Does anybody have experience using a DC as a central vac?
I have central vac for my house and the vacuum unit is old and needing replacement. I also need a DC for my shop. I was thinking about using a DC for both applications, but I don't know if the 2 applications have the same requirements. I know that a vac or a DC have 2 properties: inches of vacuum at no flow, and cfm at no vacuum.
Has anybody tried this, or what do you DC experts think?
Rex
I don't think that it will do what you want it to. A DC just doesn't have the static pressure to work well as a central vac just like a central vac doesn't move enough air to work well as a dust collector.
Someone asked this at a Penn State bulletin board a while ago. The reply was that you will end up burning the DC out because it can't handle a restricted load like that. They said if you can only afford one, to get a Fein vacuum; it isn't good as a DC, but at least it will work.
I agree that a DC won't make a good vacuum, but I'm pretty sure that burning it out on restricted load is a myth. A DC is a centrifugal device, not a positive displacement device. As you restrict the airflow, the motor load goes down. To the limit, cutting off the airflow completely puts that motor at a virtual idle state. This can be confirmed by looking the motor horsepower requirements in the blower curves.
Bob
donno; but that is what Penn State said and they should know. I don't think they meant immediately, but over time if the improper use was routine, as it would be with a central vac.
I just read an article that may be a better explanation of why a dust collector could burn out trying to use it as a vacuum. The dust collector service, unlike most power tools, represents a heavy start load. Compare the sound of a starting table saw to a starting dust collector. The saw is at full speed almost instantly. The dust collector ramps up to speed, due to the heavy impeller. This represents a heavy starting current for the motor, which can cause a heat buildup. For that reason, dust collectors should not be stopped and started frequently. A central vacuum service might represent more frequent starts than dust collection service.
Bob
I'd say that since the motor speed also cools the motor, a restricted motor would 'burn out' due to overheating.
Air flow through the motor is not restricted (with proper design) when the dust collection airflow is throttled. Motor cooling air flow results from the motor's internal fan, not the collector impeller. And the motor speed doesn't slow down when the collector system airflow is restricted/throttled - the motor speed actually increases slightly with reduced load.
Bob (with his second post) hit the reasoning for a statement that "dust collectors will 'burn out' if used like a vacuum" - it's the frequent starting. Motors don't like starting loads. The increased starting current causes heating. Too many starts in a short period will heat to the point of insulation degradation. NEMA (Nat'l. Elect. Mfgrs. Assoc.) has standards for number of starts per hour that motors should withstand. Solid-state devices are available to decrease the starting current (soft-start) if you want to start/stop your blower frequently.
Hope this helps, John Sellers
restricted
device, not a
routine, as it
Motors used in dust collectors and most power tools run at constant speed from zero to rated load. I don't know what you mean by a restricted motor. It will be moving the same amount of cooling air whether its loaded or not. The motor only sees the load through the shaft. If there's no load on the equipment, then there's no load on the motor, other than slinging the weight of the impeller around.
Bob
Thank you to all the folks who posted thoughts on this matter.
FWIW, I think I have it (partially) figured out.
A DC won't make a decent central vac. This is because a DC uses an impeller-type thing to move the air, and the impeller moves a lot of air when there is little or no resistance, but gets choked off pretty easily. So the DC develops a max static pressure of roughly
10 inches of water (or about .03 atmospheres). A vacuum cleaner uses a turbine. The better ones use a 2, 3 or 4 stage turbine. A top of the line vac moves maybe 100cfm, but the static pressure developed is roughly 100 inches of water, i.e. maybe 0.3 atmospheres. Sucking away on your carpet, you're moving very little air, but the only way to move any air at all is to have as much static pressure as possible.Thanks again to the posters.
Rex
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.