[Shop-talk] VFDs
David C.
cavanadd at verizon.net
Sat Jun 6 12:07:36 MDT 2009
I just purchased a used Delta 12/14" table saw. It has a 5 HP, three
phase Baldor motor on it. I have been doing a lot of research over at
the old woodworking machines site on how to power it. I'm looking for a
more or less plug and play solution, and would rather not start swapping
motors at this point. I have more or less reached the following
conclusions:
- Most people feel that static converters are a Very Bad Thing, although
a few folks report that they work fine;
- If you are running multiple 3 phase loads, or loads in the 5 to 7.5 HP
and up range, a rotary phase converter is the way to go.
- Buying a rotary phase converter is expensive, and apparently you can
build your own for a lot less, but it requires a lot of messing around
on Ebay, not to mention a lot of assembly.
- VFDs are very highly regarded, but the "inexpensive" ones, that is,
under about $400, top out at around 3 HP or 11 amps or so. Also,
anything over 3 HP generally wants a 3 phase input. I'll be running it
with a single phase, 220 input.
- Apparently VFDs are capable of running at 150% for a minute before
tripping out. My motor pulls 12.8 amps at FLA and the VFD I'm
considering is rated at 11 amps. Some Old Woodworking Machinery folks
report running 5 HP machinery on a 3 HP VFD with no problems.
- Since I don't plan on ripping 12/4 maple all day long with a power
feeder, I will probably never approach FLA on my saw, so a 3HP, 11 AMP
will probably work fine for me. Also, the existing saw has an Allen
Bradley push button starter mounted on the front of the saw. With a VFD
I can get rid of the starter and use low voltage switching via the VFDs
inputs to start and stop the saw. If I go with a rotary or static
converter, or a big single phase motor ($$$), then I will be messing
around with sizing the overload heaters, getting the correct coil
voltages, and so on. In my experience with 3 phase motor starters, this
can get expensive in a hurry, expecially for obsolete AB stuff.
Anyone got any experience with these thing or would otherwise like to
wade in?
thanks
Dave C
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