Power converter question

[yurtle]

Originally Posted by JohnnieB

Your two 55W incandescent bulb in parallel will draw a little less than10A once their filaments reach their operating temperature, but their cold resistance is only about 1/15 of their hot resistance, so they will attempt to draw somewhere in the neighborhood of 150A when they are first turned on.

My guess is that your 36v to 12V converter is limiting the max amps to about 15A, so it is taking the filaments several seconds to reach operating temperature rather than the normal 0.5 seconds or less.

I never thought about this. In my formal job, we used reduced voltage starters for large motors, to keep from dimming the neighborhood.

Does something like that exist for "relatively" small loads like 55 watt lights? I gotta good reducer, but don't want to hit it with that kind of "inrush".

[JohnnieB]

Originally Posted by yurtle

I never thought about this. In my formal job, we used reduced voltage starters for large motors, to keep from dimming the neighborhood.

Does something like that exist for "relatively" small loads like 55 watt lights? I gotta good reducer, but don't want to hit it with that kind of "inrush".

The soft start sequencing probably kept some high voltage transformers from popping oil seals also.

Regardless of size, both motors and incandescent light bulbs have current curves somewhat akin to a capacitor's current curve, or at least to the extent that they both draw max amps initially and then taper off over time.

The 15:1 hot/cold resistance ratio I mentioned is for a 120VAC incandescent bulbs, but the difference between a 120V and a 12V incandescent bulb is the filament thickness, so the ratio should hold fairly true. However, halogen type incandescent bulbs operate at a higher temperature, so the ratio might be greater.

If you are curious, measure the cold resistance of a 12V halogen bulb with and ohmmeter and then measure the Amps and Volts while it is operating and calculate the hot resistance.

[kellybell]

Hot resistance......reminds me of a girl I dated once...........

[gornoman]

Originally Posted by kellybell

Hot resistance......reminds me of a girl I dated once...........

I'm pretty sure I ended up MARRYING her, LOL!