Solar Charge Controllers

Hello,

I'm currently putting together a part-list for a system for someone else to build. Looking at solar charge controllers. Victron seems to be the gold standard, but they don't have any display it's all through bluetooth and you need a dongle -- so unsure how easy it will be to modify the software settings. So looking at other options like SolarEpic that have a physical display

Specifically want to handle 2x 400 watt panels. According to the calculator, needs to handle 100 volts 60 or 70 amps (depending on panel brand). Does that seem right? Any recommendations?

I used to have the same thinking about the Victron equipment. But that thinking is incorrect. The interface to your phone or computer is super easy. You only need a dongle if you have the older controllers. The new ones with Bluetooth are all wireless, but can be hooked up with a cable if need be. Adjusting the settings from your phone is super easy and once you set it, you really never have to touch it, but it's addicting to watch all numbers doing their thing. I assume you're looking to wire your panels in series?

I max out at about 27 amps with a 365 watt panel, so about 30 amps seems about right for a 400 watt panel. I was looking at voltages on some 400 watt panels and they are right at about 48 to 52 volts, so 2 of them in series might go over 100 volts. You might need a controller that can handle 150 volts for a 12 volt system..
Some of the victrons that can handle 150 volts 60 amps those are in the 500 dollar range but no LCD screen.
Currently I been using the makeskyblue 60amp (130 dollar) controller which has an LCD screen and works good on 1 panel (maxes out 80 volts/720 watts on 12 volt system). Using 1 on each panel would be more economical then buying 1 of the victrons.
The solarepic epever 80a looks like it can handle your 800 watt of panels (max 1000 watts for 12 volt system) and has 150 volt max panel input and LCD screen. Its also cheaper than the victron at less than 500 dollars.
I wouldnt buy any controller that didnt have an LCD screen and you couldn't program directly from the unit. I also recommend a controller that has a setting to calibrate the battery terminals to the controller. All the controllers I have used had voltage drop, even the makeskyblue mppt, but thats the only controller I have used that can be calibrated. A very useful feature.

PlethoraOfGuns said:

The interface to your phone or computer is super easy....

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Yes, looking to wire in series, thank you for the pictures -- didn't know it was so easy!

jonyjoe303 said:

I also recommend a controller that has a setting to calibrate the battery terminals to the controller. All the controllers I have used had voltage drop, even the makeskyblue mppt, but thats the only controller I have used that can be calibrated. A very useful feature.

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Thank you for this tidbit -- can you explain this a bit more?

The third option is get a Jackery and some foldable panels and don't touch the existing house electrics...

Username said:

unsure how easy it will be to modify the software settings. So looking at other options like SolarEpic that have a physical display

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Partly depends on where you mount it. If the controller is front-and-center a display may be useful. If it's mounted out of the way a physical display may be of limited use.

I'm not a Victron fanboi but their apps are very usable and likely the best in the business.

Username said:

Thank you for this tidbit -- can you explain this a bit more?

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In typical installs the charge controller doesn't know the actual battery voltage; it only knows what it sees on its own BATTERY terminals where the wires are connected. Wire sizes, junctions, current, etc, can cause this voltage reading to be inaccurate ("voltage sag"). Which can throw off charging. Which can affect battery perfornance and/or longevity.

Extreme example: During heavy charging the controller might "see" 14v instead of the battery's 13v. Also happens in reverse when consuming power. The battery might be 12.5v but an inverter running a big load might "see" 11.5v at its own terminals and shut off prematurely (from the user's point of view).

Some approaches to the issue:

• do nothing - this is the majority position since most are unaware of the issue, or don't judge it to be important. In solar-only charging the current is might be low enough to make it No Harm, No Foul
• run bigger wires to minimize sag
• use a separate voltage sensing circuit (just a pair of wires to the battery) for controllers that have this feature. Since it's not carrying real current it's not thrown off by sag
• use a controller that talks to a shunt at the battery - I think Vic has a shunt like this
• have a voltage calibration setting - sag varies with current so the user might need to figure out average sag in their use case.

with voltage drop the battery will never get a full charge. If you are charging lead acid and set the controller to lead acid (14.4 volts) once the controller sees 14.4 volts it start lowering the amps going to the battery and then switch to float. If the controller reads 14.4 volts but the battery terminals are at 13.8 volts (almost float voltage) that is no where near full even though the controller thinks its full. It will eventually damage the battery from chronic undercharging.
If your controller is going into float too soon (bypassing absorb mode) it probably due to voltage drop. Also if the battery is quickly charging every morning its also a sign of voltage drop.

On my ecoworthy 20 amp mppt when charging lifepo4 (14.6 volts) I had to set the bulk setting to 15.5 volts (the max that the controller went up to) just to get the terminal to read 14.6 volts. If I had left the bulk setting at 14.6 volts, it would be charging at 2 to 3 amps all day long, while at 15.5 volts the controller was pumping over 12 amps into the battery.

With lead acid its better to check the voltage at the terminals to make sure its reaching 14.4 volts and not rely on the controller. If the controller has no calibration you can adjust the bulk voltage setting upwards until you get 14.4 volts on the terminals. If you have a .5 volt drop, you might try 14.9 volts bulk setting to see if that gets you to 14.4 volts. But for longlife of a lead acid it needs to be fully charged to specs (which is 14.4 volts for most lead acids while some agms require 14.7 volts)

With a controller that has calibration, if the controller display reads 14 volts and battery terminals reads 13.6 volts, you just have to adjust the controller display voltage down to 13.6 volts and your done. I only had to adjust my controller one time. If you change wires you might have to re-calibrate it again.

I use an LED volt/amp meter to let me know in real time how my charging system is doing. The coulombmeter in the picture is connected on the battery terminals and gives me a battery percentage (lifepo4) and real time voltage.