Circuitikz; What should I do to put the + and - on the appropriate places like the pair on the picture?

Question

I try to imitate the scale style of the text book (american style), so I modified the length of the bipoles, like this

\ctikzset{bipoles/length=.8cm}

Everything went smoothly except the symbol of + and - on the american voltage source, they were mixed together, like this

An example is this

\documentclass{standalone}
\usepackage[americanvoltages,americancurrents,
americanresistors,americaninductors,
europeanports,siunitx]{circuitikz}

\begin{document}
    \ctikzset{bipoles/length=.8cm}
    \begin{circuitikz}
            \draw (0,0) to[V,invert,v<=$\dot{U_S}$] (0,2.5) 
            to[L=$\mr{j}\omega L$] (2,2.5) 
            to[short,i=$\dot{I}_C$] (4,2.5) 
            to[C=$1/\mr{j}\omega C$] (4,0) to (0,0);
            \draw (2,2.5) to[R=$R$,*-*] (2,0);
    \end{circuitikz}
\end{document}

Answer 1

The supported way to change the relative size of components is to use the class keys resistors/scale, capacitors/scale and so on. Once you have the relative scales correct, using a global scale=xxx, transform shape will give you the sizes you like.

The V symbol (really vsourceam) has the + and - symbol drawn with the current font, and it's not adjustable. Look:

\documentclass[border=6mm]{standalone}
\usepackage[siunitx, american, RPvoltages]{circuitikz}
\ctikzset{resistors/scale=0.7} 
\ctikzset{capacitors/scale=0.7} 
\ctikzset{sources/scale=0.9} 

\begin{document}
\begin{circuitikz}
    \draw (0,0) to[V, l_=$\hat{U}(s)$] ++(0,3) to[R=\SI{5}{\ohm}] ++(3,0)
      to[C=$1/j\omega C$] ++(0,-3) to[short, -*] (0,0)
      node[ground]{};
      \tiny
      \draw (5,0) to[V, l_=$\hat{U}(s)$] ++(0,3) to[R=\SI{5}{\ohm}] ++(3,0)
      to[C=$1/j\omega C$] ++(0,-3) to[short, -*] (0,0)
      node[ground]{};
  \end{circuitikz}
\end{document}

gives:

If you want to be able to change the font you have to add the configurability to the component (hey, I think I'll add it to the next version):

\documentclass[border=6mm]{standalone}
\usepackage[siunitx, american, RPvoltages]{circuitikz}

\makeatletter
%% Redefine vsourceam to have + and - customizable
\ctikzset{bipoles/vsourceam/inner plus/.initial={$+$}}
\ctikzset{bipoles/vsourceam/inner minus/.initial={$-$}}
%% Independent voltage source - American style
\pgfcircdeclarebipolescaled{sources}
{}
{\ctikzvalof{bipoles/vsourceam/height}}
{vsourceAM}
{\ctikzvalof{bipoles/vsourceam/height}}
{\ctikzvalof{bipoles/vsourceam/width}}
{

    \pgf@circ@setlinewidth{bipoles}{\pgfstartlinewidth}
    \pgfpathellipse{\pgfpointorigin}{\pgfpoint{0}{\pgf@circ@res@up}}{\pgfpoint{\pgf@circ@res@left}{0}}
    \pgf@circ@draworfill
    \pgfsetcolor{\ctikzvalof{color}}
    \ifpgf@circ@oldvoltagedirection
    \pgftext[bottom,rotate=90,y=\ctikzvalof{bipoles/vsourceam/margin}\pgf@circ@res@down]{\ctikzvalof{bipoles/vsourceam/inner plus}}
        \pgftext[top,rotate=90,y=\ctikzvalof{bipoles/vsourceam/margin}\pgf@circ@res@up]{\ctikzvalof{bipoles/vsourceam/inner minus}}
    \else
        \pgftext[bottom,rotate=90,y=\ctikzvalof{bipoles/vsourceam/margin}\pgf@circ@res@down]{\ctikzvalof{bipoles/vsourceam/inner minus}}
        \pgftext[top,rotate=90,y=\ctikzvalof{bipoles/vsourceam/margin}\pgf@circ@res@up]{\ctikzvalof{bipoles/vsourceam/inner plus}}
    \fi
}
\makeatother

\ctikzset{resistors/scale=0.7}
\ctikzset{capacitors/scale=0.7}
\ctikzset{sources/scale=0.9}

\begin{document}
\begin{circuitikz}
    \draw (0,0) to[V, l_=$\hat{U}(s)$] ++(0,3) to[R=\SI{5}{\ohm}] ++(3,0)
      to[C=$1/j\omega C$] ++(0,-3) to[short, -*] (0,0)
      node[ground]{};
   \ctikzset{bipoles/vsourceam/inner plus={\tiny $+$}}
   \ctikzset{bipoles/vsourceam/inner minus={\tiny $-$}}
   \draw (5,0) to[V, l_=$\hat{U}(s)$] ++(0,3) to[R=\SI{5}{\ohm}] ++(3,0)
   to[V, invert, bipoles/vsourceam/inner plus={\color{red}\tiny $\oplus$},
        bipoles/vsourceam/inner minus={}] ++(0,-3)
   to[short, -*] (0,0)
      node[ground]{};
\end{circuitikz}
\end{document}

Answer 2

Partial answer: The following should work (or at least have some effect), but doesn't.

\documentclass{standalone}
\usepackage{circuitikz}

\begin{document}
\ctikzset{bipoles/length=.8cm}
\ctikzset{voltage/american font=\tiny}
\ctikzset{voltage/american plus=X}
\ctikzset{voltage/american minus=O}
\begin{circuitikz}
\draw (0,0) to[american voltage source,l=$U_z$] (0,2);
\node[below] at (current bounding box.south) {\csname pgf@circ@avplus\endcsname};
\end{circuitikz}
\end{document}