# solar panel controller question



## budgetprepp-n (Apr 7, 2013)

I have a question about solar panel controllers. I'm doing some trading and I might end up with 
five 245 watt panels. I'm not sure but I think it goes like this. max volts 30.8 max amps 7.96

My question is for 5 of these what would I use for a controller? 
If I use a 40 amp mppt controller how many of these can run to it and how should they be wired?
Parallel or series?

I'm way out of my league here but an extra 1,225 watts would be nice.


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## alterego (Jan 27, 2013)

midnite solar has a fantastic sizing application for checking what device they have will suit your energy production,

MidNite Solar - Classic Sizing Tool.


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## budgetprepp-n (Apr 7, 2013)

alterego said:


> midnite solar has a fantastic sizing application for checking what device they have will suit your energy production,
> 
> MidNite Solar - Classic Sizing Tool.


Had some trouble with the chart hopping to get a answer I can understand


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## Mad Trapper (Feb 12, 2014)

P = V X I

Depends if you wire in parallel or series for volts. What sort of bats and wiring?

That should be a bit more than 10 amps at 12 volts


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## HuntingHawk (Dec 16, 2012)

Panels will be wired in parallel. That keeps the voltage the same But adds the amperage. In theory you would/could come close to 40amps. Note that those panels are for a 24volt system so your controller will have to be for 24volt also.


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## Mad Trapper (Feb 12, 2014)

(245W x 5 panels) /12V = 20.4 amps

Whoops, amps


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## HuntingHawk (Dec 16, 2012)

If those five panels were hooked up in series you would end up with about 150volts at 7.96amps.


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## paraquack (Mar 1, 2013)

Try this link. It looks pretty good
Introduction to Charge Controllers
From what I can tell from reading the label in the first post, these are 24 volt solar panels not 12 volt. The math says you'd need a minimum 40 amp, 24 volt controller and you'd probably be better off with a 60 amp controller, depending on how much clear sky and sun you get.


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## HuntingHawk (Dec 16, 2012)

Only in theory would that system reach 40amps. I've never heard of a panel getting the advertised amperage.


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## paraquack (Mar 1, 2013)

Especially the older a panel get. Oh, panels need at least 4 inches of space under them for proper cooling, other wise they overheat and performance is reduced. Didn't read if it reduced life span.


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## budgetprepp-n (Apr 7, 2013)

Ok these panels are 7.96 amps and 30.8 volts (If i'm reading the label right )

So if I go in series I will have 154 volts and 7.96 amps

And if I go parallel I will have 30.8 volts and 39.8 amps < are these numbers correct?

How does wiring parallel or series affect the watts?


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## budgetprepp-n (Apr 7, 2013)

HuntingHawk said:


> Panels will be wired in parallel. That keeps the voltage the same But adds the amperage. In theory you would/could come close to 40amps. Note that those panels are for a 24volt system so your controller will have to be for 24volt also.


I'm using a tracer 40 amp controller. I think it will adapt to what ever battery bank it is hooked to 12 OR 24 volts


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## budgetprepp-n (Apr 7, 2013)

These are the specifications of the controller I would like to use


Specifications of MPPT 40A

Model	Tracer-4210RN
Rated system voltage	12/24V auto work
Rated battery current	40A
Rated load current	20A
Max.battery voltage	32V
Max.PV open circuit voltage	100VDC
Max.PV input power	12V 520W; 24V 1040W
Self-consumption	<10mA（24V）
Charge Circuit Voltage Drop	≤0.26V
Discharge Circuit Voltage Drop	≤0.15V
Communication	TTL232 / 8 pin RJ45
Temp.compensation	-30mV/℃/12V（25℃）
Working temperature	-35℃～+55℃
Storage temperature range	-35℃～+80℃
Humidity	10%-90% NC
Enclosure	IP30
Altitude	≤3000m
Dimension	242mm x 169mm x 91mm
Mounting holes	180mm x 160mm
Mounting hole size	Φ5
Terminal	25mm2


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## HuntingHawk (Dec 16, 2012)

Yes because when you hook up a controller you hook up to the batteries first. That tells the controller whether its a 12 or 24V system.


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## budgetprepp-n (Apr 7, 2013)

Ok I'm reposing these questions they got berried and I would like to know about the watts also is the formula correct?

Ok these panels are 7.96 amps and 30.8 volts (If i'm reading the label right )

So if I go in series I will have 154 volts and 7.96 amps ----30.8 volts x 5=154

And if I go parallel I will have 30.8 volts and 39.8 amps----7.96 amps x 5= 39.8 

How does wiring parallel or series affect the watts?


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## HuntingHawk (Dec 16, 2012)

That is correct. When you wire in parallel the voltage stays the same but the amperage increases. That is probably how you have your batteries wired. Its also how you attach jumper cables when you jump start a vehicle.

When you hook up in series the amperage stays the same & the voltage increases.


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## HuntingHawk (Dec 16, 2012)

Getting posted amperage from panels posted on the labels just isn't going to happen. Its like expecting to get posted mpg of a motor vehicle. With that said, you will probably max out at 35amps at 24VDC.


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## HuntingHawk (Dec 16, 2012)

How does wiring parallel or series affect the watts? 

P=EI means wattage equals voltage times amperage.

So hooked up in series for the five panels would be 154 x 7.96 = 1225.84watts

Hooked up in parallel for the five panels would be 30.8 x 39.8 = 1225.84watts

I do not know what will happen when 24V panels are fed threw a controller to a 12V battery system. You would really need to call or email a solar company to get the answer to what change it will have on the amperage fed to the batteries versus amperage from the panels to the controller


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## budgetprepp-n (Apr 7, 2013)

HuntingHawk said:


> How does wiring parallel or series affect the watts?
> 
> P=EI means wattage equals voltage times amperage.
> 
> ...


I think I will be OK on the 12 volt battery bank. I last time I added on I used two panels that were for "grid tie in"
I did them in parallel and they work just fine.

For me I have a little trouble with wiring up in series. I have a lot of overcast days and a little shade now and then
and it seems like that really bogs everything down. On a day when there is no direct sunlight wired in parallel I still
get a good charge. When I ran my full size refrigerator for two days just to see if I could there was no direct sun light
and in the day everything charged up all the way while running the fridge.

below is the panels I used for adding on I used two of them


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## budgetprepp-n (Apr 7, 2013)

I guess sometimes the best way to see what will work is to just put on your safety glasses step back
and flip the switch. (fingers in ears)



<-- they said that running a blower on the street wouldn't work but it did 
Just ask that cop


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## HuntingHawk (Dec 16, 2012)

Solar panels are not grid tie or off grid. The controller does that.


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## HuntingHawk (Dec 16, 2012)

The ONLY reason I know of to hook panels in series is if a long distance between panels & controller. DC voltage has a huge power loss.


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## HuntingHawk (Dec 16, 2012)

If it were me, I would hook it all up but attached to just one battery that is 80% charged roughly. Something goes wrong you will destroy one battery instead of eight.

EDIT: Also you might think about only using two panels in your initial testing.


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## tinkerhell (Oct 8, 2014)

budgetprepp-n said:


> Ok I'm reposing these questions they got berried and I would like to know about the watts also is the formula correct?
> 
> Ok these panels are 7.96 amps and 30.8 volts (If i'm reading the label right )
> 
> ...


each panel must be pretty large, no? how big will the 5 panels be if put together?


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## HuntingHawk (Dec 16, 2012)

Rough dimensions of a 225 is 65.04 x 39.37 x 1.97


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## budgetprepp-n (Apr 7, 2013)

tinkerhell said:


> each panel must be pretty large, no? how big will the 5 panels be if put together?


Yea I'm not sure but yes they are pretty big. I an going to need to mount these on the roof of the 
porch. Which may cause some problems with the snow we get.


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## Montana Rancher (Mar 4, 2013)

budgetprepp-n said:


> I have a question about solar panel controllers. I'm doing some trading and I might end up with
> five 245 watt panels. I'm not sure but I think it goes like this. max volts 30.8 max amps 7.96
> 
> My question is for 5 of these what would I use for a controller?
> ...


Sorry for coming so late to the party but here is a basic reply

For every 1000 watts of solar panels you need a charge controller of 20 amps.

So for your 1200 watt system a 25 amp charge controller will be fine, if it is larger so much the better as you and add more panels and not have to upgrade your controller every time.

Its the simple answer and the correct one, if you have questions I suggest www.backwoodsolar.com they are very helpful and supplied most of my needs.


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