Can batteries provide alternating current?

[mherna48]

I was just thinking about batteries and such after my brother asked me about AC vs DC current and their pros and cons.

 

[mherna48]

Another reason why I was wondering is because my cell phone battery has three nodes. Which might just be for charging...

 

[mgb_phys]

Batteries provide DC power - the third terminal is a temperature sensor that the charger uses to monitor the rise in temperature while charging.

 

[mherna48]

So there's absolutely no way to get batteries to make AC right? Or has it just not been tried?

 

[mgb_phys]

You could build a circuit to generate AC from a battery or any other DC source. But batteries are fundamentally DC sources.

 

[mherna48]

What kind of components can do that? The only ones I would think could come close are capacitors and inductors. But those need alternating current to begin with.

 

[turbo]

If you are willing to buy a DC-AC inverter, you can get AC in remote locations using DC batteries. I use one of these to power my telescope AC drives from the cigarette lighter of my vehicle. If you need smooth sine-wave AC you should know that these little inverters give you pretty notch-ey square-wave AC. Plugging my mount into real AC results in smooth quiet operation, but the 60-cycle buzz is noticeable when operating off the inverter.

 

[vk6kro]

To supply AC from DC, you usually have to make an oscillator.

An oscillator produces AC from DC. The AC can then be used in a transformer to change the voltage of the AC.

See the following circuit:
http://www.elecfree.com/electronic/wp-content/uploads/2008/06/circuit-inverter-100w-by-ic-4047-2n3055.jpg

This starts with DC and produces a much higher AC voltage suitable for small AC appliances.

The part marked 4047 oscillates and produces outputs which drive big power transistors which then drive the transformer.

 

[Phrak]

Swap the wires on the battery back-and-forth really fast.

 

[Starwatcher16]

If you are willing to buy a DC-AC inverter, you can get AC in remote locations using DC batteries. I use one of these to power my telescope AC drives from the cigarette lighter of my vehicle. If you need smooth sine-wave AC you should know that these little inverters give you pretty notch-ey square-wave AC. Plugging my mount into real AC results in smooth quiet operation, but the 60-cycle buzz is noticeable when operating off the inverter.

Does your inverter advertise itself as a modified or pure sine wave inverter?

 

[turbo]

Does your inverter advertise itself as a modified or pure sine wave inverter?

No idea. I bought that little box about 15-20 years ago. My only requirement was that it put out 60 hz AC so I could run my drives.

 

[Andrew Mason]

So there's absolutely no way to get batteries to make AC right? Or has it just not been tried?

An "inverter" converts DC to AC. A Toyota Prius has DC batteries but supplies high frequency AC to the motor. See: http://en.wikipedia.org/wiki/Inverter_(electrical )

AM

 

[mherna48]

To supply AC from DC, you usually have to make an oscillator.

An oscillator produces AC from DC. The AC can then be used in a transformer to change the voltage of the AC.

See the following circuit:
http://www.elecfree.com/electronic/wp-content/uploads/2008/06/circuit-inverter-100w-by-ic-4047-2n3055.jpg

This starts with DC and produces a much higher AC voltage suitable for small AC appliances.

The part marked 4047 oscillates and produces outputs which drive big power transistors which then drive the transformer.

That's really cool. What does IC 4047 stand for and what is that VR 250K component coming out of pin 2?

 

[MATLABdude]

That's really cool. What does IC 4047 stand for and what is that VR 250K component coming out of pin 2?

IC 4047 is an integrated circuit. A (more-or-less) standardized part produced by a bunch of semiconductor companies. Look for CD4047 or some such. For instance, Fairchild makes one:
http://www.fairchildsemi.com/ds/CD%2FCD4047BC.pdf

VR 250k is just a 250 kOhm potentiometer (a.k.a. Variable Resistor) used to tune the duty cycle of the circuit.

EDIT: As per the notes that accompany this very similar design:
http://www.elecfree.com/electronic/100w-square-wave-inverter-by-cd4047-lm3582sc10612n3055/

 

[vk6kro]

The CD4047 is a CMOS logic integrated circuit.
There is a whole family of such chips that all have numbers starting with CD4... and they are very useful for making circuits like this one. They are a little slow for some things so there are other chip families for faster logic jobs.
In this case it is a multivibrator which produces two outputs that are 180 degrees out of phase with each other. It is adequate for this purpose.

Type CD4047 into Google to download a data sheet if you like.

The VR 250 K is a variable resistor with a maximum resistance of 250 K ohms. It would be used to set the frequency of the oscillator in combination with the capacitor Cx.

 

[cabraham]

There was a nuclear cell which not only provided ac, but outputted constant current as well, unlike the constant voltage types in common use. If you google the word "nucell", you should find it. The main physicist who was developing it died in a car accident and I don't believe anybody picked it up. It should make interesting reading.

Claude

 

[mherna48]

That's really cool. I wonder if they stopped developing it. Maybe they don't trust people with radioactive materials.