MPPT Controller Sizing?

[RobOfYork]

Do I understand this correctly?

I will have 600 watts of solar panels and a 12 v battery or battery bank.

600/12 = 50 amps

So I would need a 60 amp MPPT controller to be safe?

I'm learning slowly but still not sure.

 

[JDub]

Sounds about right to me. I have a 40 amp CC for 400 watts of panel - 24 amp load with some slosh but remember you're not going to get 600 watts out of your panels. An average would probably be ~ 70% of that. I'm not a solar guru though!

Cheers

 

[highdesertranger]

So your panels are not 12v they are probably 21v. So 600/21 = 28.57. That's the input to the controller.

It's important to remember that 12v panels are not actually 12v. Now I am just guessing on yours. What does the sticker on the back say? it tells you the amps too.

Also they don't charge at 12v more like 14 something

Highdesertranger

 

[B and C]

I have a 30 amp MPPT controller with 4-100 watt panels. This is right on the edge for the controller. Two 100 watt panels in series permanently mounted and another 200 as portables (for winter or shade parking). These two sets are wired in parallel. Mine are all wired with 10GA cable.

A 60 amp MPPT controller would be a good fit for the described application. You just want to make sure your panel voltage does not exceed the rated input of the controller.

 

[jimindenver]

General rule of thumb for a 12 volt system works out to

300 watts is a 20 amp controller

400 watts + 30 amp

500 watts = 40 amp

600 watts = 50 amp

800 watts = 60 amp

That said it is always important to check the guidelines of the controller that you are looking at. Some of my early 20 amp controllers downgraded their capacity from 300 watts to 275. In the opposite direction , Victron controllers tend to be able to handle more watts than the rule of thumb suggest.

 

[RobOfYork]

So your panels are not 12v they are probably 21v.  So 600/21 = 28.57.  That's the input to the controller.

It's important to remember that 12v panels are not actually 12v.  Now I am just guessing on yours.  What does the sticker on the back say?  it tells you the amps too.

Also they don't charge at 12v more like 14 something

Highdesertranger

I'm very new to this and confusing myself a lot. This is the panel I am getting. Not sure what voltage to look at. Lists a few.

Amazon.com : Renogy 100 Watt 12 Volt Monocrystalline Solar Panel, Compact Design 42.2 X 19.6 X 1.38 in, High Efficiency Module PV Power for Battery Charging Boat, Caravan, RV and Any Other Off Grid Applications : Garden & Outdoor

 

[RobOfYork]

I think I am a little confused. I thought the formula for minimum MPPT size was

Solar panel array wattage / battery bank voltage = minimum solar controller amp rating

I  got that from Mobile Solar Power Made Easy by William Prowse IV

 

[XERTYX]

Same here. The epever controller I was interested in supports up to 520 watts up to 100 volts input. 40 amps.

520w÷13v= 40a.

 

[XERTYX]

It seems that based on this the charge profile is equal to the amp rating of the charge controller.

 

[gtinseth]

I think I am a little confused. I thought the formula for minimum MPPT size was

Solar panel array wattage / battery bank voltage = minimum solar controller amp rating

I  got that from Mobile Solar Power Made Easy by William Prowse IV

highdesertranger is giving you the actual calculation. What you mentioned is a rough rule of thumb. Generally a 60a charge controller can supply up to 60a to the battery bank. The solar panels you hookup to it should be determined by the voltage and wattage rating of the controller. Those panels you listed can operate at over 20v each. In series, 120v+. Amps will be around 6a or less. You can also do two parallel panel banks of three panels to get half the volts and double the amps if that matches your controller better. If the controller can handle 120v and 600w, you should be fine with the panels in series.

 

[MrAlvinDude]

These are the specs (https://m.media-amazon.com/images/I/C1+gtN6MOES.pdf) of the panels you have linked to (https://www.amazon.com/Renogy-Monocrystalline-Solar-Compact-Design/dp/B07JXYTFF7)

So these numbers are part of what will be on the sticker on the back of the panel

"Electrical Data
Maximum Power at STC*: 100 W
Optimum Operating Voltage (Vmp): 17.9 V
Optimum Operating Current (Imp): 5.72 A
Open Circuit Voltage (Voc): 21.6 V
Short Circuit Voltage (Isc): 6.24 A
Maximum System Voltage: Cell Efficiency 21.0%
Maximum Series Fuse Rating: 15 A"


If you put all six panels in parallel, then your controller maximums are like:
- needs to be able to deal with 21.6V
- needs to be able to do about 6 x 6.24A = 37.44A

(a very theoretical max of 21.6V x 37.44A = 809W)

the practical max numbers are however more likely to be:
17.9V x (6 x 5.72A) = 17.9V x 34.32A = 615W

These are the limits, but your are not likely to see quite those numbers in the practical world.



If you connect two panels in series (repeated three times), the your max ratings look like this:
- max voltage : 2 x 21.6V = 43.2V
- max amps: 3 x 6.24A = 18,72A

 

[RobOfYork]

First, thanks everyone for responding and putting up with my learning curve.

I'm starting out with 600 watts of solar. 400 watts on all the time with a portable 200 watts I can plugin when needed.

Would this MPPT controller do what I need? Any opinions on it? I do want a little wiggle room and be able to use either AGM batteries or Lithium.

https://www.amazon.com/EPEVER-Contr.../B07J2GJJK4/ref=psdc_2236627011_t1_B081JWQJZL

Thanks for everyone help. WOW this is a learning process.

 

[MrAlvinDude]

So long as all the panels are the same, then you can use one solar charge controller.
If the portable solar panels are however different, then you will need two charge controllers.


With 12V coming from solar panels, the linked charge controller can manage: "Rated charge Power: 750W (12V) "

 

[RobOfYork]

After reading thread after thread and doing more research I think I am going to bite the bullet and just buy the following MPPT for my 600 watts of solar panels. Hate spending so much but...

Victron SmartSolar 150v 50a tr model at $540.00 ouch

https://www.amazon.com/Victron-Smar...t+250+60&qid=1616358322&s=lawn-garden&sr=1-13

 

[jimindenver]

Good choice

I would suggest getting the Smart sense bluetooth voltage and temperature sensor. It will tell the controller what the voltage and temperature is and can even be used to stop the charging of lithium batteries if they are below freezing.

https://amzn.to/38Z79uM

 

[RobOfYork]

Good choice

I would suggest getting the Smart sense bluetooth voltage and temperature sensor. It will tell the controller what the voltage and temperature is and can even be used to stop the charging of lithium batteries if they are below freezing.

https://amzn.to/38Z79uM

Thanks, I was wondering about that sensor and if it was worth adding.