### Author Topic: Battery Question  (Read 1947 times)

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#### Thomas Countz

• Jr. Member
• Posts: 30
##### Battery Question
« on: December 26, 2008, 06:00:52 PM »
Alright. I'm at the point were I need to purchase batteries for my robot (or lack there of.) But, first I must decide what my options are, so I have a few questions. I used the battery calculator here: http://www.societyofrobots.com/battery_calculator.shtml (or at least tried to) but I need help selecting a battery rather than calculating how long it will last and things like that. I also read the battery tutorial here: http://www.societyofrobots.com/batteries.shtml.

My question (which will help alleviate all of my other questions) is weather or not I should use different sources for my drive motors and my servos.

I have 2 drive motors (Solarbotic GM9s http://www.solarbotics.com/assets/datasheets/motor_data_summary-gm9.pdf) which has an idle current draw of 52mA @ 6v and a stall current of 700mA @ 6v. Multiplied by 2 motors is idle: 104mA and stall: 1400mA.

I'm also using 2 servos (HiTec HS-311 http://www.makingthings.com/teleo/products/acc_datasheets/acc_srv_hs311.htm) which has an idle current draw of 7.7mA @ 6v and a stall current of 180mA @ 6v. Multiplied by 2 servos is idle: 15.4mA and stall: 360mA.

If my math is correct, I need a 6v battery at ~2000mAh for ~1 hour of use... is this correct??

Note: I'm using a voltage regulator along with the batteries, and 2 tri-state switches with an SN754410 to drive the motors.
« Last Edit: December 26, 2008, 07:02:43 PM by Thomas Countz »

#### jamort

• Supreme Robot
• Posts: 375
##### Re: Battery Question
« Reply #1 on: December 26, 2008, 08:48:16 PM »
sounds about right but also note that at first the batteries will over perform the voltage rating and near the end they will under perform the voltage rating... nd i would use rechargebal lithium batteries
my english teacher once said, "dont talk about what you dont know in public...."

so I replied the truth, " Exactly why I dont ever talk about English."

#### Thomas Countz

• Jr. Member
• Posts: 30
##### Re: Battery Question
« Reply #2 on: December 26, 2008, 08:51:50 PM »
Great, sounds awesome. Thank you.

#### jamort

• Supreme Robot
• Posts: 375
##### Re: Battery Question
« Reply #3 on: December 26, 2008, 09:37:20 PM »
no prob just let me know if you need anything else
my english teacher once said, "dont talk about what you dont know in public...."

so I replied the truth, " Exactly why I dont ever talk about English."

#### Thomas Countz

• Jr. Member
• Posts: 30
##### Re: Battery Question
« Reply #4 on: December 26, 2008, 09:38:55 PM »
Another Question....

How are mAh compounded when you wire in series? In the battery tutorial it mentions what wiring in series increases in voltage and wiring in parallel increase current. So here is my scenario:

I'm choosing to use NiMH batteries because they're readily available to me and they're cheap. I have a AA cell that is rated at 1.2v and 2000mAh and I want 6v and 2000mAh, so if I wire 6 cells together in series, that should give me what I want....is that correct?

#### Razor Concepts

• Supreme Robot
• Posts: 1,856
##### Re: Battery Question
« Reply #5 on: December 26, 2008, 11:22:00 PM »
Yes

Well you wire 5 together in series not 6

#### Thomas Countz

• Jr. Member
• Posts: 30
##### Re: Battery Question
« Reply #6 on: December 26, 2008, 11:28:27 PM »
Yeah...I guess it would help if I could do simple math....nah...who needs it..haha

Thanks again.

Just in case anyone caught this, I said I was going to use the SN754410, but it can only handle up to 1A max and the stall current for both of my motors combined is 1.324A....that's a problem, but I'm using an L298 instead....not that anyone was paying attention enough anyway.....haha

#### Thomas Countz

• Jr. Member
• Posts: 30
##### Re: Battery Question
« Reply #7 on: December 27, 2008, 09:58:22 PM »
I like to bring to light this battery program I found that offers cheap or even FREE batteries to students/innovators for your projects. You just fill out the form and....well that's as far as I got. Hope some of you can get some free batteries!

#### Webbot

• Expert Roboticist
• Supreme Robot
• Posts: 2,132
##### Re: Battery Question
« Reply #8 on: December 27, 2008, 11:06:00 PM »
Just in case anyone caught this, I said I was going to use the SN754410, but it can only handle up to 1A max and the stall current for both of my motors combined is 1.324A....that's a problem, but I'm using an L298 instead....not that anyone was paying attention enough anyway.....haha

The SN754410 can handle 1A per driver - ie per motor

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#### Thomas Countz

• Jr. Member
• Posts: 30
##### Re: Battery Question
« Reply #9 on: December 27, 2008, 11:14:25 PM »
Just in case anyone caught this, I said I was going to use the SN754410, but it can only handle up to 1A max and the stall current for both of my motors combined is 1.324A....that's a problem, but I'm using an L298 instead....not that anyone was paying attention enough anyway.....haha

The SN754410 can handle 1A per driver - ie per motor

oh....haha I knew that...