What does an MPPT charge controller do?
- Lyall Burgess
- 4 hours ago
- 3 min read
During the Annapolis Boatshow, and also on the podcast 'Ask the Pros' with SeaPeople, we were asked several questions about needing an MPPT controller:
What is a MPPT controller?
Do I need one?
Where is it located?
Is it waterproof?
Do I need one per solar panel?
Can't I just hook my solar panel directly to the battery?
The short answer is 100% you need to install a controller in your system which is why we made it easy and set up bundles that includes an MPPT controller(s) and other system components to get you up & running. The MPPT controller acts as a kind of 'middleman' regulating the flow of power from the solar panel to the battery and importantly it will prevent over-charging.
If you did not have a controller the solar panel would not know when to stop. If the sun was shining it would just continue to send power through to the already fully charged battery leading to all sorts of issues.
A controller will be talking to the battery to see what it needs and talking to the solar panel to see what it can provide. It takes a voltage that is fluctuating and regulates it to the voltage required by the battery at that time. The voltage from the panel is fluctuating with conditions, sun is shining then a cloud passes over, or some shade is cast on the panels from the rigging/sails etc.
A controller is installed inside in a dry location close to the battery bank you're charging. You want a long wire run from panel to MPPT and a short wire run from MPPT to battery. This is because after the MPPT you are sending power at a lower voltage and higher amperage, which is harder to do, there are more wire losses & potential for heat build-up and you need thicker gauge wire.
The Victron MPPT SmartSolar charge controllers have built-in bluetooth which allows for easy system monitoring from the VictronConnect app on your phone/tablet. Also when there are multiple MPPT controllers you can set up a smart network using the battery sense so that the controllers all "talk" to each other and are not competing.
With the cost of the Victron MPPT controllers having really come down I don't see any advantage to using a PWM controller. The advantage of an MPPT controller is that when it lowers the voltage from the panel to the MPPT it takes the difference and converts it into amps (current). It's not really "extra" power but an MPPT is certainly more efficient at the job than a PWM. Same inputs, very different outputs!
The advantage of an MPPT controller over a PWM controller is magnified the higher the panel wattage
Let's take for example 1x100W panel wired either to an MPPT or PWM controller where you could see up 25.4% more solar from using an MPPT controller.
Voltage in from solar panel | Current in from solar panel | Voltage out to battery | Current out to battery | |
MPPT Controller | 17.1V | 5.9A | 13.5V | 7.4A |
PWM Controller | 17.1V | 5.9A | 13.5V | 5.9A |
Or with a larger 1x425W panel wired either to an MPPT or PWM controller you could see 194% more solar from using an MPPT controller!
Voltage in from solar panel | Current in from solar panel | Voltage out to battery | Current out to battery | |
MPPT Controller | 39.8V | 10.68A | 13.5V | 31.48A |
PWM Controller | 39.8V | 10.68A | 13.5V | 10.68A |
The Victron MPPT controllers are pretty bullet proof and are backed by a 5-year warranty from Victron. Let us know if you have any other questions about going solar on your boat.
