Brain Scratcher for the Sparkies Here....

Ox · Aug 13, 2018

Alrighty y'all that like to debate digital this and sine wave that ...

Riddle me this:

What makes the starter on the air compressor decide to close at the same time that some other heavier load happens to kick in too?

A few times and a fella can write it up to coincidence, but over the last 30 years I have seen this happen way too many times to be coincidence. This is an outright phenomenom!

I am sure that the compressor is just about ready to fire, but for some reason when something else pulls a load on the buss, for some reason that puts the starter over the edge.

What gives?

3ph compressor

Buss is on large RPC

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Think Snow Eh!
Ox

DDoug · Aug 13, 2018

First contactor coil sends
a spike down the line, by the inrush (ala pre 92 ford
starters) ?

If so, put a 3-5 second timer on the air compressor between the air controlled
switch, and the contactor.

Or....where is the new puppy piddling as of late ?.....

Ox · Aug 13, 2018

I understand that there is a spike (or - should be a drop) in V on the buss, but the M/S on the compressor is still a mechanical see/saw at this stage yet. Waiting for when the spring pressure overcomes the air pressure. This is why I don't see how the buss V plays a roll in this equazsion....

???

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Think Snow Eh!
Ox

DDoug · Aug 13, 2018

Ox said:
I understand that there is a spike (or - should be a drop) in V on the buss, but the M/S on the compressor is still a mechanical see/saw at this stage yet. Waiting for when the spring pressure overcomes the air pressure. This is why I don't see how the buss V plays a roll in this equazsion....

???

--------------------

Think Snow Eh!
Ox

Yeah me too.

But, recall how the Ford starters (the ones with the wedge shaped
cover) would make a spike (voltage above applied voltage) by the
inductive action of the magnetism, and then the abrupt change
in that core when the flapper slams in. The solenoid on the firewall,
the Auto parts store stock 2 kinds, one with a diode to eliminate
the spikes.

If the other contactor is big, it might do this.

How it jumps over the air portion of the switch I dunno.

thermite · Aug 13, 2018

Ox said:
I understand that there is a spike (or - should be a drop) in V on the buss, but the M/S on the compressor is still a mechanical see/saw at this stage yet. Waiting for when the spring pressure overcomes the air pressure. This is why I don't see how the buss V plays a roll in this equazsion....

???

--------------------

Think Snow Eh!
Ox

It may be a mystery because you are looking at the wrong end of it. Not electrical at all.

How much of a minor tremor in mechanical vibration might that "heavy machine" transmit to trip the mechanical pressure gadget over the edge? Does it cause itself or some OTHER consumer of air to take even the merest sip of air? Does it simply shake the air lines running all over the shop or reflect a sound-wave into them and apply a pneumatic "spike" to the pressure sensor?

We don't really care, do we?

Where it is problematic, the cheap solution is to put a duty-cycle timer in the line as a commutator. Done this for years to stagger heavy starting loads.

Simple example is a lamp timer of the sort sold to make an empty house look occupied. Slide-out tabs choose on and off times.

If the compressor can only find "enable start" power available every odd-numbered minute of the hour, [1] and some other consumer only every even-numbered minute of the hour, their run-time is not affected. But they'll not START in the same 60-second "window" (or whatever else works for you) EVEN IF their "demand" switch is already asking for a start, 2 seconds into the window.

It has to wait its turn. Ordinarily, there's no effect on service delivery.

Not unless you delay it ten minutes or such, anyway.

[1] One --DT relay, as "XOR". Exclusive OR logic. Load A enable, load B enable, never both at once. My kitchen garbage disposals are even wired this way so I don't need larger service and breakers, nor the safety hazard of trying to manage both operating at once.

DDoug · Aug 13, 2018

Can't we put a PLC on the thing ?

thermite · Aug 13, 2018

digger doug said:
Can't we put a PLC on the thing ?

Simple damned timer (who made those? Intermatic was it? Torquematic? been around for a hundred years or so, anyway) runs BOTH loads off ONE __DT relay as a "Start" button commutator. Mag starter type logic does the runtime hold-in.

Another way is wired NOR logic. INclusive NOT OR. Pick up an "I am starting now" mode signal off the mag starter (equivalent) of each of the three or four heaviest loads.

Use that to inhibit compressor-start. IOW it may start only when NOT ANY OF A OR B OR C OR D loads are starting.

I use ignorant "4-Way" AKA DPDT light switches for the garbidge grinders. No relays required.

Why add spike-vulnerable shit that breaks?

DDoug · Aug 13, 2018

thermite said:
Simple damned timer (who made those? Intermatic was it? Torquematic? been around for a hundred years or so, anyway) runs BOTH loads off ONE __DT relay as a "Start" button commutator. Mag starter type logic does the runtime hold-in.

I use ignorant "4-Way" AKA DPDT light switches for the garbidge grinders. No relays required.

Why add spike-vulnerable shit that breaks?

Well, with Ox's background...I was thinking more like putting a Fanuc
on it.

Simple "delay to on" in an octal socket timer, should work nicely eh ?

ignator · Aug 13, 2018

I'm guessing that the other heavier load (e.g. RPC) has a contactor, that introduces a micro vibration, this sound is transmitted through the concrete floor and structure, where the trigger point of the compressor pressure switch over comes stiction from this micro vibration.
It also can be the wires from this heavy load undergo a magnetic slapping which also can produce micro vibrations that the pressure switch triggers on.

cyanidekid · Aug 13, 2018

I'm with thermite, purely mechanical. pulse wave, vibration type thing. elementary.

for a delay, I'd go analog and use the trusty AGASTAT.

Ox · Aug 13, 2018

digger doug said:
Yeah me too.

I know the parts that you are refering too, but no - I don't recall anything aboot the V spike.

thermite said:
It may be a mystery because you are looking at the wrong end of it. Not electrical at all.

How much of a minor tremor in mechanical vibration might that "heavy machine" transmit to trip the mechanical pressure gadget over the edge? Does it cause itself or some OTHER consumer of air to take even the merest sip of air? Does it simply shake the air lines running all over the shop or reflect a sound-wave into them and apply a pneumatic "spike" to the pressure sensor?

We don't really care, do we?

Where it is problematic, the cheap solution is to put a duty-cycle timer in the line as a commutator. Done this for years to stagger heavy starting loads.

Simple example is a lamp timer of the sort sold to make an empty house look occupied. Slide-out tabs choose on and off times.

If the compressor can only find "enable start" power available every odd-numbered minute of the hour, [1] and some other consumer only every even-numbered minute of the hour, their run-time is not affected. But they'll not START in the same 60-second "window" (or whatever else works for you) EVEN IF their "demand" switch is already asking for a start, 2 seconds into the window.

It has to wait its turn. Ordinarily, there's no effect on service delivery.

Not unless you delay it ten minutes or such, anyway.

[1] One --DT relay, as "XOR". Exclusive OR logic. Load A enable, load B enable, never both at once. My kitchen garbage disposals are even wired this way so I don't need larger service and breakers, nor the safety hazard of trying to manage both operating at once.

Been looking at this for <30 yrs ... well, I guess I'm not sure if I've seen that for that long ... I don't know if my old Joy ust'a doo that or not anymore, but 20 yrs for sure!

I have not seen where any of the times that it has done it has been in app of a large air surge. Just electrical. And it would be too far away to be vibrating anything that quickly. Nothing has had a chance to move yet - it's instantaneous.

I was looking very seriously at a job several years ago for a major player in Louisville, that would have required 3 cells each. A 12" chuck lathe and a small D&T mill. I was concerned about too many spindles all ramping up at the same time, and I planned to install a PLC for them all to acquire permission to start.

The job didn't fly, and I was kind'a glad as I just pictured it going to China long before I recouped my set-up costs. It wold be interesting to know if it stayed here or not. (Or if it even ever got off the ground here?) Or maybe I don't want to know?

----------------------

Think Snow Eh!
Ox

thermite · Aug 13, 2018

Ox said:
Been looking at this for <30 yrs ... well, I guess I'm not sure if I've seen that for that long ... I don't know if my old Joy ust'a doo that or not anymore, but 20 yrs for sure!

I have not seen where any of the times that it has done it has been in app of a large air surge. Just electrical. And it would be too far away to be vibrating anything that quickly. Nothing has had a chance to move yet - it's instantaneous.

Stagger-start fixes it EITHER way, reason I said "don't really care".

Used to be enough of a problem spinning up RAID hard drive arrays, it became a standard option setting in all the controllers. Might sync-start a mere 2-drive RAID1, but stagger a rackfull of anything more complicated.

cyanidekid · Aug 13, 2018

Ox said:
I know the parts that you are refering too, but no - I don't recall anything aboot the V spike.

I have not seen where any of the times that it has done it has been in app of a large air surge. Just electrical. And it would be too far away to be vibrating anything that quickly. Nothing has had a chance to move yet - it's instantaneous.

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Think Snow Eh!
Ox

as pointed out above by ignitor, don't forget the "right hand rule".

as welders know well, the force is exerted all along the conductor carrying the current. even if you haven't personally seen the cable jump, we have all herd the "buzz" or hum of a high current flowing, so it doesn't need to be a vibration or pulse all the way back from the high draw load to the compressor.

Ox · Aug 13, 2018

I don't know aboot right hand rules, but you betcha that I have seen the wires jump!
Even slap inside the conduit!

Seems kind'a "out there" that _ that would somehow effect a motor starter that isn't under power tho.
Apparently it is (and of course this is what I have witnessed time and aggin) but just seems "out there" to me ...

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Think Snow Eh!
Ox

cyanidekid · Aug 13, 2018

not so far "out there".. the pressure switch is a diaphragm or bellows moving a contact. a simple mechanical system that must overcome friction to turn on the motor. it has a "tipping point" past the actual pressure where it finally takes up the slop and overcomes that friction. if you tapped on the switch when it was about to trip, that would do it, just a little vibration is all the additional energy it needs to trip.

additional energy input reduces the mechanical hysteresis differential of the system.

PeteM · Aug 13, 2018

Could also be a matter of perception.

You'll likely hear or see the effects of a the voltage dip when two big loads try to start at about the same time -- and make a mental note of it. Maybe not pay so much attention the many other times when they start apart?

You'd have to keep a log of every stop and start to be sure.

What I want to know is how come lights always seem to turn yellow as I'm approaching -- leaving me in that existential question -- do I put on the brakes or run the light? Even more an existential question now that one adjacent town is funding itself with automated stop light cameras and $400 just-barely-red-light tickets. Could be me -- but this light "always" seems to be yellow when I approach it . . .

Ox · Aug 13, 2018

I'm just not seeing this "vibration" tho.

In the case that (I think) has happened 2wiced in the last few days - Big Bertha (a 50hp CNC lathe) has tripped her spindle drive out, and I think that the compressor tripped it out. I wasn't there and paying attention either time. I pushed GO and walked away, and the spindle won't start for a number of second later until after the turret has indexed to position, but I did note that the compressor was running when I noticed that Bertha wasn't, so ...

But Bertha is CNC, and as such, she has a major slow ramp up and doesn't git above 50% spindle load while ramping. It's not like I just hit the M/S on a 30hp Acme.

Besides, the wires and conduit are 20' run from the buss.

The wires aren't under any stress (like we talked above) as they are not under any load. There is no connection in the cabinet at all until the M/s closes.

"Does it matter?"

Prolly not. Not been an issue so far.
When things are running tight - I put the compressor in "continuous" cycle anyhow. (Then there IS power through those wires at all times!) LOL!

-------------------------

Think Snow Eh!
Ox

Dan from Oakland · Aug 14, 2018

It's actually pretty simple when you think about it for a moment- "things hate people".

thermite · Aug 14, 2018

Dan from Oakland said:
It's actually pretty simple when you think about it for a moment- "things hate people".

No they don't. They are impartial. This has been out there since early days, Written inside of pyramids and stuff? Maybe:

!!! Warning !!!
This machine is subject to breakdowns during periods of critical need.

A special circuit in the machine called a CRITICAL NEED DETECTOR senses the operator's emotional state in terms of how desperate he or she is to use the machine.

The CRITICAL NEED DETECTOR then creates a malfunction proportional to the desperation of the operator.

Threatening the machine with violence only aggravates the situation.

Likewise, attempts to use another machine may cause it also to malfunction. They belong to the same union.

Keep cool and say nice things to the machine. Nothing else seems to work.

robert123 · Aug 14, 2018

PeteM said:
What I want to know is how come lights always seem to turn yellow as I'm approaching -- leaving me in that existential question -- do I put on the brakes or run the light? Even more an existential question now that one adjacent town is funding itself with automated stop light cameras and $400 just-barely-red-light tickets. Could be me -- but this light "always" seems to be yellow when I approach it . . .

Clearly you're driving too slow. If you were to drive a little quicker, you would arrive at the light before it turns yellow.

Brain Scratcher for the Sparkies Here....

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Titanium

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Stainless

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