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Scott, Auto Service Technician
Category: Car
Satisfied Customers: 1190
Experience:  A.S.E. Master ,Chrysler Master, 33yrs experience
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Calculating the Total Energy Content of Batteries.

How do I calculate the total energy content of a car battery or a golf cart battery?

NAPA model 8146

Model 8270,

I want to use an inverter to convert DC to AC for an energy power pack.

I would add more details, specifications of these batteries, but I cannot, due to the character limitations placed on me by this web site.

Customer: replied 8 years ago.
Reply to Scott's Post: NAPA model 8146 batteries. I was given the following information about each battery. It is 6 volts. It has a reserve capacity of 132 minutes. Cranking amps 488. Cold cranking amps 235.

I understand how to calculate energy content in terms of volts, amps and time. But there are two different kinds of amps, and the reserve capacity is not clear. Does the reserve capacity of 132 minutes mean that I get a full 6 volts for that period of time, or does the voltage decrease in a linear or non-linear fashion? This would have some bearing on the total energy calculation. I want to calculate how many KWH’s of energy I can get out of each battery. Furthermore I don’t know if a set of golf cart batteries is assembled in a parallel or series configuration, or perhaps a combination of both. And does the way in which they are configured have a significant effect on how much total energy I can get from all 6 batteries.

NAPA makes a 12-volt battery, model 8270, which is a deep cycle battery with the following specifications. Reserve capacity of 150 minutes, 625 cold cranking amps and 770 cranking amps. Perhaps this would be a better battery to use. Still I need to calculate the energy capacity of this battery to compare it with the previous 6-volt model.

I am looking at the possibility of making a battery storage unit configured in such a way that I can combine them with an inverter and use them to run a concession trailer for 6 to 8 hours, recharge them at night, and use them again on a daily basis.
Or perhaps there is a still better battery that someone could advise me of, which would be still more suited for this task.

Furthermore I will need a DC-AC inverter. The concession trailer has two separate 120v circuits. Should I get a 240v inverter and split off the circuits from it, or should I get two 120v inverters and use them separately. I have a feeling that I should get the 240v inverter so it could adjust its output to whichever circuit was demanding power. Otherwise I would have to buy two oversized larger than needed 120v inverters.

I notice that large capacity inverters cost quite a bit more than smaller ones. Is it possible to use several smaller cheaper inverters and run them in a parallel configuration so as to achieve the total amount of power needed?

As a further curiosity, Perhaps someone could tell me where to get the information necessary to calculate the total energy content of the smaller standard size 1.5v batteries such as AA, AAA, C, D etc. in alkaline, Nichol cadmium or NMH batteries.

Hello , A reserve capacity related to the amount of time a battery can deliver 25 amps to a load before the voltage drops below 10.5 volts for a 12 volt battery and I thinks 4.4 volt for a 6 volt battery at 70 deg starting with a full charge. So that battery would last for 113 mins at 25 amps draw before the volts dropped below the cutoff voltage.

The voltage delivery is non linear , A lead acid battery will discharge with a fairly even loss of voltage over time, Then there is the transition point where the voltage drops off quickly over time. This will graph out differently for each battery. The drop out voltage is different between battery types.

The battery configuration has a great effect on the efficiency of the storage pile. But the total energy will remain the same- Let me explain. An inverter needs to have a input that has a consistent voltage. As the voltage drops the inverter draws more current. The increased current causes more heat to be made. The heat is lost power. You need to configure the batteries to provide voltage and current over time and reduce parasitic losses to heat.

A battery pile needs to be balanced to provide current and voltage over time for the expected loads. This can be done many ways using parallel and series batteries. The use of two or three inverters have advantages and dissadvantages. You will need to calculate your power consumption and figure in idle time .

I recommend you look at the information that's availible on line. Try the "free sun power" web site. They solar energy web sites are the leading edge of the inverter technology. They charge batteries then use inverters to convert to a/c . You will find so much info on batteries, inverters , distribution , load calculations and the like to keep you busy for hours. These sites have the knowledge on the latest . You may find that it easier than you think. Please Click Accept, Thanks Again. Scott

Scott, Auto Service Technician
Category: Car
Satisfied Customers: 1190
Experience: A.S.E. Master ,Chrysler Master, 33yrs experience

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