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Questions on VFD and 3 phase motors

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Forum topic by Loren posted 06-30-2012 03:56 PM 1941 views 0 times favorited 27 replies Add to Favorites Watch
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Loren

7723 posts in 2334 days


06-30-2012 03:56 PM

I recently acquired a Holz-her laminate trimmer (600 lb machine,
not a router) with a 3 phase motor. I thought I might just
switch it out for a single phase motor but the motor in it appears
to run at 9500 rpm… or that’s the cutterhead speed – there’s
a plate on the side of the machine but not plate on the motor.
In any case, the electrics are in good shape so I’ve decided to
try setting it up with a VFD.

It’s rated at 8.5 amps at 220 volts @ 3 phase… so does that
make it a 2 or a 3 HP motor?

-- http://lawoodworking.com


27 replies so far

View SASmith               's profile

SASmith

1606 posts in 1673 days


#1 posted 06-30-2012 04:14 PM

I would call it a 2HP motor.
This is the VFD I am using.
Just a note of caution, mine came set at 400Hz.

-- Scott Smith, Southern Illinois

View barecycles's profile

barecycles

253 posts in 1014 days


#2 posted 06-30-2012 04:29 PM

One of the few things I remember from Dr. Rachon’s physics class is HP=(V x A x eff) / 746. If that is the case then you’ve got a 2.5 HP motor when running at 100% effeciency. And if that is true you’ll want to bump up to a 3HP VFD.

A word of caution: I may be fuzzy on this… It’s been 30 years since I sat in Dr. Rochon’s class!!!

-- Sweeping up sawdust in Texas

View waho6o9's profile (online now)

waho6o9

5074 posts in 1263 days


#3 posted 06-30-2012 04:48 PM

One horsepower for rating electric motors is equal to 746 watts.

Watts = Volts x Amps 220×8.5 = 1870 watts. 1870 divided by 746= 2.506

2.5 Horse power.

This is a guess. Please consult a professional before spending money. YMMV.

Congrats on the new to you laminate trimmer.

View Loren's profile

Loren

7723 posts in 2334 days


#4 posted 06-30-2012 09:28 PM

Ok. Thanks. The plate reads 2000 or 2200 watt so I guess that
puts the VFD needed squarely in the 3HP class.

-- http://lawoodworking.com

View AHuxley's profile

AHuxley

208 posts in 2008 days


#5 posted 06-30-2012 10:08 PM

For VFD sizing forget the HP or Kw output just look at the FLA and size it from there. The Chinese drive SASmith linked to seem to be fine (many people use them) BUT they tend to have slightly low FLA output compared to the name brand drives. For low dollar VFDs I use Teco FM50s from http://www.factorymation.com/s.nl/sc.2/category.13/.f

The 8.5amps is going to allow use of most any 3hp VFD, the Chinese ones are 10amp output. The 2hp FM50s are 7.5 amps full load output so you would have to move to the 3hp.

View TopamaxSurvivor's profile

TopamaxSurvivor

14855 posts in 2362 days


#6 posted 06-30-2012 10:40 PM

If you are going to put single phase in, get a 5 hp or at least 1.5x your motor rating.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Tyrone D's profile

Tyrone D

314 posts in 1019 days


#7 posted 06-30-2012 11:13 PM

FactoryMation really sucks. They haven’t got a new shipment of the Teco FM50-203-C(Which is the 3HP model) since I tried ordering one ~3 months ago.
Get it at www.dealerselectric.com

-- --Tyrone - BC, Canada "Nothing is ever perfect, we just run out of time."

View killerb's profile

killerb

150 posts in 1084 days


#8 posted 06-30-2012 11:36 PM

I have heard good things about both places listed above. I would do the 3 hp. Don’t worry about the 5 hp thing above . That is for static converters, not vfd’s or rotary phase converters.
bob

-- Bob www.bobkloes.com

View TopamaxSurvivor's profile

TopamaxSurvivor

14855 posts in 2362 days


#9 posted 06-30-2012 11:43 PM

Yeah, don’t worry about it. Single phase power has just as much out put as 3 phase per amp ;-))

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View AHuxley's profile

AHuxley

208 posts in 2008 days


#10 posted 07-01-2012 12:06 AM

@Topomax With a VFD that is rated for single phase input their is NO need to derate the drive, period. This is a myth that is often propogated. I can not speak to the Chinese drives but the Teco FM50 does not need to be derated for single phase input. When you get to drives at 5hp and above this does happen but they are NOT rated for single phase input but MOST will operate on single phase input. That is the reason why VFDs are economical for a single machine up to 3hp but beyond that unless you gat a surplus or used drive for cheap they are not usually economical compared to a RPC, even for one machine.

You are correct about the difference between 1ph and 3ph regarding work but drives rated for single phase input take this into consideration.

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TopamaxSurvivor

14855 posts in 2362 days


#11 posted 07-01-2012 12:40 AM

If they are rated for single phase input and 3 out, that is true. No mention of that above. That square root of 3 conversion multiplier can cause a lot of grief ;-))

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View AHuxley's profile

AHuxley

208 posts in 2008 days


#12 posted 07-01-2012 02:33 AM

@Topomax it is important to make such a distinction since without it this is what prolongs peoples misunderstandings. I knew he probably didn’t want a multi-page diatribe on how AC drives work but merely wanted to size a drive, I saw Loren probably didn’t understand you don’t size a drive via output but instead you must size on a motor’s required input. I try to give specific examples of what I KNOW will work since there are a LOT of drives out there and too many caveats to go into. I “know” the Chinese drive is rated for single phase input as I know many people that use them at or near their rated FLA on single phase input, however, since this is not personal experience I opted to reference a drive I personally know will work but not break the bank since he did not mention any “high end” requirements for the drive like sensorless vector drive etc.

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TopamaxSurvivor

14855 posts in 2362 days


#13 posted 07-01-2012 03:05 AM

I took a quick look at them. It says they will take 1 or 3 phase input. Any drive will take 1 phase input, but you generally have to over size to accommodate the 1 phase in with 3 phases out. If you say they will work, OK. My experience is mostly with Allen Bradley, Eaton, Sq D, and ABB.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Loren's profile

Loren

7723 posts in 2334 days


#14 posted 07-01-2012 03:33 AM

Thanks everyone. I just want to know what size to buy, hook
it up and plug it in and see what I’ve got.

The machine has 1 elaborate German-made fuse panel with
a on/off switch, a magnetic switch and a 2nd box with a
fuse for each leg and a 3rd switch on it… an elaborate
system in my opinion but I dunno, maybe it steps down
from 440 volts or something. I’ll post pictures sometime.

-- http://lawoodworking.com

View AHuxley's profile

AHuxley

208 posts in 2008 days


#15 posted 07-01-2012 03:41 AM

MOST VFDs will indeed work with single phase imput whether they say they will or not, there are a few that will NOT function on single phase power but it will say that in the full documentation, if one every bothers to read those tomes in full. The key is whether the drive is rated with a single phase input or not. Most sub-micro AC drives ARE. The derating almost always begins at 5hp with most suggesting a doubling of the AC rated output (seems strange to me since the power factor is much different from that BUT it is their engineers and their product). It seems I have this discussion mostly with people with significant factory floor experience, which makes sense because they rarely have much if any experience with sub-micro drives and even less power those said drives with single phase. I havn’t had experience with all the manufacturers except AB and Eaton, I know Eaton,s NFX9000 series is rated for single phase input and AB’s Powerflex 4 and 40 are rated single phase input (again not the whole range just specific ones), my guess is Square D and ABB also have single phase rated micro drives.

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