[Sussex] Outcome Re: OT: another hardware question

[Desmond Armstrong]

> The circuits you found got me wondering: could a simple triac controller
> like [3] be run in DC mode as in [4] circuit 1c, and fitted with an RC
> on the gate so as to ramp up when power is applied?  It's beyond my
> skills though - any offers?
>   

No.

As one that has been working with motor control I am well aware of some 
of the problems.

It has already been mentioned about the use of DC and certainly I have 
been using bridge rectifiers in some of my power tools for years.
The reason that DC motors last longer is that the particles which wear 
from the brushes remain as lubricant while there is current.
With AC the current drops to zero (100 times per second) and the 
lubricant collapses leading to much faster brush wear and hotter commutator.

The triac is an on-off avalanche device with 4 quadrants. One quadrant, 
that of negative 'anode' and positive gate has been particularly 
troublesome in that its presence in the design of the silicon badly 
compromises the characteristics of the other quadrants. I proposed many 
years ago that we should not have this mode of operation and I am 
pleased to see that Philips did take up this proposal and make triacs 
with only the 3 quadrants of usability. The benefit is vastly improved 
dv/dt capabilities.

It would be interesting to do more motor speed control work using this 
new generation of triacs. But that would require much time.