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  1. #1
    Join Date
    Mar 2007
    Location
    Orange County NY
    Posts
    212

    Soft start or VFD

    I'm wondering if any one here has tried installing a softstart or a VFD drive on any of the newer rooftops using 3450 RPM motors on the indoor blowers? Mostly 10 ton units with 5 HP motors that i'm having problems with keeping the belts adjusted or intact for more than a couple of month's on these beasts. There is just to much torque on startup to keep the belts from slipping.
    Yes the pulleys are properly aligned and the belts are properly adjusted.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,267
    assuming that the belts are properly tensioned and aligned...do you have enough belts? are the sheaves big enough?

    obviously, if you do not have enough belts (it needs 3 and you only have 2 for example) this could be the problem. also, sheave size is very important. a 3" drive sheave and a 6" driven sheave results in a 1:2 speed ratio. a 6" drive sheave and a 12" driven sheave also results in a 1:2 speed ratio, however, the amount of surface area for the belt is way different. more surface area = less slippage. larger belts will do the same thing. moving up from an "A" belt set to "B" belt set will also perform the same action, although you will have to change out both sets of sheaves.

    are the belts a "matched set"? in a multiple belt installation, matched sets are a requirement (IMO).

    belt temperature (belt ambient temperature) is also critical. for every 18F below 140F, belt life will double. over 140F...just don't do it.

    tell us more about your installation.
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  3. #3
    Join Date
    Jun 2005
    Posts
    128
    I guess VFD will be a good solution, expensive though

  4. #4
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    you could either;

    1 slap a vfd on

    2 leave fan on continuous

    3 change belts bi-monthly



    .

  5. #5
    Join Date
    Dec 2001
    Location
    Southern Tier, NY
    Posts
    6,066
    4) ask the Manufacturer to explain the solution to your problem

  6. #6
    Join Date
    Mar 2007
    Location
    Orange County NY
    Posts
    212
    The Trane 10 ton Precedent seems to eat the most belts, it comes from the factory set up with single B belt. 10 ton Lenox rooftops come setup the same way but the belts seem to last for 6 months something I can live with, and the customer doesn't seem to hear the belt squeel on startup.
    I service six of these same units at differant locations and they all have the same issue. The previous Voyager model has an idler pulley and is a well engineered unit. Can't say that about the newer model though.
    My concern with installing a double pulley system is that then the bearing brackets and blower mounting hardware will then probably fail from the excessive torque.
    Called Trane for a solution and was told to align the pulleys and that they knew of no other solution to the problem. Not the first time in 35 yrs. in the trade that manufacturors have denied having a design problem and leave it up to the guys in the field to solve.

  7. #7
    Join Date
    May 2006
    Posts
    69
    "Matched set" belts are not all that important anymore because the quality is much better now.

    VFD would work but min speed/airflow issues would have to be dialed in or just use a soft start like a Benshaw.

    Or if you can set the units to run the fan all the time during occupied mode and eliminate the s/s all day long. We have to do this sometimes for circulation issues to make cust. happy.
    And yes the filters will get dirty faster but its not that bad, plus less belt dust everywhere.

  8. #8
    Join Date
    Nov 2005
    Posts
    574
    Matched set" belts are not all that important anymore because the quality is much better now.

    Do not believe this for a minute.

    I was in a hurry last month and could not wait to order matched belts now I have to go back and re-do many belts that have stretched in 1-3 weeks time.


    Matched belts are very important if you care about the equipment and your customer.

  9. #9
    Join Date
    Jun 2003
    Location
    Cracker Country
    Posts
    62

    Cool

    Jack, if your staying with a single belt then get a BX Gripnotch Raw Edge one. It will not slip near as much as a reg. B.What are your pitch- Dia. on these units?Like Jayguy said check the arc of contact for this unit.

  10. #10
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,267
    Quote Originally Posted by chillin cracker View Post
    Jack, if your staying with a single belt then get a BX Gripnotch Raw Edge one. It will not slip near as much as a reg. B.What are your pitch- Dia. on these units?Like Jayguy said check the arc of contact for this unit.
    i have seen quite a few Precedents with a real small drive sheave on them. i spoke with a sales engineer once on a job where the motor only drew about half of the nameplate amps. he said that it was cheaper to install a really big motor at order time (if the customer did not have any idea what was going into the space) and have the air balancer sheave it down. cheaper than replacing the motor i guess.

    the balancer may have sheaved the drive down too far (too far for the belt anyway).

    minimum pitch diameter for a "B" belt is 5.0"
    a "Bx" belt gets to go down to 4.0"
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  11. #11
    Join Date
    Nov 2005
    Location
    Shreveport, Louisiana
    Posts
    2,329
    [QUOTE=jimmyhoffa;1430604]"Matched set" belts are not all that important anymore because the quality is much better now.


    SO you have good resuls when you buy a browning belt and a dayton belt and put it on a pulley and PROPERLY align and tighten them

  12. #12
    Join Date
    Oct 2004
    Location
    Metro ATL
    Posts
    454
    I have used the Goodyear V-belts on several AHU's with 15 to 20hp motors and have so far seen very good results.

  13. #13
    Join Date
    Jun 2005
    Location
    The Gray Northwest
    Posts
    661
    Use a belt tensioning gauge. You'll be amazed at how much longer they will last and peform. It will "feel" like they are too tight, but it works.

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