Connect wires in high ambient temperature  - Page 1
Forum section: electronics / projects

author: MarkoAnte
author_rank: Regular Contributor
timestamp: March 12, 2021, 03:19:14 pm
content: Hi,I build a new costume 3d printer and I don't know what would be the best way to connect 2 wires together.The printer bed is heated by a mains silicon heater, that has 2 wires coming out of it. Also on the bed is a thermal fuse, that has 2 short wires coming out of it. I need to connect this fuse in line with the heater. The heter is 500W @230V so cca. 2A. The heat bed runs at 120C continuously during prints.Right now I'm using some bullet connectors I had on stock (i don't know the part number) with extra high temp fibre glass insulation tubing around them. But when I tried to find some generic bullet connectors they are (like most other connectors) rated cca 80C. On Farnell I found even some non-insulated eye type connectors rated for 75C (totally mystified why a plated copper connector with no insulation is rated for 75C but ok).I might be over complicating things, as I doubt that the actual connector heats up to 120C (It is near the heater but the max ambient I managed to get in the printer enclosure is 70C). But I would like to have a over build connection as the printer would run over night unattended. I'm a bit worried that the bullet connection would loose its spring after a long time at higher temperatures.What would be the best option for connecting these wires? My main concern is high temp and thermal cycling form 120c to ambient many times. They would only need to be undone if I needed to change the fuse. The top 2 options on my mind now are screw terminal blocks (they are usually rated for 110C and don't need springiness to work) or just soldering the wires together.Best regards,Marko

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: March 12, 2021, 04:31:24 pm
content: Screw terminal block but made of ceramichttps://uk.rs-online.com/web/p/standard-terminal-blocks/7033861/

author: MarkoAnte
author_rank: Regular Contributor
timestamp: March 12, 2021, 05:09:51 pm
content: Yes I also had these in mind. The connection should remain solid after thermal cycling right? I'm more worried about bad electrical connection than insulation failing.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: March 12, 2021, 06:55:21 pm
content: Yeah it shouldn't be a problem. Especially if you use a ferrule on the stranded wire.They're rated to 800c and used routinely in things like pottery kilns to attach to the heating elements without much trouble.

author: wizard69
author_rank: Super Contributor
timestamp: March 13, 2021, 03:03:27 am
content: Quote from: MarkoAnte on March 12, 2021, 05:09:51 pmThe insulation will likely fail at elevated temperatures Usually the plastic gets hard and cracks if it is a low temp wire insulation.As for electrical connections failing there are several things to consider. First if you are working at elevated temperatures forget about terminals or connector blocks with out a thermal rating or one close to your operating temperature. It is better off to go with terminal blocks rated a bit higher than your expected max temperature. Also depending upon your terminal block, use high temp ring terminals or wire ferrules. Wire ferrules are especially good when undersized wires need to go into a larger set screw type blocks.you might get faster results looking into suppliers to the plastics or molding industries.

author: beanflying
author_rank: Super Contributor
timestamp: March 13, 2021, 03:34:24 am
content: Unless you are making a Core XY type make sure you use a high strand count wire on the bed, plenty of fails by manufacturers of 3DP's over recent years at this point with mechanical stress. Silicon covered too as already mentioned.Generally the terminal blocks inside coffee machines are ceramic and run for decades the wire is generally glass covered as it is static unlike the 3D beds. Gold bullets 'should' be ok but mains and high ambient might be an issue with the springs.