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Member postings for Stuart Bridger

Here is a list of all the postings Stuart Bridger has made in our forums. Click on a thread name to jump to the thread.

Thread: vfd
16/01/2020 21:28:07

For a suds pump, you can get away with a motor run capacitor across the 3rd phase. No need for a VFD.

Thread: Does solder seep into copper plate ?
16/01/2020 13:48:52

Yes soldering does result in alloying between the solder and the surfaces of items being joined.

Thread: Colchester Bantam power feed problem
15/01/2020 14:58:00

I have the same issue on my Chipmaster, which shares a common apron I think? From memory the article in MEW implied it was quite a task to resolve? If I test it by winding the chuck manually feeding up to the stop, the pressure builds up and then the feed drops out with a hell of a bang. Under power it just tends to drive the stop along the bed. I am just living without the feature although it would be a nice to have.

Thread: VFD Question
14/01/2020 08:48:52
Posted by Robert Atkinson 2 on 13/01/2020 23:07:59:
Posted by Stuart Bridger on 13/01/2020 17:18:03:

A bit more research on VFD operation (specifically on the Emerson Commander that I use) shows that the the VFD will modulate output voltage progressively up to the "base frequency" set. Above the base frequency full supply voltage is applied and just the freqeuncy is varied This is where the 29Hz comes in. Setting the base frequency to 29Hz ensures that this voltage/frequency curve is optimised for 230V operation. Agreeing with Robert's post above

Edited By Stuart Bridger on 13/01/2020 17:19:52

No it's NOT.

The VOLTAGE is reduced when the FREQUENCY is BELOW the rated frequency of the motor.
The VFD instructions you are reding assumes the motor you are using has the same rated voltage as the VFD output. Some VFDs can increase the voltage as the frequency rises to maintain torque and increase power but this depends on the insulation of the motor being able to withstand the higher voltage. Motors with increased insulaton ae available for this purpose. Note that the motor will not run any hotter with higher voltage because the main heating effect is I squared R and the current and resistance of the windings has not changed (yes there are increased bearing, windage and AC losses like skin efect but these are insignificant for the levels we are talking about).

I'll say it again it is FREQUENCY (speed) and CURRENT (torque) that determine the motor power, the voltage rating just sets the current at one frequency.

Robert G8RPI.

Robert, I have to say that I completely agree with your statement, effectively you are just describing what happens when you reduce the frequency from base/rated frequency downwards, whereas I described what happens when you increase frequency upwards to the base frequency. Exactly tthe same.

From the VFD manual
"The rated voltage is used in conjunction with the motor rated frequency (Pr 5.06) to define the voltage to frequency characteristic applied to the motor. The following operating methods selected by Pr 5.14 are used to define the drive frequency to voltage characteristic"

" Fixed boost mode: Fd A linear characteristic is used from 0Hz to rated frequency, and then constant voltage above rated frequency. Low frequency voltage boost as defined by Pr 5.15"

As mentioned previously the "trick" here is to set the base frequency to 29Hz, which changes the voltage /frequency curve to get the best out of the compromise of supplying 230V to a 415V motor

Fror reference see p76 onwards from Commander SK advanced user guide


13/01/2020 21:24:02

 

1. No one has suggested that you don't exceed 29Hz. It is a VFD setting to optimise performance at slower speeds. I can still get the rated 3000 RPM spindle speed out of my chipmaster, albeit with reduced torque. The clue is the V in VFD variable.

2. There is no doubt that this solution is a compromise, but it does work for those who have a single voltage motor and no 3 phase 415v supply available. It was much easier for me to fit a VFD than to replace the motor. It certainly is a viable option that can be considered, IF you don't need the full torque of ex industrial machine.

Edited By Stuart Bridger on 13/01/2020 21:25:36

13/01/2020 17:18:03

A bit more research on VFD operation (specifically on the Emerson Commander that I use) shows that the the VFD will modulate output voltage progressively up to the "base frequency" set. Above the base frequency full supply voltage is applied and just the freqeuncy is varied This is where the 29Hz comes in. Setting the base frequency to 29Hz ensures that this voltage/frequency curve is optimised for 230V operation. Agreeing with Robert's post above

 

Edited By Stuart Bridger on 13/01/2020 17:19:52

13/01/2020 16:30:40

The much discussed document from Inverter Drive Supermarket may not be the best worded. What I believe that he is saying that you can get equivalent peformance supplying a 415V motor with 230V up to 29Hz, Efficiency above this frequency starts to drop off. Setting 29Hz as the "base frequency" of the inverter optimises the inverter operation for this situation. Most importantly the full load current must be set to match the motor as it will draw more current for the same power and this needs to be limited ot prevent overheeating the motor. Nowhere in the article does it say don't exceed 29Hz. I run mine up to 50Hz purely so I don't exceed the design rating of the lathe.

This "trick" is ONLY required if you can't rewire your motor for 230V operation. My 1963 motor falls into this category. As mentioned before it does work, so the article can't be complete BS.

13/01/2020 12:19:01
Posted by Steviegtr on 12/01/2020 23:22:46:

I still do maintain that fact. I was not pointing at you. But a star connected motor on 240v will have the windings basically connected in series for each pair so 2 240 windings in series with 240v applied will give a pretty crap power curve

Your statement may well be true for industrial use. For hobby use, I have been running a Colchester Chipmaster on 240V with the original 1963 415V motor star connected motor using the 29Hz configuration suggested by Inverter Drive Supermarket for the last 9 years. I have never been lacking in torque/power for the use I put it to. I did try turning 1.25 inch mild steel at 2000RPM witha hefty DOC and feedrate with carbide tooling once. It did slow down the spindle speed a bit, but I was getting seriously hot chips and a stunning surface finish. But that is way beyond my typical usage.

Edited By Stuart Bridger on 13/01/2020 12:19:51

10/01/2020 16:22:06

As mentioned above I use the technique highlighted in the article by Colin@Inverter Drive Supermarket.
I don't pretend to fully understand it either but it works! They are a very helpful supplier.
The 29Hz is not the maximum you can set, but will be the value up to where you get full torque with 240V. Above this frequency the motor still runs, but with reduced power. I run mine up to 50Hz and the reduction in power is not significant for hobby use. More significant I beleive is getting the current setting correct.

Edited By Stuart Bridger on 10/01/2020 16:36:01

Thread: To use chuck or collets
10/01/2020 11:12:33

Depends what you are doing and accuracy required.
If all operations can be completed without removing the stock from the chuck , then no harm in using a 3 jaw

Thread: VFD Question
10/01/2020 10:13:55

This is a good explanation and the technique I use on my Chipmaster with a 415V star connected motor with a 240V VFD
**LINK**

Thread: The blind leading the blind
09/01/2020 12:13:57
Posted by not done it yet on 09/01/2020 11:48:15:

Video or pic? Could be a difference between ‘looking at’ and ‘using’. However, eye protection should be the order of the day whenever in that working area - there may be others making flying chips! Most certainly not a good advert.

100% agree. When I worked in industry over 30 years ago, all machine shops were designated eye protection areas. It was mandatory even if just walking down the gangways.

Edited By Stuart Bridger on 09/01/2020 12:14:11

Thread: Colchester Student Mk1 Won't Start
23/12/2019 15:07:54

if the holes are small, what about coating with an Epoxy sealant?

Thread: 2nd Hand Hearing Aid Reprogramming?
18/12/2019 13:50:55

I would highly recommend Tripp hearing, not used them for the subject in question though.

Thread: Colchester Student Mk1 Won't Start
17/12/2019 10:12:56

This may be of interest, It is the technique I use on my Chipmaster for a VFD conversion.
My lathe has the original 1963 motor which cannot be wired for 240V (or at least not without digging into windings for star point). There is some loss of power, but it is fine for hobby use.

**LINK**

Thread: A reminder to take care with aerosols...
16/12/2019 20:33:28

When I was a lad, I grew up on a farm. In those days a bonfire was the standard way of dealing with waste. My father asked me to dispose of a sack from the dairy. On the fire it went. A couple of minutes later there was a bang and an aerosol whizzed past my ear very fast and very close. My dad was mortified and very apologetic that he forgot that he had put it in the rubbish sack. It could have been very nasty.

Thread: What is it
16/12/2019 13:26:05

I would also say tacho generator and aviation related. Evershed were acquired in 1965, so it is older than that.

The part number does show up on google with FBRT1051015 as an associated part, bit no real detail other than hits on aviation part sourcing websites.

A search on ebay for "evershed tacho generator" does bring back some more modern variants

Thread: Colchester Student Mk1 Won't Start
13/12/2019 18:49:51

My money would be on the converter not having enough oompf. The "phantom" 3rd phase approach of thesedevices is not ideal.

Also if it as not been run for a while, ltet it warm up for a while before trying the top speeds. It may need the oil needs warming up. When I first got my Chipmaster it wouldn't go a full pelt (3000 rpm).
There is not much that can go wrong in an induction motor, so I expect the motor is OK

Thread: VFD Switch on Frequency
12/12/2019 14:39:15

Check your minimum and maximum speed settings in the VFD config

Thread: More evidence that the world has gone mad!
07/12/2019 08:42:23

I work for a US software company. There is currently a debate going around regarding the terms whitelist and blacklist. These are industry standard terms for inclusion or exclusion of objects. However there is a concern amongst some that the terms are no longer PC. Given how much other work we need to to keep our product ahead of the market, it's certainly not got to the top of the list.

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