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hardikcool
05-23-2009, 08:51 AM
today when i got up something got stuck in my mind..a strange problem...


if i have to use 3 motors of 25000 rpm with 12V dc supply with a single switch then how will i do that....

if i join them in parallel then suppose all have 1ohm resistance then total resistance becomes 0.33 ohms and the current goes to 36A!!
how can simple 1.2 Ah supply dat!!

and if in series then the voltage gets dissipated and all 3 get 4V each!!
then how will it run at 25000 rpm??

strange!!may be i sound a bit newbie but try to solve my querry!

suhasm
05-23-2009, 09:19 AM
if i join them in parallel then suppose all have 1ohm resistance then total resistance becomes 0.33 ohms and the current goes to 36A!!

the in circuit resistance of any dc motor is very unlikely to be so low. it is more likely to be in the order of a 100ohms or so.

robonics
05-23-2009, 10:14 AM
Other than resistance the motor also has properties like inductance which opposes change in current and magnetic reluctance.

So according to my guess there wont be so much of current flowing. The motors will just draw the current needed for running at no load.

I guess you are using Permanent magnet DC motors ?

allbits
05-23-2009, 12:15 PM
assuming that you are using motors with two wires, and that they are identical:

1) never connect in series.
2) Rotate one motor @ 12 V, with required torque, and at required rpm and measure the current.
3) Use a battery which can deliver that much current x 3.

Its as simple as this.

firoz
05-26-2009, 09:12 AM
@hardikcool don't mind.but iam more interested in motors than your question.
12v motor with 25,000RPM.that's amazing.can you give me some more data.i mean,from where did you bought it.and how much it costed it etc.
Thanks

hardikcool
05-26-2009, 09:22 AM
@firoz
here is the link of that motor:
http://robokits.co.in/shop/index.php?main_page=product_info&cPath=2&products_id=208
hope it will help!