't allow it because my weekend cabin electrical usage is so low .... $10 per month max on average ... they size the system based on load / usage and monthly bill etc. I am pretty familiar with them as my principal residence in the city has a 5KW grid tie system on my roof... 7 years old now and it has just paid for itself ! Cost me $15k 7 years ago and my electrical bills went from $250 a month to $250 for the year .....

If and when the old Trace inverter dies I'll upgrade to a new True Sine Wave , and possibly do a hybrid grid tie ..... but for now I'd like to use the set up that I have and the new panels ....

I just need the right Charge Controller to take 600V / 84 amps from my array into my DR3624 Trace ...

**sensij** · 10-20-2017, 12:47 AM

You should probably be looking for a 40-60 A mppt CC, with 150 Voc string input. That would let you wire your array into four strings of 3 panels each. Outback FM60 is a popular choice, usually around $500. You'll need a four string combiner with over-current protection as well, and wire from the combiner to the charge controller that can handle the combined Isc's... 8.25 * 4 *1.56 = 51.5 A, so probably either 4 awg or 6 awg depending on how long the run will be. For $100-$150 more, the Midnight Classic 150 is an even more capable controller, although you'd have to remember to set the charge maximum to be 60 A or less so you don't hit the battery with full amount of current your array would be capable of.

**AzRoute66** · 10-20-2017, 01:09 AM

I got 6.7 x 12 = 80.4, not 84 - a minor distinction to be sure. Either way, I think I would be looking for two 40 amp controllers, or smaller, rather than one to take the whole bite. Perhaps not, I have a terrible sense of the price of stuff.

**littleharbor** · 10-20-2017, 08:34 AM

The Midnite Solar Classic SL 150, solar only controller, is selling online for slightly over $500.00 . 96 amp max output.

**AngliaUSA** · 10-20-2017, 11:29 AM

Thank you all .. your advice is very much appreciated ... OK .. so getting my head round your suggestions .. I didn't realize you can wire in parallel and in series at the same time to the same charge controller ... sorry I am a newbie at this ... figuring it out as I go along ...

so four strings of 3 panels .... each string of 3 panels are in parallel - resulting in 4 x 33.4V / 21 amps on each string

giving me a combined total of the 4 strings of approx. 134V / 84A at the charge controller ...

makes sense .. thanx.

So now ... HOW do I figure the wiring of the panels correctly ... could anyone draw me a map showing the right way ? + to + or + to - etc

The panels each have the standard plus and minus MC4 connectors. ... but that only allows to me to connect as one single string of 12 as configured.

I guess I need the right adapters for the MC4 connections to reverse the polarity .. thus allowing me to connect + to + etc ....

Suggestions on which four string combiner with over-current protection to get ?

Thanx again . James.

12 panels - wiring map.pdf

12 panels - wiring map.jpg

**littleharbor** · 10-20-2017, 11:37 AM

You bring the 4 strings together in a fused combiner box. You can buy MC-4 connectors and crimp your own home run wires or buy various lengths of pre terminated MC-4 wire. You cut these lengths in half and bring the raw ends into the combiner. Some combiner boxes have MC-4 inputs, in which case you use whole MC-4 terminated wires and just plug them in.

**Raul** · 10-20-2017, 12:22 PM

You guys missed the nominal batt. Voltage? Or I'm reading it wrong.

So your system is 24v. That means 12x226=2700wp/24v nom= 112,5 potentially charging amps.
That is 2 60A chargers if mppt .
Also with a 60 cell panel you will not be able to charge a 24v ; so the 12 paralel is out. The 4 strings of 3 will work well . You will have 99,3v at 6,7A per string in paralel the charger will see 99,3 at 26,8A at the input. The output will be your total panel power 12x225 wich is 2700wp divided by the batery bank voltage 24 v = 112,5A. That's why I suggested you need atleast 2 60A chargers to use the 12 panels.

**AngliaUSA** · 10-20-2017, 12:31 PM

If each string of 3 panels is wired in parallel then the output voltage off the string is still 33.3V ...right ? .. only the amperage increases to 21 V

so when run the 4 strings through to a combiner box I'll end up within a total of 4 x 33.3 = 134V and 84 amps .. or am I missing something ?

Is this the right combiner box to consider ? and plugs ?

https://www.amazon.com/Midnite-Solar..._&dpSrc=detail

https://www.amazon.com/Findyouled-Fe...3GWZFD5N75V0R5

https://www.amazon.com/Signstek-Branch-Parallel-Connector-Adapter/dp/B00Q26PC04/ref=pd_sim_86_7?_encoding=UTF8&psc=1&refRID=5QRACSK0ANR033QB01FT

Thanx.

**Raul** · 10-20-2017, 12:42 PM

No, it's (33,1x3) when you put 3 panels In series add the voltage and amp remains the same . When you put the strings in paralel Voltage remains the same (at string level) and ad the amps . Read properly, I explained it above.

**AngliaUSA** · 10-20-2017, 12:57 PM

That's my point ... I'm NOT wiring the string of 3 in series ... in order to reduce the total voltage I need to wire in parallel. Hence the output of each string in parallel is still only 33.3 V with a combined amperage of approx. 21A.

If I have 4 of these strings going to a combiner box then my output from the combiner box is 4 x 33.3 = 134V and 84 amps .. or am I still missing something ?

This is all new to me so please forgive my lack of knowledge .. I am reading , rereading and hopefully asking the right questions .. Thank you for your patience.

**littleharbor** · 10-20-2017, 01:33 PM

A string IS series wired. Amperage will not increase, voltage will. The 4 paralleled strings will add the amperage of the 4 strings. Your illustration is actually incorrect. It shows 4 groups of parallel wired panels, nothing more. Nothing in the illustration is series wired.

**littleharbor** · 10-20-2017, 01:39 PM

Series wiring.jpg

This is 3 in series

**AngliaUSA** · 10-20-2017, 01:56 PM

ok so my terminology is wrong .. sorry .. I didn't know a group of panels wired in parallel isn't called a string ... I'll just call it a 'group' so as not to confuse anyone .. LOL .. me mostly

I understand the difference between wiring in series vs parallel and what it does to the respective voltage and amperage. ...

going back to what SENJI wrote .. 'You should probably be looking for a 40-60 A mppt CC, with 150 Voc string input. That would let you wire your array into four strings of 3 panels each.'

so yes if I wire 3 panels in series as a string then my combined voltage will be approx 100V and 7 amps.

then if I combine them all together I'll have 400 amps at the charge controller ....not really what I want to avoid the cost of a huge charge controller ..

But if I wire the 3 panels in parallel then I'll have 33.4 V and 21A going to the combiner box ...

So 4 lots of these 3 (parallel wired) panels and I'm back to where I want to be which is approx 133V and 81A ... does this sound right and doable ?

My diagram is mean't to show my 4 groups of 3 panels wires in parallel. As suggested.

My confusion grows .. perhaps back to the drawing board ...?

Help choosing the right MPPT Charge controller ....

Help choosing the right MPPT Charge controller ....

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