Parallel two solar controllers??

[skipmac]

Originally Posted by hpeer

10A means you will never ever get more than that.

Your assumption is very wrong.

That is why I included the links and diagram, to provide a better explanation.

I have made the mistake you are making. SOME manufacturers and dealers will lead you astray.

Just trying to help.

How many panels do you want to mount?

If it is 2 (seems logical for your size and type boat) then what I sketched out a ways back shows the math.

If you think I made a mistake please point out where.

I always enjoy a bit if humble pie!

Isn't this what the solar charge controller does? It will take 10 amps at 40V an convert that to 26 amps at 12V.

So yes, out of the panel will be 10 amps but at 40 V. Feed that to the MPPT controller and you get the same power but lower volts and higher amps.

[hpeer]

Originally Posted by skipmac

Isn't this what the solar charge controller does? It will take 10 amps at 40V an convert that to 26 amps at 12V.

So yes, out of the panel will be 10 amps but at 40 V. Feed that to the MPPT controller and you get the same power but lower volts and higher amps.

This is a what is SOLD, it is not what HAPPENS.

Your panels will NOT put out 320WATTS. You need to look at the maximum Power Point voltage and current. Unfortunately you spec sheet does not list that.

In reality you will have something like 8-1/2A at 30Volts or very roughly 250Watts MAXIMUM discounting wire loss, dirt and everything else.

Then the MPPT controller takes that 8-1/2A and 30Volts and outputs about 14Volts at some specified Amperage. Lets say 15A for a Victron 75/15.

So 15A at 14V is 210 WATTS. THAT is about the MAXIMUM power you will get.

But even if you could put 2 each 75/15’s in parallel you will get something less than 250Watts because the devices are not 100% efficient.

That is why describing a solar panel as 320W may be correct but is completly misleading. Your actual MAXIMUM available power is about 2/3 of that “advertised” power.

Again, if something I have written is substantially wrong please point it out.

PS:

One could ask; Why not just get a bigger MPPT controller, say 25A? Fair question. Above I was using MAXIMUM capability. In real world installations you plenty of additional factors which limit the available power. The maximum numbers are calculated at a standard temperature with full brilliant sunshine directly overhead. Very rare to get those conditions. The the installation has resistance in the wire and the connectors and connections. Then there is dust, panel angle, shadow, clouds, bird poop….. all of which degrade your output. You will be lucky to ever see 200W. All in the 75/15 is a good pragmatic match to a 320 watt panel. One on one.

[thomm225]

Originally Posted by skipmac

Isn't this what the solar charge controller does? It will take 10 amps at 40V an convert that to 26 amps at 12V.

So yes, out of the panel will be 10 amps but at 40 V. Feed that to the MPPT controller and you get the same power but lower volts and higher amps.

Just FYI about the only time you will get anywhere near that VOC voltage of 40 volts or so is by hooking up a voltmeter to the panel when it's not connected to anything. (assuming it's rated for a 12 volt system. My panels VOC is around 22 volts)

Or depending on how well your controller isolates the panel from the batteries, you might read something close to VOC on the panel side of the controller if the batteries are at total full charge and can take no more so current flow is near or at 0.

PS. If you hook the panel directly to the batteries it's voltage will equal battery voltage and will rise as the battery voltage rises..

With the controller in the circuit the controller will decrease panel input to the batteries at the setting you have selected. Then stop except for a trickle once the batteries are full charged

Without the controller, you get all the panel can give which is why I unhook the panels I have hooked directly to the batteries after the battery voltage gets to around 14.4 or so and let my panels that are connected thru controllers had the Float

[s/v Jedi]

What a load of BS in this thread

So here’s some info:

The panels:

- 320W
- Voc 40.13V
- Isc 10.09
- efficiency 19%

Voc is called Open Circuit Voltage, not float or anything else. This is the maximum voltage that can appear when the panel is NOT connected to anything, which means the current is 0A (zero Amps).

Isc is called Short Circuit current. This is the maximum current that can flow when the panel output is shorted. This means that the Voltage is 0V (zero Volts)

You can not multiply these: 40x10=400W won’t happen because we know that at 40V the current is zero so 40x0=0W and at 10A the voltage is zero so 0x10=0W. You will have no output at all at any of these settings: their purpose is to show maximum possible values that are required for selecting matching gear like controllers.

You also can’t use these panels with a PWM controller. Ignore all that talk about them being usable. All that is history from the time you would buy 12V panels for charging 12V batteries. With these panels you will never reach high output using PWM controllers.

The panel is rated for 320W. Of course you can get 320W out of them, ignore all the talk about only getting 250W etc. which is all BS. In fact, reputable panels will perform well over their rating when new because of warranty requirements. My LG panels have recorded 115% of rated output and that was in the Bahamas during May so you will get even better numbers when closer to the equator or when the sun is at it’s highest point.
To get good numbers you need good panels and good mppt controllers. Victron controllers and panels are great, LG panels are great, any of the cheapies are suspect.

At an efficiency of 19% you know you have old tech because current panels are much higher. But years ago these same panels were at 19% as well and they perform great; you just get less production from equal surface area.
My panels are the same size and are rated at 375W so it is a big difference.

Now for matching to controllers for two of these panels. Victron uses two numbers in their model nrs, like 100/15. This means a maximum of 100V Voc solar array and a maximum of 15A battery charge current.

So with 40V panels you can connect them in series and that will work for a 100/15 controller but not for a 75/15 controller. It best to keep more than 5V head room so 86V minimum for the controller.
Now we get the current. Let’s assume a bulk voltage of 14.4V. This would give a maximum power transfer of 14.4x15=216W. When you have two 320W panels, this won’t be a good match but let’s assume you connect both panels in series to this controller and hook it up to an empty 12V AGM battery. In that case nothing blows up and you will be charging the battery at 216W, wasting most of the 640W array. The controller simply does what it can. When it is cool it will do a bit more than 15A, when it gets hot it will do less than 15A regardless of how much more solar power is available.

Calculating the other way around: 320W/14.4=22.22A. In this case, a 100/20 controller would be fine for one panel or a 100/50 for two panels in series.

You can not connect one panel to two controllers but you can connect a controller for each panel and tie them all together at the battery busbars. This will work elegantly with Victron smart controllers because they will act synchronized but in real life it will work with anything when the bulk, absorption and float charge voltages are set the same.

So now let’s see what happens when you have a 24V battery. In that case you were smart to go for 24V and you get double power for the same controller. Because the controller will now do the same 15A at 28.8V = 432W.

[s/v Jedi]

Originally Posted by thomm225

Without the controller, you get all the panel can give which is why I unhook the panels I have hooked directly to the batteries after the battery voltage gets to around 14.4 or so and let my panels that are connected thru controllers had the Float

Absolutely not. When you connect a Voc=40V panel to a 12V battery, you force a power point at battery voltage and the panel will only produce part of it’s rated capacity.

This is why you must have an MPPT controller, which will seek the point of maximum power transfer, which may be at 30V or 34V or 22V and that may change during the day, which is why the controller tracks that point of maximum transfer. Example: early in the morning the voltage is low and the MPT will be at a lower voltage than later during the day when the sun is higher.

[sesmith]

Originally Posted by s/v Jedi

What a load of BS in this thread

So here’s some info:

The panels:

- 320W
- Voc 40.13V
- Isc 10.09
- efficiency 19%

Voc is called Open Circuit Voltage, not float or anything else. This is the maximum voltage that can appear when the panel is NOT connected to anything, which means the current is 0A (zero Amps).

Isc is called Short Circuit current. This is the maximum current that can flow when the panel output is shorted. This means that the Voltage is 0V (zero Volts)

You can not multiply these: 40x10=400W won’t happen because we know that at 40V the current is zero so 40x0=0W and at 10A the voltage is zero so 0x10=0W. You will have no output at all at any of these settings: their purpose is to show maximum possible values that are required for selecting matching gear like controllers.

You also can use these panels with a PWM controller. Ignore all that talk about them being usable. All that is history from the time you would buy 12V panels for charging 12V batteries. With these panels you will never reach high output using PWM controllers.

The panel is rated for 320W. Of course you can get 320W out of them, ignore all the talk about only getting 250W etc. which is all BS. In fact, reputable panels will perform well over their rating when new because of warranty requirements. My LG panels have recorded 115% of rated output and that was in the Bahamas during May so you will get even better numbers when closer to the equator or when the sun is at it’s highest point.
To get good numbers you need good panels and good pwm controllers. Victron controllers and panels are great, LG panels are great, any of the cheapies are suspect.

At an efficiency of 19% you know you have old tech because current panels are much higher. But years ago these same panels were at 19% as well and they perform great; you just get less production from equal surface area.
My panels are the same size and are rated at 375W so it is a big difference.

Now for matching to controllers for two of these panels. Victron uses two numbers in their model nrs, like 100/15. This means a maximum of 100V Voc solar array and a maximum of 15A battery charge current.

So with 40V panels you can connect them in series and that will work for a 100/15 controller but not for a 75/15 controller. It best to keep more than 5V head room so 86V minimum for the controller.
Now we get the current. Let’s assume a bulk voltage of 14.4V. This would give a maximum power transfer of 14.4x15=216W. When you have two 320W panels, this won’t be a good match but let’s assume you connect both panels in series to this controller and hook it up to an empty 12V AGM battery. In that case nothing blows up and you will be charging the battery at 216W, wasting most of the 640W array. The controller simply does what it can. When it is cool it will do a bit more than 15A, when it gets hot it will do less than 15A regardless of how much more solar power is available.

Calculating the other way around: 320W/14.4=22.22A. In this case, a 100/20 controller would be fine for one panel or a 100/50 for two panels in series.

You can not connect one panel to two controllers but you can connect a controller for each panel and tie them all together at the battery busbars. This will work elegantly with Victron smart controllers because they will act synchronized but in real life it will work with anything when the bulk, absorption and float charge voltages are set the same.

So now let’s see what happens when you have a 24V battery. In that case you were smart to go for 24V and you get double power for the same controller. Because the controller will now do the same 15A at 28.8V = 432W.

Yes! This is the only post you should pay attention to in this entire thread. Spot on and couldn't have said it better myself.

[s/v Jedi]

Originally Posted by sesmith

Yes! This is the only post you should pay attention to in this entire thread. Spot on and couldn't have said it better myself.

Thank you. Reading back I mistyped some things but I corrected it in my post

[thomm225]

Originally Posted by s/v Jedi

What a load of BS in this thread

So here’s some info:

The panels:

- 320W
- Voc 40.13V
- Isc 10.09
- efficiency 19%

Voc is called Open Circuit Voltage, not float or anything else.

Lets take this one at a time as I have the time.

First you not knowing what a floating voltage is tells me you have no electronics background so anything you say after that is suspect

You're just beating your chest on stuff you have learned about solar.

As I mentioned before, we old school electronics techs called a floating voltage that which you would read in a circuit where there was an open. (allowing no current flow)

An open being a transistor, diode, resister etc that had opened/failed stopping current flow allowing you to see the voltage supplied to that circuit which was usually 5-24 volts depending on what year we are talking.

TTL was 5 volts.

VOC means Voltage Open Circuit. Get it? No current flow.

It was an excellent troubleshooting method because once you saw that high voltage with your meter or O'Scope you knew you were close to the problem.... failed component

[thomm225]

Originally Posted by s/v Jedi

Isc is called Short Circuit current. This is the maximum current that can flow when the panel output is shorted. This means that the Voltage is 0V (zero Volts)

This was pointed out earlier.

[thomm225]

Originally Posted by s/v Jedi

When you connect a Voc=40V panel to a 12V battery, you force a power point at battery voltage

All 12 volt rated panels will drop to the level of the battery voltage when you hook one directly to the battery.

Pointing this out wasn't about the panel's rated capacity, it was simply to demonstrate to the OP how a panel reacts when attached to the battery. (the load)

You will never see VOC .........after you attach direct unless maybe you fry the battery by leaving it attached too long.

Why some of you folks go into attack mode when you simply do not understand what is being said I will never understand.

[hpeer]

Originally Posted by thomm225

Why some of you folks go into attack mode when you simply do not understand what is being said I will never understand.

^+1

Polite behavior is appreciated.

While Jedi and I disagreed about what you can expect from a panel his charging maths and mine were within 5%.

The OP has already purchased the panels and the controllers. I believe the point is to help him use what he has to best usage.

The Victron 75/15 will only do so much.

[Wotname]

Originally Posted by s/v Jedi

What a load of BS in this thread

So here’s some info:

The panels:

- 320W
- Voc 40.13V
- Isc 10.09
- efficiency 19%

Voc is called Open Circuit Voltage, not float or anything else. This is the maximum voltage that can appear when the panel is NOT connected to anything, which means the current is 0A (zero Amps).

Isc is called Short Circuit current. This is the maximum current that can flow when the panel output is shorted. This means that the Voltage is 0V (zero Volts)

You can not multiply these: 40x10=400W won’t happen because we know that at 40V the current is zero so 40x0=0W and at 10A the voltage is zero so 0x10=0W. You will have no output at all at any of these settings: their purpose is to show maximum possible values that are required for selecting matching gear like controllers.

You also can’t use these panels with a PWM controller. Ignore all that talk about them being usable. All that is history from the time you would buy 12V panels for charging 12V batteries. With these panels you will never reach high output using PWM controllers.

The panel is rated for 320W. Of course you can get 320W out of them, ignore all the talk about only getting 250W etc. which is all BS. In fact, reputable panels will perform well over their rating when new because of warranty requirements. My LG panels have recorded 115% of rated output and that was in the Bahamas during May so you will get even better numbers when closer to the equator or when the sun is at it’s highest point.
To get good numbers you need good panels and good mppt controllers. Victron controllers and panels are great, LG panels are great, any of the cheapies are suspect.

At an efficiency of 19% you know you have old tech because current panels are much higher. But years ago these same panels were at 19% as well and they perform great; you just get less production from equal surface area.
My panels are the same size and are rated at 375W so it is a big difference.

Now for matching to controllers for two of these panels. Victron uses two numbers in their model nrs, like 100/15. This means a maximum of 100V Voc solar array and a maximum of 15A battery charge current.

So with 40V panels you can connect them in series and that will work for a 100/15 controller but not for a 75/15 controller. It best to keep more than 5V head room so 86V minimum for the controller.
Now we get the current. Let’s assume a bulk voltage of 14.4V. This would give a maximum power transfer of 14.4x15=216W. When you have two 320W panels, this won’t be a good match but let’s assume you connect both panels in series to this controller and hook it up to an empty 12V AGM battery. In that case nothing blows up and you will be charging the battery at 216W, wasting most of the 640W array. The controller simply does what it can. When it is cool it will do a bit more than 15A, when it gets hot it will do less than 15A regardless of how much more solar power is available.

Calculating the other way around: 320W/14.4=22.22A. In this case, a 100/20 controller would be fine for one panel or a 100/50 for two panels in series.

You can not connect one panel to two controllers but you can connect a controller for each panel and tie them all together at the battery busbars. This will work elegantly with Victron smart controllers because they will act synchronized but in real life it will work with anything when the bulk, absorption and float charge voltages are set the same.

So now let’s see what happens when you have a 24V battery. In that case you were smart to go for 24V and you get double power for the same controller. Because the controller will now do the same 15A at 28.8V = 432W.

Another vote for this being the only truly worthwhile accurate post in the thread!


I dunno why some people who claim an electronic background just don't understand that electrical theory is a fixed thing, it is isn't up for debate. It is either correct or it is not.

In this instance what the Jedi wrote is correct (apart from some typos ) and if any person wishes to disagree with the theory, well they are wrong - sorry to be blunt but Ohms law doesn't accomodate you own pet theory.

[s/v Jedi]

Originally Posted by thomm225

Lets take this one at a time as I have the time.

First you not knowing what a floating voltage is tells me you have no electronics background so anything you say after that is suspect

You're just beating your chest on stuff you have learned about solar.

As I mentioned before, we old school electronics techs called a floating voltage that which you would read in a circuit where there was an open. (allowing no current flow)

An open being a transistor, diode, resister etc that had opened/failed

You’re wrong, Google it. Voc is open circuit voltage, never called floating voltage by anyone. Any mention of “floating voltage” is related to ungrounded AC or for DC related to battery charging.

Your description of “an open” is accurate and often Voc or similar in-circuit voltage would be called an “open voltage” which is just short for “open circuit”. Also, Voc, it’s the abbreviation of Voltage Open Circuit. I don’t know why you persist in calling it floating voltage.

About my background: I was an electronics designer before switching to IT Systems Analyst and Software Architect, followed by founding one of the Internet providers that built the Internet in Europe. Even though it’s a long time ago, I actually designed around TTL and CMOS IC’s as well as microcomputer chipsets. That’s not beating on my chest, I normally don’t mention it but you force me by questioning my background.

My description of Voc as well as Isc is 100% accurate, there can’t be discussion on that because it’s factual.

[s/v Jedi]

Originally Posted by thomm225

Pointing this out wasn't about the panel's rated capacity, it was simply to demonstrate to the OP how a panel reacts when attached to the battery. (the load)

You will never see VOC .........after you attach direct unless maybe you fry the battery by leaving it attached too long.

Why some of you folks go into attack mode when you simply do not understand what is being said I will never understand.

You missed the quote I inserted straight from you. I attach it again here, where you state: “without the controller, you get all the panel can give…”

My comment to that was: Absolutely not, you only get a part of what the panel can give, because you force it to a static power transfer point, namely at battery voltage, where the panel can not transfer it’s rated power.

This too is factually correct. When we had 12V solar panels you could come up with a comment that you did, but not for someone connecting a 40V panel to a 12V battery.

I don’t make this up, things are what they are and every EE will confirm my comments in this thread.

[Wotname]

Originally Posted by thomm225

Lets take this one at a time as I have the time.

First you not knowing what a floating voltage is tells me you have no electronics background so anything you say after that is suspect

You're just beating your chest on stuff you have learned about solar.

As I mentioned before, we old school electronics techs called a floating voltage that which you would read in a circuit where there was an open. (allowing no current flow)

...........

Ahh...No. I am not disputing that you learnt this definition of 'floating voltage' but I can say you were incorrectly taught. Your definition maybe helpful to you in some circumstances but it can not be used as a definition of floating voltage.

A relativity simple definition that closer approximates the truth is

A voltage induced by electromagnetic fields (or charge accumulation) within the conductor rather than being due to the usual external potential difference.


However the subject matter is more complicated so I'll leave to others to research more deeply if they care.