# Light globe

1. Aug 18, 2009

### dvn

Is it possible to light a globe - a normal energy efficient globe of 10 Watt usually powered by 240v or so.

Can the globe be powered if I use 24v and put a lot of amps to power it up? According to the PIE formula (Watt/Current*Volt)

thanks

2. Aug 18, 2009

### tiny-tim

Hi dvn!

Perhaps I'm missing the point, but isn't the resistance of the golbe fixed, so that I = V/R, and W = V2/R?

3. Aug 18, 2009

### negitron

No. Or rather, yes. Let me explain. The currect a device draws depends on its supply voltage and its impedance. You have little control over a device's impedance, that's set by design. So, if you have a different supply voltage, you need to convert that to the device's expected voltage. If you have 24 volts and need to step it up to 240, you either use a transformer if you have AC or use a device called an inverter if you have DC.

4. Aug 21, 2009

### dvn

Thanks Negitron. That is the exactly the answer I needed.

One more question, the light globe have Hz. So what is Hz and what it does?

5. Aug 21, 2009

### negitron

Hz is the abbreviation for Hertz; it is a unit of frequency--it tells you how many times per second the voltage alternates. For an incandescent lamp, it doesn't matter since it will work on either AC or DC (it's included anyway because it's a standard parameter on electrical labels) but for equipment with motors or transformers the frequency is important. In the US, the power frequency is 60 Hz; in Europe it is 50. Aircraft use 400 Hz, because at higher frequencies, transformers can be smaller for a given power-handling capability. Railroads use 25 Hz for historic reasons.

6. Aug 21, 2009

### dvn

So if I use the DC motors to power up the globe then I need to adjust the correct Hz for the globe?
If that is so, how can I adjust the correct Hz?

7. Aug 21, 2009

### negitron

You don't need to. Incandescent lamps don't care about Hz. As long as the voltage is correct, it will work.

8. Aug 21, 2009

### dvn

I understand about the normal old globe will work perfectly but what about those new energy efficient globes. I would like to use those since they use a lot less power than the old globes. Old globes are usually 60W to 100W and the energy efficient globes only use aound 10W. So that is why I asked if it is possible to adjust the Hz or a way to control Hz.

9. Aug 21, 2009

### negitron

Oh, are these compact fluorescents? No, those won't work on DC. If you only have DC available, you'd have to convert it to AC with an inverter. You can buy automotive inverters which take 12 VDC and supply 120 VAC (in the US; presumably 240 V units are available for Europe).

10. Aug 21, 2009

### dvn

Ok, if I make my own circuit to get DC to AC from the motor then will the globe work?