Two Pentz cylcone motor questions

[Todd Willhoit]

Tom,
You are confusing the terminology. VFDs are often derated when a three-phase VFD is fed from a single-phase source. A three-phase VFD has six rectifier diodes on the input. When used with a single-phase source, only four diodes are used, limiting the overall current. As an example, a three-phase 3 hp VFD may be derated tor 2 hp when supplied from a single-phase circuit.

No one is addressing motor derating because it is not something one does. One can apply a 3 hp motor at a capacity below its rating (2 hp for example), but it is still a 3 hp motor. Likewise, an unloaded 100 hp motor may be "consuming" 5 hp in losses just sitting there under power, but it is still a 100 hp motor.

On the other hand, manufacturers specify motors with a Service Factor (SF). The average motor may have a service factor of 1.0, meaning it can operate continuously at 100% of its nameplate rating. Industrial and other special motors may have a service factor of 1.1, 1.15, 1.5, which correlate to continuous operation at 110%, 115%, and 150% of nameplate rating. A 10 hp motor with a 1.5 SF is essentially a 15 hp motor in disguise.

In your case, if you want to run both motors at 2 hp, fix the VFD settings for the 2 hp motor and a standard volts/hertz (non-vector control) mode. If you want to keep both motors at rated hp, the easiest way is to use a mechanically-interlocked reversing motor starter with an auxiliary contact. The "forward" contactor can power the 2 hp motor, the "reverse" contactor can power the 3 hp motor, and the auxiliary contact can be used to signal the VFD to switch motor parameters. One selector switch can control everything, although it would be smart to use some relay logic to keep either contactor energized until the VFD has decelerated.

[Dan Friedrichs]

Todd's got it right. The motor is not "derated" because you're using less than the maximum nameplate horsepower.

The nameplate HP rating is simply the maximum the motor can continuously draw. If the ducting, impeller, filters, etc, allow more than x HP of work to be done, the motor will try to do it, and it will overheat if you're loading it too heavily. The logical solution is NOT to use a VFD to slow the motor down, but to reduce the load on the motor (by restricting the airflow, etc).

If you had a 300HP car, have you "derated" it by only driving it at 20MPH? Of course not. Likewise, if you loaded a heavy trailer that required 350HP to move, the solution is to take some of the load off so that you have sufficient HP available to pull it. There is nothing about the HP rating of your car that physically restricts the load you can try to pull with it - just as there is nothing about the HP rating of a motor that controls how much work it can be asked to do.

[Tom Trees]

Hello folks,
I must say thanks again, for your most thorough reply's.
I took from the other thread a completely wrong impression...
I just wanted to hear what I wanted to hear.

So I suppose I will be looking for a 3hp motor so...
I wonder how much starting current, say a 14" impeller draws
I still think with everything closed off, this would be a lot easier with 3 phase and VFD.
Especially the way I'm gonna be using it ...turning on quite frequently, after saw cuts.

It seems that I will have to have have minimum load on this by not having long runs.
From what I've seen, most 3hp motors have a 24mm shaft, so I presume Asian 14" impellers use the 24mm bore ...
Anyway I don't want to be annoying you guys and drifting off topic...fire away if ye want though
I'll learn eventually ...


I still am under the impression that a flange mounted motor is used for a reason ...
Is it simply to cut costs, not needing pillow blocks and whatever else, more bracing and framing ?
I think people would still cough additional this cost up if it meant that they could put one of these in their basement.
I just would like to know if I'm going out of my way finding a flange mounted motor .... when I could be making this work in other ways.
Thanks again folks
Tom

[Chris Parks]

The starting current is defined by the ramp up speed set in the VFD. A 15" impeller on a 3kw motor draws 16 amps at 240V for about two seconds on the VFD we use without altering the ramp up speed. After that is reduces as the speed rises but I can't remember the figures.

A 14" impeller is not a good thing to use as the losses in the cyclone are too large. The impeller is the stumbling block everyone comes up against and I made that point above.

Why do you want to re-invent the wheel? What height is under the ceiling where you want to put this cyclone? Your two biggest issues are going to be the impeller and noise, until someone experiences the noise they do not understand how loud they are.

[John K Jordan]

The house supply is 60A and as i said my shed is a 30A MCB.

I am not a power expert or an electrician (except in Mexico). I have done my own wiring in three different houses and three shops and this is the way I understand it:

The capacity limit you have is most likely in your electrical panel and maybe in the wires in your service entrance leading from the utility lines. The wires from the utility can usually supply far more power than you can use.

Would it be reasonable to rewire your service entrance to provide more power to the house and then to the shed/shop? It might not cost as much as you might imagine.

45 years ago I had a small house with a limited capacity fuse box (not breakers) - I think it was a 30 amp box. When I built a detached shop I ripped out that fuse box, installed a 200 amp breaker panel, and rewired the house. (I did all the work myself so it wasn't too expensive.) I left the old box in place feeding the house until I had the new service entrance done. After inspection the utility just switched the lines from the pole to my new drop. I ran a temporary line to the old fuse box to keep the house powered until I had time to switch all the circuits.

Years later I bought this farm with a 200 amp breaker box in the house fed by a transformer on the property. When I built my new shop I did not run power from the house. Instead, I installed an external breaker box by the transformer and supplied 200 amps to the house and 100 amps underground to the shop and barn. Light dimming comes from the voltage drop from conductors that are too small for the electrical load. You can find on-line voltage drop calculators to help size the wiring. The size and length of the run determine how much voltage drop you will get from a given load. (If I remember correctly the usual "acceptable" voltage drop is 3% but I wanted 1% or less.) I based my calculations on supplying a full 100 amps to the shop.

My shop is 250' from my primary panel so I had to use fairly heavy copper to minimize the voltage drop. No lights dim in the shop even when my 5 hp air compressor and 5 hp cyclone cut on. BTW, I measured the current on the 5 hp cyclone and it drew about 14 amps at worst case when the blast gates were open. (The current is significantly less with all the blast gates closed since the impeller is running in reduced pressure and not doing as much work.) I also have HVAC, a 3 hp table saw, several other 220v wood working machines, plus some big welders and plasma cutter.

After using the 5 hp ClearVue with 6" ductwork for a few years I would personally hate to go to a smaller DC. Maybe I'm spoiled now.

JKJ

[Todd Willhoit]

I wonder how much starting current, say a 14" impeller draws

A standard efficiency motor started across the line at full voltage will draw 6-7x the nameplate current for a very short period of time. The starting current draw when using a VFD is entirely dependent upon the acceleration time you set in the VFD. I would start at ten seconds and see what happens. With the blast gates closed, you can probably keep the current in the low single digits until it gets to 50% speed and starts doing some work.

[Tom Trees]

Thanks again for your input
John, I'm defiantly not going to get electrical work done on the house as I'm only renting and their is no long term agreement.

Chris, interesting that you say a 14" impeller is no good.
I would have thought there was a formula for a smaller impeller relating to the diameter of the unit, to get a marginally smaller result.
I.e Bill Pentz's 5hp with 15" impeller compared to a 3hp with suitable impeller (guessing that's 14") = loss of 40 percent best case scenario (pulling this figure off the top of my head) So runs/run would made according to this rule.
I know I'm way off on the above , sorry for annoying you.

I have got to ask about reinventing the wheel statement
Guessing this is in relation to just buying a motor and jumping in, but if it's about the non flange mounted motor question
I'm just asking as I see some foot mounted ones go for cheap, and no suitable flange mounted ones in 2 or 3 years of looking.
I would not mind doing the stuff required to make it work ..I've got time
Thanks guys
I will have a look at some impellers and see what hurdles I encounter...
I guess I can figure out shaft diameter sizes and such,
Its gonna take some studying,
Tom

[Chris Parks]

Tom, go and read BP's site....several times as it will take that to absorb it all. The parameters and standards he set will move enough air to collect the sub micron dust particles that remain suspended in the air due to their low mass. The big stuff can be picked up with a shovel, it is the small stuff that causes health issues. There is way more information, studies with ongoing development work etc on the Australian forums, it is at this time the best information to be had on the internet. Nothing in any other forum and I have seen a lot of them comes even close to the information and study being done in Australia at this time and I think it is the only forum the BP ocassionally contributes to these days. Best of luck with it.

[John K Jordan]

John, I'm defiantly not going to get electrical work done on the house as I'm only renting and their is no long term agreement.

Sorry, I didn't see where you said this was not your house. Might be simpler to look for a new place.

[John Lanciani]

Thanks Bill
Sorry, I should have mentioned, as it probably confused lots of folks ....
I wasn't talking about running these both at the same time.
I probably would have to make some mini cyclone thing like Marius Hornberger for use at the same time with the machines.
The cyclone is for cleaning up after a few cuts at a time ...that kind of thing.
Maybe one day I can get a place with proper power and swap the 13a cable with 16a.
I won't hold my breath though

Tom

So if you're not intending to run the collector while you're actually making dust what is the point? If you're just going to use it to clean up after the fact why not just get and use a shop vac and skip the cost and expense altogether? A dust collector is designed the way it is so that it can move a large volume of air to capture and collect airbourne dust from a machine. To pick up dust that has already settled out a decent vacuum at a tenth of the cost works just fine (or better)

[Alan Schaffter]

I think Todd and a couple of other folks touched on it, but to clarify the discussion about "derating"- unless the specs say differently, when you run a VFD on single phase (assuming it will work on single phase. All VFDs will not operate on single phase) instead of 3 phase, the VFD specs change. It will no longer support the same hp. It really is a wrong use of the term "derate." You are not physically derating anything, the vfd simply will not handle the load. For example, if you have a VFD rated for 2 hp @ 3 phase, when you operate the VFD on single phase it will only safely handle a 1.5 hp (approx) motor so you must choose a smaller motor.