Re: Sizing of braking resistors for a VFD

I used a bank of 2.2K - 10Watt resistors (32 in parallel), to get a
final value of 69 Ohms at 320 Watts.

This is used with a Model GS-23 Drive (Automation Direct) and a 3Hp
Motor on my Lathe.
AD recommended 70 Ohms at 300 Watts.
After about 3 hours of constant starting and stopping, they were
still cool.

I was careful in the construction leaving an air gap between each
resistor for air flow, these were sandwiched (lengthwise) between 2
copper clad boards (unetched circuit board) with 2 pcs. of 0.5" x
0.5" angle aluminum for mounting. Ended up with a nice block about 2"
x 2" x 5" high.

Use the Wire Wound type that is sealed in a rectangular ceramic case.
These can be had from Allied for about a quarter each.
Your total cost would be less than $5! Not bad, considering AD's
prices.

I agree with Jon, the Motor size is probably the most important
consideration. I would think that there is considerable leeway as to
value. I'd use AD's recommendation. I would think that difference
between VFD's is just a few ohms in the drive transistors.

Tom M.