...Public art project - Lights running on DC
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> > Have you looked at using DC instead of AC ? It makes the control
> > easier, but looses some of the peak brightness of the light.
AND,
> > regular incandescant bulbs can be run on either.
> >
> > And of course, how many channels are you looking into ?
> >
> > Dave
>
> Hi Dave, thanks a lot for replying,
> I'm using 57 bulbs. And yes, what I was looking for was a easy way
to slowly
> dim the lights instead of just going On and Off.
> So, do I need also 110v of DC current to light a bulb?
> Thanks
> F
Check me if I'm wrong, but you can put a bridge rectifier on your AC
line and connect the output to a light bulb.
That would offer an idea of how bright your lights would be. As I
mentioned, your lights would dim if only rectified.
Add some huge capacitors to get a very bright light as the CAPs would
offer a higher voltage as it would charge up to near the peak of the
AC wave form and not just the RMS value.
Calculate the capacitance needed by (80,000*I)/V
for your 100 watt light, you have roughly 0.9 amps.
(80k * 0.9)/115 = 610uF
As for the voltage, the RMS of your 115VAC is not the same as the
peak. The power supply (bridge and cap) would reveal near the peak
of your voltage. Figure 115 * 1.414 to get around 170 VDC from this
configuration.
That puts a 600uF cap with a 200 V rating in the neighborhood.
Jameco part # 203289 is $ 2.35 per cap, and you would need to figure
out how many you would need. I only looked at ONE light of 100 watts
at 115 VAC.
AND... since I think you would blow out the bulb if you used 170 VDC
on it, you would immediately require a duty cycle on your PWM out of
about 67% to get 115 VDC at the bulb.
Another thought is that if you KNOW you will never have more than one
bulb lit, all you need it that one cap. figure out how many bulbs
you might ever have lit at one time and then you can select how many
caps would be required.
I would not figure that since you are using 67% of the current, you
can de-rate the caps and get less. OF course, you can buy a few and
do some testing.
If you have connections to a motor supply house, you should be able
to get motor start capacitors of high voltage and similar ratings.
I am not sure if you can monitor the DC voltage and adjust the duty
cycle to keep roughly 110 Volts on the bulbs... but that would be
slick.
Of course, you would probably benefit from having a triac and dimming
the AC due to the 57 bulb count you have.
Dave
> > easier, but looses some of the peak brightness of the light.
AND,
> > regular incandescant bulbs can be run on either.
> >
> > And of course, how many channels are you looking into ?
> >
> > Dave
>
> Hi Dave, thanks a lot for replying,
> I'm using 57 bulbs. And yes, what I was looking for was a easy way
to slowly
> dim the lights instead of just going On and Off.
> So, do I need also 110v of DC current to light a bulb?
> Thanks
> F
Check me if I'm wrong, but you can put a bridge rectifier on your AC
line and connect the output to a light bulb.
That would offer an idea of how bright your lights would be. As I
mentioned, your lights would dim if only rectified.
Add some huge capacitors to get a very bright light as the CAPs would
offer a higher voltage as it would charge up to near the peak of the
AC wave form and not just the RMS value.
Calculate the capacitance needed by (80,000*I)/V
for your 100 watt light, you have roughly 0.9 amps.
(80k * 0.9)/115 = 610uF
As for the voltage, the RMS of your 115VAC is not the same as the
peak. The power supply (bridge and cap) would reveal near the peak
of your voltage. Figure 115 * 1.414 to get around 170 VDC from this
configuration.
That puts a 600uF cap with a 200 V rating in the neighborhood.
Jameco part # 203289 is $ 2.35 per cap, and you would need to figure
out how many you would need. I only looked at ONE light of 100 watts
at 115 VAC.
AND... since I think you would blow out the bulb if you used 170 VDC
on it, you would immediately require a duty cycle on your PWM out of
about 67% to get 115 VDC at the bulb.
Another thought is that if you KNOW you will never have more than one
bulb lit, all you need it that one cap. figure out how many bulbs
you might ever have lit at one time and then you can select how many
caps would be required.
I would not figure that since you are using 67% of the current, you
can de-rate the caps and get less. OF course, you can buy a few and
do some testing.
If you have connections to a motor supply house, you should be able
to get motor start capacitors of high voltage and similar ratings.
I am not sure if you can monitor the DC voltage and adjust the duty
cycle to keep roughly 110 Volts on the bulbs... but that would be
slick.
Of course, you would probably benefit from having a triac and dimming
the AC due to the 57 bulb count you have.
Dave