How to use a DC

[Ben Grunow]

Now it's getting good, I'm glad I asked the question!

Thanks for the replies, now all I need is a DC.

[Terry Hatfield]

Dale,

Well....actually the others are correct. The motor draws the least amps with all the gates closed. As the air flow increases the motor is loaded more and draws more amps. Really. The impeller is not moving any air with all the gates closed. Moving air is what sucks the amps that's why the highest is with no ductwork at all and as ducts are added resistance is added and the amperage goes down. Not an engineer or anything but that's what my ammeter tells me.

t

[Dale Thompson]

Dale,

Well....actually the others are correct. The motor draws the least amps with all the gates closed. As the air flow increases the motor is loaded more and draws more amps. Really. The impeller is not moving any air with all the gates closed. Moving air is what sucks the amps that's why the highest is with no ductwork at all and as ducts are added resistance is added and the amperage goes down. Not an engineer or anything but that's what my ammeter tells me.

t

Terry,
Sorry to disagree again but I think that you have answered your own question. As resistance is added, the work involved MUST be increased. It's as basic as pulling a log out of the woods. If someone sits on the log (resistance), more work will be required (ie. amps are directly proportional to the work done by a motor) to pull it out! DAH!!

Dale T.

[Bill Pentz]

You got quite a bit of good advice. The Long Ranger remote is an excellent way to control your dust collector or cyclone, but there are a few rules.

Unlike most woodshop machines, a cyclone's motor operates at full power all the time. (In contrast, your table saw only consumes its full 3 hp when it under full load, like ripping 3"-thick oak real fast.) A 2 horsepower cyclone like a Gorilla will consume about 2500 watts any time it is running. That is a lot of money if you leave it running all the time. Mine runs only when there's sawdust being generated by some other machine.

Although these do eat the power, we also need to pay attention to two of the better known motor makers who power many cyclones, Leeson and Baldor. Both say the maximum on off cycles should not exceed 6 an hour and recommend we not turn the motor on and off more than 3 to 4 starts an hour. What happens is a lot of heat is generated on startup and it takes a while for that heat to dissipate. If you cycle too often then the heat can build enough to ruin your motor and starting components.

Todd Crow sums it up pretty well and gives the advice I most agree with.

Ben,
...
Motors on dust collectors work the hardest when they are moving the most amount of air. So if you leave blast gates open that you don't need, not only are you reducing the available airflow at the location you are working, you are also making the motor work harder. (this can be verified by an amp meter) You never want to exceed the rated amperage of you motor!

I would recommend that if you are doing milling operations where you are wanting the DC available, with just a short time between the operations, that you just shut the gates and leave the DC on. Most motors have a hourly start/stop cycle rating, and this is the hardest working motor in your shop...

Dust collectors are almost all cooled by an external cooling fan, unlike a vacuum cleaner that depends upon the air going through the system to keep all cool. Cutting the airflow through the ducting has no effect on the motor except to allow it to loaf along doing minimal work because it is pushing very little air. As long as the motor is not trying to push too much air and has ample air getting to the motor it should run within limits.

With no ducting at all, the blower is wide open and moves the maximum amount of air, highest current. Add duct work, even wide open, and the airflow is constrained, less flow, less current. Close the gates, nominally no airflow, and you have minimum current. (With no load, the motor speeds up - try blocking a shop vacuum hose)

My web pages and I are in total agreement with Charlie here. Most overheat problems occur from a heat buildup from a blower trying to move too much air. A cyclone with no ducting or filters attached will move a maximum of air drawing the most amps and can very well burn up a motor. Adding ducting and filters automatically constricts that airflow enough so that a properly configured cyclone will not try to move too much air with the shortest open ducting run. Because we use cyclone dust collectors with 2 and 3 hp motors that are right on the ragged edge of their maximum amps, a poorly configured cyclone or ducting design can move too much air. In these challenged systems having a larger main and multiple gates open can allow enough airflow to push the amps too high and eventually burn up a motor. Sometimes in a poorly configured system even one really close large ducting connection can also cause the motor to overheat.

Please don't run your cyclone with more than one gate open at a time unless you are collecting from machines that require little airflow. I also strongly recommend use of an amp meter to verify there is no configuration or combination of open gates that can cause your motor to exceed its rated amperage. If it does, those amps will generate more heat than the motor cooling fan can dissipate and your motor will be short lived. Likewise, an amp meter will show closing all gates down uses the least energy. Still, this can collapse lightweight HVAC pipe, but the heaver grade 26-gauge galvanized snap lock pipe available at the box stores does just fine.

Additionally, there are a number of other ways to create a motor overheat and ruin your motor besides too many start stop cycles. Cutting airflow to the motor cooling fan such as pushing it right up against the ceiling cuts the air going to the cooling fan, stuffing the motor up between a couple of rafters creates a hot pocket as does putting it into a tightly boxed in area, and even running it on a super hot day can cause overheats. If you have limited room to mount your motor or your motor becomes too hot to touch with your palm, you should consider adding an extra air fan to blow cool air to the motor.

Bill Pentz

[Terry Hatfield]

OK so I'm terrible at explaining things but here are the nekked facts.

All the gates are closed...10.0 amps

<IMG SRC="http://www.fluiddt.com/terry/a1.jpg">

All the gates are open...20.4 amps

<IMG SRC="http://www.fluiddt.com/terry/a2.jpg">


Really

t

[Bill Pentz]

Terry,
Sorry to disagree again but I think that you have answered your own question. As resistance is added, the work involved MUST be increased. It's as basic as pulling a log out of the woods. If someone sits on the log (resistance), more work will be required (ie. amps are directly proportional to the work done by a motor) to pull it out! DAH!!

Dale T.

Dale,

You and Terry are both right, but you are thinking about ducting resistance being the major load the motor must overcome instead of how much air is being pushed. For instance, in testing a friend's system with a 14" Jet impeller on my cyclone design it pulls 10.19 amps through his full ducting system with filters while moving a real 1200 CFM across a 3-car garage sized shop. Disconnecting the cyclone from the ducting and running it with just a short large diameter test pipe bumped the amps to 18.7 and the airflow to just under 1600 CFM. With the duct sealed so no air can move the motor fell to drawing only 8.78 amps. Both the ducting overhead and the amount of airflow are important.

bill

[lou sansone]

OK so I'm terrible at explaining things but here are the nekked facts.

All the gates are closed...10.0 amps



All the gates are open...20.4 amps




Really

t

wow... the meter does not lie

nice work terry

lou

[Jeffrey Makiel]

Might I bloviate...

Centrifugal fans and centrifugal pumps require more power when moving more air or liquid. Unlike vaneaxial and tubular fans, they draw the least amps when choked off. Old fashioned HVAC systems did this using control dampers, but more efficient variable frequency drive motors replaced this old methodology.

What I think confuses folks the most is that when the flow is restricted, then the fan must work harder to overcome the resistance. However, this is not the case because because the fan will respond by producing much, much less air flow.

A fan's power needs are a function of both pressure and flow. However, if you increase the resistance by two times, the fan will respond by decreasing the flow by almost four times. The exact relationship of a particular fan's performance at varying resistance (that is, static pressure from the duct, filters and status of your gates) is called a 'fan curve'.

The fan curve is unique to each centrifugal fan design and mostly depends on wheel diameter and blade configuration (radial, foil, backward inclined, etc). But one thing they all have in common is that when the pressure (or resistance) is increased, the flow will decrease almost twice as fast, and therefore, the amp draw will decrease overall.

cheers, Jeff

[Jamie Buxton]

Although these do eat the power, we also need to pay attention to two of the better known motor makers who power many cyclones, Leeson and Baldor. Both say the maximum on off cycles should not exceed 6 an hour and recommend we not turn the motor on and off more than 3 to 4 starts an hour. What happens is a lot of heat is generated on startup and it takes a while for that heat to dissipate. If you cycle too often then the heat can build enough to ruin your motor and starting components.

I've read this caution before, and I've wondered about it.

For one, most motors of this size have thermal cutouts. If they get too hot, they turn themselves off.

For two, it seems to me that the start-up transient isn't very long, and wouldn't add a lot of heat to the motor. For instance, the motor on my cyclone draws about 10A in normal operation. That is, it can dissipate 10A worth of power indefinitely. During start-up, the motor draws more current. I don't know exactly how much, but it doesn't trip a 20A breaker. The motor in my cyclone is running normal speed in about 3 seconds. For three seconds or so, the motor is getting something like 20A worth of heating (that is, twice as much as normal). That's the same amount of heat energy as 6 seconds of 10A worth of heating. So one start-up transient has the same heating effect as running the motor normally another few seconds, and less effect than running the motor normally for any longer than that.

[Norman Hitt]

I've read this caution before, and I've wondered about it.

For one, most motors of this size have thermal cutouts. If they get too hot, they turn themselves off.

For two, it seems to me that the start-up transient isn't very long, and wouldn't add a lot of heat to the motor. For instance, the motor on my cyclone draws about 10A in normal operation. That is, it can dissipate 10A worth of power indefinitely. During start-up, the motor draws more current. I don't know exactly how much, but it doesn't trip a 20A breaker. The motor in my cyclone is running normal speed in about 3 seconds. For three seconds or so, the motor is getting something like 20A worth of heating (that is, twice as much as normal). That's the same amount of heat energy as 6 seconds of 10A worth of heating. So one start-up transient has the same heating effect as running the motor normally another few seconds, and less effect than running the motor normally for any longer than that.

Jamie, one thing you can be sure of, is that the Motor Mfr's have done considerable testing on their motors under numerous different conditions, and if there was not a potential heat problem from too many startups/hour, you can BET MONEY that they would NOT have printed that caution in the motor's documents, because Cautions, Limitations and disclaimers DO NOT help to sell their products over the competitor's products.

[Glen Gunderson]

You shouldn't assume that simply because the startup doesn't blow a 20 Amp breaker that the motor isn't pulling more than 20 Amps. Breakers normally don't trip instantly. I believe they operate on the same principle as fuses, as the wire heats up it will trip, however, this can take a little while. Many motors pull much higher than their rated amperage for a few seconds. For instance, the Leeson motor used on the Clearvue cyclone apparently pulls around 100 Amps at startup.

[Dale Thompson]

Might I bloviate...

Centrifugal fans and centrifugal pumps require more power when moving more air or liquid. Unlike vaneaxial and tubular fans, they draw the least amps when choked off. Old fashioned HVAC systems did this using control dampers, but more efficient variable frequency drive motors replaced this old methodology.

What I think confuses folks the most is that when the flow is restricted, then the fan must work harder to overcome the resistance. However, this is not the case because because the fan will respond by producing much, much less air flow.

A fan's power needs are a function of both pressure and flow. However, if you increase the resistance by two times, the fan will respond by decreasing the flow by almost four times. The exact relationship of a particular fan's performance at varying resistance (that is, static pressure from the duct, filters and status of your gates) is called a 'fan curve'.

The fan curve is unique to each centrifugal fan design and mostly depends on wheel diameter and blade configuration (radial, foil, backward inclined, etc). But one thing they all have in common is that when the pressure (or resistance) is increased, the flow will decrease almost twice as fast, and therefore, the amp draw will decrease overall.

cheers, Jeff

Jeff,
Thanks for the clarification! It doesn't sound logical but, as proven by your comments and ammeter readings, it is obviously true. I assume that the same is not true of shop vacs?

Anyway, I've posted on this board quite a few times and I have ALWAY been wrong!! I'm quite proud to admit that my record remains perfect!

Who else could say that with a straight face and a feeling of REAL conviction?

Thanks, Jeff, and others. I learned something on this post! For a bone-headed Norwegian from the northwoods of Wisconsin, that is saying a lot.

Kudos to all!!

Dale T.

[Norman Hitt]

Jeff,
Thanks for the clarification!

Anyway, I've posted on this board quite a few times and I have ALWAY been wrong!! I'm quite proud to admit that my record remains perfect!

Who else could say that with a straight face and a feeling of REAL conviction?

Thanks, Jeff, and others. I learned something on this post! For a bone-headed Norwegian from the northwoods of Wisconsin, that is saying a lot.
Dale T.

Pye Kolly, Dale, I'm glad to see you didn't "Blow It", and Ruin your Record. After all, a Perfect Record is definitely NOT EASY to come by, but be Keerful about this Larnin' new stuff though, 'cause it might lead ta problems keepin' that RECORD in tact, (iff'n ya slip up, that is).

[Bill Pentz]

Jeff,
Thanks for the clarification! It doesn't sound logical but, as proven by your comments and ammeter readings, it is obviously true. I assume that the same is not true of shop vacs?
...
Dale T.

Dale,

Closing the airflow off to a vacuum also ends up drawing minimum amps but can burn up the motor. A closed airflow again means the motor is pushing the least air, so doing the least work and drawing the least amps. Because vacuums are normally configured to be on the clean side of the filters, most use the main air stream for cooling instead of a separate motor cooling fan. So closing off the airflow to a vacuum will soon leave your motor burning up.

bill

[Bob Dodge]

Hi Dale,

You said;
When ducting is added, the amperage should increase because more resistance is being added.
---------------------------------------------------------

That would be true if the airflow remained at a constant CFM, but this is not the case. The CFM decreases with the added resistance. When you add length to a pipe, that added resistance lowers the pressure at the mouth of the duct.(lowers velocity pressure)

Take for example a 10 foot length of 6" metal pipe (plain-end) flowing 800 CFM. Total static pressure-loss is 2.438"SP. Increase that pipe to a 100 foot length, and you now have 6.383 "SP losses at 800 CFM.

Your blower will not increase it's speed to deal with the added resistance; it will simply pull less air, which in turn lowers amp-draw.

Bob