Solar Panel , how do I know it's working?

[Applescruffs]

Hello there.....

I've inherited a solar panel, I think it's from Maplin but as there is no led I have no way of telling if it actually works.

I've got a multimeter but it's been a long time since I've used one to measure voltage and current, I've only ever used it to check continuity.

Any hints or tips most welcome,

Cheers

 

[rob2]

You should be able to simply measure open circuit voltage from the panel and this will well exceed the battery voltage.

Rob.

 

[Kelpie]

You will need:
- a multimeter set to DC in a range of somewhere around/above 20v
- access to the bare wires of the panel
- a sunny day

Check that the panel can produce around 16v or more (I think this varies depending on the make/model/size). Avoid any shadows at all on the panel.

 

[Madhatter]

Don't do what my mate did yesterday when the sun stuck it's head out - he tongue tested it , what a plonker squealed like a stuck pig ,I couldn't stop laughing

 

[Applescruffs]

Hi and thanks for the replies, I set the multimeter to 200 v and tested across the wires....looked like 24 volts !

That seems quite a lot for a 12 volt battery....or is that good ?...t not even that sunny here !

I guess I can assume it's working then ?

Not going to try the ' tongue test, madhatter.....even I'm not that daft ! :0)

Cheers.

 

[ghostlymoron]

24v is on the high side. I've just fitted a 20w panel on 'Cobblers' together with a 5 quid charger I think it's open circuit voltage is around 18v. My charger has a green led to show when it's charging and three red leds to show the state of charge of the battery. If your registering above 14v, it's working.

 

[C08]

Don't do what my mate did yesterday when the sun stuck it's head out - he tongue tested it , what a plonker squealed like a stuck pig ,I couldn't stop laughing

My father who was an electrician had a mate who always tested light sockets for being live by sticking his thumb into the socket when he would get a tingle through the thick skin...until one day he stuck his thumb into a socket and dislodged one of the prongs which shorted out the mains and the heat essentially cooked his thumb.
Interestingly people vary tremendously in their susceptability to electric shock. I suppose it is to do with the natural dampness of individual's skin and skin thickness. As a lad I worked at the Mines Research Establishment where we used whole arrays of post office relays for scanning temperatures in coal dust explosions. These were 50V DC and all the people I worked with never bothered to switch them off and appeared only to feel a slight tingle. I would be literally knocked out, feel pale and shakey and would feel the effects for days. I can also feel 12v as a distinct tingle!

 

[johnalison]

I'm pretty sure my 36w panel gave something in the mid 20s when I checked it while fitting and I think this is quite normal. What matters is whether you need a regulator and this depends on the relation between the size of your panel and the battery bank, which I am not qualified to advise on.

 

[Scotty_Tradewind]

My old panels give in the low 20v's.

For charging I've seen a max of 7+ amps in mid summer with sun directly overhead,

In the last couple of years I havn't seen them charge at more than 6 amps.

Often I see around 3 - 5.5 amps.

 

[VicS]

Hello there.....

I've inherited a solar panel, I think it's from Maplin but as there is no led I have no way of telling if it actually works.

I've got a multimeter but it's been a long time since I've used one to measure voltage and current, I've only ever used it to check continuity.

Any hints or tips most welcome,

Cheers

You may find the early sections, including the one on the "Use of meters" in the boat electrical notes from Tom Brooks' TB-Training website useful

http://www.tb-training.co.uk/cover.html

As suggested measure the volts out from the panel in bright light when it is disconnected from the battery. Expect readings up into the low 20s in full sun.

Measure the battery volts with no load on. Expect a reading up to around 12.7 ish depending on the state of charge. A little more if it's recently been on charge .

Connect the solar panel and you should see the volts slowly rise, perhaps to 18volts or more without a regulator if the panel is performing.

When you understand measuring amps try that after discharging the battery a little. The current you see will depend up the size of the solar panel and by how much you discharge the battery.

You may be able to estimate the size , in terms of watts output, by comparing the dimensions with similar panels on the maplin website.


A common rule of thumb for needing or not needing a regulator is if the ratio of panel power to battery capacity is no more than 1 watt per 10Ah you do not need a regulator although one is usually recommended for panels in excess of 10 watts.

 

[William_H]

You need to be able to use your multimeter on amps range. Often up to 10 amps. This on cheap meters usually means moving the +ve plug in the meter to "10 amps" hole.
You cna then use this to measure current in to a 12v battery. Without a regulator you should measure about .5 amp for a 10w panel. (roughly30cms by 30cms.)
You can if you wish simply connect the amp meter across the wires of the panel alone. This will short circuit the panel but should show again about .5 amp for 10w panel.
(don't forget to return the plug and the switch to volts after this test)
This shorting the output would be a terrible thing to do to a battery but is OK for solar panel. The solar panel has an internal resistance so that power is wasted in the panel itself. it gets hotter but not damaging or to a noticeable degree. This also explains why it is OK to connect a panel generating 20 volts to a 12v battery. The current draw max for the panel will reduce the panel voltage to that of the battery. On the negative side the high voltage no load will mean that it can continue to pump current into the battery regardless of battery charge state.
So it can overcharge the battery to the limit of the panel capability. ie .5 amp for 10w. So this current will not damage a big battery but can damage a small battery or a big panel can damage a bigger battery. Often suggested 1% of amp hour rating of the battery in solar panel amps or in any case 10watts is max to eb used for battery charging without a regulator. The regulator in various ways will stop overcharging the battery. good lcuk olewill

 

[john_morris_uk]

I wouldn't worry about the open voltage figure of twenty plus volts. The panel won't be anywhere near that when it's connected to the battery. The battery voltage (on charge) should be at least 13.8 volts and will probably be nearer 14.5 (if that helps?)

 

[Seajet]

Applescruffs,

is there a diode and/or regulator with the panel ?

The diode prevents it discharging your battery at night, and the regulator from overcharging; my regulator on a 30 W panel has red and green LED's, green for good, charging - red for not so good !

A battery monitor installed on the boat is very helpful too, especially if relying on electrics such as depthsounder, gps, compass light etc.

 

[Applescruffs]

Bloody Brilliant Link !

Many thanks for that VicS....and all the other replies....that's probably enough for me to be getting on with for the time being .....I can't wait to try it out now.

Cheers,

 

[BruceDanforth]

I often do that with no squealing. Perhaps your mate is a bit of a drama queen?

Don't do what my mate did yesterday when the sun stuck it's head out - he tongue tested it , what a plonker squealed like a stuck pig ,I couldn't stop laughing