Troubleshooting solar setup... or troubleshooting my troubleshooting!!

[CatNewBee]

you will overcharge / boil the battery, the voltage Vmp, Voc are too high to connect the panel and not watching the voltage permanently.

[thomm225]

Originally Posted by noelex 77

A simple example is when the controller/regulator drops from absorption to float. The current flowing into the battery will decrease dramatically. The controller/regulator has made this change. The battery is exactly the same.

But as you stated and as the other poster points out, the battery controls that final current usage which is why on my PWM controller after Float is reached the voltage on the panel side slowly approaches VOC as the battery nears 100% SOC.

This morning I was at 12.6 volts after sailing this weekend. Usually when I stop by it's still at or very close to Float because I haven't sailed in a few days and the battery is near 100% charge. Panel side will read a voltage nearing VOC after work

[CatNewBee]

Originally Posted by thomm225

But as you stated and as the other poster points out, the battery controls that final current usage which is why on my PWM controller after Float is reached the voltage on the panel side slowly approaches VOC as the battery can take less and less of a charge

It is the controller, that disconnects the panel and causes the Voltage to rise to Voc.
It does it hunderts of times per second, thats why it is called PWM (PULSE WIDTH MODULATION), your voltmeter does integrate about those impulses and shows you the mean voltage on the panel side of the circuit.

Mppt controller simply move the power point towards Voc, to reduce the primary current and regulate the output power.

[john61ct]

Originally Posted by noelex 77

However, the controller/regulator only decides the voltage. The battery decides the current it is going to accept at the voltage the controller/regulator is set at.

That is the key point. Many believe falsely that the regulator is dynamically controlling current and/or the timing of the CC-to-CV transition point.

Of course the battery's "control" is a passive process, just the nature of lead's chemistry, but the metaphor drives home that those aspects of the charge process is *not* controlled by the charger.

[thomm225]

Originally Posted by CatNewBee

It is the controller, that disconnects the panel and causes the Voltage to rise to Voc.
It does it hunderts of times per second, thats why it is called PWM (PULSE WIDTH MODULATION), your voltmeter does integrate about those impulses and shows you the mean voltage on the panel side of the circuit.

Mppt controller simply move the power point towards Voc, to reduce the primary current and regulate the output power.

Well, this would support what a poster said above concerning a straight panel to battery charge and the current curve staying the same during the charging.

I was thinking the battery would decrease the current flow as it neared full charge (during a low current solar charge)

This also seems to support your point:

What is PWM?
Quite a few charge controls have a "PWM" mode. PWM stands for Pulse Width Modulation. PWM is often used as one method of float charging. Instead of a steady output from the controller, it sends out a series of short charging pulses to the battery - a very rapid "on-off" switch. The controller constantly checks the state of the battery to determine how fast to send pulses, and how long (wide) the pulses will be. In a fully charged battery with no load, it may just "tick" every few seconds and send a short pulse to the battery. In a discharged battery, the pulses would be very long and almost continuous, or the controller may go into "full on" mode. The controller checks the state of charge on the battery between pulses and adjusts itself each time.

Thanks for the input!

[CatNewBee]

Originally Posted by john61ct

That is the key point. Many believe falsely that the regulator is dynamically controlling current and/or the timing of the CC-to-CV transition point.

Of course the battery's "control" is a passive process, just the nature of lead's chemistry, but the metaphor drives home that those aspects of the charge process is *not* controlled by the charger.

The controller is called controller, because it controls the charging, it does so by simply regulating the Voltage either linear in old conntrollers, also by some MPPT, or by controlling the switch-on time by pulsing in PWM controllers and other MPPT controllers.

[john61ct]

Yes, that does not conflict with what I wrote.

Some think that "control", actually controls more than just voltage, as just occured with rg thinking he was selecting CC vs CV on his power supply.

I clarified adjusting the max setpoint for V or A does not mean that's what's going to happen - that depends on the battery chemistry and SoC.

[noelex 77]

Originally Posted by skenn_ie

Correction, at Isc, all the power is dissipated within the panel.

If you take into account the voltage drop in the wiring (internal and external) and the voltage drop in the multimeter itself, in practice there is a very small amount of power that is produced when measuring Isc.

So apologies if my simplification was confusing

But when measuring Isc in sunny conditions you need not be concerned that the panel is producing and therefore needs to internally dissipate anything like its rated power even if the measured Isc conforms to the specifications.

The panel would get very hot it this was the case, as you have discovered with your resistive test.

[CatNewBee]

I have not objected what you said, just tried to clarify, explain it how it is done in the circuits of the controler.

[noelex 77]

Originally Posted by john61ct

That is the key point. Many believe falsely that the regulator is dynamically controlling current and/or the timing of the CC-to-CV transition point.

Of course the battery's "control" is a passive process, just the nature of lead's chemistry, but the metaphor drives home that those aspects of the charge process is *not* controlled by the charger.

Suggesting that the battery controls the charging (which is often posted on these forums) is a bit like arguing that when driving it is the car that controls the speed.

It is true that if the driver presses down an inch further on the accelerator (gas pedal) it is the car (together wth environmental factors) that will determine the new speed, but in practice it is the driver that will modulate the accelerator to control the desired speed.

In the same way as the driver has the ultimate control of the car’s speed, the controller/regulator determines the battery charging.

[thomm225]

Now in this case the battery is controlling the charge by decreasing current as it nears fully charged: (there's no controller)

Charging with a Power Supply
Learn how to charge a battery without a designated charger.

Batteries can be charged manually with a power supply featuring user-adjustable voltage and current limiting. I stress manual because charging needs the know-how and can never be left unattended; charge termination is not automated. Because of difficulties in detecting full charge with nickel-based batteries, I recommend charging only lead and lithium-based batteries manually.

Lead Acid
Before connecting the battery, calculate the charge voltage according to the number of cells in series, and then set the desired voltage and current limit. To charge a 12-volt lead acid battery (six cells) to a voltage limit of 2.40V, set the voltage to 14.40V (6 x 2.40). Select the charge current according to battery size. For lead acid, this is between 10 and 30 percent of the rated capacity. A 10Ah battery at 30 percent charges at about 3A; the percentage can be lower. An 80Ah starter battery may charge at 8A. (A 10 percent charge rate is equal to 0.1C.)

Observe the battery temperature, voltage and current during charge. Charge only at ambient temperatures in a well-ventilated room. Once the battery is fully charged and the current has dropped to 3 percent of the rated Ah, the charge is completed. Disconnect the charge. Also disconnect the charge after 16–24 hours if the current has bottomed out and cannot go lower; high self-discharge (soft electrical short) can prevent the battery from reaching the low saturation level. If you need float charge for operational readiness, lower the charge voltage to about 2.25V/cell.

[CatNewBee]

To be precise, its the battery voltage, that controls the current.

The current is driven by the voltage difference of the charger and the battery. assume the voltage of the battery is 12V, and the charger has 14V, there is two volt difference, that drives the current, lets say 10A. There are then 2V x 10A equals 20W of power going into the battery, the resistance is 2V / 10A = 0.2 Ohm.

The voltage of the battery rises to 13V, the resistance is still 0.2Ohm, since not much changed to the circuit, the Voltage difference is now 1V, that leads to a current Ì = V / R = 1V / 0.2Ohm = 5A and a power of 1V x 5A = 5W.

That is the way the current drops. Because the charge voltage of absorption is set slightly higher than the chemistry voltage difference of the cell poles, there will be always a low current / tail current driven by this difference through the cell. Usually it is chosen low enough to prevent gasing.

I know, you will complain, that a battery is not a linear resistor, and you are right, that math is only for illustration / explanation why the current drops when the battery gets full.

[Paul Elliott]

Unless your solar panels are huge, and your battery very small, during the initial bulk stage of charging the typical solar controller will deliver all the power it can pull from the panel. This is true of MPPT and PWM chargers. The charger doesn't "set the voltage" -- it doesn't have enough current available to do that. Instead, it delivers as much current as it can, and the battery determines the voltage.

Then, based on battery voltage, and perhaps time, the controller starts to reduce the current. You could say that it does this by controlling the output voltage, but it's probably more accurate to say that the controller monitors the battery voltage and adjusts the current accordingly.

And a solar panel is not a power supply. With no controller a solar panel will send roughly the same current into a dead battery as into a dangerously overcharged battery. Again, look at the panel V-I curves that I linked to many posts back.

Connecting a solar panel directly to a battery is perfectly OK, as long as you monitor the battery voltage. On one long passage my MPPT controller died so I did just that. Since my 24-hour drain was greater than the panel output, we only had to worry about overcharging when we ran the engine every few days to make up the charging deficit. If the battery got full we disconnected the solar panel. This worked well and there was no danger because we knew what we were doing.

[skenn_ie]

Originally Posted by CatNewBee

you will overcharge / boil the battery, the voltage Vmp, Voc are too high to connect the panel and not watching the voltage permanently.

IF you eliminate the controller, and don't watch the battery voltage, then disconnect when it reaches 29V. Basically, when the battery voltage starts to rise significantly faster, it is time to disconnect.
As for the controller, it IS A CONTROLLER that provides (average) current dependent on average output voltage. The output voltage is dependent on battery state and charge current.

[skenn_ie]

Originally Posted by CatNewBee

To be precise, its the battery voltage, that controls the current.

The current is driven by the voltage difference of the charger and the battery. assume the voltage of the battery is 12V, and the charger has 14V, there is two volt difference, that drives the current, lets say 10A. There are then 2V x 10A equals 20W of power going into the battery, the resistance is 2V / 10A = 0.2 Ohm.

The voltage of the battery rises to 13V, the resistance is still 0.2Ohm, since not much changed to the circuit, the Voltage difference is now 1V, that leads to a current Ì = V / R = 1V / 0.2Ohm = 5A and a power of 1V x 5A = 5W.

That is the way the current drops. Because the charge voltage of absorption is set slightly higher than the chemistry voltage difference of the cell poles, there will be always a low current / tail current driven by this difference through the cell. Usually it is chosen low enough to prevent gasing.

I know, you will complain, that a battery is not a linear resistor, and you are right, that math is only for illustration / explanation why the current drops when the battery gets full.

That is true if, and only if, there is no charge controller.