transformer question

[capybara]

i want to use a transoformer from car batttery (primary 12v) to computer
(120v secondary).
450 watts (MAX) = AMPS x 12 V.
AMPS = 4
WIRE SIZE = 18 gauge
my question is in the windings.
12 windings primary and 120 windings secondary or the other way arounnd?
windings prrimary/ volts primary = windings secondary/ volts secondary ??????????

 

[nick1985]

i thought this was about the action figures

 

[f95toli]

Won't work. Transformers only work with AC, car batteries give DC. What you need is a DC/DC converter, a step-up converter to be more specifik.

 

[dkozloski]

1:10, primary to secondary. How do you plan on converting the 12volt DC to AC so that a transformer will work. Why not go to the local RV store or Radio Shack and pick up an inverter rather than trying to reinvent the wheel?

 

[bigshooter]

Originally posted by: nick1985
i thought this was about the action figures

damnit, someone beat me to it

 

[dym]

transformer only works on AC...
BTW, the car battery isn't pwerful enough...

 

[DrPizza]

Numerous plans available on the internet if you google it. Some of the plans are higher efficiency than commercial inverters.... I don't know how cost effective it is.

 

[User1001]

just curious how hard is it to convert dc to ac? What would you need?

 

[dkozloski]

Back in the dark ages of tube car radios, a vibrator (doorbell buzzer) was used to create a DC square wave. Next came the synchronous vibrator which also rectified the high voltage AC back to DC. Now a solid state multivibrator circuit is used to create the required DC square wave at a much higher thus more efficient frequency.

 

[Special K]

Can someone explain to me how an inverter works in terms of individual circuit components? (is it similar to the "DC transformer" I asked about in an earlier thread?) I did a search on google for "how inverters work", but it really didn't return anything of the level I am wanting. It was just sites that were selling them and provided brief descriptions of what they do, but not how they do it.

 

[Mark R]

Essentially an inverter works by connecting a transformer to a DC supply via a series of switches - the idea being that the transformer is connected to DC for a short period of time, the switches then change over so that the positive and negative connections are reversed. In modern electronic inverters the switches are solid-state devices - in low-power devices like domestic UPSs these are MOSFETs, in industrial devices these may be GTOTs or IGBTs.

Essentially, the transformer gets AC power in, and AC power must come out. In some industrial systems, (e.g. variable speed motor drives) a transformer is not necessary, and the switches can be connected directly to the load.

The simplest circuit to describe is the 'H bridge' - so called because it looks like an 'H'. See here. This would work by closing switches S1 and S3 and opening S2 and S4. Then opening S1 and S3 and closing S2 and S4. This provides a Square wave.

To produce a sine-wave, instead if simply closing the switches - pulse-width modulation (PWM) is used. The switches are opened and closed at high frequency (e.g. 20 kHz) with the on-time being varied - so that near the peak of the wave the switches spend most of the time on, but near zero volts they are swicthed off for most of the time.