Solar panel negative charge?

[Tristannelson]

Hi everyone,

I'll try and keep this simple.

I have recently installed a battery monitor on my boat which has a 300ah battery bank. The monitor uses a shunt which is installed basically in line within the batteries existing negative earth (ie shunt connects to negative battery and negative load).

The system already had a solar charger installed which is an 80w panel connected to a regulator which both the positive and negative is connected directly to the battery terminals.

After installing the monitor, at night with everything off the amp draw on the battery is zero which it should be, and when I turn a light on the draw is negative which is also correct. However during the day when the solar panel is working and everything is off, the amp draw shows approx -2 amps which is obviously not correct as it should be positive?

Two questions -
Why is the amp draw negative when solar is working?
Is this actually draining the batteries?
Is my assumption below correct?

My thoughts are because the shunt is positioned between the negative earth and negative battery terminal and solar is connected directly to both battery terminals this is giving a false reading. I think I need to move the negative of the solar charger from the battery to the main earth, which would then run it through the shunt? Thoughts?

Thanks in advance..

[nigel1]

The negative for all your charging sources should go via the shunt.

[fallingeggs]

I don't have a specific answer, but I highly recommend you review Maine Sail's site (linked below) for how to install the shunt. He installs them (among other things) for a living and sees them done wrong all the time.

http://www.pbase.com/mainecruising/boat_projects

It might be too late for this, but now days Maine Sail recommends a new type of monitor from Balmar. Uses fancy algorithms rather than a shunt for a higher quality read on SOC. Can read about it on his site as well!

(I have one in a box waiting to be installed once it warms up outside. Purchased from Maine Sail, of course. )


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[Sailmonkey]

There should be nothing connected to the batteries other than the shunt (on the negative post). This is in fact the source of your erroneous reading.


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[reed1v]

Originally Posted by nigel1

The negative for all your charging sources should go via the shunt.

Absolutely correct. All devices' negative leads should go to the same ground. Otherwise you risk having a floating ground, potential live circuits when everything is suppose to be closed, and in general death and destruction.
BTW: Only the emergency radio should have a direct connection to the battery, and that isolated from all other devices.

[Paul Elliott]

The correct answer is indeed to connect the panel / charger to the battery (+) and to the ground / shunt.

But, connecting it as you have done should not give you a negative reading, it should give you a zero reading. Or, almost zero if you have any always-on low-current devices in your system. The fact that you are reading -2A tells me that the connections are not as you think they are. Does the battery voltage increase when you are running the panel? (Is the panel actually charging the battery?)

[facciatosta]

Originally Posted by Tristannelson

Hi everyone,

is installed basically in line within the batteries existing negative earth (ie shunt connects to negative battery and negative load).

Hi, where exactly you cut-in the shunt in negative circuit - immediately to the battery terminals or somewhere else. If it is somewhere else then it may affect your readings depending on how branching of all other circuits - loads and chargers - is done.

If shunt is connected immediately to battery terminals and you still get erroneous readings then there is something wrong with monitor or your solar battery. At this point current unambiguously flows into battery when battery is charged and out of battery if battery is discharged. therefore signs of the readings should be different.

What kind monitor you are using? Any particular instructions?
Did you try to swap wires connected to shunt? In this case more likely that you always will get positive readings.

I do not think it matters if shunt connected in negative or positive wires as long as respective corrections to wiring are made.

If you ave handy cheap DC amp clamp meter( which are a plenty on the market) then you can connect it around battery wire and compare it against monitor's reading.

[yachttie]

g'day Mate
You are correct. EVERYTHING should be forced through the shunt, otherwise you won't get a correct reading. I would be inclined to move the solar negative cable to the load side of the shunt, rather than to a point further away. You need as few as possible terminations.
The reason you are getting -2A through day could be small current consuming devices turned on. Maybe depth sounder/wind instrument, radio, etc.
NO, NO, NO you must not connect shunt to positive side of battery. I can't remember reason but it is a no no.
Happy Sailing.

[newhaul]

Originally Posted by reed1v

Absolutely correct. All devices' negative leads should go to the same ground.
BTW: Only the emergency radio should have a direct connection to the battery, and that isolated from all other devices.

Almost correct your bildge pump and control switch for said bildge pump should also be direct wired to battery

[twinboat]

The reason you don't hook the shunt to the + side is that you would then need to hook the power wire to negative. That would burn out the monitor. If you hooked the + to the + side, there would be no ground for the display.

On the original question, all negative wires, that you want to monitor, need to be together on 1 side and only battery neg. on the other.

[Tristannelson]

Hi guys thanks so much for your replies!!
I will move the negative of the solar charger to the ground and see if that works, this makes sense..
Also when pondering in my sleep, I have and idea of why the negative charger. The system has an auxiliary battery which is connected by a device which automatically connects the batteries when voltage is above a certain limit. So when the solar is charging the main bank, current must be leaving the main bank and running to the auxiliary via the shunt which gives a negaive reading. This also makes sense now. What do you think?

What do you think will now be the result when I move the solar negative to the ground? Current will then be flowing into main bank but also still into auxiliary will I get full reading or something different?

Cheers for all your replies! Much appreciated.

[Pete7]

Originally Posted by twinboat

The reason you don't hook the shunt to the + side is that you would then need to hook the power wire to negative. That would burn out the monitor. If you hooked the + to the + side, there would be no ground for the display.

On the original question, all negative wires, that you want to monitor, need to be together on 1 side and only battery neg. on the other.

Some of the battery monitors can be wired to the positive side, indeed my Sterling battery monitor is wired this way.

https://cdn.shopify.com/s/files/1/06...a6a620.pdf?806

Pete

[Redline452]

The negative readings were coming because the solar, directly on the battery negative, was powering house loads during the day, so that return current was going through the shunt "the wrong way".

Only the batteries should be on the battery side of the shunt.

FWIW, I have three battery monitors in parallel on the shunt and all read the same, without affecting each other.

[Sempersafloat]

Originally Posted by Tristannelson

Hi everyone,

I'll try and keep this simple.

I have recently installed a battery monitor on my boat which has a 300ah battery bank. The monitor uses a shunt which is installed basically in line within the batteries existing negative earth (ie shunt connects to negative battery and negative load).

The system already had a solar charger installed which is an 80w panel connected to a regulator which both the positive and negative is connected directly to the battery terminals.

After installing the monitor, at night with everything off the amp draw on the battery is zero which it should be, and when I turn a light on the draw is negative which is also correct. However during the day when the solar panel is working and everything is off, the amp draw shows approx -2 amps which is obviously not correct as it should be positive?

Two questions -
Why is the amp draw negative when solar is working?
Is this actually draining the batteries?
Is my assumption below correct?

My thoughts are because the shunt is positioned between the negative earth and negative battery terminal and solar is connected directly to both battery terminals this is giving a false reading. I think I need to move the negative of the solar charger from the battery to the main earth, which would then run it through the shunt? Thoughts?

Thanks in advance..

Hi, It matters not which leg (pos or neg) your shunt is in. The battery monitoe is measuring the small voltage drop across the shunt which is normally in the order of 1 ohm. What does matter in your case is where the wires from the solar panel, or for that matter any generating source( wind etc)are connected. If your shunt is in the neg cable your pos from the panel, or solar regulator will go to the Pos bus bar or battery terminal, and the neg from the solar panel should go to the upstream side of the shunt, ie the side ferthest away from the neg bus bar or terminal, thus the battery monitor will read the volt drop across the shunt. Frankly I'd put the shunt in the pos cable because appart from anything else it helps to make life easier connecting things( you don't have to think as much)
If you're still getting a discharge reading after the above, one possible source of leakage is the blocking diode for the solar panel, usually built into the panel or almost certainly into a solar regulator, easily checked with a multimeter. Hope this helps.

[Badsanta]

When I installed my shunt the directions were very specific to be placed on the neg. With every negative flowing through it then to neg side battery. Mine may be different but that is what was specified.

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