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Home > Archive > Electrical Engineering > May 2007 > Can this be done simply using contactors and switches...
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Can this be done simply using contactors and switches...
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| Stephen 2007-05-15, 5:25 pm |
| Imagine if you will...
The supply is 115Vac single phase.
This is passing to a Uninterruptible Power Supply (UPS) rated at 3kVA.
This powers a few computers.
What I need to do is provide an emergency stop facility. A push button
which will simultaneously:
* Isolate the incoming supply.
* Isolate the output of the UPS.
* Trigger the UPS to shutdown.
I presume that something like 30A 2-pole contactors would be required
for the isolation points.
The UPS has an enabling connection, two terminals which when shorted
together, allows the UPS to start up and operate. When the connection
goes open circuit, the UPS shuts down immediately.
Any ideas on how to accomplish this?
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| gfretwell@aol.com 2007-05-16, 3:25 am |
| On 15 May 2007 15:14:10 -0700, Stephen <srmoll@gmail.com> wrote:
>Imagine if you will...
>
>The supply is 115Vac single phase.
>
>This is passing to a Uninterruptible Power Supply (UPS) rated at 3kVA.
>
>This powers a few computers.
>
>What I need to do is provide an emergency stop facility. A push button
>which will simultaneously:
> * Isolate the incoming supply.
> * Isolate the output of the UPS.
> * Trigger the UPS to shutdown.
>
>I presume that something like 30A 2-pole contactors would be required
>for the isolation points.
>
>The UPS has an enabling connection, two terminals which when shorted
>together, allows the UPS to start up and operate. When the connection
>goes open circuit, the UPS shuts down immediately.
>
>Any ideas on how to accomplish this?
Sure, one pole on the UPS input, one pole on the output and get a
contactor with a SPDT side switch to shut down the UPS (they are
commonly available)
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| Stephen 2007-05-16, 3:25 am |
| On 16 May, 03:25, gfretw...@aol.com wrote:
> On 15 May 2007 15:14:10 -0700, Stephen <srm...@gmail.com> wrote:
>
>
>
>
>
>
>
>
>
>
>
> Sure, one pole on the UPS input, one pole on the output and get a
> contactor with a SPDT side switch to shut down the UPS (they are
> commonly available)
My problem is not so much where to place the contactors, as that is
pretty much a given fact. The problem lies is how to drive the coils
of them.
For example to start the system, only the main supply is available for
activating any contactor coils. Once it is all started of course, the
UPS is there to hold up the power should the main power fail.
Therefore, the contactors need to remain closed if the main power
source fails, and therefore need to be held closed by the UPS supplied
power. At any point though, hitting the push button needs to cause the
isolation and shutdown as described.
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| Palindrome 2007-05-16, 3:25 am |
| Stephen wrote:
> On 16 May, 03:25, gfretw...@aol.com wrote:
>
>
>
>
>
> My problem is not so much where to place the contactors, as that is
> pretty much a given fact. The problem lies is how to drive the coils
> of them.
>
> For example to start the system, only the main supply is available for
> activating any contactor coils. Once it is all started of course, the
> UPS is there to hold up the power should the main power fail.
> Therefore, the contactors need to remain closed if the main power
> source fails, and therefore need to be held closed by the UPS supplied
> power. At any point though, hitting the push button needs to cause the
> isolation and shutdown as described.
>
>
You use almost any emergency stop button that provides 3 (0r more) NC
contact sets.
eg:
http://docs-europe.electrocomponent...66b805d708f.pdf
These rope switches are good for providing "instant accesss"
emergency-off across the entire workshop/equipment room.
You use one NC set to use mains power to hold a mains supply contactor
on until the button is pressed.
You use one NC set to use UPS power to hold a UPS output side contactor
on until the button is pressed.
You use one NC to enable the UPS until the button is pressed.
The pushbutton locks mechanically in the "emergency" position -
preventing the contactors being powered whether the supplies are present
or not and preventing the UPS from starting.
--
Sue
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| Stephen 2007-05-16, 9:25 am |
| On 16 May, 09:22, Palindrome <m...@privacy.net> wrote:
> Stephen wrote:
>
>
>
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>
>
>
>
>
> You use almost any emergency stop button that provides 3 (0r more) NC
> contact sets.
>
> eg:http://docs-europe.electrocomponent...0766b805d708...
>
> These rope switches are good for providing "instant accesss"
> emergency-off across the entire workshop/equipment room.
>
> You use one NC set to use mains power to hold a mains supply contactor
> on until the button is pressed.
>
> You use one NC set to use UPS power to hold a UPS output side contactor
> on until the button is pressed.
>
> You use one NC to enable the UPS until the button is pressed.
>
> The pushbutton locks mechanically in the "emergency" position -
> preventing the contactors being powered whether the supplies are present
> or not and preventing the UPS from starting.
>
> --
> Sue
Yes, that sounds good, I had imagined something along those lines.
That would satisfy my immediate needs, and I think I can probably
identify the right sort of components.
At some point I'm thinking of extending this further, and would for
example like some way of automatically triggering a full and immediate
shutdown by using a thermal sensor. Although in this case something a
little more complicated. I.e. an audible warning to start when the
temperature is about 60 deg C, and automatic shutdown at 70 deg C.
Does anyone know of a DIN-rail type module that could act as the
trigger. Also how do I ensure that the temperature module is able to
operate when either or both main and UPS power is available?
I am thinking two 24Vdc DIN rail PSU modules, one just downstream of
the mains contactor, and one downstream of the UPS output contactor,
with the 24V outputs paralleled. Then finding a suitable DIN-rail
module to do the sensing. How does that sound?
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| Palindrome 2007-05-16, 9:25 am |
| Stephen wrote:
<snip>
> At some point I'm thinking of extending this further, and would for
> example like some way of automatically triggering a full and immediate
> shutdown by using a thermal sensor. Although in this case something a
> little more complicated. I.e. an audible warning to start when the
> temperature is about 60 deg C, and automatic shutdown at 70 deg C.
> Does anyone know of a DIN-rail type module that could act as the
> trigger. Also how do I ensure that the temperature module is able to
> operate when either or both main and UPS power is available?
>
> I am thinking two 24Vdc DIN rail PSU modules, one just downstream of
> the mains contactor, and one downstream of the UPS output contactor,
> with the 24V outputs paralleled. Then finding a suitable DIN-rail
> module to do the sensing. How does that sound?
>
An unusual approach for over-temperature of equipment sensing. 60/70
degrees trip points are hardly going to be there to protect occupants.
A more usual one is to sense the operation of the environmental control
system (eg the aircon) and/or sense the operating temperature of
equipment susceptible to high temperatures and ensure that they are not
allowed to go out of specification.
--
Sue
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| Stephen 2007-05-16, 9:25 am |
| On 16 May, 11:40, Palindrome <m...@privacy.net> wrote:
> Stephen wrote:
>
> <snip>
>
>
>
> An unusual approach for over-temperature of equipment sensing. 60/70
> degrees trip points are hardly going to be there to protect occupants.
>
> A more usual one is to sense the operation of the environmental control
> system (eg the aircon) and/or sense the operating temperature of
> equipment susceptible to high temperatures and ensure that they are not
> allowed to go out of specification.
>
> --
> Sue
The temperatures were only examples, but to answer your point, the
system has no control over its environment. It has forced are cooling,
but must be shut down if its gets too hot, prevent gasses or fumes
being generated by over heated lead-acid batteries in the UPS, and to
prevent any conditions that may lead to a fire. So yes 60/70 may sound
high, but we're talking internal temperatures here, and the cabinet
will at most times be operating in an unoccupied space.
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| gfretwell@aol.com 2007-05-17, 3:25 am |
| On 15 May 2007 22:56:56 -0700, Stephen <srmoll@gmail.com> wrote:
>My problem is not so much where to place the contactors, as that is
>pretty much a given fact. The problem lies is how to drive the coils
>of them.
>
>For example to start the system, only the main supply is available for
>activating any contactor coils. Once it is all started of course, the
>UPS is there to hold up the power should the main power fail.
>Therefore, the contactors need to remain closed if the main power
>source fails, and therefore need to be held closed by the UPS supplied
>power. At any point though, hitting the push button needs to cause the
>isolation and shutdown as described.
>
Go with a DC contactor, plug a wall wart in utility power and another
one in UPS power. Use a couple diodes to isolate them from each other
but common to the coil and put your N/C thermal switch in series with
the coil.
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