Just to update this for completeness. I finally got round to modding the TC420 with this mosfet
, for use with the Twinstar 900S.
I bought some 6 amp cable from Maplin and a couple of DC jacks (2.5/5mm). This means that I didn't have to mod the Twinstar cables in any way.
The power from the Twinstar adapter feeds the mosfet power in. I then have a jumper cable coming off the mosfet to the TC420 power.
Soldering the PWM gate on the TC420 to the PWM input on the mosfet was a bit fiddly but ok.
I then attached the mosfet to the roof of the TC420 case with a 'no more nails' strip and closed it back up.
It is working perfectly and, unlike some of the cheap dimmers you can buy for Chichoros style lights, there is no buzzing when dimmed.
I am running a full schedule today and will keep any eye out for heat from the TC420, but I do not expect any problems.
Thanks to zozo for giving me the confidence to try this out!
If anyone else wants to program their Twinstar 900 on the relatively cheap, I'd be happy to answer any questions you have.