Robert Baer Inscribed thus:

I have this circuit that will "trip" a PIC (as a controller), but
it
had no delay so i added a resistor.
SPICE circuit is attached.
The added resistor seems to give abou a 2 second delay to trip from
initial input drive.
But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.
The idea is to shut down a machine by turning off the motor and
other
things if the motor has an excess load (gears seize, etc).
I do not know if that excess should be set to more or less that the
surge current; that is to say what is a "safe" method / setting?

Hi Robert,

In general, industrial motors have a current overload mechanism that is
thermally based. This allows any surge current to pass before it has
time to trip on over current. So unless you give time for any surge
current to subside before monitoring for overload, the surge current
plus a percentage would be the value to trip out at.

--
Best Regards:
Baron.

On Wed, 31 Mar 2010 13:24:28 -0800, Robert Baer wrote:

I have this circuit that will "trip" a PIC (as a controller), but it had
no delay so i added a resistor.
SPICE circuit is attached.
The added resistor seems to give abou a 2 second delay to trip from
initial input drive.
But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.
The idea is to shut down a machine by turning off the motor and other
things if the motor has an excess load (gears seize, etc).
I do not know if that excess should be set to more or less that the
surge current; that is to say what is a "safe" method / setting?

snip


Personally I wouldn't be tempted to use a PIC for this, unless it's just
a programming exercise?

Motors are usually installed with a thermal or electronic overcurrent
device mounted on the contactor. There is nothing to stop you taking a
"motor tripped" signal from the contact on this, of course. The
overcurrent relays are adjustable over a limited range so that they can
be trimmed to suit the particular motor & application. They are also
available with different tripping curves, allowing fans, for example, to
have a longer start time than, say, pumps (because of the inertia of the
blades).

As a rule of thumb, allow 5-7 times full-load current for a 3-phase motor
and about 8-9 times flc for a single phase as normal starting current
(direct-on-line starting, ordinary induction motor). The PIC should
adjust it's trip delay depending on the overcurrent detected. As the
current increases the delay should reduce, until there is a very short
trip to deal with "locked rotor" situations (not instantaneous as this
will happen at the beginning of the start curve anyway).

Nowadays many motors use electronic soft-start or variable speed drive
units, incorporating all the protection (and sometimes a contactor) in
the same unit. These build a software model of the motor and compare it
with the real one, giving far better protection than anything else.

Not often I see a post that fits in with my (previous) job... ;-)


--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

I have this circuit that will "trip" a PIC (as a controller), but it
had no delay so i added a resistor.
SPICE circuit is attached.
The added resistor seems to give abou a 2 second delay to trip from
initial input drive.
But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.
The idea is to shut down a machine by turning off the motor and other
things if the motor has an excess load (gears seize, etc).
I do not know if that excess should be set to more or less that the
surge current; that is to say what is a "safe" method / setting?

Version 4
SHEET 1 880 680
WIRE 128 -16 80 -16
WIRE 80 0 80 -16
WIRE 480 0 400 0
WIRE 624 0 480 0
WIRE 400 32 400 0
WIRE 480 32 480 0
WIRE 160 112 80 112
WIRE 176 112 160 112
WIRE 256 112 240 112
WIRE 128 128 128 -16
WIRE -32 144 -144 144
WIRE 80 144 80 112
WIRE 80 144 48 144
WIRE 96 144 80 144
WIRE 624 144 624 0
WIRE 688 144 624 144
WIRE 256 160 256 112
WIRE 256 160 160 160
WIRE 400 160 400 96
WIRE 688 160 688 144
WIRE -144 176 -144 144
WIRE 96 176 64 176
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WIRE 64 224 64 176
WIRE 64 224 0 224
WIRE 400 224 400 160
WIRE 480 224 480 96
WIRE 0 240 0 224
WIRE 64 240 64 224
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WIRE -32 320 -32 224
WIRE -32 320 -144 320
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WIRE 480 320 480 288
WIRE 480 320 400 320
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FLAG 480 352 0
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SYMBOL voltage 80 -16 R0
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WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 10V
SYMBOL voltage 64 224 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 10V
SYMBOL res 256 96 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 110K
SYMBOL res 64 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
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SYMATTR Value 10K
SYMBOL res 352 144 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL res 640 240 R180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R4
SYMATTR Value 1Meg
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL cap 400 144 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
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SYMATTR Value 4.7µ
SYMBOL cap 704 224 R180
WINDOW 0 24 64 Left 0
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SYMATTR InstName C2
SYMATTR Value 4.7µ
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WINDOW 0 24 72 Left 0
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SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode 496 288 R180
WINDOW 0 24 72 Left 0
WINDOW 3 -74 -5 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL diode 416 96 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL diode 496 96 R180
WINDOW 0 24 72 Left 0
WINDOW 3 -74 1 Left 0
SYMATTR InstName D4
SYMATTR Value 1N4148
SYMBOL voltage -144 160 R0
WINDOW 3 -100 -81 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 60mV 60 0 0 0 1e6)
SYMATTR InstName V3
TEXT -176 376 Left 0 !.tran 0 5sec 0 1mSec

In article ,
Robert Baer wrote:

But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.

The initial surge is a magnetic circuit phenomena and does not
depend on the load. You will get precisely the same initial
current with the shaft disconnected from the load or with the
shaft locked. (Assuming the same voltage and initial point of
conduction in the voltage waveform.)

The initial surge is called 'inrush' current and is analogous to
transformer energizing inrush. Once the transient has past, the
current will be dependent on the speed of rotation of the rotor
which is primarily a function of the load inertia and applied
voltage and time. If the rotor doesn't turn the current will be
'locked rotor' current which is nominally about 4 to 10 times the
rated load current. The inrush can be something like 1.6 or 1.7
times that times the ratio of the applied voltage to the rated
voltage.

How long the motor draws 'starting' current does depend on the
load.

The overload device needs to protect the motor from prolonged
starting or locked rotor current. It must ignore the inrush
current. Typically, a separate instantaneous trip device is used
for short circuit protection for currents above about 2-3 times
the maximum inrush current.

--
Fred Lotte

On Fri, 02 Apr 2010 13:36:03 -0800, Robert Baer wrote:

snip
The motors that will be used have / do not come with external sensors
or contactors, hence this sensor "trick" i came up with.
The PIC is also being used for a number of equipment related things
(a sample): forward / reverse; run / jog; tank lo level, high level,
extreme level detection; if too cold, a heater goes on for a settable
predeterimed time before tank transfer pump (one of the motors) is run;
transfer motor timeout (as it is not rated for continuous duty so want
to protect it from burning out).
Adjustable trip delay is something not known / thought of; a
different kettle of fish.


Sorry, I don't have SPICE and have no experience of it, so your "circuit"
means nothing to me! I'm hoping that you are switching the motor(s) with
a contactor or relay - just electronic switching is not good, and
generally results in escape of magic smoke or someone getting a shock off
the motor while it's stopped...

I assume these are small, fractional HP motors then? Sometimes that sort
are difficult to protect - and don't really need protection in most
applications as the impedance of the winding is enough to restrict the
current to a safe (non smoking!) value. The motor just sits there,
stalled, and gets a bit hot! There isn't really enough difference between
running current and stalled current to allow reliable overload
protection. The power factor *does* change though, so you can protect by
measuring power rather than current if you really need to.

You are probably ok without an overload relay for motors up to about 1/4
HP. Quite often they include a thermal trip mounted either on the case or
internally (especially up to about 1/2HP). Don't forget to use fuses or a
circuit breaker to protect your contactor against short circuits though!

I like your idea, but if I were you I wouldn't rely on the PIC for motor
protection if the motor rating is more than 1/4HP. There should be some
kind of overload relay or thermal trip (internal or external) to drop out
the contactor. YMMV of course!

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

baron wrote:
Robert Baer Inscribed thus:

I have this circuit that will "trip" a PIC (as a controller), but
it
had no delay so i added a resistor.
SPICE circuit is attached.
The added resistor seems to give abou a 2 second delay to trip from
initial input drive.
But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.
The idea is to shut down a machine by turning off the motor and
other
things if the motor has an excess load (gears seize, etc).
I do not know if that excess should be set to more or less that the
surge current; that is to say what is a "safe" method / setting?

Hi Robert,

In general, industrial motors have a current overload mechanism that is
thermally based. This allows any surge current to pass before it has
time to trip on over current. So unless you give time for any surge
current to subside before monitoring for overload, the surge current
plus a percentage would be the value to trip out at.

Thanks.

mick wrote:
On Wed, 31 Mar 2010 13:24:28 -0800, Robert Baer wrote:

I have this circuit that will "trip" a PIC (as a controller), but it had
no delay so i added a resistor.
SPICE circuit is attached.
The added resistor seems to give abou a 2 second delay to trip from
initial input drive.
But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.
The idea is to shut down a machine by turning off the motor and other
things if the motor has an excess load (gears seize, etc).
I do not know if that excess should be set to more or less that the
surge current; that is to say what is a "safe" method / setting?

snip


Personally I wouldn't be tempted to use a PIC for this, unless it's just
a programming exercise?

Motors are usually installed with a thermal or electronic overcurrent
device mounted on the contactor. There is nothing to stop you taking a
"motor tripped" signal from the contact on this, of course. The
overcurrent relays are adjustable over a limited range so that they can
be trimmed to suit the particular motor & application. They are also
available with different tripping curves, allowing fans, for example, to
have a longer start time than, say, pumps (because of the inertia of the
blades).

As a rule of thumb, allow 5-7 times full-load current for a 3-phase motor
and about 8-9 times flc for a single phase as normal starting current
(direct-on-line starting, ordinary induction motor). The PIC should
adjust it's trip delay depending on the overcurrent detected. As the
current increases the delay should reduce, until there is a very short
trip to deal with "locked rotor" situations (not instantaneous as this
will happen at the beginning of the start curve anyway).

Nowadays many motors use electronic soft-start or variable speed drive
units, incorporating all the protection (and sometimes a contactor) in
the same unit. These build a software model of the motor and compare it
with the real one, giving far better protection than anything else.

Not often I see a post that fits in with my (previous) job... ;-)


The motors that will be used have / do not come with external sensors
or contactors, hence this sensor "trick" i came up with.
The PIC is also being used for a number of equipment related things
(a sample): forward / reverse; run / jog; tank lo level, high level,
extreme level detection; if too cold, a heater goes on for a settable
predeterimed time before tank transfer pump (one of the motors) is run;
transfer motor timeout (as it is not rated for continuous duty so want
to protect it from burning out).
Adjustable trip delay is something not known / thought of; a
different kettle of fish.

Fred Lotte wrote:
In article ,
Robert Baer wrote:

But i know nothing about motors except that they work and have an
initial surge current which probably depends on load.

The initial surge is a magnetic circuit phenomena and does not
depend on the load. You will get precisely the same initial
current with the shaft disconnected from the load or with the
shaft locked. (Assuming the same voltage and initial point of
conduction in the voltage waveform.)

The initial surge is called 'inrush' current and is analogous to
transformer energizing inrush. Once the transient has past, the
current will be dependent on the speed of rotation of the rotor
which is primarily a function of the load inertia and applied
voltage and time. If the rotor doesn't turn the current will be
'locked rotor' current which is nominally about 4 to 10 times the
rated load current. The inrush can be something like 1.6 or 1.7
times that times the ratio of the applied voltage to the rated
voltage.

How long the motor draws 'starting' current does depend on the
load.

The overload device needs to protect the motor from prolonged
starting or locked rotor current. It must ignore the inrush
current. Typically, a separate instantaneous trip device is used
for short circuit protection for currents above about 2-3 times
the maximum inrush current.

Thanks.

In article ,
Robert Baer wrote:

Thanks.

Your welcome.

--
Fred Lotte

On Sat, 03 Apr 2010 09:10:11 -0800, Robert Baer wrote:

snip
That is LTSpice aka SwitcherCAD i(if i remember correctly). Anyway,
the transfer pump is a small one, prolly 1/4HP at the most
but the main motor can run from 1/4HP to perhaps 2HP at the top end (but
not for a few years).
Am using optically isolated triac switching circuitry to drive
relays, where the relays do all of the work including turning on and off
that resistive heater mentioned.
**
On rare occasion i hear some buzzing of a relay when it is on - any
ideas?


AC powered relays and contactors do occasionally buzz. It's usually
because the magnetic circuit isn't fully closing because of dirt on the
pole faces or just that the pole faces aren't accurate enough. Some sorts
seem to be worse than others. The buzz is harmless (but can be annoying).
On some gear (usually contactor panels for switching interior lights) we
use rectified AC feeding DC contactors. That gives a nice silent system,
but costs more. BIG contactors (100A plus) are often DC operated anyway
as the magnetic system is more reliable that way.

Just make sure that your relays are definitely rated for your motor load,
otherwise their life will be *very* short! Generally relays are rated for
resistive loads, whereas contactors are rated for inductive loads. A
typical 10A relay will only switch about 7A inductive (max). For motor
starting you should look for a class AC3 rating. You should be ok using
relays at 1/4HP, but 2HP won't do it. That's a small contactor. Actually,
the difference in price between a good quality plug-in relay plus base
and a small DIN rail contactor is minimal. You may as well use contactors
- but they don't fit on PCBs.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

mick wrote:
On Fri, 02 Apr 2010 13:36:03 -0800, Robert Baer wrote:

snip
The motors that will be used have / do not come with external sensors
or contactors, hence this sensor "trick" i came up with.
The PIC is also being used for a number of equipment related things
(a sample): forward / reverse; run / jog; tank lo level, high level,
extreme level detection; if too cold, a heater goes on for a settable
predeterimed time before tank transfer pump (one of the motors) is run;
transfer motor timeout (as it is not rated for continuous duty so want
to protect it from burning out).
Adjustable trip delay is something not known / thought of; a
different kettle of fish.


Sorry, I don't have SPICE and have no experience of it, so your "circuit"
means nothing to me! I'm hoping that you are switching the motor(s) with
a contactor or relay - just electronic switching is not good, and
generally results in escape of magic smoke or someone getting a shock off
the motor while it's stopped...

I assume these are small, fractional HP motors then? Sometimes that sort
are difficult to protect - and don't really need protection in most
applications as the impedance of the winding is enough to restrict the
current to a safe (non smoking!) value. The motor just sits there,
stalled, and gets a bit hot! There isn't really enough difference between
running current and stalled current to allow reliable overload
protection. The power factor *does* change though, so you can protect by
measuring power rather than current if you really need to.

You are probably ok without an overload relay for motors up to about 1/4
HP. Quite often they include a thermal trip mounted either on the case or
internally (especially up to about 1/2HP). Don't forget to use fuses or a
circuit breaker to protect your contactor against short circuits though!

I like your idea, but if I were you I wouldn't rely on the PIC for motor
protection if the motor rating is more than 1/4HP. There should be some
kind of overload relay or thermal trip (internal or external) to drop out
the contactor. YMMV of course!

That is LTSpice aka SwitcherCAD i(if i remember correctly).
Anyway, the transfer pump is a small one, prolly 1/4HP at the most
but the main motor can run from 1/4HP to perhaps 2HP at the top end (but
not for a few years).
Am using optically isolated triac switching circuitry to drive
relays, where the relays do all of the work including turning on and off
that resistive heater mentioned.
**
On rare occasion i hear some buzzing of a relay when it is on - any
ideas?

On Sun, 04 Apr 2010 08:26:26 -0700, Robert Baer wrote:

snip
All relays / contactors are placed on a separate panel in the NEMA
box. For switching the heater (resistive), transfer pump motor, and a
tripwire to capture a belt, i am using the Panasonic VC15F (4 poles)
rated 1/3HP 120V, 1HP 240V, 2HP 3phase 240V.
For foewrd / reverse of the main motor i am using the Panasonic / LS
Industries GMC(D)-12MR-10-AC120V relay apparently rated at 1HP 1 phase
115V, 2HP 1 phase 230V, 3HP 3 phase 230V and has ratings at 460v as well
as 575V (7.5HP 3 phase); it was made at the factory using two GMC-12M
relays with a mechanical lockout that prevents both relays from working
at the same time (one of them "wins" and the other "loses").


AH! Apologies if I was trying to teach grandmother to suck eggs! Sounds
as if you are doing it properly. It was your use of the term "relay" that
was making me wonder if you were using the right gear. Here in the UK we
would normally refer to those as contactors. I'm pleased to see that
you've used a mechanically interlocked pair for forward/reverse. Some
people try to get away with just electrical interlock then wonder, later,
where the smoke is coming from... :-)

If your stuff is NEMA I'm rather surprised that there isn't a thermal
trip of some sort on the motors. Sometimes it's a block with a red button
(manual reset), other times it's just a pair of wires or terminals. In
both cases you can use it to kill the contactor on over-temp. I thought
it was part of the NEMA spec, but I've not worked to that for a long,
long time.

It's nice to wire a contactor auxiliary back to the controller (PIC) so
that it knows if the contactor has failed to close or has opened on fault
or if someone has jammed it in with a piece of wood (no laughing at the
back! I've seen it done!). If you don't have one then too bad, but it's a
good idea. If electrical interlocking is added to the coil later then the
controller automatically takes it into account as it won't proceed to the
next stage unless the contactor has closed.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

mick wrote:
On Sat, 03 Apr 2010 09:10:11 -0800, Robert Baer wrote:

snip
That is LTSpice aka SwitcherCAD i(if i remember correctly). Anyway,
the transfer pump is a small one, prolly 1/4HP at the most
but the main motor can run from 1/4HP to perhaps 2HP at the top end (but
not for a few years).
Am using optically isolated triac switching circuitry to drive
relays, where the relays do all of the work including turning on and off
that resistive heater mentioned.
**
On rare occasion i hear some buzzing of a relay when it is on - any
ideas?


AC powered relays and contactors do occasionally buzz. It's usually
because the magnetic circuit isn't fully closing because of dirt on the
pole faces or just that the pole faces aren't accurate enough. Some sorts
seem to be worse than others. The buzz is harmless (but can be annoying).
On some gear (usually contactor panels for switching interior lights) we
use rectified AC feeding DC contactors. That gives a nice silent system,
but costs more. BIG contactors (100A plus) are often DC operated anyway
as the magnetic system is more reliable that way.

Just make sure that your relays are definitely rated for your motor load,
otherwise their life will be *very* short! Generally relays are rated for
resistive loads, whereas contactors are rated for inductive loads. A
typical 10A relay will only switch about 7A inductive (max). For motor
starting you should look for a class AC3 rating. You should be ok using
relays at 1/4HP, but 2HP won't do it. That's a small contactor. Actually,
the difference in price between a good quality plug-in relay plus base
and a small DIN rail contactor is minimal. You may as well use contactors
- but they don't fit on PCBs.

All relays / contactors are placed on a separate panel in the NEMA box.
For switching the heater (resistive), transfer pump motor, and a
tripwire to capture a belt, i am using the Panasonic VC15F (4 poles)
rated 1/3HP 120V, 1HP 240V, 2HP 3phase 240V.
For foewrd / reverse of the main motor i am using the Panasonic / LS
Industries GMC(D)-12MR-10-AC120V relay apparently rated at 1HP 1 phase
115V, 2HP 1 phase 230V, 3HP 3 phase 230V and has ratings at 460v as well
as 575V (7.5HP 3 phase); it was made at the factory using two GMC-12M
relays with a mechanical lockout that prevents both relays from working
at the same time (one of them "wins" and the other "loses").

Robert Baer wrote:

I thank you for your comments; i am just a dumb electronic technician
that had to this power stuff with zero background.
So i am thankful to find that the choices i made were not too stupid
after all.
Concerning the motors, i do not have them and in fact they have not
been bought or otherwise designated (ie: make, model and so on).
I am assuming worst case - a piece of iron and copper that
"magically" rotates when powered correctly; if there are any extra
do-dadds that add safety, that is better.
NEMA.
Swearword; have no idea as to how a complete controller box gets its
own sticker.
Just using items that have NEMA approval, like the box itself, the
wire i use, the relays / contactors, etc.
Now when one gets to the electronics.......all bets are off; then one
gets to the software being used in the PIC microcontroller......worse i
assume.
This stuff is in a different universe for approval, i think.


Robert, would you set the clock on your system?


--
Lead free solder is Belgium's version of 'Hold my beer and watch this!'

mick wrote:
On Sun, 04 Apr 2010 08:26:26 -0700, Robert Baer wrote:

snip
All relays / contactors are placed on a separate panel in the NEMA
box. For switching the heater (resistive), transfer pump motor, and a
tripwire to capture a belt, i am using the Panasonic VC15F (4 poles)
rated 1/3HP 120V, 1HP 240V, 2HP 3phase 240V.
For foewrd / reverse of the main motor i am using the Panasonic / LS
Industries GMC(D)-12MR-10-AC120V relay apparently rated at 1HP 1 phase
115V, 2HP 1 phase 230V, 3HP 3 phase 230V and has ratings at 460v as well
as 575V (7.5HP 3 phase); it was made at the factory using two GMC-12M
relays with a mechanical lockout that prevents both relays from working
at the same time (one of them "wins" and the other "loses").


AH! Apologies if I was trying to teach grandmother to suck eggs! Sounds
as if you are doing it properly. It was your use of the term "relay" that
was making me wonder if you were using the right gear. Here in the UK we
would normally refer to those as contactors. I'm pleased to see that
you've used a mechanically interlocked pair for forward/reverse. Some
people try to get away with just electrical interlock then wonder, later,
where the smoke is coming from... :-)

If your stuff is NEMA I'm rather surprised that there isn't a thermal
trip of some sort on the motors. Sometimes it's a block with a red button
(manual reset), other times it's just a pair of wires or terminals. In
both cases you can use it to kill the contactor on over-temp. I thought
it was part of the NEMA spec, but I've not worked to that for a long,
long time.

It's nice to wire a contactor auxiliary back to the controller (PIC) so
that it knows if the contactor has failed to close or has opened on fault
or if someone has jammed it in with a piece of wood (no laughing at the
back! I've seen it done!). If you don't have one then too bad, but it's a
good idea. If electrical interlocking is added to the coil later then the
controller automatically takes it into account as it won't proceed to the
next stage unless the contactor has closed.

I thank you for your comments; i am just a dumb electronic technician
that had to this power stuff with zero background.
So i am thankful to find that the choices i made were not too stupid
after all.
Concerning the motors, i do not have them and in fact they have not
been bought or otherwise designated (ie: make, model and so on).
I am assuming worst case - a piece of iron and copper that
"magically" rotates when powered correctly; if there are any extra
do-dadds that add safety, that is better.
NEMA.
Swearword; have no idea as to how a complete controller box gets its
own sticker.
Just using items that have NEMA approval, like the box itself, the
wire i use, the relays / contactors, etc.
Now when one gets to the electronics.......all bets are off; then one
gets to the software being used in the PIC microcontroller......worse i
assume.
This stuff is in a different universe for approval, i think.

Michael A. Terrell wrote:
Robert Baer wrote:
I thank you for your comments; i am just a dumb electronic technician
that had to this power stuff with zero background.
So i am thankful to find that the choices i made were not too stupid
after all.
Concerning the motors, i do not have them and in fact they have not
been bought or otherwise designated (ie: make, model and so on).
I am assuming worst case - a piece of iron and copper that
"magically" rotates when powered correctly; if there are any extra
do-dadds that add safety, that is better.
NEMA.
Swearword; have no idea as to how a complete controller box gets its
own sticker.
Just using items that have NEMA approval, like the box itself, the
wire i use, the relays / contactors, etc.
Now when one gets to the electronics.......all bets are off; then one
gets to the software being used in the PIC microcontroller......worse i
assume.
This stuff is in a different universe for approval, i think.


Robert, would you set the clock on your system?


Noticed it; should be OK now.

On Tue, 06 Apr 2010 12:11:31 -0700, Robert Baer wrote:

snip
I thank you for your comments; i am just a dumb electronic technician
that had to this power stuff with zero background.
So i am thankful to find that the choices i made were not too stupid
after all.
Concerning the motors, i do not have them and in fact they have not
been bought or otherwise designated (ie: make, model and so on).
I am assuming worst case - a piece of iron and copper that
"magically" rotates when powered correctly; if there are any extra
do-dadds that add safety, that is better.
NEMA.
Swearword; have no idea as to how a complete controller box gets its
own sticker.
Just using items that have NEMA approval, like the box itself, the
wire i use, the relays / contactors, etc.
Now when one gets to the electronics.......all bets are off; then one
gets to the software being used in the PIC microcontroller......worse i
assume.
This stuff is in a different universe for approval, i think.


Too right... If you need software approving then that can be difficult.
Better to just test it - hard - then give your client a demo.

Try to make out a check list of *everything* that can go wrong while the
program is running (no matter how stupid) and test all combinations. Not
easy, but you can bet that unless you catch almost everything your client
will, eventually, make the system do something that it wasn't intended to!
(been there, done that.. )
Unless your customer is very trusting, though, you may find that he won't
accept motor protection using your software. After all, if it fails and
the motor is still running under overload (e.g. triac failed s/c or idiot
with lolly stick) you could have a fire situation.

I *think* the NEMA system works just like you say - use all NEMA bits and
you end up with a NEMA approved system. Our system doesn't work like that.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Tue, 06 Apr 2010 12:11:31 -0700, Robert Baer wrote:

mick wrote:
On Sun, 04 Apr 2010 08:26:26 -0700, Robert Baer wrote:

snip
All relays / contactors are placed on a separate panel in the NEMA
box. For switching the heater (resistive), transfer pump motor, and a
tripwire to capture a belt, i am using the Panasonic VC15F (4 poles)
rated 1/3HP 120V, 1HP 240V, 2HP 3phase 240V.
For foewrd / reverse of the main motor i am using the Panasonic / LS
Industries GMC(D)-12MR-10-AC120V relay apparently rated at 1HP 1 phase
115V, 2HP 1 phase 230V, 3HP 3 phase 230V and has ratings at 460v as well
as 575V (7.5HP 3 phase); it was made at the factory using two GMC-12M
relays with a mechanical lockout that prevents both relays from working
at the same time (one of them "wins" and the other "loses").


AH! Apologies if I was trying to teach grandmother to suck eggs! Sounds
as if you are doing it properly. It was your use of the term "relay" that
was making me wonder if you were using the right gear. Here in the UK we
would normally refer to those as contactors. I'm pleased to see that
you've used a mechanically interlocked pair for forward/reverse. Some
people try to get away with just electrical interlock then wonder, later,
where the smoke is coming from... :-)

If your stuff is NEMA I'm rather surprised that there isn't a thermal
trip of some sort on the motors. Sometimes it's a block with a red button
(manual reset), other times it's just a pair of wires or terminals. In
both cases you can use it to kill the contactor on over-temp. I thought
it was part of the NEMA spec, but I've not worked to that for a long,
long time.

It's nice to wire a contactor auxiliary back to the controller (PIC) so
that it knows if the contactor has failed to close or has opened on fault
or if someone has jammed it in with a piece of wood (no laughing at the
back! I've seen it done!). If you don't have one then too bad, but it's a
good idea. If electrical interlocking is added to the coil later then the
controller automatically takes it into account as it won't proceed to the
next stage unless the contactor has closed.

I thank you for your comments; i am just a dumb electronic technician
that had to this power stuff with zero background.
So i am thankful to find that the choices i made were not too stupid
after all.
Concerning the motors, i do not have them and in fact they have not
been bought or otherwise designated (ie: make, model and so on).
I am assuming worst case - a piece of iron and copper that
"magically" rotates when powered correctly; if there are any extra
do-dadds that add safety, that is better.
NEMA.
Swearword; have no idea as to how a complete controller box gets its
own sticker.
Just using items that have NEMA approval, like the box itself, the
wire i use, the relays / contactors, etc.

Then you may wish to investigate a widget called a "motor saver". It can
really help avoid having to mess with the approvals with new uP and firmware
in the power controls. I have been seeing a lot of them in motor controls
of late. Kind of like using NEMA approved protective relays in bigger power
distribution systems.

Now when one gets to the electronics.......all bets are off; then one
gets to the software being used in the PIC microcontroller......worse i
assume.
This stuff is in a different universe for approval, i think.