[Sussex] OT: another hardware question

[Jacqui Caren]

Antony wrote:
> Hardware people
> 
> Where can I find a circuit (or buy a gadget) to slow-start DIY tools
> e.g. circular saw up to 1200W?  I've Googled MAO in forums etc. without
> success.
> 
> TIA ( + apologies for list abuse)

Hmm I would pop into the farnborough maplins, Ask for Jim
and ask him this question. he would probably find the appropriate
project notes and hunt around the store for the bits for you.
Seriously nice guy!

It has been over 20 years since I did any EE work but in those days
a "triac" was used to switch on single phase and switch off as the
voltage/current went through the zero point. Micorporcessor
based systems now abound and conversion to DC to extend motor life
are more common.

A ~2KW triac device should not require much of a heatsink as there is
no need to control current flow - the device starts current flow but
only cuts off when current flow stops. The second part of the
circuit is a variable delay controling when the current is enabled.

An example - our kitchen has 6 120W halogens and the dimmer for this
os rated at 2KW and has no heatsink and fits in a standard deep
single wall plate. Note that halogens are NOT an inductive load!

I would expect the whole shebang to be a single IC these days.

Some refs:
http://www.quasarelectronics.com/kit-files/electronic-kit/3019.pdf
http://www.maplin.co.uk/Module.aspx?ModuleNo=19095

http://www.st.com/stonline/products/literature/an/2477.htm

And possibly a good place to ask...

http://www.eng-tips.com/viewthread.cfm?qid=70120

Jacqui

p.s. I usually get someone else to do mains stuff these days. I no longer have
very dry skin and therefore am no longer "immune" to getting electrocuted.