More solar panel questions.

[Tiddler]

Hi.

In order not to hijack the previous solar panel thread here are more questions:

1/ I have a couple of 1.3 watt amorphous panels left permanently in circuit with a 12 volt battery to keep it topped up. Assuming that the battery is somewhere near being fully charged, could any damage be done in doing this? As there is no control circuits I am assuming the battery will refuse the input as fully charged condition is achieved.

2/ Would having the above said panels in direct sunlight in open circuit damage the panels?

3/ Is it ok to leave the above said panels in circuit whilst the outboard motor (unregulated 4 amp charge) is running?

Many thanks for any light anybody can throw on these questions.


Regards.


Tiddler.

 

[Rigger Mortice]

1. The usual rule of thumb is that for a 100 AH battery you shouldn't have more that an unregulated 10 watt panel. Unless your battery is very small a couple of 1.3 watt panels will be fine. They won't do much either, but that is another matter.
2. No
3. Yes.

 

[Tiddler]

Thanks Rigger Mortice for your reply. I really just need them to keep the battery up when the boat is not in use and I really don't want to cook it either so all appears to be well then. when the boat is in use there is usually four or so hours a day when I can charge from the engine and I need the battery for lighting, phone charging, computer charging and wi-fi unit charging so all appears to be well. I also have another 4 watt briefcase type solar panel that I plug in if the boat is in use but not using the engine which appears to help somewhat.

Regards.

Tiddler.

 

[[2574]]

Tiddler,

you perhaps should understand how little your panels will do for you. I reckon at absolute best you'll get half an amp from the panels, more likely quarter of an amp. Assuming you get that for 8 hrs each day you'll be getting less than 5AH per day. Your laptop charger will likely draw a good deal more than that in one hour. The best plan would be to acquire some bigger panels.

Rob

 

[JumbleDuck]

1/ I have a couple of 1.3 watt amorphous panels left permanently in circuit with a 12 volt battery to keep it topped up..

you perhaps should understand how little your panels will do for you. I reckon at absolute best you'll get half an amp from the panels, more likely quarter of an amp.

If they really are 1.3W panels then he won't even get 100mA, since the 1.3W will be at more than 13V. I've heard "five times the watts" as a rule of thumb for daily output (seems a bit optimistic to me), which would mean 500mAh = 0.5Ah per day.That's not terribly much, to put it mildly.

 

[[2574]]

If they really are 1.3W panels then he won't even get 100mA, since the 1.3W will be at more than 13V. I've heard "five times the watts" as a rule of thumb for daily output (seems a bit optimistic to me), which would mean 500mAh = 0.5Ah per day.That's not terribly much, to put it mildly.

I was adding it all up - 2x1.3w + 1x4w is 6w, at 22v open circuit voltage is about 300ma. As you suggest it amounts to the square root of very little! Maybe they are 13w panels? That would make more sense.

 

[JumbleDuck]

I was adding it all up - 2x1.3w + 1x4w is 6w, at 22v open circuit voltage is about 300ma. As you suggest it amounts to the square root of very little! Maybe they are 13w panels? That would make more sense.

Whoops. I didn't see (in other words, I didn't read) the bit about "a couple of" panels. However, you didn't spot that the outboard (which I missed altogether) gives 4A, not 4W, so I think we're quits here. OK, OK, I did worse.

It's still not a great amount of solar oomph. The smallest panel I can find on the Maplin website is 5W ... OP, can you confirm your panel output?

 

[[2574]]

I also have another 4 watt briefcase type solar panel that I plug in if the boat is in use but not using the engine which appears to help somewhat.

Regards.

Tiddler.

Jumbleduck,

I think you might have misread the bit about 4A from the outboard!

Rob

 

[JumbleDuck]

I think you might have misread the bit about 4A from the outboard!

Oh bugger.

 

[Tiddler]

OP, can you confirm your panel output?

Hi JumbleDuck.

Thanks for your reply and thanks to everybody else too.

I have two 1.3 watt panels connected in parallel which are permanently connected to the battery via a fused circuit. These are there to keep a trickle charge to the battery when not in use. Also, when the boat is in use but without the engine running I park a 4 watt briefcase type solar panel on the cabin roof. This I believe will give me around a half an amp.

When the engine is running I get around 4 amps (4 by 12 = 48 watts).

Regards.

Tiddler.

 

[JumbleDuck]

In that case I think the answers are (1) no, leaving the two small panels connected will cause no damage (2) no, leaving them out in full sunlight won't damage them and (3) yes, absolutely fine to leave them connected with the outboard running, not least because they will almost certainly have a blocking diode in them to stop current flowing the wrong way.

 

[VicS]

Hi JumbleDuck.

Thanks for your reply and thanks to everybody else too.

I have two 1.3 watt panels connected in parallel which are permanently connected to the battery via a fused circuit. These are there to keep a trickle charge to the battery when not in use. Also, when the boat is in use but without the engine running I park a 4 watt briefcase type solar panel on the cabin roof. This I believe will give me around a half an amp.

When the engine is running I get around 4 amps (4 by 12 = 48 watts).

Regards.

Tiddler.

What JumbedDuck says but I dont think a 4 watt solar panel will give you ¹/₂ amp. Be lucky if its ever much more than ¹/₄ amp

Have you checked the outboard output. You may have to run at near WOT to get 4amps.

 

[Tiddler]

Thanks everybody for your replies. The way things are work well, I get adequate charging for my usage when the boat is in use and when it is not in use the battery is around fully charged so the little 1.3 watt panels provide a trickle to combat the slow discharge inherent in lead acid batteries. the main purpose of the original post was asking whether any damage would occur in my usage. Once again, thanks everybody.

Tiddler.