Kerfuffle - Dust Collection - Vacs and Amps

[Sycamore67]

There was recently a thread about dust collection and some comments came up concerning how hard a vac was working if the vacuum hose was blocked or closed down.  Rather than adding on to that thread, I thought that I would post some test results that I obtained from two of my vacuums. 

In a recent post about dust collection, I mentioned that “With dust collectors, if you constrict it with a small diameter hose, it draws less amps.”  And “The amount of current or work is related to the amount of air being moved.”   I also included a graph with results from my dust collector.

There were some who disagreed strongly. 

Since I did not have actual data from a vacuum or shop vac, I decided to do some testing with two different vacs.  These were a Ridgid 6.0 hp 14 gal shop vac and a Festool CT26.  I tested them with no hose and different hoses with them either blocked or open.  I wanted to determine if the motor was working harder when you had a full open flow from a hose or when it was blocked.

When you block the end of a hose it certainly sounds like it is working harder BUT.....

I measured the amps using a clamp on ammeter and a line splitter that I bought on Amazon.  The specific one that I used was Tekpower UT202A (Uni-Trend) Auto-ranging AC 600 Amp Clamp Meter with Tekpower Line Splitter M920.

 I also tried using a meter Poniie PN2000 Plug-in Kilowatt Electricity Usage Monitor Electrical Power Consumption Watt Meter Tester w/ Extension Cord.  This can provide the volts, amps watts and power factor.  It is a handy device to use to determine who much power a tool or fan is using.  It will monitor the watts over a period of time and you can then calculate kilowatts and then the cost of running the tool.

The results were consistent with all hoses and both vacuums.  When you blocked the end of the hose, the amps dropped compared to having the end of the hose open.  While it is making noise, it is not moving air and is doing less work.   I got the same result no matter what instrument that I was using to measure the amps.  

       

 

 

While some may not agree with my results, you are free to do the same test yourself.  If you get results that are different, I would be glad to compare the results and methods to understand the differences.   (Please note that the voltage was more like 118 VAC rather than the 110 shown on the graphs.)  

 

[Rockytime]

This has been interesting because I always assumed with all the gates closed the motor would overwork and possible burn out. I have to quit assuming.

[OCtoolguy]

7 minutes ago, Rockytime said:

This has been interesting because I always assumed with all the gates closed the motor would overwork and possible burn out. I have to quit assuming.

It does make me wonder why a vacuum with a clogged filter would burn up. You'd think it would be just the opposite. Air flow is air flow. Or the lack of it.

 

 

[kmmcrafts]

I've always heard that if you choke off the air to a shop vac it'll run hot and possibly burn up? Possible because of not enough air flow?  When choking off the hose on a shop vac it makes it sound as though it's working harder.. But with the results you show.. I'm wondering if it is more like free wheeling or racing the motor RPM's so to speak.. rather than working it harder.. 

@octoolguy maybe the free wheeling / racing motor RPM's is creating more heat? Just guessing.. While I get the concept of no air to move = less drag on the motor... It kinda makes sense that the loud " working " sound may actually be the thing spinning many more RPM's = creating more heat.. Just guessing.. but it's the only thing I can think of..

[Sycamore67]

With some vacuums, the air flow cools the motor.  However, with both my Ridgid and Festool there is still air coming out of vent areas and not getting hot.  I do not know the cause of the change in sound when the hose is blocked.