Solar system output

rmk818 · April 2020

Good day, I have two 160 w panels on my RV running in series. When I look at my solar controller (EPever-30ans) I am showing my panels are producing 41 volts but 0 amps. I am running two 6v batteries in series and the controller shows 12.7 volts. When I check the amps using a multimeter I get 4.41 amps where the panels attach to the controller. This seems real low to me. Shouldn't it be around 8 amps? when I check each panel at the panel each is putting out 20 volts at 4.4 amps. My wiring to the controller is 6 gauge running 35 feet to the controller. The panels lay flat and were checked at 1:00 pm pst on 4/4/2020. Neither panel is shaded.

Thanks in advance for any help.

mcgivor · April 2020

To provide any insight a few details are needed, was the battery perhaps in float or recently transitioned to float and have you seen higher current before? The array voltage at 41V would indicate that the controller output is being regulated and or the battery is dropping in voltage from a recent transition from bulk/absorb, given the time of day the observation was made.

BB. · April 2020

I am guessing that this is your charge controller?

https://www.amazon.com/EPEVER-Controller-Regulator-Backlight-Lead-Acid/dp/B071XP39BK

MPPT type, with Vmp-array max of 92 volts(?).

Guessing your panels:

Pmp = 160 Watts
Vmp = ~18 Volts
Imp = 160 Watts / 18 volts = 8.89 Amps
Vmp-array (2x series) = 36 Volts
Imp-array (series) = 8.89 Amps
Panels mounted flat to roof
Location ~ Fresno California

If my guesses are pretty close to accurate--That all looks good. So--Debugging questions.

First, the correct order to power up your solar charge controller is to 1) connect controller to battery bank. And 2) connect solar panels to controller. If you connect the controller first to the panels, it is possibly to "confuse" the charge controller, or even possibly damage it. Most solar charge controllers use the "stable" battery bus voltage to boot correctly, and set their basic operational voltage (12/24 volt battery bank).

Second, the voltages seem OK for charging... Vmp-array ~ 36-41 Volts should be OK when charging (could go to Voc-array ~ 45+ Volts when battery approaches full charge and no DC loads).

The 12.7 volts at the battery bus... With some charging current--Sounds like your battery bank is significantly discharged and will need quite a few hours of full sun charging (or even a couple days without much load). Ideally, the charge controller should be passing maximum charging current (power) to the battery bank until it hits ~14.75 volts (if flooded cell lead acid battery). And hold there for 2-6 hours (or until sun sets, continue charging next day). ~2 Hours "absorb" charging for lightly discharged bank. ~6+ hours for heavily discharged bank (assuming 10% rate of charge).

Charging for your battery bank... 2x 6 volt @ 205 AH "golf cart" FLA batteries:

2 panels * 160 Watts * 14.5 volts charging * 0.77 panel+controller derating = 17 Amps (typical best case charging current--noon time, cool weather, panels pointed at sun, very clear day).
205 Amps * 0.05 minimum rate of charge = 10.25 amps minimum suggested charging current
205 Amps * 0.10 nominal rate of charge = 20.5 amps nominal suggested charging current

So, the basic configuration looks good.

What to expect from the 320 Watt array (note: just to be clear, MPPT controller Vpanel current input does not equal charging current for battery bank--These are "power converters" that take "high voltage/low current" from array and down convert to "low voltage / high current" for the battery bank).

From the array: 2x 160 Watts * 0.77 derate * 1/36 volts Vmp-array = 6.84 Amps typical best case (don't expect more in normal usage)
Your Array Measurement: 4.41 Amps * 41 volts = 181 Watts

I would not call 181 Watts on a "typical" decent solar day bad... I have seen roughly 1/2 rated current from my (Grid Tied) power system on a typical day with a very little bit of haze in the sky---Our eyes do fool us, 1/2 the amount of sunlight looks virtually the same as 100% full sun.

And the charging current into the battery bank should be around:

181 Watts * 0.95 MPPT controller eff * 1/12.7 Volts = 13.5 Amps into battery bus (based on your numbers above--How MPPT controllers work)

If we take sun angle (noon, April 4th), into account with a flat mounted array... 60 Degree above horizon (solar noon is 1:01PM for Fresno today). Or 30 degrees off angle:

https://www.timeanddate.com/astronomy/usa/fresno

360 Watt array * 0.77 panel+controller deratings * Cos 30 Degrees {=0.87 due to angle) = 241 Watts typical "best" for flat mounted array power harvest for today.

So, your 181W/241W = 0.75 or 75% of "average best case" harvest... Actually, not bad.

So--Other than the controller showing Zero Amps (?) going through it (LCD display working correctly?)--I am not sure I see anything "wrong" at this point.

Other questions... Do you have a hydrometer to measure battery specific gravity (state of charge)? Do you have a DC current clamp DMM (vs having to connect a DMM or install a current/voltmeter in your array wiring)?

So, the last question is what is the battery charging current at this time (or at 1PM today)?

If you are using a standard DMM and attaching the leads to the charge controller output ("breaking" the connection and placing the meter, on 10 amp full scale, in the wiring)--Your maximum current from the solar array is less than 10 amps. However, the charging current from the EPEVER can vary easily be over 10 amps, and would blow the fuse/damage your DMM. Note, if disconnecting your Charge Controller battery connection, you have to turn off/disconnect solar panels first, then break battery bus connection, then reconnect the array last).

Long term, if you do not have one yet, I highly recommend getting some sort of DC Current Clamp DMM (really AC+DC). They can take much higher current, and there is no breaking electrical connections to do current measurements:

https://www.amazon.com/gp/product/B019CY4FB4 (nicer--Mid range meter)
https://www.amazon.com/UNI-T-Digital-Current-Capacitance-Multimeter/dp/B0772FYF5M (lower cost, good enough for our needs)

-Bill

Photowhit · April 2020

BB. said:
First, the correct order to power up your solar charge controller is to 1) connect controller to battery bank. And 2) connect solar panels to controller. If you connect the controller first to the panels, it is possibly to "confuse" the charge controller, or even possibly damage it. Most solar charge controllers use the "stable" battery bus voltage to boot correctly, and set their basic operational voltage (12/24 volt battery bank).n (solar noon is 1:01PM for Fresno today). Or 30 degrees off angle:

My guess is this is the important part of what Bill has said.
That combined with;

rmk818 said:

I am showing my panels are producing 41 volts but 0 amps. I am running two 6v batteries in series and the controller shows 12.7 volts.

Would indicate to me that it may be likely the solar panels were connected first, so the charge controller believes it is a 24 volt system. When the battery bank was connected the out of gambit voltage was too low for the charge controller to attempt to charge, since it thinks you have a 24 volt system. Sometimes this will self correct overnight when there is no energy coming from the solar array. You may find everything fine in the morning if you have left it, I wouldn't be frustrated if you have to disconnect and reconnect in the proper order.

12.7 volts is correct for being fully charged. if it was connected properly, it would rapidly go through the stages in a short time (dependent on how much energy is available) and rest in the float stage with the solar panels feeding very little into the fully charged batteries and the voltage around 13.5-13.6 volts.

I suspect if you disconnect everything, and wait a bit 10-15 minutes and reconnect it will take off and be just fine.

If not if you could provide a photo of the screen it might be helpful.

Here is some information about charging stages of a lead acid battery;

The voltage you are seeing on the charge controller is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

BULK;
First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

ABSORB;
Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries.

The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

FLOAT;
Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

rmk818 · June 2020

Bill and Photowhit, thank you. You two are AWESOME....and have helped me immensely. Thank you.

Solar system output

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