MPPT maximum voltage - why no safety margin?

[peufeu]

Suppose they're using 600V MOSFETs or IGBTs, this is all hard switching converters so you need margin for voltage spikes during switching, this sets a limit around 500V for the DC bus. Now the MPPT is a boost converter so in order to actually work (and coordinate with the other if you have two) it needs to boost voltage, even if just a little. So if you feed in 500V you're already at max, the MPPT will not do anything. Hence the 450V max MPPT voltage.

 

[shadowmaker]

Well, the Sol-Ark 15K specs are 125-425V MPPT Voltage Range, 500 max and the manual also says “Damage will occur if PV VOC > 550V”

That's weird. My Deye 15/12K has 200-650V MPPT Voltage range, rated PV input 550V(160V~800V). When I asked Deye how to setup my panels with 47.8Voc, they said 16S, which means 764,8Voc. And we have -35C easily (though not in this winter). I though my Deye and Sol-Ark 15K are about the same.

I’ve had a 1971 CB350F at 92mph on early 1980s tube tires on spoke wheels…?

Last summer I rode my 1986 Suzuki RG500 Gamma with 13 years old tires (unused but old). Easily 250kmh (highly tuned, nothing original anymore). This summer they are going to be 14 years old... I just use GRIP tyre softener and they are like new.

 

[Warpspeed]

This is hilarious.

A ten amp fuse is rated to carry ten amps.

So why cannot manufacturers make ten amp fuses that can safely carry thirty amps ?
It would save a lot of blown fuses, and the user should be allowed a bit more margin than the rated maximum.

Its totally outrageous that a ten amp fuse cannot carry more than ten amps.

If a solar controller is rated for a maximum voltage, that is what it is.
Its based on the ratings of the internal components, mainly the mosfets, but also capacitors among other things.
Safe maximums are exactly what they say they are, and definitely not more.

 

[sunshine_eggo]

This is hilarious.

A ten amp fuse is rated to carry ten amps.

So why cannot manufacturers make ten amp fuses that can safely carry thirty amps ?
It would save a lot of blown fuses, and the user should be allowed a bit more margin than the rated maximum.

Its totally outrageous that a ten amp fuse cannot carry more than ten amps.

If a solar controller is rated for a maximum voltage, that is what it is.
Its based on the ratings of the internal components, mainly the mosfets, but also capacitors among other things.
Safe maximums are exactly what they say they are, and definitely not more.

I had a WTF moment until I saw the username and got to the end...

 

[WindWizard]

I have a question I've been meaning to ask for some time: why use Voc?
I mean, once the panels are connected to the controller, they're not going to be open circuit, are they?
I thought, maybe when the battery reaches maximum voltage, PV input goes to Voc. But I measured the voltage at the controller's input, charging 0A as the battery is fully charged, 43.2V, when Voc is 48.5. So it must be for some other reason. Which?
-

I live in Maine where the temperatures can dip to -30 degrees and then if you have a partially cloudy day where the sun hits the leading edge of the cloud and boosts your solar way beyond the panel specs, then indeed the voltage can suddenly go over the max and wipe out your Charge Controller before it has a chance to stabilize. I here what gets taken out is the mosfets. If they are rated at 150 volts and you get a 200 volt spike then they can be damaged permanently.

 

[Warpspeed]

Mosfets particularly have a very low tolerance for overvoltage and overcurrent.
Quality control is excellent these days with fully automated manufacturing.
They are tested during manufacture to meet the specified maximum only, and it takes very little extra than that to destroy the device.

The idea that the manufacturer is being hugely overcautious is just not so.
Also, the idea that any equipment the user purchases should be able to protect itself form any form of abuse, is also pretty unrealistic.

Its not even a question of how much extra safety margin there is.
Its necessary to stay WELL BELOW any published maximum.

If you know that the cliff edge is only three feet away, deciding that to walk four feet will probably be o/k is not such a good idea.

 

[WindWizard]

It depends on temperature. Even with a load on them my panels almost hit Voc today because it was cold and somewhat windy.

My panels were doing the same thing occasionally so I changed out my Charge Controllers to 250 Volts so I would not find them zapped.

 

[sunshine_eggo]

My panels were doing the same thing occasionally so I changed out my Charge Controllers to 250 Volts so I would not find them zapped.

I feel as though you are my twin... swapped a Victron 150/100 for a 250/100 rather than re-wire my array.

 

[littleharbor2]

I live in Maine where the temperatures can dip to -30 degrees and then if you have a partially cloudy day where the sun hits the leading edge of the cloud and boosts your solar way beyond the panel specs, then indeed the voltage can suddenly go over the max and wipe out your Charge Controller before it has a chance to stabilize. I here what gets taken out is the mosfets. If they are rated at 150 volts and you get a 200 volt spike then they can be damaged permanently.

Cloud edge effect will spike the current, not the voltage.

 

[sunshine_eggo]

Cloud edge effect will spike the current, not the voltage.

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:



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.

 

[zanydroid]

What is the definition of cloud edge effect? I thought it was some cloud/sunlight sorcery that causes irradiance in excess of that assumed in STC?

In which case, that is first order a current impacting effect.

 

[Supervstech]

What is the definition of cloud edge effect? I thought it was some cloud/sunlight sorcery that causes irradiance in excess of that assumed in STC?

In which case, that is first order a current impacting effect.

Thats what i thought as well, but it may indeed be a cooling effect from low loads and limited production challenged by sunlight amplifying at the edges of the clouds causing a voltage spike.

But i thought it resulted in increased production over the rated wattage, so id think amperage goes up.

 

[WindWizard]

I will give you an example of what I experienced today. It is a cold day around 20 degrees and partially cloudy. I have 4500 watts of panels. My peak power today was 5530 watts and 137 volts. I have hit 142 volts so I know the voltage does go up with the cloud edge. It is something to consider if you have panels that are pushing the Voltage limit on your Charge Controller. My new Charge Controllers are the Victron 250/100. I got concerned when looking at my data on the Outback FM-80. It is rated at 150 Volts and I saw voltages that were up to 155 Volts so I pulled them. I figured that it was only a matter of time before I would get an extremely cold partially cloudy day and I would lose my investment.

 

[sunshine_eggo]

Thats what i thought as well, but it may indeed be a cooling effect from low loads and limited production challenged by sunlight amplifying at the edges of the clouds causing a voltage spike.

But i thought it resulted in increased production over the rated wattage, so id think amperage goes up.

I guess we're talking about two different things, and the terminology error is mine.

I've never observed cloud edge effects on the timescale that my system logs data - 1m, i.e., I've NEVER seen current over rated. I expect that phenomena is over the moment the cloud as passed and is measured in seconds.

I routinely see events where I'm at notably reduced power for several minutes followed by a couple of minutes of over-rated power production. Happened quite a bit yesterday with intermittent clouds. I saw 3200W out of my 2970W array and we're still about 6 weeks away from my optimal tilt. With sustained sun, this tapers off after a few minutes depending on the wind. With a stiff 20mph wind @ < 10°C, I may see elevated output a lot of the day.

 

[niktak11]

Cloud edge effect is from both cooler cell temp and increased insolation. Even with 20C cooler temps, my panels only get a 7% boost based on the data sheet, but I've seen a 20%+ cloud edge effect boost before.

 

[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.