Attention all Solar Guru's!

Hi,
I have been having issues with my 12v system in the camper and was hoping someone may be able to help.
I keep running my battery flat despite having plenty of solar.

I have a CTEK D250S Dual, 1x 120AH AGM battery, and 2x 120w portable solar panels.
I had the solar panels in full sun today and connected up a "watt meter" and it showed that the panels were producing approx 20-40 watts each (ie 60-80 watts in total). Out of a possible 240w this seems quite low. Is this normal for a winters day?
My other problem...the CTEK is continually turning itself off and restarting. I was watching it for hours today trying to work out a pattern of when it restarts but I could not work it out. Sometimes it would keep charging when panels are only producing 10w, others it would turn off when it got to about 50-60w.
I am using 7 metres of 8 B&S cable from solar to CTEK. (Bypassing regulator on panel)
It also seems that when my fridge compressor kicks in, this also causes the CTEK to restart.

Any help would be much appreciated.
Tim
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Reply By: allanw - Sunday, Jun 23, 2013 at 23:03

Sunday, Jun 23, 2013 at 23:03
The amount of output from the solar panel is going to depend on the amount of sunlight actually reaching the panels and that is going to depend on the weather conditions and the angle of the panels relative to the sun.

i assume that you have the panels connected in parrallel, ie red-red, black-black.

In the middle of the day on a clear winters day you should be able to get the full rated output of a solar panel if the panel is facing the sun almost perfectly.

I think the first thing to test is the panels . Disconnect one of the panels from the CTEK and connect it directly to the battery (red to +ve, black to -ve), then measure the voltage and current (or the "watts" if you have a wattmeter). You should be getting around 12-14volts on the battery and up to 10 amps (though probably more like 7-8Amps) in the cable connecting the panel to the battery. If not then you need to do open circuit and short circuit tests on the panel.
Do the same with the other panel as well.
If the panels check out ok, you should get someone to test the ctek. I have read that they do strange things when connections are incorrect, but dont know much else about them.

Allan
AnswerID: 513687

Follow Up By: V8 Troopie - Monday, Jun 24, 2013 at 00:26

Monday, Jun 24, 2013 at 00:26
The above suggested solar panel test assumes the battery is low on charge, which might not be the case.

A far better way to test a solar panel's output is firstly to disconnect it from everything, chargers, battery, etc.
Then use a multimeter, set to DC about 30V+ range and directly measure the voltage at the panel terminals when the panel is in full sun.
This should correspond with the open circuit specs labelled on the back of the panel (~21V for a 12V nominal panel).

Next, set the multimeter to DC 10A range (the + probe might have to go into a different socket) and measure the short circuit current of the panel, again, this should correspond to the SC specs on the label.
If you did get a voltage reading above but no current then 2 things might cause it:
the meter's Amp range is blown - check meter's fuse.
the panel wire/ terminals / test leads have a bad connection.

BTW, with digital multimeters it does not matter which way its leads are connected to the panel, if they are the wrong way round the display shows a negative reading - that's all.

If both those measurements are OK you have eliminated the panel from your problem.
Using a watt meter is best done after its function is thoroughly understood. For example, one would only get the full panel output wattage reading if, and only if, the battery is very low on charge and *can* accept the full charging current available.
0
FollowupID: 792438

Reply By: Krooznalong - Monday, Jun 24, 2013 at 13:17

Monday, Jun 24, 2013 at 13:17
Tim
You didn't buy the panels from Mr Shonky on ebay did you? Can't recall his name but there are quite a few posts about him selling solar panels with inflated ratings. Have seen posts on this in last few weeks.
This may explain why they are producing less than expected.
AnswerID: 513719

Reply By: Nomadic Navara - Monday, Jun 24, 2013 at 14:54

Monday, Jun 24, 2013 at 14:54
Quote "I had the solar panels in full sun today and connected up a "watt meter" and it showed that the panels were producing approx 20-40 watts each (ie 60-80 watts in total). Out of a possible 240w this seems quite low. Is this normal for a winters day?"

That is an unusual way to measure your panels. What is the details of the meter you were using and how was it connected? The usual way to check your panels is to connect an amp meter across their terminals and measure the short circuit current. (Its safe to short out solar panels, they don't produce enough power to blow anything.) You should get around 14 A or a little more (7 A each one) short circuit current with the panels aimed square on to the sun. I can't comment on the "60-80 watts in total" unless I know how the tests were made.

Quote "My other problem...the CTEK is continually turning itself off and restarting."

Not sure about what you are worried about here. The D250S is an MPPT solar regulator. They periodically interrupt the charging to check the available output from the panel and adjust their operation to achieve the maximum possible charge rate.

Quote "It also seems that when my fridge compressor kicks in, this also causes the CTEK to restart."

This is a feature of most smart chargers. Their absorption stage maintains a constant voltage charge. With this constant voltage the charge current drops off as the charge level of the battery rises. When the charge current drops to a few percent of the chargers maximum the charger assumes the battery is fully charged and it switches to float charge.

When you draw some current from the battery, if there were no charger attached the terminal voltage will drop a little. With a charger in operation the charger supplies more current to counter the drop in that terminal voltage. If this increase in charge current exceeds the current where the charger switches to float voltage, the charger reverts to its full charge cycle. All the chargers I have had experience with will do this. I am yet to see one that advertises that it does not.
PeterD
Retired radio and electronics technician

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AnswerID: 513724

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