# How do I calculate firing angle of single phase RL circuit?

#### fazlio

Joined May 19, 2009
2
Hi. How do I calculate the firing angle of single phase ac/ac full wave if i am only given resistive load 1.5 ohm, Vs 120v, 60 Hz and oP 7.5Kw? Thanks Guys

#### jasperthecat

Joined Mar 26, 2009
20
fazlio

Try googling "thyristor firing angle"

I got this first up

www.reseeds.com/thyristor%20control%20question.doc

The question only mentions a resistive load not a RL circuit

#### t_n_k

Joined Mar 6, 2009
5,455
There is no "simple" way of solving this but it can be done numerically.

If the power at firing angle 0 degree is Po and the power at firing angle α is Pα

then it can be shown that

Pα/Po=k=1-α/Pi + (1/(2*Pi))*sin(2α) [with α in radians]

Since you are given Pα=7500W and you can work out Po (thereby giving you the required value of k) you can then solve for the value of α using some numerical approximation technique (or graphical method) or a programmable calculator (if you have one) might have an equation solver function.