Full wave bridge Mains DC

[Mosaic]

Hi:
When I use a fullwave bridge on an AC voltage of 6.3V I get close to 9VDC. Which I suppose is the effect of RMS on the AC sine wave.

If this is so would I see 169VDC if i full wave bridge rectify 120VAC?

 

[ARandomOWl]

If this is so would I see 169VDC if i full wave bridge rectify 120VAC?

Theoretically yes. However it will most likely be a volt or so less due to the forward voltage drop across the diodes.

 

[Reloadron]

Hi:
When I use a fullwave bridge on an AC voltage of 6.3V I get close to 9VDC. Which I suppose is the effect of RMS on the AC sine wave.

If this is so would I see 169VDC if i full wave bridge rectify 120VAC?

No, not quite. I would venture a guess you are measuring across a capacitor? If you rectify 120 VAC RMS you will get about 120 VDC less the forward voltage drop of alternate sets of diodes in the bridge conducting on alternate half cycles of the AC signal.

If you have 6.3 VAC RMS the rectified value will be less than 6.3 volts DC. However, if you have a capacitor across the full wave bridge output that cap will charge to the peak value or 6.3 * 1.414 = 8.9 volts DC.

The RMS value of a sine wave is the DC equivalent.

Ron

 

[Mosaic]

If I were to have 12 , 14VDC loads that i want to run from the mains.....in series, can I place the smoothing caps across each of the loads....12 caps rated at 25VDC?
Or do i have to have like a 200VDC cap across the rectified mains?

 

[Reloadron]

If I were to have 12 , 14VDC loads that i want to run from the mains.....in series, can I place the smoothing caps across each of the loads....12 caps rated at 25VDC?
Or do i have to have like a 200VDC cap across the rectified mains?

No, that is not a good idea. First do a Google of Caps in series. You will find that the capacitance of caps in series is calculated the same way resistors in series is calculated, so what happens to C total. Next, what happens when a cap fails shorted? Doing it this way is not a good practice for your application.

How much current do your loads draw? Must the loads have exactly 14 volts?

You can get a 2 amp 12.6 volt transformer pretty cheap as well as a full wave bridge and a few caps and have your power supply.

Ron

 

[eerizal]

1/o address on system bus

hi, i have a project on analab 2.0. my instructor ask me to make a hardware for a stepper motor and plug it in the system bus of analab 2.0.my problem is i don't know how to get the i/o address of the system bus.please help.

 

[Reloadron]

hi, i have a project on analab 2.0. my instructor ask me to make a hardware for a stepper motor and plug it in the system bus of analab 2.0.my problem is i don't know how to get the i/o address of the system bus.please help.

Please start another thread with your question. It has nothing to do with this topic.

Thank You
Ron

 

[crutschow]

No, that is not a good idea. First do a Google of Caps in series. You will find that the capacitance of caps in series is calculated the same way resistors in series is calculated, so what happens to C total.

You should do that Google search yourself. Caps in series are calculated the same as resistors in parallel. Caps in parallel are calculated the same as resistors in series.

 

[Reloadron]

You should do that Google search yourself. Caps in series are calculated the same as resistors in parallel. Caps in parallel are calculated the same as resistors in series.

My bad, sorry. Caps in series are calculated the same as resistors in parallel and caps in parallel the same as resistors in series. That works better. That's what I get for thinking as I type. Damn

On another note what would be your thoughts on caps in series for his application if you see this post?

Ron

 

[crutschow]

Caps in series are usually not used unless absolutely necessary. One disadvantage is that you generally need bleeder resistors to help equalize the voltage across each cap.

And, of course because of the series connection, each cap has to have a value X times the desired total capacitance for X number of series caps. Thus if you wanted 10µf of total capacitance with 12 caps in series, then each cap would need to be 120µF.

 

[crutschow]

If I were to have 12 , 14VDC loads that i want to run from the mains.....in series, ...

If you run loads in series, then each load has to take exactly the same current.

 

[Mosaic]

If we have 12 loads in series of all equal resistance. Pulling about 3 Amps with a voltage drop of 14VDC each with a 1000uf Cap across each shouldn't each load see the full 1000uF at 14VDC smoothed?

 

[crutschow]

If we have 12 loads in series of all equal resistance. Pulling about 3 Amps with a voltage drop of 14VDC each with a 1000uf Cap across each shouldn't each load see the full 1000uF at 14VDC smoothed?

Yes, each load will see it's own 1000uF cap.

But it won't be smoothed much. Even increasing to 10,000µF will give a ripple of over 2V from a full wave-rectifier output with a 3A load.