Solar Charging and Amp Hours

[DarkSkySeeker]

Is the amperage from a solar panel constant as the battery it is charging charges up?

I.e., as your battery reaches full charge, the current drops to zero either via the charge controller or the equalization of the panel and battery, right?

So this simple math is false? 120 watt panel, 12 volt system, 10 amps, 10 hours to charge a 100 Amp Hour battery?

[full_mosey]

DarkSkySeeker wrote:
Thank you for this help. In my mind, I thought only the battery side of the controller was modulated. Now I understand the charge controller allows current flow from the panel in the same way.

Amps are DRAWN by the consuming device. That is why your 1 Amp incandescent bulb does not explode when connected the same battery that can send 200A to the starter motor. You explode the bulb by applying too much Voltage.

HTH;
John

[DarkSkySeeker]

Thank you for this help. In my mind, I thought only the battery side of the controller was modulated. Now I understand the charge controller allows current flow from the panel in the same way.

[time2roll]

DarkSkySeeker wrote:
And the power output of the panel drops down? Eventually meaning a 100 watt panel no longer puts out any power?

Power (watts) = amps x volts..... Zero amps, zero power.

[red31]

yes, cuz it is not connected to anything!

excess power is not made, the panel is disconnected from the controller.
The on/off connection to the panel is done at high freq, the OFF time gets longer and longer to limit power to the controller/battery.

add a big load and then the battery is getting very little but the controller allows the extra to run the load.

[DarkSkySeeker]

And the power output of the panel drops down? Eventually meaning a 100 watt panel no longer puts out any power?

[time2roll]

DarkSkySeeker wrote:
If the controller gradually limits current to the battery as the battery charges up, where does the power from the solar panel go? I assume the panel continues to gather solar energy and sends the power it generates to the controller. What does the controller do with the power it no longer sends to the battery?

Does not go anywhere.

Same as a 15 amp outlet at home. If you plug in a lamp that draws 1 amp where does the other 14 amps go?

The controller limits voltage not amps. The controller provides a fixed voltage and the electrochemistry of the battery decides how many amps will flow.

[BFL13]

The controller does not gradually limit the current to the battery. The battery is the one doing the limiting as amps taper.

One way the controller does limit amps to the battery is suddenly, not gradually, if it drops voltage from 14.x to 13.x as part of its programmed charging profile. The battery will then accept fewer amps at that lower voltage at the same SOC.

Another way is at first during Bulk, the controller (if an MPPT type) will "clip the amps" to ensure it does not over-heat by going over its output amps rating.

[pianotuna]

Unless there is a diversion load, that extra energy is simply wasted. When that happens to me, I turn on the inverter and turn on the water heater for a few minutes.

[DarkSkySeeker]

If the controller gradually limits current to the battery as the battery charges up, where does the power from the solar panel go? I assume the panel continues to gather solar energy and sends the power it generates to the controller. What does the controller do with the power it no longer sends to the battery?

[red31]

DarkSkySeeker wrote:
Is the amperage from a solar panel constant as the battery it is charging charges up?

ignoring changes in sun, temp etc the answer is yes. At a given set of conditions the IV curve of a panel shows the amps nearly constant over a wide range of voltage. A PWM controller lets the panel connect directly to the batt and all the power goes to charging UNTIL a set pt voltage of the batt is reached and then the controller begins to regulate power to the batt not letting the battery exceed the st pt voltage. Less and less power is needed as the battery tops off.

If sun, temp etc conditions stayed the same over time then the charging amps would be the same, say a 100w panel 'makes' 5A, then the 12v battery would get 5A (60w) and later would get 5A @ 14v (70w).(watts = v * a)

A mppt controller forces the panel to operate @ the mppt (16-18v for a '12v' panel), the power would be constant if conditions stayed the same, more amps into a 12v batt than a 14v battery (A=W/V). At set pt voltage, the controller limits power to maintain set pt.

During regulation (at set pt voltage) excess power is available for other uses or is never produced.




changes in conditions changes solar output power
below is the effect of light variations

[pianotuna]

StirCrazy wrote:

pianotuna wrote:

jdc1 wrote:
It really depends on your charge controller. Some are "smart chargers", slowing the charge rate as the battery nears the full stage.

JDC1,

Pretty much all solar charge controllers at some point in charging use PWM, so they are all "smart" chargers.

''Except for MPPT controllers which act as a DC charger.

Steve

No MPPT also have a PWM function.

[StirCrazy]

pianotuna wrote:

jdc1 wrote:
It really depends on your charge controller. Some are "smart chargers", slowing the charge rate as the battery nears the full stage.

JDC1,

Pretty much all solar charge controllers at some point in charging use PWM, so they are all "smart" chargers.

''Except for MPPT controllers which act as a DC charger.

Steve

[pianotuna]

jdc1 wrote:
It really depends on your charge controller. Some are "smart chargers", slowing the charge rate as the battery nears the full stage.

JDC1,

Pretty much all solar charge controllers at some point in charging use PWM, so they are all "smart" chargers.

[time2roll]

Nothing is constant in solar unless the sky is perfectly clear and you can stop the sun.

Your controller will prevent overcharging by reducing voltage as the battery becomes full.