Saturday, August 5, 2017

Battery/Charger Question

I have a solar charge controller charging a 12VDC AGM battery from a solar panel.  The controller has two LEDs: charging, and charged.  The charging LED is pretty much always on while sunlight hits the panel.  The charged LED never turns on.  The battery is certainly charging; I have an inverter connected to the battery and I can turn on the inverter and run AC lights, even at night, so I know the charge controller isn't powering the inverter.  How should I determine the defective part?  Would taking the battery to a dealer enable them to determine if the battery is ready to be replaced?  How do you verify that charge controller is doing it right?


Jim Dunmyer said...

The "charged" voltage is different for the various battery chemistries: AGM, GelCel, or FLA (flooded lead acid) Bear in mind that all 3 are basically lead acid, but there are differences. By rights, you should have a controller that has a "AGM" setting. Of course, if it's working, why sweat it?

hga said...

Check the voltage of the battery, that'll tell you everything from "charged" to needs replacing, the appropriate ranges are all over the Internet.

Kevin said...

so I know the charge controller isn't powering the inverter.

Did you mean to say IS powering the inverter?

If you have a multimeter:
Disconnect the charge controller in the morning and measure the voltage across the battery terminals.
Reconnect and charge the battery from the panel during the day, but don't use the inverter or any other load.
At night, disconnect and measure voltage again.

If the voltage went up, your battery is being charged. So the question would be why the "charged" LED does not come on.

Clayton Cramer said...

Charge controller is not powering the inverter because the inverter powers a light even when the Sun is down.

Kevin said...

I don't understand. Is this your setup:

Solar Panel -> Charge Controller -> Battery -> Inverter

or something else?

Will said...

Battery voltage may tell you if the charger is working, but not how good the battery is, or how well the charger works. That would require a load tester. For automotive size batteries, the guts look very similar to the heating coils of an electric clothes dryer. Hook it up, flip the spring return toggle switch, and hold it for a designated time, then read the meter for voltage/condition.
Horror Fright Tools carries this.

Bear in mind, this type of tester is intended to ascertain if your battery is capable of spinning the starter of a vehicle engine. If your batts are not doing any heavy lifting, this may be overkill.

clark myers said...

To the question of checking the "charged" LED one answer is to connect the charger to a known charged battery - preferably a modern battery that shows a higher voltage at full charge. My best guess would be a current 6 cell lead acid battery maxes out at a voltage below the LED threshold.

As everybody says, the situation is analogous to the transition in cars from dashboard gauges to idiot lights and long ago the aftermarket sold plenty of gauges to transition back.

I don't know about Horseshoe Bend but there used to be and may still be a nice pull your own parts salvage yard on the south side of 55 heading to downtown Boise that has been there since it was a gravel road but buying or converting or even catching an an included at no extra cost digital multi-meter from Harbor Freight would allow eyeballing voltage and so state of charge as well as current flow in and out of the battery.

Given the relatively low unit output on solar cells - unless you have a massive array which IIRC you don't - I'd guess you have an automotive/diesel size battery that never does reach the voltage/resistance threshold to trip the LED light. Most chargers with LED lights that do trip seem to me to be cell phones, flashlights and such using lithium batteries.

Lead Acid

The nominal voltage of lead acid is 2 volts per cell, however when measuring the open circuit voltage, the OCV of a charged and rested battery should be 2.1V/cell. Keeping lead acid much below 2.1V/cell will cause the buildup of sulfation. While on float charge, lead acid measures about 2.25V/cell, higher during normal charge.


In consumer applications, NiCd and NiMH are rated at 1.20V/cell; industrial, aviation and military batteries adhere to the original 1.25V. There is no difference between the 1.20V and 1.25V cell; the marking is simply preference.


The nominal voltage of lithium-ion is 3.60V/cell. Some cell manufacturers mark their Li-ion as 3.70V/cell or higher. This offers a marketing advantage because the higher voltage boosts the watt-hours on paper (voltage multiplied by current equals watts). The 3.70V/cell rating also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series rather than the more familiar 10.80V and 14.40V respectively. Equipment manufacturers adhere to the nominal cell voltage of 3.60V for most Li-ion systems as a power source.

How did this higher voltage creep in? The nominal voltage is a function of anode and cathode materials, as well as impedance. Voltage calculations include measuring the mid-way point from a full-charge of 4.20V/cell to the 3.0V/cell cutoff with a 0.5C load. For Li-cobalt the mid-way point is about 3.60V. The same scan done on Li-manganese with a lower internal resistance gives an average voltage of about 3.70V. It should be noted that the higher voltage is often set arbitrarily and does not affect the operation of portable devices or the setting of the chargers. But there are exceptions.