Should they stop listing panel wattage as a specification for SCC?

[Mattb4]

Solar Charge Controllers all seem to use a panel watt rating that they base on max charge current they can deliver to the battery. As an example a 30 amp SCC will say 360w for 12v, 720w for 24v and so on. This causes no end of confusion since way too many people think that potential wattage will overwhelm the SCC.

Supply potential wattage is not actual wattage until a load occurs. Loads are what determine how many watts (amps at a voltage) flow.

You can have a huge supply and it does not overwhelm a load. Think of your house that likely has a 200 amp service at 240vAC - OMG that is 48,000 watts! It will burn your house down. But since all it is is potential that you could draw you are safe because you only need a few thousand watts to run various things.

Solar panels do not push power at the SCC. The SCC pulls power from them.

You want to add 3000w of panels to feed a 30 amp SCC? Go for it. You will safely max out at what ever amperage and charge voltage the SCC outputs. W=VA. I hear you asking where does the excess watts go? Are they clipped by the SCC? The answer is they were never generated. Not clipped or somehow shunted away.

So what is the one real danger of damaging a SCC from too many panels adding up to voltage higher than rated for? Excessive voltage. Same way if you plug a low voltage lightbulb into a high voltage socket. It goes poof.

 

[Solar Guppy]

The danger is how fast the charge controller can react to insolation changes. Mppt chargers are optimized for expected input power, if you over panel beyond the specifications, it is very likely the control loop will not react in time and overcurrent will occur which could cause permanent failure with the charger or worse it propagates to the output side.

So you are incorrect in your assumption, these are hard limits for reasons you may not understand, designers and manufactures specify limits on the input for real reasons.

 

[Mattb4]

How fast does a home battery charger react to all the potential wattage from a home outlet?

Sorry but sunlight (insolation changes) do not develop current flow without loading.

You can not draw current without a load.

Take for instance my SCC is now outputting zero watts from a 900 watt array in full sunlight. Is it going to go poof?

 

[Solar Guppy]

You obviously do not have a background is power electronics and are applying some type of logic that doesn't apply.

For solar, the mppt controller is a variable step-down converter typically ( can be step up in AIO ), using duty cycle, usually controlled by a microprocessor that samples the Voltage and Current and adjust the PWM as necessary. The rate of these changes can be in seconds ( it is on my Solis 5G ), while the energy source of solar is highly variable, think of a passing cloud. So in a few milliseconds, one goes from 100 to 900 wmsq on the solar, and until the pwm can react the current exceeds the design limits of components, and the output will rise as well. Limiting the power on the input is the only protection.

There is allot beyond this, to dig deeper, you need to understand how A to D converters, filters, control loops work and how this plays into how to prevent the algorithms used to find and track mppt work from getting lost. For example if you have infinity of solar on the input, a single pwm step could go from no power out , to exceeding limits, as typical pwm gives you 1024 steps, my design of the XW-mppt-60 is a 4096 step ( 12 bit ADC ).

As to the load, batteries or the grid of selling energy are close in infinite loads, controlled by lowering or raising the output voltage

Line based conversion has small voltage window and typically is multi-stage ( AC to DC, Then DC to DC )

This is the best I can do for you without making a lecture series, I hope it enough to satisfy your interests.

 

[timselectric]

Over paneling is a great way to stretch out your production over the course of the day.
My setup is working exactly as expected.
9800w on a 6000w SCC.
Right now in summer, I'm getting a constant 4800w to 5200w for 6 hours of the day. I expect it to be 6000w in the cold of winter. The SCC is clipping the current at 17.6a (rated for 18a). And adjusting to the voltage available. (Depending on sun intensity)

 

[Samsonite801]

Yeah, I like how Victron lays out the wattage specs on their charge controller data sheets...

If you check out the link below, they call it 'Nominal PV power', and list them for all the different supported battery bank voltages:

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf

And on my 250|100 SCC's (running 12v battery bank), when I am pegged at 100a battery charging peak on both of my controllers, I'm seeing about 1400-1450w on the PV (x2 = 2800w), which is about what they are reflecting in the data sheet.

I never tried it yet on a 48v battery bank (to also compare), but I want to in the future at some point later...

 

[32 volt boater]

I remember car stereo decades ago where a so called 600 watt amp was nothing compared to a real 150.

 

[Mattb4]

You obviously do not have a background is power electronics and are applying some type of logic that doesn't apply.

For solar, the mppt controller is a variable step-down converter typically ( can be step up in AIO ), using duty cycle, usually controlled by a microprocessor that samples the Voltage and Current and adjust the PWM as necessary. The rate of these changes can be in seconds ( it is on my Solis 5G ), while the energy source of solar is highly variable, think of a passing cloud. So in a few milliseconds, one goes from 100 to 900 wmsq on the solar, and until the pwm can react the current exceeds the design limits of components, and the output will rise as well. Limiting the power on the input is the only protection.

There is allot beyond this, to dig deeper, you need to understand how A to D converters, filters, control loops work and how this plays into how to prevent the algorithms used to find and track mppt work from getting lost. For example if you have infinity of solar on the input, a single pwm step could go from no power out , to exceeding limits, as typical pwm gives you 1024 steps, my design of the XW-mppt-60 is a 4096 step ( 12 bit ADC ).

As to the load, batteries or the grid of selling energy are close in infinite loads, controlled by lowering or raising the output voltage

Line based conversion has small voltage window and typically is multi-stage ( AC to DC, Then DC to DC )

This is the best I can do for you without making a lecture series, I hope it enough to satisfy your interests.

Sounds good, as in baffle with BS type of good, but you are talking around the facts. I have little doubt that the MPPT is seeking the best voltage- amp production window. The fact it can handle going from full production to zero production is quite a wonder. However you still have not explained how the SCC draws more current when already running at peak.

BTW I am trained in power generation electricity (nuclear) and not electronics. The first thing you learn in the production of power is loads determine power used. If you can show that a SCC is using power beyond what it is converting to output,and the mechanism it does so, than I will accept it as important information. However you have not done so but instead used insults, big terms, and appeal to authority arguments.

ETA: If you can limit your SCC charge current does that mean you now exceed panels limits? Why not?

 

[Mattb4]

Over paneling is a great way to stretch out your production over the course of the day.
My setup is working exactly as expected.
9800w on a 6000w SCC.
Right now in summer, I'm getting a constant 4800w to 5200w for 6 hours of the day. I expect it to be 6000w in the cold of winter. The SCC is clipping the current at 17.6a (rated for 18a). And adjusting to the voltage available. (Depending on sun intensity)

I think the biggest drawback to over paneling is the cost of extra panels and the fact that can bother people that they are not getting full production from a panel. Grid tie people of course would expect that max power would always happen.

 

[HRTKD]

The watt rating is a good number to aim for. Most people can read that number, add up the watts of their panels and see where they stand.

 

[rhino]

I think the biggest drawback to over paneling is the cost of extra panels and the fact that can bother people that they are not getting full production from a panel. Grid tie people of course would expect that max power would always happen.

Not sure why it confuses people that something that is directly dependent on many variables would not always produce the single number people use for what they think the panel should produce (the "watts"). That number is directly based on STC (Standard Test Conditions). If the panel is not experiencing same conditions as the STC then you will either get more or less than those watts listed.

 

[Mattb4]

The watt rating is a good number to aim for. Most people can read that number, add up the watts of their panels and see where they stand.

It does serve that function. My concern is all the people that carry the impression that panels push watts out versus the load dictating how much watts are drawn.

Heck a battery has the potential to deliver large amps/wattage but people do not worry it will overwhelm their inverter. Inverters do not have a battery capacity limit just a voltage and output wattage rating. Now true you want to have fuses and wire based on max current but that is another topic.

 

[HRTKD]

Victron put a link in the VictronConnect app to explain why the solar charge controller was "off". I've been on the forum and absorbed enough knowledge that I have avoided the temptation to click on that link. No charging? Hmm, let's add a load and see what happens: Bingo!

 

[Samsonite801]

Victron put a link in the VictronConnect app to explain why the solar charge controller was "off". I've been on the forum and absorbed enough knowledge that I have avoided the temptation to click on that link. No charging? Hmm, let's add a load and see what happens: Bingo!

Yeah totally, best time to check the performance of my system is maybe in the morning, around 10:00 to 11:00 am-ish (once the Sun starts kicking tail) when the batteries are still charging (that is typically enough by itself to hold the chargers at max charging amps), but then I can turn on the roof AC unit if I really want as well, and watch both chargers pegging at their maximums of 100a each, on the battery side (200a total). Then can really see what the PV circuits are reflecting, in order to meet that demand (since that is all the watts the Victrons' can ever be allowed to draw at 12v bank voltage on this setup). I am about double-size overpaneled, so I never see peaks that the solar arrays would be capable of.

I really enjoy the Victron eco-system with the VictronConnect and the BMV in this regard, because all relevant information is right there in single pane of glass... I also added the optional Victron LCD displays onto the front of the SCC's so you can walk right up there and tell the chargers are pegging on 100a each at quick glimpse...

BTW, I haven't clicked on that link either yet hehe...

 

[timselectric]

I think the biggest drawback to over paneling is the cost of extra panels and the fact that can bother people that they are not getting full production from a panel. Grid tie people of course would expect that max power would always happen.

True, but panels are cheap. And it's well worth it to me. Although I understand that if limited by space, you want to get all that you can from each sq mm.
In my case I have plenty of room. And prefer getting more production per day.

 

[Samsonite801]

True, but panels are cheap. And it's well worth it to me. Although I understand that if limited by space, you want to get all that you can from each sq mm.
In my case I have plenty of room. And prefer getting more production per day.

Yeah, and I know I also appreciate the over paneling in the morning hours, the evening hours, the high-Sun hours when patchy clouds roll over off and on while the AC is running, and in the Wintertime, etc...

They really are for adding extra performance buffer, for when the Sunlight is not ideal conditions, which can be quite a bit at times, depending on the weather and season.

 

[Mattb4]

Revisiting this Thread now that I feel I understand what is going on with the solar panel watt ratings for SCC.

The purpose of limiting the number of solar panels is that the SCC can not maintain its rated max charge amperage for more than a short time before it overheats the circuitry. It is not because the panels produce too much power since panels only produce power as loads and the amount of sunlight allow. However if you have full amperage production of the SCC due to more panels (Note: the SCC does not clip production it simply does not take anymore than its max.) producing for a longer time than expected a problem develops. The SCC is like a long distant runner in that it can go a long time at a slow pace but if you force it into a full out sprint it quickly overheats and collapses.

Sure some of these SCC are built of better components and have better heat dissipation so they can operate for longer before an issue happens. But all of them fail to tell you that their max charge amperage is based on intermittent duty cycle and not continuous.

There is a lot of deceptive ratings in the industry.

 

[hydrox]

Short conclusion:
Do not exceed amps or voltage specs of inverter.Wattage does not matter.
Is that right ?

 

[Mattb4]

Short conclusion:
Do not exceed amps or voltage specs of inverter.Wattage does not matter.
Is that right ?

I would say you do not want to develop max charge amperage of your SCC for longer than few hours per day. In the case of real cheap SCC the hours might be as low as 1or even less.

ETA: However as a practical easy for people to understand advise is stay with in max voltage and max wattage limits.

 

[Samsonite801]

I would say you do not want to develop max charge amperage of your SCC for longer than few hours per day. In the case of real cheap SCC the hours might be as low as 1or even less.

ETA: However as a practical easy for people to understand advise is stay with in max voltage and max wattage limits.

Well and it really depends on the manufacturer when it comes to how well a given model can tolerate overpaneling.

Also to mention, there are SCC's like Victrons where they can support multiple battery bank voltages, and in these cases, they will clip at different wattage maximums, depending on which battery bank voltage is being used.

In the case of Victron 250|xx, they show in their spec sheets a hard Isc wiring limit of 70a, but in reality, it will clip a lot lower than that. I'm running mine at 12v and it does clip at 1450w, as the spec sheets show it should.

I consider this model to be straightforward in the documentation, and I appreciate that they provide the extra detail on what you can actually get away with, where a lot of manufacturers are not as clear about how many amps you can wire to on the PV circuit technical Isc hard limit.





Basically my 250|100's just peak up to the maximum 100a battery charging, where the input amperage (at maximum power point) is a lot lower than 70a... (Note: It may also vary too depending on where Voc is installed at (running lower circuit Voc, may cause it to pull amps up higher, where running higher Voc may cause it to run lower amps on the input).

BTW, when mine are each charging full-bore at 100a, they can simply hold that 100a all day pegged (is a continuous-duty rating), until the battery gets full and tapers off. They do get hot, so I blow a fan on them since they are down in a motorhome basement (to kind of keep the air moving around them)...