Run time refers to how long a lead acid battery charge will last under a given load. We will assume the battery has full charge beforehand. How long this lasts depends on three things. First, the mechanical condition of the battery, and secondly the amount of current the load draws. The third factor is the integrity of the system, namely the inverter and the wires that join everything up.
The Formula to Calculate Battery Run Time
We will assume 100% efficiency between the battery and the appliance for purposes of this discussion. Although in practice, this seldom is the case.
We use the formula: (10 x battery capacity in amp hours) divided by (appliance load in watts). This information appears on the lead acid battery label and in the small print on the appliance.
Say we are going camping and want to know how long we can run a 100-watt television off a battery rated 60 amp hours. Using our formula the calculation is [(10 X 60) ÷ 100] = 6 hours maximum run time. We recommend recharging after four hours in these particular circumstances. Since running a lead acid battery flat is bad for its health, and reduces future run time.
Tips for Happy, Healthy Batteries and Their Owners
Try to prevent a lead acid battery discharging completely. The maximum discharge depends on the battery type. The quickest way to ruin one is running it ‘flat’ and leaving it in that condition. Be extra careful when working with a lead-acid battery too. It contains acid and packs a powerful charge.
You are in the presence of volatile fumes when topping it up. These fumes could ignite in the presence of a cigarette or spark.
Therefore please play it safe. Remove watches, rings, necklaces, and bracelets.
Wear safety goggles and be extra careful to avoid a dead short between the terminals with a spanner. Because this could permanently bring your battery run time down to zero and that we do not need.
Related
Sealed Lead Acid Batteries – The Basics
What Is An Ampere Hour Rating (Amp Hour or Ah) of a Battery?
6 Comments
I think yours is more accurate. The multiplier is the battery voltage. For two 12V batteries, it will be 24 and for a single 2V battery it will be 2.
Thanks
Running 100 watts on a 60ah battery for 7 hours is too generous . let’s do the math .
When you multiply 12v to 60 ah you get 720 VAh not 720 watts . 100 watts = 125VA @ 80% . 720 VAh/ 125 VA = 5.76 hours .
Off grid living has turned me into that guy I used to hate lol .
Benny
How do they get 125
I can’t understand why it came up with 6 hours as the final unit. If you have:
10 x 60 Ah then it’s 600 Ah divided by 100 W is 6 Ah/W which is confusing. It’s also not stated if Batteries were connected in Series/Parallel or the voltage requirement of the television.
Actually they say in the article they are assuming 100% efficiency, but then multipliying times 10, that 10 instead of 12v is where they are actually considering losses between battery, cables, inverter, etc. I always use 10 multiplier instead of 12, also for simplicity in my head
I think *10 is more preferable since you won’t utilise 100% of the battery charge, some will be lost in form of heat.