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Member postings for Robert Atkinson 2

Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Smart TV
25/01/2022 19:31:34
Posted by Howard Lewis on 25/01/2022 14:31:38:

If you can find a cable with a HDMI connector one end and three Phono lpugs on the othere, you can feed the Audio and Video output from the player into the TV

The TV also has Phono sockets on the back. Are they for Input or Output?

If for Input, three Phono leads should do the trick.

Howard

If you find a cable with HDMI and phono donnectors don't buy it or plug it in!
HDMI is digital (Low Voltage Differential Signal at the hardware level) Phono is analog. Totally incompatible. Just because smeone in China makes it dies not mean it will work.

Cn you provide a photo of the labels by the 3 phono sockets on the back of the TV? or the full model number of the TV?
If the sockets are video (CVBS) and left right audio IN your old plyer will work with a simple phone to phono lead. Picture qulity will be poor though.
While I hate the waste, best to buy a new DVD player and ive the old one to charity (yes some do take electrical goods).

Robert G8RPI.

Thread: Another Scam
22/01/2022 10:57:52

This is a old one. It predates online market places like ebay. It used the prined autotrader and the like to identify marks.
They will end up "overpaying" you the transport agent fee and askig you to pay it in cash to the collection agent. Later the cheque is rejected by the bank and you are out the item and the cash fee.
A friend of mine had one on used car. it was identified early so police were involved nd it was worked through and resulted in prosecutions. They were even using stolen company cheques.

It's a bit differnent from the common bank details theft of today so maybe people are fallling for it again.

Robert G8RPI.

Thread: Electro etching
21/01/2022 20:17:25

Yuo could use a photo sensitive resist like this:

https://uk.farnell.com/kontakt-chemie/positiv-20-200ml/positive-resist-photo-sensitive/dp/801010

and use a negative of the sacle to expose it Devlop (in sodium hydroxide/ casutic soda typically) then etch with ferric cloride. Scle cn be printed on clear film in a laser printer.

Robert G8RPI.

Thread: How can I bond ABS (plastic) to NRL (rubber)?
21/01/2022 08:59:39

Rubber to ABS with high dynamic peel forces is a severe challenge for any adhesive.
Peel was not mentioned in your original post.
Sikaflex might do it given long enought to cure.

I wish you luck but won't be placing any bets......

Robert G8RPI.

Thread: Parts storage
20/01/2022 18:20:49

LPS4 is an excellent spray on inhibitor

Robert G8RPI

Thread: Adcock Shipley Bridgeport motor
20/01/2022 11:42:51

Yes I'll be around.

19/01/2022 21:05:39
Posted by Howard Lewis on 19/01/2022 18:07:22:

Halving the voltage (Disregarding Impedance effects ) will halve the current (V = I * R ) so I would expect half the power, and as the speed is frequency related, half the torque.

Howard

?????

Voltage is reduced / increased by the square root of 3 (1.73) for a STAR /DELTA transformation. So 240V x 1.73 = 415V for Delta and Star. Note it's the quare root of the number of phases for other multiphase systems.

You cannot ignore "impedance effects". It is the impedance and back EMF that sets the current . The resistance of the windings is a small part of the impedance and is only rsponsible of losses.
The Frequency (speed) also affects the current.

All else being equal the current and Torque reduces by about 40% when a Delta connected 415V rated motor is is connected to a 240V supply.

Note that the standard method for specifiying 3 Phase voltage is Phase to Phase. In the UK "low" voltage AC 3 Phase supply is 415V. There is no 240V 3 Phase supply as standard but one can be obtained with a one to one ratio 3 phase transformer with the Primary wired Star and Secondary wired Delta.. The 240V single Phase supply is Phase to Neutral of the 415V.

Robert G8RPI.

19/01/2022 20:28:52

I think Clive nailed it with a comment at the end of one of his earlier posts.

The other 3 wires are on the underside of the paxolin terminal plate. The tell-tail is the "unused" 4th terminal post. If in STAR thi will be the star point. You should be able to tell without taking the plate out by doing a resistance check. With the mains disconnected, check the resistance between the spare terminal and each of the three used ones. If the is a connection (probably only a few ohms) between the spare terminal and the other three the motor is wired as STAR. If there is no connection (>100 ohms) then it's wired DELTA.

Robert G8RPI.

Edited By Robert Atkinson 2 on 19/01/2022 20:29:40

Thread: For newcomers
16/01/2022 18:07:45

Why the diatribe? However since you bought it up so don't complain to me.

Re your VFD installation.:

The Omron Mini VS J7 VFD shown connected to your Myford lathe DOES NOT have adequate EMC filtering built in.
The manual is aavailable here https://www.manualslib.com/manual/1550591/Omron-Vs-Mini-J7.html?page=43#manual

The specifications say the drive is EMC compliant to EN50081-2 Thi is an INDUSTRAL specification not domestic / light industrial (EN50081-1) which has lower limit and is applicable to your installation.
Even to meet EN50081-2 section 2-2-6 of the mnual "Conforming to EC Directive" requires a line filter on the input, "clamp core" (ferrite sleeve) and screened cable on the motor. Your installation does not have an input filter, or clamp core. I can't tell if the motor cable is screened or not.

Then there is the physical location, again the manual says:

Do not store, install, or operate the product in the following places. Doing so
may result in electrical shock, fire or damage to the product.
• Locations subject to direct sunlight.
• Locations subject to temperatures or humidity outside the range specified
in the specifications.
• Locations subject to condensation as the result of severe changes in
temperature.
• Locations subject to corrosive or flammable gases.
• Locations subject to exposure to combustibles.
• Locations subject to dust (especially iron dust) or salts.
• Locations subject to exposure to water, oil, or chemicals

Install the Inverter in a clean location free from oil mist and dust. Alternatively,
install it in a totally enclosed panel that is completely protected from floating
dust.
When installing or operating the Inverter, always take special care so that
metal powder, oil, water, or other foreign matter does not get into the Inverter.

Again you do not meet these requirements.
Additionally here should be 100 mm clear space above the drive for ventillation. Scaling from t 130mm drive height it is too close to th shelf.

As an electrician you shoud know that a flexible mains lead must have adequate strain relief. The VFD has none and you have not added any.

You mention electrical knowlege, I have that, but more importanty, I have EMC (interference) knowlege. Having got similar drives past light industrial EMC standard testing. They typically need extensive additional filtering on both input, output and control lines. Plus a metallic screened enclosure and screened cables.

Robert G8RPI.

Thread: Inverter for 3 phase supply
16/01/2022 14:47:59

Ideally you would add the 3 PH to 3 PH VFD between the existing control gear but connect the stop /start and reverse control signals to the VFD control instead of the control contactors. You only need one power contactor connected to the main ON/OFF switch and emergency stop. Any reversing contactor(s) can be bypassed (ideal) or left in the power circuit with coil disconnected (not ideal, operating the contactors "cleans" the contacts. Leaving them in one position permanently can lead it failure in the long tern) The emergency stop signal should be connected to the VFD as well s the power contactor. This reduces the stopping time.
This arrangement will allow you to preset the required speed and make full use of the drives speed ramps and torque control. You can put a remote speed control potentiometer in the existing control panel.

Make sure to follow the drive manufacturer's instructions for enclosing the drive and EMC filters. Just screwing it to the wall, connecting it directly before the motor and using the buttons on the front of the drive is not good practice or safe.

Robert G8RPI.

Thread: C3 Minilathe Electrical Fault - Fixed
16/01/2022 12:50:39

There are a few possible causes of type of failure.
1\ It was over tightened and cracks propagated over time
2\ Plastic shrank due to loss of plasiciser or moisture.
3\ Contmination (oil coolant etc) affected the plastic.
It could even be a combination of these.
I have frequently found this style of holder where the nut could not be removed without the holder breaking. So my money is on 2\

Robert G8RPI.

Edited By Robert Atkinson 2 on 16/01/2022 12:51:35

Thread: How can I bond ABS (plastic) to NRL (rubber)?
15/01/2022 18:58:03

3M VHB stays flexable long term. It' used for things like sticking th aluminium sides of commercial vehicles on.

Thread: 3 phase supply (again)
15/01/2022 15:29:52

The drive self protection only works for the conditions the drive is designed for. For most VFDs this does not include connecting or disconnecting the load with the VFD output energised.
It might work but that does not mean it's right.

Thread: How can I bond ABS (plastic) to NRL (rubber)?
15/01/2022 15:15:15

Spray / mist is best. A tiny amount, literaly a drop in a liter of washing up liquid can help with wetting. Final bond is just as good as dry but takes longer. pressing on join forces the water out.
It's similar to how car "wraps" are applied

Edited By Robert Atkinson 2 on 15/01/2022 15:16:31

14/01/2022 21:24:18

+ 1 for 3M VHB tape suggested by John. If you need fiddle time wet one of the surfaces with water.

Second choice would be a toughened acrylic adhesive such as Loctite Multibond 330. Permabond also make these. They are a clear glue (like UHU) but it needs an activator brushed on one surface. In this case ativator goes on the ABS

Robert G8RPI.

Thread: 3 phase supply (again)
14/01/2022 21:15:05

Mark,

Only if the switch gear has overload cutouts and they operate correctly with the waveforms from the VFD neither of which is a given.
The machine switchgear does not protect the drive.
The REO filters you linked to are quite nice but they are not low cost. Did you buy a new one for a hobby installation?
Additionally the VFD may not like having a resonant filter on it's output loaded or otherwise. The smaller REO filters likely to be used in a home workshop are resonant at about 2.5 kHz so the PWM frequency needs to be a fair bit higher than this e.g. >4 kHz. Newer drives are probably OK but be sure to check that your drive is suitable for use with a filter.
I'm not that out of date. Part of my day job today involved similar issues with a multi kilowatt 3 phase converter.....

Robert .

Edited By Robert Atkinson 2 on 14/01/2022 21:17:09

14/01/2022 16:54:13
Posted by Andrew Johnston on 14/01/2022 10:34:06:

A funny thing happened just now, I've had to sit down to recover. I agreed with the whole of a post by SoD. smile

There is only a current surge when starting an induction motor direct offline because full voltage is applied with the motor not turning. A VFD should control the applied voltage to keep the current within the set parameters. There should be no need to select a VFD of four times the rating. A little over the motor rating may be helpful if using a speed/over-current tradeoff to overcome short terms overloads when running.

My understanding of digital phase converters is the same as SoD. They create two phases from the incoming supply and create a third phase using a half bridge and PWM drive, which is then filtered to provide a sinewave output.

I've got a couple of VFDs on my CNC mill, but for the rest of the workshop I solved the problem once and for all by installing a 3-phase supply. This is particularly useful as some of my machines have two speed motors, and star-delta switching in one case.

Andrew

It's unusual but I have to disagree with you a bit Andrew,
VFDs are intended to be permanently connected to a motor and control start-up currents when they are commanded to start the motor. Even if set to maximum speed at turn-on there is some ramp up. Some also increase the current limit during ramp up at maximum rate. If you turn the VFD on and then switch a load onto it the only protection is the over-current. This is a fault condition and exceeding it will trip the drive off-line. Thus it has to be set high and may also be part of the 4x oversize recommendation. Of course setting the current limit high means the motor is no longer protected against over-load.

Starting a smaller motor first has also been mentioned on this thread and even running an un-loaded motor permanently connected is suggested by some sources. Not very efficient.
I'm not making this up I've had a serious look at and experimented with using VFDs as 3 phase converters. Just the amount of filtering required to tame the emissions when running off load was a show stopper.

Robert G8RPI.

13/01/2022 22:08:39
Posted by Clive Foster on 13/01/2022 12:28:31:

Neil

Apart from Phase Perfect and similar devices which are built as industrial 3 phase utility replacement devices with corresponding costs, all these boxes are based on VFD internals so stepping up to 60 hz should be no problem. Certainly the (expensive) ones from Drives Direct will do the deed.

Have to accept that 220 to 380 /420 volt boxes inevitably loose voltage and overload current headroom when compared to normal same input and output voltage devices. But the 50 to 60 hz change will have no noticeable effect.

Clive

Edited By Clive Foster on 13/01/2022 13:12:27

Hi Clive,

I don't need to ring them. The simple fact that they do not publish a datasheet, never mind an instruction manual on their website means I would not even bother.
Almost certainly the units pictured do not comply with UKCA electrical safety and EMC (interference) regulations. If they have modified them then they will have to re-qualify them.
I'm not too sure about drives direct either.

Robert G8RPI.

13/01/2022 21:44:10

Clive,
You are missing some things. While using a VFD as a phase converter may work, it is far fom ideal. Apart from the start-up load issues switching loads on a VFD can generate significant voltage transients. These can damage the drive just over-sizing the drive is not good enough to prevent this. VFD's are also not intended to have long leads as would be required if wiring to several machines. This can daamage the drive and will also radiate excessive interference. Almost all VFDs have limitations on powered connection and disconnection of loads and on the length of leads on the VFD output.. These should be observed. Use one VFD per mchine.

Colin,

VFDs are popular because they allow control of the speed, torque, ramp speed (accel and decel) etc but cost litttle more than a phase converter
VFDs do however require one drive per machine.
Rotary phase converters are completely out of date and very inefficent. Not a minor consideration with the rising cost of electricity.

Robert G8RPI.

Thread: Packing
11/01/2022 12:54:57

I would not use chipboard, old or new. It can have a lot of abrasive material in it. Kitchen worktop routers etc use carbide cutters for good reason.

Robert.

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