Pushing the charge controller specs

corndog

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I ordered five of the 445w version of these from SanTan Solar, which I had planned to use with this, but now they're out of stock until October, which isn't going to help much for summer fire outages, plus a budget change is forcing a 24v setup, so I need to put something together sooner, even if it means having to swap equipment around later on. Also, I had planned on using four of these panels, but even if I could only use two to get through summer, that would be fine.

I've been round and round on the common AIO/controller/inverter items and I think the setup I like most at this point is to use a Victron 75/15 for each panel and charge in parallel. Feel free to suggest anything, but my question boils down to this: If you look at the specs for that 445w panel, you can see it absolute peaks at 15.0a in *short circuit* only while making max use of the bifacial gains and, normally, I would not use a technically-possible-15a-panel with a 15a max charge controller, however, the fact that it's a Victron and not a cheapy unit and the fact the most the controller will ever see is 14a when there's snow on the ground, has me thinking that maybe getting this close to the current limit may be fine...what say you gents?
 

DThames

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The 15amp rating of the charger is what it can send to the battery. The max amps of the panel is what the current will be when loaded for max power or shorted output. Use that number for wire and fuse sizing. Those are different and matching them serves nothing.

Not sure what the Victrons cost but one EPFver like this could handle 3 panels in series. Less wire cost to just run one pair of wires to the charger, one pair of cables to the battery.
 

corndog

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The 15amp rating of the charger is what it can send to the battery. The max amps of the panel is what the current will be when loaded for max power or shorted output. Use that number for wire and fuse sizing. Those are different and matching them serves nothing.

Not sure what the Victrons cost but one EPFver like this could handle 3 panels in series. Less wire cost to just run one pair of wires to the charger, one pair of cables to the battery.

48.9v open circuit, which is 146.7v on a 150v controller, plus each panel could be over 500w with snow on the ground, so two panels would be the way to go with that model. It's about the cost of two Victron 75/15's, so no real economic gain there, but you could go to the 80a version and would be safe with two panels, but then you're approaching the cost of three Victron 75/15's.
 

corndog

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If you haven't seen this already here is form you can use to check what Victron charge controller would work with your panel configuration: https://mppt.victronenergy.com/

Also in this article there is a section on "Oversizing a PV Array": https://www.victronenergy.com/blog/...ar-modules-to-the-new-mppt-charge-regulators/

I had not seen that, thanks for linking it. They call out for the 100/20, which would clearly be safe. It's $40 more, so not a ton more, but also not nothing if buying several. As a bonus, it does have the benefit of 48v expandability.
 

DThames

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48.9v open circuit, which is 146.7v on a 150v controller, plus each panel could be over 500w with snow on the ground, so two panels would be the way to go with that model. It's about the cost of two Victron 75/15's, so no real economic gain there, but you could go to the 80a version and would be safe with two panels, but then you're approaching the cost of three Victron 75/15's.
Good point on the voltage. I have been dealing with 60cell which are about 40v.
 

DThames

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48.9v open circuit, which is 146.7v on a 150v controller, plus each panel could be over 500w with snow on the ground, so two panels would be the way to go with that model. It's about the cost of two Victron 75/15's, so no real economic gain there, but you could go to the 80a version and would be safe with two panels, but then you're approaching the cost of three Victron 75/15's.
You could do 2s2p on that 60amp charger and get more power to your battery than two 15amp chargers.
 

corndog

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Kinda leaving a whole panel on the table though? These things are big!
 

DThames

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Kinda leaving a whole panel on the table though? These things are big!
"Also, I had planned on using four of these panels, but even if I could only use two to get through summer, that would be fine." I thought you were looking for something to get by pending an AIO purchase.
 

corndog

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Yes but at the same time, I want to spend/build efficiently. If I were to use that EPever, I'd rather buy two and use two panels with each controller and charge in parallel, which also works just fine to "baby step" my way there if I want to start with one, so that's cool, but what I wouldn't do is use four panels for one. Does that make any sense?
 

DThames

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200v 80a
Yes but at the same time, I want to spend/build efficiently. If I were to use that EPever, I'd rather buy two and use two panels with each controller and charge in parallel, which also works just fine to "baby step" my way there if I want to start with one, so that's cool, but what I wouldn't do is use four panels for one. Does that make any sense?
Makes sense but 4 panels for one of the 150v 60a would be a pretty good fit. ~1800watt panel rating on a 1500watt charger is about right.....you can almost never get the rated watts from a panel and the charger will regulate at 60amps.
 

corndog

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So I think the EPever point comes down to this, because the prices work out roughly similar, would you rather have a Victron and be closer to the max current, or have an EPever and be well within max current?

And using the 2s2p configuration, you would be charging at max on the EPever.
 

DThames

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So I think the EPever point comes down to this, because the prices work out roughly similar, would you rather have a Victron and be closer to the max current, or have an EPever and be well within max current?

And using the 2s2p configuration, you would be charging at max on the EPever.
That is what the rating is for. If a unit can't operate at its rating, I wouldn't want it. Normally your battery will come up a bit and the current will start tapering off, or the sun will start moving again (after noon) and the peak solar will drop off.

Note, My first charger was a 10a EPEver AN with about 200% of the panel watts that the charger would load at. It peaked out at 9.7amps on the display and just did what it was designed to do....almost 10 amps.
 

corndog

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I'll have to chew on that for a bit. I know I'm more comfortable being within the max spec on anything, but I know that when I want to get close to the max spec, I want the higher quality item. Interestingly, the Victron calculator pushed me to the 100/20, even though the 75/15 is within spec. And I just used the base numbers with no bifacial gain. So, is that salesmanship, or is it really that important to stay away from max spec?
 

DThames

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I'll have to chew on that for a bit. I know I'm more comfortable being within the max spec on anything, but I know that when I want to get close to the max spec, I want the higher quality item. Interestingly, the Victron calculator pushed me to the 100/20, even though the 75/15 is within spec. And I just used the base numbers with no bifacial gain. So, is that salesmanship, or is it really that important to stay away from max spec?
I work in the electric motor industry. If we design, build, and sell a 1hp motor, we expect that our customers will load it to 1hp and it can run at that load for some number of years, at the load specific temp. Same with a pump, if you purchase a 1/2 hp pump, you expect it to do that level of work. Look at well pumps and as the "head" increases the flow rate decreases because by design, it will not destroy itself when the load increases because the water level in the well drops (making the pump work harder).

An MPPT charger will create a load on the panels and draw amps from them, if solar conditions permit. If the battery can take the amps (without the voltage getting high enough that the charger throttles back) the charger will adjust the load on the panels to get the max power that is available under the current conditions. This is done by a computer that can measure both current and voltage from the panels and the current and voltage of the battery connection. The programming of the charger will not allow it to cause amps to flow that would cause it to overheat and destroy itself. Recall I said my 10a EPEver would just go to 9.7amps and that is all it would do. That is the device self regulating to stay within its design limits.

It is a fairly common practice to put panels on a charge where the panels' watt rating is 110%-150% of the charger's watt rating. This allows the charger to operate close to or at its rating for more than a few minutes a day (ideal sun angle).

The example below is a bit extreme but easy to describe. Suppose you purchase an AIO that can charge at an amp rating that the power on the PV side is 4000w (consumed) when the charger is charging at rated amps. Now you start out putting in 4000w worth of panels. On a great solar day on 21 Sept, you get a curve like the one on the left. You hit or almost hit 4000w for a few minute. Tomorrow will be worse because the earth tilt will be a little different. But worse than that, there are considerable clouds most of the day and you get power under the second curve from the left. After some amount of time you learn that you are not getting anything like what you need so you decide to increase your array size and you have learned that Overpaneling is not a bad thing. So you add panels to the array, make a parallel wire run, and combine the two runs at the AIO unit. You are excited to see what you produce the next day but it is cloudy and you don't every really get full sun (3rd image from left). However, even at partial power, you are doing pretty well. However, when the sun does come out, you don't get more than 4000w worth of charge to the battery because the charger is maxed at its rating and is "clipping" what could come off the array if you had more current capacity. The next day the sun is out (right most graph) and the clipping shows you had a lot more you could have got but you missed it. After some consideration you remember you live where a sunny day is pretty rare, so you just leave it as is and are thankful to be doing better and all you did was to add some more panels.

Overpaneling to 200% is a bit extreme and most installs would not go over 150% unless there was some specific reason. I used 200% for better visuals.


1659631473019.png
 

corndog

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I hear you, but with many chinese companies, recourse plays heavily into the formula. With your company, you're probably solid enough that your customers have recourse for a decent amount of time through a warranty period, which you honor, and maybe even some good faith warranty beyond the standard warranty period. If I buy through amazon, I have recourse through them for what...thirty days? There are lots of horror stories about how warranty claims are like pulling teeth, even through some of the more reputable resellers. And I'm cool with taking on that risk, it just needs to have the right price correction attached to it.

Also, I realized I was being a bozo. The 75/15 is 75v max input and 15a max charge output, which at 24v, is 360w. That's probably why the Victron calculator pointed me to the 100/20, because it's the first size that could make full use of the 445w panel information that I entered. The 100/20 would be 480w max, which means I'd need to go to the 100/30 if I reeeaaally wanted a controller that were capable of making max use of the bifacial gains. But, I do understand your point about how, in practice, what you're really paying for is just a very short period of charge time, assuming conditions are such that your panels are even able to hit it. Which, I do think these panels will put out over 500w with snow on the ground when in full sun, it can be utterly blinding outside sometimes.

Anyway, taking in your point about what you're really paying for by worrying about making peak use of panels and also taking in the fact that the price jumps to $225 for each 100/30, which is $900 if I wanted them for all four panels, I'm now down to buying either the EPever 60a you linked, or maybe the 80a version to unlock a bit more power, along with the Giandel 2kw inverter that everyone seems to like, or maybe an MPP AIO. The only thing I don't quite like about the EPever/Giandel setup is that I'd have to strictly rely on the BMS for low voltage cutoff, which is just a minor nitpick I guess. It would be about $700 for the inverter and 80a EPever, which happens to be the same price as the MPP LV2424 and that has a ton of great features, of which generator charging would be particularly useful for us. My only nitpick with the AIO is that it's an AIO, so you have to buy the whole thing if the inverter dies, the charge controller dies, or the utility charger dies. Buuuut it has a 1yr US warranty and tech support, which I've already emailed watts247 a couple questions and they were responsive, so I think that's going to be the winner.
 

DThames

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Notice that the EPEver 80a has a 200v input, would work nice if you had 6 of those panels in a 3s2p setup. 500w in bright sun with snow on ground....only if the charger demands 500w. I am stating this largely for those that might read and not understand that the output power of the panel is never more than the load created by the charger (when connected to a MPPT charger). In order to see what my array can output I have to lower the SOC of the batter more than just a little and then test around solar noon with a clear sky. Even then the battery will come up enough that I see max amps for only a short period, unless the battery is really low.

I like my AIOs in that you can set max charging amps, if desired.

I have purchased 4 EPEvers. I have yet to have one fail but I know I will have to eat it if it does.
 

corndog

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Well that's odd, it looks like there are two different specs on Amazon, an 80a/150v for $335.59 and an 80a/200v with some accessories for $428.99.

I ordered the Hybrid LV2424 from Watts247 yesterday, but am not counting out the EPever, because I'll have an extra panel for another project.

Also, another thing that affected my decision is that I have a new Grundfos SQ well pump sitting on the bench that I plan to swap out sometime this year and with a second LV2424, I'd be able to run it from solar, which would be awesome. As it is now with our power hungry well pump, I'll get a few IBC totes and fill those via generator, then just run a few small items in the house via solar.

Side note, I placed the order from Watts247 at 2:36pm yesterday and just received a tracking number at 9:11am today. I've also received a total of six emails between yesterday and today. These guys are friggin on it and know how to make you feel comfortable with your purchase.

Next up is a big Amazon order of cables and tools and disconnects/breakers and whatnot, then a BMS and some cells from Docan...
 
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