Member postings for Adrian West

Agreed Emgee and one reason why I will not sign up for a smart meter. One never knows how the measurements will change over time and what trickery is going on in the background.

Good old real power kWh as per current situation in the UK is good enough for me !

Adrian

Dave,

I absolutely agree with you and the numbers will be small. But I would be remiss as an Electrical Engineer not to point out the effect of power factor on this type of measurement. Very significant if the rotary converter runs at light load for long periods of time. The measurement could be significantly out depending on the load profile leading you to think it is costing much more to run than you think.

I might actually be concerned to hear that the converter costs me more than 0.6kWh to run on no load which should not be the case. All about getting the correct numbers into peoples minds so they feel comfortable using the kit at all.

Also to point out that some low cost power measurement meters might also have this error.

What could be said in absence of a good power meter measurement is that the cost to run at all states of load should be "significantly less" than that computed by the apparent power method, especially at light loads.

Also good to have a lively discussion which is my first as a newbe to ME forums !

Adrian

Emgee

Yes I saw this and the stator current figures seem reasonable for an induction motor no load to top end load.

Just beware that low cost power meters might just measure line current and not take PF into account.
Careful checking of the specs required !

Adrian

The problem is if the rotary converter is running light at low power factor (which it probably is most of the time) then the current and volts measurement of apparent power will be much higher than the utility meter will measure. So will provide a grossly inflated view of running costs.

You can see this from the 2.6A running light measurements which are getting on for 50% of the on load values.

There's no way you could push 624W into a small rotary converter with no output load. This would all end up as heat and overheat the converter. This does not happen due to the power factor when the real power absorbed (and measured at the utility meter) may be a couple of hundred watts, most of which will end up as heat in the converter motor.

All solved though if a correct power measurement is taken similar to the utility meter.

Adrian

Emgee.

What you don't want to do though is to take an electrical measurement that grossly inflates the cost of running the gear and that must be the point.

It's a tough call Brian if you already own the rotary converter and it powers several machines. It might take many years of running the rotary converter to pay for the VSD's. Unless there are other reasons for doing so eg. "I'd quite like variable speed operation".

Adrian

Guys....Do not forget about the power factor in AC circuits !

Independent measurement of line current and line voltage only gives real power in kW assuming the load is purely resistive eg an electric fire element. In this case the power factor, which is a measure of the phase relationship between voltage and current is close to 1.

For any equipment with coils and windings (inductance) eg motors, solenoids and traditional ballast type fluorescent fittings the power factor is less than 1 and it is more complex to measure the real power that the utility meter will measure.

Assuming that the rotary converter is driven by an induction motor, this may operate at a power factor of say 0.8 at full load. So in this case, using round figures if the line current is measured at 4A with the clamp meter and the voltage is 250V this gives an apparent power of 1kVA.

If the power factor is 0.8 this gives a real power of 1kVA x 0.8 = 0.8kW. A residential utility electricity meter only measures and aggregates to kWh the real kW = 0.8kW whereas you might incorrectly think this is 1kW by just measuring the line current and voltage.

For an extreme case of a purely inductive load the power factor will be close to zero. So even though 4A is flowing in the line, the electricity meter will read close to zero kW. All the current is "wattless" and just heats up the cables and utility distribution transformers without doing anything useful. The very reason why utility companies don't like poor power factor and many industrial companies use capacitive type power factor correction devices to avoid being penalised !

An additional problem is that the power factor for an induction motor gets worse as the mechanical load decreases. So a motor may take 30 to 50% of it's full load current even with no mechanical load connected and the current is mainly used to magnetise the motor. So with no load on the rotary converter you might incorrectly think that significant real power is being consumed just by measuring current and volts.

The only way is to measure the rotary converter power input is with a power meter, making sure that this measures both line current and voltage and can take account of the prevailing power factor.

Beware though that there have been a number of low cost domestic power meters which were only provided with a current probe and no voltage measurement. There was a big hoo ha with over reading of these meters in dwellings using traditional ballast type fluorescent fittings simply due to the low power factor.

I would have thought that the low cost "plug in" type power meters that can be obtained these days ought to include the voltage measurement but there is no guarantee of this though so careful reading of the specification is required to make sure that power factor is accounted for.

Lots of info out there on the interweb about power factor if there is interest eg. https://en.wikipedia.org/wiki/Power_factor

Variable speed drives are better in the fact that the "wattless" current just sloshes around between the drive and the motor and is isolated from the AC input supply by the internal DC link within the drive. However there are other supply issues introduced by VSD's such as harmonics and high frequency emissions but that is another story !

Sorry for my ramblings and hope this helps.

Adrian

Thanks Howard. Always good to be part of and help out within a knowledgeable community.

Adrian

Thanks Brian and no issue with advice and help on the electrics. Been involved with the design and application of VSD's and motors for 37 years so happy to give something back !

Re the mill, I've no real space issues as I've a large double garage to play with. More concerned with weight, lifting and transport together with reasonable money.

There is a VMC 626 turret mill in the classifieds which is of interest although it is right down on the south coast and I'm in Lancashire which could be an issue. This is a nice to have but a simple belt driven Clarke CMD1225 or Sealey SM25 probably would be good enough for current requirements.

Adrian

Hi Dave, I kind of guessed this would be the reason. I've posted an intro anyway which may be of interest.

Adrian

Hello All.

Just to introduce myself as a new member to ME. I am a Chartered Electrical Engineer, specialising in motors, variable speed drives and control systems for industrial and renewable energy projects.

Am now a Freelance Engineering Consultant; see www.opusds.com for more info. I have a small home workshop used mainly for my business, making small test rigs and the like. Have a 1950 Colchester Master lathe in good order, a New Progress drilling machine (bought for £7.50 and restored) together with an elderly power hacksaw which requires some TLC. My Dad was a tool maker so engineering runs in the blood.

Currently looking for a small vertical milling machine for an exciting ongoing R+D project requiring the manufacture of some small alloy parts. Already looking at a couple for sale but would prefer a small turret type, ideally with a quill feed for reasonable money. Otherwise a solid benchtop type with belt drive would do. Location close to Lancashire would be ideal to simplify collection.

That's all folks ! If anyone needs advice about motors of all types, VSD's, three phase to single phase conversions etc. just give me a shout.

Adrian

Thanks Oldiron. All sounds a bit long winded just to view items for sale !

Adrian

I'm in the market for a vertical milling machine. There are a couple of interest on ME classifieds. I'm new to ME and the ads say make some forum posts to obtain more details. Can anyone tell me the best way to find contact details, machine location etc for these ads ?

Thanks. Adrian