How to test a solar setup?

[DaktariEd]

I have a Sunsei solar panel (18 watt IIRC) and charge controller (CC10000?), about 4 years old at the most. I left my Adventure trailer up at my land in New Mexico, and left the solar panel out to keep the battery fully charged.
This past week or so, despite leaving the panel in full sun for ~8 hours a day during the preceding week, my battery discharged down to 9 volts (in less than 36 hours; ambient temps around 50-80 degrees) with only the ARB fridge drawing from it.
I brought the battery home, recharged it and had it tested...works fine.

The data from the charge controller says:

Nominal Voltage: 12 Volts
Array Voltage, Max (Voc): 30 Volts
Charging Current, Continuous: 10 Amps
Operating Voltage at Battery, Min Charging starts at: 7 Volts
Current Consumption: 2 milliamps
Boost Charge Voltage (2 hours): 14.5 Volts
Float Charge Voltage: 13.7 Volts
Regulation Accuracy: +/- 0.150 Volts
Voltage Drop, Array to Battery:< 170 millivolts

The manual says:

Charger will charge battery until float voltage of 13.7V and
maintain using Pulse Width Modulation (PWM). If battery
voltage falls below 12.5V, the charger will charge the battery
until boost mode of 14.5V is reached and maintain it for two
hours and then go into float mode of
13.7V using PWM.

So, how do I go about testing the solar panel and charge controller?

I presume the output of the solar panel in full sun should be on the order of 12-13 volts.
And the output of the charge controller would depend on the battery voltage. But if I disconnect the battery for testing, I should expect it to enter Boost mode and put out 14.7 volts. Does that sound right?

Thanks for any help...

 

[Martyn]

Ed

Your controller has 4 screw down connectors, two (+ and -) for the wires from the solar panel, and the other two (+ and -) for the wires from the controller to the battery.

The first thing I would do is make sure all the wires are in securely and the screws are tightened down.

First I would use a volt meter with probes and see if you are getting current from the solar panel to the controller.

Second I would test to see that I was getting current coming from the controller to the battery. Unless you have physically damage to the panel the controller is the most likely culprit.

Simple controllers like this are difficult to diagnose without using other tools. Some of the controller have red and green LED lights indicating if the unit is working or not, others have nothing. We use a controller that has a digital display that shows both the voltage of the battery and the amperage from the solar panel. It's more expensive but it allows for diagnosis of problems like this.

 

[Rando]

If the solar panel is outputting 12V in full sun then there is something wrong. Open circuit voltage on a 12v nominal panel should be something like 17v. However the output voltage of the panel doesn't really tell you much, you want to measure the short circuit current. In full mid-day sun it should be pretty close to the rated current (ie rated Watts/17V). That will confirm that your panel is okay. You can then hook your panel up to your charge controller and measure the current flowing from the panel to the controller. That will tell you if your controller is at least trying to charge your battery. If you have an oscilloscope you can check the PWM voltage going to the battery.

Have you tried hooking up your solar system after you charged the battery? One thought is that the solar charger may have shutdown because the battery voltage went too low. In which case charging the battery by another means and reconnecting the solar charger may fix everything.

 

[adventureduo]

Something is dead wrong if you have an 18 watt panel and your getting 10 amps out of it.

That's not possible.

 

[Rando]

I think his charge controller is rated at 10 amps, not his panel (18W) which should be about 1 Amp.


As an aside, an 18W panel is not going to be able to keep up with a fridge. I would gestimate that the fridge is using on the order of 10 - 20ah a day, particularly if it is inside a vehicle and you are only producing about 8Ah a day from your solar system. Depending on the size of the battery it maybe completely normal that the battery was flat in 36 hours. How big is your battery?

Something is dead wrong if you have an 18 watt panel and your getting 10 amps out of it.

That's not possible.

 

[adventureduo]

Gotcha, i think i read it backwards.

And i agree... 18watt panel for a Fridge isn't going to cut it.

 

[Mlachica]

If you use a traditional voltmeter you would need to put the meter in series with the circuit to read current flow. Meaning you'd have to disconnect the positive lead on the controller coming from the panel and connect the meter to the terminal on the controller and the lead you disconnected. Then do the same for the lead coming from the controller to the battery. You would perform these tests with everything else connected.

If you have or know somebody who has a DC clamp on ammeter like this

http://www.myflukestore.com/p1252/fluke_337.php

then you wouldn't have to disconnect any wires to read current flow.

If there's nothing wrong with the solar system then it's likely the solar panel and battery could not keep up with the fridge. If your battery has been drained to 9v multiple times it will have a harder time sustaining your fridge. Meaning it may charge to 12.8 volts but will drain faster than when new.

 

[DaktariEd]

Thanks, folks. :sombrero:
I have not yet returned to New Mexico to re-install the battery and test the charge controller. I'll be heading back there next weekend.
I just needed some guidance as to how best to approach the diagnosis part of it.
I did check all the connections when I first noticed the fridge temp going up and the voltage going down. They were ok, but I re-seated the wires anyway just to be sure.

One odd thing I noticed, was that during the night the green LED light continued lit, implying that it was charging when it was pitch dark.
I don't recall ever seeing that before, and the "manual" doesn't say anything about the light staying lit after the solar input drops below levels needed to produce adequate output.

I've used this setup for several years and only once had the fridge draw down the battery like this...when I camped in the shade at the Expedition Trophy event 2008. Temps were similar but actually hotter then compared to now.

So, I guess I'll test voltages with my voltmeter, verify first that the panel output is around 17 v., then see what the charge controller is putting out. If needed I can check current draw in series...

Hope I got that right!

Thanks for the guidance!

 

[Martyn]

Ed

If you have the older ARB fridge it's going to pull an average of 1.2 amps per hour (the compressor isn't running all the time so this is an average with the fridge set a normal fridge temperature).

As someone pointed out the solar panel is providing 1 amp of power for lets say 8 hours a day, plus some sunlight in the shoulder hours. So you are running at a deficit of 19 amps a day. A good group 31 deep cycle should run that fridge by itself for 3 -5 days depending on how many times you open it and if it's in direct sunlight or not. It should run it for longer given the little bit of help the solar panel is giving.

Something is not 100% here.

 

[DaktariEd]

Yeah, Martyn,
That's been my previous experience. It usually will run 3 days w/o running down, even w/o the solar charger. And since I had the solar panel charging for a full 5 days (while I was back in Tucson) with no load on it at all, I would think the battery would be at 100% when I returned.
It's in the Horizon, so no direct sun; I don't open it too often; and it has a transport cover.
So, yeah, I think something is amiss... :ylsmoke:
Thanks for the help...and I'd bet it's the controller.
Any suggestions for a better controller?

 

[Martyn]

Yeah, Martyn,
That's been my previous experience. It usually will run 3 days w/o running down, even w/o the solar charger. And since I had the solar panel charging for a full 5 days (while I was back in Tucson) with no load on it at all, I would think the battery would be at 100% when I returned.
It's in the Horizon, so no direct sun; I don't open it too often; and it has a transport cover.
So, yeah, I think something is amiss... :ylsmoke:
Thanks for the help...and I'd bet it's the controller.
Any suggestions for a better controller?

Ed

If when you last left the battery was drained very low as someone mentioned earlier the small panel may not have been able to bring the battery back to full charge. I don't have any experience with a situation like this, but it's possible.

If you want a controller with more diagnostic capabilities we sell a 20 amp controller with LED read out. It will allow you to monitor the battery and the panel. If your just looking for a small replacement unit we have a 4 amp controller that we have not experienced any issues with.

 

[BigJim]

Imo

Your solar panel is undersized and drawing down the battery. Most good charge controllers shut off if the sensed battery voltage drops below 9 volts or so. I suspect this is what is happening to you.

You can verify this with a volt or amp meter. When you experience this same situation again see if the charge controller is outputing a charge, voltage >12 or current near your panels output. If its sunny and you would expect a charge current jump another 12 volt battery to your dead battery. I'll bet your charge controller will now output a voltage.

Then you need to size and match your load with your supply.

I have a Sunsei solar panel (18 watt IIRC) and charge controller (CC10000?), about 4 years old at the most. I left my Adventure trailer up at my land in New Mexico, and left the solar panel out to keep the battery fully charged.
This past week or so, despite leaving the panel in full sun for ~8 hours a day during the preceding week, my battery discharged down to 9 volts (in less than 36 hours; ambient temps around 50-80 degrees) with only the ARB fridge drawing from it.
I brought the battery home, recharged it and had it tested...works fine.

The data from the charge controller says:


The manual says:



So, how do I go about testing the solar panel and charge controller?

I presume the output of the solar panel in full sun should be on the order of 12-13 volts.
And the output of the charge controller would depend on the battery voltage. But if I disconnect the battery for testing, I should expect it to enter Boost mode and put out 14.7 volts. Does that sound right?

Thanks for any help...

 

[Martyn]

Your solar panel is undersized and drawing down the battery. Most good charge controllers shut off if the sensed battery voltage drops below 9 volts or so. I suspect this is what is happening to you.

You can verify this with a volt or amp meter. When you experience this same situation again see if the charge controller is outputing a charge, voltage >12 or current near your panels output. If its sunny and you would expect a charge current jump another 12 volt battery to your dead battery. I'll bet your charge controller will now output a voltage.

Then you need to size and match your load with your supply.

I think Ed is just trying to supplement the battery with a little energy from the sun. His panel is way too small to run anything very much.

As you explained his issue may have been that the battery was too discharged to begin with to take a charge from the controller.

 

[DontPanic42]

There haven't been any postings here in several days so I guess this won't be much of a hijack but I also have a question about testing the output of my solar panel.
I have a 100 watt AMSolar panel with an HPV22 controller that can handle up to 3 - 100 W. panels. They have with full sun about 26 VDC and 4 ampsDC. In theory anyway. I have been attempting to measure the variation of output with changing sky conditions and panel position. I have 2 data loggers that can easily record a full day's worth of data at 1 minute intervals. The volt logger goes to 30.00 maxDC +/- 50mDCV. Here is a typical result:

While the plot does show output variation with sky conditions from what I read it is really measuring the temperature variation of the panel. I wish to measure the amperage output to the battery.
I have another data logger that measures 4 - 20maDC +/-0.05 ma.
I know that a DC shunt can be used with a DC Volt meter to convert to MV to MA.
So my question is with the equipment I have what is the best way to hook it up to get the information I am looking for, i.e., amperage to the batteries? If it is a DC shunt, how do you size them as I have found pages of shunts listed online.
As an aside, I have also purchased a time lapse camera to record sky conditions while the tests are running so I don't have to run and take a picture every hour. That I know how to setup.
Any comments and help are welcome beyond "Are you nuts? Why waste the time" Inquiring minds want to know.
Thanks for any help

 

[Rando]

This sounds like an interesting project. As you have probably already noticed, the voltage from the panel doesn't give you a whole lot of information, you really need to know the current it is providing. Under almost any daylight illumination, you get almost the full voltage output from the panel, but current (and therefore power) will track insolation very well. The easiest way to measure the current is with a shunt resistor (as you suggest), however your 30.00 maxDC +/- 50mDCV data logger won't give you the resolution you need to measure the voltage drop across the shunt. For instance, if you were to use a 0.01 ohm shunt, 4amps would give you a signal of 40mV, or less than one bit on your system. A larger resistance shunt will end up dissipating a lot of heat.

You do something crafty with a pair of shunts to split the current flow in a known ratio, say 200:1 and measure the current on the higher resistance shunt directly with your current sensor. For example you could use a 0.001 ohm shunt and a 0.2 ohm resistor in parallel and measure the current through the 0.2 ohm resistor and multiply it by 200 to get the total current.

There haven't been any postings here in several days so I guess this won't be much of a hijack but I also have a question about testing the output of my solar panel.
I have a 100 watt AMSolar panel with an HPV22 controller that can handle up to 3 - 100 W. panels. They have with full sun about 26 VDC and 4 ampsDC. In theory anyway. I have been attempting to measure the variation of output with changing sky conditions and panel position. I have 2 data loggers that can easily record a full day's worth of data at 1 minute intervals. The volt logger goes to 30.00 maxDC +/- 50mDCV. Here is a typical result:

While the plot does show output variation with sky conditions from what I read it is really measuring the temperature variation of the panel. I wish to measure the amperage output to the battery.
I have another data logger that measures 4 - 20maDC +/-0.05 ma.
I know that a DC shunt can be used with a DC Volt meter to convert to MV to MA.
So my question is with the equipment I have what is the best way to hook it up to get the information I am looking for, i.e., amperage to the batteries? If it is a DC shunt, how do you size them as I have found pages of shunts listed online.
As an aside, I have also purchased a time lapse camera to record sky conditions while the tests are running so I don't have to run and take a picture every hour. That I know how to setup.
Any comments and help are welcome beyond "Are you nuts? Why waste the time" Inquiring minds want to know.
Thanks for any help