PTC - Compressor starter - Positive Temperature Co-efficient
Hey, simplicity works but it has its limits The most cheapest compressor starting device, and can I say it is not a relay , more a resistive switch. For very small class capillary system refrigerator, usually a bar fridge or cubic fridge enter the PTC. Now these are not high tech, and they need to have decent intervals in time before starts so they can cool down. Also the system must equalise pressure between the high and low sides to allow for a low compression start. The PTC starter is similar to the potential relay not by design but where the start winding is engaged immediately from first power up. . At start up the PTC is cool and has no opposition to current flow by a preset low resistance which is in series with the compressor start winding. The compressor starts by resistive start and induction run, as the current flows through the PTC , it heats up increasing its internal resistance until it will not allow more current to flow , disengaging the start winding. The start winding is isolated and will not engage further as a trickle of current to the start winding will maintain heat and high resistance during the operation of the compressor. When the unit stops the PTC MUST!!! cool down to allow current to flow again on next start-up. If it trys to start to early the internal overload will activate in the compressor. So it really is not designed for frequent starts and requires very low starting torque. Don't expect too much , price and capacity dictates control, yet I do like how simple these are. The PTC is small, no bigger than a 10c (Australian) coin and as about 4mm thick. Note also the compressor terminals are inverted to this design as per the Danfoss types. I have marked them. These starter types are typically only used on low capacity, low torque compressor where off cycle pressure equalisation occurs , as you see in capillary systems Now does anyone see a Star Trek logo on the PTC relay disc in the pictures above? , or am I just seeing things :D
joe head
9/9/2018 10:10:44 am
Hi. I think you have mislabeled the start and run winding in the third picture. When ohming compressor windings there are the three values. The lowest value is the run or main winding. The next higher value is the start winding. The highest value is the sum of the run and start winding together.
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Admin
9/9/2018 11:23:48 am
I agree with your analogy but the readings are as shown , Nothing has been represented differently.
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Dirk
3/7/2019 11:38:34 pm
Good Day,
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admin
4/25/2019 01:00:47 pm
Hi Dirk, thanks for your feedback and kind words
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Dana Perry
4/11/2021 01:59:19 pm
is this the dirk i no how you doin
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Richard Dixon
4/24/2019 11:29:41 am
You're right! That is a Star Trek Logo. I keep telling people that this piece of ceramic must be Alien Technology. One piece of ceramic acting as a capacitor, relay and starter all with no moving parts. It must be alien tech from what it costs, one of these little jewels for a Whirlpool fridge is $60.
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admin
4/25/2019 12:53:14 pm
Hi Richard, thanks for posting in
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JEAN RUTHEMANN
8/1/2019 02:11:33 am
HI and thanks for explanations :) , my fridge is a samsung and my ptc start relay DA35-00135A has one more part : a m8jz47 BI−DIRECTIONAL TRIODE THYRISTOR SILICON PLANAR TYPE and gave me a 1200 ohms reading and is out of stock a few weeks to get it and the transistor is availlable in a different contry far far away ...
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admin
8/2/2019 05:36:44 pm
Hi Jean.
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Lola
9/11/2019 04:46:48 am
Great page - done obviously by someone who gets their hands on the equipment!
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Admin
9/11/2019 06:37:41 pm
Hi Lola
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Lola
9/17/2019 09:19:35 am
Thank you. As it turns out, it worked. I found something that looked both physically and otherwise to be very close to the original for $7 - worth a try. Installed and still no go until I realized that there were a few corroded wires. Repaired those and presto: freezer is working well. I plan to run it for a week to be sure, then clean it and use it.
Andy Earnshaw
11/26/2019 10:40:49 pm
Hello & thanks for the article. I'm in a similar position of having a PTC disc still in one piece, but its cold resistance is 1.2kΩ & so I've no idea what it should be other than obviously quite low?
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Admin
11/27/2019 07:27:28 pm
Hi Andy, thanks for your message
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Matt
6/10/2020 12:27:54 am
Hi.
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Angus Jones
5/21/2021 06:28:32 pm
I have the same question whats the difference between a QPT 15G and 15L
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Glen Bulman
11/2/2021 08:57:45 pm
Hi Matt, did you ever find out an answer to your question? (Obviosuly not on this website) I have the same issue. Thanks, Glen
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admin
11/5/2021 09:58:32 am
Hi Matt, sorry about the horrid delay but I have not been able to access my site for a while. Unfortunately , I do not have the technical specifications for your relay or even know about the part number nomenclature. PTC relays can should be access from the manufacturer or agent for specific models unless there is an approved multi range type from refrigeration wholesalers. These days the generic types either wont fit or, are not suitable for a customer model type. If the refrigerator is running on hydrocarbons , then in the interests of intrinsic safety , only genuine parts should be used.
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cletus noronha
7/27/2020 10:24:18 pm
liked your explanation on the working of the PTC. However if I can't get the exact ohm PTC for my mini Westinghouse fridge, can you suggest an alternative design.
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Admin
8/2/2020 04:21:25 pm
There will be solid state relay or solid state relay/overload combinations from refrigeration wholesalers. These basically take the place of most small to medium domestic compressor starters. They will need to your compressor capacity size to see if it can be matched then it requires installtion by qualified personel.
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kitt
10/26/2020 08:33:52 pm
Wow very nice info. I need help on my samsung ref. I am caught which part could be the problem. Run capacitor, PTC relay, OLP and compressor.. It is RSCR type of motor meaning PTC will help start it then once started, the Run capacitor will take over and connect with the start winding. My questions are the OLP will trigger and turn off the compressor and I measured some 8 amps. This happens around 7 seconds from startup of motor. My run cap is new 5uF at 450V AC and my PTC relay is new with 22ohms ambient reading. the old PTC relay is 33 ohms. What could be the problem. My guess is it could be the PTC which could be defective. I tried to heat the PTC using hair dryer heater but the resistance goes lower. how can this be? I thought it should go higher? Cud it be the compressor d problem? Thanks for your help.
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admin
11/5/2021 10:19:10 am
Hi Kitt
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Jim Ruedebusch
4/27/2021 07:30:37 pm
Have 50 year old Sears refrigerator—- need compressor start relay. Know ohms for start and run windings on compressor. I can find a relay for this old compressor but they require purchase of10 units at $250. How to design and select relay??
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Admin
11/5/2021 10:27:06 am
Thats an old fridge Jim, sizing is either based on horsepower or refrigeration kW. They make combination solid state relays for even the older hot wire relay starts on classic fridges. You do need to know the capacity of your fridge and that might be hard if there is no info on it.
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Malx
5/26/2021 03:59:14 am
Brilliant, thanks for explaining this, refrigeration seems a bit like a black art, particularly now electronics are involved. The prices of these electronics seem to be stunningly expensive. Fortunately the PCRs seem reasonably cheap. I will run the tests you suggested, I have measured the current consumption on switching on, it starts at 60W and falls quite quickly, Down to 25 W. But the freezer has cooled Down once after failure to a sufficiently low temp -22. Deg C. But testing after that it seems to stick at 25w, but only cool to about 0 deg.
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Admin
11/5/2021 10:29:35 am
Hi
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admin
11/5/2021 10:30:56 am
Hi
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