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wangito
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Blowing air against a dead head or dead end/

02/07/2009 9:05 AM

Can any one refer me to where I can find air blower electric motor current curve vs. pressure built-up.

Here's a bit more information: I have a split-unit air conditioner that blows warm or cool air into a metal duct. The metal duct is supplying the air into 4 small sealed units through 4 dumpers upon demand. It is possible that all 4 dumpers will be shut-off, and the blower will keep blowing air into a dead end, (I can't stop it due to it's design). obviously there will be a pressure built-up inside the duct. This happening, what is the effect on the blower motor and it's current curve?...The blower is a blade type.

Wangito

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North of 60
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#1

Re: Blowing air against a dead head or dead end/

02/07/2009 5:54 PM

If you can not stop the blower due to its design and if it does not like pumping cooled air when all four dampers are closed, you will need to add a fifth damper and let it vent to atmosphere when no zone calls for cooling.

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wangito
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#2
In reply to #1

Re: Blowing air against a dead head or dead end/

02/07/2009 6:15 PM

Thanks,

I know that, But what I what to know is how to find motor's current (rise or fall) while blowing against a dead head (or dead end...) So I can give an open/close command to that fifth damper. and I must do it through a motor current sensor.

Wangito

What's your opinion, will the current rise or fall?

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North of 60
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#3
In reply to #2

Re: Blowing air against a dead head or dead end/

02/07/2009 6:42 PM

If you must use motor current, then it is time for a shunt and an analog input card to something. Why not just interlock what ever controls the dampers now?

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North of 60
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#4
In reply to #2

Re: Blowing air against a dead head or dead end/

02/07/2009 9:40 PM

As to what the current will do, it should rise.

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#5
In reply to #4

Re: Blowing air against a dead head or dead end/

02/07/2009 11:12 PM

the current will fall - same as horsepower.

See figure 6:

www.greenheck.com/technical/files/Product_guide/perf_basics.pdf
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North of 60
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#6
In reply to #5

Re: Blowing air against a dead head or dead end/

02/08/2009 12:21 AM

Interesting... I could not open the link you provided. I'll try again later. My ISP has been flaky of late.

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PWSlack
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#14
In reply to #2

Re: Blowing air against a dead head or dead end/

09/25/2024 6:18 AM

As the <...blower...motor...[is]...blowing against a dead head...> there will be no flow, and therefore its load on the supply will drop compared to when there is a flow, as it is doing very little work.

One can determine these things from the manufacturer's performance curve for the <...fan...> in question.

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The Prof
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#15
In reply to #2

Re: Blowing air against a dead head or dead end/

10/31/2024 4:25 AM

power (current) will decrease as the head increases.

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sb
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#7

Re: Blowing air against a dead head or dead end/

02/08/2009 12:29 AM

Tha was a good link and very lucid.

The Guest deserves a GA

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#8
In reply to #7

Re: Blowing air against a dead head or dead end/

02/08/2009 12:31 AM

Thanks.

(Signed XMech/Guest.)

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sb
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#9
In reply to #8

Re: Blowing air against a dead head or dead end/

02/08/2009 12:50 AM

Not you. again

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#10
In reply to #9

Re: Blowing air against a dead head or dead end/

02/08/2009 1:38 AM

Yep!!
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sb
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#11
In reply to #10

Re: Blowing air against a dead head or dead end/

02/08/2009 3:14 AM

Where did you lose your -. ? (the . of -: was anyway never there )

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#12

Re: Blowing air against a dead head or dead end/

02/08/2009 7:09 AM

Can't you use a weighted damper? When the other dampers close, the pressure will push the venting damper open until another damper opens and drops the pressure enough to close it again.

regards,

Vulcan

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markar
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#13
In reply to #12

Re: Blowing air against a dead head or dead end/

02/08/2009 9:45 AM

GA............Great example of "keep it simple".

Low Voltage controls are great but they can be a pain. Consider dumping some back to the return.

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Users who posted comments:

Anonymous Poster (3); markar (1); North of 60 (4); PWSlack (1); sb (3); The Prof (1); Vulcan (1); wangito (1)

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