MPPT maximum voltage - why no safety margin?

[stienman]

Most electronic systems and parts, both consumer and professional, include hefty safety margins in their design and specifications:

Sometimes the true specifications are much more robust than the printed ones...

Human factors matter, and it seems to me that if most other specifications have a safety margin, people will naturally and reasonably get used to there being a general "safety margin" with most published specs.

Why not in this case?

Additional questions:
* are there other specifications which have no safety margin?
* since MPPTs are for Solar Panels, and Solar Panels have the property where their VOC can go UP in cold weather, is this simply a bad way to specify maximum voltages? E.g. maybe MPPTs should have to give their ratings for maximum VOC for a solar panel at 20,000 feet elevation, -40 temperature, and pointed directy at the sun?

These are weird assertions to make.

If you cross a bridge rated for 50 tons with a 60 ton load and it sustains damage, that's your fault. The bridge might not collapse, or the damage might not even be noticeable, but you've degraded it by going over its limit.

Because it's a human safety rated construction, though, and a public good, then the government demands that while it may sustain damage, it doesn't result in injury or death unless it's grossly exceeded. So you and the people under the bridge are going to be fine even though you've exceeded the rated limits.

But that does NOT mean that it's EVER ok to exceed them.

As far as human safety factors go, these inverters will, assuming they are UL rated, support an overvoltage condition of 2,000V.

They will likely be damaged, but they are not allowed to start a fire, cause an electrical shock, or spew harmful chemicals into dwellings.

So they do have a safety margin - but that's what it is - margin for the safety of the user and those around them, not a margin for the device's own safety.

Further, manufacturers have an incentive to advertise and document the operable maximum rating - you can buy a 250VOC controller to use with your 150V system and build that margin in yourself, but you're going to pay extra. If a manufacturer builds it and then rates it for only 150VOC, then they're paying for margin you don't need or want - and at the end of the day you are paying for it.

Lastly, these are maximum ratings not ideal ratings. If they've documented it correctly you'll find the MPPT controller performs its best at a specific voltage range. If you're constantly operating around its maximum then you're throwing power away. So if an MPPT controller has a maximum VOC at 150, it's operating range is likely 90V-120V. It'll operate outside that range, and it may even continue to perform the MPPT algorithm, but it'll do so at a lower efficiency than its design range.

So even if they over-designed it to handle 250VOC, wrote "Max VOC 150" in the documentation, if you're putting panels on it that get into that range, you're way outside the range they actually designed the components to operate best at.

The maximum VOC is a number you should make sure you don't exceed to avoid damage to the inverter.

But the entire solar system should be designed around the MPPT's operating range, and if your setup is within that range, then it's unlikely to exceed the maximum VOC.

This margin doesn't exist in most consumer products, and people aren't "used to" having a little extra headroom - except in safety critical applications. This is not one of those, and so unless you're equating the collapse of a building with the internal damage of a solar charge controller, you should not be assuming this either.

If you do think people are used to a little extra headroom, just ask around - "I see your laptop has a power adaptor with a 19.5V output, but this charger outputs 24V. Are you comfortable using it in your laptop?"

 

[littleharbor2]

Nope. Current isn't affected much by temp (about 1/5th as much as voltage), and it definitely doesn't increase it. The clouds allow the cells to cool raising their voltage. The only thing that spikes the current is additional insolation.

Consider my Talesun 330W 72 cell panels:

View attachment 137438Looks like we

Power varies by -0.40%/°C
Voc varies by -0.31%/°C
Isc varies by +.06%/°C - i.e., current actually goes DOWN with increasing temperature.

Looks like we're going to have to agree to disagree here. You can get near full VOC. under indoor light . Tempratute has a clear effect on cell Voc. as you have shown. Cloud edge effect is not a temperature related phenomenon. It is an increase in solar intensity which has everything to do with current output. Granted there will be some temp. fluxuations on partly cloudy days the higher than STC. output will be mostly due to increased current. I have demonstrated this rapid increase in current many times while testing solar panels for my buying customers.

 

[D71]

The truth it really doesn't cost a lot to make a great product vs make an average or below average product...... so in a GREEN minded world why not just make the great product vs any average or below average products? Why not regulate substandard average products?

wrap your brain around that for a moment.... substandard equipment is a waste of energy, materials, and time. Pollution to cancel green desires. Based on monetary.... Greed.

with bifacial panels the VOC can be anywhere in a range.... why not make panels and mppt that are matched as a set

 

[400bird]

Here's my 1920 watt STC array. Panels facing in two separate directions (one series pair east and a second series pair south) it was an overcast day, about 40-45 F. Sun peaked out from the clouds for a few minutes. Current spiked well above panel ratings and voltage stayed mostly constant.

I'd say cloud edge effect is current, not voltage.
That is if this was cloud edge.

 

[400bird]

The truth it really doesn't cost a lot to make a great product vs make an average or below average product...... so in a GREEN minded world why not just make the great product vs any average or below average products? Why not regulate substandard average products?

wrap your brain around that for a moment.... substandard equipment is a waste of energy, materials, and time. Pollution to cancel green desires. Based on monetary.... Greed.

with bifacial panels the VOC can be anywhere in a range

Then consumers need to start buying based on quality not just price. But most consumers make the vast majority of purchase decisions based on price as the most heavily weighted factor for most items.

 

[D71]

Then consumers need to start buying based on quality not just price. But most consumers make the vast majority of purchase decisions based on price as the most heavily weighted factor for most items.

Manufacturers need to start making based on greatest best designs by regulations. Again unwrap and rewind your brain. Make mppt and panels all in one for system designs.... would that not allow the most production.?

the only way ppl are going to get to Green is to change their whole thinking process with manufacturing marketing and purchases ..... mppt matching to panels is probably more of a minor as this is all across manufacturing and purchasing. Volume sales should mean lower pricing ... greed is your enemy just like development of electric meters.

what am communicating to you for a thought process is like an alien language most ppl will never get it

 

[WindWizard]

Here's my 1920 watt STC array. Panels facing in two separate directions (one series pair east and a second series pair south) it was an overcast day, about 40-45 F. Sun peaked out from the clouds for a few minutes. Current spiked well above panel ratings and voltage stayed mostly constant.

I'd say cloud edge effect is current, not voltage.
That is if this was cloud edge.

View attachment 137456

It is really difficult to tell since the MPPT controller is constantly trying to find the most wattage by adjusting the voltage to produce the most power. It really is all the same as the real measurement of power is wattage which is simply volts times amps so if the voltage goes up then so does the watts or if the amps goes up then so watts. I know that on the partially cloudy days when it was cold outside, I was concerned because my Charge Controller was over 150 Volts. When it was just sunny and cold then it was never an issue. It may have been the Charge Controller spiking due to it trying to find the best voltage for maximum power.

 

[TomC4306]

Manufacturers need to start making based on greatest best designs by regulations. Again unwrap and rewind your brain. Make mppt and panels all in one for system designs.... would that not allow the most production.?

the only way ppl are going to get to Green is to change their whole thinking process with manufacturing marketing and purchases ..... mppt matching to panels is probably more of a minor as this is all across manufacturing and purchasing. Volume sales should mean lower pricing ... greed is your enemy just like development of electric meters.

what am communicating to you for a thought process is like an alien language most ppl will never get it

I will choose free will.
If I want the cheapest thing I can buy that is my choice, not government's.
Conversely, if I choose to buy top of the line, that also is my choice.
You just don't seem to want to acknowledge that this topic is beyond your ability to design or engineer.
Give me lots of options and I will choose how they go together, not some faceless bureaucrat in a Faraway City.

 

[D71]

I will choose free will.
If I want the cheapest thing I can buy that is my choice, not government's.
Conversely, if I choose to buy top of the line, that also is my choice.
You just don't seem to want to acknowledge that this topic is beyond your ability to design or engineer.
Give me lots of options and I will choose how they go together, not some faceless bureaucrat in a Faraway City.

Do you deny it takes almost same amount of energy, materials, and process to deliver a substandard, average, and great product with say the simple design of an mppt compared to other more advancements such as locomotive motor controls and communications? You don't know me at all.

Your govt and the green ppl are ruling you. Either go green or cancel it. Picking mppt and solar panels should be so easy that even if you had clay dough between your ears it would be easy. Is it that easy?

The Original poster asking for additional safety measures just so an inch can become a mile is the root of this post beginning. Go back and start there. Your desire to control what is out of your and my control is your problem and mine. No one likes to be regulated. But at the same time if Green is the take over scream then everything has to go with new thinking and processing. The regular evolution process is and will be to slow.

we did pick the same 3048 with me as a single vs your dual.

 

[TomC4306]

Do you deny it takes almost same amount of energy, materials, and process to deliver a substandard, average, and great product with say the simple design of an mppt compared to other more advancements such as locomotive motor controls and communications? You don't know me at all.

Your govt and the green ppl are ruling you. Either go green or cancel it. Picking mppt and solar panels should be so easy that even if you had clay dough between your ears it would be easy. Is it that easy?

The Original poster asking for additional safety measures just so an inch can become a mile is the root of this post beginning. Go back and start there. Your desire to control what is out of your and my control is your problem and mine. No one likes to be regulated. But at the same time if Green is the take over scream then everything has to go with new thinking and processing. The regular evolution process is and will be to slow.

we did pick the same 3048 with me as a single vs your dual.

Right. He wants to pay for an inch and get a mile. The mile is available, he just doesn't want to pay for it. And that's his choice.
Belly aching about it isn't going to change it.

 

[400bird]

It is really difficult to tell since the MPPT controller is constantly trying to find the most wattage by adjusting the voltage to produce the most power. It really is all the same as the real measurement of power is wattage which is simply volts times amps so if the voltage goes up then so does the watts or if the amps goes up then so watts. I know that on the partially cloudy days when it was cold outside, I was concerned because my Charge Controller was over 150 Volts. When it was just sunny and cold then it was never an issue. It may have been the Charge Controller spiking due to it trying to find the best voltage for maximum power.

You realize the second graph I posted was voltage and current?
If the voltage increased, the MPPT would have tracked it up. But the voltage didn't increase, the current went up by a factor of something like 5-10!

Cold effects voltage yes, but the point I was making is the cloud edge effect is current not voltage. The edge of the cloud doesn't make the panel colder and increase the voltage. The panel was already cold, the extra light doesn't lower panel temp, if anything it would warm it up.

 

[Warpspeed]

My observations of cloud effect are that things change very quickly indeed, almost instantaneously.
That suggests to me that its more of a direct optical effect than an actual temperature change of the panels.

 

[WindWizard]

You realize the second graph I posted was voltage and current?
If the voltage increased, the MPPT would have tracked it up. But the voltage didn't increase, the current went up by a factor of something like 5-10!

Cold effects voltage yes, but the point I was making is the cloud edge effect is current not voltage. The edge of the cloud doesn't make the panel colder and increase the voltage. The panel was already cold, the extra light doesn't lower panel temp, if anything it would warm it up.

I can't argue with your data because it indeed shows that the current spiked and the voltage remained the same.

How can you explain my voltage spiking? That is really my question. What caused my voltage to spike and go over 150 volts? It never does that on a sunny day no matter how cold it is but it did happen and I was so concerned that I replaced both of my charge controllers. Maybe someone can help me understand what was going on if it was not cloud edge effect. I made an assumption that that was what caused it to happen but if it didn't what was going on?

 

[Warpspeed]

It probably has a lot to do with the speed of response of your solar controller.

If the solar controller responds very quickly, the voltage will hardly change, but the current will.
Its a result of the controller being able to pull more watts from the panel by very quickly increasing the loading on the panels.
The maximum power voltage hardly changes from twilight to full sun, its printed on the rating plate.
If you have a very fast MPPT you will hardly see any voltage change with very sudden insolation changes.

On the other hand if your MPPT is really slow in correcting, the voltage may spike and dip, while the MPPT tries to catch up.
So different folks are going to see some very different voltage effects, depending on the type of solar controller you have.

 

[sunshine_eggo]

I can't argue with your data because it indeed shows that the current spiked and the voltage remained the same.

How can you explain my voltage spiking? That is really my question. What caused my voltage to spike and go over 150 volts? It never does that on a sunny day no matter how cold it is but it did happen and I was so concerned that I replaced both of my charge controllers. Maybe someone can help me understand what was going on if it was not cloud edge effect. I made an assumption that that was what caused it to happen but if it didn't what was going on?

Maybe it's because we have Victrons, and they behave differently. "Cloud edge effect" is not the right term to describe the bulk of what you and I are seeing as that's reserved for the increased irradiance effect. We have substantial wind that rapidly cools panels not in direct sunlight. In intermittent clouds, while staring at the numbers, I see a bump in voltage and power that tapers off with no obvious spike in current.

Even with 25A logged, that really doesn't feel "well over" rated for a ~2kW array... maybe 10% over... within the range of Imp and Isc difference?

I don't know that anybody is logging data fast enough to actually measure any "spike." One of these days, I'll use Trends on VC to try and capture it as it collects data every few seconds.

In any case, I'm going to stop using that description for what I see because I have been applying it incorrectly.

 

[Warpspeed]

I have home made solar controllers that maintain a fixed solar panel voltage no matter what.
It uses a simple switching power supply to measure panel voltage and adjust loading on the panels to maintain that fixed voltage.
I see full panel voltage even with the sun well below the horizon, and charging current down in the milliamp range.
It responds very fast too, sub millisecond type response.

I see no voltage spiking, its not really possible.
Control of solar panel voltage is entirely up to the solar controller and its characteristics.
Any voltage spiking or dipping can only be due to a lazy controller.

 

[LeoThomson]

I don't know that anybody is logging data fast enough to actually measure any "spike." One of these days, I'll use Trends on VC to try and capture it as it collects data every few seconds.

I am using an electrodacus BMS and DSSR20's. The way I understand it, the DSSR20 is basically an ideal diode and my panels are essentially connected directly to my 24V battery. I do not see a voltage spike, (the battery drags the voltage down) but I have seen a charge current spike with the "edge of cloud" around 10% - 20% higher. It freaked me out the first time I observed it, but was told the equipment could easily deal with it and not to worry.

I do expect the voltage on the panels to go up and down depending on the amount of light that hits the panels, but I could be wrong. Following with interest...

 

[Warpspeed]

The voltage on the panels can be anything from zero (with a dead shorted output ) to full open circuit voltage.
The panels are a current source, the voltage you measure depends entirely on how much the panel is loaded down.

The function of an MPPT controller is to constantly adjust the loading on the panels to find the power peak, and that power peak will ALWAYS be pretty close to the maximum power voltage printed on the rating plate. It does vary from that with insolation and temperature, but not by enough to be worth bothering about.

A fixed panel voltage controller works just as well as a proper perturb and observe algorithm, I have done back to back tests to prove this.
In fact under highly variable conditions, the fixed voltage controller wins because of its speed of correction.
Over steady conditions the mppt wins because it can correct for temperature and slight variations in the peak power voltage.
I am talking about differences of maybe 2% here between both types of controller.

 

[sunshine_eggo]

I am using an electrodacus BMS and DSSR20's. The way I understand it, the DSSR20 is basically an ideal diode and my panels are essentially connected directly to my 24V battery. I do not see a voltage spike, (the battery drags the voltage down) but I have seen a charge current spike with the "edge of cloud" around 10% - 20% higher. It freaked me out the first time I observed it, but was told the equipment could easily deal with it and not to worry.

I do expect the voltage on the panels to go up and down depending on the amount of light that hits the panels, but I could be wrong. Following with interest...

Yes. That should be very evident on the DSSR20 or a PWM controller in bulk phase.

 

[Zwy]

I am using an electrodacus BMS and DSSR20's. The way I understand it, the DSSR20 is basically an ideal diode and my panels are essentially connected directly to my 24V battery. I do not see a voltage spike, (the battery drags the voltage down) but I have seen a charge current spike with the "edge of cloud" around 10% - 20% higher. It freaked me out the first time I observed it, but was told the equipment could easily deal with it and not to worry.

I do expect the voltage on the panels to go up and down depending on the amount of light that hits the panels, but I could be wrong. Following with interest...

Electrodufus = PWM, if I recall correctly .... big difference compared to MPPT.