Hello,

I am working on designing an electrical apparatus. I will be using a Toroidal Tx that will output 40VAC @ 37.5A. From this I need to rectify 30VDC @ 30A with a secondary circuit of 10VDC @ ~13.5A.

I am trying to ascertain the size of capacitors I will need to divide my 40V into 30V & 10V (negating losses and rectification factors). I can calculate the Capacitance, Voltage drop, and Impedence for this circuit but I'm not sure if the capacitors have to carry the full load current or just an "arbitrary" custodial current.

Being the nature of a Capacitor I struggle to wrap my brain around the physics. Essentially I am trying to envision a complicated "Edison Three Wire Circuit" or even a simple resistive or potentiometer circuit but I figured I'd just ask some experts.

Thank you for your time.

 

Let's see your proposed circuit.

 

That didn't work at all... guess I'll have to make you a schematic; bare with me I only have cellular internet.

 

Hopefully that works for you.

 

Nope. Can't do dat. Are you designing the transformer?

 

You can't explain if my circuit current needs to be factored into the capacitors?

Essentially I'm wondering if I can use 1uF and 3uF respectively to get 30VAC @ 30A and 10VAC @ 13.5A, or if I need to use 2700uF and 8100uF so they are calculated to "handle" the high current.

Just looking to fill in the blanks on this simple divider circuit.

 

How much current can flow thru a capacitor?

 

I don't think we're getting anywhere...

 

I posted that you can not do that. Have you ever studied or built with electronics before?

 

Capacitive voltage dividers at these kinds of currents are not trivial.

Plus you have the same issues (only compounded) as you would have with a resistive voltage divider. First off, the load currents still have to flow through the capacitors, so they have to have sufficiently low impedance to take this current. Then, unless the base current is sufficiently higher than the load current, the load will have a significant effect on the voltage (and hence on the other load). Typically you need the no load current to be at least 10x the max load current to get decent regulation.

So, for the numbers you have thrown out, you need to forget this idea.

 

Thank you WBahn, that was my assumption but I needed clarity.

I will go another route.

 

If the transformer is also being designed then a simple way is to add a tap to the secondary winding, or possibly a whole another secondary winding, either could work. Also there is a real question about the two required voltages: Do they need to be isolated from each other, or can they share a common connection between them? And will they both be delivering current at the same time?
Without knowing the specific requirements the best you can get is guesses, some better and some worse. That is common with most questions asked in this forum, very few folks with the ability to know the unknown with no information provided. Some make good guesses, most do not. So we need more information about the specific requirements., also including the allowable changes in voltage as the load current changes.

 

Use two transformers appropriately rated or a custom transformer with two secondary winding's, followed by a full wave bridge rectifier on each secondary winding and filter capacitors for a basic unregulated DC supply, that will meet those specs you have listed.

 

Have you considered a 30 Volt Buck-Inverter and a 10 Volt Buck-Inverter after the 40 VAC + Bridge Diode + Filter Cap ?
They are actually quite inexpensive.