AA battery max current draw

[MarkJC]

I'm working on a project that will need to use standard 1.5V batteries to run the power antenna from a car. I want to use AA batteries to do this, but i'm concerned they will not be able to handle the current draw.

Since power antennas run off of 12V car batteries, I will need to have 8 x 1.5V batteries connected in series to achieve that voltage. A standard AA battery is rated about 2400mAh. In theory, that should provide me with 2.4Amps for 1 hour. I only need to run the power antenna for less than a minute though, so capacity should not be an issue.

I had trouble finding how much current a power antenna draws, but I believe it's in the range of 500mA. Since I will have a load on the antenna, it could draw considerably more - maybe 1-2Amps. My concern is the batteries will not be able to handle that much of a current load. I'm wondering if anyone can shed some light on this for me?

 

[mneary]

A couple of reality checks:

1) A "12V" automotive power is 13.8V most of the time.
2) When loaded, alkaline battery voltage is 1.3V within minutes.
3) A 2400mAH battery is generally tested for capacity over a 10-hour cycle, such as 240mA for 10 hours. It won't be 2400mA for one hour.

It's probably worth a try, and if you don't get the results you want there are special AAs made for digital cameras and flash units etc. They cost about twice as much.

 

[picbits]

I would use NiMh AA batteries - they will provide you with a lot of current and a fairly stable voltage until the end of their charge.

An alkaline AA will struggle with an electric aerial motor after the first couple of lifts. The motors can draw up to 10 amps so NiMh is the way to go.

Even consider using a couple of 7.2v racing packs in series - you will have 14.4v but thats not a million miles away from what a lot of cars have as their standard running voltage anyway.

 

[mbarazeen]

you still can try using a lead acid rechargable battery of 12V. can be chaper than 10 number of NiMH batteries.

 

[DirtyLude]

It's a motor, so likely the voltage can be varied somewhat and it will still work. You might want to test it to see how low a voltage you can get and still have enough pull to get it up and down.

Like mentioned, NiMH batteries are the way to go, they will supply current quickly. If you can get away with a lower voltage, there are 'battery packs' you can buy cheap that are meant for remote control cars. 9.6v is the standard, but I'm sure you can get higher if it's needed. They are already packaged up with a nice connector and everything.

EDIT: NiMH have a higher self discharge rate that might be a concern for you. What it means is that they will discharge over time without actually being connected to anything. This might be a problem for you if your application requires that this thing be ready to use at any time.

 

[Speakerguy]

They now have low self discharge NiMH batteries that are supposed to retain >70% of their charge after two years. Sanyo makes them under the Eneloop brand name, and there are three other companies that make them too.

The Energizer e^2 lithium batteries have extremely low self discharge (will last 10 years) and can handle heavy current loads. I think either of these batteries will work well for you.

 

[crutschow]

If you have room you might also consider using alkaline D cells. They have much high capacity and maximum current capability than AAs.

 

[audioguru]

AA alkaline cells have their capacity rated at only 25mA and an end voltage of only 0.8V per cell. At 500mA their capacity is half.

At 0.5A and 1A their voltage quickly drops like a rock.

 

[MarkJC]

Thanks for the suggestions. The discharge curve was very informative. The reason I was considering using standard, nonrechargable alkaline batteries was that the antenna will be used in a rather unique design for a competition that is limited to 1.5V batteries. I'm planning to use the antenna as a sort of linear actuator since I require a long extension.

I was leaning toward using AA batteries since i'm on a tight budget, but to my surprise, it appears that D's aren't nearly as higher priced as I expected given their much larger capacities. Perhaps the safest bet would just be to use D's. (space isn't an issue)