On Mon, May 03, 2004 at 08:23:01PM -0400, Marc Joffe wrote:
> Hi,
>
> I am currently building a robot and need some recommendations for a battery
> source.
>
> I require a 12V source that can source approximately 300mA for at least 15
> minutes.

OK. A sealed lead acid comes immediately to mind. Their amp-hour ratings are
normally given for a 20 hour discharge curve. However they will happily
supply virtually as much current as you like as long as you have juice.
Of course the runtime is derated as you go above the C/20 discharge curve.

That being said let's make C/20 = 300maH. So that gives you a C of 6AHr.
So a standard 7 AHr battery would have no problem, except for size.

Mouser has a whole range from 0.8AHr to 100 AHr. Everything up to 7 AHr is
less than $20 a battery. Page 1206 of their catalog. Maybe you can go to
the PowerSonic site and see what the discharge curves are and fit the
appropriate size/weight for the task.

> I have
> considered using remote control car batteries, but was hoping that there
> may be
> a cheaper source.
>
> A friend has also recommended using solar power, but
> I do not want to limit the robots use to bright places.

I agree. When prototyping my robo-mower, I discounted the power budget.

>
> Lastly, cost is a major factor as I am a student and do not want to spend
> all of my money on a battery
> and charger, and then not have money to work on other projects.

Well the charger is no problem unless fast recharging is critical. Get a
16-18VDC supply (like many discarded laptop supplies) and use a LM317 to
regulate to 14.4V. Voila! instant cheap charger.

>
> Any recommendations would be greatly appreciated.

My 2 cents. A small sealed led acid will take less space and less weight than
C or D rechargable ni-cads. They'll probably cost less too.

BAJ

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