Clipper Bridge Rectifier Three Phase Voltage Question

[RichardB]

This might be a silly question, but hopefully someone can explain it to me.

If I've got a hydro turbine generator, generating wild three phase AC.
This is connected to the Clipper and the Clipper connected to a Classic 150.
The bridge rectifier in the clipper converts the three phase AC to DC current.
I would like the voltage going from the Clipper to the Classic to be 120V DC --- does this mean that the three phase current going in also needs to be at 120V? Or can it be much higher from the turbine generator, say 400V and if so how is this "stepped down" by the clipper?

Cheers
Richard

[dgd]

The Clipper will protect the Classic from over-input-voltage by clipping its DC output voltage if it is too high for the Classic to work with.
This limiting is set by a little screwdriver twiddled pot on the Clipper's main circuit board.
Its well explained in the Clipper manual with 150v, 200v and 250v settings depending on which CLassic model you are using.

The Clipper has no DC voltage step up or down capability. Its 3 phase bridge rectifier produces DC voltage that is about 1.35 times the Vac.

dgd

[vtmaps]

I would like the voltage going from the Clipper to the Classic to be 120V DC --- does this mean that the three phase current going in also needs to be at 120V?

Welcome to the forum,

dgd answered: "Its 3 phase bridge rectifier produces DC voltage that is about 1.35 times the Vac."

To elaborate a bit....  Usually when we talk about AC voltage, we are referring to the RMS (root mean squared) voltage.  The actual AC voltage is constantly changing... the RMS voltage is an average voltage, calculated in a way that tells you how much power the AC sine wave is carrying. 

For example,
if you hook up a 120 ohm resistive load to 120 volts DC, 1 amp will flow (ohm's law), and that would be 1 amp X 120 volts = 120 watts.

if you hook up a 120 ohm resistive load to 120 volts AC (RMS) that would also be 120 watts, but not because 1 amp is flowing... the current is constantly changing as the voltage changes. 

Another way of describing AC voltage is "peak" voltage.  The AC sine wave goes from zero to peak voltage, and back to zero, and then to negative peak voltage, and then to zero.  And it does this 60 times per second (for a 60 hz AC sine wave). 

The peak voltage of a sine wave is 1.4 times the RMS voltage.   The positive peak to negative peak voltage is twice that.

A bridge rectifier will reverse the negative peaks and give you a DC voltage that fluctuates from zero to positive peak 120 times per second. 

Therefore, if you start with 120 volts AC (RMS), the bridge rectifier will output up to 120 X 1.4 = 168 volts (there will be a few volts lost by the rectifiers themselves).

--vtMaps

[RichardB]

Thank you so much for taking the time to explain that. You've cleared up a long standing question for me.