# Solar charge controller ?

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#### Clarkdale44

##### Member
Hello

I have got one last confusion about charge controllers doesn't matter whether it is pwm or mppt.

Thing is i have seen many CC with variety of output amps on 12v and 24v with different manufacturers... But they are all different..

Which number in a charge controller defines that how many panals can be connected to it..?

For example..

All are pwm based except F

Charge controller A is 12v 30A and 600Wp panals can be connected. 75% efficiency

Charge controller B is 12v 30A and 500Wp panals can be connected. 90% efficiency

Charge controller C is 12v 40A and 750Wp panals can be connected. 98% efficiency

Charge controller D is 12v 20A and 550Wp panals can be connected. 70% efficiency

Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency

Charge controller F is 12v 40A and 600Wp panals can be connected. 99.2% efficiency

These are all different brands... I don't understand these numbers... Why are the manufacturers restricting users from adding more panals even though their unit can handle this much current?

For example

Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency

500/18.9 = 26 Amps... No where near 40.. It should easily handle 600Wp with 31Amps, then why are they restricting to 500Wp only?

Is it something am i missing?

Last edited:

#### ronsimpson

##### Well-Known Member
For example
Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency
500/18.9 = 26 Amps... No where near 40.. It should easily handle 600Wp with 31Amps, then why are they restricting to 500Wp only?
Is it something am i missing?
Where did 18.9 come from?

12v X 40a = 480w which is close to 500 watts.
I think the voltage to charge a "12V" battery is 15V.

Sorry for the funny graph below.
Voltage 0 to 15V
Current 0 to 40A
Watts 500 max
Must stay in the green area. Where the voltage is less than 15V and the current is less than 40A and below the 500W line.
Can not get in the white area or the red area. Start out with a low battery.
V=11, A=40, W=440.
V=12, A=40, W= 480.
V=13, A=38, W=500.
V=14, A=35, W=500.
V=15, A= 33, W=500.
Now the battery is almost full.
V=15, A=20
V=15, A=10
V=15, A=5 (trickle charge)

#### Clarkdale44

##### Member
Where did 18.9 come from?

12v X 40a = 480w which is close to 500 watts.
I think the voltage to charge a "12V" battery is 15V.

Sorry for the funny graph below.
Voltage 0 to 15V
Current 0 to 40A
Watts 500 max
Must stay in the green area. Where the voltage is less than 15V and the current is less than 40A and below the 500W line.
Can not get in the white area or the red area.

View attachment 101462
Start out with a low battery.
V=11, A=40, W=440.
V=12, A=40, W= 480.
V=13, A=38, W=500.
V=14, A=35, W=500.
V=15, A= 33, W=500.
Now the battery is almost full.
V=15, A=20
V=15, A=10
V=15, A=5 (trickle charge)

Thanks for the neat graph.. it helped...

18.9v is the panal voltage... I forgot in pwm power is wasted a lot... so 18.9 would become same as battery voltage once connected to it.

Won't the battery will be fried if charged till 15v?
Also How will you explain 12v 40A and 750Wp?
The only reason i can think of is panal efficiency.

Last edited:

#### ronsimpson

##### Well-Known Member
Won't the battery will be fried if charged till 15v?
Probably the battery is like a car battery. The regulator limits the voltage to 14.5 volts. (more or less)
If you have a car with a real voltage meter on the dash; In the morning the battery voltage is 12V and full charged. When the motor is running well (charging) the voltage will charge to about 14.5V.
Also How will you explain 12v 40A and 750Wp?
12v X 40a = 480 watts.
18.9v is the panal voltage... I forgot in pwm power is wasted a lot... so 18.9 would become same as battery voltage once connected to it.
Assume 100% efficient: (PWM)
18.9V at 10A in will give you 12v at 15.75a out
18.9v X 10a = 189 watts, 12v X 15.75a = 189 watts

A PWM is much like a gear ratio in a transmission. If you reduce the RPM you get more torque. If the speed of the shaft is reduced 2:1 then the torque is 2x more. (if no loss in the bearings)
-------------------------------
18.9v X 10a = 189 watts, 12v X 15.75a = 189 watts at 100%
12v X 15.75a = 189 watts - 18.9 watts of loss in heat = 170 watts.
OR
15.75A - 1.575A of loss = 14.175A
>>12v X 14.175A = 170 watts
----------------------------
A linear regulator looses energy on purpose.
18.9V at 10A in and 12V at 10A out. Heat loss = (18.9 - 12 = 6.9v) X 10A = 69 watts of heat loss.

A PWM regulator tries to conserve power not wast power.
If 90% passes through then 10% is lost in heat. ( not on purpose)
170 watts in and 153 watts out. or 17 watts of heat.

A PWM is real good if the voltage of the panel and battery are very different.
24V panel 12V battery
A linear supply will loose 50% of the power.
A PWM will loose 10%.

48V panel 12V battery
Linear will loose 75%, keep 25%.
PWM will loose 10%.

Hope this helps
RonS

#### ronsimpson

##### Well-Known Member
MPPT: Maximum Power Point.
This a controller that works to get the max power out of a panel.
This graph shows three light levers. 1000, 800, 600. Note at room temperature.
>If you short out a this panel it will only give you 6.8A at 0V =0 watts at 800 W/m2
>If you open up the wires you get 0A at 36V = 0 watts
>The MPPT is at 6A X 28V = 168W.
>This point moves with temp. and light.
>A MPPT controller works to find this point and pull the right voltage and current from the panel. Probably checks every second. This panel could be used with a 24V battery with out a controller because the charge voltage will be in the 24 to 31V range which is close to MPPT. If this panel was used on a 12V battery the voltage is all wrong and you need a controller. At 12 to 15V you can only get 1/2 of the power out.

#### Clarkdale44

##### Member
Probably the battery is like a car battery. The regulator limits the voltage to 14.5 volts. (more or less)
If you have a car with a real voltage meter on the dash; In the morning the battery voltage is 12V and full charged. When the motor is running well (charging) the voltage will charge to about 14.5V.

12v X 40a = 480 watts.

Assume 100% efficient: (PWM)
18.9V at 10A in will give you 12v at 15.75a out
18.9v X 10a = 189 watts, 12v X 15.75a = 189 watts

A PWM is much like a gear ratio in a transmission. If you reduce the RPM you get more torque. If the speed of the shaft is reduced 2:1 then the torque is 2x more. (if no loss in the bearings)
-------------------------------
18.9v X 10a = 189 watts, 12v X 15.75a = 189 watts at 100%
12v X 15.75a = 189 watts - 18.9 watts of loss in heat = 170 watts.
OR
15.75A - 1.575A of loss = 14.175A
>>12v X 14.175A = 170 watts
----------------------------
A linear regulator looses energy on purpose.
18.9V at 10A in and 12V at 10A out. Heat loss = (18.9 - 12 = 6.9v) X 10A = 69 watts of heat loss.

A PWM regulator tries to conserve power not wast power.
If 90% passes through then 10% is lost in heat. ( not on purpose)
170 watts in and 153 watts out. or 17 watts of heat.

A PWM is real good if the voltage of the panel and battery are very different.
24V panel 12V battery
A linear supply will loose 50% of the power.
A PWM will loose 10%.

48V panel 12V battery
Linear will loose 75%, keep 25%.
PWM will loose 10%.

Hope this helps
RonS

Last edited:
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