Relay Behavior -- Any Ideas?

[Espressopithecus (Java Ma]

I know very little about electronics (E=IR is about my limit).

A relay on the control board for my espresso machine switches power to
the 1200W heating element. Normally, it closes each time power is
called by the thermostat device. But lately, the relay clicks but
doesn't stay closed.

I've checked many possible causes and found only one anomaly.
Resistance of the heating element should be ~ 12 ohms, but a check with
a digital multimeter shows it as only ~ 1 ohm.

Is it likely that the relay is failing to stay closed because the
current drawn by the heating element is too high?

Thanks,

Rick

 

[Al]

On Fri, 09 May 2008 17:21:28 +0000, Espressopithecus (Java Man) wrote:

I know very little about electronics (E=IR is about my limit).

A relay on the control board for my espresso machine switches power to
the 1200W heating element. Normally, it closes each time power is
called by the thermostat device. But lately, the relay clicks but
doesn't stay closed.

I've checked many possible causes and found only one anomaly. Resistance
of the heating element should be ~ 12 ohms, but a check with a digital
multimeter shows it as only ~ 1 ohm.

Is it likely that the relay is failing to stay closed because the
current drawn by the heating element is too high?

Thanks,

Rick

The resistance of heating elements typically rise as they heat up. Check
the resistance of a light bulb. It happens rapidly.

You may have a defective driver for the relay.

Al

 

[Espressopithecus (Java Ma]

In article <xM0Vj.1886$Uz2.1270@trnddc06>, no.spam@wanted.com says...

On Fri, 09 May 2008 17:21:28 +0000, Espressopithecus (Java Man) wrote:

I know very little about electronics (E=IR is about my limit).

A relay on the control board for my espresso machine switches power to
the 1200W heating element. Normally, it closes each time power is
called by the thermostat device. But lately, the relay clicks but
doesn't stay closed.

I've checked many possible causes and found only one anomaly. Resistance
of the heating element should be ~ 12 ohms, but a check with a digital
multimeter shows it as only ~ 1 ohm.

Is it likely that the relay is failing to stay closed because the
current drawn by the heating element is too high?

Thanks,

Rick

The resistance of heating elements typically rise as they heat up. Check
the resistance of a light bulb. It happens rapidly.

You may have a defective driver for the relay.

Thanks, Al.

I removed the heating element and checked it again where I can get my
multimeter probes on the terminals easily. It's a dead short, or close
to it -- it reads 0.000 ohms. So I guess we know it's kaput.

Now, about the relay. Sorry, I don't know what you mean by a "defective
driver" for the relay. Does that mean the input line to the relay may
not be hot, or that some other component on the logic board may not be
controlling the relay appropriately? Or?

Thanks,

Rick

 

[Michael A. Terrell]

"Espressopithecus (Java Man)" wrote:

I removed the heating element and checked it again where I can get my
multimeter probes on the terminals easily. It's a dead short, or close
to it -- it reads 0.000 ohms. So I guess we know it's kaput.

Now, about the relay. Sorry, I don't know what you mean by a "defective
driver" for the relay. Does that mean the input line to the relay may
not be hot, or that some other component on the logic board may not be
controlling the relay appropriately? Or?

What resistance did you expect at 1200 watts?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Espressopithecus (Java Ma]

In article <4824D93A.CF1424CB@earthlink.net>, mike.terrell@earthlink.net
says...

"Espressopithecus (Java Man)" wrote:

I removed the heating element and checked it again where I can get my
multimeter probes on the terminals easily. It's a dead short, or close
to it -- it reads 0.000 ohms. So I guess we know it's kaput.

Now, about the relay. Sorry, I don't know what you mean by a "defective
driver" for the relay. Does that mean the input line to the relay may
not be hot, or that some other component on the logic board may not be
controlling the relay appropriately? Or?


What resistance did you expect at 1200 watts?

Around 12 ohms. (120V squared/1200watts) Generally, espresso machine
heating elements test out at 10 to 20 ohms.

Rick

 

[JeffM]

Java Man Espressopithecus wrote:
A relay on the control board for my espresso machine
[...]1200W heating element.

Java Man Espressopithecus wrote:

it reads 0.000 ohms. So I guess we know it's kaput.

No. When you used Ohm's law, you got the *HOT* resistance

of a 120V 1200W element.

Al wrote:
The resistance of heating elements typically rise as they heat up.

That's the part you ignored. The cold resistance of the device

is RADICALLY different from its resistance at temperature.

Check the resistance of a light bulb.

Something else that would have given you a useful data point

--except that you ignored it as well.

If the element isn't OPEN, it probably isn't a source of any problems.
If you can't find a *visible* short across it, that section is likely
OK.
....and I'd expect a much more dramatic failure mode
in the case of a shorted heater element.
..
..

lately, the relay clicks but doesn't stay closed.

You may have a defective driver for the relay.

Yes. The most logical explanation

is that the *control* side of the circuitry is screwed up.

I don't know what you mean by a "defective driver" for the relay.

There are 2 significant sides to a relay.

A relay that handles line-level (electrical) stuff on its output
often has low-voltage (electronic) stuff on its input.
http://www.google.com/search?q=cache:HK3NQYnqMU0J:en.wikipedia.org/wiki/Relay+*-*-*-*-another-electrical-circuit

"Driver" in this case is a way of saying "circuitry in front of the
relay".
http://www.google.com/search?q=cache:2yiD_qebaYkJ:www.uoguelph.ca/~antoon/gadgets/relays/relays.html+*-*-*-amplifier-that-*-*-*-*+relay-driver

The best way to find out what temporal anomalies are
is to use an oscilloscope.

 

[Don Kelly]

"Espressopithecus (Java Man)" <rickk@letterectomyTELUS.net> wrote in message
news:MPG.228e6f553a3ab7c98983e@shawnews.vc.shawcable.net...

In article <xM0Vj.1886$Uz2.1270@trnddc06>, no.spam@wanted.com says...
On Fri, 09 May 2008 17:21:28 +0000, Espressopithecus (Java Man) wrote:

I know very little about electronics (E=IR is about my limit).

A relay on the control board for my espresso machine switches power to
the 1200W heating element. Normally, it closes each time power is
called by the thermostat device. But lately, the relay clicks but
doesn't stay closed.

I've checked many possible causes and found only one anomaly.
Resistance
of the heating element should be ~ 12 ohms, but a check with a digital
multimeter shows it as only ~ 1 ohm.

Is it likely that the relay is failing to stay closed because the
current drawn by the heating element is too high?

Thanks,

Rick

The resistance of heating elements typically rise as they heat up. Check
the resistance of a light bulb. It happens rapidly.

You may have a defective driver for the relay.

Thanks, Al.

I removed the heating element and checked it again where I can get my
multimeter probes on the terminals easily. It's a dead short, or close
to it -- it reads 0.000 ohms. So I guess we know it's kaput.

Now, about the relay. Sorry, I don't know what you mean by a "defective
driver" for the relay. Does that mean the input line to the relay may
not be hot, or that some other component on the logic board may not be
controlling the relay appropriately? Or?

Thanks,

Rick
------------

It is possible but unlikely. And what scale is the multimeter on? Does it
say ohms or Kohms.? Many multimeters are often questionable when measuring
low resistances and the cold resistance of the heater will be considerably
less than the operating resistance of about 12 ohms.
If the heater is actually 0, then the circuit breaker should have tripped
and I doubt whether the relay would be able to break the circuit under short
circuit conditions -it would do something more dramatic than just clicking.
Suspect the control.



--

Don Kelly dhky@shawcross.ca
remove the X to answer
----------------------------

 

[Espressopithecus (Java Ma]

In article <yj8Vj.128823$Cj7.82532@pd7urf2no>, dhky@shaw.ca says...

"Espressopithecus (Java Man)" <rickk@letterectomyTELUS.net> wrote in message
news:MPG.228e6f553a3ab7c98983e@shawnews.vc.shawcable.net...
In article <xM0Vj.1886$Uz2.1270@trnddc06>, no.spam@wanted.com says...
On Fri, 09 May 2008 17:21:28 +0000, Espressopithecus (Java Man) wrote:

I know very little about electronics (E=IR is about my limit).

A relay on the control board for my espresso machine switches power to
the 1200W heating element. Normally, it closes each time power is
called by the thermostat device. But lately, the relay clicks but
doesn't stay closed.

I've checked many possible causes and found only one anomaly.
Resistance
of the heating element should be ~ 12 ohms, but a check with a digital
multimeter shows it as only ~ 1 ohm.

Is it likely that the relay is failing to stay closed because the
current drawn by the heating element is too high?

Thanks,

Rick

The resistance of heating elements typically rise as they heat up. Check
the resistance of a light bulb. It happens rapidly.

You may have a defective driver for the relay.

Thanks, Al.

I removed the heating element and checked it again where I can get my
multimeter probes on the terminals easily. It's a dead short, or close
to it -- it reads 0.000 ohms. So I guess we know it's kaput.

Now, about the relay. Sorry, I don't know what you mean by a "defective
driver" for the relay. Does that mean the input line to the relay may
not be hot, or that some other component on the logic board may not be
controlling the relay appropriately? Or?

Thanks,

Rick
------------
It is possible but unlikely. And what scale is the multimeter on? Does it
say ohms or Kohms.? Many multimeters are often questionable when measuring
low resistances and the cold resistance of the heater will be considerably
less than the operating resistance of about 12 ohms.

It says ohms. Now that the element has thoroughly dried out, it reads
0.5 ohms. Another espresso machine owner measured his new element as
11.5 ohms when cold. I know resistance increases as the element heats
up, but there's a limit to how much resistance can increase since the
element is always immersed in water. The water temperature tops out at
~ 235F (since the boiler is under pressure). Undoubtedly the element
gets hotter than that, but not red-hot.

If the heater is actually 0, then the circuit breaker should have tripped
and I doubt whether the relay would be able to break the circuit under short
circuit conditions -it would do something more dramatic than just clicking.
Suspect the control.

That makes sense.

Like more espresso machines, mine has a pressure switch connected to the
boiler that "tells" the relay to close whenever the temperature in the
boiler is below ~ 225F, and to open when the boiler exceeds ~ 235F. The
switching device that does this is functioning normally. I can't tell
how to troubleshoot this danged thing. I could always buy a new master
control board, but the darned thing is $483, and I don't really want to
buy and install it, only to discover that it wasn't the problem.

Is it conceivable that the circuit board might have a function
programmed into it to open the relay in the event of a high current
reading (I.e. short)?? Wow, I'll bet that would burn the contacts!

Rick

 

[John Fields]

On Fri, 09 May 2008 18:31:57 GMT, Al <no.spam@wanted.com> wrote:

On Fri, 09 May 2008 17:21:28 +0000, Espressopithecus (Java Man) wrote:

I know very little about electronics (E=IR is about my limit).

A relay on the control board for my espresso machine switches power to
the 1200W heating element. Normally, it closes each time power is
called by the thermostat device. But lately, the relay clicks but
doesn't stay closed.

I've checked many possible causes and found only one anomaly. Resistance
of the heating element should be ~ 12 ohms, but a check with a digital
multimeter shows it as only ~ 1 ohm.

Is it likely that the relay is failing to stay closed because the
current drawn by the heating element is too high?

Thanks,

Rick

The resistance of heating elements typically rise as they heat up.

---
While that's true, it's immaterial since the material heater elements
are made of (usually Nichrome) has only a slightly positive
temperasture coefficient.

Check the resistance of a light bulb. It happens rapidly.

---
Apples and oranges. The filament in an incandescent lamp is made of
tungsten and is designed to operate at a temperature far higher than
that experienced by an expresso machine heater.
---

You may have a defective driver for the relay.

---
I doubt it.

JF

 

[John Fields]

On Sat, 10 May 2008 03:49:31 GMT, Espressopithecus (Java Man)
<rickk@letterectomyTELUS.net> wrote:

Like more espresso machines, mine has a pressure switch connected to the
boiler that "tells" the relay to close whenever the temperature in the
boiler is below ~ 225F, and to open when the boiler exceeds ~ 235F. The
switching device that does this is functioning normally. I can't tell
how to troubleshoot this danged thing. I could always buy a new master
control board, but the darned thing is $483, and I don't really want to
buy and install it, only to discover that it wasn't the problem.

Is it conceivable that the circuit board might have a function
programmed into it to open the relay in the event of a high current
reading (I.e. short)??

---
Yup, but probably anything higher than, say, 12 or 15 amps or so...
---

Wow, I'll bet that would burn the contacts!

---
Not likely. You'll have the wiring resistance in there, so current
will be limited somewhat by that, and the heater is running on AC, so
once the relay opens any arc formed across the contacts will be
quenched when the voltage across the contacs goes through zero.

Since you know you have a bad heater and you're going to have to
replace it no matter what, what I'd do would be to buy a new one,
install it, and see what happens.

Short of that, if you have an appliance (laundry iron, hair dryer)
which dissipates 1200 watts or so, say +/- 10%, I'd hook it up in
place of the heater, momentarily, just to see if the relay maintained
its clicking behavior. If it did, I'd suspect a problem with the
controller in addition to the one with the burned-out heater.

JF

 

[Espressopithecus (Java Ma]

In article <kl5b24t8nd3pdibm70o3en4fv18bhmdjmo@4ax.com>,
jfields@austininstruments.com says...

On Sat, 10 May 2008 03:49:31 GMT, Espressopithecus (Java Man)
rickk@letterectomyTELUS.net> wrote:


Like more espresso machines, mine has a pressure switch connected to the
boiler that "tells" the relay to close whenever the temperature in the
boiler is below ~ 225F, and to open when the boiler exceeds ~ 235F. The
switching device that does this is functioning normally. I can't tell
how to troubleshoot this danged thing. I could always buy a new master
control board, but the darned thing is $483, and I don't really want to
buy and install it, only to discover that it wasn't the problem.

Is it conceivable that the circuit board might have a function
programmed into it to open the relay in the event of a high current
reading (I.e. short)??

---
Yup, but probably anything higher than, say, 12 or 15 amps or so...
---

Wow, I'll bet that would burn the contacts!

---
Not likely. You'll have the wiring resistance in there, so current
will be limited somewhat by that, and the heater is running on AC, so
once the relay opens any arc formed across the contacts will be
quenched when the voltage across the contacs goes through zero.

Since you know you have a bad heater and you're going to have to
replace it no matter what, what I'd do would be to buy a new one,
install it, and see what happens.

Short of that, if you have an appliance (laundry iron, hair dryer)
which dissipates 1200 watts or so, say +/- 10%, I'd hook it up in
place of the heater, momentarily, just to see if the relay maintained
its clicking behavior. If it did, I'd suspect a problem with the
controller in addition to the one with the burned-out heater.

Thanks -- that is a common-sense and practical suggestion even I can

try. I'll do it.

Rick