# Car battery amps?

by MountainDew
Tags: amps, battery
 P: 1 Ok folks, this is freshman electronics. CCA is the measurement of the amount of amperage a battery can produce under extreme load. Amp Hours is the amount of amperage a battery can produce over a longer period of time at a lower load, say for instance a car radio. RC is equal to approximately 1/5 of CCA. Amp/Hours = (Reserve Capacity / 2) plus 16 I know this because I work for a data company and I have to test and certify every battery back up, every quarter, in every security panel and ups we have installed in the midwest. I learned it at ITT Tech.
 PF Patron Sci Advisor P: 10,120 That, above, will be a rule of thumb for a particular battery. The "16" in the formula gives it away; it would not be the same for a large battery as for a small one.
 P: 1 I just read all the posts in this four-year thread and feel much more knowledgeable with all the back and forth. My reason for following this thread is that I was hoping to find out how long my 5 24-V deep cycle batteries in series (for example) could power a 1,500-Watt SkilSaw after inversion to 120-V AC. Assuming no loss in the inversion process, I'm figuring the Saw will be drawing 12.5 Amps (1,500 / 120); but I'm still not sure how to figure out how long these fully-charged batteries can generate 12.5 amps without a recharge (from a solar panel or wind turbine).
P: 2
650 CCA means it can deliver 650 amps at peak capacity, which is only a few seconds. It does not mean you have 7800 watt hours. 650 doesn't say anything about how much watt-hour or amp-hour. You have to get that from the manufacturer directly because often the battery doesn't label them. I had this problem and had to go to the manufacturer's website to look up the detail specification. They list the amp-hour (AH).

A 650 CCA battery usually has about 10-14 Amp-hours.

There is no simple mathematical equation that relates the amp-hour to the Watt/Volt/Amp because the amp-hour is determined by a combination of the physical size of the battery as well as its chemical internal structure. In general, a bigger battery will have more amp-hour than a smaller one, but that relationship involves too many variables to calculate.

Once again check the manufacturer's website for the detail spec. You can't get the amp-hour from calculations or explanation of physics. The manufacturer determine the amp-hour by measuring the battery, not by calculation.

You can measure it too by turning on your car radio and see how long it lasts :)p
If you know the watt. of the car radio, the voltage of the battery, you can determine the amp. Multiply the amp with the hours that your car radio lasts, then you get the amp-hour. ;)p
P: 2
 Quote by bcw I just read all the posts in this four-year thread and feel much more knowledgeable with all the back and forth. My reason for following this thread is that I was hoping to find out how long my 5 24-V deep cycle batteries in series (for example) could power a 1,500-Watt SkilSaw after inversion to 120-V AC. Assuming no loss in the inversion process, I'm figuring the Saw will be drawing 12.5 Amps (1,500 / 120); but I'm still not sure how to figure out how long these fully-charged batteries can generate 12.5 amps without a recharge (from a solar panel or wind turbine).
what's the make and model of the battery? google for that model and go to manufacturer's site.

From my preliminary google for "24v deep cycle battery" I've found that they range as much from 14AH to 100AH, depending on the size.

since you connected the batteries in series in order to achieve 120 volts, the AH capacity of the entire system will be the same as the capacity of a single battery. So find out that AH from the manufacturer and divide by the 12.5 amps that you've already figured out. That will give you the hours it last.
PF Patron
P: 1,958
 i googled and learned to use the formula Watts x volts = amps, how are you getting 10 watts from a 100 watt bulb if you don't mind, from what i've read i've learned to do it like this. 100 watt bulb at 120 volts draws 100/120 = .8 amps 100 watt bulb at 12 volts draws 100/12 = 8.3 amps or you could do watts like this for example: .8 amps from 120 volts draws .8 * 120 = 96 watts per hour 8 amps from 12 volts draws 8 * 12 = around 96 watts per hour
You are missing the point that averagesupernova made a few msgs back

a 100W bulb is designed to draw/use 100W AT 120V NOT 12V, at 12V its resistance is going to be somewhat higher that its gonna draw next to nothing and its probably not even going to glow.

a 100W bulb for 12V is going to have a very different cold and hot resistance than a 100W bulb at 120V

ok hunted around the house for a couple of globes closest in wattage I could find .....

40W 240VAC globe (we have 240V mains here in Oz) and a
20W 12V globe

cold resistance of 40W globe = 100 Ohms

cold resistance of 20W globe = 5 Ohms

On a 13V supply the ...

40W 240V globe drew 53mA (no Glow)
20W 12V globe drew 320mA (normal bright glow)

there's my 2 cents worth

cheers
Dave
 PF Patron Sci Advisor P: 1,958 interesting.... that 20W globe .... 13V x 320mA = 4.1W maybe its been mislabelled will have to try and find another 12V rated globe for a test :) Dave
 P: 2,380 You cannot expect cold filament ohmeter readings to reflect wattage.
 PF Patron Sci Advisor P: 10,120 Why not use auto bulbs (say 100W worth) and just measure current? If it's that vital to know the actual capacity of the battery then test it under real conditions. But mind you don't let it dip much below 12V or you will start to damage the battery.
 P: 2 hello, i am going to do my project work on automatic hydraulic jack which will be driven by an electric wiper motor.for this wiper motor it requires of 100 watt to operate and requires a torque of 40 nm so can the vehicles battery power can provide that sufficient amount of power to this wiper motor???your help will be very grateful to me.
PF Patron