Electrician Question - Air Cleaner

[Don Abele]

I am looking to build my own air cleaner and have access to a 1000CFM fan which only produces about 60 dB when running (it's REALLY quiet). The fan is free, so the only cost will be for the filters (use scrap ply for the box).

Here's the question for the electrician's (mine at work is on vacation) - it's a 220 fan which draws 0.3 amps. Can I tie the two hots together and connect it to a 110 outlet, thereby drawing 0.6 amps at 110? If I did this, it seems to me it would get the right amount of electricity but there would be no neutral (though there is a ground) and this sounds like a no-no.

I just don't want to have to put in another 220 outlet - but for the very small price I'll pay for this, I now that's what I'll end up doing any way. Just wanted to know if I could do it easier.

Be well,

Doc

[Jason Beam]

Big bad no-no the way you describe it. The voltages don't add up, really. Doing the opposite may shed some light on why: 240v lines are two 120v hots that are "out of phase" - think of a wave - when one leg is 'up', the other leg is 'down' - if you tied THOSE together, they'd cancel each other out - the up one would counteract the down one - and they'd switch positions about 60 times a second. A tester would yield 0v.

Taking that the other way - a motor wired for 240v is flat out EXPECTING and relying upon those two 120v legs to be out of phase. By just tying them together, at best you'll end up with a motor that fights itself. One (or a set of) winding expects the opposite polarity of the other. If they're both down, the electromagnetisim is the same polarity - cancling the other one out. The most you'd get is maybe a bit of a hum, but the motor will actually be electromagnetically locked.






Disclaimer: I don't have ANY qualifications and I'm not an electrician. I probably shouldn't have even answered this question but I have poor impulse control. Consult a qualified person before believing what I've just said :)

[Mike Cutler]

Doc

The short answer, with your description, is no. The motor would probably just sit there.
But... That is a very small motor,and could possibly be rewired for 120vac, but it's just not apparent. How many wires are coming out of the connection enclosure, and what color are they? (There is a US and European standard for wiring color convention in small motors.)
Also can you identify the original manufacture,and model # of the motor?
Sometimes motors are sourced as dual voltage from the OEM, but wired for a specific application without any supporting info. My TS is that way. It came wired for 120, and there are no instruction in the manual to convert it over to 240, but there's diagram is inside the motor enclosure to direct how to do this.

[John Terefenko]

The answers you got are correct and you can not do what you wrote. Is the motor dual voltage??? If so there is a chart on the motor somewhere or on the cover and it will show you the connections to change over.

[Jeffrey Makiel]

Most direct drive residential blowers for air handlers are 220V only...but that's no hard rule. However, having dual voltage capability in this size and type motor would generally be the exception.

If it has the capability to be internally wired to accept 110V, it would draw 0.6 amps at unrestricted flow (that is, no filters). This amp draw is very low indicating that the fan has very little static pressure capability, which is typically the case for home heating fans. You may not get much flow thru a pre-filter and low micron bag filter especially when they begin to load with dust.

Air cleaners like Jet, JDS and Grizzly generally have 2.5 to 3.5 amp fans (at 110V).

It should be noted that centrifugal fans draw less power as flow is choked off. It is only when there is inadequate flow across the motor, which is in the airstream for direct driven fans, that will reduce the cooling ability of the motor. An auto thermal overload switch is a nice feature to look for on your fan for protection from burnout.

-Jeff :)

[Rob Russell]

Don,

As the above posters have said, you need to wire this as a 240v device or rewire to 120v if the motor is dual voltage.

Whatever you decide to do, I would put a fuse on your filter. Go to a Radio Shack and buy a fuse holder for one of those little glass fuses. Put a 1 amp fuse on one of the hot conductors. You'll need some sort of box on your filter for your wiring connections - put the fuse in there. That way, if your motor starts to draw way too much current, the fuse will blow instead of your motor burning up and potentially starting a fire. Do yourself a favor and make sure you put a cord-with-plug on this - don't hardwire it to your house.

Rob

[Don Abele]

Guys, I was pretty sure it wasn't a good idea - I just couldn't visualize the answer in my head so I was kinda talking out loud.

I don't have the fan, it's still at work and I won't be back for a week (heading on a trip to Topeka). I'll check it out when I get back though.

Jeff, your comments are really interesting and lead me to believe this fan just isn't going to work. For free though, I'll check.

Rob, I wouldn't have thought to put a small in-line fuse, but based on your comments and Jeff's it makes A LOT of sense for something that draws so little amperage. And I was planning on wiring with a plug.

Jason, your comment about two 120's out of phase canceling each other out sounds wrong to me. On a 240 breaker, If I measure the voltage from one hot to neutral I get 123 VAC. If I measure between the two hots I get 245 VAC. These are actual measurements I just took on my breakers.

These measurements first came to light 2.5 years ago when I bought my house and had the old 60 amp fuse panel replaced with a new 200 amp breaker panel. I watched the electrician closely during the change-out (interesting evolution - especially when he cut the mains coming into the house while they are hot :eek:). I saw him measure the voltage of each house main, then measure across them. It was originally because of this that I THOUGHT you might be able to tie them together for 240 VAC.

Be well,

Doc

[Rob Blaustein]

Electrical issues aside, if you haven't yet decided on a filter type, these (http://solutions.3m.com/wps/portal/3M/en_US/Filtrete/AirQualityProducts/ProductInformation/FiltreteProducts/HighPerformanceFilters/) are supposed to be quite good (Consumer Reports rated them tops in its category--ie filters that go on your furnace blower). I've been using their Ultra Filtrete 1200 filter (formerly rated #1), but will probably switch to these when I run out of them.
--Rob

[Wade Lippman]

Can I tie the two hots together and connect it to a 110 outlet, thereby drawing 0.6 amps at 110? If I did this, it seems to me it would get the right amount of electricity but there would be no neutral (though there is a ground) and this sounds like a no-no.


Ingenious; and you got answers!

Funny thing is that there is actually a commercial product that takes the hots off two outlets for 240v. Have to be crazy to use it, but it exists.

[Jason Beam]

Jason, your comment about two 120's out of phase canceling each other out sounds wrong to me. On a 240 breaker, If I measure the voltage from one hot to neutral I get 123 VAC. If I measure between the two hots I get 245 VAC. These are actual measurements I just took on my breakers.



Interesting. Your experience is exactly what I'd expected when I tested the 240v air conditioner outlet in my living room. Hot to hot, for me, tested at 0v. Either hot to ground tested at 118v. Maybe my tester is doing something different than your tester? Scientifically speaking, though, the 0v result makes sense to me since both hot legs are out of phase. Maybe there are cases where the two hots are NOT out of phase? I'd like to understand this further, myself.

[Pete Bradley]

Single phase 240 is two hots that are 180 degrees out of phase, so they wind up being additive. As others have pointed out, if you compare AC voltage of either hot to neutral, you'll see 120. If you're seeing something else (e.g. 0), your multimeter is probably set for DC or something other than volts AC.

Electricity is one of those things where misunderstandings can kill you. If you're thinking about adding two 120s to get a 240 line, it's probably time to call an electrician or just buy an air cleaner.

Pete

[Don Abele]

Electricity is one of those things where misunderstandings can kill you. If you're thinking about adding two 120s to get a 240 line, it's probably time to call an electrician or just buy an air cleaner.
Pete

Pete, I am quite familiar with electricity (and much more than plain old household stuff). But I know my limitations and when to ask for advice/help. Just like I said earlier, I hired an electrician to change out my main panel - I understand how to do it, but it's a task better left to the pros. It's also why I was asking this question here (because my electrician is on vacation) before I even thought about doing it. Regardless of any advice here, I will still wait for my electrician to come back.

Now, I was not asking if you can combine two 120 lines to get 240 (though that's exactly what a 240 outlet does). I was curious if you could use one 120 hooked to both the red and black on the fan. In theory it should work as it's providing 120 to each leg. The phase part is where I was confused. If each leg is 180 degrees out of phase from one another, then it won't work, not because of voltage, but because of phase. But I thought residential electricity is single phase, which would mean both lines are the same. All the research I've since done tells me I'm wrong - that each of the lines coming from the pole are 180 degrees apart, therefore each bus in the panel is the same. Since the 240 breakers grab a leg from each bus, it creates the 180 degree out pair.

This whole idea came from the way many shop tools are wired for 120/240 and I thought if you could do it for them, would it be POSSIBLE to do it here. Obviously, if it's possible but not safe (ie: no neutral) then there's no way I would move on with the idea.

At this point, I think the question is moot, because based on what Jeff said, the fan (wired at 240) doesn't sound like it'll be powerful enough to work in this application.

I would though, for my general understanding, really like to figure this out.

Be well,

Doc

[Don Abele]

This is what started the whole idea...this is the wiring diagram for my drill press (though my other tools have a similar schematic for rewiring them).

And this is why it's so confusing :confused:

Be well,

Doc

[Pete Bradley]

Pete, I am quite familiar with electricity ...
I was curious if you could use one 120 hooked to both the red and black on the fan. In theory it should work as it's providing 120 to each leg. ...
I would though, for my general understanding, really like to figure this out.


If you're quite familiar with electricity, I don't think I'm understanding your question. Rick Christopherson has a good electricity page that you may find helpful.

It's here:

http://home.att.net/~waterfront-woods/Articles/Electricity/electricity.htm

Pete

[Steve Leverich]

I know this is confusing, but "single phase" in a home (in the US) means that there is really only one "phase", in that it's not some ODD number of degrees out of phase from conductor to conductor - it's either "in phase", in which case you'll measure 0 volts from one "hot" to another, or it's "out of phase" by 180 degrees, which makes the voltage additive and you'll get 240 volts AC across the two hot wires.

Most residential breaker centers are set up with two "rails", or metal busses that run usually down the length of the box inside, parallel to each other - one hot lead connects through the main disconnect to one of these rails, and the other hot lead connects through the main disconnect (the OTHER set of contacts) to the OTHER rail.

For a 120 volt circuit, you snap a breaker in place on the rail and this gives you ONE hot lead of 120 volts referred to neutral or ground (since the neutral IS grounded)

For another 120 volt circuit, you might snap the breaker onto the OTHER rail, which is ALSO at 120 volts reference to ground, but is at OPPOSITE polarity compared to the first breaker's rail - so if you were to measure from the hot lead of a receptacle on the first breaker to the hot lead of a receptacle on the SECOND breaker (in this case) you'd measure 240 volts AC.

This is all a 240 volt breaker does - it has TWO contacts that snap onto BOTH rails, so one contact is 120 volts and the other is 120 volts OUT OF PHASE with the first, so those two contacts will measure 240 volts AC between them.

If a 240 volt motor isn't wired so that the windings can be "split", it won't work using 120 volts to both wires because (unless you find two receptacles that are fed from opposing "rails") you will see the exact same voltage on both wires of the motor. Net result = 0 volts BETWEEN the two wires(but if you touch them, you'll wish you hadn't)

A simple 240 volt motor only needs 2 wires, one coming from each rail of the power source, for 240 volts - they have a third wire for ground, but normally no current flows through this ground - it's all flowing between the two hot leads. Newer appliances, and clothes dryers, need a 4th wire (although 3 could work, it's just not to code any more) - the 4th wire is a true neutral, and is used along with ONE of the hot wires to provide 120 volts to the electronics/drum motor.

The ground wire in these cases is ONLY for safety, in the event a short happens inside a motor - it keeps chassis parts at ground potential or blows the breaker, whichever works. Ground wires are NOT supposed to carry current, so if a 240 volt device (like a clothes dryer) ALSO has need for 120 volts, a neutral is necessary for the return path of the 120 volt side. The 240 volt side only conducts between the two hot leads, so doesn't NEED a neutral - only the ground for safety.

Most of the "phase" confusion in residential electricity, I think, arises from using the word "phase" when it really should be "polarity" - if the two hot leads are OUT of polarity with each other, you get 240 volts across them.

True phase differences can be anything from a degree to 359 degrees off - true 3-phase power, for example, has 3 separate hot wires that are 120 degrees different in phase from each other. I won't go into more on that, it'd make this long post REALLY long.

If anybody's still awake, I hope this clears up a few questions... Steve

BTW, if anybody cares about qualifications, I carry two different electrical licenses (one for low voltage signal stuff) and work in industrial automation and control (for the last 30 years) - prior to that it was broadcast/closed circuit TV, recording, electronic design, etc.

[Don Abele]

Most of the "phase" confusion in residential electricity, I think, arises from using the word "phase" when it really should be "polarity" - if the two hot leads are OUT of polarity with each other, you get 240 volts across them.

Steve - that's it! That's exactly where I was getting confused. Phase and polarity are two completely different things.

So with the phase/polarity cleared up, I can see why only a motor designed for 120/240 will work that way. I'll have to check the fan once I get back to work in a week.

Thanks for helping clear up the confusion.

Be well,

Doc

[Jeffrey Makiel]

There was a recommendation that a small fuse will provide protection. This is not completely true because there are two ways a centrifugal fan motor can fail...

(1) If a direct drive fan is starved airflow, the motor will burn out due to heat and not amperage. If fact, amperage draw is at a minimum when it is starved. Even at a low amperage draw, a motor that is starved cooling air will get hot. A thermal overload switch provides protection to the fan's motor by opening when temps exceed a certain value.

(2) If the fan is run without any filters or resistance, it then draws maximum amps. The max amps may be more than the fan can handle depending how the manufacturer has matched the fan with the motor. Many fan manufacturers caution against free airflow. In this case, amperage protection can work, but since we are talking about amperage less than 1 amp, you will not be able to find a fuse or breaker this sensitive as a hobbyist. This is the second reason why it should be equipped with a thermal switch.

cheers, Jeff :)

[Rob Russell]

Steve,

Nice explanation on a bunch of "stuff".

Please note that there is a difference between the "groundED" and "groundING" conductors under the NEC.

The "groundED" is what we typically call the Neutral. The groundING is what we typically call the equipment grounding conductor.

I'm truly not trying to quibble with your explanation.

The problem is that "ground" is misinterpreted by many people and we need to be clear about the definitions of the conductors.

Rob

[Steve Leverich]

Rob, thanks for adding that - I'd meant to go there but the post was getting 'way long already. I'm glad that with everyone's input things have become a bit clearer on this - the same confusion exists in pro audio as well, even console manufacturers rarely get it right - most have a "phase" switch per channel that is NOT... Steve