switcher cad question

[williB]

is there any way to give a cap an initial voltage??

 

[Roff]

is there any way to give a cap an initial voltage??

1. Name both nodes that the cap connects to (unless one is GND) by clicking on the "A in a box" icon on the toolbar and typing in a name. Attach the name to the node.
2. Click on the .op icon (upper right on toolbar) and create a spice directive as in the example below, substituting your node names and the voltages you want as initial conditions (ic means Initial Condition).

 

[williB]

and if one node is ground?
same procedure?
EDIT :: without naming ground of course..

 

[Roff]

and if one node is ground?
same procedure?

I should have clarified that. Yeah, just name the node that isn't grounded. GND is defined as node 0, and is zero volts by definition. You can't set an initial condition on GND.

 

[williB]

Thanks i'll try that..

 

[williB]

it worked !!
i used the assigned node name though , but it worked..!
thanks Ron..

 

[williB]

Having an initial voltage on a very large cap is essential when it is in parallel with with a battery..
because the battery just drains into the cap otherwise..

 

[Roff]

Having an initial voltage on a very large cap is essential when it is in parallel with with a battery..
because the battery just drains into the cap otherwise..

Under what conditions? Can you post a schematic? When I place a 10 farad cap in parallel with an ideal (zero resistance) battery, the initial voltage on the cap is the battery voltage. Spice does that automatically.

 

[williB]

ok lemmy wait till the sim is done ..
but i've got or i had a 1.2V battery series resistance = 0.08 ohms. in parallel with a 100 Farad cap series resistance = 0.003 ohms , and when i started the sim ( without initial conditions) the battery voltage went down , not up..

 

[Roff]

ok lemmy wait till the sim is done ..
but i've got or i had a 1.2V battery series resistance = 0.08 ohms. in parallel with a 100 Farad cap series resistance = 0.003 ohms , and when i started the sim ( without initial conditions) the battery voltage went down , not up..

That makes sense.

 

[williB]

hmm i cant seem to reproduce the problem ..
but anyway i was checking out the charging ability of a three phase generator on a 1.2V battery and a 100F cap..
the difference is amazing ( to me ) between single phase a three phase..

on a side note if you eliminate the diodes and battery and cap , and replace them with three resistors to ground it makes a real nice three phase pattern..

 

[williB]

pretty neat - huh?