24/12 volt

[Henry's Cat]

Should I buy extra solar panels, and have 24 volts coming from solar panels, whilst still only having a 12 volt battery?

 

[Daddy Tanuki]

henry,

you will need to have above 14.7 volts in order to charge a battery with solar panels so minimum would probably be about 20 volts give or take. you would then need a controller of some sort, that controls the voltage that the battery receives.

now depending upon the chemistry of your battery you would need much more to charge the battery in the solar day.
simply put certain chemistries need more time to fully charge then others as the internal resistance of the battery rises the closer it gets to being fully charged.

take lead acid for instance say its at 50% which is the recommended lowest normal state of charge for lead acid it charges fast to about 70% maybe an 2 or 3 hours or so depending upon how much juice you can give it, and then the resistance rises high enough that it might take an additional 4 hours as it tapers down to receive a full charge and then go into float. that leaves you one or two hours shy of getting fully charged which for lead acid is an absolute must to be fully charged at least once a week, preferably more often for long life.

if so it would make sense to have more panels and power to get it up to the initial 70% as quickly as possible to allow it to slowly finish the charge in the remaining hours available.

lithium on the other hand is so low in its internal resistance that you can have just enough panels to get it charged in your 5-6 hour window that there is not a real need to over panel, (this is very location dependent).

why don't you give us some more information, location within the UK (for solar calculations) what sort of battery, what sort of charge controller, how many panels of how many watts, HOW MUCH ARE YOU DRAWING TO POWER OTHER THINGS WITH THE SAME PANELS WHILE TRYING TO CHARGE? (caps because this is very important as well...)

good luck and get back with us.

 

[Henry's Cat]

I currently have two 100 Watt 12 volt solar panels, connected in parallel, into a charge controller, and a 105Ah 12 volt lead acid battery.

I'm just north of London.

I plan, I have an idea to add two more 100 Watt solar panels, then connect,

100W Pv________|
100W Pv________|
|-Charge controller --12v battery
|
100W Pv________|
100W Pv________|

 

[Daddy Tanuki]

OK can you take a photo of the label on the back of the panel? it has a bunch of specs we need to see. and jsut because it says it is a 12 volt panel does not mean it puts out 12 volts...

also if you can give us the model or the specs for your controller will let us figure out how much it can handle.

 

[Henry's Cat]

I'm so sorry, this is cool, Ty for your reply.

I have an epever 40 Amp charge controller.

I do appreciate your reply, but feel the points somewhat moot.

-------------------

So, ideal world, I have solar, giving out 24 Volts/ 200 Watts. This is fed into Charge controller (I use 40Amp Epever),

I would then want a 24 Volt battery, but batteries are expensive and I wish to carry on using my 12 Volt battery with my system.

I'm not being rude, but it is more a hypothetical question, rather than a practical here and now question (though it likely will happen at some point).

 

[rodrick]

I'm so sorry, this is cool, Ty for your reply.

I have an epever 40 Amp charge controller.

I do appreciate your reply, but feel the points somewhat moot.

-------------------

So, ideal world, I have solar, giving out 24 Volts/ 200 Watts. This is fed into Charge controller (I use 40Amp Epever),

I would then want a 24 Volt battery, but batteries are expensive and I wish to carry on using my 12 Volt battery with my system.

I'm not being rude, but it is more a hypothetical question, rather than a practical here and now question (though it likely will happen at some point).

I don’t think you quite understand what voltage is required for your system to work, your 24 volt system with 200 watts wouldn’t charge a 24 volt battery you need to be 5+ volts higher than your battery full charge voltage

your 40 amp Epever can take 100 volts dc and it will lower the voltage to the battery requirements while increasing the amps

you can put 600 watts on a 12 volt system with that scc with very little over paneling. The Epever scc can typically handle up to 50% over paneling

so the answer to your question is yes with more panels you will charge faster on a sunny day and it will help on low pv days to get your battery to a full charge

 

[MrNatural22]

Two 12v panels in series for 24v 1 MPPT charge controller 1 12v battery
Connect battery to charge controller first so controller knows battery voltage.
Then connect your two 12v panels in series (24v) to the charge controller.
Your 12v battery will be charged at correct voltage.
Does this help?

 

[mikefitz]

I have solar, giving out 24 Volts/ 200 Watts. This is fed into Charge controller (I use 40Amp Epever

Let's try to clarity the situation.
Take the Epever solar controller, this unit converts solar panel power into a voltage suitable to charge a battery. There will be a maximum limit on the panel voltage input to the controller (100 volts), and the controller has a maximum current output (40 amps). Additionally the panel voltage needs to be around 4 to 5 volts higher than battery volts to 'wake up ' the controller.

The '12v' 100 watt panels will have an OC volts around 22 volts and a maximum power volts around 17 volts.

wish to carry on using my 12 Volt battery

There is no problem in keeping a 12v system with more panels apart from the practical aspect of not overcharging the battery. The 105 Ah battery , idealy for long life, should not be charged at too high current, 10 to 15 amps for sealed battery, 15 to 25 amps for AGM battery.

Consider the situation with two 100 watt panels and your 12v battery. With the panels, either series or parallel connected, the charge current at a charge voltage of 14 volts, will be a maximum of 200/14 = 14 amps. This would be under ideal conditions, in reality not much more than 10 amps.
Adding two more panels will double the current. The better arrangement of panels would be two in series, connected to a further series pair.

In summary, 1, so called '12v' panels have a voltage 17 to 22 volts, and 2, the controller automatically converts panel power to a suitable charge voltage.

Mike

 

[BillWNC]

Two 12v panels in series for 24v 1 MPPT charge controller 1 12v battery
Connect battery to charge controller first so controller knows battery voltage.
Then connect your two 12v panels in series (24v) to the charge controller.
Your 12v battery will be charged at correct voltage.
Does this help?

This is the simple answer that's useful to beginners. I've got a 40 amp renogy rover. I'm still a bit unclear how many watts I can input at 12 volts and 24 volts.

 

[Reed Cole]

This is the simple answer that's useful to beginners. I've got a 40 amp renogy rover. I'm still a bit unclear how many watts I can input at 12 volts and 24 volts.

The manual says 520 watts for a 12v system and 1040w for 24v system.

This checks out as it's a 40A charger.
W/A=V
520w/40a=13V.
1040/40=26v

But that number is really how many watts the unit can output, you could have 3 x 200w panels for a 12v system and be fine as long you don't exceed the maximum input voltage of 100v.