Electronic advice Off Topic I know but yous guys is smart

I know this is off topic, but I know some of you know the answer.
I need to monitor the temperature of a heating element. I need to know
when it is on and when it is off. I don't need to know the
temperature, just that when it is getting hot and when it is not hot.
It is the defrost coil on my freezer. I have had more than one defrost
controller fail. One failed at Christmas and one at Thanksgiving. I
would like to monitor the temperature of the coil using my PC over
time so I can see that the temperature has increased and then
decreased over some time, probably 24 hrs.
When the defrost controller fails, the freezer freezes up over a 2
week period. If I can find a way to verify that the heating element is
heating or not, I can tell if I'm headed for trouble.
This is a 5-year-old Maytag. Expensive, so throwing it out isn't an
option. I just want to see a freeze-up coming. I have a spare
controller. I just need to know when the existing one failed.
I would like to monitor this with a PC input device that can handle an
input of some kind. Like an RTD or even a 120VAC pulse. The controller
switches the element to ground so I'm not sure how to pickup the 120
pulse.
I know you smart guys can come up with something I can use to see that
this dam thing is heating and defrosting the freezer coil.
Thanks Guys,
Reply to
Dan
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Are you capable of writing the software necessary to monitor an external device? what sort of PC? An old one running DOS is a piece of cake if you use the game port, or even a serial port and one of the RTS/CTS pins. You might even get away using one of the input pins on a parallel printer port.
If you want it to be monitored using a Windows based computer, then it gets a wee bit more complicated. Perhaps what would be easier and cheaper would be a freeze monitoring device with an alarm bell.
Paul
Reply to
co_farmer
An initial thought would be a DVM with thermocouple input and RS232 output. These are available relatively cheaply these days. You might find one with monitoring software or you may have to knock up a simple app to pick up the data.
Reply to
David Billington
Radio Shack sells cheap DVMs with PC interface. You can just monitor the voltage across the defrost coil to detect whether it is on or off.
There are more clever ways to roll your own PC-interface line voltage detector, but the Radio Shack product is just ready to go.
I've used this method to log water heater duty cycles and disprove the myth that idling water heaters waste (any significant amount of) power.
Reply to
Richard J Kinch
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This is Digikey TE-1020-ND, a current transformer. Its small and will fit within a 1" cube. Disconnect the defrost heater and thread its wire through the hole in the middle of this part, then reconnect it. Solder a 100 ohm 1/8W resistor across the output of the transformer. Every amp flowing into your defrost heater will now be indicated by a voltage of about 0.1V AC at the output of the transformer, across the resistor.
Connect one of these loggers (US$25.00)to the output of your current transformer and log the data to your PC.
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That's what I would do.
--Winston
Reply to
Winston
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That's what I would do also. Or you could find a toriod choke coil and do the same. It could even light a LED for direct visual indication.
Tom
Reply to
Tom M
How about a low tech approach. You're not checking temp, but need to know if the controller is cycling power. Buy a cheap HH/MM/SS timer. Set it to NN hours. Put a relay coil across the heating element terminals. Wire the relay contacts across the timer reset contacts to reset the timer. If the timer is not reset, the alarm goes off. The dog then barks, alerting you to the need to change controllers.
Kevin Gallimore
Reply to
axolotl
You will have both, voltage and current. That equals power (heat).
Using the current transformer means you don't need to disturb any factory wiring and gives excellent isolation.
Sometimes the defrost heater is really buried inside the unit and would be a pain to get to place the thermister (or any temp probe). Since he already replaced the timer, it's a good bet the heater is bad or intermittent.
Tom
Reply to
Tom M
One thing to remember on this go bad all the time stuff -
My stove was under insurance covered. But I paid a walk in fee.
On the third controller for the kitchen range - I was there every second. Trouble shooting skills were lacking - they were 'black box' exchange guys. The controller was replaced and it worked - then I moved a wire within. It went out just like before. This burnt looking wire was ok - the far end was to a pcb trace and it was not soldered! It had been working on press fit and a hope.
I showed it to the tech and he wondered how that could be fixed. I went to the shop and got a few tools - taught him how to solder.
I hope he got an iron at Radio shack, but those guys - service calls keep them paid. Mine hasn't failed yet.
Might be something like that on the far end of the harness - wire vibrates off a screw...
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.
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Tom M wrote:
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Reply to
Martin H. Eastburn
This is exactly what I was looking for. Thank you guys.
As far as why the defrost controllers are failing, I feel it is a manufacturing problem. I took the cover off the latest failed controller and found a burnt capacitor. 22uf 50V. I bought 3 of them for $.75. I'll solder it in and have a spare.
I did a search on the web for Maytag MSD2556AEW defrost controller failure and found a ton of information. These things are failing at a high rate. And they fit several model refrigerators. The next one that goes, I'm going to extend the wires so the controller and plug sit on the top shelf and changing it will take about 30 seconds, instead of the 1 hour it takes me now. Thanks again for all your suggestions. Dan
Reply to
Dan
Dan -
What do you mean burned up on the capacitor ?
It is an electrolytic or is it a plastic drop looking ?
If a drop looking - that is the issue bad manufacturer of Tantalum caps. This was long time a problem - PC motherboards and so many others.
You can replace it with a wet slug or tubular type or pick a new company. Be careful how you solder drops in - or any for that matter - there are + and - ends on them and in reverse they will burn.
That might be the issue - they might have a design goof and mark one lead as + when (and only maybe) it is -.
You would have to measure the voltage across it - the higher + is on the red dot side or the + side. If it is in reverse - we found the bug.
TWN issued lots of these in their plants. Might be starting again. Often the burned is the center of the tip is burnt. It might all glow! Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.
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Dan wrote:
Reply to
Martin H. Eastburn
It is an electrolitic cap. When I looked at it the end had popped out and some of the goo came out. I made wure to mark which way it came out so I put it back in correctly. The second controller lasted for about 15mos. Hopefully, if I get the now spare board fixed, I'll never need it. Dan
Reply to
Dan
If you are going to build something, why not a general-purpose power line current recorder? You should be able to recognize the defrost cycle heater current and see it shut off after the thermostat trips.
Jim Wilkins
Reply to
Jim Wilkins
Do you know why the previous cap failed? What steps have you taken to be sure the new cap doesn't fail? What other components failed or were weakened?
1. Do you really want to be in the refrigerator repair business? 2. Do you have a way to test the repaired board?
--Winston
Reply to
Winston
the new cap doesn't fail? What other components failed or were weakened?
No I don't know why the cap failed. I'm hoping it was just a bad cap.
Either I fix it or I pay someone else to do it. I'm standing here with lots of tools and knowledge, why not.
No I wish I did.
Reply to
Dan
the new cap doesn't fail? What other components failed or were weakened?
It *is* possible that this one component failed and you repaired the board by replacing the cap. That is not a safe bet however. Fast forward 15 months. You will be very unhappy if the currently installed board fails and your 'repaired' board is revealed to have other issues which prevent it from working properly. You are now into a third board that you need to purchase during another 'refrigerator emergency'.
Disclaimer: I own a Maytag fridge as well and am not looking forward to dealing with their design issues:
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Anyhow, best of luck to you.
--Winston
Reply to
Winston
I read all that also. Doesn't bode well for hte Maytag repairman. I hope the cap is an isolated incedent, but I guess I'll find out. Maybe don't run your refrig on a generator, which I believe started this whole mess. Dan
Reply to
Dan
I wouldn't blame the generator. Maytag is the Chevrolet of appliances. Not at all good RWT reliability but it has the best reputation that advertising dollars can buy.
In 2004, I said 'Enough of this, I'm buying an *Amana*.'
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'.....D'oH!' :)
--Winston
Reply to
Winston
What's that Lassie? You say that Dan fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Thu, 14 Feb 2008 02:53:47 GMT:
you can always use a higher voltage cap. in its place. Might last longer if it is failing from over voltage spikes.
Dan
Reply to
dan
That lashup won't detect any problem if the heater element happens to burn out (it happens all the time) I think a thermocouple is the better idea, that removes all doubt.
Vaughn
Reply to
Vaughn Simon

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