Original message
| ChaoticStasis
 |  "Current Sensing Relay - 220V variable blower?"
, posted Tue 18 Mar 14:40  
My Trane has a 220V variable-speed blower. Doew it matter which 110VAC leg I use for my Aprilaire humidifier's current sensing relay (switching 24VAC)? Does the blower draw current from both legs at all speeds and/or and/or will current cease to be sensed on both legs when the blower stops? Thanks.
RJH
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Replies:
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| ChaoticStasis
|  "Re(1):Current Sensing Relay - 220V variable b"
, posted Wed 19 Mar 00:17
Thanks for the feedback. I wasn't all that happy with using the relay in the first place. I was fairly sure current would be detected equally on the two 120V legs, but wanted a second, more seasoned opinion.
I've not heard good things about sail switches for this application, but the pressure switch idea is a truly inspired alternative. It would add the capability to have an adjustable 'tripping' pressure. Grainger sells one from TJERNLUND that might work like a charm.
I don't know why pressure switches aren't mentioned more often in humidifier discussions online, nor why the likes of Aprilaire doesn't sell them as an alternative to the relay.
Do pressure switches get dirty and stop working with the same ease as sail switches? Might the current sensing relay still be the most reliable solution for the longer term?
RJH
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| Northern1
| "Re(1):Current Sensing Relay - 220V variable b" , posted Tue 18 Mar 22:18
On a variable speed motor I would recommend using either leg to prove current draw but also installing an air pressure switch and/or flap switch in the duct and set it to initiate at medium speed so your humidifier can not operate during the ramp up or ramp down speeds of your blower (unless this is a set up feature of your humidifier where a certain current draw that corolates to your specific blower speed has to be met before operation)
When asked what steps to take while smelling natural gas please take my advice "long and rapid!!!"
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| bigglenn357
| "Re(1):Current Sensing Relay - 220V variable b" , posted Tue 18 Mar 20:19
Check wiring diagram and use common wire for fan most likely white wire
Big Glenn
"Imagination is more important than knowledge" (Albert Einstien)
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| | ChaoticStasis
| "Re: Current Sensing Relay - 220V blower" , posted Wed 19 Mar 19:06
I've heard this suggestion from my local supplier guy. Problem is, for a 220 blower, there is no common or neutral wire - the red and black wires are both 120VAC, out-of-phase by 180 degrees to provide he 220V potential. I've also heard from this same guy (now of dubious credibility) that these variable speed blowers appear to *always* draw current. I'm liking the pressure switch idea better and better.
RJH
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| | yuri
| "Re(1):Re: Current Sensing Relay - 220V blowe" , posted Wed 19 Mar 20:16:
A "sail switch" works good. The pressure switches can get clogged with dirt and are hard to calibrate etc. The sail can be visually watched/inspected. Honeywell makes them. I used them a lot with electronic air cleaners.
Yuri
[this message was edited by yuri on Wed 19 Mar 20:19] |
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