PTC Thermistor heaters - Page 1
Forum section: electronics / projects

author: nfmax
author_rank: Super Contributor
timestamp: June 16, 2015, 11:21:18 am
content: Can anyone point me at a supplier ofpackagedPTC thermistor heaters? I'd like something I can just bolt to a small metal part and wire up. Alternatively, does anyone have experience of packaging bare chip PTC heaters like those from TDK, to meet moderately severe shock & vibration conditions? I'm looking for a low voltage 12V/24V, part, with a reference temperature somewhere near 0°C. the exact values aren't at all critical.

author: SeanB
author_rank: Super Contributor
timestamp: June 16, 2015, 11:25:11 am
content: RS does them as rack heaters, but they are expensive...... You might want to google that term.

author: nfmax
author_rank: Super Contributor
timestamp: June 16, 2015, 02:04:31 pm
content: Ow yes they are expensive! And mostly 110/240V as well. I'm trying to heat a small metal block holding various items of optics, so I Googled 'optics heater' and found a selection of specialist devices - maybe one of those will be suitable (though they are mainly targeted at telescope optics, much bigger than my little gadget.)

author: Gyro
author_rank: Super Contributor
timestamp: June 16, 2015, 02:30:47 pm
content: Does it actually need to be a PTC thermistor?You mention the set value being not critical and around 0'C - are you looking to thermally stabilize for precision optical reasons or simply avoid condensation?If it's the latter then you could probably get away with a resistor, either running constantly at low dissipation or in conjunction with a temperature sensor. It might make your shock and vibration goals easier to meet anyway.

author: Pjotr
author_rank: Frequent Contributor
timestamp: June 16, 2015, 02:39:03 pm
content: Those heaters are usually very cheap:https://www.google.nl/search?q=ptc+heating+element&biw=1158&bih=904&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMInObXzLaUxgIVSewUCh1GdADMYou'll find them in many household appliances and tools with a fixed temperature like hot glue guns. They are self regulating for a fixed temperature, usually between 120 degC and 180 degC. Bare units are often assembled in silicone rubber socks. A cheap source for them are wall mart paper laminators.If you want to regulate lower temperature you will need a temperature controller anyway. But in that case you can just use a resistor or any other heating element as suggested before.

author: BradC
author_rank: Super Contributor
timestamp: June 16, 2015, 02:49:31 pm
content: It might be worth looking at A/C compressor crank case heaters. Usually a tape, but there are a myriad of units and the temp range is about right.

author: nfmax
author_rank: Super Contributor
timestamp: June 16, 2015, 03:35:35 pm
content: The situation I find myself in is that the hardware design is *finalised* but the optics does not quite meet spec at low temperatures (we do temperature compensation, not temperature control). If I can just strap a small PTC to the optics block & wire it to the incoming DC supply (24V nominal) to stop it from chilling out entirely, then job done; but I can't put a controller circuit in. I think about 2W at 0°C would be plenty, but I'd rather not add any additional heating when the unit is at at 50°C ambient temperature. I don't want a thermostat, as I think the dT/dt when it switches on & off will be too fast for the temperature compensation.

author: SeanB
author_rank: Super Contributor
timestamp: June 16, 2015, 03:57:55 pm
content: Aluminium cased power resistor screwed to the optical block, and a PTC thermistor in a clip on the one screw, select one that will trip at around 10C and you will have it work fine. No controller board, simple series wiring and a very slow switch on and off. 240R 5W resistor will be fine on 24V.

author: Gyro
author_rank: Super Contributor
timestamp: June 16, 2015, 05:26:35 pm
content: If you need smaller, then TO220 pkg resistors would be easy to mount.It doesn't help with the control bit though - PTCs are normally for higher temperatures - I found some on Farnellhttp://uk.farnell.com/webapp/wcs/stores/servlet/Search?st=ptc+heater&catalogId=15001&categoryId=700000005532&langId=44&storeId=10151but they _start_ at 50'C.I was hoping that you might be able to squeeze a compromise resistor value that would just manage to clear your low temp problem without pushing you over the top at 50'C (might still be worth doing the sums).

author: mikerj
author_rank: Super Contributor
timestamp: June 16, 2015, 11:26:06 pm
content: You could use an NTC sensor to control a transistor/resistor which would actually perform the heating. e.g. a heavy duty version of the circuit inthis thread.