Re: (ET) E15 control board #1

[Paul Abendroth <pabendroth dma org>]

Rhett T. George wrote:
 The board I am working on has in locations C104, C104, and C105 50 
uF, 50 V caps.
 The schematic shows 1 uF, 100 V caps at those locations.
 My question is, "Has anyone come across this discrepancy and 
resolved it to his/her
 satisfaction?"

As my card failed, I just connected pins (10) to (11), etc. Let me 
take a cut at this circuit: The cap cause a delay between switch 1A 
closing (10) and energizing the coil of relay 1A (11) determined 
mostly by C103 and R 109. They delay uni-junction transistor Q101 
from triggering SCR 106 on. The SCR then connects (10) to (11). 
Larger cap or resistor increases the delay. The circuit may also 
protect the switches from in-rush current while the contacts are 
just making. Not as big a deal as avoiding arcing when the switch 
opens. CR106 and R105 may help this.


"Also the 100V caps probably have twice their 'rated' capacity at 
half the voltage."  Not true. Capacity is related to area of the 
foils connected to the wires, and the thickness and type of 
dielectric between them. Doesn't vary with applied voltage (much). 
What is true is that capacitors built for half the voltage could 
have nearly twice the capacity in the same size package, as the 
dielectric can be thinner without shorting. Both would store about 
the same energy at rated voltage if I remember right.