question

ogione avatar image
ogione asked

Chosing the right system for my boat.

I am new to solar and I would not like to make a mistake. My plan is to charge 100 aH Lifepo4 24v battery that I use on my boat to run a trolling motor ocassionally.

Solar panel that I would like to use is Victron 215W-24V Mono (size and weigth fit). I would not mind more power but space is limited.

305W-20V Mono would also fit, but that one is 20V so I am not sure if I can use it to charge 24v battery.

I have conflicting information on which mppt controler to use. What are pros and cons of using smart solar mppt 75/10 or 100/30. Or many another one?

Any advice is apriciated.

thanks



smart solar set-up help
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2 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

With Victron MPPT controllers, you need a panel that has a voltage 5 volts greater than your maximum battery voltage to start up, then 1 volt greater after it's started. Your battery voltage will likely be above 24 volts when fully charged so take that into consideration. I'd expect you'd see 28.8 volts so you'd need a solar panel with an open circuit voltage of at least 34 volts.

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ogione avatar image ogione commented ·
Hi Kevin, thank you for your answer. My battery nominal voltage is 25,6.

So if I understod correctly I cannot fully charge my battery with 24v solar panel?

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Kevin Windrem avatar image Kevin Windrem ogione commented ·
It all depends on the actual voltages provided by the panel as "24 volt" in the panel classification doesn't mean much. Look for the voltage at maximum power and the open circuit voltage. These will give you an idea of what might be possible.


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kevgermany avatar image
kevgermany answered ·

For the MPPT controllers, the numbers indicate max input voltage and output current.

So the 75/10 can take max input voltage of 75V and can output up to 10A at battery voltage.

Couple of things to be aware of.

Panel voltage increases as temperatures drop. So you need to check the panel specs and compensate for local winter conditions.

Output current will depend on how much power the panel provides. A 200W panel with full sun will not give 10A at 24V.

It's ok to have more panel power than the controller can output, the controller throttles the output. But don't exceed the controller Isc rating.

There's an online Victron calculator which will handle most of this for you. https://www.google.com/url?q=https://www.victronenergy.com/mppt-calculator


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ogione avatar image ogione commented ·
Hi Kevgermany, thank you too. I did check victron energy calculator befor posting this is where I got the info so far, however there is no consideration of the battery voltage and type in the calculator, so I still dont know if it would work or what I need to make it work
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kevgermany avatar image kevgermany ♦♦ ogione commented ·
But @Kevin Windrem gave you that information.

Not knowing your installation, we can't say much more. If you're struggling with voltage, you may need to mount two smaller panels in series.

.



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