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Old Jan 25th 2016, 02:16 AM   #1
A80
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6V motor 9V battery

Hi! I have a 6V motor
Image link : http://i.ebayimg.com/00/s/ODAwWDgwMA==/z/-5UAAOSwl9BWIJZ~/$_12.JPG

I connected it with this 9V battery


But it did not work. Then i connected it to a AA battery(1.5V) and it worked fine. Can someone please tell me what is happening here.

TIA

Last edited by topsquark; Jan 25th 2016 at 04:59 AM.
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Old Jan 25th 2016, 05:10 AM   #2
MBW
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There are two features of Batteries, the voltage supplied and the current available.
I am guessing that the problem is the current available from the 9V battery.
9Volt batteries are usually intended for use with transistor circuits which only draw a fairly small current.
An electric motor requires a relatively large current
I suspect that the 9V battery just didn't have enough oomph.

Although the AA battery only delivers 1.5 volts, it can deliver this at a high current.
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Old Jan 27th 2016, 05:43 AM   #3
A80
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Thanks!
But another question is which is more important for the motor to run, current or voltage?
By observation it seems that lower voltages can do the job if the current is enough. Can you explain the relation between current and voltage for the case of a motor?
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Old Jan 27th 2016, 06:22 AM   #4
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Remember Safety First

One feature of batteries is that the Voltage quoted is generally the theoretical voltage available if you don't draw any current!
As you actually draw any current, the Voltage drops.
The physical size of a 1.5V AA battery is NOT 6 times smaller than a typical 9Volt battery,
and this relative additional size allows it to deliver more current without a huge drop off in voltage.
If you put several 9V batteries in parallel, you will probably find the motor will start working.

These are two key equations that might help:
V=IR and W=IV
Volts = Current * Resistance
and
Watts = Current * Voltage.

Thus for power, you want as much current as you can get for the voltage.
Don't go (much) above quoted voltage for the motor, or you will burn it out.

If you measure the resistance of the coils in your motor, you will find that it is actually quite low.
This means that it is always trying to pull a large current from you battery
1 amp is actually a LARGE current, most (household) batteries will struggle to provide 0.1 Amps.

You can get more power by combining several batteries,
join them in series to increase voltage, in parallel to increase current.
But don't go over the top, at minimum you could damage the motor, then there would be fire risks as the wires get hot, then...
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Last edited by MBW; Jan 27th 2016 at 06:26 AM.
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