Solar panel, MPPT, Battery switching

[duetto]

Background - My boat's solar wiring is as follows: Wires from solar panel go to MPPT controller input. Wires output of MPPT to a circuit breaker, then to battery. As long as there is sunlight, solar power is always available to the MPPT and switching on the breaker sends power to battery. I don't use my solar all the time, so the breaker is often switched off.

I was recently told the MPPT should not have power to it without also being connected to the battery (breaker switched on). I was told I need another circuit breaker between the solar panel and the MPPT as well. This will allow the battery connection to made first with the circuit breaker, then the solar panel connection made with the new circuit breaker switched on. Reverse procedure to turn off.

The question - Is this the correct method and sequence to connect and disconnect the solar panel to the MPPT and battery properly?

Thank you

[StuM]

That's a strange procedure. Why do you keep disconnecting the battery?
Assuming that your house loads are connected to your battery, that means you are constantly cycling your battery and decreasing it's life.


To answer your question: The connection between the paness and any other devices (including the controller) shoudl always be the last thing to connect and the first thing to disconnect.

[Paul Elliott]

Originally Posted by StuM

The connection between the paness and any other devices (including the controller) shoudl always be the last thing to connect and the first thing to disconnect.

This depends on the controller. My (old) Genasun controller says this:

Connect the solar panel to the +PANEL and –PANEL terminals. While connecting the battery first will not damage the GV-10, we recommend connecting the panel first. This eliminates the risk of short-circuiting the panel while the GV-10 is operating, which can cause damage.

[StuM]

Originally Posted by Paul Elliott

This depends on the controller. My (old) Genasun controller says this:

Renogy and Morningstar and Outback are the opposite:

https://renogy.force.com/helpcenter/...e-Solar-Panels
Answer
When connecting to a Renogy charge controller it is likely you have seen a warning like the following:
WARNING! Connect the battery terminal wires to the charge controller FIRST, then connect the solar panel(s) to the charge controller. NEVER connect solar panel to charge controller before the battery.
You might be asking yourself why? Or if there are any exceptions? The purpose of this article is to answer those questions and shed light on connecting solar order of operations.

https://www.morningstarcorp.com/faq/...ntroller-work/
When installing a solar charge controller, it is recommended that you connect and disconnect in the following order:
Battery to the controller first
PV array to the controller
Electrical load to the controller
When disconnecting, you reverse that order. The battery provides power to the controller so always make sure that solar and loads are disconnected before connecting or disconnecting the battery from the controller. Connections between the battery, load, PV array, and the controller should have disconnect switches to enhance safety and facilitate ease of installation and breakdown.

Outback FLEXMax manual
To power up the charge controller:
1. Ensure PV and battery circuit breakers are OFF.
2. Turn ON the battery circuit breaker only.

[bensolomon]

Victron manual for my MPPT controller also says to connect controller to battery first.

Put a blanket on the panels when connecting to the system. The panels cannot have any power when connecting or you risk damage. I only know that from reading.

You want the breaker between the MPPT controller and your battery. That is in case the controller goes bad, all the voltage from the panel won't cause a fire.

Ben

[donradcliffe]

My experience with cheap PWM controllers is that there is about a 30% chance of frying the controller by disconnecting it from the battery and leaving it connected to the panels during the day. I don't try this with more expensive controllers.

[noelex 77]

One extra point to add to the excellent replies received so far, is that if you have three or more solar panels in your array you may need overcurrent protection (fuses or circuit breakers) on the solar panel side as well as the battery side of the controller.

If this extra circuit protection is needed, a common solution is to use circuit breakers. As well as providing the needed overcurrent protection this provides a convenient means of disconnecting the power coming into the controller.

There is a mistaken belief that circuit protection is never needed on the solar panel side of the controller and this myth needs to be corrected before we have (more ?) electrical fires.

[thomm225]

Originally Posted by donradcliffe

My experience with cheap PWM controllers is that there is about a 30% chance of frying the controller by disconnecting it from the battery and leaving it connected to the panels during the day. I don't try this with more expensive controllers.

My 2-5 cheap PWM controllers were disconnected from the batteries some times and from the panels other times. Both many times over the years.

Over the Winter, I would disconnect them from the batteries about once every two weeks. (with panels still attached)

And from one of the panels every day or so. My Renogy Panel has plugs close by so I would disconnect one cable there.

Both PWM's that I have been using the last 2-5 years were still working when I disconnected them over the weekend to install my new Victron. One has been in there for 5 years bouncing around unattached (it has a bit of rust on it's USB connector)

I had a Victron before that failed it may have been from the constant connecting and disconnecting. (or it could have been the polar freeze we had. It was warm in the 60's one day and in the teens the next and there was some condensation on my controllers)

Also it didn't seem to like the PWM's being hooked up to the same batteries it was either.

As mentioned above, Victron says attach to batteries first.

I have already though done a couple "resets" on the new Victron when it appeared not to be working. I disconnected Battery Power from the "system" with Victron totally connected to both panels and it reset fine.

Once it came up with the wrong light on and the reset allowed the Victron to correct that and it then came up with just the small blue Bulk Charge light on.

[Secondshift]

I remember something like

If the short circuit capacity of the panels is more than the line capacity

a breaker or fuse should be installed between panels and controller.


If the short circuit capacity is less than the line capacity then a switch should

be installed to disconnect the panel power.



I've used a Blue Sea 285 klixon circuit breaker as a water proof resettable

switch on a past installation where the breaker capacity far exceeded the

panel ability.


Regards

[Paul Elliott]

Originally Posted by Secondshift

I remember something like
If the short circuit capacity of the panels is more than the line capacity
a breaker or fuse should be installed between panels and controller.

I don't get it -- why would you ever use a wire that couldn't safely carry the full panel current? Isc on a panel isn't *that* much greater than Imp.

On my three-panel / three- MPPT controller system I have per-panel breakers and a breaker between the combined MPPT outputs and the battery. I also have little per-panel volt/amp meters and a V/A/W/Ah meter on the feed to the battery. This is all just because I like to see how it's all working. If I were to put this together now I would probably use Victron stuff with the built-in monitoring.

[noelex 77]

Originally Posted by Paul Elliott

I don't get it -- why would you ever use a wire that couldn't safely carry the full panel current? Isc on a panel isn't *that* much greater than Imp.

Everyone forgets about the wiring inside the solar panel. These wires are kept as thin as possible to minimise shading and typically they only have a maximum current rating around 2x or less of the Isc (the max fuse rating can be found in the solar panel specs). Thus two other connected panels can provide enough current to exceed the rating of the wires in the event of short circuit in one panel.

If the current capacity is exceeded and there is no appropriate circuit protection, they pose a similar fire risk to any wire where the capacity is exceeded. The risk is especially concerning for flexible panels mounted on a bimini.

With three or more solar panel in an array (depending on how they wired and the specifications) there is a risk of overloading these wires if a fault occurs. No input from the battery is needed to exceed the wire rating. Hence the fuse on the battery side of the solar controller is of no help in this case. Circuit protection on the solar side of the controller (in addition to the battery side) is needed.

If you have less than three panels circuit protection is only needed on the battery side of the controller as only the battery can supply enough energy to to overload the wiring.

[GreenWave]

I have a switch on my boat that I am 99% sure disconnects between the panel and the controller. If the controllers has no input then it doesn't do anything. And this makes the panel be in the state as if you just took it out of the box before connecting any wires.


I believe that sending power from panel to controller with no place to go would be bad.

[thomm225]

Originally Posted by GreenWave

I have a switch on my boat that I am 99% sure disconnects between the panel and the controller. If the controllers has no input then it doesn't do anything. And this makes the panel be in the state as if you just took it out of the box before connecting any wires.


I believe that sending power from panel to controller with no place to go would be bad.

Usually when I have disconnected the batteries in the past with the panels still attached the controller voltage display just "floats" around from like 14.7 to 13.2 for a while then it goes dark until I reconnect the batteries in a day or two

The controller though is probably just confused without the batteries to power it. You are probably just getting VOC from the panels.

(like when you hook a meter to my panels when they are "floating" or unattached. You get VOC and on my panels that's about 21 volts.

Basically when I leave the voltage is still floating/bouncing around on the controller's display and when I return the following day the controller's display is dark. (no display until I reconnect the batteries then it displays battery voltage)

I've done this lots of times with my $12 PWM Controllers without damaging them. There'd be very little current flow I'm thinking anyway. (until you reattached the batteries)

I bet the $12 PWM's have a pretty simple circuit running.....and I'd like to see the schematic for one

[Paul Elliott]

Originally Posted by noelex 77

Everyone forgets about the wiring inside the solar panel. These wires are kept as thin as possible to minimise shading and typically they only have a maximum current rating around 2x or less of the Isc (the max fuse rating can be found in the solar panel specs).

Good point. Yes, the breaker/fuse has to protect the weakest link in the circuit. Specs I have for a panel similar to the ones I have show an Isc of 4.7A and a series fuse rating of 15A (this is a Vmpp of 33V, the panels I actually use have a Vmpp around 16V). So there's a 3x spread.

Originally Posted by GreenWave

I believe that sending power from panel to controller with no place to go would be bad.

This depends on the controller design. In general, when "there's no place to go" power will not be taken from the panel. There may be other issues.

[noelex 77]

Here are just a couple of articles on circuit protection between the solar panels and the controller (in addition to the commonly used and always necessary fusing between the controller and the battery).

Electrical systems and solar arrays are becoming more sophisticated on boats. Unfortunately, many boats are wired using techniques that worked fine with the simple electrical systems of old. There is a vast difference between a high voltage solar array fitted to many modern cruising boats and older systems where one or two low wattage 12v panels was typical.


https://www.explorist.life/how-to-**...y-not-need-to/

https://www.cedgreentech.com/article...-when-not-fuse