diy solar

diy solar

MPPT maximum voltage - why no safety margin?

Reduce the design spec by 10% - 20% and you will have a safety margin. 150v controller? Keep your panel Voc about 120v max.

Same with your 2000 watt inverter. Load to 1800 watts max.

Keep your engine 500+ RPM below redline.

Use only 80% of the full capacity of those lithium batteries.

Equipment in general will treat the user better this way.
 
Don B. Cilly said:
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?
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It depends on temperature. Even with a load on them my panels almost hit Voc today because it was cold and somewhat windy.
 
Another situation where you might feed open circuit panel voltage into your SCC: something goes wrong and there is nothing on the battery side of your SCC.

I've had someone call me in to troubleshoot that exact situation, as it happens. A tier 1 SCC and inverter, but the connection between them was somehow faulty. Not clear if it was a loose connection, one that worked loose, or something else, but it burned up a wire. Once I figured it out, got a piece of suitable wire to replace it with, and wired the batteries back in, it was fine. If they'd relied on a load to prevent hitting Voc, the SCC might have been toast, too.
 
12VoltInstalls said:
Time period. Honda designed these for production in ~1971

Not much that happened many moons later is not really relevant to 1971
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Exactly. And they were still running 2-stroke road racers at that time that went 25K rpm - not really relevant. The little Honda was definitely unique. So was the 6-cyl one. So was the Kawasaki mach 3.

Honda was always better at building motorcycles than cars - I just never liked their cars. Probably the only brand of car I've never bought out of some fifty over my driving career. When we were kids one of the locals had a 'honda car' - we picked it up and shoved it into the box of somebody's dad's Ford pickup. :ROFLMAO:
 
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.
 
Danke said:
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”
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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.

12VoltInstalls said:
I’ve had a 1971 CB350F at 92mph on early 1980s tube tires on spoke wheels…?
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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.
 
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.
 
Warpspeed said:
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.
Click to expand...

I had a WTF moment until I saw the username and got to the end... :p
 
Don B. Cilly said:
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?
-
Click to expand...
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.
 
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 said:
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.
Click to expand...
Cloud edge effect will spike the current, not the voltage.
 
littleharbor2 said:
Cloud edge effect will spike the current, not the voltage.
Click to expand...

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:

1677689192474.png

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.
 
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.
 
zanydroid said:
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.
Click to expand...
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 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.
 
Supervstech said:
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.
Click to expand...

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.
 
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.
 
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