Member postings for Stuart Smith 5

I don’t think it is simple. I found this via Hackaday on the internet, where someone has reverse engineered the pi outs and data protocol: **LINK**

If you are into electronics it would be an interesting project to make, but no doubt it is cheaper and easier to buy a complete lcd with sensor and fit this.

Stuart

Martin

Sorry, but that is not correct.

Single phase as you say one of the three phases plus neutral, but a three phase supply is 415v between phases. Actually both could be higher or lower depending on where you are on the network and loads locally and in general.

Stuart

Dave

It’s single phase.

This design of transformer has 1 HV winding and 2 LV windings as you thought. It is a type that can be connected as single or split phase by changing the links you can see. As this one is connected, the 2 windings are connected in parallel. The 2 terminals on the left are the live phase connections in this case, and the 2 right hand terminals are the neutral. If the 2 links were removed and only one of them connected across the top 2 terminals, this would be the neutral and the bottom 2 would then be the 2 live split phases. It is difficult to see the earthing, but the LV neutral will normally be earthed separately from the HV earth which is just used for the transformer tank and other metalwork.

The HV voltage could be either 11kV or 6.6kV, the design and construction are the same.

Single phase or split phase transformers are connected across 2 of the HV phases.

Three phase transformers have a delta HV and star LV with the star point the neutral which is earthed at the substation.

Stuart

Where can you buy one for £130? The only ones I have seen are at least £280, mostly £300+.

Stuart

Andy

I have sent you a PM. See your inbox at the top of the screen when logged in.

Stuart

Robert

Although the fuse carriers on your main DNO fuses may be labelled as 100A , you would be advised to check what current you can actually take from the network. I used to work at Electricity North West and the maximum supply capacity there was specified as 20kVA for a single phase supply ( ie 80A). The other issue may be that the rating of the pole mounted transformer may be a limiting factor. Also there are limits on voltage fluctuations caused by motor starting currents or welders (see ENA ER P28).

Stuart

It sounds like the plastic gear in the headstock has lost a few teeth on the low range gear.

It happened to my cj18a mini lathe but just 2 teeth broken. It ran ok in high range but was knocking in low range.

You can get steel gears as replacements which is what I did, but some people regard the plastic gears as a useful weak point .

Stuart

Andy

My lathe is a cj18a mini lathe from amadeal - I think the same as yours.

Here is another photo of the way I mounted the caliper for the crosslide. It stops access to the carriage lock, but other than that I haven’t found it a problem. The caliper for the top slide is ok apart from when you want to set it at an angle - I have to unscrew it then.

I found a couple of issues with the cheap calipers which I managed to fix in the software/ interface. Because I am powering the calipers from the interface PSU, when I switch it on it always starts in inches mode and after a while, the output from the calipers stops (they go to sleep). I have used extra outputs from the Arduino to automatically change to mm mode and to detect if the output stops and switch it back on.

The touch DRO app has the facility to add 2 readings so I have mine add the top slide and carriage caliper outputs and display as one.

If you decide to have a go with these calipers, let me know and I can send you the code and interface details.

Stuart

Edited By Stuart Smith 5 on 16/05/2020 21:34:49

Ian

The voltages are 180 degrees apart because the opposite ends of the LV windings are connected to neutral ( and earthed at the transformer). So when the ac voltage in one winding is at its maximum positive value, the one in the other winding is at its maximum negative value (relative to the common neutral connection).

Andrew

Single phase distribution transformers are connected across 2 of the HV (usually 11kV or 6.6kV) phase conductors.

Duncan

My previous post explains how a split phase transformer is connected. It is not the same as 2 of the phases in a 3 phase system which are 120 degrees apart. This is not unique to the Shetlands and could be found anywhere where there is only a single phase (ie 2 wire) HV line. It is not that common, the standard supplies provided now are either single phase or 3 phase.

Robert

Even though the EU harmonised nominal voltage is now 230v, distribution transformers in the U.K. are still specified as 250 volts output for single phase transformers and 433/250 v for 3 phase transformers.

Stuart

Edited By Stuart Smith 5 on 16/05/2020 20:51:42

Edited By Stuart Smith 5 on 16/05/2020 20:52:20

Quotes from the OP:-

‘The 2 phases are coming in from a "split phase" transformer, taking the two phases from overhead, putting a meter across the two reads 445v, and each phase to neutral is 239. that is what i have, so any suggestions would be greatly appreciated.’ and ‘Just to say, the DNO people said when they were installing the power cable that it was a 2 phase supply, split 180 degrees apart on a center tapped transformer. hope thats of some help?’

Andrew

This is what I would expect with a split phase supply. Depending on the network voltage drops and loads, you could get anything from about 220v to 250v on each and 440v to 500v between the two. The discrepancy in each phase to neutral and between the two could be because the load and therefore voltage drops changed between readings or one of the phases has a higher load than the other because of other properties connected to the same transformer.

Stuart

Edited By Stuart Smith 5 on 16/05/2020 16:31:24

No, it wasn’t a typo. The split phase arrangement is used in some rural areas in the U.K. where there is only a single phase (2 wire) HV 11kV or 6.6kV overhead network available. It is now considered to be non-standard and only used when there is no alternative. For normal single phase supplies, a standard single phase transformer is used with a phase and either separate neutral and earth conductors or a combined neutral/earth conductor.

With a split phase network, a transformer with a single HV winding and either a centre tapped secondary winding or two separate windings connected as below:-

The neutral is common, but the two phases are 180 degrees apart. So between each phase and neutral you get a nominal 230v (actually up to 253 v depending on transformer tapping and voltage drops etc). Between the two phases you will get double this. In a single property, you could have say storage heaters on one and the rest of the house on the other ( with 2 consumer units).

In this case, running the workshop (with a single phase to 3 phase converter for the lathe) from one supply and rest of the property from the other.

Obviously in all cases needs there to be separation and labelling so that anyone doing work understands that there could be up to 500 volts between items on the 2 supplies.

Stuart

What you will have is as you say, a transformer fed from a single phase (2 wire) HV overhead line.

A common neutral but with 2 single phase 230v ( but could be up to 253v ) live supplies 180 degrees apart. You would expect somewhere in the range 440 to 500 volts between them.

See my other post on fitting a cheap DRO system using the TouchDRO app and digital calipers.

**LINK**

The app allows switching between radius and diameter

I made a cheap DRO for my CJ18a mini lathe using 4 cheap Aldi workzone digital calipers, an interface using an Arduino nano and a cheap Android tablet running the TouchDRO app.

I have intended to post about it for a while and todays post about cross slide dial calibrations on the same lathe has prompted me to actually do it.

I can’t claim any originality in this - I have followed ideas from various others on the internet and based the circuit on the one posted by Les Jones on here.

I think it cost about £80 in total.

I am quite pleased with it as a beginner.

Photos in my Lathe DRO album.

Velleman also make a Range of kits or complete scopes. They do a kit with a black and white lcd screen for £49.

I have a self contained Velleman scope which is handy as it is battery powered but it has quite a small screen with poor contrast, so I only use it for portable uses.

Stuart

Re my previous post

The instructions for programming the Arduino and the software to run on your pc are here **LINK**

This is a screenshot of the sort of display you get

It depends how much you want to spend and what you want to get from it. As has been said, Pico make a range.

I have a PoScope basic usb oscilloscope which is a few years old now. The later version to mine is sold as the PoScope Mega1 bundle with usb scope and leads **LINK** . It is 109 euro from the makers. Robot shop.com advertise it at £91.42 but awaiting stock.

I also have a Rigol DS1054z but at £350 it is probably more than you want to spend.

A cheap option if you just want to analyse digital 0 to 5 volt signals is a diy usb scope using an Arduino. This is a link to a site showing how to use an Arduino uno. **LINK** . I have made one using an Arduino nano which is a bit cheaper than a uno. The last one I bought was only about £5 from hobbycomponents.com inc p&p

Stuart

Chris

I’ve just checked and I can login ok and see my previous orders etc

Stuart

Re Phil Whitley’s comment about removing the cut out fuse.

This is not something that individuals should do. It belongs to the local electrical network operator and should only be removed by someone authorised by them, following appropriate training and knowledge and using the correct PPE.

‘Mr Factotum’ on youtube has been doing a series of videos of his Metre Maid loco build.

The latest one shows him fabricating the saddle from aluminium sheet and ‘Lumi-welding’ it together.

**LINK**