Quick answer: For most boats, pick a Victron SmartSolar MPPT controller so that three things line up: (1) its battery-voltage rating matches your 12V, 24V, or 48V bank, (2) its output amp rating is at least your array's watts ÷ battery voltage, and (3) its maximum PV-input voltage rating — the first number in the model name (75, 100, 150, 250, or 450) — comfortably exceeds the cold-weather open-circuit voltage of your panel string. A 200W panel on a 12V system, for example, is a clean fit for a SmartSolar MPPT 100/20.

What an MPPT controller actually does

A solar charge controller sits between your panels and your battery bank and regulates charging so the batteries are topped up correctly and never overcharged. An MPPT (Maximum Power Point Tracking) controller does more than a basic PWM unit: it continuously finds the panel's most efficient operating voltage and converts the excess voltage into extra charging current. In real-world marine use that typically means 10–30% more harvest than a PWM controller from the same panels, and it lets you run higher-voltage panel strings over smaller, cheaper wire.

MPPT vs. PWM — which do you need?

• Choose MPPT when you care about harvest, run panels whose voltage is well above battery voltage, have longer cable runs, or run arrays above roughly 150W. This is the right call for nearly every cruising or liveaboard setup.
• PWM is acceptable only for small, low-voltage maintenance panels wired close to the battery — a trickle panel for a starting battery, for instance.

Step 1 — Match the controller to your battery voltage

SmartSolar controllers auto-detect 12V and 24V systems (larger models also do 48V). The controller must support your bank voltage, so confirm this first. Your battery chemistry matters too: Victron SmartSolar units have preset and fully custom charge profiles for flooded, AGM, gel, and lithium (LiFePO₄) banks, which you set in the VictronConnect app.

Step 2 — Size for your solar array

There are two numbers in every model name, e.g. 150/35. The first number is the maximum PV (panel) input voltage; the second is the maximum charge current in amps.

• Charge current (the second number): Estimate it as array watts ÷ battery voltage. A 500W array on a 12V bank needs roughly 500 ÷ 12 ≈ 42A, so you'd step up to a 150/45 or 100/50. It is always fine to fit a larger controller than the minimum — it simply runs cooler and leaves room to add panels later.
• PV voltage (the first number): Add up the open-circuit voltage (Voc) of your panels in series and make sure it stays below the controller's max PV rating — with margin, because panel voltage rises as temperature drops. On a cold, clear morning a string can exceed its rated Voc, and exceeding the controller's limit can damage it. When in doubt, size the voltage rating up (150V or 250V models give comfortable headroom for two or more panels in series).

Step 3 — Wiring, fusing, and connectors

• Fusing: Fit a fuse or breaker on the battery side sized to the controller's charge current, and follow ABYC practice for conductor protection. We can spec the correct MEGA/MIDI fuse and holder for your model.
• Cable: Size battery cable for the controller's full output current and the run length to keep voltage drop low. Higher-voltage panel strings let you use thinner, longer PV cable.
• TR vs. MC4: Larger SmartSolar models come in two terminal styles — Tr (screw terminals) and MC4 (pre-fitted solar connectors). Pick whichever matches how your array is wired.
• Marine environment: Mount the controller in a dry, ventilated space, vertically with terminals down, away from spray and engine heat. Give it airflow — these units derate if they can't shed heat.

SmartSolar MPPT selection chart

Use this as a starting point, then confirm your panel Voc against the max PV voltage. "Max array" figures are Victron's recommended maximums by system voltage.

Monitoring and networking

Every SmartSolar has built-in Bluetooth, so you can set charge parameters and watch live yield from your phone in VictronConnect. For an integrated system, the controllers link over VE.Direct or VE.Can to a Cerbo GX and the VRM portal, giving you remote monitoring of solar, battery, and loads from anywhere — a real advantage on a boat you don't sit on every day.

Frequently asked questions

Can one MPPT controller charge two battery banks?

A SmartSolar charges one main bank directly. To maintain a second (e.g. a start battery), add a Cyrix or Argo-style combiner/isolator, or use the controller's load/relay features where applicable. We can design this for your specific banks.

Should I wire my panels in series or parallel?

Series raises string voltage (better for long runs and MPPT efficiency) but you must stay under the controller's max PV voltage in cold weather. Parallel keeps voltage low but current high. Boats with partial shading from rigging often do better with careful series/parallel grouping — worth planning per vessel.

What size controller for a 100W panel?

Roughly 100W ÷ 12V ≈ 8A, so a SmartSolar 75/10 or 75/15 is ideal.

Can I add panels later?

Yes — and it's the best reason to buy one size up now. Just keep the total within the controller's charge current and PV voltage limits.

Will an MPPT work with lithium (LiFePO₄) batteries?

Yes. SmartSolar controllers have lithium charge profiles and integrate with Victron BMS systems so charging stops cleanly on a BMS signal.

Need help choosing — or installing?

Marine Electric Systems is an ABYC-certified marine electrical shop based at Bert Jabin's Yacht Yard in Annapolis, MD. We stock the full Victron SmartSolar line and can size the right controller, fusing, and wiring for your vessel — or handle the complete installation. Browse our Victron SmartSolar MPPT controllers or reach out to our Annapolis shop and we'll spec the right system for your boat.