add Soft Start on Cyclone?

[Will Blick]

I have a ClearVue Cyclone...the Leeson motor (5hp, 240V) is abused with start/stops when moving from machine to machine throughout the day... not good for motor life...

has anyone added a soft starter to increase motor life? If so, what model? Price?

For those not familiar, a soft starter ramps up the starting of a motor over several seconds to reduce the stress vs. instantaneous on.


TYIA

[Dennis Ford]

An alternative idea; consider a time delay relay to keep the cyclone running a few minutes while you move to a different machine. This should reduce the number of starts and would be much less expensive than a soft starter.

[Will Blick]

I have an EcoGate GreenBox 12, that leaves cyclone on for programmable time after stop...but only a few minutes... i hate hearing the thing all day... it seems I use machines for few minutes 5 -7 times an hour, vs. using one machine for extended time.... the motor is in an awkward spot, so I rather preserve it, vs. letting it burn out and have to replace it. Maybe these Leeson motors can take a beating? Most motors from my experience do not like excessive start /stops...

[Bruce Wrenn]

How often do you start / stop your table saw or air compressor? My DC is controled by a sensor that senses anytime there is current in any one of the machine circuits. Sometimes this is ten to fifteen starts per hour. Soft start is a technology that is used on universal motors to ramp up the speed and reduce reaction torque.

[Will Blick]

> My DC is controled by a sensor that senses anytime there is current in any one of the machine circuits.

My post above yours, describes the same system I use...

I never kept track, but DC starts/ stops 40x a day....

In addition to reducing start up torque, soft starters increase life span of motors that start / stop often, hence my interest. But maybe its possible these DC motors survive 10 years with no help... this is what I am curious about. A TS motor starts unloaded, DC motors start loaded, specially when the gates are closed for a few seconds....

[Howard Acheson]

Check with the motor manufacturer before you add a soft start. Dust collector fan plates are very heavy and draw lots of current from the moment the electrical connection is made. A tool like a table saw starts with no load on the motor. Dust collectors and compressors have high load on start up.

[Chip Lindley]

I never kept track, but DC starts/ stops 40x a day....

In addition to reducing start up torque, soft starters increase life span of motors that start / stop often, hence my interest. But maybe its possible these DC motors survive 10 years with no help... this is what I am curious about. A TS motor starts unloaded, DC motors start loaded, specially when the gates are closed for a few seconds....

WIll, with a 5hp, 240v motor, each time you start it up, the inrush current is huge. Rather than soft-start, consider just leaving the DC running for longer periods. Oneida cautions against excessive frequent starts of their systems, yet offers no soft-start feature.

40 starts / 8 hours = once every 12 minutes! Geez! IMO, your motor will last longer if you just let it run, PERIOD! You certainly won't spend much more for electric power. Frequent starts of a big 5hp motor surely adds kw-hours to your bill.

I think if soft-start were a big issue with DC systems, the BUZZ would be BIG in this forum. You are the first I recall, mentioning it.

[Will Blick]

Chip, my guess is, you are right, if DC motors burned out often, this thread / forum would have heard about it.... maybe the motors can take lots of start / stops without failing. I do notice the DC makers do not offer Soft Starters, I assume its because the price is so high, it makes economic sense to just replace the motors. My motor is 12ft high, and like a fool, some workers ran some duct holding structure and conduit above it... so I was just trying to avoid the huge hassle of trying to replace it in the future. If I ever install one of these in the future, I will be sure it remains in a more serviceable area. I emailed the new ClearVue owners, maybe they will have feedback on the life span of these motors when they start stop often...

Its the constant noise that I want to avoid, both annoying in shop, and to neighbors :-)

oh, btw, the high inrush current is less than a second, it costs virtually nothing.... but at about 20 amps per leg, running continuously would cost $5 per 10 hours at 10 cents per kwh... still not huge. But, my guess is, the motor draws a lot more amps with all the gates closed, which is what would occur if I just left it running.... that is the beauty of the Eco Gate system, you can forget about DC and just use the machines.

[Dennis Ford]

One reason you don't hear much about soft starters is the expense, it is industrial equipment. I have never even seen one for single phase motors, I am sure it can be done but would not want to pay for it.

[mreza Salav]

the motor draws a lot more amps with all the gates closed, which is what would occur if I just left it running....

Actually it's the opposite, it will draw much less amp if all the gates are closed, it may sounds counter intuitive but the motor has to do a lot less work if there is no air
to be moved (thus not much amp drawn).

I too think the electricity cost of running the motor all day might be more than the cost of changing the motor when it dies (depending on how frequently the motor dies).
I have not seen anybody on these forums complain their DC motor died because of too frequent start/stop cycles.

[Will Blick]

> Actually it's the opposite, it will draw much less amp if all the gates are closed,

Interesting, I will have to test this sometime, it does seem counter intuitive....

Agreed on the price issue... I have seen 240Volt soft starters, and the ones I stumbled across cost more than the motors, but never shopped for them.... like all electronics, there is industrial grade, prosumer grade and consumer grade levels... Interestingly enough my Festool TS75 Circ. Saw has a soft start built into it...

[Peter Clark]

I just put a soft start VFD (veriable frequency drive) on a 5hp 3 phase motor. I'm using it to convert from single phase. Cost was about $480.00 delivered from Factorymation.com you might take a look and see what they have to offer.

[Noah Katz]

My DC is controled by a sensor that senses anytime there is current in any one of the machine circuits.

Bruce, could you give some details?

Will, can the Ecogate be used w/o gates?

Even if it can, I suspect it's pretty pricey.

[Chris Parks]

As mentioned a few posts up a VFD will do this and you can also use it to change the speed if you want. Bill Pentz who designed the fan does not recommend running it over 4000 RPM. The VFD's we use have an RPM display on them though it only reads at half speed so a bit of basic mental maths is involved.

[Bruce Wrenn]

The system I use is based upon an article on FWW, Aug 2000. There is a sensor (made by SSAC) through which the machine leads pass. When it senses current flow, it trips relay to start DC. When it shuts off, a cube timer (not included in original article) allows the unit to run for about ten seconds to clear pipes. I never have to look for a remote. When I taught shop, the shop had only one control for the DC is a 3000sq ft shop. I vowed then to make mine automatic.

[Jonathan Spool]

+1 for a VFD

[David Kumm]

I also run my DC on a vfd. Start up is programmed for about 5 seconds. By watching the amp draw when gates are closed and when fully open you can judge whether the system pipes and filters are balanced with the size of the motor. This allows for tweaking the speed-within the rpm capability of the fan- or adding filter material, sizing pipes, etc. In my case it allows me to use single phase in which saves my RPC capacity. I also have a mag starter with a plug so the DC can be hooked directly to the RPC but I find I don't use it because I like the slow start and adjustability. The vfd is a 10hp- derated by half found on flebay for about $300. Dave

[Alan Schaffter]

mreza is indeed correct about current draw with gates closed vs open.

If I read your post correctly (5 - 7 starts per hour) you don't have a problem. The manufacturers numbers I have seen which I believe are just educated guesstimates are 6-8 starts per hour max.

I would set your Green box for the maximum delay on shut-down and leave it at that. Does the delay on shut down affect both the gates closing and the DC blower? If it does not and the gate closes immediately, that is actually easier on the DC blower motor (see first sentence). I have an electro-pneumatic autogate system- much like the Ecogate gate, activation is triggered by a current sensor switch at each machine outlet. When any gate is opened (automatically via a machine current sensor or manual via buttons when I am using my DC as a vac or during filter cleaning) the DC blower will start. I intentionally designed it so when the gate closes it doesn't turn the DC off- I do that via manual control stations. In hindsight after examining how I work, if I hadn't wanted to retain the ability to turn the DC off immediately, a time delay of 3 - 5 minutes would have worked just fine.

Noise is another issue better served by sound proofing and possibly a muffler.

[Will Blick]

yes, Ecogate can be used without gates....but that would defeat its purpose.... its claim to fame is, PC program the system for all its parameters. On machine start, you can program when gate and DC turns on... on machine stop, you program when gate closes and when DC turns off. It has a feature for VFD as well...not sure I need to utilize that, I was more concerned about the motor burning from start / stops...

you can get ecogate pricing at their web site, its been a few years....not cheap, but its quite a luxury to forget about DC....

I do program mine to turn off DC and gate 1 minute after machine shut down, once I get the laptop back in shop, I will change that to 3 minutes, as others have suggested, its incredible how many times I go to use a machine, and DC just shut down in the past 30 seconds or less...

If 6-8 starts per hour are max., then I am probably safe... I will see if the ClearVue owners have any knowledge about this subject and report back anything I learn. Glad to see some are using VFD.

[Noah Katz]

There is a sensor (made by SSAC) through which the machine leads pass. When it senses current flow, it trips relay to start DC. When it shuts off, a cube timer (not included in original article) allows the unit to run for about ten seconds to clear pipes.

Great, thanks.

[Alan Schaffter]

Can you set different delays for the gates and the DC? If so set your gate delay for about 5 seconds and the DC delay to 3 min.

The main reason to keep the gate open is so the dust clears the ducting and cyclone. If you measure your longest run and divide by the typical DC air velocity of 3500-4000 FPM you will see it takes almost no time for the dust to reach the DC and bin. In my shop it is .5 seconds which is much less time than it takes me to clear wood and my hands from the machine and turn it off. If you have a machine that produces clouds of dust not immediately captured then set the gate delay for longer.

[Chris Mahmood]

A soft start with a universal motor like a circular saw has is easy (pretty much all routers do this, for example) since you're just varying the voltage. Soft starting a single phase induction motor is much trickier because the start capacitor has to be sized to survive however long it will take the motor to get going fast enough for the centrifugal switch to remove it from the circuit. None of this is an issue with three phase motors.

[Ole Anderson]

There is a happy place between leaving your DC running all of the time and starting it for every operation. Just aim for 6 starts per hour or less and you will be ok.

[Myk Rian]

You can lessen the start-up current by completely blocking the inlet with a gate.
Compressors (huge industrial ones) use this on start-up. The reason is you are not moving and compressing air, hence less current.
Once it is running, open the inlet.
Of course this would be inconvenient in a shop, unless you could rig something up to open it for you.

[Jon van der Linden]

The main reason to keep the gate open is so the dust clears the ducting and cyclone. If you measure your longest run and divide by the typical DC air velocity of 3500-4000 FPM you will see it takes almost no time for the dust to reach the DC and bin. In my shop it is .5 seconds

I think that the DC should stay on much longer than that. There's ambient dust that isn't collected immediately. The % of dust that isn't immediately collected and circulates inside and around a machine takes a lot longer to collect than it takes for the material to clear the pipe, even in a commercial shop with 100'+ long pipes.

[Samuel Butler]

Bruce
I have created the system described in FWW but I am intrigued about the "cube timer"
What is it?

[Will Blick]

Chris, thx for that info, interesting.... it explains why two phase (240V) motors rarely have soft starts, but yet single phase (120V) and 3 phase motors quite often do... I never realized the added the complexity.

Yes, the spreadsheet-like program of the EcoGate system allows you to control the gate open/close delay, and the DC start/stop delay, independently of each other. I agree with Jon, it pays to leave the DC running at the gate open for as long as possible after a machine turns off, as it pulls residual dust from the air which the DC missed during machine usage. It also allows you the opportunity to get to the next machine without more start/stops.

Good point regarding low amp draw on start-up with closed gates.... since the DC starts up immediately on machine start up, and the gates take 5 seconds to open, the DC system is prob. getting much less of a slam on start-up than I previously thought. It guess it just sounds harsh, but then again, a 5hp motor is powerful beast. So overall, maybe this Leeson 5hp motor will last many years.... I will throw it an assist by increasing the DC off delay settings, thereby reducing the number of starts required throughout the day. In my case, the motor would never die from run-time, instead, it will die from start/stops, as I don't run a production facility where the motor runs for hours at a time, its usually just a few minutes, so all the motor wear is start/stops. I am sure many other hobbyist fall in this category as well.

[Alan Schaffter]

I think that the DC should stay on much longer than that. There's ambient dust that isn't collected immediately. The % of dust that isn't immediately collected and circulates inside and around a machine takes a lot longer to collect than it takes for the material to clear the pipe, even in a commercial shop with 100'+ long pipes.

Read my last sentence.:rolleyes:

[Alan Schaffter]

Bruce
I have created the system described in FWW but I am intrigued about the "cube timer"
What is it?

It is a small electro-mechanical or solid state electronic relay that has an adjustable time delay before the contacts break. The name comes from the metal or plastic can enclosure "cube" . You may also need to purchase a special socket to mount and wire it. You can get them from DigiKey, Factorymation, etc. and any number of electronic suppliers. Just Google "Delay on off relay".

http://www.accesscontrolsales.com/Time_Mark/images/381l.gif

[Will Blick]

ClearVue has no suggestions, and simply stated, leave the motor run....
New owners, so they have bigger issues at hand, understood....
this thread was helpful... I will make the mods to programming, and let it be....

[Erik Christensen]

I posed this exact question to Ed the original clearvue guy a few years ago. He didn't have a hard answer but did say they had one they used for testing - I think the impellers but could have been the finished cyclones - that got started a dozen or more times an hour (every 5 minutes!) for 8 hours a day and had been happy for over a year.

I got from that conversation that as long as I doing something less than that I would be fine. I sure hope so as mine is buried in the overhead in a muffled closet and would be a world class PITA to swap out.

[David Castor]

Just to clarify one point - starting a motor on a soft starter does not really reduce the heat produced in the motor during the start. It does reduce the starting torque and this may be easier on the driven equipment (fan, blower, etc). Starting on a VFD is different and it does drastically reduce the heating in the motor during acceleration. The motor does not really go through a start when on a VFD - it just runs up from 0 Hz to whatever speed is desired, with the VFD maintaining a fairly constant motor slip as it accelerates. If too frequent starting is causing a motor to overheat and fail, a VFD will usually solve the problem - a soft starter probably will not.

[Noah Katz]

You can lessen the start-up current by completely blocking the inlet with a gate.
Compressors (huge industrial ones) use this on start-up. The reason is you are not moving and compressing air, hence less current.
Once it is running, open the inlet.

Is there evidence to support this or is it speculation?

I believe the problem is the huge rotational inertia of the impeller and the energy it takes to get it up to speed, not pushing air.

The HP required to push air through a centrifugal blower increases with the square (or is it cube) of RPM.

Therefore there is very little load at lower RPM, and perhaps nothing significant until after the start windings have kicked out.

Speaking of which, I don't believe it's the running windings that are a concern, but the start caps, centrifugal switch contacts, and maybe the start windings.

A VFD only works on 3-ph motors, which have none of those things, so if you have a 3-ph motor I don't think there's a concern to begin with.

Not for the motor anyway; if one is being used as a phase converter, a slow rampup is a good idea because there are caps inside which, like 1-ph motor caps, are rated for a certain number of starts per hour.

[hank dekeyser]

Once again I am baffled by all the hoopla about "soft-start" and "my DC motor is gonna burn up" etc, etc, etc. I've been running my cyclone whenever I need it on and off not caring for how long it runs or when it last ran etc. for well over 10 years now with a Leeson 5hp motor and guess what ? It still works when I turn the switch, day in- day out - every day. It's burried in the rafters in a closet no less. No ventilation, no fancy nuthin'- If I manage to let the smoke out of it, I'll get it rebuilt and keep on abusing it like I have been. I like spending my money on tools I need rather than worrying that the sky is fallling- my 2 cents

[Myk Rian]

Is there evidence to support this or is it speculation?
For 35 years, I worked as an Instrumentation Journeyman Leader at Ford Motor Company, Rouge plant, Dearborn, Mi. It was my job to make sure compressor controls worked, correctly.
I worked in every building and tunnel in the entire 1200 acres of the plant, plus other plants.

Cases in point;

The oxygen plant.
We produced liquid O2 as a final product. The main compressor was driven by a 5000hp motor. It produced 70 psi air pressure to the plant. A 32" inlet pipe fed it from the filter house.
It was started with the intake vanes closed. To do otherwise the breakers would trip. It was designed that way.

After producing the liquid O2, it was pumped to a 40' diameter ball storage tank. To turn it back to a gaseous state, it was pumped into a steam heated vaporizer, then to 1000hp compressors producing 450psi @ 45,000 cfm. The compressors were started with the intake vanes closed. To do otherwise the breakers would trip. Etc. Etc. The gaseous O2 was fed to the basic oxygen furnace where steel was produced.

A2 compressor station.
This compressor fed the south west 1/4 of the Rouge plant. A 2000hp motor turning a turbine compressor, producing 120 psi plant air. It was started with the intake vanes closed. To do otherwise, blah, blah, blah.

It doesn't matter the size of a compressor, or fan. Huge industrial, or home shop, the same rules apply. It just isn't done in a home shop because you aren't drawing current measured in thousands of amps, at 13,200 volts.

Need I say more?

[Will Blick]

From Jerry, new ClearVue Owner

> It is not recommended to start/stop more than 5 times per hour. And make sure the impeller has come to a complete stop.


Erik, that is great info, thx for sharing...sounds like you are in the same situation I am in... replacing my motor would be 15 hour job, in awkward positions 14ft high.... dumb planning by others who help build my shop... oh well....


> I don't believe it's the running windings that are a concern, but the start caps, centrifugal switch contacts, and maybe the start windings.


Agreed, as I mentioned, my motor would never burn out from "mileage".... as mentioned by a previous poster, they do make single phase and two phase VFD / soft starters...


Hank, that is the best testimony I have heard yet, and what I was hoping to hear....thx... I was not aware ClearVue has been around 10 years, have you really had yours that long? Do you use your ClearVue daily? How many start /stops on avg. per day?

[Jon van der Linden]

Read my last sentence.:rolleyes:

LOL My point is that ALL stationary machines have significant amounts of dust that aren't immediately collected, there is no "if." My last machine has a 12" pipe, it pulls in a lot, but I still leave it open for a while. Keeping the ambient air clean is really important in an enclosed space.

[ian maybury]

I'm another that's gone the VFD/220V 3 phase route with a Clear Vue fan and cyclone, in my case primarily to reduce the start up amps draw on the fairly low 60A supply limit we have. Can't say how well it will work, as it's still mid install.

There's quite a few advantages to using a VFD though:

1. Reduced current draw on start up. (ability to ramp the start)
2. Ability to tune RPM to suit system and specific machine requirements.
3. Ease of hooking up a remote/radio start stop switch and other controls - speed adjustment, E stop and the like. (no need for heavy relays etc - use the inverter's 24V control inputs)
4. Toleration of frequent start/stops. (from this thread)
5. Lower cost 3 phase motors..
6. Gets over the issue of 5hp single phase motors often not being available in UK/Ireland. (the current draw on start up is too high for most domestic installations)
7. Speculative, but it probably greatly adds to the available range of control functions - it probably wouldn't be too hard to use a small PLC or something to arrange a ramped start, selection of stock speed settings and the like.

The downside is that it's more expensive, and installation takes a bit of time and work - vented enclosure, shielded and grounded power cables, wiring the controls etc

It's quite normal by the way for servo actuated inlet vanes to be fitted to the fans in air handling units to reduce the current draw on start up - they are closed when the motor starts, and normally don't open until the motor is up to speed. (their operation can be switched by the star/delta start mechanism I seem to recall)

ian

[Alan Schaffter]

LOL My point is that ALL stationary machines have significant amounts of dust that aren't immediately collected, there is no "if." My last machine has a 12" pipe, it pulls in a lot, but I still leave it open for a while. Keeping the ambient air clean is really important in an enclosed space.

I won't even go there- won't talk about those ceiling hung "dust circulators."

[CPeter James]

Does this mean that I should not start and stop my table saw, lathe, drill press, jointer, more than a few times each hour? For safety reasons, I often start and stop them many times when using them. If I am using my 5 hp IR Type 30 air compressor to run a sand blaster or air sander, it starts and stops quite frequently. I do not understand why DC systems should be different.

CPeter

[Alan Schaffter]

Does this mean that I should not start and stop my table saw, lathe, drill press, jointer, more than a few times each hour? For safety reasons, I often start and stop them many times when using them. If I am using my 5 hp IR Type 30 air compressor to run a sand blaster or air sander, it starts and stops quite frequently. I do not understand why DC systems should be different.

CPeter

The difference is that the DC motor is under load trying to move air from the get go, while the others aren't under load until you start working stock.

That being said, I don't see what the fuss is all about. You really need to be one speedy or disorganized woodworker to cycle your DC so often it will damage the motor. There is not much difference between 5 times per hour and 7, 8, etc. times per hour, especially if during the next hour you cycle it only 3 times!

I removed my 3 hp DC motor from an old Grizzly dust collector I got from a defunct lumber yard- it is very old with no model number, so it could be 20 years old now. They had it for many years and really abused it- it was so caked with dust that I needed to use a chisel first to clean it. I've been running it for ten years never paying attention to the number/frequency of cycles. Other than replacing the bearings once and polishing the contacts on the centrifugal switch, it has had no problems and continues to work great!

[Will Blick]

Peter, it was made clear many times in this thread, there is no harm in starting TS frequently, as its fully unloaded, this is obvious from the sound alone, as the blade seems to instantaneously make it to full run speed... no stress at all... like you, for safety reasons, I start / stop mine very often, usually to remove small peices before continuing.... same true with all the other tools you mentioned.... the DC as mentioned is unique, evidenced by its struggle to get to full run speed on start up....

> I don't see what the fuss is all about.

"fuss" ? it was a question... a discovery process, the stated reason were because

1) no data was provided for start / stops per hour on the motor
2) the location of the motor made it VERY difficult to replace, otherwise, I wouldn't care, as I would just wing it, and let the motor life play out....

through this thread, it was obvious, the answers were not universally understood... I thought that was the purpose of forums, to discuss these issues? To me, this was an educational thread, I don't consider it "fuss'in"..... Instead, I would classify it as "learning" as there was some great contributions.

But, as commonplace, a thread eventually ends with the classic quote.....

"whats this all about??"
"why the fuss'in"

[CPeter James]

I was not being sarcastic, just curious as to the difference. I will say that my compressor starting against 150 PSI tank pressure starts hard. IR engineered it that way, but I did put an unloader on the head and intercooler to help it. Also, while I have a fairly small band saw, those larger ones, say 30", 36" and 40" come up to speed pretty slowly as well. On electric motors, there are a lot of unknowns and several urban legends. I have followed the thread about the resistor on the start capacitor on the Baldor motors closely and want to follow up on that because, mine has a really hard bank on shut down and it comes just at the time that the start contacts would be closing leading to the inrush of current to the field.

CPeter

[Noah Katz]

It doesn't matter the size of a compressor, or fan.

You may have missed my point, which I admit is a bit academic..

A compressor and a fan may both have high starting loads, but for different reasons – the former because of high inertia and the latter because of high pressure.

I was questioning the assertion that moving air is a significant part of the starting load of a fan.

[Alan Schaffter]

Peter, it was made clear many times in this thread, there is no harm in starting TS frequently, as its fully unloaded, this is obvious from the sound alone, as the blade seems to instantaneously make it to full run speed... no stress at all... like you, for safety reasons, I start / stop mine very often, usually to remove small pieces before continuing.... same true with all the other tools you mentioned.... the DC as mentioned is unique, evidenced by its struggle to get to full run speed on start up....

> I don't see what the fuss is all about.

"fuss" ? it was a question... a discovery process, the stated reason were because

1) no data was provided for start / stops per hour on the motor
2) the location of the motor made it VERY difficult to replace, otherwise, I wouldn't care, as I would just wing it, and let the motor life play out....


Maybe fuss was the wrong term, but lets look at the facts and evidence- previous posts on here and other forums have reported the info and quotes from motor manufacturers as to the "recommended start frequency." Has anyone ever seen a start frequency caution in a DC manual? I doubt that is because they want their DC's to fail so you must buy a new one. Remember, everyone operates a tool differently and start frequency can be computed differently! 10 starts in 15 minutes may not be all that bad if the tool is not used again for an hour or it runs continuously for a half hour. No motors used with home and small commercial shop DCs that I know of have ever included soft start. I have never seen a report (5 different forums over 10 years) of a DC motor failing due to excessive start cycles and that includes a lot of low quality imports. In fact the only DC I have ever read reports about where a motor (and/or switch) failed was the HF and I suspect it was not being used as designed!

My DC blower/motor isn't hidden away, but at nearly 10' in the air, repair is it a task I don't take lightly. It doesn't have or need soft start and I don't count starts-

http://www.ncwoodworker.net/pp/data/1329/medium/P10100382.JPG


through this thread, it was obvious, the answers were not universally understood... I thought that was the purpose of forums, to discuss these issues? To me, this was an educational thread, I don't consider it "fuss'in"..... Instead, I would classify it as "learning" as there was some great contributions.

But, as commonplace, a thread eventually ends with the classic quote.....

"whats this all about??"
"why the fuss'in"

But, you must separate the wheat from the chaff, and if folks would take time to do some research, they would find, to quote a common trial objection, "Asked and answered."

[Will Blick]

Mr. Prosecutor, your case was well presented, your position is clear....
the judge has ruled on your closing argument -
the forum should be closed, as there is no need for it,
ww's should do their own independent research and refrain from asking ww questions on internet forums,
the risk of learning in such a manner represents too much risk to our intellectual health...

case closed....

next....

[Chris Parks]

I put this up for comment only as it blows a theory of mine and also surprised me with the start up results. I have a VFD driving a ClearVue cyclone so I can read the amp draw and during start up the amps do not exceed the running current draw. I expected the current draw to exceed the running current draw by a substantial amount but it does not seem the case at all. The running current draw at 60hz is between 8.9 and 9.2 amps but the surprise to me was that figure does not vary between all gates open and all closed and that little bit of information surprised me as I thought there would be a noticeable difference with it being higher with all gates open. If it does vary it is only in a decimal point or two. What I have noticed is that as the motor has had more running the current draw has dropped from a figure that was always 9.0 plus generally about 9.3, 9.4 to now it has dropped to just under 9.0, roundabout 8.9, 8.8 but generally 8.9. Comments welcome as I know little to nothing about VFD's except they get my cyclone to run at 60hz and have the potential to do all sorts of magic things if I ever get to understand the thing. I am also going to use one on my DP to vary the speed between the gears.

[Dan Hintz]

Chris,

VFDs can control current draw... it's very likely your VFD has been programmed to soft-start, preventing the draw from surging.

[ian maybury]

I guess it all depends on the duty the motor is designed and specified for - versus how often it's started and stopped.

Start up draws much higher currents than does steady state running, and so produces lots more heat. Plus the cooling delivered by the fan is compromised by the lower rpm run for part of the time.

A marginally specified/cheapo motor that's sailing close to the wind on ability to handle high currents, dissipate heat and tolerate raised temperatures is going to be more at risk of failure than a more robust model. After that it's a matter of the duty cycle, and especially of whether or not it reaches some critical temperature above which stuff (the insulation on the windings?) starts to degrade. i.e. how often you start and stop it. How much time it spends running raised currents, and how much time there is to cool. (it'll probably cool faster if left running at full speed than if stopped given the forced draught created by the fan)

It seems that something like a VFD may help because by ramping the start it reduces the start up current draw from the single phase supply on start up to about x3 the running current versus the x5 or more of a direct started single phase motor. Plus three phase motors are usually more robust anyway.

In practice good quality modern motors seem to have much more tolerance of this sort of thing (higher temperature capabilities due to better insulation materials on windings etc), although it may be that cheapie models are not so good. The big three phase motors used on large (full building) HVAC applications have quite a long start cycle and certainly don't like to be started too often.

As the joke goes - they need the smoke to run. Let it out and they stop...

ian

[george wilson]

I know that DC's draw less current when the pipes are all closed,but WHY does my Oneida manual say to always have a pipe open when starting up the DC?

I think I must have a weak breaker,because I can only start my Dust Gorilla 2 h.p. 3 times each hour,or it cuts off. Could be that I seldom run the DC for more than a few minutes at a time to saw a board,etc.,and don't give the motor time to cool enough? It has a Baldor motor. Its so loud I don't like to leave it running.

[Dan Hintz]

I know that DC's draw less current when the pipes are all closed,but WHY does my Oneida manual say to always have a pipe open when starting up the DC?
Are they using any of the air flow to cool the motor? If so, that's a good reason...

[David Kumm]

Chris, the start up is normal. Vfd's are programmed to avoid the inrush. The fact that the amp draw doesn't change leads me to think your system either has enough leaks around the drops or the piping and bags are maxed out so the blower can only force so much air out and opening gates doesn't change the amount passing through the fan. My amp draw doesn't change alot but more than yours and there is a point where it tops out. That is the point at which the capacity of the pipe and filters is maxed out. You didn't say what size motor you are running, the size uf the pipes and the type of filter. That info would help. Dave

[Noah Katz]

I don't think heat at startup is an issue for the motor windings, as the time startup time is brief and they have a lfair amount of thermal mass.

Not so the caps.

As a point of interest, I put an ammeter on my 5 HP 1-ph Leeson, and inrush is a bit over 100 A.

[Myk Rian]

I was questioning the assertion that moving air is a significant part of the starting load of a fan.
I thought I explained that, as did Ian.

[Chris Parks]

Chris, the start up is normal. Vfd's are programmed to avoid the inrush. The fact that the amp draw doesn't change leads me to think your system either has enough leaks around the drops or the piping and bags are maxed out so the blower can only force so much air out and opening gates doesn't change the amount passing through the fan. My amp draw doesn't change alot but more than yours and there is a point where it tops out. That is the point at which the capacity of the pipe and filters is maxed out. You didn't say what size motor you are running, the size uf the pipes and the type of filter. That info would help. Dave

No filters or bags, 5hp Leeson motor, six inch pipes. What I did BEFORE I put the ducting on was test it by blocking the inlet then running it with just the open inlet. That takes out any variables and the current hardly changes, remember this is with nothing on the exhaust. How much does yours change and are you using a VFD or a clamp meter to measure it?

[David Kumm]

Chris, What size fan are you running? I'm wondering if you have no bags so there is no outlet restriction, the motor might have enough capacity that the amps don't change on the input side because you aren't close to maxing it out. I run a 5hp with 8" pipe and a 15.75 onieda fan rated at 1950 cfm. It may be that the 6 inch pipe restricts the cfm enough - 6= 55% of 8- that the gates are irrelevant. If you are running a smaller fan your motor may never use more amps. mine runs more fully closed than yours does open. Dave

[Chris Parks]

It is a 15" fan, standard CV. I was always of the notion and it stood to reason, my reasoning any way, that if the fan was pushing air then it was drawing more current than if the air was stalled as occurs if the inlet is blocked off. A funny thing happened the other day, I started it (accidently) in reverse and the amp draw (running) was only 6.5. I am there looking at the VFD, scratching my head and only getting splinters in the end of my fingers trying to work out why and also the different noise it was making. BTW nothing fell off it so no harm done.

[David Kumm]

Chris, I know only enough to be dangerous but think your motor and fan with no outlet restrictions pull basically the same open and closed because the pipe size doesn't allow enough air to cause the fan work any harder. Turn the hz up or down and see what happens to the amp draw. It should move some then. I believe you should rethink your pipe size if possible. You are only taking advantage of about half of your system's potential. Dave

[Doug Palmer]

The typical inrush to start your motor is 6-8 times full load amps for approximately 6 cycles (or 1/10th of a second). If you install a soft start, it will pull about 3 times full load amps for 3 to 5 seconds. As David properly stated earlier, a soft start will not significantly reduce the heat in the motor and in some cases can actually increase it. I have seen many motors burn up in an industrial setting due to over starting. Usually this is because the user has disable the thermal protection on the motor and has excessively jogged a stalled motor one reason or another. This is much more severe than what we are talking about in the shop. Bottom line, IMO, save your money.

5-6 times per hour is indeed the recommended start frequency, but realize that that is the mfg recommendation and it includes a safety factor of approximately 2 times. I would not hesitate to start the motor 10 - 12 times in an hour, but would not want to do that for several hours in a row. If you suspect the motor may be heating up, let the DC run for a while (even if that means leaving a tool running). The motor will cool the best when running. The best inexpensive solution is to install a $30 time delay relay as recommend by others earlier to keep the DC running between stations. Most likely you will not change stations often enough to worry about your DC motor even without the timer. Please note that the effect of heat in the motor is not cumulative. In other words, you are not shortening the life by your method of operation unless you destroy the motor all in one day. You should have thermal protection on your motor to prevent that from happening.

FYI, I am an Electrical Engineer and Licensed Master Electrician with 28 years of heavy industrial experience.

[David Connors]

That motor is capacitor start / capacitor run. I think soft start is applied to straight induction motors.