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anton-rodionov avatar image
anton-rodionov asked

Some questions about connecting MPPTs

Hello I have MPPT Smart Solar 100|30 and 4 x 100W solar panel on a sail yacht. All solar panels connected parallel.

Q1: do I need install a fuse between each solar panel and MPPT?

Q2: which fuse to mount between MPPT and battery: 30A, 35A or 40A?

Q3: I also have MPPT Blue Solar 75|15. I'm planning to install for it 2x75W and 1x50W solar panels. Can I connect Blue Solar 75|15 and Smart Solar 100|30 in parallel? And is it possible to link between each other. I would like to read information from both MPPTs via Bluetooth. Is it possible?

Thank you.

MPPT Controllers
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solgato avatar image solgato commented ·

One thing to keep in mind is the relationship between your battery voltage and panel voltage. From what I understand, you want to feed the 100/30 with as much voltage as you can without exceeding the 100V max of the unit in order for it to work best.

Therefore, you should consider wiring your 100W panels in series (depending on their Vmax specs) to maximize voltage input to the 100/30.

You need more V coming in from the panels than the voltage of the bank you are charging. I’ve been reading on here that most of the MPPT’s wont turn on unless they are getting 5V more than your bank and will stay on until it falls below 1V. The more the better without exceeding because the panels don’t put out max voltage unless conditions are perfect.

This is the advantage of MPPT chargers as I understand, in that you can “over volt” them so that extra voltage not being used to maintain the batteries can be used instead to power a load while still maintaining the bank.

Others can correct me if I’m wrong, but that is what I’ve learned and what is important to keep in mind and understand when configuring your MPPT system. You have a 100V/30A capable unit and enough solar to feed it, so why not take advantage and use the components as efficiently possible.

Of course that’s all based on a scenario where you are actually using the MPPT units to charge batteries which you didn’t mention any details about.

The other caveat is shading. If these 4 panels aren’t going to see similar sun conditions and are say mounted on port and starboard, then wiring in series can obviously work against you depending on the scenario and their specs.

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2 Answers
Paul B avatar image
Paul B answered ·

Q1: do I need install a fuse between each solar panel and MPPT?

A:- NO but it it recocmended

Q2: which fuse to mount between MPPT and battery: 30A, 35A or 40A?

A:- same size as the max output of the MPPT. ( The units have a internal NON replaceable fuse inside you dont want to blow that)

Q3: I also have MPPT Blue Solar 75|15. I'm planning to install for it 2x75W and 1x50W solar panels. Can I connect Blue Solar 75|15 and Smart Solar 100|30 in parallel? And is it possible to link between each other. I would like to read information from both MPPTs via Bluetooth. Is it possible?

A:- Yes paralleling the Outputs is fine

You would need to buy 2 x bluetooth Dongles and then you can read each one

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wkirby avatar image wkirby ♦♦ commented ·

For Q1, I would say that with that many in parallel. it is necessary to have fuse for each string (panel in this case).
The reason is that if one panel fails in some way then the other three could back feed the faulty panel with much more (up to 3x) the current that it is designed to carry. This could lead to a nasty fire.

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r2d2wat avatar image
r2d2wat answered ·

On a sailboat there is often too much shading to set up the pv in series. If not too much shading of each pair, look into 2 pair in series.

Always a good idea to use circuit breakers.

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