filter blinding - effect on energy useage?

[J.R. Rutter]

I am still trying to figure out why my DC amp draw has increased over time. It occurred to me today that, other than running the shaker on my baghouse, I haven't cleaned my filter tubes. They are just cotton sateen (I just got quotes on the Beane fabric replacements) and came to me used, but washed.

As filters load up, does amp draw increase or decrease?

[Jim McCarty]

It would seem to me that you'd use less amps since the fan is able to move less air (do less work). Just my $.02.

[Rob Will]

As filters load up, does amp draw increase or decrease?

Interesting question considering the filters are downstream of the blower.

With clogged filters the CFM is obviously less but the air density inside the blower is potentially greater thus more amps(?). I have no idea but I need to know as well.

Rob

[Jim Becker]

Well...sounds like a good experiment: measure the amps again just to be sure, clean the filters, re-measure the amperage with the same gate setup as the previous test.

[Andrew Williams]

Here's an uneducated guess...


More dust = more resistance = more load on the motor trying to reach synchronous turning speed. The motor doesn't care what it is attached to, whether a ship's propeller trying to push a ship through molasses or a fan trying to blow air through a few less tiny holes than it used to.

[J.R. Rutter]

Well...sounds like a good experiment: measure the amps again just to be sure, clean the filters, re-measure the amperage with the same gate setup as the previous test.

I agree in principle, but in this case it is just too much work!

I've run the shaker good and long on a fairly regular basis, but I'm thinking that the media has become clogged with entrained dust to some extent over time. In hindsight, a reverse pulse jet system might have been a better choice. But it was WAAAY more $$$$. I'll see what happens with new filter tubes...

[Jim Nardi]

I'd have a look at your blower to check the impeller's to see if they are clean. It doesn't take much to cause a blower to vibrate and draw more amps. I'd also check your bearing to see if you have a bad one or the need for lubrication. The cleaner your baghouse the more amps you will draw. The cooler your air intake the more amps you will draw. When your motor's on it's last leg's the motor will draw 30 percent more than normal. If your voltage has dropped you will draw more amps. Have a electrican check all your electrical connection's to make sure they are tight and clean. Dust does some terrible things to electrical connections.

[Noah Katz]

Current should decrease w/restriction.

If the air flow is restricted, the same air just goes round and round. The load on the motor comes from the impeller accelerating air.

Leaks would decrease restriction and increase current draw.

[Jules Dominguez]

The more air the unit moves, the more horsepower it will draw. Any restriction reduces air flow, and therefore reduces horsepower.

[Richard Keller]

By your guys estimation, the thicker the wood, the less your table saw would draw.

The most likely cause is a restriction in the dust collector. If the filters are clogged, it can't push the air easily. Put your hand on the end of your shop vac hose, and listen to it SCREAM. It's working harder.

Richard.

[Jules Dominguez]

The physics involved in cutting wood with a saw is not analagous to moving air with a fan.

The horsepower drawn by a centrifugal pump, fan, blower, whatever, which is moving a fluid is a function of the pounds of fluid (liquid or gas) moved per unit of time and the resistance (head) against which it is moved. The design of the machines is such that a relatively small change in the resistance (head pressure) causes a large change in the pounds of fluid (liquid or gas) being moved. Thus the horsepower goes down when the head pressure goes up.

[Randy Denby]

Jules is right. Also....and this is a biggy that screws up most peoples reasoning, a dust impeller is not a positive displacement pump, such as a piston machine. The reason the vacuum screams is lack of airflow, and the impeller has no load which causes a universal type motor to overrev....because the vacuum has hardly any work, not working harder :D

[Will Blick]

I worked with fan systems for years.... in your case...

First rule out any electrical issues, bearings, motor integrity, etc.

The general rules on fan motors as they relate to DC systems. A motor is designed to run at a specific RPM, regardless of load. A motor with no load will pull very few amps. A motor with a heavy load will pull more amps, till, the load becomes so great, it exceeds the motors amp capacity (similar to HP rating, but not always the same), the motor will soon trip out on high temp. Or if your breaker circuit is rated low enough, it can trip first.

With DC systems, plugged filters = greater resistance, which in turn is a larger load on the motor. This would be the simple explanation why your DC is pulling more amps. However, this is also true if you use smaller micron filter bags, as it too creates added load on the motor.

The easy answer is, clean the filters. But, keep in mind, plugged filters act as more efficient filters. When you plug the small holes in a filter with dust, the reason it creates resistance is because the filter has essentially become a higher eff. rated filter (less micron). Many filters are actually rated, "after use", not when they are new for this very reason.

Sub micron particles are the dangerous ones (it could be < 2 or 3 microns, I can't recall exactly). So while you are burning more electricity, it provides a slightly safer working environment as smaller dust particles are trapped. Of course, there is a point of no return here also....i.e. when you have so much resistance the motor can overload. (to further that discussion, one must have the fan curve or performance curve of the motor to see how it reacts under load, but for here, we use generalizations) Also, the greater the resistance of the filters, the less CFM you will pull at the ww tools, creating a hazard on that end..... as you can see, it's a balancing act.

I have concluded after researching this subject for some time.....the safest, and most energy efficient DC system is a cyclone system. But after the the air leaves the cyclone, it does not feed a set of filters in the workspace, but rather it dumps the <5 micron particles (the dangerous ones) directly outside, away from the workplace.

I understand this is not always possible, as it creates negative pressure in the workspace, so for those in basements or other confined areas, it will require air inlets to the space and will unfortunately substantially increase your heating / cooling cost. But for those who don't work in extreme climates and their workspace has an outside wall, this system offers many advantages....not just health advantages. By reducing the over all resistance with a no-filter system, you will pull MUCH greater CFM at the ww'ing machines and the motor will draw much less current. It's a win/win/win, assuming your workspace can allow for this. The more I learn about how toxic wood dust is, the more concerned I am over these issues. So be sure to consider all these factors before changing those filters to save energy ;-)

[J.R. Rutter]

Maybe I could get away with a diverter that would let me exhaust to atmosphere in the summer and return the exhaust in the winter. That sounds like a great idea. But I do have a neighboring buisiness employee parking lot beside the collector, so fine dust on their cars may be an issue.

I have an acquaintence with an in-town sawmill who recently had to spend >$100K on a several story tall afterfilter because the car dealerships in the area were complaining to the clean air regulatory agency about dust.

[Al Willits]

Been my expreience with plugged filters before the blower amp draw is less, with the filter after the blower amp draw is more than with a clean filter.
Works with furnace blowers anyway

Al

[Randy Denby]

After stopping to think about how I stated my missive above , Al is right :o Filter clogged after the blower will make amps go up.....sorry if I mislead. Filter before the blower or restriction will make amps go down. ....................