Noob Question - Solar Panel Voltages

[MrBEEF]

Hey Guys,

New to this forum, new to solar cells, but not new to electronics.

I am looking to design my own Solar <==> Battery <==> AC power system. I see a lot of already made controllers on amazon for dirt-cheap. Some have pictures of their ciruitry of what is inside..seems like some sort of a current control circuit using some IRF MOSFET and some other stuf I can't tell. Anwyays, there is also some MPPT IC's such as the one from TI, and so on. On Amazon, these controllers are using 12V batteries and 12V solar panels. For these MPPT IC's and well for any general circuitry, the incoming source(panel), has to be greater than the battery. So I think I am missing some info on the solar panels. I do not see how a 12V panel can charge a 12V battery using MPPT, when MPPT basically use Buck Regulators with a voltage tracking algorithm.

So I guess my question is when I go on amazon and find all of these 12V panels, are they actually used to power 12V system but THEIR ACTUAL output vooltage is higher...kinda like alternators run like 13-14V, while a car battery is 12V?

I think I am missing some details...any help would be great!

Thanks guy, solar seems to be a fun hobby,
-MrBEEF

[PV_boy18]

A 12v solar panel produces around 17v of max voltage . That voltage will be step down by the charge controller to somewhere around 14v to charge the battery. Thats why the solar panels produces higher voltage.

[inetdog]

...

So I guess my question is when I go on amazon and find all of these 12V panels, are they actually used to power 12V system but THEIR ACTUAL output vooltage is higher...kinda like alternators run like 13-14V, while a car battery is 12V?

I think I am missing some details...any help would be great!

Thanks guy, solar seems to be a fun hobby,
-MrBEEF

That is absolutely right. The MaximumPower
voltage of a nominal 12 volt panel (Vmp) will typically be 18 volts or more and the Open Circuit Voltage (Voc) will be even higher. The output voltage needs to be as high as 14.8 volts for some batteries at some times, and the input voltage has to be high enough to give some room for the controller work.
When you use a Pulse Width Modulation (PWM) controller for which the input and output currents are identical it is not good to make the panel output voltage too high.
But with an MPPT controller (with a decent input range) you can use much higher voltage panels (~36 volts or more) which are primarily intended for Grid Tie systems and you can put multiple panels in series to reduce the amount of current the wires need to carry.

Keep looking at the sticky threads for additional basic information.

[Naptown]

A 12 V panel will at max power or Vmp produce about 18V.
Open circuit or Voc is in the 22V range.

[MrBEEF]

That is absolutely right. The MaximumPower
voltage of a nominal 12 volt panel (Vmp) will typically be 18 volts or more and the Open Circuit Voltage (Voc) will be even higher. The output voltage needs to be as high as 14.8 volts for some batteries at some times, and the input voltage has to be high enough to give some room for the controller work.
When you use a Pulse Width Modulation (PWM) controller for which the input and output currents are identical it is not good to make the panel output voltage too high.
But with an MPPT controller (with a decent input range) you can use much higher voltage panels (~36 volts or more) which are primarily intended for Grid Tie systems and you can put multiple panels in series to reduce the amount of current the wires need to carry.

Keep looking at the sticky threads for additional basic information.

Hey guys,

Thanks for the reply.....that is just weird to me...but I guess they do this '12V' label b/c it's easy for non-engineers to understand that it will work for 12V system.



For me, and my little hobby project, I was going to use TI's BQ24650 MPPT IC(they can run 6-cells, and high VIN), and then use Diode OR'ing from the panel and the battery, going to the load. The problem is that if I use a 24V panel and a 12V battery, my load voltage varies by 12V, which means I also need a 12V buck regulator for my 12V load. IF I get the panel voltage to 12V(18Vmp), this may work, and I can use a Liner regulator, but then my efficiency will be poor...ehhhh...

I am basically building my own controller....reason you ask? Well I need a specific form factor. ...very thin and skinny PCB....low profile..

Anyone know of the smallest MPPT's in market?

Any other advice from the experienced would be great...

Thanks guy,
-MrBEEF

[FloridaSun]

Anyone know of the smallest MPPT's in market?

smallest I know of, ok for hobby work, $40 delivered from fleabay....

System Voltage 12V∕24VAuto switch
Charging mode MPPT
Rated Charging Current 10A
Max PV Input 50V
Max Solar Panel 130W(12Vsystem)∕260W(24Vsystem)
Waterproof Class IP68
Dimension 104*81*28.3mm
Weight 360g

[hillmanie]

PWM Charge controllers, maximum input voltage

Hello
On a related issue - no prob. to you gurus - can I join two 30A solar charge controllers in series to double the max input voltage. Example, 30A 12/24 PWM controllers where the solar panel array puts out eg. 40, maybe 50V? Most I've seen quote PVs in the 30s. I note from sales specs that the more expensive MPPT types can safely handle the above Vs and more.
Thanks for any advice
(Hope I've got my terminology right!)

A 12 V panel will at max power or Vmp produce about 18V.
Open circuit or Voc is in the 22V range.

[inetdog]

Hello
On a related issue - no prob. to you gurus - can I join two 30A solar charge controllers in series to double the max input voltage. Example, 30A 12/24 PWM controllers where the solar panel array puts out eg. 40, maybe 50V? Most I've seen quote PVs in the 30s. I note from sales specs that the more expensive MPPT types can safely handle the above Vs and more.
Thanks for any advice
(Hope I've got my terminology right!)

No you cannot.
What you can do is split your panel array in half and wire one half to each CC. You also cannot just put two CCs in parallel on the same panel array even if they are both charging the same battery bank.

[hillmanie]

CC series/parallel question

Many thanks for advice Inetdog. Else must save pennies for a good MPPT controller.

No you cannot.
What you can do is split your panel array in half and wire one half to each CC. You also cannot just put two CCs in parallel on the same panel array even if they are both charging the same battery bank.

[Sunking]

A PWM controller actually doe not do much of anything except turn itself off or on. If your battery is discharged, the PWM controller connects the panel directly to the battery. A PWM controller is nothing more than a switch, and a solar panel is nothing more than a current source.

If you take say a typical 100 watt solar panel which has a Vmp of 17.8 volts and Imp of 5.61 amps, and connect it to a 12 volt battery, the charge current is 5.61 amps. Use a PWM controller and the max charge current is the same 5.61 amps @ 12 volts = 67 watts.

[hillmanie]

Thanks for clarification on PWM cc

Having looked at quite competitive pricing for MPPT CCs I will shortly have one as the PWM price difference doesn't make it worthwhile.
Rgds

A PWM controller actually doe not do much of anything except turn itself off or on. If your battery is discharged, the PWM controller connects the panel directly to the battery. A PWM controller is nothing more than a switch, and a solar panel is nothing more than a current source.

If you take say a typical 100 watt solar panel which has a Vmp of 17.8 volts and Imp of 5.61 amps, and connect it to a 12 volt battery, the charge current is 5.61 amps. Use a PWM controller and the max charge current is the same 5.61 amps @ 12 volts = 67 watts.

[SunEagle]

Having looked at quite competitive pricing for MPPT CCs I will shortly have one as the PWM price difference doesn't make it worthwhile.
Rgds

I understand your reasoning concerning why should I spend that much more for something but I have to agree with the others that even though the MPPT charger costs more it is worth it for anything other than a very small system.

What you save in $ by buying a PWM charger you will need to spend on more PV panels. It's just math.

Take the example from Sunking concerning a 100watt panel. If you really need 400 watts of charging capacity then 4 - 100 watt panels on a PWM charger is really only about (4 x 67 = 268 watts). To get up to the 400 watts you need to purchase 2 more 100 watt panels (6 x 67 watts = 402 watts). Even at a cost of $1/w you have to spend another $200 on panels instead of putting it on a MPPT charger which also gives you many more voltage input options.

[hillmanie]

step-downs high wattage wirewoundsIt's just math etc

Sure thing. The math applies even in my case which is not main stream solar user and may never get that far even. Let me explain - I'm just beginning to experiment with the battery charging side of things and may never go farther than buying my first modest powered panel. Even so and at the lower priced end of controllers the MPPT isn't painfully more expensive than the PWM.My interest began when I read about using an arc welder for battery charging in another forum - and I have just such an animal virtually unused lying around in my garage and likely to remain so. Plus I have al the bits 'n bobs like step-down tfr, diodes, voltage droppers and various meters/hardware at no incremental cost.
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[QUOTE=SunEagle;70189]I understand your reasoning concerning why should I spend that much more for something but I have to agree with the others that even though the MPPT charger costs more it is worth it for anything other than a very small system.

What you save in $ by buying a PWM charger you will need to spend on more PV panels. It's just math.

[Sunking]

My interest began when I read about using an arc welder for battery charging in another forum

You need to get away from that Forum. That is a sure fire recipe and a good way to make a battery explode.

[SunEagle]

You need to get away from that Forum. That is a sure fire recipe and a good way to make a battery explode.

Or weld it to the ceiling.