Re: Industrial drives, (was: what is the max bus voltage)

[Lee Hart <leeahart@earthlink.net>]

jcmassey@netspace.net.au wrote:
> The weight of an Australian 415VAC industrial drive is half the
> size and weight of a US 220VAC drive for the same power. In these
> controllers Amps = mass. Double the volts, halve the amps, roughly
> halve the mass. Why? amps = heat, mostly. Less amps + heat = smaller
> everything.

Yes. And to dig a little deeper, it is because they are using IGBTs as
their power semiconductors. IGBTs have a roughly fixed on-state voltage
drop around 3 volts. The higher the voltage, the smaller this 3v is in
comparison, so the higher the efficiency. It also means halving the
current halves the heat. Thus raising the voltage increases the
efficiency and cuts the heat.

However, IGBTs are not the only way to build controllers. MOSFETs can
also be used. They have a roughly fixed on-state resistance. They also
have the interesting characteristic that halving their rated voltage
cuts their on-resistance by 4:1. Thus, a controller built with MOSFETs
has the same efficiency regardless of its design voltage and current.
Below a couple hundred volts, designers uses MOSFETs. Above a couple
hundred volts, designers use IGBTs.
-- 
Lee A. Hart                Ring the bells that still can ring
814 8th Ave. N.            Forget your perfect offering
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leeahart_at_earthlink.net  That's how the light gets in - Leonard Cohen