Member postings for Robert Atkinson 2

I was only quoting what the supplier says their equipment is capable of. Don't blame the messenger.

A lot of people including suppliers suggest de-rating the low-cost drives even when used as a normal VFD. I assume this is to improve reliability. The quality branded drives will of course run at their full rating 24/7 365 days a year with no issues.......

Robert.

One problem with simple* "passive" converters is they do not provide 120 degrees of phase shift. This means you loose the low torque ripple advantage of 3 phase motors. This can affect surface finish and generate noise.

Robert.

* You can generate proper 3 phase passivly using capacitors to generate phase quadrature and then a a Scott-T trhansformer to get 3 pahases but as far as I know the low cost units don't do that..

That is not what DD say. Quote :

"All this range of DIGITAL Plug and Play Converter allow you to take a 150% overload for 30 seconds so the 6HP starting requirement of the 2HP mill can be accommodated by this 7½ HP converter"

So they say to use a 71/2 HP inverter for a 2 HP motor i.e. > 3 times de-rating.

https://www.ebay.co.uk/itm/154157588494

Robert

The Drives Driect unit linked to by Mark Rand does not provide a neutral as standard. It requires an optional "neutral generator". Presumably a star transformer of some type and not just a resistor network. It also requires additional filters for some machines. Perhaps the unit you have included these. Unsurprisingly DD do not publish enough information to determine exactly what modifications they have done. Possibly none other than underrating it and setting for no or a very fast turn on frequency / voltage ramp. They certainly know how to charge for them though.
They now seem to sell only throgh ebay (odd for a "direct " company...) and currently don't list the required neutral generator or filters on ebay.

The 3-4 times underrating means that the 71/2 HP £3800 converter is not big enough for the OP task of a 4 HP load. He would need a 12 to 16 HP which may not be available. The 71/2 HP is stated as needing a 40A input supply so the larger one will presumably need a 80A feed, well above the OP's supply capacity.

Robert.

Drain cocks open and heat up cylinders with hot air gun? A small squirt of WD 40 and then add o
Lidll sometimes sell a variable temperature hot air gun. Commom use is paint stripping.

Robert.

It is on their website but not obvious:

https://maccmodels.co.uk/product-category/tools-drills-taps-oils-etc/oils/

Morris also sell steam oil but 5l minimum.

https://www.morrislubricants.co.uk/products/classsteam/cylinder-oils.html

Robert.

Well you can't run a 20HP drive off 45A supply for starters.

The big issue with using a VFD is that they are designed to be permanently and directly connected to a MOTOR. They are not designed to drive control gear lights etc. The control gear almost certainly needs neutral connection which a VFD does not have. A single good quality 5kW VFD could run all your motors individually but you would have to interface the controls of each machine to the VFD. IF all the machines have just a single Start / Stop E-Stop control (and maybe reverse) than perhaps you could wire a single pendant to the VFD and then move it to the machine in use when you plug that machine's MOTOR into the VFD output.

To make it more fool-proof you could have a contactor at each machine that when energised connects that machine's MOTOR to the VFD. On each machine you have a socket for the control pendant to plug into. The paendant is interlocked with the contactors so only the machine that has the pendant plugged in is connected to the VFD.
A more complex variation would be to rewire the controls on each machine to a a set of relays that only connected them to the VFD when that machine was selected. That is a lot of work though.

There are some possible issues with VFD output cable lengths, EMC etc but it is workable. An output reactor may be required.

I'm surprised that you have ten 3 phase machines without a 3 phase supply. If only I had the room.....

Robert.

Edited By Robert Atkinson 2 on 02/10/2023 17:43:20

A loop alarm is a deterrent at all times and an aid when stand is attended. You can't watch everything all the time.

Electrically a loop pases current all the time and alarms if the current stops. Simplest implementation is a a relay. Loop is in series with the coil and power source. Buzzer / sounder is in series with nomally closed contact. Disadvantage of this is the relay coil uses a fair bit of current and is powered all the time so limits life on batteries.
At least one professional system I've seen used 3.5mm "headphone" jack plugs and in-line sockets with screened cable. The center conductor is the loop and the screen is connected to 0V. This can use cheap off the shelf audio extension leads. A low current (limited by a resistor) passes through the center conductor and keeps a two transistor circuit driving the sounder off. If the circuit is broken current stops and alarm sounds. The use of screened cable makes it very hard to bypass a section by pins or clips. If you push a pin through the cable it will short the center conductor to 0V diverting the current and causing the alarm to sound.
If you want I can do a sketch....

Robert.

I agree with John. Normally with eddy current indicators the magnetic field strength is adjusted to change the calibration. Changing a return spring (normally a hairspring) will give coarse range change. The field can be adjusted by movable poles or how far the poles cover the disc or cup but often the actual magnet strength is changed.
On some aircraft instruments I've calibrated this often meant taking the magnet out, putting it in a magetiser / demagnetiser taking an educated guess at the energy setting required, zapping it, putting it back and re-checking the calibration. It you were doing a series of similar instruments you would get quite good at setting th level. If it was a one-off you might have many iterations.... If i awas a electric remote tachometer you had to do it twice. Once to set the output voltage from the generator and then the eddy current to calibrate the indicator.

You could always fit one of the modern electronic programmable speedos:
https://www.competitionsupplies.com/smiths-programmable-speedometers

Not cheap though...

Robert.

Normally if there are specific requirements outside those controlled by the standard specification of a part the specification number would not be called up in the drawing or parts list. Typically either the equipment OEM would specify their own part number or they would call up a specfic part manufacturers stock or part number. This part manufacturers number might be a special for the aplication. Using their own part numer has the added benefit of controlling the market. Sometimes a standard part will be purchased and then one or more of inspection (often for specific characteristic(s). test, modification, treament carried out before using their own number for the part.
For aviation at least this means you should always refer to the approved documentation. Just because it says ACME 1234 on the part doesn't mean you can just buy an ACME 1234 and fit it. The OEM may have bought thousands of ACME 1234s and then selected the "best" ones for their application.

Robert.

Not sure the Mini has an excentric bush. Due to the geometry of a worm and helix they can accomodate a tooth or two ratio range by adhusting the diameter and tooth shape. It changes the amount of engagement but as there is little power transmission in a spedo drive that is acceptable.

Don't know about the French test but in the UK the MOT only reqiures the speedometer to work. Assuming it is a regular annual test not a one of for approval after modification etc like the SVA in YK. There is no accuracy test. The construction rules say the speedometer must be accurate to -0 +10% when new. It also has to be "independant" so you can't use GPS.

IF accuracy is a requirement but it is over-reading can you just put a label on the speedos saying it over-reads by 20kph?

If you are of an electronics bent you could add a digital speedometer. There are plenty of RPM meter (same thing different calibration) designs and even modules out there. If the back of the speedo is plastic you can often pickup a signal from the rotating magnet inside using a coil attached to the outside.

Robert.

That is not a good description. It misses out the important fact that the heat extracted from condensing the water vapour (latent heat of evaporation 2250kJ/kg) is used to heat the air circulated back into the drum.
It only uses about 20% of the energy of a conventional dryer. They release virtually no moisture to the house and little heat. According to SWBO it is also much more gentle on the clothes as the temperature is lower.

Robert.

Edited By Robert Atkinson 2 on 28/09/2023 19:56:37

Even better than a condensing tumble dryer is one with a heatpump. Uses latent heat of evaporation to dry the clothes. No heater involved.

Robert.

Sorry mis-read 2500 as 3500. 2kW 24/7 is still a lot of heat.

Robert.

I'm going to be pedantic...

You cannot be "off-grid" if you are exporting power back to the supplier
What is a Kelvin Watt (KW)
Do you mean killowatt kW?
KW is power not energy. Do you mean kWh?
Was the previous consumption, 3500 (assumed kWh) really ALL heating? Did you have a seperate meter on your heater? 3500 kWh in a month is 3 kW 24/7 that's a lot of heating....
It's a bit worrying that the heat pump reporting software also uses Kelvin Watt hours.....

Robert

I was mainly refering to the output side of the pump. Even so the SAHPs are still air-water heatpumps. The key is in the "assisted" in the name. They have a benefit from a degree of solar capture when the sun is shining. How much this affects the air operation is not clear.

Robert

There is more than one type of heat pump. I assume you are referring to the air to water type currently being promoted by the government. These have a issue that they don't produce very hot water so the whole system needs updating and probably larger pipes and radiators.
I've had heat pumps in my last two properties for over twenty years. These were / are air to air type units that provide heat in the winter and cooling in the summer. Heating is cheap and you don't have to use the cooling. The only downside is you need another means to supply hot water. I use an instant flow gas heater and an electric shower. You can also get electric instant flow heaters. The advantage of these is you are not loosing heat from stored hot water. YMMV but they are worth a look.

Robert.

I'm firmly in the fully threaded = screw, plain shank = bolt. For load bearing applications screws should only be in tension. Bolts can be in shear, tension or both.

There are always exceptions e.g. cap head screws but even the plain shank versions of those are normally used in tension.

You can replace a screw with a bolt but should never replace a bolt with a screw.

Robert

N-E connections up-stream of the RCD or consumer unit are immaterial to RCD operation and leakage currents.

The whole point of measuring L-N differential current rather than earth conductor current is to capture all leakage.
400mA of leakage is a bit excessive. I'd want to investigate what is going on. what is the current in the protective conductor?
One thing is if you have metalwork with a low resistance to ground connected to the mains ground your system may be passing some mains return (neutral) current from your neighbors. If theter is a neutral fault in the street you could be badly affected.

Radio amateurs on TNC-S can suffer from this when their RF earth, often extensive and low resistance, is connected to mains earth via their radios. With a neutrla fault 100's of amps can flow.
The latest guidnace on NOT connecting pipework etc to TNC-S systems seems to be a way of avoiding this inhernet problem with TNC-S The only advantage of TNC-S is lower cost to the network providers.

Robert.