Replacing thermal fuse with Thermal switch - Page 1
Forum section: electronics / beginners

author: GoatZero
author_rank: Regular Contributor
timestamp: January 05, 2014, 06:50:58 am
content: I just had an electric heater fail for a second time, I already traced the failure to a thermal fuse (10A 250V, Tf=128c ) which it’s connected in series in the HOT wire of the heater.Both times it blew when I set the temperature to the max that makes the heater oscillate around 115c-140c, while pulling 13 AmperesIm more inclined to believe it was the current the one that blew the fuse twice , and not the temperature since the wire its quite far from the heatsinksInstead of replacing with the same part and repeating the whole process for a third time the next time it fails, I'm hoping to replace the fuse with a thermal switch that can mantain 13 Ampers and that will reset itself if it reaches 140c after shutting off (just like hair dryers). I'm new to thermal switches though, so I came here to post this while i do my research about themCan anybody guide me through this?? Thanks for any help you might provide!Pic related,

author: pickle9000
author_rank: Super Contributor
timestamp: January 05, 2014, 07:04:10 am
content: Do a search on ebay for thisThermostat nc resetThis is a fixed temp thermostat with a manual reset.

author: GoatZero
author_rank: Regular Contributor
timestamp: January 05, 2014, 07:16:47 am
content: will do, in case i dont find a suitable replacement i guess i will go for one of thesehttp://mexico.newark.com/nte-electronics/nte8139/fuse-thermal-141-c-15a-277v/dp/06M7503?ost=Resettable+Thermal+Fuses&categoryId=800000004761Tf 141c 15 Ampers in order to stop blowing fuses and hoping i dont burn the house down since whenever i set level 3 im always present

author: GoatZero
author_rank: Regular Contributor
timestamp: January 05, 2014, 07:28:40 am
content: is there any advantage between NO (Normal Open), Normal Closed Thermostat ?i ask because i found these NO that seem to fit my numbershttp://www.ebay.com/itm/250V-15A-125C-Normal-Open-NO-Thermostat-Temperature-Switch-/231066739937?pt=LH_DefaultDomain_0&hash=item35cca6a4e1

author: pickle9000
author_rank: Super Contributor
timestamp: January 05, 2014, 07:33:34 am
content: You really need a resettable type for safety.Here is a link on ebayhttp://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0&_nkw=Thermostat+nc+reset&_sacat=0&_from=R40

author: GoatZero
author_rank: Regular Contributor
timestamp: January 05, 2014, 07:37:17 am
content: i saw all these however, none of them are rated 15A (remember the 13A consumption) the ones i linked apparently are, however they auto resseteable

author: pickle9000
author_rank: Super Contributor
timestamp: January 05, 2014, 07:58:27 am
content: Do a google search for:KSD301 pdfI think you will find that it's rated for 16amps at 125v, the listed rating there is correct but is for 250vac.You can get a plastic tube from a hobby shot to extend the reset button through the panel. Don't use metal for the switch extension that would be very dangerous shock wise.

author: pickle9000
author_rank: Super Contributor
timestamp: January 05, 2014, 08:25:01 am
content: Here is what I found, these things are made by many companies.KSD301 thermostat Specifications? Electric parameters: 1) CQC, VDE, UL, CUL AC250V 50 ~ 60Hz 5A / 10A / 15A(Resistive load) 2) UL AC125V 50Hz 15A (resistive load)? Operating temperature range :0-300 ? (optional), temperature accuracy: ± 2 ± 3 ± 5 ± 10 ?? response and action temperature difference: 8 ~ 100 ? (optional)? Connection: plug terminal 250 # (0 ~ 90 ° bend optional); plug terminal 187 # (0 ~ 90 ° bend optional thickness 0.5,0.8 mm optional)? Life: ? 100,000 times

author: strangelovemd12
author_rank: Regular Contributor
timestamp: January 05, 2014, 08:35:22 am
content: Don't full size water heaters almost always run on 240v, even in the 120v riddled US? 120v is just what our wall outlets are at, houses all tend to have 240v split phase for the water heaters, ovens, washer/driers etc. I have seen some 120v units/ replacement heaters, but they all tend to be <5kw units, which is "fairly weak" by modern US standards. /AFAIKAlso, if the unit heats with intensity proportional to demand, adding insulation to the tank may solve the problem, as well as saving money.

author: SeanB
author_rank: Super Contributor
timestamp: January 05, 2014, 08:42:35 am
content: You will find the NC thermoswitches in every scrap microwave oven, in a small black bodied unit screwed to either the magnetron outer housing or to the oven cavity itself. They are there for the same purpose, and have probably the same setting. Your thermal fuse in the heater however is working correctly, as the heaters are very often marginal at full output power, and will trip the fuse after a few hours of running. The fuse you have is a 128C unit, and if the heater body ( in your oil filled unit's case) is at 140C then the fuse is well past the trip point. Turn down the thermostat a little, and then you will have no problems, and the unit will not run any less.

author: pickle9000
author_rank: Super Contributor
timestamp: January 05, 2014, 08:58:04 am
content: Manual reset thermostats and so called "thermal fuses" (temp activated fuses) are used when the designer decides it is too dangerous to do otherwise. Typically the question is, "Will this device be left unattended?". These are typically installed when fire is a possibility (even if it's remote). If you use a self resetting (automatic) device, for example and the heater was covered or on its side the risk continues.

author: GoatZero
author_rank: Regular Contributor
timestamp: January 05, 2014, 04:56:16 pm
content: yea after reading that makes a lot of sense going for manual reset instead of auto reset, however as i said i have no experience with these manual reset ones, exactly how is the process to reset them, i dont see any kind of switch, do i need to turn off the appliance, how does in the practice the manual reset work?also I still have a doubt about what temperature do they end up using to cut off the energy,is it the one of the wire which in theory could be overrided by increasing the size of the wireorthey just feel the ambient temperature around them, (as i said before the thermal fuse that blew twice was at least 5cm away from the heat sinks)

author: pickle9000
author_rank: Super Contributor
timestamp: January 05, 2014, 06:47:02 pm
content: The reset is located between the connections. Typically it will be connected to a rod or tube about 2 inches long. You can buy plastic tubing from a local hobby shop. The only important thing is that if the rod is to go through hole (in your case the panel of the heater), it must not jam. Remember this is a mechanical device and the rod will move out when it's tripped.Although not evident in the picture the mounting plate moves and will lay flat when attached. Try to locate the device in the same approximate location as the original an uninsulated. You should find that this one will not trip as often as the disposable even if you have it set at the same temp, the other units are very sensitive to vibration and will break with even the lightest tap.You may have notice the contacts inside your unit are welded or crimped, no solder. Use the same method (crimps are fine but give them a good tug to make sure they are secure. Loose connections get hot.Feel free to ask if you have any more questions.