Yet another solar wiring question

[Maine Sail]

Originally Posted by GrahamHO

I'm not aware of a voltage sensing circuit on my Morningstar. Perhaps in my ignorance I assume that the controller senses the battery voltage from the cable attached to the battery; and that it senses the panel voltage from the cable attached to the panel. I know the controller also has a couple of terminals labeled "load" with I think a graphic of a light bulb. Is that what you are thinking of? That is an extra accessory connection I believe and probably 80% of owners including myself don't use it.

The Morningstar TriStar MPPT units are the ones with the dedicated voltage sensing circuits. Sorry for mistyping PS or ProStar if I did....... Load is not a volt sensing terminal and not one we'd normally use on boats...

[sailormed]

Attached my 45A Morningstar with all cables connected.
Left to right: (picture is turned, now is bottom to top) iPhone bug?
Panel +55V Wire
Panel -55V Wire
Bat 12V charging - wire
Bat voltage sense + wire
Bat voltage sense - wire
Remote temp sense wire 1 (no polarity)
Remote temp sense wire 2
Bat 12V charging + wire
Housing is grounded to boat ground (black wire on grounding lug below)

[Serapium]

So with the above comments in mind I went back and looked at the picture I took of our current charge controller on our new boat. Sure enough, the 'voltage sense' terminals are not hooked up. When I saw that originally, I got out the manual and looked it up. Manual says: "4. Connect the battery Sense. This is recommended, but not required, if the battery is located more than 5 meters from the controller."

It's a little vague as to the purpose of these terminals, and since my battery bank is only a meter from the controller I left these disconnected.

The current system has 5x50W panels connected in series to the PS-30M controller. My intention is to replace these with 8x300W panels on top of our 25'x6' pilot house roof and install a couple of charge controllers with the new panels run in series/parallel.

The existing system I intend to move to the rear davits I'm building and use it to run the 12V watermaker, underwater lights, and the fresh water shower on the swim platform. So my question is, since the new location of the existing system will be less than a meter between charge controller and battery bank, do I need to connect these terminals? What would I gain/lose by doing so? The manual is vague on the subject. It's a non-issue to run the wires, I was just wondering what these terminals actually do in a short run situation.

[jeepbluetj]

The purpose of the dedicated voltage sensing is to compensate for voltage drop from the controller to the batteries.

So if you have (for example)
* .1v drop at between the controller and batteries
* the controller was trying for a 14.4v absorb

Without the voltage sense, the batteries would be at 14.3v

With it, the batteries are at 14.4v and the controller is actually outputting 14.5v

Not needed when the drop is tiny (when the leads to the batts are short)

[GrahamHO]

Originally Posted by Maine Sail

The Morningstar TriStar MPPT units are the ones with the dedicated voltage sensing circuits. Sorry for mistyping PS or ProStar if I did....... Load is not a volt sensing terminal and not one we'd normally use on boats...

Thanks for the link to the TriStar. It looks a lot bigger than the ones I use. I'll have a read of it while I wait at SFO to take off on a Pacific cruise. Nothing goes to windward like a Boeing.

[Serapium]

Here's another newb question that one of you may be able to help explain in real worlkd terms. I've looked at charge controllers both MPPT and non, and am a little confused what benefit I would see in real world application of these units. For instance, the Tristar MPPT 45 listed above is $450. The non-MPPT version of the Tristar 45 is only $150. Does a person really gain $300 in value by going MPPT? I could buy another entire 300W panel for that price.

[Maine Sail]

Originally Posted by Serapium

Here's another newb question that one of you may be able to help explain in real worlkd terms. I've looked at charge controllers both MPPT and non, and am a little confused what benefit I would see in real world application of these units. For instance, the Tristar MPPT 45 listed above is $450. The non-MPPT version of the Tristar 45 is only $150. Does a person really gain $300 in value by going MPPT? I could buy another entire 300W panel for that price.

If you can fit another 300 watts do that first. When you run out of space then the MPPT makes a lot more sense. You also don't need to spend $450.00 for an MPPT controller. The TS 45 is one of the top end controllers and has functions you're paying for that many owners never use...