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what does a bed heater cable failure look like?

Posted by alkempster 
what does a bed heater cable failure look like?
September 01, 2016 01:58PM
For reference, i started to get periodic cutting out of the heated bed during a print. After stopping the print and checking the power cable for the bed we can see that the power cable failed. This started as snapping of some cores in the cable which reduced the current carrying capacity. Once the current carrying capacity was lowered enough, the wire effectively became a resistor at the point of mechanical failure, over-heated and caught fire (picture attached).

I have added monthly visual and resistance checks of this cable to my maintenance schedule. (with this particular fault, the resistance was read at 100ohms, way above that of an undamaged cable length)
open | download - 20160901_214425.jpg (84.4 KB)
Re: what does a bed heater cable failure look like?
September 02, 2016 06:54AM
Hi Alex,
That isn't the cable supplied with the kit. What happened to the original? I think the coloured rainbow wire is less flexible. Did you have the polypropylene strip installed on the inside of the bend?

Re: what does a bed heater cable failure look like?
September 02, 2016 08:02AM
Hi Chris,

its no problem with your kit. The Cable that was supplied with my kit got snagged on some tools and some of the insulation was stripped off as a result, so i had to replace with similar cable. The rainbow wire is less flexible but was still within bounds for the minimum bend radius for frequent flexing as indicated by the datasheet. The polypropylene strip was installed on the inside of the bend.

I am wondering if there is benefit to rotating the cable through 90 degrees so that the bend radius can be increased by running under the right hand side smooth rod, for the y-carriage, to increase the area of cable which is placed under the flexing motion. Either way, a cable that flexes will wear eventually, its just a case of when. That is why i plan to check periodically for wear. What are your thoughts?
Re: what does a bed heater cable failure look like?
September 02, 2016 08:17AM
I have had a machine built from an early kit printing almost continually for the rest of the kit production and its ribbon cable is still working so the lifetime should be in excess of three years of printing. It is a fairly dangerous failure if it does go though, so perhaps it is advisable to inspect it say every six months. Maybe if you print lots of small things it concentrates the wear in the middle whereas most of my builds are about half the bed travel.

Yes a wider bend would help but the idea was to keep it constrained between two surfaces so it behaves like a cable chain. I think the supplied cable is too wide to go under the smooth rod.

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