I don't know. I never tried to run a 90 volt switching supply at 80 volts.
Do you mean all designs of all switching regulators, or one you can name?

 

Correct, the formula needs to be changed to be able to calculate for Improper operating conditions like if the AC line voltage goes under to 80VAC , what is the ripple and how do I calculate it?

1) No, it doesn't.
2) First, you specify all conditions of voltage and current for input and output, then you post the schematic of the power supply. Then you might be able to create one formula for one power supply, but you will not get the Universal Truth for All Circuits.

 

All kinds , every power supply will react differently when you supply it at 80VAC , the output DC voltage will either be stable or the power supply will turn off from the cut off and threshold point.

What is determining the power supply threshold point and cut off point

You adjust the AC variac until the linear or switching power supply turns off. What is determining this cut off point and threshold point? it might be 80vac or it might be lower depends on the power supply

 

The answer to both of your questions is: "The way it's designed."
If you can't name the power supply, nobody can name how it works when you abuse it.

 

The ripple rises because of the filter cap values are only ment for filtering at 120vac and not 80vac

No.
A larger value is required at a lower voltage to maintain a certain % ripple value for a given load.
Max.

 

adding more capacitors in parallel will maintain a constant % ripple value not to drift or change with the AC input voltage goes down to 80vac?

 

No, adding more capacitance will not cause a constant % of ripple voltage.

 

No, adding more capacitance will not cause a constant % of ripple voltage.

What will then?

 

Absolutely nothing.
There is no way to force the percentage of ripple on a power supply capacitor to remain the same for all operating conditions of load and line, including an input voltage below the design limits.

 

There is no way to force the percentage of ripple on a power supply capacitor to remain the same for all operating conditions of load and line, including an input voltage below the design limits.

I have seen very large capacitors 10,000 uf cap in power supplies that is before the filter caps for input line sag to keep the percentage of ripple on the output of a power supply in case the ac line drops down

 

Do you think that will work for All Circuits Everywhere?

 

Do you think that will work for All Circuits Everywhere?

Not sure, maybe

I'm just saying what i have seen in the past

 

To answer your question
actually UPS power supplies can have the AC voltage very low without any change to the DC output and ripple

 

That's because they get their output power from a battery which still has the same voltage when the power line voltage gets too low.

 

That's because they get their output power from a battery which still has the same voltage when the power line voltage gets too low.

Yes it switches over,
you take the battery out of the circuit and and use an AC variac to lower the AC input and measure the cut off or threshold of the UPS switch over point which is about 90VAC

 

90 volts? Not 80 volts? Why is that?
So that means I can expect every UPS everywhere to work without a battery until the power line gets to 90 volts?

 

90 volts? Not 80 volts? Why is that?

Because the UPS wants to switch over as close to 115vac , that is what UPS designers set the threshold point of switching over

 

so it's just magic?
it happens for a reason with a formula

It is clear from your questions and responses to our answers that you do not understand how power supplies work. Without some basic understanding, none of the answers to your questions are going to make sense. If a device - ANY device - is operated outside of its design parameters, there are consequences. What those consequences are depends on what the device was designed to do. Without a schematic of a particular power supply design, general explanations will not satisfy your questions.

ak

 

Because the UPS wants to switch over as close to 115vac , that is what UPS designers set the threshold point of switching over

If the switching point is designed to be close to 115 volts, why do the UPS devices keep working with no battery as low as 90 volts?

 

If the switching point is designed to be close to 115 volts, why do the UPS devices keep working with no battery as low as 90 volts?

with no battery? or the battery is at 90VDC?