Battery selection - Wh or V ?

Thread Starter

Track99

Joined Jun 30, 2022
18
Mike has a toy that is rated for 2 Amps at 6 Volts. If the toy is getting 2 Amps at 6 Volts, the toy works good.
Mike has calculated that the toy consumes 12 Watts of power in 1 hour; if he plays with it non stop for 1hr.

Later, the battery died.

Mike went to the store and bought a battery whose Energy output is 24Wh but the battery voltage is only 3 volts. ( That was the only battery available in the store and all other batteries were out of stock)

1) Will the toy work with the new battery for 2 hours because it is connected to a battery that can provide it with the required 12 Watts of power ( 24Wh / 2 hours = 12 Watts)?

or

2) Will the toy not work because even though the energy of 24Wh is present in the battery, the battery voltage is only 3 volts and not the required 6 volts for the toy?

Thank you
 

Thread Starter

Track99

Joined Jun 30, 2022
18
Is this homework? (the arbritarily chosen name "Mike" gives it away)
No my friend. It is not homework. I am trying to understand the electron physics. I used Mike as a example. I want to know what is more important when buying the battery. Is the toy going to work because the energy is present but the voltage is not OR is the toy not going to work even if the energy is there but the voltage is not.
 

BobTPH

Joined Jun 5, 2013
5,489
The correct answer is not listed, because the toy I gave to mike works, but runs slower at 1A at 3V, so it runs for 8 hours on the 24WH battery.
 

Thread Starter

Track99

Joined Jun 30, 2022
18
The correct answer is not listed, because the toy I gave to mike works, but runs slower at 1A at 3V, so it runs for 8 hours on the 24WH battery.
So you are saying that 1A X 3V = 3W. So a 24Wh battery will run the toy for 8 hours because 24Wh / 3 W = 8 hours.
 

crutschow

Joined Mar 14, 2008
30,455
Will the toy not work because even though the energy of 24Wh is present in the battery, the battery voltage is only 3 volts and not the required 6 volts for the toy?
Depends upon the toy's low voltage operating limit, which is not given in your example.
So, from your information, the answer is unknown.
 

Thread Starter

Track99

Joined Jun 30, 2022
18
Depends upon the toy's low voltage operating limit, which is not given in your example.
So, from your information, the answer is unknown.
Fantastic answer my friend. You cleared all my questions in my brain. Sometimes the systems will operate, sometimes they will not even turn on.
 

BobTPH

Joined Jun 5, 2013
5,489
So you are saying that 1A X 3V = 3W. So a 24Wh battery will run the toy for 8 hours because 24Wh / 3 W = 8 hours.
Yes, in the hypothetical toy I defined. The point was, you have to know what the toy would do when given 3V. I hypothesized one that used half the current and ran slower. This is actually somewhat realistic. Many things will draw less current at lower voltage.
 

nsaspook

Joined Aug 27, 2009
10,117
Be careful if the toy has motors.

It might seem counter-intuitive but a lower voltage can over-heat a motor/fry control circuits. The motor stalling drops the back EMF to the point the coils look mainly resistive.
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boostbuck

Joined Oct 5, 2017
222
I'm not sure it's complicated - the basis of any consideration is power available, and within that is the designed voltage of the appliance.

It is intended to run at a given voltage, and varying that will cause problems. It is designed to consume a given power, and how much is available (eg size of battery) determines it's run time.
 
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