Amp conversion from 12 VDC to 120 VAC

[ryebred]

I am filling out my light controller spreadsheet and calculating all of my loads and have a question about DC to AC.

I have 5 rainbow floods which say that for each flood at 100% intensity they draw .64 amps at 12 Volts DC. Times that by 5 and you get 3.2 amps total. Since these are plugged into an AC line I am trying to figure out how much load is on that circuit? Is it still 3.2 amps being drawn off the 120 volt AC socket?

Or does it convert? IE -
3.2 amps x 12Volts = 38.4 watts.
38.4 watts / 120 volts ac = .32 amps at 120 VAC

[CLD Kevin]

DC to AC power conversion was always confusing to me. So I took actual DC and AC reading for each type of light I used. Once I had everything figured out, I would connect my Kill-A-Watt meter and turn all on at 100% for each controller and take a reading….make sure I didn’t screw something up.

I’m not sure which RF your using, but the one I got from earlier this year actual DC reading 100% on was 0.72A @ 12VDC via Volt Meter. The AC power draw via Kill-A-Watt meter was 0.15A @ 120VAC (or 18W).

It would be nice if the formula you used worked (I used the same), but never did add up.

Kevin

[pyromill]

ryebred wrote:

I am filling out my light controller spreadsheet and calculating all of my loads and have a question about DC to AC.

I have 5 rainbow floods which say that for each flood at 100% intensity they draw .64 amps at 12 Volts DC. Times that by 5 and you get 3.2 amps total. Since these are plugged into an AC line I am trying to figure out how much load is on that circuit? Is it still 3.2 amps being drawn off the 120 volt AC socket?

Or does it convert? IE -
3.2 amps x 12Volts = 38.4 watts.
38.4 watts / 120 volts ac = .32 amps at 120 VAC

one thing you have to take into account is the loss of the conversion circuit too!! .. straight math would be nice but no power supply is working at 100% efficiency to convert 120ac to 12v dc I go with cracker on this one and opt for a kill-a-watt .. or a current meter on the ac side of things.

[Richard Hamilton]

Agree that it is easiest just to get one of those $10 watt meters at a Home Improvement store to use for occasions like this.

It sounds like your flood are drawing about 7 Watts each (.64A * 12 Volts). I am guess those are LED floods because it sounds like to little power for incandescent bulbs.

As a rough rule, your calculations are correct. Promill makes a good point. Assume a 5% to 15% inefficiency in converting... depending on if the conversion is done by a step down transformer (worst efficiency) or by an electronic switching circuit (as in LOR).

Again, you are looking for ball-park calculations. Try to keep a 10% safety margin on the wall plug and taking into consideration what else might be plugged into that circuit in the home.

[gizmomkr]

There are several factors -

The transformer is the bigest one. It would depend mostly on the rating of the transformer rating of the power supply.

The spec for the RF tells you only what the light needs at full power, you could feed it with a 10 amp supply, its still only going to draw whatever is on the data sheet.

Now even with the transformer, if I get a power supply rated at 12v 10 amp, thats a rating on the DC side. on the ac side, the draw will be less. higher voltage means less amperage.