joule heating

hello everyone, I'm new. I got a engineering equation to solve & need some help.

i am doing a project that uses joule heating of a wire & i wanted to come up with an equation to calculate the time it takes to heat up the wire to a certain temperature.

i tried using the heat balance equation:
I^2R - hA(T-Ta) = Mass.Cp.dT/dt
but realised that the time calculated was too far out from the actual measured one.

I am able to collect the following data using a data acquisition system:
- resistivity vs temperature
- current vs temperature
- temperature vs time

how should i go about formulating the equation? is the heat balance equation appropriate?
thanks