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Old 07-09-2019, 03:22 PM   #381
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On the BMV712 vs BatterySmart topic. I believe the BMV does temperature compensation. The reason I went with the BatterySmart was for the Voltage Compensation. I was told you cannot install both as they both would try to do temperature compensation which would conflict. I chose to have the Voltage compensation versus battery monitoring. I prefer devices that improve operation versus monitoring devices. The BatterySmart improves two functions, Voltage and Temperature. The BMV only does Temperature.

I’m not a fan of battery monitoring. I don’t believe it would be useful to me. I love data as evidenced by my posting all my Solar production each month. But what good does it do to know precisely how many Amphours were removed from an unknown pool of Amphours? Sure we all know our battery bank’s rated Amphours, but in real life no one knows their true available Amphours. As batteries age, AmpHour capacity diminishes. Even new batteries rarely provide their Lab rated Amphours. To me it’s like knowing your exact gas mileage but not the size of the gas tank.

Even though I’m obsessed with my solar production data, I’m not that concerned about abusing my batteries. I treat them like my propane exchange tanks. When my batteries run out of juice, I’ll just drive down to Sam’s Club and buy new ones. I’m not going to turn off my furnace or fantastic fans if my Voltage drops below 11.8V. I’ll just run them until they quit and buy new batteries if they cannot run the furnace all night or the fantastic fans day and night. I now have 200 days of dry camping on my batteries with this attitude and they still test and perform as new. That puts my battery cost at about $1.00 per day and falling with each additional day of use. My battery cost is one of the smallest daily costs of Airstreaming.
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Old 07-09-2019, 04:12 PM   #382
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Quote:
Originally Posted by pteck View Post
Not bad, but I do believe your system can do better with a minor tweak.

Lots of great oaks up in Northern CA. It was only partial cover in this picture. With as tall as these trees are, there was significant oblique cover throughout the day as the sun moves. This is where parallel can and will shine as every panel individually maximizes it's potential contribution.

Attachment 345817

By the numbers parallel is certainly not holding up any peak product either over factory solar prewire.

Attachment 345818

Pteck, I wish we could park side-by-side to test this situation. I agree with your suggestions that one can run full parallel on the factory prewire and rarely (never) approach 30A peak production and therefore it’s probably never going to be a significant issue. I agree that the losses on sunny days are not going to be noticed. I agree that sometimes parallel will outperform series-parallel. But I still prefer series-parallel because:

1) it’s the factory recommended configuration for 100W panels.
2) it doubles the voltage and halves the Amps which is a double-double reduction of Voltage loss between the panels and the controller. This keeps the Amps significantly below the 10 gauge prewire’s rated capacity.
3) the gain you speak of only occurs in one specific scenario where a single panel is significantly affected by shading out of four. I’ve documented this in my shading posts. If two, three or four panels are shaded, the shading effect would be no different than full parallel . . . and then you still get the double-double voltage loss benefit which makes series parallel outperform in three out of four scenarios.
4) I’ve documented that my system performs perfectly 97% of days. Are you saying full parallel world work better than that? I’d wager it would be the same.

I understand where you’re coming from on this issue. You are providing an alternative configuration for others to consider. I have no problem with that. I believe the real life performance of either configuration would be indistinguishable. I’m tempted to re-wire to full parallel for next summer to prove that point. I wish we could park side-by-side. Maybe we can do that sometime. I frequently travel all around the country. I also wish that someone would start posting months of solar production from a full parallel configuration, but so far nobody has done that.

So I’ll keep documenting my performance on this thread and let everyone see how my series-parallel configuration performs. Then they can decide if they want to use the factory prewire with a series-parallel configuration.
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Old 07-09-2019, 04:28 PM   #383
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Even though I’m obsessed with my solar production data, I’m not that concerned about abusing my batteries. I treat them like my propane exchange tanks. When my batteries run out of juice, I’ll just drive down to Sam’s Club and buy new ones. I’m not going to turn off my furnace or fantastic fans if my Voltage drops below 11.8V. I’ll just run them until they quit and buy new batteries if they cannot run the furnace all night or the fantastic fans day and night. I now have 200 days of dry camping on my batteries with this attitude and they still test and perform as new. That puts my battery cost at about $1.00 per day and falling with each additional day of use. My battery cost is one of the smallest daily costs of Airstreaming.
I agree, if you consider batteries as a consumable, to be replaced as needed, then why worry. There are however, people that have invested in batteries to the point that they become an asset; that should be monitored and protected. I'm at the far end of the spectrum, with 8K invested to two batteries that provide the equivalent of 800AH at 12V. The batteries are quite small and only weigh 63lbs. apiece.

I pamper them.

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Old 07-09-2019, 09:41 PM   #384
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Pteck, I wish we could park side-by-side to test this situation. I agree with your suggestions that one can run full parallel on the factory prewire and rarely (never) approach 30A peak production and therefore it’s probably never going to be a significant issue. I agree that the losses on sunny days are not going to be noticed. I agree that sometimes parallel will outperform series-parallel. But I still prefer series-parallel because:

1) it’s the factory recommended configuration for 100W panels.
2) it doubles the voltage and halves the Amps which is a double-double reduction of Voltage loss between the panels and the controller. This keeps the Amps significantly below the 10 gauge prewire’s rated capacity.
3) the gain you speak of only occurs in one specific scenario where a single panel is significantly affected by shading out of four. I’ve documented this in my shading posts. If two, three or four panels are shaded, the shading effect would be no different than full parallel . . . and then you still get the double-double voltage loss benefit which makes series parallel outperform in three out of four scenarios.
4) I’ve documented that my system performs perfectly 97% of days. Are you saying full parallel world work better than that? I’d wager it would be the same.

I understand where you’re coming from on this issue. You are providing an alternative configuration for others to consider. I have no problem with that. I believe the real life performance of either configuration would be indistinguishable. I’m tempted to re-wire to full parallel for next summer to prove that point. I wish we could park side-by-side. Maybe we can do that sometime. I frequently travel all around the country. I also wish that someone would start posting months of solar production from a full parallel configuration, but so far nobody has done that.

So I’ll keep documenting my performance on this thread and let everyone see how my series-parallel configuration performs. Then they can decide if they want to use the factory prewire with a series-parallel configuration.
Like you said prior, we are generally in violent agreement. The trade and optimization here is the last bit of tweaking we are not in agreement on and that is okay. It is your choice and your system after all.

But, and here's my driver... I strongly understand it to be more significant than you suggest. When posting on forums like this where many others may follow, there's responsibility to be correct and not mislead. Because at that point, it effects more than yourself. Much as we've all come across the new generation influencers on social media that state questionable information.

Per your points:
1) it’s the factory recommended configuration for 100W panels.

- Application is important. Many many Victron systems are installed in static systems where shading is controlled, i.e. small homes. RV solar installers also use Victron components, but will install in - parallel.

2) it doubles the voltage and halves the Amps which is a double-double reduction of Voltage loss between the panels and the controller. This keeps the Amps significantly below the 10 gauge prewire’s rated capacity.

- Choosing to optimize for minor percentage points of perceived transmission loss is never worth whole panels of efficiency loss due to series/parallel inter-dependencies in shading

3) the gain you speak of only occurs in one specific scenario where a single panel is significantly affected by shading out of four. I’ve documented this in my shading posts. If two, three or four panels are shaded, the shading effect would be no different than full parallel . . . and then you still get the double-double voltage loss benefit which makes series parallel outperform in three out of four scenarios.

- Sorry, I do not agree. Shadows happen very frequently throughout the day from branches, clouds, RV A/C/vent shrouds, etc. Nevermind bird droppings and other contaminants on the panels.

4) I’ve documented that my system performs perfectly 97% of days. Are you saying full parallel world work better than that? I’d wager it would be the same.

- Absolutely
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Old 07-10-2019, 04:40 AM   #385
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It’s quite obvious both approaches work fine. You’re both happy with your systems. The rest is about tweaking to get the very last few available watts. This quibbling over series-parallel vs. pure parallel seems fairly pointless and brings to mind Lilliputian arguments about which end of a boiled egg to crack first.
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Old 07-10-2019, 07:15 AM   #386
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Hi

Just for the record - The BMV-712 will do the same voltage monitoring / voltage feedback to an MPPT (or other device) that the Battery Smart module will do. If you have a Bluetooth MPPT, it will "network" up wirelessly.

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Old 07-10-2019, 07:23 AM   #387
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It’s quite obvious both approaches work fine. You’re both happy with your systems. The rest is about tweaking to get the very last few available watts. This quibbling over series-parallel vs. pure parallel seems fairly pointless and brings to mind Lilliputian arguments about which end of a boiled egg to crack first.
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Old 07-10-2019, 08:08 AM   #388
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Series / parallel / series-parallel?
It certainly does depend. When localized shading occurs on individual panels parallel works best, it has to. But, if a uniform shading occurs, casting over all panels equally both suck. It happens.

The question in my Pea-brain is whether in overcast / low light / early morning / late evening can series make more power? It seems feasible. I have no data. So in these less than perfect situations, and using series connectivity, does it amount to a hill of beans?

To not have to go thru time and expense rewiring the equipment to roof, thus allowing the factory 10awg to be used with up to 400w of PV, while not exceeding desired voltage drop is a very good reason to use series-parallel. Anyone who rewires knows how much work that is, or those who pay know how expensive that is. If you have to rewire, I’d go with parallel on an Airstream No question. That’s what I did.

Rather than going Victron, I stayed with tried and true Trimetric. To each his own. I don’t need to have another reason to keep obsessing over a smartphone. And trying to figure out what happened when it fails. The price difference between PWM and MPPT would buy another panel. To each his own.

Trimetric will work with 24v panels if you have 24v battery bank. This will allow a more efficient 24v inverter (less sag under high amp loads) and only require a cheap DC/DC converter to run certain low load 12v components. I should have gone that route. Live and learn. Next time. Have a good day.
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Old 07-10-2019, 08:57 AM   #389
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I completely agree Bob. Both will perform acceptably and our discussion is splitting hairs.

I also agree with Clint that the series parallel configuration minimizes voltage drop with the factory prewire. But I probably lose more voltage because of my dirty solar panels.

Bottom line is that 400W series parallel configured solar on the factory prewire can supply enough Amphours for me to dry camp indefinitely as long as I avoid significant canopies of tree shade. My recent post was to show and tell just how much tree canopy still worked for me. I was able to produce 400-500 Watthours in that location which was enough if I didn’t continuously use my Fantastic Fans.
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Old 07-10-2019, 10:40 AM   #390
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I am continuing to enjoy this game of ping-pong, as I have everything else installed and wired up in my trailer...last couple bits and pieces will arrive today and it'll be time to put the panels up. So I am reaching the final moment of required decision...which I haven't made yet.

Leaning toward series/parallel using the 10 ga factory prewire, not because I believe it works 'better,' but out of laziness not wanting to pull bigger wire. My hope is that overall, it will work 'as well' as parallel, or at least 'good enough' given my location in the abundant sunny landscapes of the west, and my miserly use of power.

On the other hand, I might get up one morning this week and just get on with it and run new wire
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Old 07-10-2019, 02:49 PM   #391
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I am continuing to enjoy this game of ping-pong, as I have everything else installed and wired up in my trailer...last couple bits and pieces will arrive today and it'll be time to put the panels up. So I am reaching the final moment of required decision...which I haven't made yet.

Leaning toward series/parallel using the 10 ga factory prewire, not because I believe it works 'better,' but out of laziness not wanting to pull bigger wire. My hope is that overall, it will work 'as well' as parallel, or at least 'good enough' given my location in the abundant sunny landscapes of the west, and my miserly use of power.

On the other hand, I might get up one morning this week and just get on with it and run new wire
Actually, Pteck is suggesting to run 400W in parallel on the factory prewire. His point is that this configuration would rarely hit the 30A maximum amperage that the 10 gauge is rated for so you will get the single panel shading advantage on the factory prewire. I do not disagree with his point. I rarely exceed 20A. You can look at my historical data to see that he is right. But you will have more voltage loss and could occasionally hit the 30A limit. The Zamp rooftop box is fused at 30A. I feel more comfortable running at less than 1/2 the fused amperage and wire capacity rating with series-parallel. There is less voltage loss on the 10 gauge with 400W of series-parallel than if you run new 6 gauge wire with full parallel. The only possible issue with series-parallel is significant single panel shading. Single panel shading has never been the factor that caused me to use my generator for boost charging.

I continue to discuss this issue because I believe it is educational for those trying to decide if they want to use the factory prewire. I would definitely use the factory prewire even if I wanted to run full parallel for the reasons Pteck noted. I’m not saying I would do it, just that if one truly believes parallel is better, then configure parallel on the factory prewire. Then come back and report your results on this forum.

I have enough leftover wire and connectors to rewire full parallel at the cost of an afternoon of my labor. If I felt it was better, I would certainly do that. But I find no reason to rewire because my series-parallel configuration works perfectly for me. This thread was started to document the performance “good, bad, or ugly”. I think it’s proved to be good and therefore I have no need to reconfigure to full parallel.
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Old 07-10-2019, 03:07 PM   #392
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Hi

Compared to most of the sites we get up here, that's a wide open "lots of sun" site ....

Bob
To further this point again for educational purposes, here are pictures of actual sun locations in the tree canopy where I got about 500W of solar production.
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Old 07-10-2019, 03:15 PM   #393
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I’ve since (last three days) moved to the other side of the tree so I get at least a few hours of direct sunlight on my panels. Here is a picture and the solar production I received. Choosing a location that gets a few hours of direct sunlight really makes a difference. Even if I’m surrounded by trees, I typically can position my Airstream to get at least a couple hours of direct sunlight. My batteries will be much happier with this 20 foot location change since they now are floating daily.
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Old 07-10-2019, 03:51 PM   #394
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I'll see how this goes but I could possibly rewire to parallel if needed with branch connectors no harm done but I think I'll get some data this way first.

I actually had daydreams of relays allowing me to switch from series to parallel, that's some serious overkill
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Old 07-10-2019, 04:14 PM   #395
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But you will have more voltage loss and could occasionally hit the 30A limit. l.
If my panels are 100w/18v/6amps, parallel would be 18v/24amps from the combiner box to the controller...could it ever actually hit 30a? How?

You also mentioned you rarely get to 20amps...with series parallel wouldn't the max you'd ever see be 12 amps to the controller? Or were you saying that 20amps is the most you see OUT of the controller, so obviously you are never seeing more than that from the combiner box to the controller?

Renogy's sizing calculator says 10ga would be ok, as long as 5% losses is acceptable, for a run of up to 18 feet, which on my unit, I believe would not be exceed as I have to guess how they ran the wire from the roof. Reducing losses to 2% would require 6ga.

Series/parallel would be 36V/12amps, correct? This allows up to 30 feet with a loss of 2%.


I think I might be getting too focused on wire losses of 2% vs 5% vs whatever? Maybe because it's a variable I can control/minimize, whereas shade and sunlight is something I cannot control?
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Old 07-10-2019, 05:01 PM   #396
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If my panels are 100w/18v/6amps, parallel would be 18v/24amps from the combiner box to the controller...could it ever actually hit 30a? How?

You also mentioned you rarely get to 20amps...with series parallel wouldn't the max you'd ever see be 12 amps to the controller? Or were you saying that 20amps is the most you see OUT of the controller, so obviously you are never seeing more than that from the combiner box to the controller?

Renogy's sizing calculator says 10ga would be ok, as long as 5% losses is acceptable, for a run of up to 18 feet, which on my unit, I believe would not be exceed as I have to guess how they ran the wire from the roof. Reducing losses to 2% would require 6ga.

Series/parallel would be 36V/12amps, correct? This allows up to 30 feet with a loss of 2%.


I think I might be getting too focused on wire losses of 2% vs 5% vs whatever? Maybe because it's a variable I can control/minimize, whereas shade and sunlight is something I cannot control?
Let me try to explain. I’ve confused you because I mixed wire Amps to the controller with wire Amps from the controller. I believe you understand as your explanation made sense to me. You can look at my historical data to see max solar (PV) and Voltages from the panels to calculate Amps.

Last month, My maximum solar production was 304W of Solar at 41.43V (see attached table). Since Watts / Voltage = Amps, the maximum possible amps From the panels is 304/41.43=7.34A. Well below the 30A breaker and wire capacity. If configured in full parallel, the Amps would double and the Voltage would half. Therefore you might have had 14.68A at 20.72V. Again, well below the rated capacity of the prewire fuse and wire. This is Pteck’s point. Just wire full parallel on the factory prewire and you will be below the 10 gauge wire capacity and voltage loss will be well below maximum levels.

Now that these Amps, Volts, and Watts get to a MPPT Solar Controller, it reconfigures them into charging voltage. Assuming a charging voltage of 13.5, the 304W turn into 304/13.5=22.5A. This is why I increased the cable size to 6 gauge between the Solar Controller and the busbars. It is possible to reach 30A between the Solar Controller and Busbars. I’ve seen 30A on a couple of occasions, but it is very rare (see attached photo). And you are correct that even in a full parallel configuration, you would never get 30A into the controller because it would be near 20 Volts, not at 13.5V.

Again, this is why Pteck is of the opinion that you can just run full parallel on the factory prewire. My data proves his point. Your voltage losses will be way less than 5% at typical operating Voltage and Amperage.
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Old 07-10-2019, 09:09 PM   #397
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Thanks AirMiles. To your credit, you are a well written. Laying out thoughts logically in an easy to read manner, and backing it up with sound observations and logic. A classic influencer in ways that I regard with high esteem.

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I think I might be getting too focused on wire losses of 2% vs 5% vs whatever? Maybe because it's a variable I can control/minimize, whereas shade and sunlight is something I cannot control?
The 3% difference may sound like something to optimize. It is less significant than that. As AirMiles qualified above, peak current output in a parallel connected system is within the acceptable ranges for 10 gauge wire. Additionally, so much of solar production is done outside of the 1-2 hours of peak solar alignment/peak output, that it is only some 10% of total daily generation that is affected. We can double it and say 20% for kicks.

Simplified, but 3% of the 20% total output that is subject to wiring/transmission loss is... 0.6% of total output potentially affected. Materially, on an exceptional production day, optimistically still represents less than 1 amp hour. 1 Ah extra that was not needed anyhow based on the data for good sunny day scenarios where there is a lot of production excess.

On a terrible shaded and overcast production day, all parallel wiring will surely minimize more than 1 amp hours worth of production loss from inter-dependent panels. In a rainy day scenario where it's actually needed.

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The question in my Pea-brain is whether in overcast / low light / early morning / late evening can series make more power? It seems feasible. I have no data. So in these less than perfect situations, and using series connectivity, does it amount to a hill of beans?
One thing to separate and understand is that the panels themselves are what generates power. Power as in watts, which doesn't matter whether that is transmitted with more volts or amps when carried over wire. Wiring does not create power and therefore series wiring will not magically conjure up more power.

Overcast / low light / early morning / late evening light is all variations of effectively the same situation - poor and indirect solar alignment with likely uneven light energy reaching each panel. It's a situation where parallel allows each panel to stand on its own to maximize power output additively over the array. Without inter-dependencies dragging down neighboring panels in power due to voltage and current inter-dependencies when arranged as a series-parallel array.
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Old 07-11-2019, 06:28 AM   #398
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pteck, I'm aware of that. Series produces less voltage drop at the same load compared to parallel, and since power (in watts) is volt x amps, higher voltage produces higher power. Even if it is only two or three watts.

My question was does panels (the source) in series produce more total daily power than parallel since it would seem they reach a higher and thus more usable voltage before parallel panels do. This is in low light conditions. I'm not talking shade that might only touch one panel, rather all of them... such as in early morning or late evening, foggy or hazy conditions. Or, complete cloud cover.

I wonder about this because my new project with three 200W panels in series on an MPPT controller, I have seen a slight charge above the draw of a fantastic running, to the batteries under a street light; all night long. Could these in parallel do that, I wonder?

I have gone by Bogart Engineering specs when designing every system I have ever built. From their chart which is based on 12 volt nominal for calculation purposes; not whatever the panel voltage is we settle on buying, and with no more than 3% voltage drop (VD).

My factory prewire length is 22.5 feet or slightly more. AS ran it to the rear fantastic vent, ignoring the logical place for 2 panels would be in the front. I kid you not.

Adding 2 panels would be right at or slightly over 3% VD, but 3 drove me to run 6AWG to the roof just behind the front fan, 15 feet to the SCC, almost to the inch. Add 0.8 VD to the left rear panel I am still good to go. Four panels should be possible considering VD.

Clint
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Old 07-11-2019, 06:52 AM   #399
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Here we go again Pteck. I agree with everything right up to the point that you say full parallel works better in low light situations. I’m certain it’s the opposite. Multiple panel series configurations only drop off if the voltage on a series linked panel is significantly lower than the others. On an overcast day, the panels will have similar voltages and will all provide power. There will be less voltage drop across the wire to the controller because of the double voltage and half Amperage and therefore series will provide more Watts to the controller and more Amps to the batteries. Higher charging will also happen in low light situations with thicker tree shading. As I keep saying, a four 100W panel parallel configuration has an advantage in only one situation, where one panel is significantly shaded and the other three are in bright sunlight. In that one situation, only the two panels with high voltage will provide power to the batteries. But with 200W in bright sunlight, it doesn’t matter that two panels drop off because the two panels will produce up to 15A to the batteries in bright sunlight. It’s in the low-light overcast conditions where series parallel will outperform full parallel.

Pteck’s point is the equivalent to me arguing that you don’t want full parallel because a Victron controller needs 5 Volts over battery voltage to turn on. If your batteries are at 12.2V, it takes 17.2V to turn on. It’s possible on overcast days and in densely canopied locations that your solar controller will never turn on. This situation is possible, but very rare, just like Pteck’s argument against series parallel is possible but very rare.

Bottom line is both 400W configurations will effectively charge your batteries 97% of the time. You can’t go wrong either way you choose to configure your panels. Sometimes one configuration will slightly outperform the other but the difference will not be the cause of needing to use a generator to boost charge your batteries.

I think we’ve beat this horse to death. Can we just move on to Solar Show and Tell and not bring back this argument every time I document how my system performs in challenging situations?

The funny part of this is that Pteck and I almost completely agree with each other. It’s only on the very smallest details where we disagree. Pteck has added many valuable comments on this and many threads and I look forward to his continued posts and comments. Please post data showing your solar performance in challenging situations. This is how we all learn from each other.
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Old 07-11-2019, 08:05 AM   #400
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Originally Posted by AirMiles View Post
...... The Zamp rooftop box is fused at 30A. ......
Hi

You *would* think that's the case wouldn't you? .....At least I would.

Turns out that at least in my case, the magic fuse was a 40A fuse.

Before everybody goes off about 10 gauge is only 30A, go back to the tables and take a look. There are various ratings for how the wire is run and the type of insulation involved. (... and a whole bunch of rabbit holes to wander down as a result ...).

Bob
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