Re: [CAD_CAM_EDM_DRO] Re: Power supply for Servos - Energy dump and such

Dave,
Using incandescent lamps is a very poor choice for your application.
They have a very non-linear response with time, measuring only a
fraction of an ohm when cold, but increasing to a much higher resistance
as they heat up. The cold resistance of a filament can be less than one
tenth of its hot resistance. There are times when you want a variable
resistor to act as a sort of regulator, but your application is not one
of them.

Your circuit will be far more predictable using an appropriately sized
power resistor, with a heat sink if necessary. Power resistors are
designed to have stable resistance characteristics over their operating
temperature ranges.

Check eBay -- there are always lots of power resistors available, and
many go really cheap. You can series/parallel multiple units if your
precisely desired value is not immediately available. Power dissipation
always adds.

HTH,
Dave

>
>I'm looking for a cheap way to get a 20 watt resistor !
>
>Wirewound are huge, longer than my board.
>
>Aluminum cased will probably be best as I can mount it remote, to the
>side of the enclosure.
>
>Thick film are about the same cost as the aluminum heat sink type,
>but are small enough to put on the board.
>
>Decisions...
>
>Dave
>
>