Solar panel, MPPT, Battery switching

[goboatingnow]

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.

Loads draw power from sources , not the other way around . Pv panels have zero issues with no current being drawn , it happens all the time on my panels when the batteries are full and th3 battery charger is dong the work

Some solar power controllers requires the battery to be connected first , it’s bad design to have that vulnerability but it’s common enough

[zstine]

I'm pretty sure (from memory) my Victron mppt controller was required to be connected to the battery before the panels, and disconnected from the panels, before the battery. I guess it wanted a place to put the power from the pannels, and also be able to start up any software from battery power before being connected to panels.


I just put a disconnect switch between the panels and mppt controller, otherwise identical to OP.

[thomm225]

Originally Posted by goboatingnow

Loads draw power from sources , not the other way around . Pv panels have zero issues with no current being drawn , it happens all the time on my panels when the batteries are full and th3 battery charger is dong the work

Some solar power controllers requires the battery to be connected first , it’s bad design to have that vulnerability but it’s common enough

So with a couple of my old PWM Controllers they would stop showing a charging voltage after they went to Float. (Voltage would remain at the Float setting)

There was usually no drop down to Float as these controllers didn't have a visible Absorption Phase.

Instead when they got to the setting like for example 13.5 volts they would go to Float Mode.

If you measured the voltage on the panel side of the controller then it would read about the same as the displayed Battery Voltage, BUT if you measured it a couple days later the panel side voltage would be near VOC of the panels since the batteries were still receiving a small charge current until they had finally gotten fully charged.

The Victron MPPT's do this all at one time, and when they go/drop to Float the panel voltage is close to VOC depending on the Sun and it's visibility and angle as they have an Absorption Phase.

My 12 volt panels read near their VOC at 19.6 volts first time it (the Victron) went to Float. Pretty much the same as the PWM's on panel side after a couple days in Float mode.

[Secondshift]

[QUOTE=Paul Elliott;3642836]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.


I think my summation was lacking.

In a large parallel system a short can overload the wiring of the panel itself.

NEC specifies fuses between the the panels to prevent this if the system

design can not handle the full short circuit of the panels.


NEC also specifies a shutoff if no fuses are required.



Best Regards

[goboatingnow]

Originally Posted by thomm225

So with a couple of my old PWM Controllers they would stop showing a charging voltage after they went to Float. (Voltage would remain at the Float setting)

There was usually no drop down to Float as these controllers didn't have a visible Absorption Phase.

Instead when they got to the setting like for example 13.5 volts they would go to Float Mode.

If you measured the voltage on the panel side of the controller then it would read about the same as the displayed Battery Voltage, BUT if you measured it a couple days later the panel side voltage would be near VOC of the panels since the batteries were still receiving a small charge current until they had finally gotten fully charged.

The Victron MPPT's do this all at one time, and when they go/drop to Float the panel voltage is close to VOC depending on the Sun and it's visibility and angle as they have an Absorption Phase.

My 12 volt panels read near their VOC at 19.6 volts first time it (the Victron) went to Float. Pretty much the same as the PWM's on panel side after a couple days in Float mode.

Reading pwm waveforms with a multimeter can be misleading. You need a scope to see what’s actually really happening. I carry a portable scope and find it useful.

I don’t fuse my panel side nor do I have a disconnect on the panels , why would I wish to turn off my panels !!!!!, for maintenance I can pull the connectors apart

[goboatingnow]

[QUOTE=Secondshift;3643103]

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.





I think my summation was lacking.



In a large parallel system a short can overload the wiring of the panel itself.



NEC specifies fuses between the the panels to prevent this if the system



design can not handle the full short circuit of the panels.





NEC also specifies a shutoff if no fuses are required.







Best Regards

I would agree that any wiring from the panels should be rated at the panels maximum current rating. ( this is not a short circuit per se as a panel is not a voltage source )

[goboatingnow]

Originally Posted by thomm225

So with a couple of my old PWM Controllers they would stop showing a charging voltage after they went to Float. (Voltage would remain at the Float setting)

There was usually no drop down to Float as these controllers didn't have a visible Absorption Phase.

Instead when they got to the setting like for example 13.5 volts they would go to Float Mode.

If you measured the voltage on the panel side of the controller then it would read about the same as the displayed Battery Voltage, BUT if you measured it a couple days later the panel side voltage would be near VOC of the panels since the batteries were still receiving a small charge current until they had finally gotten fully charged.

The Victron MPPT's do this all at one time, and when they go/drop to Float the panel voltage is close to VOC depending on the Sun and it's visibility and angle as they have an Absorption Phase.

My 12 volt panels read near their VOC at 19.6 volts first time it (the Victron) went to Float. Pretty much the same as the PWM's on panel side after a couple days in Float mode.

Despite some what misleading quotes elsewhere , mppt controllers and Pwm operate in a fundamentally different way , MPPT controllers contain power conversion circuitry in effect a dc to dc converter , PWM controllers do not contain such circuits , in PWM controllers regulation is performed by connecting the panels directly to the battery for a portion of a cycle.

The duration of that cycle results in control of the power transferred by the difference is that the panels are dropped to the battery voltage anytime the pwm cycle has them connected , this means that , for example pwm controllers are very inefficient if there is a big voltage difference between the optimum panel voltage and the battery nominal voltage.

This is explained in the Victron document I referenced earlier

Mppt on the other hand is significantly more efficient with higher voltage operating points , like panels in series etc, as the power conversion circuitry can simultaneously maintain the panel voltage at a different voltage to the battery charge voltage , resulting in optimum power availability

Both pwm and mppt controllers will require heatsinks due to switching looses but pwm systems require bigger heatsinks generally because the nature of the pwm used in these controllers. Modern power mosfets with extremely low Rds on resistance offer much better power dissipation opportunities.

[StuM]

[QUOTE=goboatingnow;3643118]

Originally Posted by Secondshift

I would agree that any wiring from the panels should be rated at the panels maximum current rating. ( this is not a short circuit per se as a panel is not a voltage source )

Many Codes stipulate wiring from panels should be 125% or similar of maximum current rating (Isc) to allow for higher insolation/lower temperature

[Secondshift]

[QUOTE=goboatingnow;3643118]

Originally Posted by Secondshift

I would agree that any wiring from the panels should be rated at the panels maximum current rating. ( this is not a short circuit per se as a panel is not a voltage source )

A "shorted" panel in a large parallel system could conduct the current from

the other panels overloading the wiring with which the panel is built.



As detailed

https://www.windynation.com/jzv/inf/...olar-pv-system

Best Regards

[StuM]

Originally Posted by goboatingnow

PWM controllers do not contain such circuits , in PWM controllers regulation is performed by connecting the panels directly to the battery for a portion of a cycle.

The duration of that cycle results in control of the power transferred

For those unfamiliar with subject:

That is why they are called PWM controllers.
PWM = Pulse Width Modulation. The name describes the way they work.

(MPPT = Maximum Power Point Tracking - which also describes what that type of controller does)

[thomm225]

Originally Posted by goboatingnow

Reading pwm waveforms with a multimeter can be misleading. You need a scope to see what’s actually really happening. I carry a portable scope and find it useful.

I don’t fuse my panel side nor do I have a disconnect on the panels , why would I wish to turn off my panels !!!!!, for maintenance I can pull the connectors apart

I was making a point about the lack of current flow on the panel side when not hooked up to the controller or if the batteries are fully charged.

Basically agreeing you don't need to fuse the panels.

Also I wasn't looking at waveforms as I didn't need to. Why would I use a scope to check a DC Voltage level?

I do miss using O'Scopes though, but they are usually just collecting dust these days

As far as turning the panels off, one of my controllers was acting up so I would disconnect that panel at the panel with one lead when I wasn't on the boat to monitor it leaving just my 65 watt panel to charge the batteries.

Other times, I'd unhook everything for a couple weeks in Winter.

I didn't see the need to constantly charge the batteries.

They would still be at about 12.5 -12.6 volts when I plugged the controller and panels back in.

[thomm225]

Originally Posted by goboatingnow

Despite some what misleading quotes elsewhere , mppt controllers and Pwm operate in a fundamentally different way , MPPT controllers contain power conversion circuitry in effect a dc to dc converter , PWM controllers do not contain such circuits , in PWM controllers regulation is performed by connecting the panels directly to the battery for a portion of a cycle.

The duration of that cycle results in control of the power transferred by the difference is that the panels are dropped to the battery voltage anytime the pwm cycle has them connected , this means that , for example pwm controllers are very inefficient if there is a big voltage difference between the optimum panel voltage and the battery nominal voltage.

This is explained in the Victron document I referenced earlier

Mppt on the other hand is significantly more efficient with higher voltage operating points , like panels in series etc, as the power conversion circuitry can simultaneously maintain the panel voltage at a different voltage to the battery charge voltage , resulting in optimum power availability

Both pwm and mppt controllers will require heatsinks due to switching looses but pwm systems require bigger heatsinks generally because the nature of the pwm used in these controllers. Modern power mosfets with extremely low Rds on resistance offer much better power dissipation opportunities.

I've read how the PWM Controllers aren't as efficient as MPPT but on my boat you don't really notice it especially now that I have these two 220 ah Golf Cart Batteries.

They are so strong they rarely go below 12.4 volts even when running fans (AC or DC) , depth, etc overnight. Then using the computer and inverter more in the early AM before the Sun is up or up enough to help recharge. This while also charging the phone as it is the Hotspot

I don't have any big power users though just lights, VHF, Depth, small 400 watt Inverter, autopilot, laptop, HDTV, computers etc.

I may now though hook up my 1500 watt Inverter and get a small Microwave or get a small fridge or electric cool box

[StuM]

Originally Posted by Secondshift

A "shorted" panel in a large parallel system could conduct the current from
the other panels overloading the wiring with which the panel is built.

As detailed

https://www.windynation.com/jzv/inf/...olar-pv-system

Best Regards

Good point, we haven't discussed how you actually join panels in parallel.

I have just been considering the combiner(s) as part of the array and the wires out of the (final) combiner as "wires from the panel(s).
(My combiners are on the underside of the panels. There is only one set of wires coming from the arch.)

[Sailmonkey]

[QUOTE=Secondshift;3643125]

Originally Posted by goboatingnow

A "shorted" panel in a large parallel system could conduct the current from



the other panels overloading the wiring with which the panel is built.







As detailed



https://www.windynation.com/jzv/inf/...olar-pv-system



Best Regards

Edit….this post should be in the other solar panel thread. But it’s here now so here it will stay…….



That Point I will concede that a panel, or a specific series of panels would need fusing to prevent multiple panels from smoking a single failed panel.

But, to my previous point, any single panel operated in short circuit in full sun will not be subject to harm.

[goboatingnow]

[QUOTE=Secondshift;3643125]

Originally Posted by goboatingnow

A "shorted" panel in a large parallel system could conduct the current from



the other panels overloading the wiring with which the panel is built.







As detailed



https://www.windynation.com/jzv/inf/...olar-pv-system



Best Regards

Yes but this requires each panel to be fused not the feed to the solar controller