|
Posted by AndrewV on April 28, 2006, 9:37 am
Please log in for more thread options
> AndrewV wrote:
>> I have a 7.5 hp vfd currently used to run a 4500 cfm blower fan.
>> Since the use is intermittent I want to power my drill press as well. The
>> DP is an old delta soon to have a new to me 3ph 2hp 230 1740 rpm motor
>> transplant (more questions on that project later). What I was thinking
>> for the wiring goes like this--- place a 240v dpdt shut off on wall next
>> to DP. wire it to shut off power(240 sp) to vfd. next wire a twist lock
>> to the 3 ph output of the vfd and twist lock plugs to the DP and Blower
>> fan. Plug in what I want to use and get to work. Also keep my eye out for
>> another vfd for the future when the dp is farther away from the fan unit.
>>
>
> If the voltages of both motors are the same, then the VFD shouldn't care
> which motor it drives as long as its within its capacity, which yours seem
> to be.
>
>> About the motor change on the DP, I drill mostly mild steel holes to
>> about 3/4" a few to 1" I'd like to set this up with annular cutters for
>> the larger holes. I'm not sure what my target rpms should be. That is
>> rpm's before I use the vfd to adjust the Hz. The driven pulley is 8" so
>> I figure a 3" (I have a 3" & a 7") drive pulley @ 1740 rpm gives me 652.5
>> rpm @ the spindle before I lower it with the vfd, that's faster then it
>> runs now but probably a good top end for me. I'm also not sure how the
>> torque drops off when you lower the motor speed or what Hz = what rpm.
>> Anybody do this before? I'd like to size the drive pulley so there's
>> plenty of torque @ the low end.
>
> The motor speed is directly proportional to the frequency displayed by the
> VFD. If the motor runs at 1750rpm at 60Hz then it will run at 3500rpm at
> 120Hz and 875rpm at 30Hz.
> Normally, at speeds below the base frequency (the frequency the motor was
> designed for) the torque remains constant and, since power is rpm x
> torque, this means that at 30Hz, for example, the power is half that at
> 60Hz. Above base frequency the torque drops so that the power remains
> constant, so you get half the torque at 120Hz. So its constant torque up
> to and including base frequency, and constant power above base frequency.
>
> I hope this helps.
>
> --
> Regards, Gary Wooding
> (To reply by email, change feet to foot in my address)
Thanks for a very informative post , its just what I'm looking for. As far
as "sharing" the VFD, given what will happen if something comes loose while
the vfd is powered if I can find a 2hp vfd to dedicate to the DP I'll go for
it, otherwise what's life without a little risk. On the DP I think I'll go
for a lower fixed reduction so it has more power @ low rpms and then just
overspeed for higher rpms. I'll look around for a 2" pulley so I'll have 435
rpm's @ 60 Hz & 2 hp and 217.5 rpm's @ 30 Hz & 1 hp. I end up with a top end
of about 870 rpm a bit slow for something's but ok for what I do with it.
Of course maybe I'll get lucky and find a step pulley with a 7/8's center.
Thanks again
Andrew
--
NewsGuy.Com 30Gb $9.95 Carry Forward and On Demand Bandwidth
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
> the use is intermittent I want to power my drill press as well. The DP is an
> old delta soon to have a new to me 3ph 2hp 230 1740 rpm motor transplant
> (more questions on that project later). What I was thinking for the wiring
> goes like this--- place a 240v dpdt shut off on wall next to DP. wire it to
> shut off power(240 sp) to vfd. next wire a twist lock to the 3 ph output of
> the vfd and twist lock plugs to the DP and Blower fan. Plug in what I want
> to use and get to work. Also keep my eye out for another vfd for the future
> when the dp is farther away from the fan unit.
>