Voltage drop when plugged into charge controller? (18-19V -> 12.7V)

Hey folks. I'm new to solar and I'm trying to figure out an issue on my camper.
Basically, I'd been having some trouble with my old SCC and installed a Renogy Adventurer 30A PWM controller. I have a 100W panel and 2 x sealed lead acid batteries (Interstate HD24-DP).
I initially installed the PV leads first (was an issue in the battery power circuit so wanted to isolate it), but then disconnected everything. With open circuit, the battery reading is 12.7V, the PV reads 18 or 19V. I figure great, that'll definitely be enough to charge the batteries, should be set. However, when I connect the battery and PV leads back up, the batteries still read 12.7V but now the PV is down to 12.7 or 12.8V. Not running all kinds of stuff on the circuit. Any ideas what may be causing the drop? I have the charge controller set to 12V SLA settings. Is it possible it's pulling very little because the batteries are fully charged?
Comments
12.7 vdc is close to full so you may not see much activity on the controller. Put a substantial load on the batteries and you should see the incoming current or watts, whatever your display shows, rise. SLA batteries can take up to 20% of their amp hour rating so you have 128 amp hours in batteries, you can charge at up to 25 amps. I think one 100 watt panel is about 6 amps at best. Two more panels would give you a good match for keeping those batteries happy.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
Understand that 100watt panel isn't very large.
The batteries you have aren't true deep cycle batteries, but at 61 ah each for a 122 ah (amp hour) total the potential 6 amps from the solar panel represents about a 5% charge rate, without "...running all kinds of stuff on the circuit". Likely the manufacturer would like to see a 10% charge rate.
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
A PWM controller basically act like a switch. When bulk charging, the panels are simply connected directly to the battery. The voltage you see will be the battery voltage, which will initially be only slightly higher than when it's not connected to the panel(s).
As the battery charges, the voltage will rise. When it gets high enough (to the absorption voltage), the PWM controller will begin to switch on/off quickly to maintain that voltage.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
It is NOT the battery voltage, but the system voltage. For the current to flow into the battery the potential of higher voltage from the solar panel will keep the system voltage higher than the battery voltage so current will flow into the battery!
In "bulk" the voltage, without a load higher than the potential, will remain higher than the battery voltage until it reaches the absorb set point at which the charge controller will limit the voltage.
If the battery is removed from the system, the voltage will drop.
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
Here are the stages of charging;
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
System voltage is different than battery voltage.
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
https://renogy.force.com/helpcenter/s/article/What-is-the-maximum-PV-input-voltage-of-the-controller-and-the-system-voltage
- https://zhcsolar.com/solar-charge-controller-settings/
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