Help with PV wire size on rv! Maybe mistake ?

[Benihanas]

Called renogy and got to the bottom of it. No issue with anything just bad marketing and communication on renogy’e behalf. I guess the 100 volts maximum PV voltage of these things is BS. They really can only handle a 24 volt nominal PV system. Rats. Looks like I now own 2 useless mppts. Time to get a bigger one.

You’d think 100vots max meant 100 volts max

 

[HRTKD]

Renogy sucks.

Friends don't let friends buy Renogy.

 

[Vigo]

Well it's a bummer that that's what it's down to.. and it's pretty crappy to run into this limitation on an MPPT, although it's expected on a PWM.

A PWM simply hooks the solar straight to the output and 'pulses' the connection to manage how much power actually flows between the two. It has no way to alter the input voltage so it has to stay within a range from input to output, because if that difference grows too large then even a very brief 'pulse' of one thing 50+v higher than something else, is going to result in an 'overcurrent', however brief. A PWM controller cannot prevent damage to itself or the battery in that situation.

With an MPPT there is usually a DC-to-DC 'transformer' voltage conversion happening such that you may have 100v going in, and it may step it down to something much lower coming out to the battery. In that way MPPTs usually can have much higher solar voltage than battery voltage. My house inverters have 400+VOC solar charging a ~48v battery, hundreds of volts difference.. Which is why with the word MPPT floating around in this thread i didn't even think about it..

But on the Renogy website it does say:

Max. PV Input Power: 12V/520W, 24V/1040W

Which requires you to read between the lines a little and do Watt's Law to it to find out that 520w / 12v = ~43v would be the 'max', and this is a poor way of stating it because a 12v battery can charge at different voltages depending on what it is, so for example a lifepo4 charging at 14.6 would be 520 / 14.6 = 35v.

It's not really a 'max' because the real max is 100v and the manual even says if it goes over 100 it will just cease using it and doesn't say it would break. It would just be the max that can be utilized. The 'hole' in this lack of explanation/documentation is that if someone had a higher voltage/lower current PV array, there's nothing in the manual to suggest that you would get more out of the array if you rewired some of it in parallel to achiever lower voltage but higher current into the controller. It would just 'clamp' the voltage down like it's doing to you, and then use whatever current came in even if you didn't get the full wattage potential of the array out as battery charging.

So while the specs do say something which could clue you in to this, i dont think it's sufficiently obvious from the specs that one SHOULDNT do what you did. So don't feel bad, i blame Renogy too. ?

 

[Pappion]

...
Which requires you to read between the lines a little and do Watt's Law to it to find out that 520w / 12v = ~43v would be the 'max', and this is a poor way of stating it because a 12v battery can charge at different voltages depending on what it is, so for example a lifepo4 charging at 14.6 would be 520 / 14.6 = 35v.

So while the specs do say something which could clue you in to this, i dont think it's sufficiently obvious from the specs that one SHOULDNT do what you did. So don't feel bad, i blame Renogy too. ?

You should be able to over panel a MPPT solar controller. That gives margin for partly cloudy days. Glad I have Victron.

BTW: did some research on VOC vs. Temperature. Generally (not always) -0.35% per 1c rise above 25c.
81.2v * -.0035 * 15c = -4.263v drop, or 77v at 40c.

 

[Vigo]

I agree.. and i THINK it is 'allowing' the overpanelling in this situation. It's just doing 'maximum power point that won't exceed 40a out to battery' instead of the actual max power point of the array.

55v x 11a = ~600w it is allowing in, and assuming max 40a out at a max of 14.6v assuming lifepo4 being charged to 100%, that's 584w out. It may be doing something less than that based on his settings and efficiency losses etc,. But it's working in its overpanelled state, but it puts the owner in a position of 'would i have bought a different controller or less panels if i had known this beforehand', so it still seems aggravating.

 

[Pappion]

I would never use so many small panels. There are 200w, 250w, 300w and 400w panels available. I have two used 250w and they work just fine at 1/3 the cost. Larger panels can save on mounting and wiring. Used panels are a bargin, if you can fetch them vs shipping.

 

[Vigo]

I had to check to make sure we were in the RV section before i opened my mouth again.. but smaller panels can have 'packaging' advantages on an RV roof with a bunch of vents, antennas, rooftop ACs etc. Lets you play a bit of Tetris to maximize your PV instead of being stuck with just a couple of large panels and a bunch of oddly shaped empty spaces.

I have a bunch of used ~2x4' panels I plan to Tetris onto the roof my 23' rv. If i had to use larger panels i could technically only fit 1 of them on such a small roof because of all the other protuberances.. I think i can fit more total watts of smaller panels.

 

[Pappion]

I agree.. and i THINK it is 'allowing' the overpanelling in this situation. It's just doing 'maximum power point that won't exceed 40a out to battery' instead of the actual max power point of the array.

55v x 11a = ~600w it is allowing in, and assuming max 40a out at a max of 14.6v assuming lifepo4 being charged to 100%, that's 584w out. It may be doing something less than that based on his settings and efficiency losses etc,. But it's working in its overpanelled state, but it puts the owner in a position of 'would i have bought a different controller or less panels if i had known this beforehand', so it still seems aggravating.

From what I know from lab validation of switcher designs: The panel voltage should rise when current is throttled at max. At that point MPPT algorithm is idled.

 

[Vigo]

Well, we've exceeded what i know about MPPT function as a forum observer.. I have heard that some, maybe all (?) mppt controllers revert to PWM function when outside of their 'window' or envelope, although i don't know enough about that to say anything more. If that were happening one could potentially make a huge improvement in the energy 'throughput' by rewiring the array. But if he is already getting 40a out, he's already maxed on throughput.

 

[Pappion]

I had to check to make sure we were in the RV section before i opened my mouth again.. but smaller panels can have 'packaging' advantages on an RV roof with a bunch of vents, antennas, rooftop ACs etc. Lets you play a bit of Tetris to maximize your PV instead of being stuck with just a couple of large panels and a bunch of oddly shaped empty spaces.

I have a bunch of used ~2x4' panels I plan to Tetris onto the roof my 23' rv. If i had to use larger panels i could technically only fit 1 of them on such a small roof because of all the other protuberances.. I think i can fit more total watts of smaller panels.

Vents, Antennas, rooftop ACs have shadows. Doesn't take much shadow to shut down a panel or large portion (1/3, 1/2) of a large panel.

 

[Benihanas]

Vents, Antennas, rooftop ACs have shadows. Doesn't take much shadow to shut down a panel or large portion (1/3, 1/2) of a large panel.

you’re right but I’ve managed to mount them in a fashion where they’re a bit higher than my maxair vent. That’s the only thing on the roof… I have a minisplit mounted on the rear. It’s tough to fit 800 watts on a 14’ roof man. The only way I could do it was like this

 

[Benihanas]

@Vigo spot on man. I was playing Tetris trying to get them to fit.

 

[Doggydogworld]

Called renogy and got to the bottom of it. No issue with anything just bad marketing and communication on renogy’e behalf. I guess the 100 volts maximum PV voltage of these things is BS. They really can only handle a 24 volt nominal PV system. Rats. Looks like I now own 2 useless mppts. Time to get a bigger one.

You’d think 100vots max meant 100 volts max

This sounds wrong. As you noted earlier, it's no surprise MPPT throttles your 800W array down to 500-600W because it can only send 550W or so to a 12V battery. But it shouldn't throttle when you only connect four panels.

Page 26 of the Rover Elite 40A manual (PDF) shows >90% conversion efficiency at 75Vmp from 50-550W. That should be legit. Marketing language that lets people jump to conclusions is part of the game, but lying about measured technical specs is grounds for legal action.

This sounds like a panel issue. You measured 72V before connecting the MPPT. That's 18V per panel vs. the 21.6Voc or 24.3Voc spec (you never said which version of HQST 100W panels you have or gave us actual specs). Voc does vary with conditions (temp, solar intensity, etc.), but 18V sounds low to my untrained ear. Especially if you have the 24.3Voc panels.

I'd measure each panel's Voc individually. If they're all 18V then that's just what these panels do in your specific conditions. A drop from 72Voc to 55Vmp once connected to the MPPT is perfectly normal. But if three panels are near the 21.6Voc (or 24.3) spec and one is far below then you've found your problem.

 

[RVLiFe]

I have three 200W rich solar panels wired in series. 24.3 Voc. 20.4 Vmp. Victron 100/50 MPPT.
All panels read 24.3v open circuit volts.
In the early morning hours, it is not uncommon for me to see 60-61volts. As soon as the panels start to see sun, the voltage always goes down. This is normal. Think of it this way, if your panels are only producing 500W, a lot of this is due to the actual radiance of your location at the time and the panels efficiency. If the panels are producing 500W then the MPPT will output that 500W to the battery the most efficient way that it can to maximize the amp output. Due to ohms law, the more amps it outputs at 500W the less voltage you will see.
Watts are watts and that doesn’t change. As long as the radiance is constant at that moment. The MPPT will always try to maximize the amps at the batteries voltage. It is designed to have Amp priority not voltage priority.
@Vigo is correct with his math.
I personally could care less what the voltage of the panel array is as long as the Watt output and Amp output is being maximized. It’s not uncommon for my MPPT to show under 50V but my Amps are being maximized based off the Maximum Power Point at that time.

What you are seeing is perfectly normal for a 12V system. Actually, even a 48V system will display this but the math just makes the voltage look more consistent without such a big drop.

 

[Benihanas]

This sounds wrong. As you noted earlier, it's no surprise MPPT throttles your 800W array down to 500-600W because it can only send 550W or so to a 12V battery. But it shouldn't throttle when you only connect four panels.

Page 26 of the Rover Elite 40A manual (PDF) shows >90% conversion efficiency at 75Vmp from 50-550W. That should be legit. Marketing language that lets people jump to conclusions is part of the game, but lying about measured technical specs is grounds for legal action.

This sounds like a panel issue. You measured 72V before connecting the MPPT. That's 18V per panel vs. the 21.6Voc or 24.3Voc spec (you never said which version of HQST 100W panels you have or gave us actual specs). Voc does vary with conditions (temp, solar intensity, etc.), but 18V sounds low to my untrained ear. Especially if you have the 24.3Voc panels.

I'd measure each panel's Voc individually. If they're all 18V then that's just what these panels do in your specific conditions. A drop from 72Voc to 55Vmp once connected to the MPPT is perfectly normal. But if three panels are near the 21.6Voc (or 24.3) spec and one is far below then you've found your problem.

Dude I’ve said like 5 or 6 times now In a row every time someone doesn’t read this. I have the ‘compact’ polycrystalline renogy panels. 18 volt panel. They are supposed to read 72. They read 18 at panel and test 18 in full sun or a bit higher / lower. I’ve tripple checked both arrays. They don’t each have one bad panel. They are fine. The renogy charger is kicking out some voltage as soon as the breaker is flipped back on as well I can see it on my charge controller. I’m going to upgrade to the 60 I guess and put all 800 there

This sounds wrong. As you noted earlier, it's no surprise MPPT throttles your 800W array down to 500-600W because it can only send 550W or so to a 12V battery. But it shouldn't throttle when you only connect four panels.

Page 26 of the Rover Elite 40A manual (PDF) shows >90% conversion efficiency at 75Vmp from 50-550W. That should be legit. Marketing language that lets people jump to conclusions is part of the game, but lying about measured technical specs is grounds for legal action.

This sounds like a panel issue. You measured 72V before connecting the MPPT. That's 18V per panel vs. the 21.6Voc or 24.3Voc spec (you never said which version of HQST 100W panels you have or gave us actual specs). Voc does vary with conditions (temp, solar intensity, etc.), but 18V sounds low to my untrained ear. Especially if you have the 24.3Voc panels.

I'd measure each panel's Voc individually. If they're all 18V then that's just what these panels do in your specific conditions. A drop from 72Voc to 55Vmp once connected to the MPPT is perfectly normal. But if three panels are near the 21.6Voc (or 24.3) spec and one is far below then you've found your problem.

According to the renogy rep who I honestly started pretty much arguing with. They said that I couldn’t connect 4 12v nominal panels in series. And only could with the 60amp charger.

 

[Doggydogworld]

Dude I’ve said like 5 or 6 times now In a row every time someone doesn’t read this. I have the ‘compact’ polycrystalline renogy panels.

You didn't say poly even once.

18 volt panel. They are supposed to read 72. They read 18 at panel and test 18 in full sun or a bit higher / lower.

When not connected a HQST HSP100P-L 100W poly panel should read 21.6V in full sun and moderate temperatures. Four panels in series should read 86.4V. I don't know why you insist 72V is a normal open circuit reading for your setup.

The renogy charger is kicking out some voltage as soon as the breaker is flipped back on as well I can see it on my charge controller. I’m going to upgrade to the 60 I guess and put all 800 there

That's how an MPPT works. You are obsessed over this drop from 72V to 55V, but a ~20% drop is perfectly normal. Look at this chart for a single smallish solar cell. When not connected it reads a little over 0.62V in full sun. But that's with zero current and thus zero power. A MPPT will reduce the voltage and increase the current to operate at the maximum power point at 0.5V (a ~20% drop). That's the voltage drop you see when you flip the breaker. It's not a malfunction or "poor marketing".



The MPPT will always try to operate at the max power point UNLESS your panels can put out more power than the MPPT can feed into the battery. Then the MPPT will drop the voltage even further. That should not happen when you connect four panels. So a 60A MPPT should not act any differently when you connect four panels.

Will a 60A MPPT pull more power from eight panels? It depends. As long as your array measures 72V when disconnected I'd say no, the 60A unit will not help. If conditions change and your Voc gets closer to the 84.6V spec value then a 60A MPPT might help. But it will still show a ~20% voltage drop when you flip the breaker, because that's what it's supposed to do.

According to the renogy rep who I honestly started pretty much arguing with. They said that I couldn’t connect 4 12v nominal panels in series. And only could with the 60amp charger.

Frankly, I believe the test data published in their manual over some random customer support dude.

 

[Benihanas]

You didn't say poly even once.


When not connected a HQST HSP100P-L 100W poly panel should read 21.6V in full sun and moderate temperatures. Four panels in series should read 86.4V. I don't know why you insist 72V is a normal open circuit reading for your setup.


That's how an MPPT works. You are obsessed over this drop from 72V to 55V, but a ~20% drop is perfectly normal. Look at this chart for a single smallish solar cell. When not connected it reads a little over 0.62V in full sun. But that's with zero current and thus zero power. A MPPT will reduce the voltage and increase the current to operate at the maximum power point at 0.5V (a ~20% drop). That's the voltage drop you see when you flip the breaker. It's not a malfunction or "poor marketing".

View attachment 110678

The MPPT will always try to operate at the max power point UNLESS your panels can put out more power than the MPPT can feed into the battery. Then the MPPT will drop the voltage even further. That should not happen when you connect four panels. So a 60A MPPT should not act any differently when you connect four panels.

Will a 60A MPPT pull more power from eight panels? It depends. As long as your array measures 72V when disconnected I'd say no, the 60A unit will not help. If conditions change and your Voc gets closer to the 84.6V spec value then a 60A MPPT might help. But it will still show a ~20% voltage drop when you flip the breaker, because that's what it's supposed to do.


Frankly, I believe the test data published in their manual over some random customer support dude.

I’m confused why the 21 volts would read. I tested every one of these panels at 18 volts(or close to it) before ever connecting anything. I would have been in agreement but today they seemed totally convinced on the phone that I couldn’t run the voltage that high. The charge controller started to kick out the 55volts to zero later in the day today by the way. I’ll get on the roof tomorrow and check the panels but I’m seriously doubting that I hooked up two arrays incorrectly the exact same way

 

[Doggydogworld]

I’m confused why the 21 volts would read. I tested every one of these panels at 18 volts(or close to it) before ever connecting anything. I would have been in agreement but today they seemed totally convinced on the phone that I couldn’t run the voltage that high. The charge controller started to kick out the 55volts to zero later in the day today by the way. I’ll get on the roof tomorrow and check the panels but I’m seriously doubting that I hooked up two arrays incorrectly the exact same way

I can't think of a wiring issue that would cause this, then again I'm told I lack imagination..... At any rate, when things don't make sense I start small and take one boring little step at a time. Start with a single disconnected panel. Does the label say 21.6Voc? if so it should measure close to that in full sun. If it doesn't match the spec you've found a problem. Maybe it's a bad panel. Maybe it's getting way too hot. Their web page says Voc drops 0.3% per degree C, so 85 deg C panel temp (STC + 60C) would drop Voc from 21.6 to ~18V.

If it matches the spec you check that box off and then test the four panels in series. If that's 4x (e.g. 86.4V) as it should be, check that box off then test down at the breaker. Should be the same 86.4V. And so on....

 

[Benihanas]

I can't think of a wiring issue that would cause this, then again I'm told I lack imagination..... At any rate, when things don't make sense I start small and take one boring little step at a time. Start with a single disconnected panel. Does the label say 21.6Voc? if so it should measure close to that in full sun. If it doesn't match the spec you've found a problem. Maybe it's a bad panel. Maybe it's getting way too hot. Their web page says Voc drops 0.3% per degree C, so 85 deg C panel temp (STC + 60C) would drop Voc from 21.6 to ~18V.

If it matches the spec you check that box off and then test the four panels in series. If that's 4x (e.g. 86.4V) as it should be, check that box off then test down at the breaker. Should be the same 86.4V. And so on....

Damn so if I climb up there tomorrow and they read 18 do I have an issue

 

[Doggydogworld]

Damn so if I climb up there tomorrow and they read 18 do I have an issue

Well, unless the label says Voc should be 18V. That's not what the website shows, but maybe you have a slightly earlier version with different specs. It's tedious to nail down every single detail like this, but as they say the devil is usually in the details.