question

John avatar image
John asked

Are 50vdc solar panels wasted on a 12vdc system?

Hi, I am just trying to get my head around this and wonder if someone can confirm it please?

For a 12-15vdc battery off grid system needing to charge through a charge controller via a solar panel array of course which the panels are rated at around 55Vdcmax.

With the cheaper Ebay MPPT controllers (link to example type bellow), they cut off the solar panels inputs if the solar panel voltages are above around 15Vdc, so effectively the panel would only charge the system when the panel voltage is within the 12vdc - 15vdc, effectively only for a VERY short time in the morning and again at sunset.

With a Victron charge controller like (link of example type below), to charge the 12-15vdc from the panels (55Vdc). Does the Victron charge controller cater for the full 0-55vdc from the panel or does it also have built in cut out solar voltage cut offs, resulting in the same issue as the cheaper Ebay charge controllers?

I guess I am looking to have some device which converts the 0-55Vdc to a more usable 12-15vdc range so as to charge the batteries. Is the Victron charge controllers able to do that, regardless of the voltage from the solar panels are producing?

Kind regards

John.


https://www.google.com/aclk?sa=l&ai=DChcSEwikvN3NkZ7nAhWBjY8KHc7qD1UYABAhGgJzYg&sig=AOD64_2zKdLOh-0DDQJdeH1s63koYtHLcg&ctype=5&q=&ved=2ahUKEwipx9XNkZ7nAhVE9XMBHb87AssQ9aACegQIGxBk&adurl=


https://www.victronenergy.com.au/solar-charge-controllers/smartsolar-100-30-100-50


MPPT Controllersoffgrid
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Mike Dorsett avatar image Mike Dorsett commented ·
Those cheap Chinese "mppt" controllers are NOT mppt controllers, but mis-labled PWM controllers - hence cutting off the PV at high voltage input.

Get a real MPPT controller from Victron with 100V input - these have proper switch mode converters to reduce the module voltage to 12 - 15V.

The PWM controllers are very inefficient.


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klim8skeptic avatar image klim8skeptic ♦ commented ·

Your google link does not work.

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman klim8skeptic ♦ commented ·

Here it is:

7512-screenshot-2020-01-25-at-103236.png

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screenshot-2020-01-25-at-103236.png (2.4 MiB)
klim8skeptic avatar image klim8skeptic ♦ Warwick Bruce Chapman commented ·

Looks like the cheapest PWM controller, that is guaranteed to boil your batteries.

Avoid.

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mdbrown avatar image mdbrown klim8skeptic ♦ commented ·

If it's too cheap to be believed, it's not true MPPT.


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Fra avatar image Fra Warwick Bruce Chapman commented ·
These is garbage. Guaranteed. Is not mppt. I've seen many of these things in rv sistems of my clients.

It's possible that these things damage your battery becouse the voltage accuracy and control is very very poor. They are some good mppt (Real) Chinese at good price if you want save some money. But they cost at least around 80/120 euros for a 30 amp model.

Like epever tracer/triron etc or helios ms series mppt or other brands.

They work fine and also accessories to monitoring are cheaps.

Obviously the software and charging options are not comparable with victronenergy mppt. But they are mppt and have good quality construction and reliable components.

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secessus avatar image secessus commented ·

With the cheaper Ebay MPPT controllers (link to

As others have noted, it's a PWM. This design is typically single stage (you get one charging voltage, so choose wisely).


15Vdc, so effectively the panel would only charge the system when the panel voltage is within the 12vdc - 15vdc, effectively only for a VERY short time in the morning and again at sunset.

For the purposes of this discussion, PWM drags the panel down toward battery voltage and runs it there (all day if demand is high enough). It's not like there are only certain times of day when it will work.

In the case of a 50Vmp panel and 12v bank a PWM will pull the panel way, way off the voltage at which it makes rated power.

An actual MPPT is appropriate for such a situation.


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abuhanzala avatar image abuhanzala commented ·

Great question, John! Just as Surah Al-Kahf (18:17) describes how Allah guides those who seek His light amidst the darkness, choosing the right MPPT controller will guide your solar system to efficiency.

Victron MPPT controllers are designed to handle higher input voltages, like your 55V panels, and convert them to suit your 12V system. They will manage the voltage effectively, ensuring optimal charging without interruptions.

With the right controller, you’ll harness the full potential of your panels. May your efforts be successful and blessed!

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6 Answers
Warwick Bruce Chapman avatar image
Warwick Bruce Chapman answered ·

Yes, so check the datasheet for details but some of the MPPTs eg 150/35 support 12/24/48V (even 36V).

You can then provide any voltage as long as it is +5V above the battery voltage and it will regulate the panel voltage to what the battery needs.

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John avatar image John commented ·

Hi Warwick, thank you for responding.

I was thinking it was the case, though am not sure when I read the specs as to it actually being the case. As it only says that the max panel input voltages are capable of over the 55Vdc, but it doesn't confirm it will actually operate the charging of the battery banks at say 12-15vdc under a panel input rang of say 0-55vdc (yes understanding it requires about 5vdc higher than the battery banks required so they charge as needed).

Its just a lot of money to spend IF it doesn't work as one, I, would assume it does.

If someone has done it, it would be of comfort to know it actually works.

thank you,

John.

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman John commented ·

See in the sheet below the notes at the bottom:

  • PV voltage must exceed Vbat + 5V for the controller to start.
  • Thereafter minimum PV voltage is Vbat + 1V.

7513-screenshot-2020-01-25-at-114941.png

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screenshot-2020-01-25-at-114941.png (157.1 KiB)
John avatar image John Warwick Bruce Chapman commented ·

Hi Warwick,

Yes, the actual charging voltage for the batteries isn't an issue, I understand how that part works to require charging batteries.

I'll try to explain my question a bit better.

My question is more as to IF the victron solar controllers will put out a constant charge voltage (MPPT) ideally to charge the batteries, when the input voltage to the controller from the solar panels varies anywhere from say 15vdc to 55vdc (depending on the sun of the daytime). As the Ebay type controllers have a Solar Panel voltage Turn off at about 14-15vdc and above. So the 55vdc panels wont work most of the daytime with said ebay controllers unless the panels are effectively in the shade and producing less than about 20vdc during the day. not practical of course.

Regards

John.



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Warwick Bruce Chapman avatar image Warwick Bruce Chapman John commented ·

Per comment ABOVE the datasheet I shared:

  1. PV voltage must exceed Vbat + 5V for the controller to start.
  2. Thereafter minimum PV voltage is Vbat + 1V.
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JohnC avatar image JohnC ♦ John commented ·

Hi John. Your panels will come with 2x voltage specs, Voc (open circuit) and Vmp (max power, what an mppt tracks). Can you quote those?

And yeh, some of that ebay kit is prepackaged landfill.

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John avatar image John JohnC ♦ commented ·

Hi JohnC,

I have tried to explain the question in more detail in a reply to Warwick, can you have a read and see IF that helps explain my question better?

Thanks,

John.
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John avatar image John JohnC ♦ commented ·

Hi JohnC,

here are the specs off of the panel. I have 6 panels in total I want to use off grid. (as my previous 2 x 12v panels have faulted with age). So I want to now use these panels.

Peak Power (Pmax) =260W
Max Power Current (Imp) = 5.07A
Max Power Voltage (Vmp) = 51.25v
Short Circuit Current (Isc) = 5.43A
Open Circuit Voltage (Voc) = 60.09V
Dimensions 1600 x 1056 x 40mm
Max System Voltage = 1000 VDC


Regards

John.
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JohnC avatar image JohnC ♦ John commented ·

Yeh Johnno, that's what I wanted to see.

6x 260W panels = 1560W.

A big call into 12V batts, but a /100A mppt would likely suffice. You'd need a lot of paralleled 12V batts to handle all of that power though, and that's rarely/never recommended to parallel a lot of auto-size batts to do that.

So maybe step back and ask whether you really want 12V batts. Maybe 24V or even 48V would suit better? The panels won't matter, a Victron mppt will handle all. Panel wiring might need consideration though.

You're out of the realm of those landfill 'mppt's?' now, please dismiss them (at any level).

Have a play with this too: https://mppt.victronenergy.com/



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Warwick Bruce Chapman avatar image Warwick Bruce Chapman JohnC ♦ commented ·

If it was 48V, you could use a 150/35.

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John avatar image John Warwick Bruce Chapman commented ·

Hi Warwick,

I currently have 2 x 120Ah 12v batteries, which is fine for night time use when fully charged. I was hoping that I could use the excess generated from the panels in the daytime to run extras through the daytime while the sun shines on the panels and ensuring the batteries are charged for the night time. If the batteries are fully charged and the excess isn't used, are you saying it will damage something?

Regards

John.

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anthony avatar image anthony John commented ·

No, he is saying you will potentially have a lot of current (up to 130 Amps) going into a relatively small capacity 12 Volt battery bank so therefore you would need to purchase a charge controller that can produce this current otherwise you will be clipping the PV array output. By choosing to charge a 12 Volt battery bank it also means 1. you need to use cable of large cross sectional area(from the charge controller to the battery) to cope with this current. 2. You need to purchase a larger more expensive MPPT charge controller(s) than for example you would need to if you chose a 24V or 48V battery configuration - warwick reply: ''If it was 48V, you could use a 150/35''.

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ko6kl avatar image ko6kl John commented ·
same problem here , i got a pile to old 170w panels for $20 each

and need to find good charge controller that will take that in ( 44v or much higher),
you should look at ones that have a 120 to 150 volt PV input spec to save on wire size... but the price goes up.... PCM devices seem to want the PV volts to be just a little over the Battery volts , seems only the mppt controls can convert the higher voltage panels to 12 volts ( often with more RFI )
I would be happy to pay extra for one that could work at higher DC inputs and have a RFI clean spec. Really who wants radio static in the RV ?? I can receive that noise all the way across the campground.

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Warwick Bruce Chapman avatar image
Warwick Bruce Chapman answered ·

6 panels is 1560Wp.

If you: 1. put two in series (120.18V @ 5.43A) in 3 parallel strings (120.18V @ 16.26A); and 2. you want to charge a 12V battery

Then, you can use a 150/100 (Max 1450W at 12V).

See the calculator at https://mppt.victronenergy.com/?locale=en:

7515-mppt-calc.png


mppt-calc.png (161.9 KiB)
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archean1 avatar image
archean1 answered ·

Do a search for "difference between PWM and MPPT". A PWM charge controller only works with 12 v panels + 12 v batteries (or 24v-24v, or 48v-48v). An MPPT can work with higher voltage panels and 12v batteries and will effectively convert the extra volts into more amps at your required charge voltage. (The MPPT you posted an image of will also work with 24v batteries). Be careful of really cheap MPPT charges online... there is one brand that is called MPPT (as in its brand name) and it is actually just a PWM charger... quite the scam.

I do agree with other comments. You might find it safer and a lot cheaper (e.g., in terms of cable sizing) to run your batteries at 24v. With the money you save on cabling (and efficiency and safety), you could buy a reasonably efficient converter (e.g., buck?) to get a 12v power supply. You said you already have dual 120Ah 12v batteries, so maybe run those in parallel to get 24v?

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Ted Thornton avatar image Ted Thornton commented ·

Running two 12 in series, not parallel will give 24v, an easy typo...

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spirou avatar image
spirou answered ·

To simplify your problem... You're trying to empty an olympic size pool amount of water into two small buckets. And judging from your answers above you are quite out of your depth in that pool.

As others have said before, the panel voltage is not really a problem with a decent controller (not the PWM crap on ebay). The real problem is the mismatch between panel output and battery capacity. You will charge those 2 batteries in about 30min of early morning light and then what?

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gro avatar image
gro answered ·

In answer to your initial question, yes a true MPPT charge controller will use the output of your panels from the lowest start voltage (12+5=17v) to the maximum voltage your panels will produce (within the max voltage capacity of your charge controller). An MPPT controller utilises a dc to dc converter so effectively transforms the panel voltage to the battery charging voltage. The MPPT charge controller takes the power produced by your panels around 1500W max which would be at the Vmp of 51.25v per panel in series. For strings of panels of 2 in series that will be 102.5V therefore 1500W/102.5v ~= 15 amps into the charge controller, when converted to 14.4V (a good charging voltage for 12 V batteries) you are going to have about 104 amps. That short of current would boil your batteries, the controller would have to be able to deliver 104 amps otherwise it will clip and keep it at its max current (less what ever it has to throttle back to manage the temperature build up).

So once again yes an MPPT charge controller will utilise whatever power is available across the whole of the day.

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elf avatar image
elf answered ·

Victron MPPT state the max voltage input, so with a 55V panel you can use a 75|15 and get a max of 15A from the panel and roughly though only 15A of the available 60A output at 13.75V (55 < 75)


Max Voltage|Max current (In or Out)


or use a 150V|60 for example and you could connect 2 55V in series (2 x 55 < 150 )

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kevgermany avatar image kevgermany ♦♦ commented ·
For anyone reading this old thread, it's also necessary to take ambient temperatures into account. Winter temps raise panel voltage and can kill the MPPT in a badly specced system. The Victron online calculator should be used.
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