Reading Voltage While Charging

[jsmit209]

I'm sure this is a total beginner question, but I'd like to clarify my understanding.

I have a Victron 100/50 SCC charging a 12v LPF battery bank. I set the rotary switch to position 7, which should output 14.2V.

I isolated the batteries with a switch and hooked up the panels. Before turning on the battery switch, the Absorption LED (yellow) was on, and I measured the output from the SCC ports at 14.19V.

However, when I turn the battery switch on, the Bulk LED (blue) came on, and the system voltage measures at 13.3V (via my Victron Smart Shunt and at the output terminals on the SCC).

The measured voltage of the battery bank before connecting the panels was 13.2V. Does all of this sound normal? Why does the measured voltage change from 14.2 to 13.3?

 

[BentleyJ]

Charge controllers are designed to regulate both voltage and current in an attempt to maximize the available solar power for the given array and outdoor conditions. If the resting voltage of the battery is 13.2 and the charge controller was outputting 13.3V then it seems like it was doing its job.
What was the charging current during that time? Volts x Amps is Watts, perhaps the amount of charging at that time was all that was available from the panels.
Keep in mind when a battery is at a low State of Charge it can absorb quite bit of current and the voltage will be well below the 14.2V limit set in the SCC. As the battery charges it "pushes" back and the SCC increases the voltage to maintain current flow. When the 14.2V limit is reached, the SCC holds that voltage until the battery is fully charged as evidenced by the current naturally falling off. The SCC then either switches to float or turns off. With LFP chemistry, float is normally not used.

 

[John Frum]

With LFP chemistry, float is normally not used.

Sure it is.

 

[jsmit209]

Charge controllers are designed to regulate both voltage and current in an attempt to maximize the available solar power for the given array and outdoor conditions. If the resting voltage of the battery is 13.2 and the charge controller was outputting 13.3V then it seems like it was doing its job.
What was the charging current during that time? Volts x Amps is Watts, perhaps the amount of charging at that time was all that was available from the panels.
Keep in mind when a battery is at a low State of Charge it can absorb quite bit of current and the voltage will be well below the 14.2V limit set in the SCC. As the battery charges it "pushes" back and the SCC increases the voltage to maintain current flow. When the 14.2V limit is reached, the SCC holds that voltage until the battery is fully charged as evidenced by the current naturally falling off. The SCC then either switches to float or turns off. With LFP chemistry, float is normally not used.

Thanks for the response. This was just a test run for the equipment and connections. I only hooked up two of my 100W panels for the test. The shunt was showing roughly 140W coming in at 13.3V, so 10.5amps. Does the bulk phase run until the voltage increases to the 14.2 for Absorption?

The manual for the batteries shows that 13.5V is 100% charge, so they were a little low at 13.2V resting.

 

[BentleyJ]

Thanks for the response. This was just a test run for the equipment and connections. I only hooked up two of my 100W panels for the test. The shunt was showing roughly 140W coming in at 13.3V, so 10.5amps.

Does the bulk phase run until the voltage increases to the 14.2 for Absorption?

So everything was in fact working. You were getting 140W of charging from a 200W STC rated array, sounds about right.

Yes, Bulk can be referred to as the Constant Current part of the cycle, while Absorption is the Constant Voltage part of the cycle.

The manual for the batteries shows that 13.5V is 100% charge, so they were a little low at 13.2V resting.

Yes, but the correlation between voltage and state of charge is not super accurate for LFP chemistry due to the rather flat chg-discharge curve through a large part of the usable range.

 

[Bud Martin]

I'm sure this is a total beginner question, but I'd like to clarify my understanding.

I have a Victron 100/50 SCC charging a 12v LPF battery bank. I set the rotary switch to position 7, which should output 14.2V.

I isolated the batteries with a switch and hooked up the panels. Before turning on the battery switch, the Absorption LED (yellow) was on, and I measured the output from the SCC ports at 14.19V.

However, when I turn the battery switch on, the Bulk LED (blue) came on, and the system voltage measures at 13.3V (via my Victron Smart Shunt and at the output terminals on the SCC).

The measured voltage of the battery bank before connecting the panels was 13.2V. Does all of this sound normal? Why does the measured voltage change from 14.2 to 13.3?

Not good idea to have panel connected before the battery, and the panels should also be disconnected first before disconnecting the battery.
SCC that has auto function to detect the battery Voltage first to set itself to run at the correct system Voltage will not know what the system Voltage will be if the panel is connected first.

 

[John Frum]

A charger charges a battery by sending current through it backwards.
The charger voltage has to be higher than the battery voltage for this to happen.
The voltage delta between the charger and the battery determines the flow rate.

 

[Lane]

I'm sure this is a total beginner question, but I'd like to clarify my understanding.

I have a Victron 100/50 SCC charging a 12v LPF battery bank. I set the rotary switch to position 7, which should output 14.2V.

I isolated the batteries with a switch and hooked up the panels. Before turning on the battery switch, the Absorption LED (yellow) was on, and I measured the output from the SCC ports at 14.19V.

However, when I turn the battery switch on, the Bulk LED (blue) came on, and the system voltage measures at 13.3V (via my Victron Smart Shunt and at the output terminals on the SCC).

The measured voltage of the battery bank before connecting the panels was 13.2V. Does all of this sound normal? Why does the measured voltage change from 14.2 to 13.3?

Current Draw of the battery is why charger voltage is low vs voltage when open circuit. As you continue to charge, over time, as the battery gets more completely "full" you will see your charge voltage rise to 14.2 and current draw amperes will drop to nearly zero amperes.

 

[Lane]

Working Rule Of Thumb About Current (Amperes) Draw And Voltage of Charge, Beit A Car or Truck Alternator Or Whatever. The Battery ALWAYS Says "I Come First"! It Will ALWAYS Demand As Much Current As You Can Supply It To Get Itself Charged. It Can Mislead One To Consider They Have A Defective Alternator Or Battery Charging Device. A Discharged Battery (any type) Has LOW Resistance Thus Exibits A High Charge Current Demand. When Demanded Current (amperes) Goes Up Then Indicated Charge Voltage Goes Down As Far As Meter Readings Go.

 

[jsmit209]

Not good idea to have panel connected before the battery, and the panels should also be disconnected first before disconnecting the battery.
SCC that has auto function to detect the battery Voltage first to set itself to run at the correct system Voltage will not know what the system Voltage will be if the panel is connected first.

Damn. Good to know for the future. How would that work in practice? Engage the battery switch first, and then plug up the panels?

 

[Bud Martin]

Damn. Good to know for the future. How would that work in practice? Engage the battery switch first, and then plug up the panels?

I use breaker as panel disconnect between panels and the SCC, this will also make it easier to troubleshoot the system.

 

[jsmit209]

I use breaker as panel disconnect between panels and the SCC, this will also make it easier to troubleshoot the system.

Ah yes. My 2-pole DC breaker is in the mail already. I'll add it in line, which should make everything easier.