Solar panels. Series, parallel or individually wired?

[Baggywrinkle]

Paul, you are confusing current protection with voltage protection.

Most solar controllers, including the Victron units, have a safety mechanism that will limit the maximum current to a safe level, but even brief over voltage will destroy most controllers.

The Victron questions and answers website confirms that Victron does not have any voltage protection. Responding to the question:

"Does the MPPT 150/35 Controller have Over Voltage protection if the Max input is over 150?"

The Victron community manager responds:

"Exceeding the maximum PV input voltage rating will destroy the MPPT.

It is also important to be aware of the role that temperature plays with panel voltage. Increasing voltage as temperature decreases. So even if a system appears to work for some time, if you are too close to the limit, it can appear to be working and then, the conditions for a particular day can destroy the MPPT."

Does the MPPT 150/35 Controller have Over Voltage protection if the Max input is over 150? - VictronEnergy

This is also my understanding, over-voltage will kill an MPPT.

Panel voltages are quoted in the panel data sheets for a cell temperature of 25°C and will climb as temperature drops due to the voltage temperature coefficient of the panel, a negative number around -3to4% per degree centigrade.

Why I really like the Victron calculator linked in a previous post ... you can see exactly where the voltage lies between the max voltage and the Vstart and Vrun voltages of the MPPT over the complete temperature range.

 

[PaulRainbow]

Paul, you are confusing current protection with voltage protection.

I know the difference between voltage and current.

FFS

Most solar controllers, including the Victron units, have a safety mechanism that will limit the maximum current to a safe level, but even brief over voltage will destroy most controllers.

The Victron questions and answers website confirms that Victron does not have any voltage protection. Responding to the question:

"Does the MPPT 150/35 Controller have Over Voltage protection if the Max input is over 150?"

The Victron community manager responds:

"Exceeding the maximum PV input voltage rating will destroy the MPPT.

It is also important to be aware of the role that temperature plays with panel voltage. Increasing voltage as temperature decreases. So even if a system appears to work for some time, if you are too close to the limit, it can appear to be working and then, the conditions for a particular day can destroy the MPPT."

Does the MPPT 150/35 Controller have Over Voltage protection if the Max input is over 150? - VictronEnergy

The Victron Connect App will give the message "input voltage exceeded" and the controller shuts down if the voltage exceeds the controllers rated voltage. There may be a limit to the amount the rated voltage can be exceeded, i don't know.

I'm not suggesting people fit under rated controllers, but i know for a fact that some protection exists.

 

[Baggywrinkle]

The Victron Connect App will give the message "input voltage exceeded" and the controller shuts down if the voltage exceeds the controllers rated voltage. There may be a limit to the amount the rated voltage can be exceeded, i don't know.

I'm not suggesting people fit under rated controllers, but i know for a fact that some protection exists.

Didn't know it did that.

Edit: Found it in the Victron Community ...

mppt 150/100 error 33 input high voltage - VictronEnergy

 

[noelex]

Hmm... in this case the company was selling the panels bundled with the power station (same vendor). The panels themselves have an operating current of 48 volts, which I know is a different thing entirely, but conveniently 57.6 is 120% of that number. I'm wondering if the vendor is simply playing closer to the limit (I saw mention of 3.5% headroom on another random site, which would be under 60), or if there is padding baked in elsewhere.

It is likely the panels have a Vmp of 48V and a Voc of 57.6V. While the panels will be operating most of the time at the Vmp voltage, it is the maximum voltage or the Voc that is of concern.

When the solar controller starts in the morning or is shut down, or regulating completely the input voltage will be at Voc for those particular conditions as no current is flowing.

57.6V is below the limit of 60V for your solar controller, but solar panels can produce a higher voltage than their STC specifications in some circumstances, especially in cold weather.

For example: The Voc listed for the panel is measured with a cell temperature of 25°C. A typical temperature coefficient for a solar panel is around 0.2V per degree Celsius. So the Voc with a cell temperature of 5°C will be 61.6V above the limit for the controller.

For this reason, most manufacturers recommend a significant buffer between the Voc specifications of the panel and the maximum input voltage of the solar controller. You have some buffer, but it is below the level that is normally considered satisfactory.

 

[Graham_Wright]

Suffering from the same uncertainty, I have a rotary switch which selects port, starboard, series or parallel.
It has been very useful.
Apart from being able to switch from parallel to series (generally to mitigate shading), viewing each panel output is useful for fault finding and angle setting (mine are pivoted).

 

[noelex]

.... using single, smaller 12v panels, the calculator can't find a suitable MPPT for panels @ 70°C.

Yes this is a good point. The Victron units have a high wake-up voltage set at +5V above battery voltage. Once the wake-up voltage is achieved, the solar panel voltage has to be +1V above battery voltage to continue operation. On some brands of controllers, the wake-up voltage is adjustable. It is a pity Victron has not incorporated this into their software.

In practice, this seems to very rarely be an issue, but you do need to be careful about teaming the Victron controllers with "12V" panels in parallel, especially in high temperatures, if the panels have a Voc on the low end of average, when the overnight battery voltage is kept high with secondary charging sources such as wind and if the solar panels have minimal ventilation.

If you select a very high panel temperature of 70°C as you have done the Victron calculator correctly warns that this is not a satisfactory combination because meeting the start up conditions may be delayed especially if some of the other factors mentioned above apply. 70°C is a very high panel temperature. The most I have measured on my rigid panels was 54.7°C in Greece during summer at solar noon on my previous yacht.

In very hot conditions with no panel ventilation I can imagine that 70°C could be rarely reached with some installations perhaps with soft panels glued to the deck, but I have never personally seen temperatures this high.

Edit: I just checked my solar panel temperature on my current yacht. This is in the Caribbean close to noon with the panels producing near full power. It was 34°C, but this is for very well ventilated rigid panels.

 

[mattonthesea]

The Victron Connect App will give the message "input voltage exceeded" and the controller shuts down if the voltage exceeds the controllers rated voltage. There may be a limit to the amount the rated voltage can be exceeded, i don't know.

Stirling DC to DC/MPPT does too - how do I know? Can't remember exact figure but it has a ridiculously low setting. Less than 38V so no series possible!

 

[noelex]

Stirling DC to DC/MPPT does too

Keep in mind the specifications for the unit warn in red letters not to exceed the maximum input voltage. The manufacturer obviously feels that a mechanism to shut the controller down will not offer protection from an over voltage condition. This warning is echoed by many manufacturers.

Note there is no such warning on the current input. The specifications even spell out "input unlimited". The unit it will protect itself reliably against currents higher than the maximum rating, but not against voltages higher than the maximum rating. This is true for most solar controllers.

 

[PaulRainbow]

Keep in mind the specifications for the unit warn in red letters not to exceed the maximum input voltage. The manufacturer obviously feels that a mechanism to shut the controller down will not offer protection from an over voltage condition. This warning is echoed by many manufacturers.

Earlier, you claim that no protection exists and that i am confused, seems you are mistaken, there is at least some protection.

 

[noelex]

If the manufacturer warns "Important - do not exceed the input voltage" (Sterling) or "Exceeding the maximum PV input voltage rating will destroy the MPPT" (Victron), then obviously no effective protection for exceeding the input voltage exists.

The vast majority of other manufacturers have the same warnings, although there are some rare exceptions, such as some of the Midnite controllers with their "Hyper VOC" circuitry.

Suggesting that the solar controller will protect itself against input voltages greater than its rating as you did in post# 39 (see below) is wrong, or at best misleading, advice. They don’t just shut down; in many cases, they are permanently damaged (or destroyed, to use Victron’s language).

Victron controllers have over voltage protection, exceed the rated voltage and they just shutdown.

 

[noelex]

Here is an example from the Victron site:
Mppt voc too high? - VictronEnergy

The question is:

"My ccgx shows a wildly fluctuating Pv wattage and an unsteady charge to the batteries. I suspect that this is because the voc and the operating voltage of the MPPT are too close, 148voc and 150v mppt.

What is the MPPT actually doing in this scenario is it being damaged is it protecting itself is it damaging the batteries???"

The answer from Victron’s community manager is:

"Much too close.
Disconnect your panels immediately and reconfigure them to reduce the voltage.
Your batteries should be fine, but your charge controller is possibly damaged. But you will not know until the panels are correctly configured below that PV VOC limit."

 

[PaulRainbow]

If the manufacturer warns "Important - do not exceed the input voltage" (Sterling) or "Exceeding the maximum PV input voltage rating will destroy the MPPT" (Victron), then obviously no effective protection for exceeding the input voltage exists.

The vast majority of other manufacturers have the same warnings, although there are some rare exceptions, such as some of the Midnite controllers with their "Hyper VOC" circuitry.

Suggesting that the solar controller will protect itself against input voltages greater than its rating as you did in post# 39 (see below) is wrong, or at best misleading, advice. They don’t just shut down; in many cases, they are permanently damaged (or destroyed, to use Victron’s language).

I'm not suggesting people use under rated controllers, but to say the Victron MPPTs have zero protection is incorrect. There is a link, with a screenshot in post #43 that proves it.

There is another quote on the Victron forum "I've just tried with my 100/30 controller to connect 5 panels (19V) in series and actually the Victron App directly told me "input voltage exceeded". So at least to some extend there is a protection here and you will not "burn" the controller when connecting more volts than needed. Of course this might not work if you exceed it too much, but I think you should be fine trying out."

I've also seen this with my own eyes. Like so many, you base everything on your own limited experience.

 

[Baggywrinkle]

As with all electronic components, they are usually designed to operate without failing at the manufacturers stated limits. This means there is a bit of wiggle room designed in, but the manufacturer will not tell anyone what that design parameter is for good reason.

What they will do to protect themselves against warranty claims is log important parameters to determine if the device has been used outside its design parameters. It appears that Victron have created the user error 33 to flag to the user that their array has exceeded the input voltage limit - probably in the hope that the user will react and correct the error before permanent damage is caused, hopefully preventing failure of the device, which although a warranty claim would most certainly be refused on a controller with a history of over-voltage errors, a customer with a dead MPPT is still an unhappy customer.



If it was me designing the MPPT I would look at maybe -30 to -40°C and apply a typical voltage co-efficient to see how far from the standard quoted 25°C voltage the -40°C voltage was, add 10% margin and design the circuits to survive that scenario, flagging a warning (error 33) for anything over the components stated max array voltage. Low temperature related over-voltage is probably way more common than a muppet installing a massive array on a tiny controller and letting the smoke out.

My advice to anyone considering Victron equipment is to use the MPPT calculator on their web site, and aim for a graph something like this ....

MPPT Calculator - Victron Energy

 

[noelex]

There is another quote on the Victron forum "I've just tried with my 100/30 controller to connect 5 panels (19V) in series and actually the Victron App directly told me "input voltage exceeded". So at least to some extend there is a protection here and you will not "burn" the controller when connecting more volts than needed. Of course this might not work if you exceed it too much, but I think you should be fine trying out."

Paul, did you read the two answers given in the Victron site in response to the comment you quote?

"Do not confuse an overvoltage alert, with an overvoltage protection."

And

"You are very lucky that you're not buying a new controller.
There are other posts here saying there is a small tolerance for over voltage, but the real answer is to prevent it from happening. I.e. correct design and installation. @klim8skeptic is perfectly correct."

 

[PaulRainbow]

Paul, did you read the two answers given in the Victron site in response to the comment you quote?

Have you read anything i have posted ? Or from Baggywrinkle ?

You claimed zero voltage protection. Amongst other things, post #53 confirms that there is, as least some, voltage protection. The controller shuts down, produces an error message, then resets. If that isn't OVP then i don't know what is. As Baggy points out, Victron are not going to say the controllers have xxV tolerance, because there will be those that deliberately push to the limits.

Of course, as i have repeatedly said, we don't know how far about the max voltage rating that protects against. I've also, repeatedly, said that the controllers should be adequately rated for the installation.

I knew for a fact that this is how the controllers work as i have been called out to just this error. Customers new solar installation was not working as expected so i was called upon to investigate. The stated panel voltages were in spec for the controller, just, but the panels produced a few more volts than stated, in bright Sunlight. The controller had been shutting down every time the voltage exceeded the max rating, by even a volt or 2. This had been happening for over a week, every day, several times. Naturally, a bigger controller was fitted, end of problem.

 

[Sea Change]

So I think the moral of the story is that it's a bad idea to risk going over the voltage on your Victron MPPT, but you may get away with it.

Similarly, having a controller connected to a solar panel but not the battery may or may not mean instant death for your MPPT. I've experienced both.