# Thread: 30 AMP MPPT Charge Controller?

1. Registered Guest
Join Date
Apr 2011
Posts
16

## 30 AMP MPPT Charge Controller?

What is the total wattage input for a 30 AMP MPPT Charge Controller according to each rated voltage example below?

Rated Voltage
12V / 24V / 48V

30A

Input voltage range
12V~20V/40V ~40V/ 48V~8OV

Over voltage protection
17V / 34V / 68V

Full charge cut
13.7V / 27.4V / 54.8V

Low voltage cut
10.5V~11V / 21V~22V / 42V~43V

In simpler terms, what will be the maximum solar array wattage for this 30 AMP charge controller at 12, 24, and 48 Volt battery banks?

Thanks

2. BB.
Just some guy
Join Date
Mar 2006
Location
SF Bay Area (California)
Posts
21,546

## Re: 30 AMP MPPT Charge Controller?

The generic recommendations for a MPPT charge controller using 0.77 as a derating... MPPT Controllers are rated on their output current (say 30 amps) and whatever the programmed charging voltage is (say 14.5 volts for a 12 volt battery bank). Note that Power = Voltage * Current, so if you have variable voltage (12 volt so 14.5 volts from "dead" to fully charged, you do get variable power numbers with a fixed charging current)...

But, anyway, here is my "cost effective" maximum array recommendation (as always, you need to meet the voltage/current input and output specifications for each controller):

• Max Array Size = 30 amps * 14.5 volts * 1/0.77 array+controller deratings = 565 Watt array cost effective maximum
• Max Array Size = 30 amps * 29 volts * 1/0.77 array+controller deratings = 1,130 Watt array cost effective maximum
• Max Array Size = 30 amps * 58 volts * 1/0.77 array+controller deratings = 2,260 Watt array cost effective maximum

Note, you can go larger (controller output is current limited so at high noon on a clear day, you will not use 100% of the available panel power).

Also, if your system is in a cold region, you could use 0.80 or 0.82 (or even larger) derating number--Cold panels have higher Vmp, which means more wattage (for an MPPT type controller).

And battery brand/type can also make some changes... AGM tend towards 14.2 maximum voltage when charging. And Trojan tends to recommend 14.85 volts rate of charge... So, you can play with those numbers too.

In reality, if you are within 10%--that is "close enough" for solar... There is enough variability in Weather, specifications, mounting, etc. that you don't need to "match" the above numbers to four places.

-Bill

3. ## Re: 30 AMP MPPT Charge Controller?

I have to ask what charge controller that is.
A couple of things about those specs bug me. For one, if it thinks a 12 Volt deep cycle is fully charged at 13.7 it's wrong. Two, the input Voltage maximums seem extremely limited. Three, over-Voltage protection on the output of a charge controller? It should have charge set-point limits.

As a general rule, the array Wattage is equal to the maximum output current * nominal system Voltage plus a little room to allow for variation in panel output (usually 20%).

As in: 12 Volts * 30 Amps = 360 Watts / 0.8 = 450 Watts. The other system Voltages would follow on those lines: 24 Volt @ 900 Watts, 48 Volt @ 1800 Watts.

Good quality name-brand charge controllers will tell you specifically in their manual what their maximum recommended array size is for any given output Voltage.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•