How long will a 300 CCA, 12V car battery last with 18Ah?

[Towtie]

If CCA can be translated directly to Amps then would I be able to run the battery at max capacity for only 3.6 minutes?

18 / 300 * 60 = 3.6 Minutes?

Or am I looking at something wrong?

 

[berkeman]

If CCA can be translated directly to Amps then would I be able to run the battery at max capacity for only 3.6 minutes?

18 / 300 * 60 = 3.6 Minutes?

Or am I looking at something wrong?

Welcome to the PF.

What's a CCA?

 

[Towtie]

Cold Crank Amps...

quoted from wikipedia

"the amount of current a battery can provide at 0 °F (−18 °C). The rating is defined as the current a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery)."

 

[Averagesupernova]

You cannot really tell anything about the one from the other. 300 CCA means that the battery will provide 300 amps for a short duration which would be suitable to start an engine. That is all it says. A larger CCA implies a longer amp-hour rating but I doubt there is a mathematical relationship. The amp-hour rating is more misleading though. A battery can be rated at 20 amp-hours but that is not to say that it can supply 200 amps for a tenth of an hour.

 

[anorlunda]

I'm not sure where you got the 18 Ah from. I'm also not sure what your definition of max capacity is. Does it include voltage? Does it imply one-time use or no permanent damage to the battery?

I think you can answer your questions yourself with the aid of Peukert's Law. http://en.m.wikipedia.org/wiki/Peukert's_law

 

[Towtie]

I got my numbers from the provided specs of this batter: http://www.scorpionbattery.com/powersports-batteries/ytx16bhl.html

I'm trying to figure out if I could convert power from it to 110 VAC with an inverter and power a 110V, 1/3 HP(250W) vacuum for at least 10 minutes.

I assume I can go P=IV --> 250 = I * 12

So I will be drawing 250/12 Amps.

However I'm not sure if these numbers are correct since I'm trying to translate to AC.

 

[anorlunda]

250 watts for 10 minutes is 42 watt-hours. Double that assuming a 50% efficient inverter and you have 82 watt-hours. At an average battery voltage of 12 volts, that is about 7 amp-hours. That is about half the claimed capacity of the battery.

Your problem will probably be voltage. Most inverters will shut themselves off when voltage falls below 11.8 volts. The CCA rating you quoted talks about drawing voltage down to 7.2 volts. Drawing that much power from such a small battery may make the voltage drop below 11.8 almost instantaneously.

As a point of reference, my boat has 220 Ah of lead acid batteries. I never allow loads more than about 100 watts that last for minutes. I would not be able to use a vacuum cleaner drawing 250 watts. Cranking the engine takes 50 amps for 1 second typical, 30 seconds max.

 

[SuperDaniel]

If CCA can be translated directly to Amps then would I be able to run the battery at max capacity for only 3.6 minutes?

18 / 300 * 60 = 3.6 Minutes?

Or am I looking at something wrong?

Hello Towtie,

Firstly, you have to understand that standard car batteries are designed for start the engine, so, these batteries can supply with 12 VDC and X Amp during 20-30 seconds.
If you need electrical current for a long period of time, you will require deep cycle type batteries.

So, you should describe how are you going to use the batteries: as an engine starter or as a power supply (for lighting, for a power wheelchair, etc.).

There are plenty of manufacturers of these kind of deep cycle batteries. I have used http://www.odysseybatteries.com and they work perfect in terms of current supply for long periods and are maintenance free. There are more brands such Optima, Trojan, etc...

You can start to read about deep cycle batteries here: http://en.wikipedia.org/wiki/Deep_cycle_battery

Finally, you cannot understand how the battery is going to work if you do not have the battery discharge curve in sight, provided by the manufacturer. The capacity you can read in a flyer is just a guide.

Good luck