Solar Panel Controller Output Voltage

[sam_d]

Hi all, just a quick one that I couldn't find an answer to.

I bought a Projecta 80w Folding Solar Panel Kit in the sales recently and today I thought I'd get it out of the bag and give it a quick test.

The kit has a built in controller but when I measured the output voltage at the alligator clips (without connecting to a battery or anything) it is showing an output voltage of 21v.

To me this seems a bit on the high side and I'm a bit reluctant to connect it to my battery but I don't really know how the controller works.

Will the controller detect that a 12v battery is present and adjust the output voltage accordingly? Or is there something dodgy going on?

Thanks in advance for your help!

[Blknight.aus]

Set you meter up for amps and connect it up with the panel.under a blanket and the battery fully charged.

Remove the blanket, if you see a lot of amps cover it back up. The regulator isn't working

If the amps are minimal (less than 2) then cover it up and reconfigure so you can read volts, uncover the panel if the volts are below 14.8 let it go.

Some regulators look for a fairly high peak voltage to let them know that they can switch from a bulk charge setting to a float voltage.

In theory once the regulator goes to its float or sustain mode it should hold the battery at around 13.8 so long as the panel has enought light on it to keep up with the load.

The cheaper regulators can let full panel voltage through until thy have some kind of load on them, the inoedence of most volt meters is simply too high for them to register as a load to the regulator.

To test these if your worrworried about your battery or electronics is to use a headlight bulb with the same or higher combined wattage of the panel. Generally a 55/50 or a 60/75 works well. Start out with both filaments bridged and connect the earth then uncover the panel in full light. Check your voltages..
Remove the bridge and check again.
I'd your happy with that hook up the bulb to the battery then connect the panel, check the voltages and then Remove the bulb.

So long as you can put a tenporary load on the system that is higher than the panels output rating you can't kill the battery while the load is connected.

[sam_d]

Thanks for the reply.

I'll charge my car battery overnight and do the test tomorrow to see what I get.

Unfortunately my little multimeter wont do current over 2 amps so I'll go to Jaycar and get something a bit beefier tomorrow.

In the meantime I did a load test using a 12v cooler (I know this thing really sucks power). I connected the clamps and measured the voltage but it came up as 0v. I disconnected it and the voltage showed 19v again.

I then did a quick test on my car battery. That read 13.4v across the terminals without the solar charger connected and read the same with the solar charger connected. Again, when disconnected the voltage at the solar charger clamps was 19v.

Does this indicate anything useful?

[bee utey]

It's important to understand the characteristics of a solar panel. They drop output voltage very quickly as you add load. Your 80W panel would be lucky to put out 4.5 amps at 14 volts, even a dead short would only reach around 5 amps. Your regulator works by reducing the current whenever the output voltage rises above its regulated limit, but will still put out a very small amount of current to counteract the self discharge of a battery. Basically a solar panel with or without a regulator won't instantaneously explode your battery as the current is limited by the solar panel size. So the best test is to connect the volt meter to your battery, connect the regulator to the battery, and sit there watching the voltage. It should rise to around 14 point something volts and stay there. If it rises over 15, disconnect the regulator and have it checked. A few minutes of 15+ volts won't kill a battery.

[Blknight.aus]

You don't need to have a multi meter, I use a selection of bulbs to give on ththely current indication and limiting.

Wire a headlight bulb up in series with the panel positive and battery positive and it will glow brightly if the current is too high.

It's a trick I've been using. for ages when I need to do some quick current limiters for charging batteries. A dead flat battery hooked up onto my 60a feed to the back of my disco will pop out almost immediately if I wire it up via a headlight bulb it till the filiment is just glowing I can then put the direct connection on.

[sam_d]

Thanks for the help guys.

I'm going to have to put this one on hold for the time being - the weather looking a big cloudy for the rest of the week. Typical!

[DeanoH]

Hi Sam, is your solar panel something like this ?

PROJECTA 80W PORTABLE FOLDING SOLAR PANEL KIT IDEAL FOR 4WD OR CAMPING P# SPM80K | eBay


If so if you look at the last photo it states that the Voc which is the open circuit voltage of the panel, that is with no load, should be 21 volts.

This is perfectly fine, the regulator manages the panel output to match your battery. If the actual open circuit voltage (in sunlight) was less than 21 volts then you would have a problem.


Deano

[sam_d]

Hi Sam, is your solar panel something like this ?

PROJECTA 80W PORTABLE FOLDING SOLAR PANEL KIT IDEAL FOR 4WD OR CAMPING P# SPM80K | eBay


If so if you look at the last photo it states that the Voc which is the open circuit voltage of the panel, that is with no load, should be 21 volts.

This is perfectly fine, the regulator manages the panel output to match your battery. If the actual open circuit voltage (in sunlight) was less than 21 volts then you would have a problem.


Deano

Yup! That's the one!

So, it seems I've got nothing to worry about and have learned something about solar panels and controllers!

And, you know, none of this would ever have been asked if I'd not been curious and measured the voltage of the thing!

Thanks all!

[sam_d]

Well, with some unexpected sunshine this evening I thought I'd hook up the solar panel to my well charged battery.

There was a little bit of cloud cover but enough for 19.5v to be generated. I hooked with leads upto the battery with my multimeter in place and the voltage across the terminals started to climb from a start point of 13.4v.

Slowly but surely the voltage increased until it plateaued at 14.6v. It stayed at this level for a few minutes and then rapidly dropped back down once the light on the solar controller was telling me that the battery was fully charged.

I'm going to take this as being a successful test and that everything is working as it should.

[Blknight.aus]

Yep, it's doing absorbsion charge and the float.

What will be interesting will be to see what it does with a cyclic load on it during the day.