Member postings for Clive Steer

Although the UK seems to favour water/radiator heating systems, a ducted hot air heating system could provide efficient ventilation and heating if coupled to an air sourced heat pump. It is far easier for a heat pump to heat air to 25 C than water to the 50 C needed for radiator system. Also by using a system of ducting and shutters the same system could provide cooling in the summer. The heat pump could also act as a dehumidifier to reduce condensation issues in the winter as well as the summer. During the colder periods of the winter a supplementary heat source may be needed and if this was by using a gas "boiler" then the heat pump could be used to provide even higher efficiencies than current "condensing" boilers. Unfortunately this would be a complex system and not easily retro-fitted to many properties but new builds might benefit if developers didn't add the normal 3x markup.

Ducted hot air systems are common in the States probably because their houses have large basements able to house the necessary kit. Where hot air systems were installed in the UK these have often been blocked off and conventional radiator systems installed because the systems used expensive electric heat source for cheapness.

CS

I have upgraded several watchmakers lathe drives using a 135W 24V BLDC Nanotec motor supplied by Farnell and a ZS-X11D1 BLDC motor controller through an eBay supplier together with a 150W 24V mains power supply from either Farnell or eBay. This is not a plug and play system so several other components are needed together with some form of enclosure arrangement. In my case the lathes were mounted on cast iron bases which could house the various bits.

There may be cheaper suppliers of a motor similar to the Nanotec one but wanted to be certain what I was buying.

The Sewing machine motor kit is good on price and comes plug and play but is just a bit too powerful for a small lightweight lathe but would be good on a Pultra or Schaublin type machine.

CS

Plumbers may think they are electricians by virtue of being members of the EETPU rather than by training. Some plumbers who are trained to work on gas boilers have to have some knowledge of electrics but I'm not sure to what level. Maybe only to the level that the know not to touch it.

CS

Mark

I had a Mk3 BCA to which I had intended to fit the BLDC motor. However a watchmaker friend lusted after it so I sold it to him and fitted the motor to my 1770 Pultra which works exceptionally well.

CS

Mark

If the belt support has been damaged maybe a simpler drive system could be implemented using a lightweight brushless DC sewing machine motor. Since the BCA is a precision jig borer a 500W BLDC sewing machine motor has more than enough torque/power. Also being a fraction of the weight and size of the BCA induction motor it could be mounted on the head assembly and directly drive the spindle. Since the sewing machine motor comes with an electronic servo speed controller you may only need a single motor to spindle pulley ratio as the BLDC motors can produce very high torque even at low speeds.

CS

Peter

Your impression is correct but the practical implementation of an accurate pendulum based oscillator is not trivial.

A major difficulty is that the bob weight on most simple pendulums has a circular trajectory which introduces a timing error( circular error) if the swing amplitude changes and the error is a square law function of amplitude change. So the timing is far more sensitive to amplitude variations than it is to say variations in pendulum length.

There have been numerous attempts at solving the "amplitude" issue with different types of escapements, methods of powering or reducing energy loss issues etc. However many of these solutions interact and when personal opinion is added to the mix there is a degree of divergence as to the "best" solution.

Things can be "simplified" by negating circular error in the first place and one solution designed by Fedchenko largely achieved this and produced one of the most accurate pendulum clocks.

Unfortunately by that time quartz and atomic clocks could out perform his clock.

Such is life.

CS

Ian P

I can recommend Nick Gauntlett who is in East Sussex and is an accredited watch repairer on the BHI site where his contact details can be found.

Most 1960's quality watch types are easy to service. However, from the 70's onwards, even quality Swiss watches, started to use plastic parts, especially in the date change area, which deteriorate with age and spares are difficult to come by. This was mainly to reduce cost as the competition from quartz watch makers took effect.

Counter intuitively, spares for early watches can be easier to get hold of than for more modern Swiss watches where supply of parts are restricted to approved repair centres. I believe to become an approved Rolex repair centre you have to go on a month long Rolex training course and buy something like £80k's worth of tooling from them.

CS

Ian

If you check out the British Horological Institute website there should be a list of clock and watch repairers. You can chose one close to where you are.

CS

As Andrew says induction motors certainly can regenerate and most VFD's provide an active braking capability which may need a load resistor if high level of regen energy has to be absorbed. Care must be used though as too harsh braking can lead to chucks unscrewing on Boxford, Myford and similar lathes.

CS

I think some electric car manufactures are looking at induction motor technology because production of modern rare earth magnets is mainly entered in China leaving Western industries vulnerable to trade restrictions.

Motors can be poly phase and servo motors for machines are often have 5 "phases".

CS

Ian P

Not necessarily. If an electric scooter/bycycle gets crashed or goes wrong it often ends up being thrown away rather than being fixed. Old Lithium batteries lose their capacity so may get dumped but are still viable. You just need more to wire up in parallel.

You could use a VFD and a ex Nissan Leaf 300V battery but that would be scary.

A 2kW motor and controller at £107 is equivalent to a tankful of fuel for the car you could use collecting salvaged stuff.

CS

I think Bazyle's point is very valid as there are some excellent 3kW brushless DC motors available together with their speed controllers from vendors such as Vevor. These are intended for electric scooters but I'm sure they can be repurposed to drive a machine. They are designed to work from a battery, which at 72V, is relatively safe to "play" with. Lithium battery packs can be obtained in various capacities depending on how long you need to machine for and extra ones can be added if needed. Lithium batteries also have very low self discharge so won't need "topping up" except possibly once every 6 months or more which favours occasional use. I've used a couple of DeWalt Lithium battery packs from my BLDC motor hand tools to power a watchmakers lathe to make it truly portable and independent of mains.

As Bazyle mentioned a big machine doesn't necessarily need a big motor if one doesn't need to remove metal at maximum rate. However a BLDC motor can produce huge amounts of torque, even if only for short periods, which can improve some machining processes.

What's not to like about BLDC motors but I'm sure someone will feel the need to enlighten me.

CS

Clive

If the battery voltage is IRO 3.6V you might consider changing to a single Lithium cell which for the same storage capacity can be much smaller than equivalent NiCad/NiMH cells. A very cheap lithium cell charge control circuit can be purchased from eBay and this allows you to use a standard mobile phone charger. I don't know what mechanical changes may be needed but if push comes to shove the charge controller circuit board can be fitted in a small external adaptor.

CS

Mark

I'd be interested to know what model of Danfoss and Tech VFD's you used so I can get some idea of the capability they have.

CS

Mark

Can you tell us what your experience has been?

CS

Many VFD and especially the cheap ones have a simple bridge rectifier and reservoir capacitor front end to derive the DC link voltage of approx 330V which is used by switched transistors to produce the 3 phase output. On a single phase supply current is drawn from the supply over a fairly short period at the peaks of the sine wave. When loaded the link voltage droops and there is high ripple current in the reservoir capacitors which can limit the maximum power available. This can be acceptable for a VFD starting a motor softly but the high very high load presented by a DOL motor start droops the DC link to the point where the VFD detects an under voltage condition. Typically a DOL motor start draws between 5 and 10 time the max load current but only for a short time as the motor accelerates from being stationary. If for any reason such as additional machine inertia, viscous drag from cold lubricant or mechanical load then the high load can last for several seconds. So for DOL use an VFD would need to be rated at 10x the motor max power rating. Even if the VFD has an active front end to reduce the amount of DC link droop the need to rate it for the DOL surge load would make it prohibitively expensive.

So the bottom line is that DOL starting is a challenging load for any supply and especially an active device such as a VFD or inverter

A passive static converter using and auto transformer and capacitors has better overload resilience and one with an idler motor even better at managing the DOL surge load but are less popular because of their size and noise.

There's no easy answer but the simplicity of DOL starting on a single phase supply leads to complexity elsewhere.

CS

Jelly

As you say a replacement 11kw motor will be difficult to come by. However I'm puzzled as to how you achieved the boost from 240V to 440V. Did you use a transformer or by using the motor windings?

Although this may not be a conventional configuration you could use a single VFD to provide a 3 phase supply bus to all the machines and convert each machine so that the DOL contactor and motor protection circuit is separately powered as the contactor circuit is usually powered at 240/110V from a transformer connect between two phases. Then each machine can be "engaged" before the VFD is run up on a soft start. You may need a small idler motor on the bus to absorb transients should you operate a machines EMO or inadvertently disengage its contactor. Usually a VFD needs to be mounted fairly close to the motor to reduce radiated interference but the idler motor would clean up the "supply". If the idler motor is a 6 or 8 pole machine then the noise it generates will much less than if you use a 4 or 2 pole motor. Although this is starting get more complicated an auxiliary dry loop contact on the machines motor contact could be used to "start" the VFD.

CS

Although I've not done this myself I see no reason for an idler motor to be connected to an inverter to suppress switching and load transients that my "upset" an inverter.

CS

Jelly

It may be better to find the problem with your converter than change your system.

A static converter is essentially a passive device consisting of an auto transformer to boost 240V supply to 440V and a number of capacitors in parallel to "generate" voltage on the 3rd phase wire. A rotary converter is the same but with a permanently connected 3 phase idler motor. The idler motor improves the balance of the 3 phases and stores energy which can cover starting loads of other motors by acting as a generator. Each motor connected to the 3 phase supply will also act , to a certain extent, as an additional idler motor. The most common cause of a failure in a static/rotary converter are the capacitors as these degrade over time although a loose connection cannot be ruled out if failure is coincident with change of physical position. On some static converters, especially the higher rated ones, a phase voltage monitoring relay is used to switch in extra capacitors to maintain phase voltage balance when motor starting loads are applied but rotary converters don't need this feature as the extra starting energy is provided by the idler motor.

What is the nature of the issue with your rotary converter?

CS

I have a Drayton Digistat +3 RF programmer/thermostat which has a very annoying algorithm which runs the boiler for short periods of time as it approaches the set point temperature. The algorithm can only be set for fast or slow responding heating systems as far as I can see in the manual and neither cures the boiler cycling issue which is very wasteful.

CS