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Hi Erich,

If you did want to use rechargeable batteries, you could package the
batteries in a typical battery case, then add a bit of circuitry to the case
to provide overload protection (similar to the circuitry in the power supply
you bought). Or use a resettable fuse that trips and resets automatically
without any intervention.  <Here's one that trips at 100mA:
http://tinyurl.com/25ftv5>
Visitors would have to connect to leads on the battery case, instead of
connecting straight to the battery. 

However, I don’t think they'll stay around long enough to learn the message
that 4AA in parallel provides more current capacity than 2AA in parallel.
(Maybe if the batteries no longer held much charge).  Visitors could charge
capacitors to light LEDs for a brief second (although you want to be careful
not to mislead them into thinking batteries are made of capacitors).  Or use
solar cells to charge capacitors, that light LEDs.

That said, I'm glad you have an assortment of motors and stuff available to
tinker with, as even writing about the "lessons" of parallel circuits makes
me yawn.  I think you hit it right on with the goal of inspiring visitors to
try this at home.  Perhaps you could boost the tinkering aspect by providing
more context and real-life application.  (While still leaving an area for
unguided exploration).  Consider ways for visitors to "incorporate" the
electronics into something creative they can imagine and build.  Think
MacGyver.  The more they can tape together and create for themselves, the
more ownership they'll have over the experience.  Here's some ideas, but
they need more work to be open-ended.

Car Stereo: I see a lot of kids get into electronics by tinkering with their
car stereo...
---Build a speaker from a variety of magnets, coils, and plastic cups.  
---Hook up several speakers to your car stereo. Try series and parallel
circuits.
---Build a filter for a subwoofer to let just the bass through, using 1
resistor and 1 capacitor. (Maybe too advanced for an exhibit).

On/Off Switches: The concept of a switch is easily grasped, allowing
visitors to tinker without a lot of lecture. 
---Build a tilt switch using a metal ball. Build a few and use them to
control a video game. 
---Rig up a safe so that a light turns on when it opens.
---Wire a hall light so that two switches can control it independently.

Shake Flashlight: Build a flashlight powered by shaking.
---Provide a variety of magnets and coils 
---Use capacitors to store the charge 
---Try hooking up multiple LEDs in series & parallel

Just some ideas.  Have fun!

-Eric

*****************************************
Eric Yuan
Exhibit Developer
Children’s Museum of Portsmouth
280 Marcy Street
Portsmouth, NH 03801
(603) 436-3853
www.childrens-museum.org
*****************************************\

 -----Original Message-----
From: Erich Rose [mailto:[log in to unmask]]
Subject: Re: [ISEN] rechargeable batteries

We recently built an exhibit where visitors build various circuits with
parts we provide such as switches, lamps, motors, etc.  Because we want kids
to go home thinking they can do the same at home we decided to use
batteries.  BUT since it would be a budget buster to constantly provide new
batteries we have rigged up a sort of fuax battery system.  

...
The only thing they don't get is how long a set of batteries would last for
a given device.  


Erich Rose
Exhibit Manager
Austin Children's Museum

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