Anybody got any ideas on this one? I've had to resort to my old flip down helmet for tig welding ally as the auto one doesn't seem to switch over properly, flickers back and forth.

It's fine on steel but no good on ally.

It's not a cheapo helmet either. not the best but not a £40 ebay jobbie either.

I've done a fair bit of ally welding using the auto helmet and not had exactly the same problem, although I've had a bit of flickering immediately after finishing the weld as though the helmet cannot make up its mind whether to switch or not. This I've put down to the fact that the ally reflects light more readily than steel.

Have you tried altering the lighting where you are welding?, try to minimise reflective surfaces.
Does your helmet have adjustment for sensitivity and shade? If mine flickers, I alter the sensitivity. The shade is altered depending on the material and amps ie:

Ally: 10 shade at 80amps, 11 shade at 100-175 amps, 12 shade 175-250 amps
12 shade 250-350 amps and so on. Mine adjusts from 9-14

Some helmets have battery power for the sensor (mine doesn't) running low?

If the photosensor is dirty or surface damaged hen this can cause what you describe.

Sorry I don't have anything definitive for you.

Cheers

dave

Unfortunately it doesn't adjust for sensitivity, only shade.

I think the problem is the sensitivity, or something linked to the AC when welding ally??

radio waves effecting it maybe. the hf needed for ac welding can effect electrical stuff.