Solar

Assume you take a discharged 12v 300Ah battery bank and charge it with 600-watt solar panels under ideal summer time light conditions. How many hours will it take for the bank of batteries to be fully charged? Could you please show me how to do the calculation. Salamat po !

Wh = V x Ah  (12v x 300Ah)
Wh = 3,600 Wh

Hours = Wh ÷ 600w  (3600Wh ÷ 600w solar panels)
Hours = 6 hours to charge (if battery is fully discharged)

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Battery back-up power: Calculating power consumption

Example 1 (In watts):
Battery voltage = 12 volts DC with 115 AH (AmpHours)
12 volts x 115 AH = 1380 watts

Assume you want to use 80% power of the battery:
1380 watts x 80% = 1104 Watts available for use

Assume you have a light that consumes 25 watts:
1104 watts divide by 25 watts = 44 hours (you can run this light non-stop for 44 hours)

 

Example 2: (In amps):

Battery voltage = 12 volts DC with 210 AH (AmpHours)
210 AH divide by 20 HRS = 10.5 amps available for use.
210 AH divide by 2 (50%) = 105 AH available for use.

Assume you have an 12 volt inverter rated at 400 watts.
Divide 400 watts by 12 volts = will give you 33.33 amps

105 AH divide by 33.33 amps = will give you 3 hours of run time.
 

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*Calculating power consumption example
1 Battery = 115AmpH               Inverter = 1800 Watts
12 v x 115AmpH = 1380 Watts
1380 w x 80% projected usage = 1104 Watts (usable power from battery)

1 CFL = consumes 26 watts
1104 w ÷ 26 watts = 42 hours (will run continuously)

1 LED small light = 6.7 watts
1104 w ÷ 6.7 watts = 164 hours (will run continuously)

1 LED bigger light = 12 watts
1104 w ÷ 12 watts = 92 hours (will run continuously)

1 TV & DVD = 55 watts
1104 w ÷ 55 watts = 20.7 hours (will run continuously)

1 Laptop = 56 watts
1104 w ÷ 56 = 19.71 hours (will run continuously)

Total watts when all devices are running = 120 watts (as shown on video but mathematically the combined watts would be 155.7 watts

1104 w ÷ 120 watts = 9.2 hours (all devices will run @ 9.2 hours)

  1104 w ÷ 155.7 watts = 7.09 hours (all devices will run for 7.09 hours)

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CPAP = .25 amps. AC

P= I x V (.25 A x 120 V) = 30 Watts
1104 w ÷ 30 watts = 36.8 hours (continuous use)

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Convert watts to amps

Actually, watts is the fundamental unit of power and watt-hours is the energy stored. The key is to use the watts you know to calculate the amps at the battery voltage .

For example, say you want to run a 250 watt 110VAC light bulb from an inverter for 5 hours.
Watt Hours = watts x hours
1250 Watt Hours = 250 watts x 5 hours

Account for the efficiency of the inverter, say 85%

Watt Hours = watts x hours ÷ efficiency
1470 watt hours = 1250 ÷ 0.85

Since watts = amps x volts divide the watt hours by the voltage of the battery to get amp-hours of battery storage

Amp Hours (at 12 volts) = Watt Hours ÷ 12 volts = 1470 ÷ 12 = 122.5 Amp Hours.
If you are using a different voltage battery the amp-hours will change by dividing it by the battery voltage you are using.

To calculate how many amp-hours storage you need:
Use your average daily usage in watts and divide by the battery voltage. For example, if you use 5 kwh (kilowatt-hours) per day, and have a 48 volt system, then dividing 5000 by 48 gives you 105 AH. Since you do not want to discharge the battery more than 50% in most cases, you would need 210 AH. If you want to keep running for 4 days of bad weather with no sun, multiply the previous result by 4, which brings you about a 850 AH total capacity.

How many Watt Hours in a battery?
Multiply battery voltage times amp-hours.
For example a 12 volt 240 AH battery can supply (under perfect conditions and to 100% discharge) 12v x 240 AmpHr = 2880 Watts.  For a result in kilowatts, divide watts by 1000.  The above example would give you a result of 2.88KWH

What size of battery to run a 300W, 12V inverter?
300 watts divide by 12 volts = 25 amps
Then divide 25 amps by 0.85 (85%)
You get 30 amps.

https://www.redarc.com.au/300-1200-1500-2000-watt-inverter-amp-draw

How to calculate battery size for inverters of any size:
Run time in hours multiply by Inverter wattage = (total watts) divide by (DC volts) = Amps required

https://theinverterstore.com/portfolio-items/how-many-batteries-do-i-need-for-my-inverter/

Cable Size Guide Link:
https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator

What are Amp Hours?
Lead Acid Battery Amp Hours (AH) Specification Defined
The Amp Hour (AH) specification provides a measurement of battery capacity.  In other words, it is an indication of how much energy can be stored by the battery. A typical Amp Hour specification might read, “100 AH @ 20HR”.

The specification is saying that the battery will provide 5 amps of current at a useable voltage continuously for 20 hours.  The “5 amps” was calculated by dividing 100 by 20. Similarly, a battery with a specification that reads “150 AH @ 15 hours” will provide 10 amps of current at a useable voltage continuously for 15 hours. It should be noted that a useable voltage is considered to about 10.5 volts and above on a battery that is under load (or has devices connected).

IMPORTANT! Having defined the AH specification, it is important to understand what the Battery Specification does not say.

https://www.youtube.com/watch?v=xRN_FFghlQE
Example:
12 volt battery rated at 210 AH
210 AH divide by 50% projected usage =  105 AH
To use a 12-volt Inverter rated at 400 watts, divide 400/12= 33.3 amps
105 AH divide by 33.3 amps = 3.15 hours of continuous use.

A Common Misunderstanding Associated with Amp Hours
Consider the 100 Amp Hour battery. As indicated above, it will provide 5 amps of current for twenty hours while maintaining a voltage above 10.5 volts.

A common mistake is made when it is assumed that the 100 AH battery will also provide 100 amps for 1 Hour.  It won’t.  In fact, a battery of this type may only provide about 40 minutes of continuous 100 amp service at best.

This is due to a well known characteristic associated with lead acid batteries. Specifically the capacity will decrease as the rate of discharge increases.

In other words the relationship between battery capacity (how much energy is available) and the rate of discharge is not a linear one.

The phenomenon being described here is known as Peukert’s law.

Other Amp Hour Rates
As indicated above, the Amp Hour specification on 12 volt batteries is normally based a twenty hour rate. In fact, the specification is so standardized that battery labels often do not include this information.

That said, it is important to be aware that deviations from this norm are not uncommon. Some battery manufacturers will establish different rates for their amp hour specification. For example five and ten amp hour rates are not uncommon. In the case of a battery manufacturer who specifies a 100 AH based on five hour rate, the claim is that the battery will provide 20 amps for five hours before dropping below 10. 5 volts.

Determining How Long a Battery Will last Using Amp Hours
While you may be able gauge the relative capacity of one battery compared to another, you may have some difficulties when you try to determine exactly how long your battery will last. There are a couple basic reasons for this.

First, the AH rating is one that is based on a specific period of time and a specific current draw. Because of Peukert’s Law, the relationship is not linear, therefore simple calculations are not always practical. Second, current draw is rarely constant in most vehicle applications. Some times all the lights are on, sometimes they are not. Sometimes the stereo volume in turned up and sometimes it is turned down. This very dynamic environment makes it difficult to determine exactly how long a battery will last. As previously mentioned, the AH hours is gauge that is useful for relative comparisons. When comparing one battery to another for example, the Amp Hour specification will tell us that a 120 amp hour battery will have more capacity than a 80 amp hour battery.

Building a portable solar power system (Fuse &/or Breaker Size)
https://www.youtube.com/watch?v=9BgM0PWPjZU
12 volt battery; 100AH
12 volt Inverter; 2000 Watts
Fuse or circuit breaker between battery & inverter is rated at 200 amps.
You typically want this fuse or breaker sized to 125% of the continuous rated capacity of the inverter (multiply nominal current by 1.25).

Fuse or circuit breaker between charge controller & battery is rated at 50 amps.
You typically want this fuse or breaker sized to 125% of the rated current output of the charge controller. So 40 amps x 1.25 = 50 amps.

https://youtu.be/FjUqEEPzJZU

https://www.youtube.com/watch?v=WhZ4b8EzS-Q

https://www.youtube.com/watch?v=eWi3cZOR6wo

https://www.youtube.com/watch?v=ogleRE50Q3Q&t=227s

 

 

 

 

 

 

 

 

 

 

 

 

Cable Gauge Size Conversion: