Solar New solar panel faulty

garfield28

Active Member
Jun 28, 2021
152
70
28
NSW
Hi all,

I just bought a 300w solar panel off ebay, it was received on Friday so I went and connected it to van today to see how she goes and straight away I have issues. It was all over the place going from o up to 2.5amps then drop dramatically to .7amps down to 0 up to 1.5 then down again up and down never even close to holding a steady amp charge and nowhere near what I would be expecting from a 300w solar panel even allowing for it not being a true 300w output.

I believe the unit is faulty, but any suggestion of a trouble shoot that could be causing please? I have tried my MMPT to see if the controller that came with it was no good, and somehow my MMPT controller made the amps even lower, and I also cheeked the wiring in the solar panels themselves and they looked ok to me.

Any help appreciated.

Thanks
Geoff
 

mikerezny

Well-Known Member
Sep 11, 2016
1,630
2,728
113
Mount Waverley, VIC
Hi,
there are two aspects to consider when using a solar panel. The first is the capacity of the panel to supply power and the second is the capacity of the load to absorb it.

Consider your domestic power supply power point. It is rated to supply 10A at 240V. But the actual power supplied by the power point is dependent on the power used by the appliance that is plugged in.

So, you need to separate the two aspects, supply and load.

The most accurate and common way to measure a solar panel output is to disconnect it, optimally align it in good sunlight, measure the Open Circuit voltage (Voc) and the Short Circuit current (Isc), and compare it to the panel specification which is usually on a label on the back of the panel.

Is it likely that your batteries are fully charged and are therefore not absorbing much current. The best way to check this is to measure the battery voltage. If it is already above 13.8V with the panel connected, the solar controller will most likely not be in bulk charge mode and is in float / absorption mode and the charge current will be reduced.

If you think that is possible, then, in good sunlight, turn on every 12V light and appliance you have in the van and see what current is generated by the panel.
Also measure the battery voltage. If it is below 13V, the solar controller should definitely now be in bulk charge mode and the current will then be indicative of the capacity of the panel.

Ignore any comments relating to panels NEVER delivering their rated output. That is rubbish. A good panel is rated to deliver its specified current with a solar insolation of 1,000W per sq m. Solar insolation throughout Australia can easily be above 1,000w per sq m. In that case, a good panel will easily deliver more than the rated current. I have a good 30W panel, with an Isc of 2.22A which will regularly deliver more than that, and in good strong sunlight on a cool day, the panel will deliver in excess of 2.65A. Note that panel output is rated at an ambient temperature of 25C. Panels in good sunlight on hot still days will easily be hotter than 25C. Increased heat on the panels reduces the output current. On the other hand, panels with an ambient temperature of less than 25C will deliver more than the rated current.

take care
Mike
 
Last edited:

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
1,804
113
Ferny Grove, Queensland
Hi all,

I just bought a 300w solar panel off ebay, it was received on Friday so I went and connected it to van today to see how she goes and straight away I have issues. It was all over the place going from o up to 2.5amps then drop dramatically to .7amps down to 0 up to 1.5 then down again up and down never even close to holding a steady amp charge and nowhere near what I would be expecting from a 300w solar panel even allowing for it not being a true 300w output.

I believe the unit is faulty, but any suggestion of a trouble shoot that could be causing please? I have tried my MMPT to see if the controller that came with it was no good, and somehow my MMPT controller made the amps even lower, and I also cheeked the wiring in the solar panels themselves and they looked ok to me.

Any help appreciated.

Thanks
Geoff
Hi @garfield28 , if your MPPT controller is any good, it will show panel voltage when on charge and in the sunlight. For a standard 12 volt panel, expect to see on your MPPT controller somewhere between 15 and 18 volts when charging and a little higher when under a very light load or on float. Output current in amps will be dependent on battery state and electrical load. One of the advantages of a MPPT over a PWM type is that there usually is more ability to monitor what is happening.
 

garfield28

Active Member
Jun 28, 2021
152
70
28
NSW
Hi,
there are two aspects to consider when using a solar panel. The first is the capacity of the panel to supply power and the second is the capacity of the load to absorb it.

Consider your domestic power supply power point. It is rated to supply 10A at 240V. But the actual power supplied by the power point is dependent on the power used by the appliance that is plugged in.

So, you need to separate the two aspects, supply and load.

The most accurate and common way to measure a solar panel output is to disconnect it, optimally align it in good sunlight, measure the Open Circuit voltage (Voc) and the Short Circuit current (Isc), and compare it to the panel specification which is usually on a label on the back of the panel.

Is it likely that your batteries are fully charged and are therefore not absorbing much current. The best way to check this is to measure the battery voltage. If it is already above 13.8V with the panel connected, the solar controller will most likely not be in bulk charge mode and is in float / absorption mode and the charge current will be reduced.

If you think that is possible, then, in good sunlight, turn on every 12V light and appliance you have in the van and see what current is generated by the panel.
Also measure the battery voltage. If it is below 13V, the solar controller should definitely now be in bulk charge mode and the current will then be indicative of the capacity of the panel.

Ignore any comments relating to panels NEVER delivering their rated output. That is rubbish. A good panel is rated to deliver its specified current with a solar insolation of 1,000W per sq m. Solar insolation throughout Australia can easily be above 1,000w per sq m. In that case, a good panel will easily deliver more than the rated current. I have a good 30W panel, with an Isc of 2.22A which will regularly deliver more than that, and in good strong sunlight on a cool day, the panel will deliver in excess of 2.65A. Note that panel output is rated at an ambient temperature of 25C. Panels in good sunlight on hot still days will easily be hotter than 25C. Increased heat on the panels reduces the output current. On the other hand, panels with an ambient temperature of less than 25C will deliver more than the rated current.

take care
Mike
Hi Mike, really appreciate the effort in explaining that I will take your tips on board and have a look at doing what you said.
Thanks very much
 

garfield28

Active Member
Jun 28, 2021
152
70
28
NSW
Hi @garfield28 , if your MPPT controller is any good, it will show panel voltage when on charge and in the sunlight. For a standard 12 volt panel, expect to see on your MPPT controller somewhere between 15 and 18 volts when charging and a little higher when under a very light load or on float. Output current in amps will be dependent on battery state and electrical load. One of the advantages of a MPPT over a PWM type is that there usually is more ability to monitor what is happening.
Thanks Boots. I think the panel is no good to be honest. I have discovered today also that my MMPT controller I bought from kings which has barely been used is not working either
 

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
1,804
113
Ferny Grove, Queensland
Thanks Boots. I think the panel is no good to be honest. I have discovered today also that my MMPT controller I bought from kings which has barely been used is not working either
Highly unlikely that you would have BOTH not functioning properly in my opinion. I have only seen the Kings MPPT on Ebay and it does not appear to have any proper readout or settings, just an indication light to show charging. Might be a good time to get out your multimeter to check each piece of equipment with KNOWN units separately before making any further rash decisions. Also make sure you have ALL the connections correctly connected. If you are unsure on how to go about it and in what order, just ask with pictures of what you have done. I am certain that @mikerezny and myself can sort out your problem, also with any necessary input from other knowledgeable members.
 

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
1,804
113
Ferny Grove, Queensland
Thanks Boots. I think the panel is no good to be honest. I have discovered today also that my MMPT controller I bought from kings which has barely been used is not working either
Hi again @garfield28 , just had another thought. If your new 300 watt solar panel has its OWN solar controller (usually they come attached to rear of panel), run the output from the solar controller direct to battery. DO NOT RUN THE PANEL OUTPUT THROUGH ANOTHER in line CONTROLLER TO YOUR BATTERY. If you want to use your Kings MPPT controller, it should be used on its own. This will mean that you MUST bypass the solar controller attached to rear of solar panel . Trying to run solar output through two solar controllers in SERIES (especially if one is a PWM type and the other is a MPPT ) will cause a very confusing result as they both work differently in converting panel power/voltage to usable battery charging.
 

Drover

Well-Known Member
Nov 7, 2013
12,723
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QLD
Yep, Boots is on the money, if I connect my portable up with its controller direct to battery while the vans set up is hooked up, depending which set of panels has the most sun on them one set will just shut down, if batteries are well down they will both happily power away in boost mode....

To have panel and reg playing up is too much of a coincidence in my book..................... disconnect your van from battery and just plug in your new set up, direct to battery, if battery is charged you won't see very much charge at all............ I have 400 odd watts on roof and hardly see more than an amp when charged if that...... a bench test will certainly show things up.... and the 200w panel charging my boat battery is mostly at 0, an amp or 2 flows at sunrise and thats it, so you often don;t see very much going on when charged.
 

peatop

New Member
Sep 30, 2021
5
10
3
Geelong
@garfield28 It is very important when connecting a solar system to connect batteries to the controller before the panels or you can burnout your controller, when setting up a system you must decide whats the most important part of the system and this is where you put the most $value, for me this was the controller and batteries as if these fail nothing else will work very well, my main battery is a lifepo4 (lithium) that I made myself from cells imported from China, My main controller is a Victron 100/50 (100Volts and 50 Amps) my second (backup) is a Renogy PWM 30Amp, the performance difference between the 2 controllers is negligible but the Victron is top end hardware while the Renogy while a reasonable brand is 1/10 the price, but a backup.

On another forum it was stated that places like Ebay, Aliexpress, Wish and so on are just disposal sites for rejected products that didn't pass qc inspections an alike.
Now we know this is not entirely true but it is also not far from the truth either, I'm not saying don't buy from these places, but it is buyer beware!

the best way to know what output to expect from a solar panel before you buy is read the description, the size of the panel should be worked out for square meters then times it by 17, for example a panel that measures 1200 x 800mm = 1.2x0.8=0.96^2m =0.96x170=163W, so the output should be rated at 160 Watts there abouts, this is only a generalization but a good guide when buying, next is the sticker on the back that gives the Vmp (Optimum Power voltage), Imp (Optimum operating current), Voc (Open circuit voltage) and Isc (Short circuit current). when selecting panels you need to be mindful of how you are going to install them (in series or parallel) in series you add the voltages and the output amps is limited to the lowest rated panel, and when connected in parallel the amps are added and voltage output is limited to the voltage of the lowest panel.

Example if you have a 140w and 160w panel of different voltages but same amps (Imp) then there will be no losses connected in series, but if they have the same voltages and different amps then the output amps will be the lower of the 2 if connected in series. so if connected in parallel the amps are added but the output voltage is limited to the lower output panel.

I have two 145W and one 100W panels also a 200W blanket (backup) I know the 145W and the 100W panels outputs are correct but I know the blankets output is going to be approximately 50% of stated if I'm lucky, now when I hook these up it goes something like this, I connect the two 145W panels in series this gives me 2xVmp which is stated at 18V and 8.06A (Imp) so 18x2x8.06=290W so i have 36V at 8.08A going into the MPPT controller and coming out is upto 290W/13.2V nominal which is around 22A if the battery will accept that amount of charge, then there is the 100W panel well this only come out if the conditions aren't the best and I'm not getting the input required to fill my battery/s and the blanket is the same and they get connected via there own controllers just to keep it simple.

As others have stated the only real way to test a panel without solar test equipment is to test the Voc and Isc using a multimeter, or a clamp meter when connected to a discharged battery via the controller, either of these tools are considered a must have when dealing with solar, I have both.
 

Boots in Action

Well-Known Member
Mar 13, 2017
2,054
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Ferny Grove, Queensland
Pretty good explanation @peatop but not quite complete. All the controllers I have seen ALL state that you must connect the battery terminals FIRST. This is because a lot will not work under a certain voltage (especially if battery is extremely low or flat), but the main reason is that most good controllers need to "sense" what the operating voltage of the system is, either 12 volt or 24 volt. This seems to be an automatic selection if battery voltages are within the scope of the controller. As for burning out the controller if panels are connected first and no load (battery voltage), that would not happen, as no current will flow, although voltage potential will be present. A good reason to ALWAYS read and follow directions. Batteries connected first, then solar input and then load connections, preferably with all loads switched off. This is also a good way of checking each step that operation is normal.
For your information, I have a great LDSOLAR Tracer Dream Series true MPPT controller which can handle up to 100v input and provide 30 amps out, plus a 30 amp load. I have 2 X 200 watt folding panels and also a 180 watt folding panel which I connect in SERIES. Panel voltage during float or low load often reaches as high as 57.8 volts thanks to the use of Schottky diodes in the panels (0.2 volt forward drop compared to 0.7 volt drop with the standard silicon type). Panel voltage is around 48 volts when under heavy load and while high charging current is being produced. So one does not usually attain max Vmp (not optimum!) under load and Imp is subject to a lot of variables including brightness, cleanliness of panels, angle to the sun, not to mention the temperature of the panels themselves. In Queensland, the surface of the panels get bluddy hot and reduces output. My solar array has reached more than 25 amps at 13.4 volts when my 120ah AGM battery voltage has been around 12.3 volts (off charge), but drops back to around 16 amps after a short time, very quickly bringing battery up to full state. All checked at the time - not guessed!!
Note that ALL figures quoted on panel are under STC at 25C in the laboratory and generally (unless you are extremely lucky!!) not realistic in the field.
I too have both a high quality multimeter and an excellent clamp meter to check all readings. These readings are also available on the screen of my MPPT controller which provides continuous figures for input panel voltage, charging current, load current, battery voltage and battery temperature and whether in MPPT mode or Float. This is in addition to continuous logging of days of operation, number of days of low voltage disconnect, and reconnect, times float status reached, total amp hours generated and total amp hours used since last reset, amongst other things for the various settings.

So welcome to the forum and your input. Cheers.
 
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garfield28

Active Member
Jun 28, 2021
152
70
28
NSW
Thanks for all the help and advice on things to check etc. After a fair few backwards and forwards emails have been told I'll be getting a full refund. Don't think I'll bother buying intricate electrical items on ebay any more. If they fail the after sales service and troubles to get a replacement or refund just isn't Worth the initial little savings.

Thanks
Geoff
 
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Drover

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Nov 7, 2013
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Thats my thoughts as well, if I do I make sure they have a physical shop preferably close, far better to bang on a counter.......... I have not had any dramas with stuff I buy from FWD Superstore, Kings gear, many seem to knock them but it all works for me and they will talk to you.