Panel voltage drops when connected to controller

[Arcarter]

Hi everyone, long time reader, first time poster.

I’ll try and be as brief as possible.

100w “Go Power” solar panel (came with my 2021 Jayco travel trailer). Recently installed a new AGM battery (79Ah). Recently purchased a Victron 75/10 with the Bluetooth battery monitor.

I won’t go into detail about the issues I was having when I was using the Renogy Adventurer PWM unless it is helpful. Let me know.

So here’s the deal: full sun today, getting open circuit voltage of 19-ish volts from the panel. When the panel is connected to the Victron controller, voltage drops to right around battery voltage. Panel is clean, no shade, sun is high, so pretty much optimal conditions. And of course, with the fact that I need batt voltage plus 5v to start the charger, I’m getting no charge from the panels.

Something I thought was interesting but may be normal - I’ll mention it just in case - my battery was at about 12.4v at rest. I flipped the breaker on to begin using house current to charge the battery, and panel voltage increased along with the increase in battery voltage.

Also odd, I put a piece of cardboard over the panel and I was still getting a reading of 12-ish volts from the panel (readout on the controller). Would have expected it to be close to, if not zero.

Basically I’m trying to confirm what I think - that the panel needs to be replaced. It’s not making enough current. Would love to understand how battery voltage impacts panel voltage - does the panel receive current / voltage from the charge controller?

I appreciate any and all insight into this, with my thanks in advance!

 

[SeaGal]

Welcome! What is Vmp of your panel? I suspect that might be less than the minimum of 17.4V (12.4V + 5V) that the controller needs to start.

 

[Arcarter]

17.4v assuming I’m reading this spec sheet correctly:

100 watt Solar Module (Polycrystalline)

The 100 watt Solar Module from Go Power! is a Polycrystalline module that provides a cost-effectivesolar power for off-grid and mobile applications.

gopowersolar.com

I do understand the +5v requirement but what stumps me is the big difference (6+ V) between open circuit voltage and the voltage the controller is showing.

 

[Louis_8]

Hi everyone, long time reader, first time poster.

I’ll try and be as brief as possible.

100w “Go Power” solar panel (came with my 2021 Jayco travel trailer). Recently installed a new AGM battery (79Ah). Recently purchased a Victron 75/10 with the Bluetooth battery monitor.

I won’t go into detail about the issues I was having when I was using the Renogy Adventurer PWM unless it is helpful. Let me know.

So here’s the deal: full sun today, getting open circuit voltage of 19-ish volts from the panel. When the panel is connected to the Victron controller, voltage drops to right around battery voltage. Panel is clean, no shade, sun is high, so pretty much optimal conditions. And of course, with the fact that I need batt voltage plus 5v to start the charger, I’m getting no charge from the panels.

Something I thought was interesting but may be normal - I’ll mention it just in case - my battery was at about 12.4v at rest. I flipped the breaker on to begin using house current to charge the battery, and panel voltage increased along with the increase in battery voltage.

Also odd, I put a piece of cardboard over the panel and I was still getting a reading of 12-ish volts from the panel (readout on the controller). Would have expected it to be close to, if not zero.

Basically I’m trying to confirm what I think - that the panel needs to be replaced. It’s not making enough current. Would love to understand how battery voltage impacts panel voltage - does the panel receive current / voltage from the charge controller?

I appreciate any and all insight into this, with my thanks in advance!

That sounds like a good start. Here’s a quick guide to troubleshooting:
Panel and Battery Voltage: When connected, it is normal for the panel voltage to drop to the battery voltage. However, if there is insufficient current from the panel, this could indicate a problem.

Charging Threshold: Your battery at 12.4V needs at least 17.4V from the panel. With 19V open circuit, it should be enough.

No Charge from Panels: Check connections, verify controller settings and measure panel output using multimeters.

Panel Under Cardboard: The residual voltage will not drop down to zero due to ambient light.

If the panel isn’t providing enough current, maybe you should get another one.

I hope that helps!

 

[Arcarter]

That’s really helpful. Will check those things. Appreciate the very quick response!!

 

[Arcarter]

That sounds like a good start. Here’s a quick guide to troubleshooting:
Panel and Battery Voltage: When connected, it is normal for the panel voltage to drop to the battery voltage. However, if there is insufficient current from the panel, this could indicate a problem.

Charging Threshold: Your battery at 12.4V needs at least 17.4V from the panel. With 19V open circuit, it should be enough.

No Charge from Panels: Check connections, verify controller settings and measure panel output using multimeters.

Panel Under Cardboard: The residual voltage will not drop down to zero due to ambient light.

If the panel isn’t providing enough current, maybe you should get another one.

I hope that helps!

Question for you - can I go to a 200w / 24 volt panel with my current configuration (12v battery)? I want to be sure I have that +5v. I’m worried that with a 200w / 12 volt I may not hit the battery +5v

 

[SeaGal]

Hopefully someone who has experience of the Victron 75/10 will be able to add something to this thread - I am only going by basic principles of voltage and current...

Edit to add: ignore my ramblings in this post, @mikefitz had more accurate info below...

I may be talking rubbish here, but IMHO, if you have a panel with a Voc of 19V, then as soon as you draw current from it, the voltage will reduce. The point of maximum power (Vmp) will be the voltage that the SCC will aim for, in order to produce maximum power for any given light intensity; it does that by varying the current it draws from the panel(s).

Typically Vmp will be around 80% of the open circuit (Voc), in bright sunlight.

So, I would expect the voltage of your panel to reduce to about 15.2V when a current is drawn from it.

BUT, the SCC will need to be charging the battery, which, before any charge current is (as you say) at about 12.4V. To charge the battery, the SCC will need to produce a higher voltage to get current to flow into the battery. A typical charge voltage will be around 13.8V.

If I am correct with those assumptions, then for the SCC to work, it will need 13.8V + 5V = 18.8V. This voltage will not be generated by the panel you have as soon as any load is attempted to be drawn from it.

So, IMHO, I believe you will need to put two of those panels in series to have a Voc of 38V and and a Vmp of around 30V in order for the SCC to charge a 12V battery. This is well under the maximum Voc of 75V that the Victron 75/10 can handle.

 

[mikefitz]

The Victron needs 4 to 5 volts higher than battery volts to start, once operational the panel volts needs to be greater than 1 volt above battery volts.

then for the SCC to work, it will need 13.8V + 5V = 18.8V.

This statement is not quite correct. In the morning the lead battery will have a voltage of less than 13 volts, perhaps lower than 12.5 if any loading over night. Sunlight on the panel will, generate a voltage around 20 volts, the controller will start up and search for maximum power, typically 16 to 18 volts. This is still higher than the set target charge volts for the battery, say 14.6 volts, thus the controller will continue to operate.

 

[SeaGal]

once operational the panel volts needs to be greater than 1 volt above battery volts

Great - didn't know that . So it sounds as though the OP's system _should_ work OK with his current configuration; in which case there must be another fault with either the wiring or the SCC itself?

 

[mikefitz]

getting no charge from the panels.

Either the panels or controller has a fault
Test the panel SC current. See you tube for details. Or setup your meter to the 10A current range and connect across the panel leads. With any light on the panels you should see some current, 2 to 3 amps or more with good sunlight.
An alternative is to connect directly to the battery. Monitor the battery volts, you should see the volts gradually increase, don't, leave unattended and disconnect if the battery volts reaches 14.7 volts.

A panel fault or panel wiring fault can still indicate a voltage but no current developed.

if the Go Power panel is a flexible type then then its most likely failed and needs replacement.