What size MPPT charge controller? 100/20 to 150/60 in one table

The short answer. Two numbers pick it. Your panels’ open circuit voltage, cold-day margin included, has to stay under the controller’s first number. Your panel watts divided by battery voltage tells you the charge amps, the controller’s second number. On a Victron SmartSolar, a 100/30 takes up to 100 V from the panels and puts up to 30 A into the battery.

You’ll need

• Your panels’ datasheet or label: the Voc (open circuit voltage), Isc (short circuit current) and watts
• Your battery bank voltage (12V or 24V on most boats, vans and RVs)
• Your daily use in amp-hours. The Battery bank size calculator works it out
• A controller from the table below, or the whole range in Solar charge controllers

Match your panels to a controller, step by step

1. Find your battery voltage column in the table below.
2. Pick the first model whose nominal PV power covers your array.
3. Check the voltage. For a series string, multiply one panel’s Voc by the number of panels, then add the cold-weather margin. Keep it under the controller’s first number.
4. Check the current. Add up the Isc of your parallel strings. Keep it under the controller’s max PV short circuit current.
5. Set the controller to your battery maker’s charge voltages.
6. Fuse the battery cable at the battery, then size that cable.

You can do this. Most people size a solar controller from panel watts alone, which gets close. The limits that can actually hurt the controller are voltage and current, and on a Victron both are printed right in the name.

How do I read a Victron MPPT name?

The name is two numbers with a slash between them.

• The first number is the most PV voltage the controller can take. Victron’s manual says the maximum PV voltage is “indicated in its product name” (S3). A 100/30 takes up to 100 V. A 150/45 takes up to 150 V.
• The second number is the charge current into the battery, in amps. It matches the “rated charge current” line on every datasheet. A 100/30 charges at up to 30 A, a 150/60 at up to 60 A.

So a 100/30 and a 100/50 take the same panel voltage. The 100/50 just pushes more amps into the battery.

Which SmartSolar MPPT fits my system?

All numbers come from Victron’s datasheets (S1, S2, S4, S5).

*On the 150 V models, Victron lists 150 V as the absolute maximum in the coldest conditions and 145 V as the start-up and operating maximum. Picking 36 V on those two takes Victron’s software tool. The 100/20 in the table is the 100/20-48V version. Victron gives 98% as the peak or maximum efficiency for every model here.

Why does the same controller take twice the watts at 24V?

The controller limits amps going into the battery, not watts coming off the panels. Watts are volts times amps. At 24V, every amp into the battery carries twice the power it does at 12V. So a 100/30 is rated for 440 W of panel at 12V and 880 W at 24V (S2). Same box, same 30 A.

Still choosing a bank voltage for a big array? That’s a real reason to look at 24V. Already on 12V in your boat or van? Read the 12V column and don’t worry about the rest.

Can I connect more panel watts than the nominal rating?

Yes, within limits. Every datasheet in the table has the same footnote: connect more PV power and the controller just caps its input. You won’t get more than the rated charge current out of it.

Two limits are hard ones. Going over either can damage the controller, so check both:

1. Short circuit current. Victron says a PV array with a higher short circuit current than the maximum “may damage the controller.” Add up the Isc of your parallel strings and keep it under the table’s number.
2. Open circuit voltage. See the next section.

Should my panels be in series or parallel?

Victron allows series, parallel or a mix of both (S3). Here’s the trade:

• Series adds the panels’ voltages and keeps the current of one panel. Higher voltage means thinner wire for the same power over a long run, and the controller starts charging earlier on a dim morning. It also brings you closer to the voltage limit.
• Parallel adds the currents and keeps the voltage of one panel. You stay far from the voltage limit, but you have more amps on the wire and more short circuit current to keep under the controller’s maximum.

To check a series string, multiply the panel’s Voc from its datasheet by the number of panels in the string. That total must stay under the controller’s first number, with the margin below.

To check parallel strings, add the Isc of each string. That total must stay under the controller’s max PV short circuit current.

The cold-weather warning, in Victron’s words

A panel’s open circuit voltage goes up when it’s cold. Victron’s manual says that for arrays in cold climates, or where night temperatures get near or below 10°C, you should allow for output above the panel’s rated Voc. Its rule of thumb is an additional 10% safety margin (S3, section 8.5.5; same text in S6).

If the PV voltage goes over the maximum, the controller stops charging and shows error #33. It starts again once the voltage drops 5 V below the rated maximum. Victron says the controller can be damaged by overvoltage, and that this damage isn’t covered by warranty. So give yourself the margin.

For the exact cold-weather rise of your own panel, read its temperature coefficient of Voc on the panel datasheet. Victron also links an MPPT sizing calculator from each controller’s product page.

Why won’t my controller start charging in the morning?

The panels need some headroom over the battery. Victron’s datasheets say the PV voltage must be more than the battery voltage plus 5 V before the controller starts. After that, it keeps running down to battery voltage plus 1 V. A single small panel on a 24V bank, or a shaded string, can sit under that line for longer than you’d expect. Panels in series get over it sooner.

How many watts of panel do I need?

That comes from your daily use and your sun. Work out your amp-hours per day with the Battery bank size calculator, then size the array with the Solar array size calculator. It pulls the controller numbers from the table above. For your peak sun hours, the free PVWatts calculator gives the solar resource for your address.

Once you know the watts, the table picks the controller. Read your battery voltage column and choose the first model whose nominal PV power covers your array. Then check Voc (with the 10%) and Isc against it.

Does this guide fit your setup?

This applies if: – You run a 12V, 24V or 48V DC system on a boat, van, RV or cabin. – You’re choosing a Victron SmartSolar MPPT, or checking panels you already own against one.

This doesn’t apply if: – You’re using a PWM controller. They work differently and this sizing doesn’t carry over. – You’re feeding a grid-tie or hybrid inverter that has its own solar input. Follow that inverter maker’s sizing. – Your panels’ datasheet is missing. Without the real Voc and Isc, don’t guess. Get the numbers first.

Charge settings matter too. Set the controller to your battery maker’s charge voltages. Upgrading a boat to lithium: everything around the battery covers that check for every charger aboard. Fuse the battery cable at the battery: Victron’s 100/30 manual calls for a 35 A to 40 A fuse on the 100/30 and 55 A to 70 A on the 100/50 (S3). Size the cable with the Wire gauge calculator.

Products used in this guide

Prices show live from the store.

Bundles for this job: Van solar starter kit, Victron smart system bundle

Quick answers

What does 100/30 mean on a Victron MPPT? Up to 100 V from the panels and up to 30 A into the battery. The first number is the PV voltage limit, the second is the charge current.

Can I put more panels on my MPPT than its rated watts? Victron’s datasheets say the controller limits input power if more PV is connected, so extra watts get capped at the rated charge current. Keep the array’s short circuit current and open circuit voltage under the controller’s limits. Going over those can damage it.

How much margin do I need for cold weather? Victron’s manual gives a rule of thumb of an extra 10% on top of your array’s rated Voc where nights get near or below 10°C. Check your panel’s own temperature coefficient for the exact rise.

Will a 100/30 work on a 24V battery? Yes. It auto-selects 12V or 24V, and its nominal PV power doubles to 880 W at 24V. It doesn’t do 48V. In this table, the 100/20-48V and the two 150 V models do.

Why does my controller sit idle at dawn? The PV voltage has to be at least 5 V above the battery voltage before it starts, per Victron’s datasheets. Panels in series reach that sooner.

Related guides: Cerbo GX: do you need one on a boat?

Sources

• Victron SmartSolar MPPT 75/10, 75/15, 100/15, 100/20-48V datasheet: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20_48V-EN.pdf
• Victron SmartSolar MPPT 100/30 & 100/50 datasheet: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf
• Victron MPPT solar charger manual, SmartSolar MPPT 100/30 & 100/50: https://www.victronenergy.com/upload/documents/Manual_SmartSolar_MPPT_100-30__100-50/29694-MPPT_solar_charger_manual-pdf-en.pdf
• Victron SmartSolar MPPT 150/35 & 150/45 datasheet: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-150-35-&-150-45-EN.pdf
• Victron SmartSolar MPPT 150/60 & 150/70 datasheet: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-150-60-&-150-70-EN.pdf
• Victron MPPT solar charger manual, SmartSolar MPPT 150/60 up to 250/70: https://www.victronenergy.com/upload/documents/Manual_SmartSolar_MPPT_150-60_up_to_250-70/29694-MPPT_solar_charger_manual-pdf-en.pdf
• PVWatts Calculator: https://pvwatts.nlr.gov/