Author Topic: Solar panel output issue (Read 3805 times)

AbyssUnderground · « **on:** October 04, 2006, 11:12:00 AM »

Ive managed to get a sunny day here in the UK but I cant seem to explain why Im only getting 1.6A into my battery or when putting the panels under load from my 60w array (3x18w and 1x6w panels). When I short circuit the panels I get a much more respectable 3.5A, so why has it more than halved when it comes to charging the battery? The battery is low so I would assume its pulling all the current it can. I also put it under load to reduce the voltage to 11v, still no effect on increasing the current.

Is this normal and Im going insane or is there some other issue?

Ive adjusted the angle of the panels today to get the best current according to the short circuit current.

Flux · « **Reply #1 on:** October 04, 2006, 05:22:56 AM »

What is the open circuit volts? Normal 36 cell panels come out about 21v depending on temperature. If yours are less than that you will not get near the s/c current.

You have got them outdoors haven't you?

Flux · « **Reply #2 on:** October 04, 2006, 05:27:19 AM »

Actually 3.5A s/c is low for 60W. Try individual currents.

AbyssUnderground · « **Reply #3 on:** October 04, 2006, 05:34:57 AM »

OC volts is 22v. The individual currents are normal, its just into the battery thats low and the SCC is 3.5A which I would consider quite high for this time of year. Yes they are outdoors. They are on the roof of my shed.

Flux · « **Reply #4 on:** October 04, 2006, 07:02:11 AM »

What about lead resistance? Try measuring volts at the panel and at the battery.

It doesn't take a lot of resistance to spoil things. I still think your s/c current is low.

Flux

Flux · « **Reply #5 on:** October 04, 2006, 07:14:47 AM »

On second thoughts your 3.5A is reasonable. Try shorting the leads at battery end and measure volts at panel end.

Flux

AbyssUnderground · « **Reply #6 on:** October 04, 2006, 07:32:42 AM »

Ive done that and they are roughly the same. I am concerned about the thickness of the wire im using though, but it doesnt explain why it will do 1.6A to the battery but 3.5A SSC.

Flux · « **Reply #7 on:** October 04, 2006, 07:47:50 AM »

"Ive done that and they are roughly the same "

Yes they should be the same but what is the volt drop.

If you look at the curve for the panels you will find that they hold short circuit current up to about 14v, at about 17v the current will have fallen to the peak power value ( probably about 90% Isc)

This will normally give you close to the peak power current into a battery up to about 15V at normal temperature. If you loose a couple of volts in the line then you will be in trouble especially at higher temperature when panel volts fall.

For your short run, you should use cable heavy enough to keep volt drop minimal to get the best possible results.

dinges · « **Reply #8 on:** October 04, 2006, 07:49:50 AM »

It's a simple matter of elimination.

You've started the elimination process by measuring short circuit current.

Now, disconnect the battery and connect a 12V/4A (55W) car headlight. How much current does flow? 3.5A, or close?

Next, connect the battery to a normal battery charger. How much current does flow?

Finally, if you're worried about the resistance being an issue: connect the panel to the battery/charge circuit with short leads. Does this change things?

The battery is my prime suspect. But, sequential elimination of problems will lead you to the answer.

AbyssUnderground · « **Reply #9 on:** October 04, 2006, 07:56:13 AM »

Thanks for the list of things to try.

Im suspecting the cable is not that good as its only thin, but Ive run 7A through it and it gets slightly warm to the touch. Im going to get some twin core mains cable, 13A rated, would this do the job better?

The sun is gone now, so I wont be able to test until the weekend as Im in college every other day (today was my day off).

Opera House · « **Reply #10 on:** October 04, 2006, 07:58:16 AM »

Have you considered internal panel resistance? Is this one of those black amorphous panels?

ghurd · « **Reply #11 on:** October 04, 2006, 08:04:10 AM »

I don't see mention of upgrading the wire from the thin speaker cable. That is most probably the trouble. It would help, a lot, to change the wire to #12 (or 2.5mm if it's common). But #12 is still marginal.

Also retighten all the screws and nuts in the monitor box. Loose stuff can do strange things.

G-

Flux · « **Reply #12 on:** October 04, 2006, 08:08:53 AM »

Current rating gives you little idea of suitability, it is merely an indication of what it will take without over heating. Try to find a figure for resistance/unit length and choose something to keep your volt drop down to less that 1/2V total, lower if it doesn't raise cost to a silly level.

AbyssUnderground · « **Reply #13 on:** October 04, 2006, 08:10:44 AM »

I will be upgrading it soon as its my main suspect after speaking on IRC with a few chaps. Ill be getting twin core mains cable (13A) to do the job.

Thanks for the recommendation on checking the monitor box wire, never thought of that but most of the tests were done without the box anyway. Still, ill have to change the cable in that too.

fungus · « **Reply #14 on:** October 04, 2006, 08:46:15 AM »

Maybe if the battery was very full then there may not be much current anyway?

AbyssUnderground · « **Reply #15 on:** October 04, 2006, 08:47:40 AM »

Its not full.. Even with a load on it the current did not increase.

Countryboy · « **Reply #16 on:** October 04, 2006, 07:50:03 PM »

I know this is going to sound like a stupid question, but are your panels still indoors?

I seem to recall a solar panel problem not that long ago, which was due to your panels being indoors...

dinges · « **Reply #17 on:** October 05, 2006, 02:36:29 AM »

Abyss, I warned you yesterday: bend over and take it as it comes. Or rather: BOHICA.

The poor guy. He must be really amazed at the good memory some of the users on this board have. Ah well, think of it this way, Abyss:

'this hurts us a lot more than it will hurt you'.

craig110 · « **Reply #18 on:** October 05, 2006, 08:18:28 AM »

Where are you measuring the SSC, at the end of the wires where they would otherwise attach to the batteries or at the panels? Also, what gauge wire are you using and what is the length of the run between the panels and the battery?

Craig

AbyssUnderground · « **Reply #19 on:** October 05, 2006, 09:46:13 AM »

If you read the rest of the topic you would see I answered this question earlier.

AbyssUnderground · « **Reply #20 on:** October 05, 2006, 09:47:38 AM »

Both the panels and the house give the same SCC current.

The wire is too thin, I established thats probably the cause of the main current problem on IRC yesterday. Its only speaker cable, but it handled 7A happily, then I was told resistance was the issue at this current, even though it could handle it.

jimjjnn · « **Reply #21 on:** October 05, 2006, 01:05:55 PM »

If the wire to the batteries is getting warm, that is the best indication that you are losing power to heating of the wires. Go with larger guage wire and I think problem will clear up.

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Author Topic: Solar panel output issue (Read 3805 times)