VFD deceleration issue - PLEASE HELP ! - Page 2
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  1. #21
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    Quote Originally Posted by TrueBor View Post
    Sorry if I caused confusion ! I have the resistor and will connect it and will also check DC injection once I find the manual. Will report back.
    The Altivar line manuals are on the Schneider website.. "somewhere" as downloadable .pdfs. Might have to delve "legacy", "former products" or some such, but finding the one for my old Altivar 71 wasn't hard.

    Get the resistor put to work, OV fault should be pushed waaay back, you can use more assertive settings, and I doubt you will even need DC injection to meet, then BEAT your old 1/4 second figure.

    You just don't have the inertia in that small machine as your/our larger lathes have.

    Annnd if you have an Altivar 58 already 20 years in-use, your capacitor bank is past its replace-by date. Might be a figure right in the manual.

    Typically six to twelve years, with not TOO much risk to go fifty-percent beyond.

    OEM's tend to err on the "not our fault, you-should-have-replaced.."! side of conservative. Phase-Perfect wants new caps installed at THREE year intervals, for example.

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    Based on what has been said, if you run both motors at 25 Hz then braking times should be similar, since you are looking at the same slope over time and same starting point. DC injection is usually used at the lower frequencies, most of the VFD's I work the maximum starting frequency is 10 Hz. To get sub second stopping times w/o a braking resistor at the higher Hz without a fault error is the exception, so starting at 25 Hz the effect of the DC injection is more significant vs. 50 Hz. Frankly I think if you are banging a lathe to a stop in 0.2 seconds from from 500 RPM repeatedly, not a good idea long term . The harder you push down the stopping time the more likely you are going to get an over voltage error as you run the RPM (Hz) higher and/or run a heavier chuck. Some (I assume newer) VFD's have settings to minimize/prevent a bus over voltage situation but this can also lead to more stopping variability. I used different programming deceleration times depending on the operation. Frankly if you can measure split second differences of 0.1-0.2 then your reflexes are much better than most, we are talking a difference of 2-3 revolutions. If you have that much fear of threading, then rig an adjustable limit switch attached to a micrometer stop. Threading is less about how fast a lathe stops and more about consistency in how you do each pass. Manuals are posted on-line "altivar 58 manual pdf", but you are probably pushing the old VFD way passed its life expectancy.

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    Quote Originally Posted by mksj View Post
    Based on what has been said, if you run both motors at 25 Hz then braking times should be similar, since you are looking at the same slope over time and same starting point. DC injection is usually used at the lower frequencies, most of the VFD's I work the maximum starting frequency is 10 Hz. To get sub second stopping times w/o a braking resistor at the higher Hz without a fault error is the exception, so starting at 25 Hz the effect of the DC injection is more significant vs. 50 Hz. Frankly I think if you are banging a lathe to a stop in 0.2 seconds from from 500 RPM repeatedly, not a good idea long term . The harder you push down the stopping time the more likely you are going to get an over voltage error as you run the RPM (Hz) higher and/or run a heavier chuck. Some (I assume newer) VFD's have settings to minimize/prevent a bus over voltage situation but this can also lead to more stopping variability. I used different programming deceleration times depending on the operation. Frankly if you can measure split second differences of 0.1-0.2 then your reflexes are much better than most, we are talking a difference of 2-3 revolutions. If you have that much fear of threading, then rig an adjustable limit switch attached to a micrometer stop. Threading is less about how fast a lathe stops and more about consistency in how you do each pass. Manuals are posted on-line "altivar 58 manual pdf", but you are probably pushing the old VFD way passed its life expectancy.
    Well, I found the programming manual and I am going to look through all the settings once more. As I mentioned I am not competent with a lathe - just a very casual user and the way it worked before felt safe. But I suspect I'll have to adjust to the new way - what else to be done ? I have the same very fast stop on my mill and I am thinking to swap the motors in between when I'll have some time. And I don't need the machine - for now it's busy making gib strips. A crappy way to put some food on the table, I must say.

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    Quote Originally Posted by thermite View Post
    Annnd if you have an Altivar 58 already 20 years in-use, your capacitor bank is past its replace-by date. Might be a figure right in the manual.

    Typically six to twelve years, with not TOO much risk to go fifty-percent beyond.

    OEM's tend to err on the "not our fault, you-should-have-replaced.."! side of conservative. Phase-Perfect wants new caps installed at THREE year intervals, for example.
    I did not see anything in the manual. Caps for these things were ( usually ) 30k hours at 100+some C. This inverter worked always dead cold and one would expect about an order of magnitude longer life. We installed hundreds of VFD's in various machines over some 25 years and we had a few bridges go bad and when caps went it was on some Brazil made stuff. Bought right caps are dirt cheap, question being the quality. And by the way, on the Altivar the small keypad was having some manuf issue - would go dim. They gave us a couple as spares and of course, since then none failed anymore.

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    As has been mentioned you can thread away from the shoulder: Threading on a manual lathe BEST TECHNIQUE EVER !!!! - YouTube

    0.2 seconds seems really fast. How is that possible without an external brake resistor? Or even with one.

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    Quote Originally Posted by TrueBor View Post
    I did not see anything in the manual. Caps for these things were ( usually ) 30k hours at 100+some C. This inverter worked always dead cold and one would expect about an order of magnitude longer life. .....
    YES.... the failure time for capacitors is EXTREMELY dependent on how much ripple current they see, and their ESR, which in combination determines how hot they get. There are other factors of voltage, etc, as well.

    The reason the PP caps fail so fast is because they presumably work them rather hard. Their 3 year replacement has zero to do with a totally different installation where the lifetime is going to be set by the time at high power of the VFD.

    There are a couple common formulas for predicting capacitor life for electrolytics, that involve a bunch of factors. Ones used for MIL applications are the best, although they are conservative. The predicted life varies all over the map depending on the numbers.

    And, yes, those are "theoretical" calculations, but they are pretty accurate vs real life.

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    Quote Originally Posted by JST View Post
    YES.... the failure time for capacitors is EXTREMELY dependent on how much ripple current they see, and their ESR, which in combination determines how hot they get. There are other factors of voltage, etc, as well.

    The reason the PP caps fail so fast is because they presumably work them rather hard. Their 3 year replacement has zero to do with a totally different installation where the lifetime is going to be set by the time at high power of the VFD.

    There are a couple common formulas for predicting capacitor life for electrolytics, that involve a bunch of factors. Ones used for MIL applications are the best, although they are conservative. The predicted life varies all over the map depending on the numbers.

    And, yes, those are "theoretical" calculations, but they are pretty accurate vs real life.
    About 20 years ago I was involved in VFD capacitor life research. And yes - ripple current and temperature are most important.

    But what we know now is that for our applications, the calculated life was extremely conservative. They calculated around 8 years for our large drives, and 20 years later many of them are still in service with original capacitors. Yes - we have had some failures, but we had failures even early on in the life of the caps.

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    The predictions are for the ambient and loading/ripple current/etc being 100% duty.


    When there s any variation in any of the parameters used, then the life will vary. Lower heating, or really, lower hotspot temperature, is going to cause the life to extend, and by MORE than the time of the lower temps, because the failure RATE at the lower temp is lower.

    So if 10% of the time is at a lower load than used to calculate life, you may find the actual life is extended, not by 10% but maybe 15%, 20% or even 30% and above, depending on how much the temp falls during those times.

    The typical life extension often quoted for temperature related failure is doubling life for every 10C reduction in temp.

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    Quote Originally Posted by JST View Post
    YES.... the failure time for capacitors is EXTREMELY dependent on how much ripple current they see, and their ESR, which in combination determines how hot they get. There are other factors of voltage, etc, as well.

    The reason the PP caps fail so fast is because they presumably work them rather hard. Their 3 year replacement has zero to do with a totally different installation where the lifetime is going to be set by the time at high power of the VFD.

    There are a couple common formulas for predicting capacitor life for electrolytics, that involve a bunch of factors. Ones used for MIL applications are the best, although they are conservative. The predicted life varies all over the map depending on the numbers.

    And, yes, those are "theoretical" calculations, but they are pretty accurate vs real life.
    Of the top of my head : since '96 ( or '97 ?) we installed around 400 inverters. The vast majority are 2-3Kw single to three phase. Only TWO had failed caps. I spoke with our former electronic tech and he says those failed because they were substandard parts. Those two inverters were made in Brazil. Our former tech guy is now in the business of making inverters and he says it is very difficult to get quality caps for reasons I will not mention here. He says best to go to the factory and pick them up yourself. Same way, 45 years ago I worked for a European bearing factory. We made any brand you cared to order and pay.

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    Just to report quickly : I installed the old 2 pole motor at 25Hz. Works as before. Perfectly. I think this means the inverter is not faulty. Next I will install a new inverter and report back.

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    I don't see a mention of what error message you're getting.

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    Quote Originally Posted by SomeoneSomewhere View Post
    I don't see a mention of what error message you're getting.
    True. The message is "overbraking".

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    Quote Originally Posted by TrueBor View Post
    Just to report quickly : I installed the old 2 pole motor at 25Hz. Works as before. Perfectly. I think this means the inverter is not faulty. Next I will install a new inverter and report back.
    I think I found out what is happening : for no reason I can see when I use the 4 pole motor DC injection is set to zero and the option to increase the DC current DISAPPEARS. Software fault I think.

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    Quote Originally Posted by TrueBor View Post
    I think I found out what is happening : for no reason I can see when I use the 4 pole motor DC injection is set to zero and the option to increase the DC current DISAPPEARS. Software fault I think.
    you don't need to tell the vfd how many poles there are. what other settings are you changing?

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    Quote Originally Posted by johansen View Post
    you don't need to tell the vfd how many poles there are. what other settings are you changing?

    Well sort of. You DO tell the VFD the motor speed if you want the readout to be correct, and that would translate to pole count. Maybe they allow DC injection for higher speed motors only, but that seems odd.

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    Quote Originally Posted by TrueBor View Post

    Anybody might know why the 4 pole motor takes much longer to stop and what's to be done about it ? Both motors 1.5Kw and same frame size. SAME RPM !
    Because initially you had the drive set for a 2.2Kw motor and now, after playing with it for a while you set it for a 1.5Kw motor. The drive does not like that and cancelled DC injection - notice it is not available.

    In the drive menu set motor plate current to 10A and cycle the power. That's all.
    If you want that (small) machine to stop on a dime leave the drive belt slightly lose.

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    Motors with more poles or reduced power factor have more inductance, which in my limited experience is harder on VFDs trying to decelerate.

    I used one VFD on a 2 pole motor and it decelerated in the 2 second ramp I wanted, with a minor inertial load. I used the same VFD to drive a 6 pole motor with an awful power factor of 0.5 and no load (beefy old motor though with decent inertia) and it could not stop that motor in under a minute without tripping out.

    A bit anecdotal, but worth checking the power factor (or kw-kva discrepancy) to see if this could be a factor.

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    A minute? That's a LONG time..... I am surprised there was no other approach (settings, etc) to get it stopped sooner, the total energy in it at 6 pole speed would have been lower by almost 9x, and only higher again by the proportion of increased mass.

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    Quote Originally Posted by JST View Post
    A minute? That's a LONG time..... I am surprised there was no other approach (settings, etc) to get it stopped sooner, the total energy in it at 6 pole speed would have been lower by almost 9x, and only higher again by the proportion of increased mass.
    Yeah, it was pretty ridiculous. But I checked all of the settings and they were correct for the motor. Only thing I could think is the horrendous 0.5 power factor.

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    does the fact that a 4 pole motor has twice the torque of a similar hp 2 pole motor factor into the additional time needed to decelerate? Dave
    Last edited by JST; 09-15-2020 at 10:37 PM.


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