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Thread: VSD Hp reduction
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10th Jan 2011, 02:11 PM #16Most Valued Member
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Dave
I could put a shear pin or key on the pulley I will have to make. But how accurate would a "2hp" shear pin be?
I was hoping that only using one Vee belt might have acted to limit horsepower(I currently run the belts pretty loose)
I don't "think" that a one off overload(read crash) would damage it much more than a with a 2hp motor, I was more worried about overloading it in day to day use.
Stuart
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10th Jan 2011, 02:28 PM #17Golden Member
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Stuart,
I read F_18 as the setting for motor current.
Example:
Inverter is rated 4 A, motor is rated 3 A: F_18 is set to 3/4 = 0.75%.
In Australia, the network grid operates at 50 Hz.
F_05 should be set to one of the 50 Hz examples.
There is a difference in the inverter for 50/60 Hz in relation to nameplate values and percentage overloads.
If you set the incorrect frequency, you could risk damaging the motor or inverter (not likely the inverter)..
The Figures 1, 2 and 3 show curves of inverter output voltage versus output frequency.
A motor draws current very nearly linearly dependent on the applied frequency due to the inductance of the motor.
Fig:1 is the standard curve, virtually linear from 1 to 50 Hz.
Fig:2 puts out additional voltage at frequencies between 1 and 50 Hz to force additional current, and thereby force some additional current to provide additional torque during the motor acceleration stage.
Fig:3 is the inverse of (2), it puts out reduced volatge to deprive the motor output of some torque.
Example:
Use (1) to start a rotary sawblade, (2) to start a compressor and (3) to start a plastic bladed fan.
(1) is a strong load that can be got to speed quickly,
(2) is a high static strong load against the cylinder compression,
(3) is a weak load that needs to be started gently.
Hope this helps,
It would be great if a user of a Teco Converter could confirm my interpretations.
John.
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10th Jan 2011, 02:33 PM #18Dave J Guest
Hi Stuart, it might be fine, I was only pointing out that the shear pin doesn't protect the whole gear train only the carriage.
Dave
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10th Jan 2011, 03:40 PM #19Most Valued Member
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John
I left F_05 at 5(not 4 as I said in my other post) as thats how it came.
F_18 is set to 70 so that must be about 2hp anyway?
Here is what Drives Direct had to say when I emailed them about the settings.
"F05 will be best set at 4 for your application but 5 is OK if you use the speed control at low RPM,
The F18 parameter should be at 70 for a machine tool application such as a lathe or mill as the load is only applied AFTER the motor is up to speed, the setting of 100 would be used on an application where the load was on the motor from start up such as a car ramp for example and it will give the motor more starting amps to overcome the overload current without the inverter tripping, "
Seems I forgot to change F_05 anyway.
I wonder if I should set F_13 to 10?
Sorry John I meant figures 1, 2 and 3 on page 38
Dave I took eskimos comment to mean "add a shear pin into the drivetrain some where". Like RayG added to his vice. Not the shear pin on the leadscrew.
Of course I could be wrong. I've been know to not read things properly in the past.
Stuart
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10th Jan 2011, 03:45 PM #20Dave J Guest
Maybe it's me on the wrong track, Eskimo what where you meaning?lol
Dave
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10th Jan 2011, 04:21 PM #21Most Valued Member
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If you take the Load off the Carriage through a Shear pin in the Leadscrew or Feed shaft that will automaticaly take the Load off the Drive Train,running a Motor of any HP on a machine which is not under Load should not have any Detremental effect at all.
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10th Jan 2011, 07:27 PM #22Golden Member
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Stuart,
I do not think the Drives Direct advice correctly interprets the manual you supplied.
Either the manual does not apply, or the advice is misleading.
I read all of the data in the manual relating to F_18 as continuous operation, not directly related to starting.
The claim that F-05 should be set to 4 or 5 is just plain wrong, the UK probably thinks Australia runs at 60 Hz.
The equivalent 50 Hz curves are 1 and 2.
Would other forum members please take the time to review the manual, the UK advice, my comments below and contribute as appropriate.
Manual page 38:
Paragraph 1 describes motor overload protection:
(1) defines the "Motor Rated Current" as a proportion of the Inverter Rated Current.
The proportional constant is defined as F_18.
(2) states that motor operation continues while the inverter current is less than the value set as the Motor Rated Current.
Note that there is no mention of starting, and I take the use of the word 'continues' to mean continuous long-term operation.
Paragraph 2 describes inverter overload protection:
Figure 3:
Curve (1) shows how the allowed operation time is reduced as the current increases for a motor running at nameplate frequency.
Curve (2) shows how the allowed curve is reduced when running at reduced frequency.
This is continuous, not starting, operation.
Figure 2:
Is for 60 Hz operation and does not apply.
Figure 1:
This curve shows the reduction in allowed current when operating continuously for any of the three selections (F_05 = 1, 2 or 3) available when operating with a 50 Hz nameplate motor.
At 50 Hz you get 100% of the Motor Rated Current (defined above).
At 20 Hz you get 90% of Motor Rated Current.
At standstill (0 Hz) the allowance is 60 % of motor rated current.
Other frequencies lie on the straight lines between these points.
NOTE
I cannot find any specific allowance in the manual for overcurrent at starting.
The conclusion from this is that all the continuous factors mentioned above apply under any conditions, including starting.
Page 34:
F_05 for a standard motor is set to Curve 1.
The table at the bottom of the page defines the Curve 1 voltages.
At starting, the inverter will output a frequency of 1 Hz at a voltage of Value C, = 8% of nominal voltage.
A standard motor will demand about full nameplate value current under these conditions, so the motor will start.
See how for the Curve 2 case the applied voltage is higher at 1 Hz, and for the Curve 3 it is lower, reflecting the cases I previously gave for a compressor and plastic fan respectively.
John.
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10th Jan 2011, 08:25 PM #23Most Valued Member
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PC Thats a very interesting thought. Seems to simple lol
John The pdf is later version of the manual that was supplied with the inverter. I agree with your interpretation of how things stand.
Thanks For explaining the graphes, they make sense now, as long as I read your discription while I am looking at them.
I'll change F_05 to 2 tomorrow. I think I'll leave F_18 as is for the minute.
Thanks
Stuart
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10th Jan 2011, 09:21 PM #24
Hi John, Stuart,
I have a Teco FM50 on the mill, and the list of the various parameters and the functions seem to be identical. John's interpretation of the manual is pretty much as I see it.
The V/F graphs for the F_05 parameter, there is a misprint, in the frequency scale, where they have 2.5Hz should be 25 Hz. I note they got it correct in the graph for F_05=3
I just have F_05 set to 1. which is the setting for voltage varies linearly with frequency. I can see an advantage in having higher voltage in the mid range, the option they call "high starting torque".
As far as F18 goes, it is set to the % of the INVERTER rated current that equates to the motor rated current, and it's a (calculated) thermal overload trip, rather than an overcurrent trip as such. Let's say the inverter is rated at 5amps, and the motor nameplate is 2.5 amps, then you would set F18=50%
But the inverter isn't going to trip on an overcurrent until the load reaches 150% of the motor rated current for 1 minute... larger overcurrents will trip in shorter times as per figure 3 in the manual.
But that's not an overcurrent trip characteristic, that's a calculated thermal overload trip,
Not much help at all when it comes to protecting the lathe in a crash!
I can't see any parameter settings for a proper overcurrent trip. Maybe it doesn't have one? Back to shear pins.. (on the mill, if it stalls, the belts will slip, but so far I haven't managed that little trick..)
Regards
Ray
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10th Jan 2011, 10:14 PM #25Most Valued Member
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Hi Ray
I'm not so sure the F_05 scales is incorrect.
If so they made the same mistake on scales 3 and 4.
The pdf is Ver 11 2010 04
My paper manual is Ver 09 2005 08 and has the same numbers.
If you look at the B point in 2 its 15%, at B in 3 its 25%. But if they were both meant to be 25Hz, shouldnt the B point in 2(the high starting torque be higher than the B point in 3?
So it looks like the only way to limit power on my lathe would be limiting rpm.
My mill is made with a 3hp motor so it should be able to look after itself.
Stuart
p.s. as always I could be wrong
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11th Jan 2011, 07:46 AM #26Most Valued Member
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11th Jan 2011, 08:27 AM #27Golden Member
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Stuart,
I think you are correct, the Curves for 1, 2, 4 and 5 are correct as drawn.
In Curve 2, the high starting torque case, if the frequency was 25 Hz the motor would need more than 50% of the volts.
The B point is tabled as15% of the voltage for 2.5/50 = 5% of the speed - a significant boost, right at the low end of the speed range where my nominal compressor would need it.
My Huanyang manual shows virtually the same curves.
Unfortunately, limiting the motor RPM does not help, the inverter will still take too long to trip.
The Huanyang manual describes an overtorque function that is settable for an amount of overcurrent for a settable amount of time.
This provides convenient overload protection.
It seems very hard (impossible ?) to believe that the TECO inverter does not have a similar function.
You should get back to the UK to assess if this inverter has got an instantaneous trip setting.
John.
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11th Jan 2011, 01:59 PM #28
Hi Stuart, John,
Yes, I see what you mean. I'ts the same V/F graphs in my FM50 manual. The table below the graphs makes it clearer.
Back to the original question, I still don't see any major issues with increasing the power from 2hp to 3hp anyway. The extra power is overall more likely to be a help than a hindrance, the lathe is still protected just exactly as it was before, the shear pins and belts haven't changed. Plus you get all the other benefits of a VFD.
Regards
Ray
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11th Jan 2011, 09:37 PM #29Most Valued Member
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Ok well I'll give it a go. I'll lock the speed a 2/3, make/buy an oversized pulley to get the spindle back to 1400rpm. That will let me boost rpm if I ever really need it. If I need more then 1400rpm I cant imaged I'll be doing heavy cuts.
Ray Does the spindle rpm make much difference to the time taken to stop on "controlled stop"? Have you fitted a separate brake resistor?(I'm thinking about using the emg stop settings as part of the "electric carriage stop" we were talking about.
Thanks all for your input. As always this may take me a couple of months. There are a few jobs infront of it, like my DRO for starters.
Stuart
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12th Jan 2011, 07:15 AM #30
Hi Stuart,
Once you fit a DRO, you'll wonder how you ever got by without it.
I haven't got a braking resistor fitted, I think bigger drives might get some benefit. But to answer your question, if you set the ramp down to a low value, it stops much quicker than just coasting to a stop. There's plenty of room for tuning to get the result you want.
Not sure you need to bother with changing the drive pulleys, just crank the frequency down on the vfd if you are at all concerned about the extra power...
Regards
Ray