# Is this as good as it gets?

Registered Users Posts: 65 ✭✭
I'm relatively new to this and have been adding to my system for a couple years. I recently added three panels and just looking to see if this is an acceptable set up and what you might change. I will go 48v when the Magnum takes a dump but... It still going sooo. I don't trust the readings I'm getting from the charge controllers but I wrote them down. Thank you!
900 watts pv (building on) on poles, off grid 60a mppt, magnum 2k 12v msw, 1400 ah forklift battery (rewired to 12v), 8k diesel gen for house. honda eu6500, 2x 8D, coleman 800w inv for shop, honda 5k for well (pumps to 1000g cistern), ryobi 2k suitcase for mobile ops.

OK... To know more about how each controller's performance... For example, the 4x75 Watt panels + MPPT controller... At noon, on a cool/clear day, battery bank under 80% SoC (needing to be charged), and/or running loads on the DC bus/AC inverter (use a 1,500 Watt room heater, if you want to "load the system").

To look at the math. Note, I am using approximate values for a warm climate, near solar noon, on a cool/clear day (77% derating of Vmp/Charge controller output). You plug in your actual measured numbers to confirm:
• 4 * 75 Watt panels = 300 Watts Pmp-std (marketing number)
• Vmp ~ 17.5 volts Vmp-std (typical)
• 4 * 17.5 Volts =70 Volts Vmp-array (full load/cool clear day)
• 70 Volts * 0.81 temperature derating * (hot/sunny day) = 56.7 Volts Vmp-array-Really Hot Day
• 75 Watts / 17.5 volts = 4.29 Amps Imp-std (since all panels in series, Imp-array-std = 4.29 Amps)
Ok, assuming battery bank need charging (at or below 14.75 volts)... Lets say 13.6 volts (discharged, or running 1,500 Watt heater as dummy load on system and battery at float voltage).
• 4.29 Amps Imp * 56.7 volts = 243 Watts from array (typical best case in cool to hot weather--A few days a year at solar noon)
• 243 Watts * 0.95 MPPT controller efficiency = 231 Watts to battery bank
• 231 Watts to bat / 13.6 volts actual battery bus voltage = 16.97 Amps @ 13.6 volts "bulk charging" (maximum controller current
• 231 Watts to bat / 14.75 volts = 15.66 Amps @ 14.75 volts "bulk to absorb charging set point voltage)
I would suggest getting a DC Current Clamp DMM (Digital Multimeter). There are inexpensive ones at \$50, and other that range from ~\$120 to \$350+ (your Fluke meter).... A midrange meter (note: these are AC+DC Current Clamp DMMs... There are AC Current Clamp DMMs and they are fine meters, but we want the DC function for our solar power systems):

https://www.amazon.com/gp/product/B019CY4FB4

The "cheap meters" are a bit thin right now with the Corona Virus and other USA/China Trade issues (?)... This is an example, but variable availability.

https://www.amazon.com/UNI-T-Digital-Current-Capacitance-Multimeter/dp/B0772FYF5M

So, to "understand" your MPPT charge controller, you need to know the voltage and current on the Panel side of the meter, and the current+voltage on the battery side too. Also, you need to know the charging state of the meter too (i.e., 13.6 volts could be meter in Bulk taking all available energy from the solar array, or it could float charging--Just supplying enough energy to keep the battery charged, and supplying what ever energy is needed on the DC bus (not drawing 100% of available power from array).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 65 ✭✭
Thanks Bill,
If I understand what your saying then yes I have a multimeter. I have verified the voltage of each panel during installation.
Four older ge panels in series are at your numbers. I have them ran parallel with the two 200w (not 230 like in the drawing), the volts on the two panels of course dropped a bit on the controller end of things but still functions well.
Two of the three 315w in series to a 60amp controller, and one to a small 25 amp. I tested all the panels at the panel. I guess what I didn't trust is the "30amps" from two 315w, 9 amp panels.
Another problem I'm having, which shall be fixed when I have the money to buy a real CC, is the new CC shuts the older (charge volts not adj) CC down about two hours into good 🌞.
900 watts pv (building on) on poles, off grid 60a mppt, magnum 2k 12v msw, 1400 ah forklift battery (rewired to 12v), 8k diesel gen for house. honda eu6500, 2x 8D, coleman 800w inv for shop, honda 5k for well (pumps to 1000g cistern), ryobi 2k suitcase for mobile ops.
• Solar Expert Posts: 6,710 ✭✭✭✭✭✭
I am having a hard time following the english here....probably me but my best guess is this is an example of multiple controllers that are not networked. It is a classic problem that will never stop unless you fool the controllers by offsetting V to think that are at the same voltage.

The controller that is programmed higher will output the most current if the rest of the group is not exactly the same. You need to get them all to be at the same output/battery voltage by offsetting, measuring, and reprogramming the setpoints.

Or, buy something decent.  I do get it that money is an issue. However there is a point that you are throwing more good money at bad.
Who wrote that song " listen to the money talk" ?

Bill, it is really weird how the supply chain is just FUBAR right now. Hope that ends really soon with folks getting back at it.
"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail [email protected]

Math:
• 2 * 315 Watt panels * 0.77 panel+controller derating * 1/13.6 volts (?) nominal battery volts = 35.7 Amps (battery bus)
So, in optimal conditions, it is certainly possible to see ~35.7 amps into the battery bus (around noon, cool/clear day, XX.X battery voltage, etc.)... It is also pretty easy to see 1/2 that amount of current in pretty typical conditions (higher battery voltage, little bit of haze, battery getting near charged, etc.)...

And and Dave says, if you have several charge controllers in parallel, the one with the highest voltage setpoint "wins" (i.e., if one is set at 14.4 volts and another set at 14.8 volts, both will supply current up to ~14.4 volts, then only the higher voltage controller will continue to supply current).

Ideally, you want all controllers set to the same charging setpoint for optimum charging... But even if they are set to the same setpoint, they will "diverge" (one will decide the battery is full before the second decides that the battery is full).

It sometimes drives people crazy, but there is no harm or issue with the controllers being "out of sync" a bit (one in bulk another in absorb, etc.).

Dave, the neat thing about "free enterprise", there are hundreds (if not thousands) of individuals/companies/etc. trying to fix the supply chain and get things moving again. I am sure everything will be "whole again" in the relatively near future (if not different from "yesterday").

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 6,710 ✭✭✭✭✭✭
edited May 2020 #6
Define relatively near future for me again Bill please?

After last nights "free enterprise" looting craziness countered by astronauts docked to the station from spacex.

Maybe that will cancel? Hoping you are right, but a bit pessimistic. Not even going there with a second C19 wave.

"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail [email protected]