Hello everyone,
Once again, a scavenger hunt is at the top of the list. As an employee, some decisions are handed to me.
In times long past, I have seen relays whose coil was wound with fewer turns and heavier wire. The coil, wired in series with a load, pulls the contacts when the current is above some level. What is such a relay called? Does anyone still make such things?
Have a good day, Robert H.
try "amperometric relay"
bye delo
"Robert" ha scritto nel messaggio news:Xns9BC95AA32F2C1someonenowherecom@69.16.186.8...
current relay
yes. Industrial suppliers have them, e.g., McMaster-Carr, MSC. Maybe electronics suppliers.
Bob
AC or DC? Would a COTS item be OK?
Carling calls it 'Shunt Trip' although they may not use it as a current trip, just a voltage trip.
Cheers
JeffM wrote in news: snipped-for-privacy@o11g2000yql.googlegroups.com:
AC
COTS ( Common Off The Shelf ) would be wonderful.
Looked at the URLs.
URL 1 Smart Power Strip
Several outlets are switched on and off with the current drawn from a control outlet.
URL 2 Current operated switch
Digikey 582-1020-ND $24 and a $30 SSR would get me there. There is a problem with the ambient temperature of 70 or 80 C that has been handed to me and most solid state devices. That is why the current driven relay came to mind.
James Sweet typed: "You can get current relays from HVAC surplus type places, they're just a relay wound with a heavy wire designed to carry the load current, the relay closes when current flows through the coil. I think I paid $2 for the one I bought, you could probably rewind the stator of an AC relay with some #12 enameled wire in a pinch too."
This is the kind of thing I remembered.
URL 3 Current Operated Switch The URL mentioned is not in working order.
Thanks for the leads. The hunt continues.
Robert H.
Robert wrote:
You seem bound & determined to have us drag every detail out of you.
Other data can also be useful in crafting a response:
-failure
Are you aware of these?
JeffM wrote in news: snipped-for-privacy@y38g2000prg.googlegroups.com:
Some off topic thoughts:
I am not shure what to make of your style. Twice you have posted a list of URLs and twice I have looked at them. They seam to be getting a bit off topic. Your last post seams to ask for more information to use in "crafting a response". Please allow me to help you clarify your response crafting. I did ask the question I intended to ask. I am also aware that the thecnology has moved forward and that the electromechanical device asked about is no longer current. If you have something on topic to put forward, please do so. I am shure you will post anything you chose to. You would be wist not to expect me to follow every URL you choose to post.
Back on topic:
The electromechanical I asked about would provide a 1-device solution.
Happy posting, Robert H.
Robert wrote:
Robert wrote:
For a moment at the start of the thread, I thought you were the Robert H who designs chips. You couldn't be farther away from his skill set.
The point of my last series of links was: YOU are not the first clueless person to post to an engineering group. The *first* step in a technical undertaking is WRITE A SPECIFICATION.
This link was the the one you should have investigated
--and still should:
How do you expect to us to help you find something when you have only given the most VAGUE idea of what you want?
If there was a point you SHOULD have gleaned from my links, that was the part that said
**put.numbers.on.as.many.things.as.possible**. I had to drag out of you whether it was even AC or DC.Here are some specs that are still unstated:
Volts on the coil / actuating circuit? Actuating level of current in the coil / actuating circuit? Dropout current? (Hysteresis) Maximum current in the coil / actuating circuit? (if different)
Maximum current to the load? Volts on the load? What is the level of isolation needed between the actuation side and the load side? What is the nature of the load? (Is it inductive?) How fast does the thing have to respond?
NOW go back to my links and see if you can make sense of them.
...and?
JeffM wrote in news: snipped-for-privacy@k29g2000prf.googlegroups.com:
About the only thing still available that is close is what is called an overload relay. The coil is typically in series with the load device and is supposed to pull in when that device is overloaded. As for meeting the rest of your design criteria, i have not a clue.
"JosephKK" wrote in news: snipped-for-privacy@4ax.com:
Good morning,
Most of the overload relays I looked at are thermal. When heated a set of contacts open. This works fine for shutting down when aced with a sustained overload. I needed contacts that opened when the current, or heating, fell too low. Compared to the usual power power levels for such devices, mine are quite low. I deeded to switch at less than an amp.
Fortunately, those in control have backed away from 80 C ambient. I am back into a temperatur range that can be met with commonly available items. An electronic current sensor, a relay to handle the load, and a momentary switch to get things started.
Having explained the application many times, I may not have done so here. Unfocused conversations and corispondance eats up a lot of time. A small motor with internal, automatically resetting, thermal protection has been used for a long time. The hazard of having it restart is now understood. A field installable way of requiring operator intervention for a restart is needed. When a requirement of 80 C ambient was added, an electromechanical device came to mind. While they may have been common at one time, that time has past.
I offer my thanks to those who offered thoughts and information on this subject. While ranking the responses is inappropriate, the term amperometric does stand out.
A good day to all, Robert H.
On Wed, 11 Mar 2009 13:38:06 GMT, Robert wrote:
:"JosephKK" wrote in :news: snipped-for-privacy@4ax.com: : : :> About the only thing still available that is close is what is called :> an overload relay. The coil is typically in series with the load :> device and is supposed to pull in when that device is overloaded. As :> for meeting the rest of your design criteria, i have not a clue. : :Good morning, : :Most of the overload relays I looked at are thermal. When heated a set of :contacts open. This works fine for shutting down when aced with a :sustained overload. I needed contacts that opened when the current, or :heating, fell too low. Compared to the usual power power levels for such :devices, mine are quite low. I deeded to switch at less than an amp. : :Fortunately, those in control have backed away from 80 C ambient. I am :back into a temperatur range that can be met with commonly available items. :An electronic current sensor, a relay to handle the load, and a momentary :switch to get things started. : :Having explained the application many times, I may not have done so here. :Unfocused conversations and corispondance eats up a lot of time. A small :motor with internal, automatically resetting, thermal protection has been :used for a long time. The hazard of having it restart is now understood. :A field installable way of requiring operator intervention for a restart is :needed. When a requirement of 80 C ambient was added, an electromechanical :device came to mind. While they may have been common at one time, that :time has past. : :I offer my thanks to those who offered thoughts and information on this :subject. While ranking the responses is inappropriate, the term :amperometric does stand out. : :A good day to all, :Robert H.
It sounds to me as if you are looking for a standard motor overload protector which has both overcurrentand thermal overload tripping. I am certain that these devices do not automatically reset once tripped - you have to manually press a button to restart. eg.
Ross Herbert wrote in news: snipped-for-privacy@4ax.com:
The motor being used is not being changed or modified. It is a small AC motor. It has internal over temp that automatically resets. It is the automatic restarting that is the problem. A way of externally preventing the restart is needed.
The item you pointed out looks like it trips with overloads and over current. I need to trip in response to the motor shutting down from the internal protection opening up.
Fortunately those who imposed the 80 C ambient rating have yeilded. Specification by a comitee that has only a single member familar with the technology can be a challenge.
Thanks, Robert H.
So, you too are in this mansion.
-- View in Courier: .AC>---+------+ . | O COM . | |- - - - - - -[COIL]K2 . S1| O NO | --------------+ JF
On Thu, 12 Mar 2009 14:42:04 GMT, Robert wrote:
:Ross Herbert wrote in :news: snipped-for-privacy@4ax.com: : :>:Most of the overload relays I looked at are thermal. When heated a :>:set of contacts open. This works fine for shutting down when aced :>:with a sustained overload. I needed contacts that opened when the :>:current, or heating, fell too low. Compared to the usual power power :>:levels for such devices, mine are quite low. I deeded to switch at :>:less than an amp. :>: :>:Fortunately, those in control have backed away from 80 C ambient. I :>:am back into a temperatur range that can be met with commonly :>:available items. An electronic current sensor, a relay to handle the :>:load, and a momentary switch to get things started. :>: :>:Having explained the application many times, I may not have done so :>:here. Unfocused conversations and corispondance eats up a lot of :>:time. A small motor with internal, automatically resetting, thermal :>:protection has been used for a long time. The hazard of having it :>:restart is now understood. A field installable way of requiring :>:operator intervention for a restart is needed. When a requirement of :>:80 C ambient was added, an electromechanical device came to mind. :>:While they may have been common at one time, that time has past. :>: :>:I offer my thanks to those who offered thoughts and information on :>:this subject. While ranking the responses is inappropriate, the term :>:amperometric does stand out. :>: :>:A good day to all, :>:Robert H. :> :> :> It sounds to me as if you are looking for a standard motor overload :> protector which has both overcurrentand thermal overload tripping. I :> am certain that these devices do not automatically reset once tripped :> - you have to manually press a button to restart. :> eg. :>
Without modification to the motor itself there can be no means by which control of an external device or protection method is possible. The only way I cansee out of your dilemma is for the external motor protector to have priority over the internal temperature overload function of the motor.
Since the motor temperature is a function of mechanical load and the current being drawn by the motor, you can use a motor protector such as the one I mentioned and set the overload current (yes, this value is adjustable) to some value below that at which causes the motor to exceed its overload temperature. That way the external protector will have priority and will trip before the motor temperature is reached and then you have manual control via the external protector.
--- View in Courier:
Like this?
.AC>---+------+ . | O COM . | |- - - - - - -[COIL]K2 . S1| O NO | --------------+
If the thermal cutout switch, S2, in the motor assembly is closed, then pressing S1 (a normally-open momentary switch) will connect the motor to the mains through the primary of T1, a current transformer. When that happens the motor will start to turn and a voltage will be induced in the secondary of the transformer which will be placed across the coil of K2, a normally-open relay with an AC coil.
When the contacts of K2 close they will be in parallel with the contacts of S1 and will provide a redundant connection of the motor and the transformer to the mains.
Therefore, when S1 is released, the connection to the mains will be maintained by the closed K2 contacts.
However, should S2 open because of motor overheating, (or any other reason) the current in the coil of K2 will be interrupted, the relay contacts will open, and the connection to the mains for the motor and K2's coil will be broken.
Once that happens, the connection to the mains will remain broken even if S2 closes once the motor cools off, pressing S1 being the only way to begin the cycle anew.
JF
On Sun, 15 Mar 2009 07:15:27 -0500, John Fields wrote:
:On Sun, 15 Mar 2009 07:28:51 GMT, Ross Herbert :wrote: : : :>Without modification to the motor itself there can be no means by which control :>of an external device or protection method is possible. The only way I cansee :>out of your dilemma is for the external motor protector to have priority over :>the internal temperature overload function of the motor. : :--- :View in Courier: : :Like this? : :.AC>---+------+ :. | O COM :. | |- - - - - - -[COIL]K2 :. S1| O NO | --------------+ : :If the thermal cutout switch, S2, in the motor assembly is closed, then :pressing S1 (a normally-open momentary switch) will connect the motor to :the mains through the primary of T1, a current transformer. When that :happens the motor will start to turn and a voltage will be induced in :the secondary of the transformer which will be placed across the coil of :K2, a normally-open relay with an AC coil. : :When the contacts of K2 close they will be in parallel with the contacts :of S1 and will provide a redundant connection of the motor and the :transformer to the mains. : :Therefore, when S1 is released, the connection to the mains will be :maintained by the closed K2 contacts. : :However, should S2 open because of motor overheating, (or any other :reason) the current in the coil of K2 will be interrupted, the relay :contacts will open, and the connection to the mains for the motor and :K2's coil will be broken. : :Once that happens, the connection to the mains will remain broken even :if S2 closes once the motor cools off, pressing S1 being the only way to :begin the cycle anew. : : :JF
Yes John, that's exactly the way I see it. The motor protection current limit is dialled up on the external motor starter/protector so that it is below that required to heat the motor up to the internal temp setting for S1 to trip.
-- There\'s no need for any of that since once the motor\'s internal thermal switch (S2) opens up the motor will be disconnected from the mains, and will remain disconnected, until S2 closes _and_ S1 is momentarily closed. JF
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