| Author | Message | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 335 Registered: 7-2006 Posted From: 75.208.105.122 Rating: N/A |
We have a number of GE under counter fixtures that we particularly like the "looks" of but each has one tube that will not light and now one is totally out of commission. I decided to take the one apart and see what gives. At each end of the fixture is a transformer, which each of which have a thermistor. Turns out that the thermistors are shot. New ones are available but at a cost of around $14 each I am not sure the fixture(s) is worth fixing. These are not a typical looking under counter fixture and if possible, I would like to save the 5 of them. The label on each transformer states "Cat No. fp8044323 For (1) 14w-20w lamp, 120v, 60 hz, 0.35a, type 1, Class P outdoor". The thermistor itself is 102 centigrade rated. Question: Is there a way around the thermistor issue? (It is obvious that the thermistor and transformer of each fixture has the same problem). Thanx  RCB | |||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 2087 Registered: 1-2001 Posted From: 75.108.85.14 Rating: N/A |
Do you have any idea what the thermistors are for? Since the units are really not economical to replace I would at least bypass the thermistor on one unit and see what happens. Richard | |||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 143 Registered: 1-2007 Posted From: 208.81.157.90  Rating: N/A |
To replace the thermistor measure the cold resistance of one of the working units and the hot resistance. Measure with power off. Then measure voltage drop across it when operating. A little math and go shopping at some place like Mouser.com. Be careful, smoke is bad! Or just order complete new power supplies. Search for 12 volt ballasts. Lot of places sell them. Good luck Don 4107 | |||
| Nick Badame Refrigeration Co. (Dnick85)
Registered Member Username: Dnick85 Post Number: 247 Registered: 2-2006 Posted From: 70.208.211.186  Rating: |
Hi Chuck, The thermister is most likely for hi temp limit so the fixture doesn't get too hot. If you bypass it, be careful of any flamable materials in that vacinity. A better idea would be to put a different or smaller wattage bulb in it if possible. Good Luck Nick- | |||
| Tim Hoskinson (Tdh37514151)
Registered Member Username: Tdh37514151 Post Number: 245 Registered: 9-2004 Posted From: 65.25.139.50  Rating: N/A |
Don Evans has your answer. Measure the resistance with a ohm meter of a working thermistor at given temperatures. Any electronics supplier should have something close enough. Are you sure that the things you are looking at are thermisters as a thermister is usually used to control something over a range of temperatures. Normally high temp. limit is done with a simple thermal fuse. The thermal fuse is one time use and if they get over heated they open. I in no way mean to insult you but I have no way knowing your knowledge level of temp sensors. If you are not sure what the unit is you may post a picture of the item. Best of luck. Tim | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 336 Registered: 7-2006 Posted From: 70.210.185.124 Rating: N/A |
Many thanx to all. BTW.....These are all AC fixtures...not DC. Tim you are correct...very little knowledge, however I was told by an electronics shop that is what the critter is. Also as I looked it up on the internet the pictures are the same. I can obtain them, but cost seems excessive for what I am buying....therefore the original question. It seems to me that the reason for "temperature control" in this instance could be that they are tightly enclosed in a plastic housing...or??? I was inclined to do as Richard mentioned but thought better to get some expert advice from this board. What I am unclear about is, are you Don and Tim, suggesting a resistor of the value of the difference in the resistance? Also, as Nick stated, if the wattage of the lamp were changed, are you saying just a jump where the thermistor was? This particular fixture is ceiling mounted next to 1/16th Oak plywood so I don't want an overheat issue. It is in the Head area and used only occasionally so is never on for long periods of time. Better safe than sorry I've been told With five of these to deal with, overall it makes sense to me to try a way to resolve the issue before I start replacing them. Thanx for all the help on this. RCB (Message edited by chuckllb on September 06, 2008) | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 337 Registered: 7-2006 Posted From: 70.210.185.124 Rating: N/A |
Have attempted to upload 2 photos but, alas, they are too big (1MB+)...and haven't the slightest on how to reduce them. RCB | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 338 Registered: 7-2006 Posted From: 70.210.185.124 Rating: N/A |
Have attempted to upload 2 photos but, alas, they are too big (1MB+)...and haven't the slightest on how to reduce them. RCB | |||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 549 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
RC, Can I join with Tim in questioning whether or not they are really thermistors? As properly described above, thermistors vary resistance according to heat, but their resistance DECREASES as their heat increases. This makes me wonder what heat-related safety function a thermistor would have. Also, thermistors provide temperature information to a controller, which you don't have, which really makes me wonder? I'm right with Tim, very possibly a thermal fuse, or else a capacitor, but that's only a WAG. Can you tell us where in the circuit it is? A couple of more questions. Two wires to it? Both out of one end? Umm, I hate to say this, but if a thermistor has a resistance reading with a multimeter, its good. Happy hunting, George (Message edited by George Mc6 on September 06, 2008) (Message edited by George Mc6 on September 06, 2008) | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 339 Registered: 7-2006 Posted From: 75.208.211.54 Rating: N/A |
George, et al. Best I can do under the (mature) circumstances) And I see that no image was forthcoming. Good grief!! It's a Deltacad file. I can open it...perhaps y'all can't  RCB
(Message edited by chuckllb on September 06, 2008) | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 340 Registered: 7-2006 Posted From: 75.208.211.54 Rating: N/A |
One more try: AW, NUITS!!! RCB
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| Dallas (Dal300)
Registered Member Username: Dal300 Post Number: 184 Registered: 3-2006 Posted From: 208.103.35.188 Rating: N/A |
Here, I changed it to a JPG for you.  | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 341 Registered: 7-2006 Posted From: 70.212.254.157 Rating: N/A |
Thanx, Dallas!!! RCB | |||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 38 Registered: 8-2008 Posted From: 71.198.253.223 Rating: N/A |
The thermistor is there because of potential for overheating. They didn't put it there for the looks, it's there because the guys who designed the thing are afraid of fire from hot transformers. Check other electronics parts places -- you may be able to find a better price on some that are rated within 10% of the ones you have (10% for a lamp transformer is will within tolerances). | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 342 Registered: 7-2006 Posted From: 70.212.254.157 Rating: N/A |
Richard...you and I didn't get it right..... ..... I jumped the thermistors(?) by twisting each to make a direct connection. At least I got power to them, where I had none before, right? Bottom line..... burned both tubes in a flash! The model Number of this fixture is GE Lighting #26914, 120vac, 60Hz, 32W, F15T8 Lamp), Class P Type Ballast ("Replace with Class P Ballast only") .....just in case someone might have or know about one. I'm not usually one who give in easily, but I may just do it on this fixture. FWIW RCB | |||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 550 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Well, In my post 3 above the drawing, I said "THERMISTORS DECREASE RESISTANCE AS THEIR TEMPERATURE INCREASES!" That's my story, and I'm sticking to it, period!! Keith can't explain a 440 amp battery charger and MSW inverters, maybe he can explain how a thermistor getting warm from an overheated transformer, and LOWERING IT'S RESISTANCE, (thus allowing MORE current thru it) PROTECTS AGAINST FURTHER OVERHEATING??????? Now lets look at it a little further. Where is the mystery device? Does look like its in the incoming power line, doesn't it? What is commonly found in incoming power lines? Couldn't be a fuse, huh? Either electric or thermal? The temp rating of 102C is real suspicious for a thermistor, but common for a thermal fuse. For a positive suggestion, get someone with a voltmeter that will read 120VAC, and read the voltage across the mystery device. If the device is a thermal fuse, the one in the working ballast will only read one or two volts, the bad one will read 120 VAC, if it is all that is open in the circuit. Catch 22 applies here too, if you don't know what a thermistor does, you don't know you're not qualified to post! Thermistors do indeed provided remote temperature information to computerized equipment, but that equipment puts less than 12 Volts DC on a thermistor to determine its temperature. I don't get any enjoyment out of being a grump, but I do caution strongly against making electrical or propane posts when you don't have a clue! RC, I'm sorry you became the vehicle, but I don't want you catching fire! George | |||
| Jim Smith (Jpsmith)
Registered Member Username: Jpsmith Post Number: 4 Registered: 1-2001 Posted From: 72.14.99.66 Rating: N/A |
George You said "THERMISTORS DECREASE RESISTANCE AS THEIR TEMPERATURE INCREASES! That's my story, and I'm sticking to it, period!!" Sorry but to keep info correct there are two types of Thermistors, Positive and Negative. A Positive thermistor increases resistance with increasing temperature. And of course a Negative thermistor decreases resistance with increasing temperature, http://en.wikipedia.org/wiki/Thermistor I would agree with you that it is most likely a thermal protection device. | |||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 553 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Jay, Just so you understand, I will reply to any question on a post that I make, and will gladly admit when I am wrong. I am not wrong here for the folowing reasons! 1. The mystery device was described by someone at "Radio Coop" as a thermistor. 2. If it were a thermistor, it would probably not have a temperature reading on it, it might read 2300 Ohms @ 70 degrees? 3. Negative or positive was never discussed, and I try to stay on subject. 4. Do us all a large favor now, go back to the Wikipedia, and post the definition of a POSITIVE TEMPERATURE COEFFICIENT RESISTOR. 5. I don't feel you read RC's entire post, especially that part reading "burned both tubes in a flash." 6. Please also post a UL listing of a "positive thermistor" used as a 120 VAC overcurrent protective device. As information to you, because you are new, I am a licensed Electrical and HVAC contractor. I work with thermistors in solar controllers and heating appliances on a daily basis. A Positive Temperature Coefficient Resistor, PTCR in the air conditioning trade, is used in the start circuit of many high-efficiency single phase compressors. Its function is to allow large starting current flow, and then reduce it to essentially nothing, as it heats up, to save energy. The current flow necessary to keep the PSC compressor motor running efficiently is provided (and limited) by the capacitor that is in parallel with the PTCR. Please read ALL of my post of Sept. 6, (which was before the tubes got burned) and note that two of us question whether they were even thermistors. Then please note that I offered an easy method to find out if the mystery device was indeed a thermistor, without doing any damage. This has gone way OT, but I am trying to tell you that I knew what both types of thermistors were, BEFORE I made the second of my 3 posts, and I didn't want to clutter it all up with something that didn't matter. Now look what's happened! Regards, George | |||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 144 Registered: 1-2007 Posted From: 208.81.157.90 Rating: N/A |
Hey RCB, If you are still listening, I think the best way to solve your problem is to replace the ballasts with new units. May cost more but it is the safest way to go if you want to keep the fixtures. If you really want to try to replace just the thermistors, if thats what they are, you must measure one of the working units with it out of the circuit. The way I would do this is to unsolder one of the leads and measure cold resistance then connect the lead with a clip lead and run the fixture with the enclosure in its normal position until the temp is stabilized then measure the device again with the clip lead removed. Maybe a couple of clip leads leading to the outside of the fixture to measure it with the enclosure assembled and another pair to open the circuit. If you are not comfortable working around hot circuits, this may not be for you. If it measures 0 ohms it might be a thermal fuse. If you measure some resistance it could be a thermistor. Trying to determine the other electrical characteristics would be a guessing game unless you can cross the numbers from the item. You said new ones are available. Maybe you can gather some info from whoever is the supplier. Even if you have to buy one to see if there might be numbers on the packaging or device to determine what it is and whether there is a cross for it. Good luck, Don 4107 (Message edited by doninwa on September 08, 2008) | |||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 2088 Registered: 1-2001 Posted From: 75.108.85.14 Rating: N/A |
RCB, Guess my suggestion was wrong. Sorry about that. This sounds like a device that was in the early vacuum tube TV's. It kept the input voltage low as the vacuum tube filament's warmed up. As the tubes warmed up their internal resistance increased and the internal resistance of the device decreased. Richard | |||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1354 Registered: 12-2000 Posted From: 76.66.18.48  Rating: N/A |
Hello RCB. Maybe just buy some new ones... this is too complicated and controversial... happy coaching! buswarrior | |||
| Nick Badame Refrigeration Co. (Dnick85)
Registered Member Username: Dnick85 Post Number: 248 Registered: 2-2006 Posted From: 75.197.140.95 Rating: N/A |
Hi Chuck, I guess the process of elimination sometimes sucks! I also am sorry for suggesting for you to jump it out. I didn't realize the age of the fixture. I would bet an entire new fixture would be cheaper then the ballest/resistor.. Good Luck Nick- | |||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 343 Registered: 7-2006 Posted From: 75.210.141.41 Rating: N/A |
Hi folks....all of you!!! What a thread this has been, right? So...sometimes it doesn't exactly work out as hoped. I am positively appreciative of all the input. I considered every aspect, premise and piece of advice offered. I am of a simple mind and usually take the "easy" (SURE) way out if possible. Now, what I have done is to put it on hold for a bit....I have found the fixture on the internet, but, would you believe, from a Publishing house....yep, you read right...only the press of a key re-directs me to a variety of lamp places. Meantime, I have seem to have a tenacity that doesn't want to "quit". That's another story entirely.... So, ...I would be willing to send one of the units, including "the thing", to anyone who might be interested in looking into what it is. Regarding replacing the parts, I have not been able to find a "unit" exactly like the ones I showed in the picture. Remember, they fit compactly into each end of the fixture and look more(to me)like a transformer with a "...istor" . This fixture was mounted overhead, in front of the vanity mirror in the head area, and is great for just the right kind of light on mornings when the side lights (on each side of the mirror) just don't do the trick....if you understand what I mean. I have not seen any other like it or even close......ergo why we wish to keep the thing. Now, if the challenge is too much, just keep the comments to yourself........ Truly....many thanx for all the ideas and conversation.....ain't this a great board??? FWIW RCB '64 Crown Supercoach (HWC) | |||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 555 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
RC, I'll put my money where my mouth is! There are some things that you just "have" to do." Email is enroute. George |
GE Ballast/w thermistor