# counter emf ???

Discussion in 'General Electronics Chat' started by firefli, Sep 8, 2013.

1. ### firefli Thread Starter New Member

Sep 6, 2013
9
0
I have a coil that is being energized and De-energized by a spinning rotor with magnets attached to it and a magnetic switch.
I am using 2 AA batteries (3v) as power.
The question is:
When I put my V-meter across the coil with the rotor at full rpm
(2-3 hundred) maybe, my meter read 30+ volts with momentary spikes over 1 hundred.
Can anyone tell me why, I guessing counter EMF, but don't rally know.
I was able to charge a CAP. to over 1 hundred Volts.
Is this useful to anyone ???
thanx Firefli

2. ### Potato Pudding Well-Known Member

Jun 11, 2010
684
92
That sounds like a motor generator system that you are describing.

Keep in mind that you might be confusing power conversion with voltage conversion.

Ability to charge a capacitor to 100V when your power source is 3V of of AA batteries seems more amazing than it really is unless you understand that the current drawn from the the batteries will be about 50 times higher than the current that can be drawn from the 100 Volt capacitor.

Power input is always greater than power output, because entropy taxes everything.

Still a constant 5mA at 3V input will likely allow high pulse currents, like a millisecond of 1 amp from the 100V capacitor.

Beware.

3. ### BillB3857 AAC Fanatic!

Feb 28, 2009
2,456
372
Is the coil in close proximity to the rotating magnet, OR, is the magnet just opening and closing the reed switch? If the reed switch is just opening and closing the current to the coil, what you are seeing is the inductive kick from the coil (think about the ignition coil in a car). If, on the other hand, the spinning magnet is close to the coil, you have built a generator.

4. ### firefli Thread Starter New Member

Sep 6, 2013
9
0
Thanx for the thoughts guys. I would post a sketch of my set up but I'm not really sure how. Any advice on how to do that.

5. ### shortbus AAC Fanatic!

Sep 30, 2009
5,644
3,235
Click the "go advanced" block under the "quick reply" block. Then there is a "manage attachments" area that lets you down load to the site.