Low current from solar panels

[Tractorboy]

During the winter we fitted a 150W solar panel to our van. Last weekend, we took the van to Download Festival, which is the first time that we have really used it in anger, and I was confused by the current output readings that I was seeing on the solar controller.

Initially, the current output was very low (around 0.3mA) which I would expect to see because the battery was fully charged. However, over time, the battery voltage dropped, and with the fridge still running (240v fridge running through an inverter), we were getting a charging current of 2.0A displayed. This was on a very sunny day, with the panel in direct sunlight, so i would expect the output of the panel to be quite a bit higher.
One thing that we noticed, was if we plugged a phone into the USB connector on the front of the controller, the current increased to 2.3A. This suggests to me that the panel is capable of giving a higher output, but for some reason the current is being limited.

Depending on the performance of the single panel over the weekend, we were thinking that we might add a second panel, but if the current output is being throttled to 2A, then this seems pointless.
Can anybody suggest what might be causing the current being delivered to the batteries to be so low? It appears to me that for some reason the charging current to the batteries is being limited, but I don't know why. The output from the controller is connected directly to the +ve and -ve terminals of the batteries.

Thank you

 

[harrow]

During the winter we fitted a 150W solar panel to our van. Last weekend, we took the van to Download Festival, which is the first time that we have really used it in anger, and I was confused by the current output readings that I was seeing on the solar controller.

Initially, the current output was very low (around 0.3mA) which I would expect to see because the battery was fully charged. However, over time, the battery voltage dropped, and with the fridge still running (240v fridge running through an inverter), we were getting a charging current of 2.0A displayed. This was on a very sunny day, with the panel in direct sunlight, so i would expect the output of the panel to be quite a bit higher.
One thing that we noticed, was if we plugged a phone into the USB connector on the front of the controller, the current increased to 2.3A. This suggests to me that the panel is capable of giving a higher output, but for some reason the current is being limited.

Depending on the performance of the single panel over the weekend, we were thinking that we might add a second panel, but if the current output is being throttled to 2A, then this seems pointless.
Can anybody suggest what might be causing the current being delivered to the batteries to be so low? It appears to me that for some reason the charging current to the batteries is being limited, but I don't know why. The output from the controller is connected directly to the +ve and -ve terminals of the batteries.

Thank you

Well the amount of current would be limited if the maximum charging voltage is also limited, obviously also any added resistance would also limit the charging current.

So I would like to see normal lead acid batteries being charged up to 14.5 volts on a bright sunny day.

 

[Tractorboy]

Well the amount of current would be limited if the maximum charging voltage is also limited, obviously also any added resistance would also limit the charging current.

So I would like to see normal lead acid batteries being charged up to 14.5 volts on a bright sunny day.

I don't really understand what you are saying.

The current from the solar panel is trying to charge the batteries, additionally, the inverter is drawing current from the batteries (to run the fridge) at the same time. so I would expect the current being drawn from the panel to be higher than the amount of current that is charging the batteries. If I am running batteries that are going flat, then I would expect to see a higher current draw on the solar panel because it is also trying to power the fridge.
If I am only able to ever supply 2A of charge from the panels to the batteries, what would be the point of more/bigger panels?

Toward the end of the weekend, we had to switch the fridge off because the battery low voltage warning came on, at this point, I would be expecting to see more than 2A being provided on a bright sunny day.

 

[Livotlout]

Have you sized your cables correctly to suit current and length, if not of correct sizes you may be experiencing voltage drop.

 

[trevskoda]

Sounds like cable size to me,or a faulty control box.
Should on full chat hit about 10ah full mid day sun,however more like about 5 or 7ah on normal day would be about right if battery a tad low with voltage from about 13.8 to 14.4 ,hope this helps.

 

[Tractorboy]

Cables are rated at 20A, and the solar panel is located directly above the battery, so I guess that at maximum there is a 2M run from the controller to the batteries. I'm assuming that 20A cable should be sufficient?
Can't check right now, but if I remember correctly, when the sun is high, the controller normally reads about 14-15V from the panel.

I have been suspecting that it could be a problem with the controller, but obviously want to try to eliminate anything else before I start changing things randomly.

To make sure I have this straight in my head, is the suggestion that if the cables have a high resistance, then the controller will sense this and reduce the current that is being supplied? Thinking it might be worth checking all of the terminals to the batteries before I start spending money, in case there is a dodgy connection somewhere.

 

[Nabsim]

Last weekend at Hollingworth lake my highest reading on 150w panel was 7.7amps although it only shows an instantaneous readout so it is possible it could have gone a little higher. That was on the hottest day last weekend in direct sunlight though

 

[Admin]

Just a question but...

Does your charge controller allow you to cycle through different readings?

The reason I ask is that you could be reading the input amps rather than the output amps. The input voltage could be much higher.

A member recently asked me for advice as their solar controller only showed a 4.5 amp output from his 210-watt panel. He figured that this meant (4.5 x 12) 54 watts. But after cycling through the readings on the display this was the solar input amps and the voltage was 42 volts, so (4.5 x 42) 189 watts. The battery charge amps was actually 14.3 amps

 

[Nabsim]

Just a question but...

Does your charge controller allow you to cycle through different readings?

The reason I ask is that you could be reading the input amps rather than the output amps. The input voltage could be much higher.

A member recently asked me for advice as their solar controller only showed a 4.5 amp output from his 210-watt panel. He figured that this meant (4.5 x 12) 54 watts. But after cycling through the readings on the display this was the solar input amps and the voltage was 42 volts, so (4.5 x 42) 189 watts. The battery charge amps was actually 14.3 amps

I wonder if that is what Barry was seeing, the readings he was getting were a lot lower than me parked next to us at Hollingworth. Barry has 100w panel so we were working on he should be seeing two thirds of my 150 but was getting about half of that

 

[wildebus]

What you see coming out of the solar panel is very dependent on what your battery requires.
If it is say at 70% or less than it will take everything the panel could harvest but if at say 90% the battery will not want so much to top it off, so two setups side by side, a 100W panel maybe producing twice as much as a 200W panel if that is what the batteries dictate.

For the OP, I am curious about the use of cable rated at 20A. That could mean the use of just 1.5mm cable potentially, which is bit small when considering voltage drops as well. When you say 'panel is above the batteries' does the cable drop straight down then? Or is it routed back and forth (e.g. my panels are above my batteries as well, but the cable goes right to the back, down the rear pillar and then forward again so something like a 6 metre run)

It sounds very much like a fault in something, and not what you should be seeing in a working solar setup.