Solar panel voltage drop and current output

[Foz]

All,

Am seeking some trouble shooting advice. I have a 30w solar panel with an open circuit voltage of ~18v, in line with manufacturers spec. When I connect it to the controller, the voltage drops to 12.45v. I have checked the voltage at the built in solar panel cable to boat cable junction and again both are 12.45v either side of the joint. The solar panel volts at the controller are also 12.43 - so not too much loss. I have a dual battery set up with the engine battery volts at 12.83, the domestic battery is at 12.3. The controller led indicators all appear normal for battery charging. My battery monitor is only showing 0.1A of charge much of the time, best I have seen is 0.3A, I was expecting ~1A? After a week battery volts remain unchanged consistent with 0.1A?

Is there a problem with the controller, have the batteries gone past their useful life or am I missing something?

Thanks in anticipation....

 

[William_H]

A simple controller (pulse width type) is just a connection via switched on transistor from solar positive to battery positive. So with a low battery voltage it should be turned letting all panel power into battery.
So you can simply bypass or remove the controller and connect solar panel to battery to see if you get any better results.
You will need to fit a multimeter on amps or amp meter in the positive line to check results. Actual amps into the battery is what really matters.
Obviously with panel connected directly to the battery the panel voltage will be the battery voltage. The voltage of the panel is pulled down to the battery voltage. This is because of the internal resistance of the panel.
Thus you can test the panel by simply placing an amp meter across the panel terminals. A near dead short circuit. A horrible thing to do to a battery or generator but OK for solar panel. The panel label should show max current obviously in bright sun facing the sun.
What you get seems normal by way of voltages. Yes you hope fully would get a max 1.5 amps from the panel.
The controller is simply a throttle to reduce current as the battery gets near fully charged. So it may be out of adjustment throttling back prematurely. You test without controller should prove that. good luck olewill

 

[Lon nan Gruagach]

All,

Am seeking some trouble shooting advice. I have a 30w solar panel with an open circuit voltage of ~18v, in line with manufacturers spec. When I connect it to the controller, the voltage drops to 12.45v. I have checked the voltage at the built in solar panel cable to boat cable junction and again both are 12.45v either side of the joint. The solar panel volts at the controller are also 12.43 - so not too much loss. I have a dual battery set up with the engine battery volts at 12.83, the domestic battery is at 12.3. The controller led indicators all appear normal for battery charging. My battery monitor is only showing 0.1A of charge much of the time, best I have seen is 0.3A, I was expecting ~1A? After a week battery volts remain unchanged consistent with 0.1A?

Is there a problem with the controller, have the batteries gone past their useful life or am I missing something?

Thanks in anticipation....

So, what you ant to know is "Where have my missing 28W gone?"
There are a few places it can vanish.
1 If your solar panel controller has an output for load (usually the symbol is a light bulb) as well as the battery, then some will be going there if anything is powered.
2 The rating on the panel is for a much sunnier day.
3 Most likely is that the panel is designed to nurture a battery without a controller. It will not pump 2 and a half amps into a fully charged battery. The voltage, current output is such that at just over 12V the current drops off.

If you want 30W at 12V then you will need a Maximum Power Point Tracking controller (mppt). This will determine the optimum current to draw such that current times volts (power) is the most that can be drawn, sacrificing Voltage in the process. In order to output 12V it will also contain a dc - dc converter.

You can plot the volts to current response of your panel by measuring both while you add more loads (filament lamps are ideal for this)

 

[lw395]

All,

Am seeking some trouble shooting advice. I have a 30w solar panel with an open circuit voltage of ~18v, in line with manufacturers spec. When I connect it to the controller, the voltage drops to 12.45v. I have checked the voltage at the built in solar panel cable to boat cable junction and again both are 12.45v either side of the joint. The solar panel volts at the controller are also 12.43 - so not too much loss. I have a dual battery set up with the engine battery volts at 12.83, the domestic battery is at 12.3. The controller led indicators all appear normal for battery charging. My battery monitor is only showing 0.1A of charge much of the time, best I have seen is 0.3A, I was expecting ~1A? After a week battery volts remain unchanged consistent with 0.1A?

Is there a problem with the controller, have the batteries gone past their useful life or am I missing something?

Thanks in anticipation....

In full sun you should get much more than 0.3A from a 30W panel loaded to 12V.
I would suggest first testing the panel, load it with something like a couple of car brake light bulbs in series to start with.
I would suspect the controller is either duff or not wired up right.

 

[Foz]

All,

Many thanks for the tips. Have disconnected No.1 (domestic battery) and charged separately with smart charger. No2 battery left connected via onboard controller to solar panel - over the course of a week volts risen to 13.1. No.1 left on the bench to check voltage drop over the week - showing steady decline at ~0.2v per day! Bought a battery tester which revealed significant under capacity in 'cold cranking amps' when fully charged. Overall conclusion: No.1 battery past its useful life!

 

[johnyjf]

Where are you located and how is you Solar Panel Orientated? If the UK and horizontal are the answers then the output for much of the day is is not going to be much different from what you are measuring. If the panel is orientated to face south and sort of close to vertical then you should be doing better than 0.1A My 36 W South facing panels give 0.6-7A at best this time of year. Again the cloud doesn't help, some panels are better in diffuse light than others (crystalline v amorphous), can't remember which way round it is though at the moment.
Good Luck!

 

[whiteoaks7]

Have a read of this, it might explain a few things. http://www.pbo.co.uk/expert-advice/solar-panels-everything-you-need-to-know-24455 There's also a guide to how to calculate the actual input you can expect wherever you are in the world. Be wary of the cheap controllers sold on eBay btw the ones I tested for PBO were rubbish.