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I have almost no experience whatsoever with the technical's of electronics so this is probably a very easy question for someone who does...

Do you know if a battery with a 200Ah rating can put out 200A for one hour or are there limitations? According to this websites third paragraph, you can:

http://www.allaboutcircuits.com/vol_1/chpt_11/3.html

but wouldn't that mean you could hook up a 200Ah battery and ask it to put out 12000A for one minute or 720000A for a second? That seems very unrealistic, lol. I'm trying to find the proper kind of off grid battery that can power a microwave through a 3000 watt power inverter. The microwave needs 1800 watts and the battery needs to be 12 volts so that would mean I need about 150 amps, I'm wondering if a battery with a 200Ah rating could do it?

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If you're off-grid (or even if you're not) it's vastly more efficient to cook things by burning something - wood, coal, gas, petrol, woodland creatures... as there's only one conversion going on (fuel -> heat) rather than something -> 12vDC -> mains AC -> microwaves -> heat as no conversion is ever 100% efficient. –  John U Jul 25 at 10:35
    
Information only: !!! The following is from a deleted post (not by me). While it relates to LiPo and not lead acid it provides some good guidelines which may be of some value. Too good to throw away: ||| Post said: There are test methods for this and useful tables, but I only have the one for LiPo batteries to give you an idea of what's involved. maac.ca/docs/2013/… –  Russell McMahon Sep 4 at 8:20

2 Answers 2

up vote 6 down vote accepted

Your hunch that batteries have a current limitation is correct. In general, it's hard to tell the current rating [A] from capacity [A·h]. You have to look it up in the datasheet. A lot depends on the design of the battery. Coin cells with 500mAh capacity may have only 3mA max current.

Lead-acid batteries are interesting in this respect, because there are two distinct types.

  1. Starter lead-acid batteries are designed specifically to deliver high peak current for a short period of time. Deep discharge, however, dramatically shortens the life of a starter battery. So, it's not suited for routine operation at high depths of discharge. Your typical starter battery in the automobile works at very shallow depth of discharge.
  2. Deep cycle lead-acid batteries are designed (as name suggests) to discharge further. But they can not provide as much instantaneous current.
    Here's an example datasheet for a deep cycle battery. Have a look at the nominal capacity on p.1. Notice that capacity depends on discharge current (i.e. the rate of discharge).

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Depth of Discharge    Starter Battery    Deep-cycle Battery

100%                  12–15 cycles       150–200 cycles

50%                   100–120 cycles     400–500 cycles

30%                   130–150 cycles     1,000 and more cycles

(Source.)

p.s. If you want to read-up, here's an excellent web site on batteries - Battery University.

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I'd add that even the highest quality deep-cycle batteries suffer when discharged badly, even if they tolerate it better than most. –  John U Jul 25 at 10:28

No, not necessarily.

Amp-hours tells you how much energy is in the battery, the amps tells you how quickly that energy can be delivered (For the most part, for a fixed voltage).

Your suspicion is well founded, because the Amp-hour doesn't tell the story on the batteries wattage capability.

Car batteries post their peak amperage because that is important when starting a vehicle. For your purposes, you'll want to find a deep cycle battery. Significantly discharging a car battery pretty much ruins it. Deep cycle batteries are designed to be discharged to a much greater degree, down to as low as 20%, and those are rated such that they can deliver the rated current continuously.

You may be able to find a suitable battery, depending on how long you are going to run your microwave. A decent 20+ amp rated deep cycle should still be able to unload 150 amps for a minute or two. Don't run the battery full blast non-stop though, it will overheat. Shop around for batteries for boats, RVs, etc to find good batteries.

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Correction: deep cycle batteries can't generally be fully discharged either. However, where a 'normal' battery can only be discharged down to 75% or so, deep cycle batteries can go as low at 50% to even 25% without damaging the battery. Make sure you check the specs of the battery. Some background on Wikipedia. –  RJR Jul 25 at 1:47
    
@RJR: You are correct. I must have always unknowningly had spiffy battery supervisors that protected the batteries whenever I've dealt with them. –  whatsisname Jul 25 at 1:57

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