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Threadless control box

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Re: Threadless control box

Postby 9fingers » 13 Nov 2016, 12:41

RogerS wrote:Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?


Its a bit of an oversimplification but as you take power from the motor the current moves more in phase with the voltage. The input power rises accordingly as the power has to come from somewhere.

Bob
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Re: Threadless control box

Postby Tusses » 13 Nov 2016, 13:40

Nice post Bob .. :)
reminds me of years ago, when factories would turn the florescent lights on in groups, rather than all at once to keep the leccy bill down .. is that the same thing ?

I didn't know Domestic meters worked like that ..
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Re: Threadless control box

Postby 9fingers » 13 Nov 2016, 16:57

Industrial users are encouraged to balance the current on each of the three phases.
No problem with a proper 3 phase load but lighting is usually single phase to bays of lighting would normally be wired to different phases in the same way as houses down the street are wired to each phase in turn.
When you next have a power cut, sometime you will see 1 house in three along a road with no lights due to 1 phase having failed.

Industrial users are also encouraged to correct their power factor to near unity by having leccy meters that measure the product of voltage and current - so called VA meters. Domestic meter measure Watts which it he useful power your extract from the mains.
The leccy generators have to generate the volts and the peak amps so they generate VA and householder pay for Watts. The cost of so called Wattless power - the difference - is lost to them which is why they want the industrial users to correct their PF to near 1.

I have done some measurements on my belt sander. About the only machine I can load up to maximum with one hand and take meter photos with the other - safely (ish!)

OK firstly off load readings

Voltage
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Current
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VA the power they have to generate and your wiring/switches etc must withstand
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Power that you are paying for
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Power factor
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Applying a near maximum load to the sander with a block of wood

We get no change in the voltage

but the current is
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The VA is
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The power you pay for
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and the power factor
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Hope this gives some idea of what to expect

The idle running cost is less than a third of the full load running cost. I'd expect nearer 4:1

Now this a bit of a bodge experiment as my belt sander is a 3 phase and I only have a single phase power meter so the sander was jury rigged to a static phase converter (not 100% efficient!) so I could measure single phase power parameters to show you.

Hope this helps a bit more

Bob

PS I've left this on the end of the original thread as fixing the control box comments had possibly been made now and it gives some context with the machine.
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Re: Threadless control box

Postby Tusses » 13 Nov 2016, 17:35

I have one of those plug in dooferies ..

I mainly use it to keep an eye on voltage drop when I have a few machines running ...
I inherited the wiring to the workshop, which is about 50m of arrnoured cable from the house fuse box.

I was never interested in more than the basic "electrics" . Just enough t get by. I prefer(d) analogue amplifiers and logic circuits .. yes I know they are completely different ! .. but I love audio .. and like programming and logic stuff.

I never get time to play any more though :(
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Re: Threadless control box

Postby Jimmy Mack » 13 Nov 2016, 19:36

Bob,

:text-bravo:

That's a great demonstration! Very kind of you to spend the time putting it together. I've learnt a lot today...I hadn't considered that the motor (when running) acts as a generator, makes total sense.

I'm going to have another read in the morning with my coffee and a repaired daddy-day-care head to digest the power factor (pf) element of the discussion.

Thanks again,

Jim
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Re: Threadless control box

Postby Jimmy Mack » 13 Nov 2016, 19:43

Andyp wrote:If all else fails could you glue a piece of wood behind the holes in the box and then use screws to hold the front on?


Andy - I like this idea, though the screw would be very close to the end of any piece of wood (split potential) as the holes are right in the corner (unless I've misinterpreted). You've got me thinking sideways though...I'm wondering it I could pop a 'red' rawl plug in the holes and wood screw in - not ideal, but a work around while I get up and running :D

Many thanks,

Jim
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Re: Threadless control box

Postby RogerS » 13 Nov 2016, 19:45

9fingers wrote:
RogerS wrote:Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?


Its a bit of an oversimplification but as you take power from the motor the current moves more in phase with the voltage. The input power rises accordingly as the power has to come from somewhere.

Bob


Any links to something a bit more in-depth ?
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Re: Threadless control box

Postby 9fingers » 13 Nov 2016, 20:49

RogerS wrote:
9fingers wrote:
RogerS wrote:Interesting explanation, thanks, Bob. Why does the power factor alter as load is applied ?


Its a bit of an oversimplification but as you take power from the motor the current moves more in phase with the voltage. The input power rises accordingly as the power has to come from somewhere.

Bob


Any links to something a bit more in-depth ?


Not really to be honest. Things that I've found get very theoretical and after a while you lose the wood for the trees. Discussions of power factor seem to end up in power factor correction.
Maybe your google foo is better than mine.

Bob

EDIT: try https://en.wikipedia.org/wiki/Induction_motor
and http://www.engineeringtoolbox.com/power ... d_654.html
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Re: Threadless control box

Postby Jimmy Mack » 23 Nov 2016, 13:29

Swapped the box round to the correct side, and closed the end (with damaged threads) with the humble zip tie.

Image

Image

I suspect it was swapped to the inside as it was getting knocked, which is why the box is damaged. ...but it's hard to get to on the inside. The contactor is working, but the lock on the stop button is broken. Any tips for online shops for this kind of component?

Jim

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Re: Threadless control box

Postby 9fingers » 23 Nov 2016, 14:32

They are all over ebay like a rash as well as Amazon. Virtually all fit a standard 22mm diameter hole and will be fitted with either a NC contact of a changeover.

hth

Bob
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Re: Threadless control box

Postby Andyp » 23 Nov 2016, 15:39

Love the cable tie solution. Those and duct tape can hold most things together. :D
cheers

Andy
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