Solar panel low voltage

[oilybilge]

I have a 10w solar panel connected to my 110ah battery. Was told this would be enough for trickle charge. But although the panel gives out 13.8v when unconnected, when I connect it to the battery it drops to the standing voltage of the battery, 12.6v. So presumably it isn't doing any charging. Could it be there is just not enough sun in Suffolk, and I need a bigger panel?

 

[PaulRainbow]

I have a 10w solar panel connected to my 110ah battery. Was told this would be enough for trickle charge. But although the panel gives out 13.8v when unconnected, when I connect it to the battery it drops to the standing voltage of the battery, 12.6v. So presumably it isn't doing any charging. Could it be there is just not enough sun in Suffolk, and I need a bigger panel?

Not much Sun here at the moment.

 

[William_H]

The 10w solar panel should give 18 to 20v when not connected to a battery. This in full sunlight with the panel square to the arriving sun rays. Obviously with not much sun the voltage will lower. However a better test is to connect to a battery via an amp meter. You multimeter on amps should do nicely. This will tell exactly how much is going in to the battery.
Solar panels for 12v system are usually designed to give enough voltage to put charge into a battery so over 13 to 14v but to do so under less than ideal sun conditions. Hence they fit enough cells in series to give that 20 v open circuit. This promptly drops to the battery voltage under load. The solar panel voltage falls with load. The excess voltage is dissipated in the panel inherent internal resistance. olewill

 

[jiris]

I have a 10w solar panel connected to my 110ah battery. Was told this would be enough for trickle charge. But although the panel gives out 13.8v when unconnected, when I connect it to the battery it drops to the standing voltage of the battery, 12.6v. So presumably it isn't doing any charging. Could it be there is just not enough sun in Suffolk, and I need a bigger panel?

Trickle charging is defined as charging with current about 1/100th of the Ah capacity of the battery. In your case it should be 1 A.
Your 10 W panel can, under perfect sunlight, supply about 1/2 of that. Taking in account your geographic location, I would be probably considering 30 W panel.
The 13.8 V output is also rather suspect. Modern panels for 12 V systems have open voltage 18 V or more. The fact it drops to 12.6 V when connect is alone not too alarming. With the small output of your panel your instrument is unlikely to detect the difference.

 

[cindersailor]

I started using a 10 W solar panel a couple of years ago after I killed by battery by leaving it uncharged over the winter. Now when I arrive at the boat the battery voltage is generally around 13.8 V and I am happy that the panel is doing a reasonable job of keeping it topped up in my absence - and this is winter on the west coat of Scotland, so likely less sun than you are getting. If your open-circuit voltage is only 13.8 V I suspect it is not working as it should.

 

[macd]

If your open-circuit voltage is only 13.8 V I suspect it is not working as it should.

...that, or it's not rated for the OP's use. What's the specified open-circuit voltage?

 

[oilybilge]

Sorry, I should have mentioned that there's a basic sort of controller between the panel and the battery. I'd assumed this was limiting the voltage to 13.8v.

Many thanks for these helpful suggestions -- I'll try measuring the amps, and also the raw voltage from the panel. I haven't tested it in full sunshine yet because there hasn't been any...

 

[LittleSister]

I haven't tested it in full sunshine yet because there hasn't been any...

That's where you're going wrong. Your solar panel's probably fine, you just need a new climate!