I want to cut AC power if the temperature drops below a close-to-freezing
temp, and I want it to work even if there's no power (takes care of the
power fails first then system freezes then power is restored - bang goes
pump motor). This needs to be accurate to about 1-2 degrees.

"unk" wrote in message
news
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care of
the
power fails first then system freezes then power is restored - bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

Can you accurately set and measure its trip point?

On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a close-to-freezing
temp, and I want it to work even if there's no power (takes care of the
power fails first then system freezes then power is restored - bang goes
pump motor). This needs to be accurate to about 1-2 degrees.

I did a lot of experimenting trying to use a thermostat to turn on
heat tape. You'd think that you could repurpose a mechanical HVAC
thermostat,
but I was unsuccessful. There's so little force that a tiny stress
on the case throws the setpoint way off. I didn't find any mechanical
systems for sale that had anywhere near 1-2 degrees F accuracy or
setability or stability.

A digital HVAC thermostat won't go that low.
I shunted the thermistor and created a calibration chart
for the range around freezing.
Has battery backup, so that's a possibility. I don't remember
exactly why I didn't stick with that one. It may have
had something to do with wanting remote sensing inside the
pipe insulation.

This device
http://www.buyincoins.com/item/45040.html#.WQDMNLkpV7k
works, but it's not passive, so won't
work if the power fails. Battery backup could solve that problem.
If you put a switch in the power to the displays, it shouldn't
take much to battery back it.
There are other devices linked to that page that are packaged.

I finally replaced it with a plug-in device from the hardware store.
Looks like a three-way AC socket expander designed for controlling heat
tape.
Nowhere near the accuracy, but it does the job at the expense of
running the heat tape at unnecessarily high temperatures.

The solution to a problem starts with a clear definition.

Are you talking degrees F or C?
"Bang" suggest that your pump is frozen and the rotor locked.
Can you not protect that with a breaker?
What is the "system?" Interesting that it can tolerate
freezing other than the pump issue. Most pumps I know
about will bust if you freeze them.
Does the system have to reset itself when the temperature
goes up?
Do different parts of the system freeze/thaw at different
rates?
Is it always the same? For example, does the same part
of the system freeze first with an east wind or a west wind?
What are the consequences of a false trip?
How long does it take to unfreeze?
How many measurement points do you need?
How long does it stay frozen? Battery backup practical?

Using my best psychic vision to make up a scenario,
I'd power the pump using a relay. Power the relay from
the pump side, so if the power goes off, it stays off.
You might want some delay in that so it doesn't go off
on a power glitch. That implies some sort of battery
backup, but it doesn't have to hold more than a few seconds.

A thermostat similar to the one referenced above can do the
thermal shutdown. If you want it to come back up on its own,
you'll need battery backup for that as well.

Are we having fun yet?

"mike" wrote in message
news
On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care of
the
power fails first then system freezes then power is restored - bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

I did a lot of experimenting trying to use a thermostat to turn on
heat tape. You'd think that you could repurpose a mechanical HVAC
thermostat,
but I was unsuccessful. There's so little force that a tiny stress
on the case throws the setpoint way off. I didn't find any
mechanical
systems for sale that had anywhere near 1-2 degrees F accuracy or
setability or stability.

A digital HVAC thermostat won't go that low.
I shunted the thermistor and created a calibration chart
for the range around freezing.
Has battery backup, so that's a possibility. I don't remember
exactly why I didn't stick with that one. It may have
had something to do with wanting remote sensing inside the
pipe insulation.

This device
http://www.buyincoins.com/item/45040.html#.WQDMNLkpV7k
works, but it's not passive, so won't
work if the power fails. Battery backup could solve that problem.
If you put a switch in the power to the displays, it shouldn't
take much to battery back it.
There are other devices linked to that page that are packaged.

I finally replaced it with a plug-in device from the hardware store.
Looks like a three-way AC socket expander designed for controlling
heat tape.
Nowhere near the accuracy, but it does the job at the expense of
running the heat tape at unnecessarily high temperatures.

The solution to a problem starts with a clear definition.

Are you talking degrees F or C?
"Bang" suggest that your pump is frozen and the rotor locked.
Can you not protect that with a breaker?
What is the "system?" Interesting that it can tolerate
freezing other than the pump issue. Most pumps I know
about will bust if you freeze them.
Does the system have to reset itself when the temperature
goes up?
Do different parts of the system freeze/thaw at different
rates?
Is it always the same? For example, does the same part
of the system freeze first with an east wind or a west wind?
What are the consequences of a false trip?
How long does it take to unfreeze?
How many measurement points do you need?
How long does it stay frozen? Battery backup practical?

Using my best psychic vision to make up a scenario,
I'd power the pump using a relay. Power the relay from
the pump side, so if the power goes off, it stays off.
You might want some delay in that so it doesn't go off
on a power glitch. That implies some sort of battery
backup, but it doesn't have to hold more than a few seconds.

A thermostat similar to the one referenced above can do the
thermal shutdown. If you want it to come back up on its own,
you'll need battery backup for that as well.

Are we having fun yet?

http://www.ebay.com/bhp/capillary-thermostat

On Wed, 26 Apr 2017 10:02:26 +0000 (UTC), unk wrote:

I want to cut AC power if the temperature drops below a close-to-freezing
temp, and I want it to work even if there's no power (takes care of the
power fails first then system freezes then power is restored - bang goes
pump motor). This needs to be accurate to about 1-2 degrees.

Check out solar water heating controllers. They're designed to
activate/deactivate pumps based on multiple sensors or snap switches,
including freeze sensors. You can reverse the contacts if needed with
an external relay.

On 4/26/2017 10:23 AM, Jim Wilkins wrote:
"mike" wrote in message
news
On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care of
the
power fails first then system freezes then power is restored - bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

I did a lot of experimenting trying to use a thermostat to turn on
heat tape. You'd think that you could repurpose a mechanical HVAC
thermostat,
but I was unsuccessful. There's so little force that a tiny stress
on the case throws the setpoint way off. I didn't find any
mechanical
systems for sale that had anywhere near 1-2 degrees F accuracy or
setability or stability.

A digital HVAC thermostat won't go that low.
I shunted the thermistor and created a calibration chart
for the range around freezing.
Has battery backup, so that's a possibility. I don't remember
exactly why I didn't stick with that one. It may have
had something to do with wanting remote sensing inside the
pipe insulation.

This device
http://www.buyincoins.com/item/45040.html#.WQDMNLkpV7k
works, but it's not passive, so won't
work if the power fails. Battery backup could solve that problem.
If you put a switch in the power to the displays, it shouldn't
take much to battery back it.
There are other devices linked to that page that are packaged.

I finally replaced it with a plug-in device from the hardware store.
Looks like a three-way AC socket expander designed for controlling
heat tape.
Nowhere near the accuracy, but it does the job at the expense of
running the heat tape at unnecessarily high temperatures.

The solution to a problem starts with a clear definition.

Are you talking degrees F or C?
"Bang" suggest that your pump is frozen and the rotor locked.
Can you not protect that with a breaker?
What is the "system?" Interesting that it can tolerate
freezing other than the pump issue. Most pumps I know
about will bust if you freeze them.
Does the system have to reset itself when the temperature
goes up?
Do different parts of the system freeze/thaw at different
rates?
Is it always the same? For example, does the same part
of the system freeze first with an east wind or a west wind?
What are the consequences of a false trip?
How long does it take to unfreeze?
How many measurement points do you need?
How long does it stay frozen? Battery backup practical?

Using my best psychic vision to make up a scenario,
I'd power the pump using a relay. Power the relay from
the pump side, so if the power goes off, it stays off.
You might want some delay in that so it doesn't go off
on a power glitch. That implies some sort of battery
backup, but it doesn't have to hold more than a few seconds.

A thermostat similar to the one referenced above can do the
thermal shutdown. If you want it to come back up on its own,
you'll need battery backup for that as well.

Are we having fun yet?

http://www.ebay.com/bhp/capillary-thermostat


Most of those don't have specs, but the cheap ones that do
are as bad as:
On-off Window : less than 16„ƒ
That's a mighty big hysteresis compared to the OP request.
Something to watch out for.

On Wed, 26 Apr 2017 10:02:26 +0000 (UTC), unk wrote:

I want to cut AC power if the temperature drops below a close-to-freezing
temp, and I want it to work even if there's no power (takes care of the
power fails first then system freezes then power is restored - bang goes
pump motor). This needs to be accurate to about 1-2 degrees.

Standard temperature switch.

https://www.google.com/search?q=temp...utf-8&oe=utf-8

If its to be in a fixed location, a less hardy version can be used

They have been around for at least 100 yrs


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

"mike" wrote in message
news
On 4/26/2017 10:23 AM, Jim Wilkins wrote:
"mike" wrote in message
news
On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care
of
the
power fails first then system freezes then power is restored -
bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

I did a lot of experimenting trying to use a thermostat to turn on
heat tape. You'd think that you could repurpose a mechanical HVAC
thermostat,
but I was unsuccessful. There's so little force that a tiny
stress
on the case throws the setpoint way off. I didn't find any
mechanical
systems for sale that had anywhere near 1-2 degrees F accuracy or
setability or stability.

A digital HVAC thermostat won't go that low.
I shunted the thermistor and created a calibration chart
for the range around freezing.
Has battery backup, so that's a possibility. I don't remember
exactly why I didn't stick with that one. It may have
had something to do with wanting remote sensing inside the
pipe insulation.

This device
http://www.buyincoins.com/item/45040.html#.WQDMNLkpV7k
works, but it's not passive, so won't
work if the power fails. Battery backup could solve that problem.
If you put a switch in the power to the displays, it shouldn't
take much to battery back it.
There are other devices linked to that page that are packaged.

I finally replaced it with a plug-in device from the hardware
store.
Looks like a three-way AC socket expander designed for controlling
heat tape.
Nowhere near the accuracy, but it does the job at the expense of
running the heat tape at unnecessarily high temperatures.

The solution to a problem starts with a clear definition.

Are you talking degrees F or C?
"Bang" suggest that your pump is frozen and the rotor locked.
Can you not protect that with a breaker?
What is the "system?" Interesting that it can tolerate
freezing other than the pump issue. Most pumps I know
about will bust if you freeze them.
Does the system have to reset itself when the temperature
goes up?
Do different parts of the system freeze/thaw at different
rates?
Is it always the same? For example, does the same part
of the system freeze first with an east wind or a west wind?
What are the consequences of a false trip?
How long does it take to unfreeze?
How many measurement points do you need?
How long does it stay frozen? Battery backup practical?

Using my best psychic vision to make up a scenario,
I'd power the pump using a relay. Power the relay from
the pump side, so if the power goes off, it stays off.
You might want some delay in that so it doesn't go off
on a power glitch. That implies some sort of battery
backup, but it doesn't have to hold more than a few seconds.

A thermostat similar to the one referenced above can do the
thermal shutdown. If you want it to come back up on its own,
you'll need battery backup for that as well.

Are we having fun yet?

http://www.ebay.com/bhp/capillary-thermostat


Most of those don't have specs, but the cheap ones that do
are as bad as:
On-off Window : less than 16?
That's a mighty big hysteresis compared to the OP request.
Something to watch out for.

That's why I asked how accurately he could measure temperature. The
hysteresis is necessary if the thermostat has to switch high current,
because the differential gives it the energy to snap open quickly to
break the arc.

Home heating thermostats compensate for the hysteresis with an
internal heater.
http://inspectapedia.com/heat/Heat-A...-Operation.php

On 2017-04-26, Jim Wilkins wrote:
"mike" wrote in message
news
On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care of
the
power fails first then system freezes then power is restored - bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

[ ... ]

http://www.ebay.com/bhp/capillary-thermostat

Not the same, but it reminds me of something used for
temperature controlling a circulating water bath.

It is a mercury thermometer with one wire through the bulb and
contacting the mercury in the bulb. The other end is a very fine wire,
inside the bore of the capillary, and adjusted up or down by turning a
magnet over the top end of the device. (That turns a wire wrapped around
the fine wire, and moves it up and down as desired.

The limiting factor is that the wire and mercury cannot
interrupt more than a 100 uA of current, so you would need battery
backup to a circuit to amplify the current to open the power relay to
the pump.

The bath that I first saw one in, and that I use one in (thanks
to a hamfest) was German made. I lucked into the thermometer part
later, at a tools flea-market, because the original thermometer had been
broken in the assembly before I got it. (I picked it up with the idea
of controlling temperatures for color photo processing.) It was settable
to well less than one degree F.

The box mine came in has a label from Fischer Scientific, and is
marked:

Thermoregulator
Roto-Stat

Cat No, 15-180-5

Following that, I find the following:

http://www.philadelphiainstrument.com/thermoregulators.asp

Download the pdf instruction sheet. You will find two of the
listed models to be within your range needs:


================================================== ====================
62451 -35 to 500 F 0.005 F
62542 -35 to 135 F 0.02 F
================================================== ====================

No clue as to the prices. I guess that you'll have to call
them, and be sitting down when you call. :-)

Good luck,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote in message
...
On 2017-04-26, Jim Wilkins wrote:
"mike" wrote in message
news
On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care
of
the
power fails first then system freezes then power is restored -
bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

[ ... ]

http://www.ebay.com/bhp/capillary-thermostat

Not the same, but it reminds me of something used for
temperature controlling a circulating water bath.

It is a mercury thermometer with one wire through the bulb and
contacting the mercury in the bulb. The other end is a very fine
wire,
inside the bore of the capillary, and adjusted up or down by turning
a
magnet over the top end of the device. (That turns a wire wrapped
around
the fine wire, and moves it up and down as desired.

The limiting factor is that the wire and mercury cannot
interrupt more than a 100 uA of current, so you would need battery
backup to a circuit to amplify the current to open the power relay
to
the pump.

The bath that I first saw one in, and that I use one in (thanks
to a hamfest) was German made. I lucked into the thermometer part
later, at a tools flea-market, because the original thermometer had
been
broken in the assembly before I got it. (I picked it up with the
idea
of controlling temperatures for color photo processing.) It was
settable
to well less than one degree F.

The box mine came in has a label from Fischer Scientific, and is
marked:

Thermoregulator
Roto-Stat

Cat No, 15-180-5

Following that, I find the following:

http://www.philadelphiainstrument.com/thermoregulators.asp

Download the pdf instruction sheet. You will find two of the
listed models to be within your range needs:


================================================== ====================
62451 -35 to 500 F 0.005 F
62542 -35 to 135 F 0.02 F
================================================== ====================

No clue as to the prices. I guess that you'll have to call
them, and be sitting down when you call. :-)

Good luck,
DoN.

These made accurate mechanical thermostats obsolete:
https://www.amazon.com/AGPtek-Digita.../dp/B00BVWYH5A
-jsw

On 04/26/2017 7:39 PM, Jim Wilkins wrote:
....

These made accurate mechanical thermostats obsolete:
https://www.amazon.com/AGPtek-Digita.../dp/B00BVWYH5A

https://goo.gl/f7e2Np is another alternative. I used one to put an
alarm in the well house if temp drops after the weekend last winter we
were -14F and the gas heater went out and froze up the pressure tank.
Took most of a day and a half to thaw it out; fortunately nothing broke.

I've got it on a wall-wart at the moment but it could easily run off
battery for ages and a small rechargeable w/ solar or the like could
make it independent...

I figured the C/F thingie would be easily done in the setup but these
are C only; I've seen datasteet for the same board but with the display
in F altho I couldn't find a link quickly today. When I looked just for
curiosity last January, seemed like they were going for $10-12/ea
whereas these are essentially throwaways at $3 or so with, some anyway,
free shipping to boot...

Works as advertised...all I added was a regulator as the power supply I
robbed was a little "hot" and noisy altho it ran directly off that
supply figured for long-term duty would be better to clean it up just a
little. I'm just driving the LED that can see from the house at night
if temp drops; add an interposing relay if need more current draw than
the onboard will supply but iirc it'll handle a fair load on its own.

--

On 2017-04-27, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-04-26, Jim Wilkins wrote:
"mike" wrote in message
news On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes care
of
the
power fails first then system freezes then power is restored -
bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

[ ... ]

http://www.ebay.com/bhp/capillary-thermostat

Not the same, but it reminds me of something used for
temperature controlling a circulating water bath.


http://www.philadelphiainstrument.com/thermoregulators.asp

[ ... ]

These made accurate mechanical thermostats obsolete:
https://www.amazon.com/AGPtek-Digita.../dp/B00BVWYH5A
-jsw


Agreed! I have a nice one by Omega for my heat-tread oven which
can be turned on, set for 1800 F, and overshoot by only one degree F.
(It pauses about 3/4 of the way to temperature and stops heating for a
bit to calculate the overshoot and compensate for it.)

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple of
relays, could do it -- with minimal battery backup. And the learning
curve, with all of the options which can be set in the controllers, may
be a problem.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote in message
...
On 2017-04-27, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-04-26, Jim Wilkins wrote:
"mike" wrote in message
news On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a
close-to-freezing
temp, and I want it to work even if there's no power (takes
care
of
the
power fails first then system freezes then power is restored -
bang
goes
pump motor). This needs to be accurate to about 1-2 degrees.

[ ... ]

http://www.ebay.com/bhp/capillary-thermostat

Not the same, but it reminds me of something used for
temperature controlling a circulating water bath.


http://www.philadelphiainstrument.com/thermoregulators.asp

[ ... ]

These made accurate mechanical thermostats obsolete:
https://www.amazon.com/AGPtek-Digita.../dp/B00BVWYH5A
-jsw


Agreed! I have a nice one by Omega for my heat-tread oven which
can be turned on, set for 1800 F, and overshoot by only one degree
F.
(It pauses about 3/4 of the way to temperature and stops heating for
a
bit to calculate the overshoot and compensate for it.)

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple of
relays, could do it -- with minimal battery backup. And the
learning
curve, with all of the options which can be set in the controllers,
may
be a problem.

Enjoy,
DoN.

I don't know where to buy a cheap, accurate and reliable one. 100C
switches can be found in hot pots and rice cookers, the application
for non-adjustable low temp switches is to protect dehumidifier
evaporator coils etc from icing but AFAIK they switch somewhat higher
than 0C to allow for tolerances and as noted have a considerable
differential. I tested a Thermocube pipe heater switch that tripped at
an outer temperature of 27F, perhaps because I cooled it faster than
it would inside an unheated house.

One of my early jobs was building custom industrial temperature
cycling ovens. When I compared the scattered readings on a 12 channel
chart recorder I found that measuring temperatures accurately was much
harder than it seems. If possible I insert an electrically isolated
thermocouple into a drilled hole in the component, its heatsink or a
thick washer under a mounting screw.

My home instruments resolve to 0.1F and show that simply approaching
the sensor throws it off by several tenths. Melting snow in a
styrofoam cup is a pretty stable 32F/0C reference but the reading of
rapidly boiling water bounces around by several degrees, on the thin
Inconel probe Omega custom-made for me (twice, to get it right) .

The thermostat in my fridge seems to hold its settings within about
one degree F. The differential is about 5 degrees, ie on at 31F, off
at 26F, where frozen food stays frosted but liquids other than water
don't freeze solid. Room temperature affects the setting somewhat so I
have to reset it for summer or winter which is why I've measured its
cycling with a Fluke 52 thermocouple meter.

I've had 12V 18A-h AGM batteries go bad in about two years, both new
ones in storage and second-hand ones that had been replaced on a
schedule. The voltage is correct but the impedance becomes high.
Charging and cycling restored some of them.
https://www.bobistheoilguy.com/forum...Number=3169459

I personally wouldn't use them in a critical application like freeze
protection unless they were located where they could easily be checked
on a schedule, meaning not in the middle of the garage ceiling. I've
been experimenting with using the HF carbon pile battery tester to
measure how much current they can actually supply when loaded down to
10V. This is quick and easy but does NOT correlate well with remaining
capacity.
http://batteryuniversity.com/learn/a...and_resistance
-jsw

On 04/26/2017 9:48 PM, DoN. Nichols wrote:
....

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple of
relays, could do it -- with minimal battery backup. And the learning
curve, with all of the options which can be set in the controllers, may
be a problem.
....

Actually, re-reading his original post, don't need battery backup, use
the NO contact so will open on loss of power. Set the hysteresis value
on the reclose coming back up to protect restoration if were to be
cold-enough for freeze to have occurred. That's doable with the little
board I posted link to simply by programming the builtin firmware; no
coding needed.

--

On Wednesday, April 26, 2017 at 1:11:29 PM UTC-4, mike wrote:
On 4/26/2017 3:02 AM, unk wrote:
I want to cut AC power if the temperature drops below a close-to-freezing
temp, and I want it to work even if there's no power (takes care of the
power fails first then system freezes then power is restored - bang goes
pump motor). This needs to be accurate to about 1-2 degrees.

I did a lot of experimenting trying to use a thermostat to turn on
heat tape. You'd think that you could repurpose a mechanical HVAC
thermostat,
but I was unsuccessful. There's so little force that a tiny stress
on the case throws the setpoint way off. I didn't find any mechanical
systems for sale that had anywhere near 1-2 degrees F accuracy or
setability or stability.

A digital HVAC thermostat won't go that low.
I shunted the thermistor and created a calibration chart
for the range around freezing.
Has battery backup, so that's a possibility. I don't remember
exactly why I didn't stick with that one. It may have
had something to do with wanting remote sensing inside the
pipe insulation.

This device
http://www.buyincoins.com/item/45040.html#.WQDMNLkpV7k
works, but it's not passive, so won't
work if the power fails. Battery backup could solve that problem.
If you put a switch in the power to the displays, it shouldn't
take much to battery back it.
There are other devices linked to that page that are packaged.

I finally replaced it with a plug-in device from the hardware store.
Looks like a three-way AC socket expander designed for controlling heat
tape.
Nowhere near the accuracy, but it does the job at the expense of
running the heat tape at unnecessarily high temperatures.

The solution to a problem starts with a clear definition.

Are you talking degrees F or C?
"Bang" suggest that your pump is frozen and the rotor locked.
Can you not protect that with a breaker?
What is the "system?" Interesting that it can tolerate
freezing other than the pump issue. Most pumps I know
about will bust if you freeze them.
Does the system have to reset itself when the temperature
goes up?
Do different parts of the system freeze/thaw at different
rates?
Is it always the same? For example, does the same part
of the system freeze first with an east wind or a west wind?
What are the consequences of a false trip?
How long does it take to unfreeze?
How many measurement points do you need?
How long does it stay frozen? Battery backup practical?

Using my best psychic vision to make up a scenario,
I'd power the pump using a relay. Power the relay from
the pump side, so if the power goes off, it stays off.
You might want some delay in that so it doesn't go off
on a power glitch. That implies some sort of battery
backup, but it doesn't have to hold more than a few seconds.

A thermostat similar to the one referenced above can do the
thermal shutdown. If you want it to come back up on its own,
you'll need battery backup for that as well.

Are we having fun yet?

I've got an old mercury relay thermostat that I put in the
garage to keep the temp at ~45-50 F. It doesn't go that low, but I tipped
it sideways and it works. I don't know if it would go all the way down
to 32 F. (and it won't have 1-2 degrees of accuracy.) I guess one could
experiment in a frig or freezer. It'd have to drive some other AC power relay... I don't quite understand his no power spec.

George h.

On 04/26/2017 9:48 PM, DoN. Nichols wrote:
....

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple of
relays, could do it -- with minimal battery backup. And the learning
curve, with all of the options which can be set in the controllers, may
be a problem.
....

Don't know why didn't think of it before, just a thermistor in the
control circuit...hadn't thought of it before then, but the HVAC
contractor when we installed the geothermal loop added it to prevent
backup resistance heating elements from coming on until outside temp was
~25F...worked just spiffy keen.

Until, of course, we went to sell the house and the buyer's inspector
couldn't figure why it wouldn't turn on and claimed needed fixing and
I'd forgotten about it being there by then...

--

On 2017-04-27, dpb wrote:
On 04/26/2017 9:48 PM, DoN. Nichols wrote:
...

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple of
relays, could do it -- with minimal battery backup. And the learning
curve, with all of the options which can be set in the controllers, may
be a problem.
...

Actually, re-reading his original post, don't need battery backup, use
the NO contact so will open on loss of power. Set the hysteresis value
on the reclose coming back up to protect restoration if were to be
cold-enough for freeze to have occurred. That's doable with the little
board I posted link to simply by programming the builtin firmware; no
coding needed.

How will the board continue to work without backup power?

As for the mercury-column thermometers controllers which I
pointed to earlier are NO, closing when the temperature reaches the set
point. But -- with the limit of 100 uA through the mercury and moving
set-point contact, you need at least a transistor to control the current
through the relay, and you *will* need power -- AC power supply, or a
battery backup -- to make it continue to work during power outages.

And, since I don't know what the price is for these, I have no
idea how affordable they will be for the task -- but they are fragile.
They *do* have a hysteresis of less than a degree F.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 04/28/2017 10:15 PM, DoN. Nichols wrote:
On 2017-04-27, wrote:
On 04/26/2017 9:48 PM, DoN. Nichols wrote:
...

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple of
relays, could do it -- with minimal battery backup. And the learning
curve, with all of the options which can be set in the controllers, may
be a problem.
...

Actually, re-reading his original post, don't need battery backup, use
the NO contact so will open on loss of power. Set the hysteresis value
on the reclose coming back up to protect restoration if were to be
cold-enough for freeze to have occurred. That's doable with the little
board I posted link to simply by programming the builtin firmware; no
coding needed.

How will the board continue to work without backup power?

....

That's the point; it doesn't need to.

--

"DoN. Nichols" wrote in message
...
On 2017-04-27, dpb wrote:
On 04/26/2017 9:48 PM, DoN. Nichols wrote:
...

But he was looking for something mechanical -- or with a minimum
of electrical, so something like what I pointed to, with a couple
of
relays, could do it -- with minimal battery backup. And the
learning
curve, with all of the options which can be set in the
controllers, may
be a problem.
...

Actually, re-reading his original post, don't need battery backup,
use
the NO contact so will open on loss of power. Set the hysteresis
value
on the reclose coming back up to protect restoration if were to be
cold-enough for freeze to have occurred. That's doable with the
little
board I posted link to simply by programming the builtin firmware;
no
coding needed.

How will the board continue to work without backup power?

As for the mercury-column thermometers controllers which I
pointed to earlier are NO, closing when the temperature reaches the
set
point. But -- with the limit of 100 uA through the mercury and
moving
set-point contact, you need at least a transistor to control the
current
through the relay, and you *will* need power -- AC power supply, or
a
battery backup -- to make it continue to work during power outages.

And, since I don't know what the price is for these, I have no
idea how affordable they will be for the task -- but they are
fragile.
They *do* have a hysteresis of less than a degree F.

Enjoy,
DoN.

I just remembered the words to search for.
http://www.sensata.com/klixon/thermostat-hvac-20600.htm

-jsw

On 04/29/2017 6:21 AM, Jim Wilkins wrote:
....

I just remembered the words to search for.
http://www.sensata.com/klixon/thermostat-hvac-20600.htm

Interesting...the interesting group from the spec table.

Highest Standard
Temperature Nominal Tolerances
Setting Differential Open Close
oF oF oF
-10 to 80 10 to 14* ±5 ±5
15 to 29 ±6 ±6
30 to 59 ±6 ±7
60 to 150 ±7 ±8

*Available in SPST construction only.

The biggest downside would appear that the only distributor I could find
that even listed a price quotes $250/ea; the rest are "Quote". One
knows when in that ballgame the answer is never going to be one one
wants...

--

On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
....

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized once
it's even remotely close to freezing, anyway...a solution looking for a
problem here.

--

On Sat, 29 Apr 2017 08:24:04 -0500, dpb wrote:

On 04/29/2017 6:21 AM, Jim Wilkins wrote:
...

I just remembered the words to search for.
http://www.sensata.com/klixon/thermostat-hvac-20600.htm

Interesting...the interesting group from the spec table.

Highest Standard
Temperature Nominal Tolerances
Setting Differential Open Close
oF oF oF
-10 to 80 10 to 14* ±5 ±5
15 to 29 ±6 ±6
30 to 59 ±6 ±7
60 to 150 ±7 ±8

*Available in SPST construction only.

The biggest downside would appear that the only distributor I could find
that even listed a price quotes $250/ea; the rest are "Quote". One
knows when in that ballgame the answer is never going to be one one
wants...

I've purchased small qtys from Grainger in the past, not sure what
they stock these days. I don't think they we're more than $10 to $15.

I recently purchased a selection on ebay from China to build a Murphy
switch for my tractor for unattended running of a PTO generator. It's
a '54 Farmall with thermo-syphon cooling system -- no water pump or
ports for a sensor, so I hope to find a place where a contact switch
will work.

I can't vouch for the calibration accuracy, but they're cheap enough
to experiment with.
http://www.ebay.com/sch/i.html?_from...SD301&_sacat=0

--
Ned Simmons

"dpb" wrote in message
news
On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint, when
power comes back on the relay won't close to restore power to AC if
the temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized
once it's even remotely close to freezing, anyway...a solution
looking for a problem here.

--

I guessed that it was a DIY solar water heater. For a one-off home
project there are thermal switches in discarded refrigerators and air
conditioners that might be suitable. Some are open-on-rise and may
require a relay, perhaps a solid state one to avoid opening during the
pump's starting surge.

-jsw

On Sat, 29 Apr 2017 12:08:18 -0400, "Jim Wilkins"
wrote:

"dpb" wrote in message
news
On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint, when
power comes back on the relay won't close to restore power to AC if
the temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized
once it's even remotely close to freezing, anyway...a solution
looking for a problem here.

--

I guessed that it was a DIY solar water heater. For a one-off home
project there are thermal switches in discarded refrigerators and air
conditioners that might be suitable. Some are open-on-rise and may
require a relay, perhaps a solid state one to avoid opening during the
pump's starting surge.

-jsw

If it's a solar water heater, then products like this with built in
freeze protection are readily available.
http://www.solarproject.co.uk/manual...structions.pdf

Under "frost protection" it seems to ignore drain down/back valves,
which are common in plain-water, uninsulated-collector setups.

On 04/29/2017 11:08 AM, Jim Wilkins wrote:
wrote in message
....

Which use begs the question of why OP would leave the AC energized
once it's even remotely close to freezing, anyway...a solution
looking for a problem here.

....

I guessed that it was a DIY solar water heater. ...

Probably better guess--I see on reading again what I skimmed as
AC" was "AC power"...

--

On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:

On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized once
it's even remotely close to freezing, anyway...a solution looking for a
problem here.


It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above freezing
when the users leave. They are supposed to drain the water as well.

But sometime they don't set it, and sometimes they don't drain the water
system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch that
will cut power to the relay.

Educating the users has not worked (twice, counting the number of times
pumps broke and pipes-had-to-be-replaced). A machine you only have to
educate once.

"unk" wrote in message
news
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:

On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if
use
the NO contact and the "COOL" side so closes on TSetpoint, when
power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized
once
it's even remotely close to freezing, anyway...a solution looking
for a
problem here.


It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing
when the users leave. They are supposed to drain the water as well.

But sometime they don't set it, and sometimes they don't drain the
water
system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to
the
pump) and a electrically operated valve, but for b) I need a switch
that
will cut power to the relay.

Educating the users has not worked (twice, counting the number of
times
pumps broke and pipes-had-to-be-replaced). A machine you only have
to
educate once.

I gave you several suppliers and search terms. Usually switches need
to close near freezing to turn on heat, except for refrigeration
thermostats which open when cold. However the fixed-setting
replacements I found had a wide tolerance, which is why I would use an
adjustable thermostat and test its setting, differential and
repeatability.

-jsw

On 04/30/2017 6:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:
....

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint,
when power comes back on the relay won't close to restore power to
AC if the temperature is below the turn-on setpoint.

....

It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing when the users leave. They are supposed to drain the water
as well.

But sometime they don't set it, and sometimes they don't drain the
water system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to
the pump) and a electrically operated valve, but for b) I need a
switch that will cut power to the relay.
....

You're still going to have to have aux power to operate the valve when
power goes out for a) then.

Are these "other people" family or renters? Would seem a damages clause
would be appropriate in the rental agreement if the latter; some
personal responsibility in case of the former altho that seems often the
most lacking place to find same, unfortunately.

--

On Sun, 30 Apr 2017 08:37:12 -0500, dpb wrote:

On 04/30/2017 6:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:
...

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint,
when power comes back on the relay won't close to restore power to
AC if the temperature is below the turn-on setpoint.

...

It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing when the users leave. They are supposed to drain the water
as well.

But sometime they don't set it, and sometimes they don't drain the
water system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to
the pump) and a electrically operated valve, but for b) I need a
switch that will cut power to the relay.
...

You're still going to have to have aux power to operate the valve when
power goes out for a) then.

Normally closed solenoid valve, or "power pill" valve. Don't know if
they still make the latter. Regardless, probably going to need a vent,
which can be passive but a potential PITA.

On Sun, 30 Apr 2017 11:29:52 +0000 (UTC), unk wrote:

On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:

On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized once
it's even remotely close to freezing, anyway...a solution looking for a
problem here.


It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above freezing
when the users leave. They are supposed to drain the water as well.

But sometime they don't set it, and sometimes they don't drain the water
system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch that
will cut power to the relay.

Educating the users has not worked (twice, counting the number of times
pumps broke and pipes-had-to-be-replaced). A machine you only have to
educate once.

http://orbitalock.en.made-in-china.c...ain-Power.html

Use one of these switches. Tell them that visa and master cards
activate the switch and if they forget to remove it repairs will be
charged to the forgotten credit card.

"dpb" wrote in message
news
On 04/30/2017 6:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:
...

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint,
when power comes back on the relay won't close to restore power to
AC if the temperature is below the turn-on setpoint.

...

It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing when the users leave. They are supposed to drain the
water
as well.

But sometime they don't set it, and sometimes they don't drain the
water system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to
the pump) and a electrically operated valve, but for b) I need a
switch that will cut power to the relay.
...

You're still going to have to have aux power to operate the valve
when power goes out for a) then.

Are these "other people" family or renters? Would seem a damages
clause would be appropriate in the rental agreement if the latter;
some personal responsibility in case of the former altho that seems
often the most lacking place to find same, unfortunately.

--

A normally open solenoid valve to drain the pipes and a vacuum breaker
outside faucet should do it.

Here's a valve that opens below 35F.
https://www.bradleycorp.com/safety/t...tection-valves
-jsw

On Sun, 30 Apr 2017 08:37:12 -0500, dpb wrote:

On 04/30/2017 6:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:
...

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

...

It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above
freezing when the users leave. They are supposed to drain the water as
well.

But sometime they don't set it, and sometimes they don't drain the
water system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch
that will cut power to the relay.
...

You're still going to have to have aux power to operate the valve when
power goes out for a) then.


No, I'm getting the kind of valve that is open when there's no power.

On 4/30/2017 4:29 AM, unk wrote:
On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:

On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized once
it's even remotely close to freezing, anyway...a solution looking for a
problem here.


It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above freezing
when the users leave.
So, you do already have a thermostat that is sufficiently accurate
to do what you need.

Add a second thermostat in parallel with the first one.
Hide it or lock it so the +5 degree one can't be modified.


They are supposed to drain the water as well.

But sometime they don't set it, and sometimes they don't drain the water
system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

That depends a lot on:
How long do they stay?
How cold does it get?
What keeps the pipes from freezing when it's occupied?

Use a wind-up timer that they have to wind up every day and
push the reset button that restarts the pump if they forgot.
Use a random Klixon sensor at a temp high enough that
tolerances don't matter.

If the timer runs out and the temp is below 40F or
the power is out,
shut off the pump, drain the system. Maybe even disconnect
the adjustable thermostat and use the 5F one.

This assumes that there's no downside to drain the system
and disable the pump when it's hot outside and unoccupied.
The devil is in the details.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch that
will cut power to the relay.

Educating the users has not worked (twice, counting the number of times
pumps broke and pipes-had-to-be-replaced). A machine you only have to
educate once.

On Sun, 30 Apr 2017 11:29:52 +0000 (UTC), unk wrote:

On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:

On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if use
the NO contact and the "COOL" side so closes on TSetpoint, when power
comes back on the relay won't close to restore power to AC if the
temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized once
it's even remotely close to freezing, anyway...a solution looking for a
problem here.


It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above freezing
when the users leave. They are supposed to drain the water as well.

But sometime they don't set it, and sometimes they don't drain the water
system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch that
will cut power to the relay.

Educating the users has not worked (twice, counting the number of times
pumps broke and pipes-had-to-be-replaced). A machine you only have to
educate once.

Change the locks and tell them that when:
1) they have paid for the cost of the 2x repairs already made,
and
2) they are ready to accept the responsibility they are assumed to
have when they inhabit the cottage,

it will again be made available.

The visa card switch might work, too.


But I'd set it up so cottage heaters were on 24 hr timers which had to
be set each day they were there. And water pumps were in a heated
area which automatically engaged to prevent freezing in the first
place. That would require backup batteries and perhaps internet
alarms, if not solar chargers.

--
Well, the trouble with our liberal friends is not that they
are ignorant, but that they know so much that isn’t so.
--Ronald Reagan

On Sat, 29 Apr 2017 10:22:42 -0400, Ned Simmons
wrote:

. It's
a '54 Farmall with thermo-syphon cooling system -- no water pump or
ports for a sensor, so I hope to find a place where a contact switch
will work.

If you need to borrow a drill bit and proper pipe thread tap, Id be
happy to send you one.


---
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