Adding PV and MPPT - 12v or 24v and other questions.

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ktisdall asked Apr 21, '22

Adding PV and MPPT - 12v or 24v and other questions.

I am planning to add solar to my mainship390 powerboat. Starting with 2-200watt Rich Solar panels and a victron mppt controller. These will charge two-8D FLA batteries. I have the following questions:

1) can I use 24v panels (sku RS-M200D) in series (total 90.8v <voc> @ 5.83a <isc>) into a Victron 150/45 mppt controller? That would allow 14 ga wire from the panels to the controller (about 35 ft) with under 1% voltage drop. The reason for the 150 /45 mppt is I could ( I think ) add a third panel (45.4voc/5.83a isc) at some point.

2) what to use as PV disconnect? Close to panels or close to MPPT?

3) I can connect charge controller through fuse/breaker to one leg of battery switch + with a yandina 100a combiner to the second battery + so the batteries will charge with main battery switch off. I this an ok strategy OR do I need to run MPPT output all the way to the batteries?

4) what fuses / breakers on the battery side of MPPT?

--Kevin

MPPT Controllers wiring voltage

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kevgermany ♦♦ commented · Apr 21, 2022 at 08:01 PM

What Voltage are the batteries? Series or parallel?

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Answer 1 · 2022-04-21T16:01:11Z

snoobler answered · Apr 21, 2022 at 04:01 PM

1) 90.8Voc on a 150Voc limit - fine. Adding a 3rd panel might be too tight depending on temperature. If the panels might be subjected to temperatures near freezing, they might exceed the 150Voc limit. Additionally, many tend to stay away from high voltage PV in a marine environment.

2) Over-current-protection (OCP) devices are best located close to their source. In your situation, I would consider an inline MC4 10A fuse between the panels and a 10a breaker near the MPPT for convenience.

3) I don't follow you, but if you're talking about bypassing the master off switch to be able to charge, that's okay, but I would use a breaker for #4 to act as a master off for the MPPT.

4) size wire for 45A and voltage drop. Fuse/breaker for 60A.

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Answer 2 · 2022-04-21T16:24:34Z

ktisdall answered · Apr 21, 2022 at 04:24 PM

Thanks! I could use 12v panels from Rich - same size dimensions. With 2 in series = 400w 48.6v voc (series) and 10.2a isc. That voltage drop with 12ga wire is almost 2% or .97 volts.

I'm not sure what that means to the charge performance. Any thoughts on that? I'd probably still use the same MPPT but have a bunch more headroom.

--Kevin

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snoobler commented · Apr 21, 2022 at 04:33 PM

2% voltage drop is a 2% loss in power.

Higher MPPT voltage is actually less efficient than Vmp = 1.5X system voltage. However, it is usually offset by reduced voltage drop. I don't have data on Victron hardware, but Outback and Midnite publish performance curves. At 2X system voltage, it's about 1% less. At 3X system voltage, it's about 2% less (all numbers approximate, working from memory).

If you add a 3rd panel, you will likely get a 3% voltage drop due to the increased current. 3% voltage drop for a 50% increase in total power seems very reasonable to me.

Note that once you go 3 panels in parallel, each panel will need it's own OCP. Recommend a 10A MC4 fuse at each panel.

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Answer 3 · 2022-04-21T17:37:32Z

ktisdall answered · Apr 21, 2022 at 05:37 PM

Ok thanks. Sounds like the 12v version and 12ga pv to mppt wire would be a 'normal' / acceptable level of voltage drop.

I don't really know what many of the acronyms / abbreviations mean and the result for an actual implementation.

But my intention is to put the panels in series, not ever parallel. Two to begin with and possibly a third down the road.

--Kevin

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Answer 4 · 2022-04-21T18:26:52Z

snoobler answered · Apr 21, 2022 at 06:26 PM

Sorry. I mixed that up. I missed the switch to the 12V version.

Still dislike high PV series voltage in a marine environment.

IMHO, get the 24V panels and put them all in parallel. Consider the 100/50 MPPT instead.

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Answer 5 · 2022-04-21T18:51:09Z

ktisdall answered · Apr 21, 2022 at 06:51 PM

Thanks. considering 48v systems on boats, is 48.6v in series all that high? I guess adding another 24.6voc panel gets into high dc on a boat but the two panels series setup shouldn't be that abnormal?

I appreciate the discussion. I'm just hoping to explore the options of this for most charge power.

--Kevin

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Answer 6 · 2022-04-21T19:30:52Z

snoobler answered · Apr 21, 2022 at 07:30 PM

Sometimes 48V is necessitated due to power requirements. I'm probably just a bit paranoid.

Of all the configurations discussed, all are likely within 1-2% of each other in terms of "most charge power."

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