What Size Victron MPPT Do I Need? Sizing Guide

What size Victron MPPT do you need? Victron names every controller with two numbers, and once you know what they mean, sizing takes five minutes. A 100/30 accepts up to 100V of panel open-circuit voltage and delivers up to 30A of charge current. You need both numbers to fit your array: the voltage rating protects the controller, and the current rating sets how much of your panels’ power reaches the battery.

Solar Saving on the most common charge controller sizing mistake.

What Size Victron MPPT: Victron’s Official Ratings

Victron publishes a “nominal PV power” for each model and battery voltage. If you connect more panel watts, the controller simply limits input power.

Model	Max PV Voc	Charge current	Nominal PV at 12V	at 24V	at 48V
SmartSolar 75/15	75V	15A	220W	440W	n/a
SmartSolar 100/20 (48V)	100V	20A	290W	580W	1,160W
SmartSolar 100/30	100V	30A	440W	880W	n/a
SmartSolar 100/50	100V	50A	700W	1,400W	n/a
SmartSolar 150/35	150V (145V operating max)	35A	500W	1,000W	2,000W
SmartSolar 150/45	150V (145V operating max)	45A	650W	1,300W	2,600W

Source: Victron SmartSolar datasheets.

Step 1: Current (the Second Number)

A quick estimate: panel watts ÷ battery voltage ≈ charge amps. 400W ÷ 12V ≈ 33A, which is slightly above a 100/30. Victron’s own rating says the 100/30 handles 440W nominal on 12V, because panels rarely produce full rated power. This is an estimate; real current depends on temperature and sun angle.

Step 2: Voltage (the First Number)

Add the open-circuit voltage (Voc) of panels wired in series, then allow for cold. Panel Voc rises as temperature drops, so a string that is fine in summer can exceed the limit on a freezing morning. Use the panel’s temperature coefficient from its datasheet and your coldest expected temperature. Victron’s MPPT calculator on its website does this math for you.

Step 3: Battery Voltage

Moving from 12V to 24V doubles the nominal PV a controller can handle: the 100/50 goes from 700W to 1,400W. If you’re building a large array, a higher battery voltage can save you buying a bigger controller.

Quick Picks (Estimates)

100–200W on 12V: 75/15 or 100/20.
300–440W on 12V: 100/30.
450–700W on 12V: 100/50.
Larger arrays or higher-voltage strings: 150/35, 150/45 or bigger.

As an Amazon Associate I earn from qualifying purchases, at no cost to you.

Buy: Victron SmartSolar MPPT 100/30 on Amazon

Datasheets and manuals for the Victron SmartSolar MPPT 150/35 and Victron SmartSolar MPPT 75/15 are on Victron’s website.

Worked Example: A 400W Van Array on 12V

Four 100W panels, each with a Voc of about 22V (a typical figure for 12V-class panels; check your label), on a 12V lithium battery.

All four in parallel: Voc ≈ 22V. Current ≈ 400W ÷ 12V ≈ 33A at full sun. A 100/30 is within Victron’s 440W nominal rating, and a 75/15 is far too small.
Two in series, two strings in parallel: Voc ≈ 44V, plus cold-weather margin. Still well under 75V, so a 100/30 fits with room to spare.
All four in series: Voc ≈ 88V before cold correction. On a freezing morning that can approach or pass 100V, so a 150/35 is the safer choice for that wiring.

Estimates: real panel voltages vary by model and temperature.

Worked Example: An 800W Cabin Array on 24V

Four 200W panels on a 24V battery bank. Panel watts ÷ battery voltage ≈ 800 ÷ 24 ≈ 33A. Victron’s nominal PV rating for the 100/30 at 24V is 880W and for the 150/35 it’s 1,000W, so either can work depending on how you wire the strings. If each 200W panel has a Voc around 45V (typical, check yours), two in series reaches about 90V before the cold correction, which points to the 150/35. Two parallel strings of two panels then give the full 800W.

Worked Example: Same Panels, Different Battery Voltage

Take a 1,200W array:

Battery	Approx. charge current (est.)	Controller that fits (by nominal PV)
12V	≈ 100A	Two 100/50s, or a larger single controller
24V	≈ 50A	150/45 (1,300W at 24V)
48V	≈ 25A	150/35 (2,000W at 48V)

Estimates: watts ÷ battery voltage. The higher the battery voltage, the smaller the controller you need for the same panels.

Cold-Weather Voltage Check

Here’s how to do the cold correction by hand:

Find the panel’s Voc and its temperature coefficient of Voc, often around −0.3%/°C, on the panel datasheet.
Subtract your coldest expected temperature from 25°C. For −10°C, that’s 35 degrees.
Multiply: 35 × 0.3% ≈ 10.5%. Add that to the Voc.
Multiply by the number of panels in series and compare with the controller’s first number.

For example, two panels with 45V Voc at −10°C: 45 × 1.105 × 2 ≈ 99.5V. That’s right at the limit of a 100V controller, so a 150V model is the comfortable choice. Estimate using a typical coefficient.

Oversizing the Array

Victron allows more panel watts than the nominal rating; the controller simply limits charge current to its maximum. Some builders add 10–30% extra panels so they reach full charge current earlier in the morning, later in the afternoon and on hazy days. The one hard rule stays the same: the string’s cold Voc must stay under the controller’s voltage rating.

Setting Up the Controller

Once it’s installed, open VictronConnect and choose the battery preset that matches your battery chemistry, or enter the battery maker’s absorption and float voltages. Connect the battery before the panels so the controller detects the system voltage correctly.

FAQ

Can I put more solar on a Victron MPPT than it’s rated for?

Yes on watts, no on volts. Victron says extra PV power is limited by the controller, but the maximum open-circuit voltage must never be exceeded.

What does 100/30 mean?

100V maximum PV open-circuit voltage and 30A maximum charge current.

SmartSolar or BlueSolar?

Same sizing. SmartSolar adds built-in Bluetooth.

Does a 24V battery need a different MPPT?

Most 75V and 100V models auto-select 12 or 24V. Check the datasheet for 36/48V support.

Should I wire panels in series or parallel?

Series raises voltage and lowers current, which reduces cable losses on long runs. Parallel keeps voltage low and handles partial shading better. Either works as long as the cold Voc stays under the controller’s rating.

Can I run two Victron MPPTs on one battery?

Yes. Many larger systems use two or more controllers, each with its own array, charging the same battery.

Sources: Victron datasheets for SmartSolar MPPT 75/10–100/20, 100/30 & 100/50 and 150/35 & 150/45 (victronenergy.com); Solar Saving, “How to Size a Solar Charge Controller? Avoid This Mistake”; SotaSolar, “How Many Watts of Solar Can You Put on a 100/50 amp Victron MPPT”.