DIY Harbor Freight Air Filter

[fallenmunk]

I 3D printed a flange to fit my 3 speed Harbor Freight blower. I already had it, but it actually seems like a better deal than most fans if you can get it on sale or coupon. It even has an optional heater you can add to the exhaust for cold areas like my basement. So it can filter and heat with one unit. I used standard dryer hose from Lowes. It's working awesome! No more complaints from my wife. Product links below. Warning: this is a modification of a device that is engineered for another purpose. Any persons modifying it in this manner assumes all liability. The author of this post in no way condones the modification by others, nor accepts any liability.

https://www.harborfreight.com/3-spee...wer-61729.html

https://www.harborfreight.com/heater...wer-93272.html

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[Toker1]

Ok. But you are increasing the resistance causing the motor on the blower to work harder and draw in more amperage. Just be caureful with these types of modifications.

[fallenmunk]

Ok. But you are increasing the resistance causing the motor on the blower to work harder and draw in more amperage. Just be caureful with these types of modifications.

Thanks for the comment. That holds true for any type of blower, including the ones marketed for the cannabis industry. I can do some full restriction amperage testing if you'd like, but I think the difference in draw would be negligible especially on the lower two speeds. I do this type of stuff for a living BTW.

These blowers have been successfully used in DIY laser cutters to filter the smoke for many years with no issues. That is what I originally purchased mine for. That is an much more industrial environment than this obviously.

[Toker1]

Plasma cutters? I was the mechanical engineer for a state contractor machine shop for many years. Mostly hydropower.

[fallenmunk]

Not plasma cutters, however building one of those is on my list. Laser cutters utilize a Co2 laser inside an enclosure that is designed to house the harmful radiation and smoke. A lot of smoke is generated, and some users vent to outside if they have enough property, but quite a few have to filter it because of close neighbors. Similar to what most growers have to deal with. Obviously a laser cutter will generate much more particulates than a typical cannabis grow, so the filter will need changed out more frequently. Most people with Co2 lasers will run the filter until it's totally plugged (fully restricted flow) , so that's how I know that it will be fine for filtering weed smell and not burn the motor out. I'm not even sure that the squirrel cage fan experiences increased motor drag and resulting amperage draw, rather just friction and flow separation losses due to its design. If anybody is really interested in the details of this type of fan, here's a link that gives the basics: https://en.wikipedia.org/wiki/Centrifugal_fan

[Toker1]

The motor is designed for a specific airflow rate. If it was not designed to bear additional load (like from the resistance of the filter and ducting) you will be shortening the useful lifespan. That might not be a big deal, just be aware that’s all.
Yes, I have loads of experience using smoke eaters. Specifically for welding, but same purpose.
I don’t have much experience using laser cutters. Torch cutting, plasma cutting, and water jets is what I am more used to.

[fallenmunk]

Ok, so I just did some testing and research on this centrifugal style of fan due to the concerns of Toker1, including talking to some experts. When the intake is blocked, the amperage draw goes down, the RPM goes up, and the electricity use goes way down. Because the fan cage is no longer loaded with air, it has very low drag and the load goes way down. So it actually does the opposite of what Toker1 is claiming. I just tested it with a piece of cardboard and an ammeter, and it does exactly that.

To address the motor intake air and potential heating of the windings, the motor air intake is on the opposite side and is unaffected by air flowing through the squirrel cage fan. This is what makes these motors perfect for furnaces, (says my experts). Because when people don't change their furnace filters, the load on the motor lessens because the squirrel cage fan has less air to move, and the motor doesn't overheat, it actually runs cooler with lower electricity use. So it's very safe.

In fact, when the filter is cleanest, that's when the motor loading is highest. Ironically enough. So if there are any other armchair experts that want to chime in, fight me, lol.

[Toker1]

How could RPM go up and amperage go down? If that was the case, why would normal operation be at a higher amperage? Something isn’t quite adding up there with this information.
How every motor in the world works is rated amp drawl will operate the motor at the rated rpm. If rpm goes down, the motor brings in more amperage trying to increase the speed. That’s how a motor gets burned.
Back to amps going down, if amps decrease there is less electric potential to push the motor and speed Will therefore
decrease.
Ok...if we are talking separate air flows, the. Yes I see the pint being made.

[fallenmunk]

You are just not getting it. It is simple physics. If there is less air available to move, there is less resistance on the fan, not more. When you block the air on either the intake or exhaust, the fan has less work to do, therefore it will speed up and the load is reduced which directly relates to amperage draw. There are literally tons of engineering links to learn about these principals for those interested in the subject. Here are two of them:

https://www.youtube.com/watch?v=qX-GodOlUuU&ab_channel=grayfurnaceman

https://cr4.globalspec.com/thread/108775/Squirrel-Cage-Blower-Speeds-Up-When-Airflow-is-Blocked

[Toker1]

Oh no... you assume too much. I got that. Didn’t you read my comments about the separate air flows? If you are not resisting the motor itself, then the fan is designed to work under higher loads. Got it. That was my only concern.
If you knew this the entire time, then why didn’t you just say that in the beginning? My guess is you really didn’t research these issues until I started questioning your modifications. Really need to consider these things when you go against the manufacturers recommendations found directly in the user manual before you go recommending to everyone online. You could be taking on a liability you didn’t mean to take on, or worse off leading someone into a dangerous situation. It’s good to have these types of discussions. Especially when safety could potentially be compromised

[Toker1]

I see it has overload protection. It trips the blower during an over amp drawl situation. That’s good. It also says multiple times in the user manual to not obstruct the vent. Telling you clearly that you could trip the device due to overload. This confirms everything I have been saying here.
https://manuals.harborfreight.com/ma...1999/61729.pdf

[fallenmunk]

It's a blower, so the manual is gonna say that. It doesn't change physics. It's ok to be wrong, you don't have to keep this going. I actually have the device here and am telling you what my testing proved, as well as links to experts on the subject. It's up to you to learn, the same as I had to do to determine what I was doing was safe when you said it wasn't.

[Toker1]

If you are saying you take full responsibility and any liability that may come with your design changes (that go against the manufacturer’s recommendation), then ok. Until I see that in writing, I will continue to question the designer to ensure they know what exactly they have done. The fact that it took us this long to describe the separate airflow, that is independent of the motor leads me to believe this potential issue was never even considered prior to recommending it to the public. That’s a dangerous way to go about recommending something. If you did your due diligence then why didn’t you say that first comment? I’m glad you are doing the proper research now, a bit late IMO.

[MJTECH]

RPM rises because with a lower air flow there is less load on the motor, this is a known factor with squirrel cage blowers.

[Toker1]

Thanks, but We already established there was 2 separate airflows. So as I stated previously, this seems to be designed to handle the load of the extra resistance on the intake of the blower. That was my only concern with the modification suggested.

[fallenmunk]

Correct MJTECH. There is less resistance when airflow is blocked. They have less work to do.

[fallenmunk]

The interesting thing is that this thread actually forced me to learn something new. Like when my shopvac hose gets plugged and the motor starts screaming really fast, it's not because it's under more load, it's under less. I've always believed the opposite and thought it was going to burn the motor up. Probably just harder on the bearings to run at the higher RPM, but if it's engineered correctly the bearing rating will be higher than the maximum motor RPM.

[fallenmunk]

"Try this:

Put an ammeter on the power to a vacuum cleaner.

Watch the amps drop when you restrict the flow.

No theory required to understand this.Simply accept it."

[fallenmunk]

It seems very smooth and quiet and I'm only running it on the lowest setting and my house has no smell for the first time in several grows. I don't know why I didn't think of using it in my grow room sooner, I already had it for several years just waiting for me to finish building my laser cutter. I've got an RPM/strobe meter and I can see if the RPM's go up as the filter gets more restrictive. Not sure how much life I can expect out of the charcoal, but I've got refill charcoal for it and a shaker table so I should be able to settle it in just as well as factory.

I DIY almost everything. I built a CNC machine from scratch a few years ago, and within two years I was machining rocket parts in my basement for the Navy ramjet missile program out at China Lake. I try to learn something new every day, and now I know the science behind blowers and it's totally counterintuitive to what I believed before this thread.

[Toker1]

CNC is so bad ass! I have had the pleasure of working with a cnc horizontal lathe. Before that we were using the old school dial in lathes. That’s a skill set in itself. Not enough machinists left in the country though. It’s a talent that is fading way to quickly!!

[fallenmunk]

I have several lathes, all manual though. The mill is the only CNC I have unless you count my 3D printers, which are technically CNC machines. I have an old WWII era screw machine too. Google that if you want to see how nuts and bolts were made pre-CNC. They are actually faster than CNC if you set them up right.

[Toker1]

All bickering aside. This is what I was referring to when I brought up these issues to this topic.
https://accendoreliability.com/effec...ectric-motors/

[Toker1]

You say the motor doesn’t work harder... you also say it runs longer. Running longer is working harder. Do you call increasing run time working less hard?
You are also ignoring the fact that the motor needs to maintain a specific air flow to push the heated air through the ducting. Otherwise it would be only hearing your heater lol. Clogged filter = less air flow. If the motor is not hitting its set point, it could cause the motor to react and burn.

[MJTECH]

Keep in mind vacuum cleaner motors are series wound and as you discovered will vary in speed, A/C motors are induction motors which are speed locked to the frequency of the power feeding them, as long as they are not overloaded they will not change speeds.

The only practical way to vary the speed of an induction motor is with a variable speed drive which is an A/C to A/C convertor which takes in standard 60 Hz power and can output various frequencies to vary the speed of the motor.

[Toker1]

VFDs can be set up to convert DC to AC as well. I have seen plenty of 3 phase motors run on single phase power when a VFD is involved.

[fallenmunk]

You must not have watched that video link I already provided. Skip to 2:13 please. https://www.youtube.com/watch?v=qX-G...grayfurnaceman

Here are a few more links if you really want to learn. Any more of your similar comments after you visit these links, I will have to consider that you are trolling me because this should make it very cut and dried for you. These are from an engineering site for mechanical and electrical engineers aka experts.

https://cr4.globalspec.com/thread/108775/Squirrel-Cage-Blower-Speeds-Up-When-Airflow-is-Blocked

https://cr4.globalspec.com/thread/28775/Blocking-off-inlet-on-squirrel-cage-blower

https://cr4.globalspec.com/thread/31800/Squirrel-cage-amperage-related-question

[Toker1]

Hmmm. I have personally worked on conveyors with USA and European made motors that had VFDs that were controlled by photo eyes, emergency stops, air flow sensors, temperature sensors, pressure sensors for many different applications. All currently used today in this country in modern day manufacturing lines.
Basic motor, as in a rotor and a stator? There is nothing basic about a motor, they are all designed with different features. Some are capable of operating on multiple voltages, some have overload protection (like your Chicago electric blower motor)., some have sensors. It all depends on what it’s designed to do.

[fallenmunk]

No kidding. Motors are usually controlled by extra electronics, but that is not integral to the motor. You are beating this like a dead horse, for what purpose I have yet to determine. You can talk about automated machinery all you want, but I'm talking about a simple $50 blower made in China that might last a year or two if I'm lucky, regardless of my modification.

[Toker1]

A Dead horse? But I was just talking to mr. ed...Now you say I killed him? Lol
Ok. Just reiterating that my cause for concern was justified. Some motors are designed to act exactly in the way I have described.
You are attempting to differentiate your blower’s motor from a motor controlled by other features. What did you think your overload protection was on the model you linked us all to? Do you think every motor comes equipped with that?
Failing to see the points of your last 2 posts. Maybe I am missing something here? Or maybe that horse’s corpse is in your back yard?

[Toker1]

I saw/read the links. Seems like the blower was designed for 9amps and was operating at 16 amps while unrestricted. This is conclusive of what you were saying. But the blower is designed to be restricted and not run unrestricted. That’s why I said unless it was designed to operate this way. Seems like it was designed specifically for restricted flow. Which is exactly what I was asking about in the beginning. Read comment #3.5 the answer to that statement is that the blower is designed for restricted flow. Confirms everything you posted plus eliminated my original concern.

[MJTECH]

Toker1 commented
01-27-2020, 04:28 PM


And if that’s the case... the pressure causes the motor to spin faster than designed you get a current back flow. And your motor becomes a Generator creating amperage, burning up the components.

Not possible, a motor cannot generate power without an external source to drive the motor, there is no such thing as current back-flow.

[Toker1]

I’m not talking about the wires. Power control devices may consist of bipolar transistors. Some are more insulated than others (depending on the rating). Ok... I wasn’t very clear and I apologize for making such a blanket statement like that. Properly insulated motor would be better terminology.
My comment should have read, assuming the insulation is enough to prevent. But we never discussed exactly how much electric we are discussing. If there is enough voltage, you can easily overwhelm the insulation in that case.

[MJTECH]

Insulation classification is a rating and is applicable to all motors, and if the insulation rating is exceeded the motor can be damaged, sometimes rather violently.

Ratings are Class: A=105°C, B=130°C, F=155°C, and H=180°C.

Then there are voltage ratings, common in the U.S. are 120/240, 277, and 480 VAC, specialty motors such as for locomotives are rated for 600 VDC and 600 VAC 3 Phase in the newer General Motors EMD units.

When insulation breaks down strange things can happen, I installed a rebuilt 3 phase 480 volt 500 hp motor for Waste Management in Pompano beach, the re-builder Hi-Potted the motor and certified as ready to go, I went into the control room, my guys closed the power into the motor controller and stood in the clear, I started the motor and there was a violent explosion, which shook the control room.

I looked out of the control room which was up on a superstructure and noticed the power was out for blocks around the area, oops.

I stepped outside, my guys opened the power to the motor, the three time lag fuses had opened as well and we put out the fire the motor started.

The motor was sent out for a forensic examination, turned out the re-builder failed to properly secure a turn of the windings, the startup magnetic forced ripped the copper windings out of the field and it made contact with the rotating rotor and the subsequent arc burned more windings hard bolting all 3 phases to ground.

Somewhere up in Juno Beach an FP&L technician in their control center was probably wondering what just happened down in Pompano.

Thirty grand down the drain, but not out of my pocket.

[Toker1]

Hells bells! 500hp is HUGE!! I could only imagine what that sounded like. I have been in a scary situation like that before. We were generating power using a Rankin cycle. The pressure built up inside the closed loop system. The emergency PRV burst and the plant walls were shaking pictures off onto the floor.
My boss ducked under the control room table and was reaching above his head to hit the emergency stop over and over.
Luckily no one got injured. A big lesson on how hot/cold in the wrong location can be quite destructive.