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VFD Braking Resistors - another question.

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  • Jim Stewart
    replied
    Originally posted by lakeside53 View Post
    Somehow it slipped into the language

    watt·age
    ˈwنdij/Submit
    noun
    a measure of electrical power expressed in watts.
    the operating power of a lamp or other electrical appliance expressed in watts.

    Jerry : where are you when you are needed? get over here and argue both sides

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  • lakeside53
    replied
    Somehow it slipped into the language

    watt·age
    ˈwنdij/Submit
    noun
    a measure of electrical power expressed in watts.
    the operating power of a lamp or other electrical appliance expressed in watts.

    Jerry : where are you when you are needed? get over here and argue both sides
    Last edited by lakeside53; 04-20-2018, 01:08 AM.

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  • Jim Stewart
    replied
    Originally posted by kf2qd View Post
    The Ohmic rating is only 1/2 half otr the data needed. The whatage is much more important for braking resistors. The Higher the wattage the more often you can use the braking funstion as a higher wattage rating has the ability to get rid of more heat. Resistors in parallel with give you a higher wattage.
    My first reaction to this post was "HUH??"

    No offense intended, but (in a technical forum (this one)) I'd expect as a licensed Advanced Radio Amateur licensee (judging by your handle) you would not make up your own terms.

    There is no such thing as an "ohmic rating". As you certainly should know, it's resistance or impedance. There is no such thing as "wattage". It's power rating.

    73, KF6R

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  • lakeside53
    replied
    resistors in series give you increased wattage too! but seriously.. you need the right ohms and a minimum sufficient wattage.

    Increasing the wattage of the resistor has little effect on duty cycle after a nominal point (i.e. "big enough"); it's more related to duty cycle capability of the VFD. The resistor part is easy - how hot can it get hot and survive? The VFD is much more limited.

    1500w is HUGE comparison to what you need for a typical 3hp motor at any reasonably sustainable duty cycle. Advantage of elements is that they are dirt cheap and can can take "red hot" temperatures. 300W works well for 2-3hp, never gets "red" or even smokes on mine even if I use it as much as possible before the vfd limits.
    Last edited by lakeside53; 04-20-2018, 12:26 AM.

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  • kf2qd
    replied
    Originally posted by lakeside53 View Post
    I use either 300W 120v (48 ohms) and 1500W 240v (39 ohms) elements on the Hitachi 3hp vfd. Dirt cheap, They work fine and exceed the 35 ohm minimum resistance requirements. The problem with using close to minimum resistance is that your braking duty cycle goes way down. Often it's better to pick one that is not as low (aggressive) and have better overall usage results. All depends on how you use your machine.

    One thing NOT to do is blindly (no pun intended) use incandescent light bulbs. The resistance varies widely as they "light up". Could be pretty though.
    The Ohmic rating is only 1/2 half otr the data needed. The whatage is much more important for braking resistors. The Higher the wattage the more often you can use the braking funstion as a higher wattage rating has the ability to get rid of more heat. Resistors in parallel with give you a higher wattage.

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  • lakeside53
    replied
    With difficulty. The switch(es) via digital inputs would be used to select preprogramed parameters, like "second motor set", or a sequence held in the internal PLD (not all VFD have access).

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  • CCWKen
    replied
    That's for the Analog Input (AI) terminals. How would you input a value of "23" with a switch?

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  • lakeside53
    replied
    Most digital Inputs are pretty simple.. switch to ground (NO or NC) or +24 depending on how you program them. You might have to read the manual

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  • CCWKen
    replied
    Originally posted by lakeside53 View Post
    I need to play with the PLD on my vfds - in theory I can read a selector switch and auto-set parameters - would be nice to have multiple changes at the flick of a switch. I can already set 2 "different" motors, so I guess I could have two discrete sets of parameters entered.
    Mine has the "two motor" option also. On my KOC100 I believe there's up to four start/stop time parameters available but their selection is via the DI (digital input) terminals. I'm not educated on how the DI terminals would be implemented. I guess you would need some external circuit to supply that.

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  • boslab
    replied
    I remember using the heating element cartridge out of a tumble dryer once, long time ago, I can’t remember the resistance but there was a hell of a load on it, I think it’s still in use (it was a small reversing mill for samples)
    Mark

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  • lakeside53
    replied
    I use either 300W 120v (48 ohms) and 1500W 240v (39 ohms) elements on the Hitachi 3hp vfd. Dirt cheap, They work fine and exceed the 35 ohm minimum resistance requirements. The problem with using close to minimum resistance is that your braking duty cycle goes way down. Often it's better to pick one that is not as low (aggressive) and have better overall usage results. All depends on how you use your machine.

    One thing NOT to do is blindly (no pun intended) use incandescent light bulbs. The resistance varies widely as they "light up". Could be pretty though.

    Leave a comment:


  • J Tiers
    replied
    Originally posted by H380 View Post
    If you ever get a chance to look over a Hass TL 1. They just use an old fashion spiral Electric stove heating element as the breaking resistor.
    While that sounds cheap and effective, you need to be careful if you try that.

    There is a minimum resistance that is allowed, because the discharge IGBT ("Braking resistor IGBT") is almost always smaller, and has limited current capability. If you pop that part, you are out of luck, because they cannot be repaired except by replacing a module that is usually as expensive as the whole VFD, if it is even available.

    OK, maybe I and a few other folks could do something else, but in general it is just not practical....

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  • H380
    replied
    If you ever get a chance to look over a Hass TL 1. They just use an old fashion spiral Electric stove heating element as the breaking resistor.

    Leave a comment:


  • kf2qd
    replied
    Another thing to consider - If you demand rapid starts and stops you are operating in the range that most VFD manufactures would call Heavy Duty operation and they would suggest a larger unit, 1-1/2 to 2 times larger. This would also allow for faster stops as there are more capacitors to charge.

    While you may be using the VFD for the convenience of running a 3 phase motor off single phase they are more designed for cost savings when operating motors. By running a motor on a pump or fan at less than full speed the cost savings can be enormous. Also - if you are starting and stopping often you may be in a Heavy Duty classification of operation and actually need a bigger VFD.

    If you are using a braking resistor and it is not heating up it is either not installed correctly, the VFD is not configured correctly, or it really is not needed in your application.

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  • MattiJ
    replied
    Originally posted by EVguru View Post
    Some VFDs can be set to limit decelleration based on the DC bus voltage.

    That's how the Huanyang on my Harrison L5 used to be set up; With the collet chuck fitted, it would stop withing the programmed decceleration time. With the three jaw fitted, you could hear the motor pulse a couple of times as it hit the DC bus limit. With the big 4 jaw fitted, it would still occasionally trip if stopped from high speed.

    Now the VFD has the braking components and an external resistor fitted and stops fine all the time.
    And on some fancier VFD's you can set the maximum desired torque used for deceleration and/or maximum motor power limit for deceleration.

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