Any tips on my setup?

[Wrybread]

> Yeah, my Tristar PWM 45 interfaces with a RS232 cable. I need to use a USB converter with it!

Ha. But actually, from some perspectives, that's a good thing, since that data is very easy to read by other gizmos. But yeah, in the modern era, I think being able to read data over the network (on your phone for example) is crucial or, at least, extremely handy.

[Wrybread]

I'm surprised being able to switch the power over to another application (a fridge for example) isn't more common on charge controllers. It seems like such an obvious need. In the language of some people earlier in this thread, you're "losing money" or "screwing yourself" once those panels stop outputting power. Personally I don't see it that way since I have yet to have to pay for any sun, but it's still nice to be able to do something with the power once my batteries are charged up. Or maybe some charge controllers can already do this?

[SunEagle]

I'm surprised being able to switch the power over to another application (a fridge for example) isn't more common on charge controllers. It seems like such an obvious need. In the language of some people earlier in this thread, you're "losing money" or "screwing yourself" once those panels stop outputting power. Personally I don't see it that way since I have yet to have to pay for any sun, but it's still nice to be able to do something with the power once my batteries are charged up. Or maybe some charge controllers can already do this?

If you have a wind turbine the charger usually has the option of redirecting the energy to a "dump load". That is built in to keep the turbine from either over spinning or burning something up if you don't have a way of stopping it by initiating a "break" or tethering the blades so it doesn't turn as fast.

I am also surprised a solar charger doesn't come with control to direct the power to a "dump load" but then again you can still use the power directly from the panels if your batteries are fully charged so you really aren't losing anything if you set up your system to take advantage of the power generated by already having the load connected. If you don't have this load connected then you are the one to blame and are losing the energy generated.

[Wrybread]

I am also surprised a solar charger doesn't come with control to direct the power to a "dump load" but then again you can still use the power directly from the panels if your batteries are fully charged so you really aren't losing anything if you set up your system to take advantage of the power generated by already having the load connected. If you don't have this load then you are the one to blame.

Do you know of a charge controller that will turn on that secondary load only after the batteries are fully charged? If the system isn't smart enough to prioritize the battery bank first, then I can't see a way to use the power productively without (often) getting in the way of charging the batteries.

[ewarnerusa]

The Tristar does this. That is what the diversion load support feature is on it. I followed a thread on rv.net about a guy who used it to divert the current to a 12V water heater element.
"Diversion Charge Control
In the diversion mode, the TriStar will use PWM charging regulation to divert
excess current to an external load. As the battery becomes fully charged, the
FET switches are closed for longer periods of time to direct more current to
the diversion load.
As the battery charges, the diversion duty cycle will increase. When fully
charged, all the source energy will flow into the diversion load if there are
no other loads. The generating source is typically a wind or hydro generator.
Some solar systems also use diversion to heat water rather than open the
solar array and lose the energy."

EDIT: I found the old thread.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25824208/print/true.cfm

[Wrybread]

> https://www.rv.net/forum/index.cfm/f...print/true.cfm

Cool Project!

But sadly it looks like the range of use for those diversion loads is limited. From the Morningstar FAQ:

What are acceptable dump/diversion loads?

Diversion loads acceptable for use are water heating elements and air heating elements (i.e. purely resistive loads). DO NOT use light bulbs, motors, inverters, refrigerators, or other electrical devices for diversion loads. These loads will sustain damage or cause the controller to disconnect the load (leaving the system unprotected from overcharge). Only heating elements should be used. Diversion load sizing is addressed in your diversion controller

Here's an interesting thread where someone recommends a voltage sensitive relay such as this one:

http://www.ebay.com/itm/Voltage-Sens...-/301360777164

For the Tracers, its a shame that it's not built-in, since it's so close. The external load can be turned on when there's light (PV input), which I know is a common feature on charge controllers, but currently there's no way to set a more specific threshhold.

[sensij]

From there it was easy to make a little app so I can monitor my panel remotely. Here's a screenshot of what it looks like in the morning with the sun coming up. The value in the center and on the graph is wattage. I plan to add the rest of the relevant data from the charge controller (pv voltage, pv amperage, battery SOC - to whatever extent that's useful) and the temperature inside the fridge and its power source at some point.

Nice programming! A couple years ago, another user was planning a 48 V system with some questions similar to yours (and a whole lot more, if you search the OP's name). Then, as in this thread, I was advocating for increasing the PV capacity beyond what the conventional "panel STC rating / battery voltage = charge current" calculation would suggest. I posted a model of what the actual charge cycle might look like in terms of volts and amps on an ideal day, but it would be interesting to see what carefully collected data on a system like yours would show.

https://www.solarpaneltalk.com/forum/off-grid-solar/off-grid-solar-panel-systems/22226-help-me-finalize-my-off-grid-system-please

It looks like you might have the ability to generate those curves, especially if you experiment with installing the 3rd panel.

The ability to use excess charging power to an "opportunity load" once the battery achieves the desired charge level is definitely a feature in some charge controllers. One implementation is an "auxiliary output" that can provide a control signal to an SSR based on the battery SoC. Using a Pi to manage that with a less expensive controller is clever, I would just suggest that you think through the possible failure modes so you don't end up sending power at the wrong time.

[Wrybread]

Thanks for the great information Sensij, as usual.

And knowing the "opportunity load" term led me to this thread, where someone almost goes down the same road I just did (by reading the ModBus output from their controller and controlling the load externally):

https://www.solarpaneltalk.com/forum...pload-question

And there's the usual distracting bickering with TheTrollThatShantBeNamed about it in this thread:

https://www.solarpaneltalk.com/forum...0-excess-power

And there's some interesting discussion on the topic here. Amazing how well people can collaborate when they're civil:

http://outbackpower.com/forum/viewto...=2865&start=25

but it would be interesting to see what carefully collected data on a system like yours would show.

I just added logging for PV current, PV voltage, battery current, battery voltage, and battery SOC (as reported by the controller). I'm averaging each of those over 15 minute periods, let me know if you think I should do that differently. It's easy enough to change it to 5 minute intervals or whatever.

I would just suggest that you think through the possible failure modes so you don't end up sending power at the wrong time.

Avoiding turning on the fridge before my batteries have had time to fully charge is of course the big riddle. Currently I'm turning on the fridge when my charge controller reports an SOC of 85% or greater and a battery wattage of more than 300 watts. Another idea is to turn on the fridge X minutes after going into float with a sustained wattage. Let me know if you have any recommendation.

Avoiding over discharging my batteries is relatively easy with my setup. Since my fridge is only 2 way (AC or propane) and not 3 way (AC, DC or propane) I have to power my fridge from my inverter, which will cut off before my batteries get too low. I don't expect that will ever happen, and would mean the Pi died or my program crashed while the fridge was turned on, but it's a nice safety to have.

That said, I sure wish my fridge let me power it with DC directly, since I'd rather not leave my inverter on all the time. But I don't care enough to upgrade my fridge.

[Sunking]

Then, as in this thread, I was advocating for increasing the PV capacity beyond what the conventional "panel STC rating / battery voltage = charge current" calculation would suggest.

Sensij you are a sharp guy and should have a good working knowledge of MPPT controllers and panels.

So what does the controller do when you over power it? Stop and think about this.

Two things happen.

1. The controller no longer operates as MPPT. It behaves like a series voltage regulator where it input current = output current right?
2. The solar panel no longer is a Current Source and turns into a Voltage source like a battery right?

Now stop and think what that means. We know if the panel is operating as a Voltage Source the voltage is greater than Vmp operating some where Voc and Vmp right? 72 cell panel Vmp is roughly 36 volts and Voc = around 46 volts right?

So lets just say conditions are the panels paralleled up together are sending 10 amps of current to a 12 volt system. Battery may or may not be charging. Could be the equipment drawing al the power.

As I said the controler is not operating in Vmp or boost mode, just a plain ole series regulator. So the panels are say pumping 38 volts at 10 amps (380 watts) into the controller. On the output of the Controller we know is outputting 10 amps at battery voltage of say 14 volts (140 watts).

Where is that missing 140 watts going? It has to go somewhere in the form of waste heat. .

[Wrybread]

Sunking, I respectfully ask you to not hijack this thread again. We'll somehow manage without your input.

[sensij]

Where is that missing 140 watts going? It has to go somewhere in the form of waste heat. .

It goes into the solar panels, as irradiance that is not converted to electricity. The MPPT function remains intact even as the controller moves off of the maximum power point; it just tracks a target that is not maximum, becoming a constant power controller by riding along the IV curve as needed to stay within the controller's output current limit. PV current drops fast as V approaches Voc, so the charge controller never gets more than the 520 W (for example) of power it can handle.

You can make an argument that operating at rated current for more time out of the day is bad for the controller, but that is a different conversation. If the alternative is to replace the controller anyway, why not let it ride, as long as the other appropriate safety measures are in place? Under the conditions discussed in this thread, it isn't going to handle max power for very significant periods of time anyway, limited by either the availability of the sun, or the transition to absorb because battery voltage has hit setpoint. (although OP's plan to add in opportunity loads changes the workload a bit).

Edit:
What I wrote above applies only to the bulk stage. In absorb or float, the controller will clearly move away from the maximum point in any case. If it transitions to straight through PWM control, in the most basic form, it rapidly connects and disconnects the array from the battery as needed to maintain the desired voltage. During the connected time, it is in the constant current segment of the IV curve (PV voltage = Battery voltage < Vmp), and you count on the PWM logic to prevent excessive power from being fed to the battery.

For this controller, the manual states:

WARNING
Controller will be damaged when the PV array straight polarity and the actual operation power of the PV array is three times greater than the rated charge power

So really, putting 900 W on it is well within their 1560 W damage limit.

I would guess that the most dangerous scenario is in bulk at noon on a cool, mostly clear day, but with dynamic partial shade or cloud reflections that scramble the mppt logic. Pages 4 and 5 talk about it a bit, but by tracking the min and max PV voltage and current at some higher sample rate (not sure how fast the RS-485 output updates), along with the 15 min interval the OP suggested, it might be possible to evaluate how well the mppt and other regulation routines are performing. If the observed voltage and current ranges are narrow in each 15 minute interval, that would be a sign it is handling the conditions properly.

[sensij]

I stumbled on another thread where someone was recommending putting you on mute, just as I had recommended.

Try to imagine if your first exposure to Sunking had been in this thread:

https://www.solarpaneltalk.com/forum/off-grid-solar/off-grid-solar-panel-systems/344573-does-my-mppt-scc-and-120v-charger-choice-make-sense-for-my-lifemnpo4-batteries/

I don't think that painting his contributions in the broad strokes you've stated here is really very fair. If I was running the forum I would struggle with determining at what point the bad outweighs the good, but if the post counter kept track of only "good" submissions, he'd still have a higher count than anyone else.

.

[J.P.M.]

Why is that? Why are you here hijacking this thread over and over and making sure it degenerates into bickering and insults even after being told it's uninvited?

I googled your previous username, from before you changed it on this forum, and found countless other postings all over the internet where you do nothing but hijack every thread and insult people under the guise of helping them. I found at least 4 other online communities that had basically kicked you out. I got a good chuckle when I stumbled on another posting where someone was recommending putting you on mute, just as I had recommended. You're absolutely toxic. In short, you're a troll.

There's lots of other threads on this board for you to hijack, and as I can see from your posting history today alone (congratulations on your 20,000th post by the way!) you're engaged in multiple other arguments on this site. And I'm sure many others all over the internet. I have a feeling I'm feeding the troll by saying all this, but please do us a favor and go harass someone else and turn off "subscribe" on this thread.

But I bet you've learned a few things since showing up here. That you're still here, in spite of all your apparently hurt feelings, may say something in the way of agreement that it hasn't been a total waste for you. Welcome to the forum of few(er) illusions.

With that in mind, having sniffed around some, and keeping in mind my limited knowledge, I'd also suggest this place is a fair amount more technical, and technically sophisticated and correct (read MORE SAFE) than some other places you can ask questions.

FWIW, while SK appears to suffer fools less well than some of the rest of us, my suspicion is he's one of the more tolerant - at least compared to what he might want to write - but has a more acerbic and direct style that some snowflakes can get in sync with. But that's conjecture on my part and NOMB anyway. 20,000 posts as you note and, by may anecdotal recollection, maybe 3 or 4 pissed off posters /yr. doesn't seem too bad. Making omelets all the time will result in a few broken eggs 1X/a while.

It may be that part of the problem you seem to want to foist on others is that your skin is a bit thin. There seems a lot of that going around these days. Anyway, you can always ignore what anyone writes. Or, accept some parts of what anyone writes and ignore the rest. There is also an ignore feature. Some things you need to do for yourself. The mods and admin. are not your mother.

From what I've seen of your output on this and other threads, if I was looking for answers or opinions about one of the many aspects of solar electricity I'm clueless and ignorant about, and had a choice between taking your stuff seriously or SK's, there would be little choice in my mind. See my 03/07/17, 12:08 P.M. post to this thread for particulars as to why.

Take what you want of the above. Scrap the rest.

[Wrybread]

To be clear, I'm not questioning his knowledge or ability, but he turns every single discussion into a shouting match. If I was building a $30k+ grid-tied system maybe I'd say "yes sir" and take my licks, but when I'm working on an RV installation it's completely ridiculous for him to go into pompous shouting mode and hurl insults. And furthermore in this discussion at least he hasn't contributed anything useful and has in fact gotten in the way of people who are, over and over again.

[Wrybread]

And looks like the Morningstar 45A MPPT at the link Sunking posted is now up to $478.