Is my Victron charge controller the correct size?

[SRS]

If any heating took place I doubt it would be much. I think the bypass diodes would get involved. I'm not sure what they would do. Maybe they would function as blocking diodes without a problem.

One thing to remember, when using Victron SCC, the controller is built to operate at different voltages. Therefore it needs to sense the voltage of the battery so it knows what voltage to use before the panels are turned on. You need a switch between the SCC and panels. It does not need to be a breaker but if a switch, it should be rated for the DC voltage of the panel array connected to it. And, that is not so easy to find at a reasonable price. I wasn't able to find one.

See my post #26 which has a video from Explorists Life and a photo of my setup. The video describes the breaker and other items needed as well as how to install although I'm sure you already know this stuff better than I. Cost for the breaker and box was about $32 on Amazon. The setup allows me to easily disconnect the roof solar and disconnect the battery from the controller making electrical mods and repairs much easier. And yes the sequence needs to be reconnect the battery then the roof solar.

 

[CE Vogel]

I would NOT parallel panels of significantly different voltages... for instance my 350W panel is a 40V PV max / 36V PV load... paralleling that with the typical 20-16V '12V' panel would probably be very bad for the lower voltage panel. I also would not series panels of significantly different amperages.

I agree with John, to a point. Paralleling panels of different voltage is problematic, and the lower voltage panel is susceptible to damage. I would also be reluctant to use significantly different voltage panels in series. On the other hand, paralleling panels of different wattage, as long as they are the same voltage, should not cause harm. It is like paralleling two 12V batteries of different sizes. However, any voltage difference between panels of different sizes will increase the risk of damage, especially if the smaller panel is also the lower voltage panel.

 

[TJD]

Hey SRS, Thanks for pointing out the 'Explorist' video trove. Thank goodness I've just retired. I've got a month of instructional videos to watch on that channel. --Tim

 

[SRS]

Hey SRS, Thanks for pointing out the 'Explorist' video trove. Thank goodness I've just retired. I've got a month of instructional videos to watch on that channel. --Tim

Your welcome TJD. I need to look at more of them myself.

 

[John in Santa Cruz]

I agree with John, to a point. Paralleling panels of different voltage is problematic, and the lower voltage panel is susceptible to damage. I would also be reluctant to use significantly different voltage panels in series. On the other hand, paralleling panels of different wattage, as long as they are the same voltage, should not cause harm. It is like paralleling two 12V batteries of different sizes. However, any voltage difference between panels of different sizes will increase the risk of damage, especially if the smaller panel is also the lower voltage panel.

in series, the current passes through all of them, and the overall voltage is the sum of the components. if you series wired a 20A panel with a 10A panel, the 20A would try and shove that 20A through the 10A. If you wire a 36V 10A panel in series with a 18V 10A panel, you'll have a net 54V 10A panel.

in parallel the voltages have to be the same, and the current is added up. a 18V 10A and a 18V 20A would combine to be a 18V 30A.

 

[BobG-ESC]

in series, the current passes through all of them, and the overall voltage is the sum of the components.

What happens when 4 equal panels, consisting of 2 strings of cells each, are in series and 1 string in one panel gets partially shaded causing the current to be diverted around that shaded string via the bypass diode? Is there a loss of current in the bypass circuitry and if so, how much does it affect the total array?

To clarify, each panel is composed of 2 strings of cells. The cells are in series and the strings are in series as is typical in they types of panels we use on RVs.

 

[John in Santa Cruz]

in series, there is a loss of voltage. say each panel is 20V, 4 in series is 80V, but if one is in shade, then the total in series is 60V. an MPPT controller should handle that just fine. or if each panel is two 10V strings in series, so there's 8 striungts total, youd' end up with 70V if only half a panel is shaded.

 

[BobG-ESC]

in series, there is a loss of voltage. say each panel is 20V, 4 in series is 80V, but if one is in shade, then the total in series is 60V. an MPPT controller should handle that just fine. or if each panel is two 10V strings in series, so there's 8 striungts total, youd' end up with 70V if only half a panel is shaded.

Ok, so if the 7 not shaded strings are producing 8 amps each the array would be sending approximately 560 watts to the controller.

Now if these 4 panels were connected to the controller in parallel, and the same 1 string of 1 panel is shaded, the output voltage of that shaded panel would be 10 volts. So, there would be 3 panels capable of operating at 20 volts and 1 panel operating at 10 volts. How many watts would the array send to the controller? Would it be 3 panels at 16 amps and 1 panel at 8 amps but all operating at 10 volts? If so that would be 240 watts.

Is something wrong with this?

 

[John in Santa Cruz]

the 10 volt panel probably wouldn't push any amps into the 20 volt system.

 

[BobG-ESC]

the 10 volt panel probably wouldn't push any amps into the 20 volt system.

Ok, so if the 4 panels are connected in parallel the output of the array would be 3 panels at 20V x 16 amps = 320 watts.

It looks like panels connected in series can work better than if they are connected in parallel because the voltage of a partially shaded panel (1 string of 2 string panel) might take out the whole panel while if connected in series, it only takes out half the panel.

In my case, I need enough volts to operate at around 30 volts (24 V battery) so if I connected 4 panels in 2S2P then there is a good chance I would loose 2 full panels if one panel was partially shaded. Whereas if they are all connected 4S, I only lose 1/2 of a panel?

Am I thinking straight?

 

[John in Santa Cruz]

Ok, so if the 4 panels are connected in parallel the output of the array would be 3 panels at 20V x 16 amps = 320 watts.

It looks like panels connected in series can work better than if they are connected in parallel because the voltage of a partially shaded panel (1 string of 2 string panel) might take out the whole panel while if connected in series, it only takes out half the panel.

In my case, I need enough volts to operate at around 30 volts (24 V battery) so if I connected 4 panels in 2S2P then there is a good chance I would loose 2 full panels if one panel was partially shaded. Whereas if they are all connected 4S, I only lose 1/2 of a panel?

Am I thinking straight?

assuming each half panel has a bypass diode? yeah, i think so. again, you'll need a MPPT solar controoller for this, not a PWM one. With the Victron MPPT 100/xx stuff, the max solar no load voltage should not go over 100V, so be sure that those panels each hafve no more than 25V open circuit.

 

[BobG-ESC]

assuming each half panel has a bypass diode? yeah, i think so. again, you'll need a MPPT solar controoller for this, not a PWM one. With the Victron MPPT 100/xx stuff, the max solar no load voltage should not go over 100V, so be sure that those panels each hafve no more than 25V open circuit.

Panels are 160 watt Voc 19.83V. I mounted 2 on each side of the trailer along side the air conditioner so if the trailer is pointed N-S part of 1 or 2 panels gets shaded in the morning and part of 1 or 2 panels gets shaded on the other side in the afternoon. They do operate similar to what you say. When I was installing them people were telling me I needed to connect them in parallel because of the shading. This is not necessarily true and I think this has been a good discussion to dispel some miss information.

 

[John in Santa Cruz]

with a PWM controller, they would have to be in parallel, since PWM can't handle higher voltages. MPPT is like a DC-DC switching power supply that can convert a higher voltage into more amps at the lower output voltage.

 

[TJD]

Response from Escape regarding under-sized controller

FYI. I received the response below from Escape. Needless to say, I am disappointed.
--Tim

Dustin@Escape
Admin

Best Answer
Hello @TJD, 2022 5.0,

At the time that your trailer was manufactured the solar port was meant to be a supplement for when the roof panels are shaded. If there is over power going into the MPPT 100/20 it will limit power to its nominal rating which for this device is 20A.


After popular requests our team upgraded to the MPPT 100/30 so it may be used in addition to the panels on the roof for current builds.

 

[TJD]

Forgot to mention--the turned the 'comments off' so I could not respond. We build for you.....

 

[NEWYORKHILLBILLY]

FYI. I received the response below from Escape. Needless to say, I am disappointed.
--Tim

Dustin@Escape
Admin

Best Answer
Hello @TJD, 2022 5.0,

At the time that your trailer was manufactured the solar port was meant to be a supplement for when the roof panels are shaded. If there is over power going into the MPPT 100/20 it will limit power to its nominal rating which for this device is 20A.


After popular requests our team upgraded to the MPPT 100/30 so it may be used in addition to the panels on the roof for current builds.

It too bad they did not correct it for you. IMO for what you pay they should have just sent you a 30 amp.

 

[GregWCIL]

Hey SRS, Thanks for pointing out the 'Explorist' video trove. Thank goodness I've just retired. I've got a month of instructional videos to watch on that channel. --Tim

Explorist Life videos should be a “must watch” for anyone contemplating installing or modifying their own system. He covers virtually every topic in concise detail. And he bases everything on code.
He is also a Victron teacher.

 

[Perry Butler]

For Parallel vs Series a slightly better site where you can input your actual situation is Mowgli Adventure's Wiring Solar Panels In Series vs Parallel: What’s The Difference + Free Calculator.

Mowgli advises series when using similar panels. However with 24v panels now available the best practice would be parallel. We chose Rich Solars 24v 200 watt panels and wired the two panels in parallel using our Victron 100/50 SCC. I finished the install yesterday and will be going on a short trip tomorrow, so we'll see how it works.

Enjoy,

Perry

 

[BobG-ESC]

... Mowgli advises series when using similar panels. However with 24v panels now available the best practice would be parallel. We chose Rich Solars 24v 200 watt panels and wired the two panels in parallel using our Victron 100/50 SCC ...

Enjoy,

Perry

Why do you say parallel would be best practice with 24 volt panels? What voltage battery are you running, 12v or 24v?

 

[Perry Butler]

Why do you say parallel would be best practice with 24 volt panels? What voltage battery are you running, 12v or 24v?

We have a 12v battery system. Victron 100 volt MPPT controllers output 12 volts from any voltage up to 100 volts. We have a 100/50 controller.

Depending on who you want to believe, MPPT controllers are efficient down to about 15 volts, that's why many run two panels in series to get well over 15 volts (closer to 25 volts) so they harvest energy earlier/later in the day, and in shading. That's why Explorist Life and Mowgli Adventures advise to run two 12 volt panels in series first.

Best practice is to series identical panels for series or parallel, and get as close with VMP in parallel as possible. Some mismatched panels in series will have severe losses.

Enjoy,

Perry