### Author Topic: Energizer AA E91 battery  (Read 2947 times)

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#### vin.lwh

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• Posts: 5
##### Energizer AA E91 battery
« on: March 02, 2009, 01:58:56 AM »
'm working on a mobile robot, and it needs 12 volts and approximately 3 ampere. Correct me if I'm wrong, I connect 8 AA E91 batteries in series which is 1.5 volts in order to achieve 12 volts. In order to increase the ampere, I need to connect another 8 more batteries parallel to the original 8. I don't know how much current does the batteries produce.

My questions:
1. What is the maximum current can the energizer AA E91 produces?
2. What other methods can be used to reduce the number of batteries used?
3. How long does it take to drain all the current away from the AA E91 battery assuming my device runs continuously?

I've search the data sheet of the AA E91 but I don't really understand what it means.
http://data.energizer.com/PDFs/e91.pdf

Thanks so much in advance. Really appreciate it.

#### cosminprund

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• Posts: 284
##### Re: Energizer AA E91 battery
« Reply #1 on: March 02, 2009, 03:02:25 AM »
Open up your datasheet, notice the "Milliamp-Hours Capacity" graph on the first page. Apparently those batteries can only deliver 500 ma each; If you want 3 amps (3000 maps) you'd need 6 in parallel! You want 12 volts so you need 8 in series. That gives 48 AA batteries at a time, and they'll only run for 3 hours (the same "Milliamp-Hours Capacity" graphs shows that the battery capacity drops to 1500mAH if you discharge at 500 mA).

You'll need to consider an other power source if you want 3 amps! I think NiMH cells can be discharged at 3 amps, so you'll only need 10 NiMH cells! They'll probably cost about the same (compared to 48 AA batteries), take up 5 times less space, provide an decent amount of runtime (divide the "mAH" rating on the cell by 3000 and you'd get runtime in hours) and are rechargeable, so you don't keep buying truck loads of batteries.

#### SmAsH

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##### Re: Energizer AA E91 battery
« Reply #2 on: March 02, 2009, 03:31:29 AM »
(divide the "mAH" rating on the cell by 3000 and you'd get runtime in hours)
wouldnt it be 1000?
Howdy

#### cosminprund

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##### Re: Energizer AA E91 battery
« Reply #3 on: March 02, 2009, 04:09:52 AM »
You divide by the expected power consumption. vin.lwh wants to draw 3 amps so he divides by 3000 (3 amps = 3000 mA).

#### SmAsH

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##### Re: Energizer AA E91 battery
« Reply #4 on: March 02, 2009, 04:14:56 AM »
You divide by the expected power consumption. vin.lwh wants to draw 3 amps so he divides by 3000 (3 amps = 3000 mA).
ahhh now i get you!
Howdy

#### dellagd

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##### Re: Energizer AA E91 battery
« Reply #5 on: March 05, 2009, 08:28:38 PM »
or if you want to go really small, you can get energizer lithium batterys. each one puts out 2900 mAH(close enough right?l)so no parallel needed.
but they are not rechargeable and are priced high. this is only if space is very limited.
« Last Edit: March 05, 2009, 08:30:32 PM by dellagd »
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#### Soeren

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##### Re: Energizer AA E91 battery
« Reply #6 on: March 06, 2009, 10:24:15 AM »
Hi,

My questions:
1. What is the maximum current can the energizer AA E91 produces?
2. What other methods can be used to reduce the number of batteries used?
3. How long does it take to drain all the current away from the AA E91 battery assuming my device runs continuously?

1) At least 5A (worst case, 10A typical) when fresh.
2) Err, using larger cells, like D-size, would help a lot and so will increasing the efficiency of the motor and drivetrain.
3) Your 'bot won't take 3A all the time, that's probably the peak drain. Besides that, several factors is mingling in, like temperature, whether running uphill, downhill or flat, how old the cells are, etc.

Remember, the 12V will only be 12V for a short time, as the capacity is rated down to 0.8V in your case (normally down to 0.9V). For most of the time it will be around 9.5V (give or take).

Don't fall pray of the usual confusion between A (Ampere), which is an instantaneous current value and Ah (Ampere Hour), which is a capacity rating.
Regards,
SÃ¸ren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?