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What is the manufactors min speed/HZ on a cooling tower fan motor rated for inverter duty. I was taught 20hz was min speed to keep from over heating. Engineer wants to run with no minimum.
"Dying aint much, its living thats hard." (Josey Whales)
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I set fan applications at 10 Hz and pumps at 18 Hz on the drives I set up. I've had no reported problems after ten years of factory start ups.
If this cooling tower is belt driven, I wouldn't go below 6 Hz or 10%.
If it is gear driven, you can't go below what the gear drive manufacturer recommends what the min. speed should be for proper lubrication.
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Was told by Marley that at 18hz your airflow pretty much stops thru the tower. I run the tower water up to 2F below setpoint before sending the drive a run command. Starts at 18hz and goes from their. If it drops 4F below setpoint the drive goes off. The towers and drives I just installed run within
.15F of setpoint and usualy closer to .04F.
Last edited by absrbrtek; 10-20-2008 at 06:00 PM.
To much work with too little time!!!!
Professional Member*
Still did not teach you anything! 20HZ is safe but I would contact the tower box rep. Some of the boxes have a slinger for "splash" lubrication. Don't work so well at slow speeds. The motors require around 20HZ to get the fans on the rear to effectively cool the motor. TEAO might need more speed since they use ambient air over them.
"I'm from Texas, what country are you from?"
Professional Member
LOL, that's what Marley recommended. Been online for a few 1000 hours with no issues.Originally Posted by stickerhead
To much work with too little time!!!!
Professional Member
Dident learn anything from you 20 years ago when you was my supervisor why should anything be different today? Hhhhmmmm is it me or you???????
"Dying aint much, its living thats hard." (Josey Whales)
Professional Member*
I would agree with the a 20HZ min. for that application , any new inverter start ups on pumps or ahu's I would set up for 15HZ to 20HZ and have had no problems at all.
A mind is like a parachute. It doesn't work if it is not open.
The best part of going to work is coming back home at the end of the day.
Hard work spotlights the character of people: some turn up their sleeves, some turn up their noses, and some don't turn up at all.
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That's why you live out in nowhereville where no one knows what you are doing is right or wrong. That's why C-alvin made so much $$$Dident learn anything from you 20 years ago when you was my supervisor why should anything be different today? Hhhhmmmm is it me or you???????
"I'm from Texas, what country are you from?"
Professional Member
Well thats what I like about it! I get to decide what is right and what is wrong! No corprate policy or little Hitlers! Its right if I say its right and wrong if I say its wrong. Like the little trip to "trailer hill", That was WRONG!
"Dying aint much, its living thats hard." (Josey Whales)
Professional Member
Thanks for the replies. I set min at 15hz as the know it all engineer agreed to. Its his motor!
"Dying aint much, its living thats hard." (Josey Whales)
Professional Member*
Whoo! You just slapped my brain! I thought you would have wanted to have forgotten that! Bad mental picture but it was funny! I will see if C-alvin remembers!
"I'm from Texas, what country are you from?"
Professional Member
The question is not if you can remember but if can you forget!
"Dying aint much, its living thats hard." (Josey Whales)
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I was innocent but you and Tio wern'tThe question is not if you can remember but if can you forget!
"I'm from Texas, what country are you from?"
Professional Member
Don't let the Mods see you fighting like this.
haha play nice..
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No fighting here. We been buds for along time. Just a "thing" that happened in the past so we will shut this one down and get back to the original post. I became a "thread high jacker" Absrbrtek, don't baned me please! LOL
"I'm from Texas, what country are you from?"
Professional Member
Can I ask a question here? Why not let it go to 0? Why run a motor without purpose. Isn't the most efficient motor, a motor that isn't running? 0 power consumption. It's a soft start, so locked rotor amps isn't a issue. Maybe I'm way off on this one too.
Professional Member
Even VFD rated motors have minimum speed ratings for the most part. There are multiple issues. Cooling of the windings, lubrication of the bearings, and probably a few others. Yes you could go from 15-20hz straight down cycle off. The invertor electronics probably take some extra heat on each start stop though, so there are trade offs.
Professional Member
I came up with some Baldore info that gave a ratio of 20to1 for Emotors and 1000 to 1 for super E motors in a variable torque application. I did not understsnd the ratio or what it meant. The way I see it is it depends on the application were like a cooling tower fan is heavy and takes some torque to get it and keep it moving. If the application has less torque requirement we could slow it down more the more the low speed torque requirement the higher the min speed. ???
The Baldor specs said something about the motor having full torque all the way down to 0 hz but I watched the amps on a 20 HP motor at 20 amps at a 5HZ output on the drive.
"Dying aint much, its living thats hard." (Josey Whales)
Professional Member
Oh by the way StickerBritches it a belt driven tower.
"Dying aint much, its living thats hard." (Josey Whales)
Professional Member
You probably do not want to go much below 20 Hz for a prolonged period. Motor cooling can become a real issue at speeds lower than that.
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