Nocturnal phantom draw driving me nuts!

Hey folks! If you like a good mystery, please consider reading my story and offering any brilliant Sherlockian insights.

Here are the characters at question:
1) A Sunpower solar panel, model SPR-90-WHT-U (peak power 90W, Voltage 18V, Current 6A) [a demonstration model]
2) A SunSaver-10 charge controller (model SS-10L-12V)
3) An Optima AGM 12V yellow top battery (D34 series)
4) 7 feet of 8 Gauge, threaded copper wire

I have simplified the system to the above components and set it up on my patio, in order to try to isolate what has been an extremely vexing problem. All of the above I have acquired new. Over the winter I have vetted the performance of the battery and I am confident it is not to blame for the following mystery. There is no load connected to the system. All of the wiring, connections, and terminals have been checked (and rechecked....) and are solid.

Putting all the above components together and testing throughout the day, I've determined that the panel is producing sufficient peak power (up to 19V), and the battery is being charged during the day (up to 12.8V when tested alone--disconnected from the charge controller). However, when the panel, charge controller, and battery are connected, into the evening and over the course of the night the battery discharges on around 0.2-0.4V. For example, last night before I went to bed well after dark, the battery read 12.75V. It probably didn't dip below 50 degrees. When I checked the battery in the morning at around 0800 (a few hours after sunrise), it was at 12.34V, and after disconnecting the battery from the charge controller to read the standing voltage, it topped out at 12.55V.

When I leave the battery connected to the charge controller, but remove the solar panel connection, the battery maintains it's voltage. Could it be that the blocking diode in the panel is the culprit? Could it be something else?

Any recommendations on installing a blocking diode into the line to the panel? Any feedback or ideas or suggestions are welcomed!!
Thank you!!


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Nocturnal phantom draw driving me nuts!

    You don't mention what the battery voltage is while actually near the finish of it's charging cycle, although you do mention 12.8 when disconnected from the controller.
    With a properly operating Sunsaver controller, you would not need blocking diodes to prevent backflow to the panels at night, the controller would do that. I'm seriously wondering if your batteries are getting properly charged in the first place - - because of the 12.8 battery volts you mention. I know you said it's measured with controller disconnected, but for how long was it disconnected? You also didn't mention what loads you have on the battery, both during the day when they are trying to charge, and in the evening before you shut the system down for the night. And, we need to know if an inverter is left connected at night, as they consume power in standby, even when not powering anything.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Nocturnal phantom draw driving me nuts!

    i think wayne is right that the battery did not attain a full charge from the sound of it. most batteries need to get to about 14.4v (with 14.1v option on that cc) or more for a full charge and that controller would hold it at that voltage allowing the current to diminish until the controller no longer receives power from the pv. while you are charging next time please keep all loads off of the battery and see if it will reach that 14.4v mark and hold there. if it manages to fully charge on absorb then you will see voltages much higher on the battery after many hours of rest compared to what you have seen. it is normal btw for the voltage to sag after a charge, but to go to 12.3v or 12.4v is a sign it is undercharged.

    let us know what you find and if it corrects itself after giving it enough charge time.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Nocturnal phantom draw driving me nuts!

    I would guess that you are undercharging your battery...

    If the battery where fully charged, sometime during the day you should see ~14.5 volts or so on the battery, under full sun, with light or no loads. ~14.2-14.8 volts is the full charging voltage by a typical battery charger into a nearly or fully charged battery. Even after a battery reaches ~14.2-14.5 volts, it should sit at that voltage for another hour or two/three to ensure it is fully charged (that last 10% or so of charging simply takes time).

    More complex charge controllers will cut back on charging voltage (to ~13.2 to 13.6 volts) to "float" the battery (keep it charged but not over charged/boiling water out).

    If you were to disconnect the battery fresh of the charger, you will quickly see the voltage drop down to the mid 13.x volt range. And if you let the battery "rest" for 3 or more hours, you should see it drop to around 12.7 volts or so (the resting voltage of a fully charged battery at ~77F). That is all without any external loads on the battery. It should be able to set for days/weeks at 12.5-12.7 volts without any loads (if the battery is in good shape).

    So, if the battery is around 12.53 volts resting voltage, then it is only 80-90% charged--Not bad, but still not fully charged.

    Battery FAQ

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Laura P.Laura P. Registered Users Posts: 4
    Re: Nocturnal phantom draw driving me nuts!

    Thank you all for your suggestions! I'm sorry-- I should have been more clear. The battery does read over 14V for much of the day, and it slowly tapers off into the evening. I only gave you the disconnected standing voltage to convey that meaningful charging is occurring. There is no load on the system at all. No inverter, no load. The discharge happens sometime during the night so that by morning, what was a full battery is now down 0.2-0.4V, with no apparent reason. I have spend the last several months testing the system, and I believe that the system is charging appropriately-- that there is enough power being generated, and that the battery is strong and sustaining of that charge. That is why I'm so confused.

    I disconnected the panel from the charge controller, leaving my fully charged battery connected, and there was no voltage loss over the course of several days, which led me to believe that there is a problem with either the panel, or the panel plus charge controller working in concert.

  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Nocturnal phantom draw driving me nuts!

    Laura, your hypothesis might be correct. To nail it down you need to demonstrate that current is flowing back into the panels at night. I presume you have an digital voltmeter (because you are measuring battery voltage). Most DVMs have an ammeter function. If yours does, and you know how to use it, you should be able to track down your loss.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Nocturnal phantom draw driving me nuts!

    or if you don't have a meter then spend a few $ and buy a blocking diode. this is the same as disconnecting at night, but you will get a small voltage drop as well due to the diode being inline.

    place the diode in series with the + output of the pv. diodes are polarized so if you put it in wrong you won't get an output during the day.

    i am confused as to why the sunsaver is not blocking the back current as it should.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Nocturnal phantom draw driving me nuts!

    The SunSaver - and nearly all but the very cheapest eBay charge controllers have a blocking diode built in. Adding another one will only server to reduce the voltage to the battery or controller from the panels, depending on where you put the diode.

    It is possible that there is a problem with the SunSaver where the power transistor or FET is not shutting down 100% at night, though that is extremely rare. Do you have another battery you can test it with?
  • telljftelljf Registered Users Posts: 20 ✭✭
    Re: Nocturnal phantom draw driving me nuts!

    Not sure why no load is connected to the batteries. It is as if the charge controller is the only load it ever sees. Please try and get the batteries to do some work, take it through a few charge discharge cycles and exercise it, socialize it. It has become lazy I think. He is trying to run away at night with the charge controller. Load is as essential as charge for a battery.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Nocturnal phantom draw driving me nuts!

    I am suspecting a bad battery, where it might be so sulfated that even the tiny load (a few milliamps) from the controller might be pulling it down.
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Nocturnal phantom draw driving me nuts!

    Hey Laura P,

    It's been a couple of months since your OP. Are you still out there?

    I wonder if your problem has to do with SunPower's positive ground issues. You tested your system by isolating it so it does not seem that it was operating at a condition of (+) voltage to ground, but there may be some other elements involved. A simple test would be to try a different (non-SunPower) module in your system. If the phantom draw goes away, then the SunPower module would seem to be the culprit.

    Elementary deductive reasoning, my dear.
    "Eliminate all other factors, and the one which remains must be the truth." -S. Holmes

    You may want to check out this thread:

    BB posted some quotes from old SP documents including;
    "If the module is operated at a positive voltage with respect to the earth ground, then minute leakage current will flow from the cells to ground. As a result, over time a negative charge is left on the front surface of a cell. This negative charge turns on the surface transistor, attracting positive charge carries to the front surface where they recombine with electrons and are lost"

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