> And what
should I consider in designing a circuit to make this coil quiet. It
operates at 24V .46A.
/>


Has to pass max current and withstand max voltage. 1N400X probably OK there.
Low speed but unlikely to be a problem as long as this is off and on for
longish periods at a time (eg >= 0.1 second) and not PWMd. . Want to get
fancy use eg BVY26 or equivalent - but probably no need.


>I guess it would just have to have a reverse bias brake down voltage
grater than 24V and be able to handle about half an amp of current.
/>

Yes

> Will the coil have enough internal resistance to dissipate the power or
should I have a resistor in series with the diode? I am very green at
this and unsure of myself so don't thrash me too hard and thanks in
advance.
/>

Coil may well be OK.
24V at 0.5 amps or so suggests 48R coil.
If so power dissipation will be I^2R = 12W at max current.
No coincidence that this also eqwuals 24V x 0.5A.

Adding extra R will increase flyback voltage of coil.
Maximum disispation PROBABLY about when Rexternal = R coil (past bed time,
brain protests, it says that  transfer theorum probably applies, ask it in
the (this) morning.

HOWEVER all the above may not work. Description is a little uncertain. If
the brake is a generator then adding the diode may make it self brake when
you don't want it to. When you say "electromagnetic brake" do you mean eddy
current, or electromagnet drives a brake show pair or ?????


        Russell McMahon

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