Honeywell thermostat

L

LSMFT

Guest
This thermostat I have has a mechanical relay. But.... When closed is a
closed circuit or dead short, fine that works for me. BUT when it's open
it still has 20 ohms and will not shut off a circulator. Why in hell do
they make it have 20 ohms when it's open?????? It should be infinity.




--
LSMFT

Simple job, assist the assistant of the physicist.
 
LSMFT wrote:
This thermostat I have has a mechanical relay. But.... When closed is a
closed circuit or dead short, fine that works for me. BUT when it's open
it still has 20 ohms and will not shut off a circulator. Why in hell do
they make it have 20 ohms when it's open?????? It should be infinity.
Click to expand...


Not if you want the anticipator to work.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
 
This thermostat I have has a mechanical relay. But.... When closed is a
closed circuit or dead short, fine that works for me. BUT when it's open
it still has 20 ohms and will not shut off a circulator. Why in hell do
they make it have 20 ohms when it's open?????? It should be infinity.
Click to expand...
I suspect that might be the resistance of the "anticipator"... a small
built-in heater, which is normally energized when the furnace is
running. The heat it generates, helps cancel out the effect of
thermal lag (i.e. the room air heats up faster than the bulky
thermostat does) and improves the ability of the thermostat to maintain
good temperature control.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
 
On 10/30/2010 1:34 AM, Dave Platt wrote:
This thermostat I have has a mechanical relay. But.... When closed is a
closed circuit or dead short, fine that works for me. BUT when it's open
it still has 20 ohms and will not shut off a circulator. Why in hell do
they make it have 20 ohms when it's open?????? It should be infinity.

I suspect that might be the resistance of the "anticipator"... a small
built-in heater, which is normally energized when the furnace is
running. The heat it generates, helps cancel out the effect of
thermal lag (i.e. the room air heats up faster than the bulky
thermostat does) and improves the ability of the thermostat to maintain
good temperature control.

All of the heat anticipators I've seen, have been in series with the
Click to expand...
heat contact, not in parallel. The anticipators for cooling are
generally across the cool contact. That's the way I've seen it for
mechanical thermostats. But, most of the good electronic
thermostats have the anticipator function built into the software.
So if the thermostat is electronic with a relay driving the output,
I'd suspect something is wrong. Some electronic thermostats have
triacs in the output, which can have leakages. I've had one that
actually slightly hold open the gas valve. Honeywell confirmed that
they had a problem with some gas valves playing nice with some of
the triac models and sent me a new one, with a relay output.
 
Art Todesco wrote:
On 10/30/2010 1:34 AM, Dave Platt wrote:
This thermostat I have has a mechanical relay. But.... When closed is a
closed circuit or dead short, fine that works for me. BUT when it's open
it still has 20 ohms and will not shut off a circulator. Why in hell do
they make it have 20 ohms when it's open?????? It should be infinity.

I suspect that might be the resistance of the "anticipator"... a small
built-in heater, which is normally energized when the furnace is
running. The heat it generates, helps cancel out the effect of
thermal lag (i.e. the room air heats up faster than the bulky
thermostat does) and improves the ability of the thermostat to maintain
good temperature control.

All of the heat anticipators I've seen, have been in series with the
heat contact, not in parallel. The anticipators for cooling are
generally across the cool contact. That's the way I've seen it for
mechanical thermostats. But, most of the good electronic thermostats
have the anticipator function built into the software. So if the
thermostat is electronic with a relay driving the output, I'd suspect
something is wrong. Some electronic thermostats have triacs in the
output, which can have leakages. I've had one that actually slightly
hold open the gas valve. Honeywell confirmed that they had a problem
with some gas valves playing nice with some of the triac models and sent
me a new one, with a relay output.
Click to expand...
I put voltage across the relay contacts that were supposed to be open
and fried the electronics that was holding it partially closed.
Everything else still works and the relay still clicks. Now I can use
the contacts like a switch like I wanted in the first place.


--
LSMFT

Simple job, assist the assistant of the physicist.
 
On 10/30/2010 11:47 AM, LSMFT wrote:
I put voltage across the relay contacts that were supposed to be open
and fried the electronics that was holding it partially closed.
Everything else still works and the relay still clicks. Now I can use
the contacts like a switch like I wanted in the first place.
Click to expand...
Well...that's one way to fix it.

Jeff
 
Jeffrey Angus wrote:
On 10/30/2010 11:47 AM, LSMFT wrote:
I put voltage across the relay contacts that were supposed to be open
and fried the electronics that was holding it partially closed.
Everything else still works and the relay still clicks. Now I can use
the contacts like a switch like I wanted in the first place.

Well...that's one way to fix it.
Click to expand...

The Bill Turner way. :(


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
 
On 10/30/2010 12:47 PM, LSMFT wrote:
Art Todesco wrote:
On 10/30/2010 1:34 AM, Dave Platt wrote:
This thermostat I have has a mechanical relay. But.... When
closed is a
closed circuit or dead short, fine that works for me. BUT when
it's open
it still has 20 ohms and will not shut off a circulator. Why in
hell do
they make it have 20 ohms when it's open?????? It should be
infinity.

I suspect that might be the resistance of the "anticipator"... a
small
built-in heater, which is normally energized when the furnace is
running. The heat it generates, helps cancel out the effect of
thermal lag (i.e. the room air heats up faster than the bulky
thermostat does) and improves the ability of the thermostat to
maintain
good temperature control.

All of the heat anticipators I've seen, have been in series with the
heat contact, not in parallel. The anticipators for cooling are
generally across the cool contact. That's the way I've seen it for
mechanical thermostats. But, most of the good electronic thermostats
have the anticipator function built into the software. So if the
thermostat is electronic with a relay driving the output, I'd suspect
something is wrong. Some electronic thermostats have triacs in the
output, which can have leakages. I've had one that actually slightly
hold open the gas valve. Honeywell confirmed that they had a problem
with some gas valves playing nice with some of the triac models
and sent
me a new one, with a relay output.

I put voltage across the relay contacts that were supposed to be
open and fried the electronics that was holding it partially closed.
Everything else still works and the relay still clicks. Now I can
use the contacts like a switch like I wanted in the first place.


There was probably a contact protection network across the relay
Click to expand...
contact that got partially destroyed. There are lots of possible
protection networks including varistors, diodes, RC or RLC, etc.
You say it measured 20 ohms. Was that done with a standard
ohmmeter? And if so, if you reverse the meter's polarity, what
does it read. Well, I know you can't do that because it was smoked.
Of course, you are not supposed to put raw power across the
contact, even if it is open.
 
Art Todesco wrote:
On 10/30/2010 12:47 PM, LSMFT wrote:
Art Todesco wrote:
On 10/30/2010 1:34 AM, Dave Platt wrote:
This thermostat I have has a mechanical relay. But.... When
closed is a
closed circuit or dead short, fine that works for me. BUT when
it's open
it still has 20 ohms and will not shut off a circulator. Why in
hell do
they make it have 20 ohms when it's open?????? It should be
infinity.

I suspect that might be the resistance of the "anticipator"... a
small
built-in heater, which is normally energized when the furnace is
running. The heat it generates, helps cancel out the effect of
thermal lag (i.e. the room air heats up faster than the bulky
thermostat does) and improves the ability of the thermostat to
maintain
good temperature control.

All of the heat anticipators I've seen, have been in series with the
heat contact, not in parallel. The anticipators for cooling are
generally across the cool contact. That's the way I've seen it for
mechanical thermostats. But, most of the good electronic thermostats
have the anticipator function built into the software. So if the
thermostat is electronic with a relay driving the output, I'd suspect
something is wrong. Some electronic thermostats have triacs in the
output, which can have leakages. I've had one that actually slightly
hold open the gas valve. Honeywell confirmed that they had a problem
with some gas valves playing nice with some of the triac models
and sent
me a new one, with a relay output.

I put voltage across the relay contacts that were supposed to be
open and fried the electronics that was holding it partially closed.
Everything else still works and the relay still clicks. Now I can
use the contacts like a switch like I wanted in the first place.


There was probably a contact protection network across the relay
contact that got partially destroyed. There are lots of possible
protection networks including varistors, diodes, RC or RLC, etc.
You say it measured 20 ohms. Was that done with a standard
ohmmeter? And if so, if you reverse the meter's polarity, what
does it read. Well, I know you can't do that because it was smoked.
Of course, you are not supposed to put raw power across the
contact, even if it is open.
Click to expand...

That's ok. The contacts will probably weld themselves together
before long, and he'll have to replace it.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
 
Art Todesco wrote:
On 10/30/2010 12:47 PM, LSMFT wrote:
Art Todesco wrote:
On 10/30/2010 1:34 AM, Dave Platt wrote:
This thermostat I have has a mechanical relay. But.... When
closed is a
closed circuit or dead short, fine that works for me. BUT when
it's open
it still has 20 ohms and will not shut off a circulator. Why in
hell do
they make it have 20 ohms when it's open?????? It should be
infinity.

I suspect that might be the resistance of the "anticipator"... a
small
built-in heater, which is normally energized when the furnace is
running. The heat it generates, helps cancel out the effect of
thermal lag (i.e. the room air heats up faster than the bulky
thermostat does) and improves the ability of the thermostat to
maintain
good temperature control.

All of the heat anticipators I've seen, have been in series with the
heat contact, not in parallel. The anticipators for cooling are
generally across the cool contact. That's the way I've seen it for
mechanical thermostats. But, most of the good electronic thermostats
have the anticipator function built into the software. So if the
thermostat is electronic with a relay driving the output, I'd suspect
something is wrong. Some electronic thermostats have triacs in the
output, which can have leakages. I've had one that actually slightly
hold open the gas valve. Honeywell confirmed that they had a problem
with some gas valves playing nice with some of the triac models
and sent
me a new one, with a relay output.

I put voltage across the relay contacts that were supposed to be
open and fried the electronics that was holding it partially closed.
Everything else still works and the relay still clicks. Now I can
use the contacts like a switch like I wanted in the first place.


There was probably a contact protection network across the relay contact
that got partially destroyed. There are lots of possible protection
networks including varistors, diodes, RC or RLC, etc. You say it
measured 20 ohms. Was that done with a standard ohmmeter? And if so, if
you reverse the meter's polarity, what does it read. Well, I know you
can't do that because it was smoked. Of course, you are not supposed to
put raw power across the contact, even if it is open.
Click to expand...
It would not shut off the circulator so current still flowed. It could
have been 200 ohms instead of 20. It was useless that way.

--
LSMFT

Simple job, assist the assistant of the physicist.
 
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