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Thread: Bell Mouth Question
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22nd May 2020, 02:38 PM #1GOLD MEMBER
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Bell Mouth Question
I would do this myself except I do not have a bell mouth to hand and if I did I would have to dissasemble my duct system to do it. If a duct has a bell mouth added is the extra load enough to show a significant difference in current draw measured either at a VFD or using a clamp meter.
CHRIS
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22nd May 2020, 03:01 PM #2.
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It depends on the flow or more specifically the pressure at the collection point. With a smaller DC at the end of a long run of ducting ie lower/pressure flow it might not be possible to pick up any difference at the 0.1A level but on my system I can see a clear 0.2A difference @50Hz. At some point I will get out my 0.01A clamp meter and get a more precise reading.
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22nd May 2020, 03:04 PM #3GOLD MEMBER
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Thanks Bob
CHRIS
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22nd May 2020, 09:54 PM #4.
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I also just tried @60Hz and the current increases by about 0.4A
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23rd May 2020, 01:05 PM #5GOLD MEMBER
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So it appears that the fan performance has not fallen over at 60hz which makes sense as these are primarily designed for 60hz. It makes the case for 3 phase more compelling.
CHRIS
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23rd May 2020, 01:33 PM #6.
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23rd May 2020, 06:21 PM #7GOLD MEMBER
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BP reckons he can turn a 15" impeller with a fraction over 3HP @60hz. I don't know at what inlet size but knowing his liking for 6" most probably that. I suppose impeller design must also affect the load as well so it is not apples for apples. If I get a chance in the next few days I might have a play and see what the 1800 does up to 70hz.
CHRIS
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