×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to determine size of small electric generator

How to determine size of small electric generator

How to determine size of small electric generator

(OP)
I am designing a small timing circuit and need a power source of around 4 volts and producing around 15 to 20 mA for around 5 to 10 seconds.

I am thinking of using a simple generator (iron core, copper coil) and need to get an idea of how large this needs to be.  Can anyone help me with some calculations that I can use to get an estimate on how many coils, size of magnet rotational speed required etc.  

Thanks


Steve

RE: How to determine size of small electric generator

15 mA seems to be awefully high current for a simple timer.
Can you give some spec's? couldn't you use a solar cell for
power ?

<nbucska@pcperipherals.com>

RE: How to determine size of small electric generator

Wouldn't it be easier and cheaper to use 3 x AAA cells?

RE: How to determine size of small electric generator

(OP)
Solar cells are not practical for this application (object may need to be used at night).  this is only a concept at this stage and I can't give out specs.

Yes, AAA cells would be easier and cheaper, but they don't meet my other requirements as they are far too large for our application, but a single 1/3N cell is possible, if I can overcome the shelf life and temperature limitations that batteries impose.

The timing circuit is only part of it.  The power source is also charging a capacitor with sufficient energy to function a device at the end of the delay.

At this stage I am just trying to see if the electric generator idea is feasible with the requirements that I have, but I don't know how large this device needs to be.  If I can get some ballpark calculations on required field strength from the magnet and number of coils of the copper and required RPM, I should be able to decide if the idea is worth pursuing further,

Thanks


Steve

RE: How to determine size of small electric generator

How much energy does the switched device need ? Can you reduce it ?How much life time do you need ? What starts the timer ? ( manual/mechanical switch, power-on, microcomputer etc.)

Can you tell what this device is ?

<nbucska@pcperipherals.com>

RE: How to determine size of small electric generator

(OP)
I'd rather not at this stage.  The switched device requires 1 amp and 1 watt to operate.  The timer is started manually by the user.  The power source only needs operate between 3 and 10 seconds maximum and only once.  The time requirement is determined by the customer.

thanks

Steve

RE: How to determine size of small electric generator

How long do you need the 1 V x 1A ? The timer is negligeable
besides this... Do you want to supply the DEVICE, too, with
the generator ?

<nbucska@pcperipherals.com>

RE: How to determine size of small electric generator

(OP)
The device needs to be fully supplied complete to the customer with no further assembly or preparation required prior to use.  We are using a capacitor to provide the 1A, 1W and the output from the timing circuit shorts the capacitor.  I can't explain more as my knowledge of electronic circuits is minimal.  I think (suspect) that the required supply length of time is in the milliseconds range.

RE: How to determine size of small electric generator

If you need only 1 Watt for 1 mSec and plus the need for
the timer for a few sec's, this is less than 2 mW -- easy
to generate by a coil/magnet.

<nbucska@pcperipherals.com>

RE: How to determine size of small electric generator

(OP)
How do I determine the physical characteristics of the coil and magnet?  eg size of magnet, proximity to coils, number of coils, diameter of wire?

Thanks

Steve

RE: How to determine size of small electric generator

The approach depends on quantity : if this is a test only
-- single piece -- overdesign it by any acceptable factor.
 
If massproduct: Start with selecting the  cheapest magnet
-- and experiment.

The coil can be the thinnest if the R is low enough -
the duty cycle is so low that it wont overheat.

You may need to build several ones, to get the cheapest
and easiest to manufacture design.

E-mail me as much data as U can.



 

<nbucska@pcperipherals.com>

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources