Electronics > Repair
GE Microwave oven with burnt connectors on thermal cutoffs [USA]
james_s:
--- Quote from: scootley on February 28, 2021, 08:52:56 am ---Who makes good quality ones? Molex?
--- End quote ---
I don't remember what brand is carried by the local (real) hardware store near me but they're quite good. Molex ought to be good in general too. See if you can find some meant for high current applications.
scootley:
Thanks. Most quick connect "data sheets" or spec documents don't seem to specify a current rating. Not sure why. Maybe there are more generic (e.g. UL) standards that they are tested to that cover many brands/parts and I didn't bother digging into that.
I will try some of these, which are at least rated for fairly high heat (150C) and voltage (600V)
https://www.te.com/usa-en/product-521081-1.html
scootley:
This document: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=82004_FASTON_TERMINALS_-_FULL_CATALOG&DocType=CS&DocLang=EN
Seems to imply that 250 series (1/4 inch) TE quick connects are tested to 20-24 amps with 12-10 AWG (respectively), but doesn't say the voltage. :palm: (page 8 )
The standard is UL 310.
In my microwave they used 16 AWG, which seems crazy to me for how much current it supposedly needs at 120VAC.
At least I will try 1/4" rather than the existing 3/16" spades that failed.
Ah yes the UL standard test for 16 AWG seems to be only 10 amps for these connectors at 1/4".
See here: https://en.wikipedia.org/wiki/FASTON_terminal
And you can sign up for a free UL account to view the standard too.
WattsThat:
Those faston lugs need to be steel and then nickel plated. Anything less will fail at those temperatures. If they are the usual tinned brass lugs, it’s no wonder they failed. Tinned brass or bronze has two problems. The tin plating burns off and the surface oxidizes, causing an increase in contact resistance and the brass expands due to the temperature, causing a loss in contact pressure. Again, more high contact resistance which becomes a thermal run-away. It’s a double whammy failure mode.
The problem may be the size. You can usually source crimp on nickel plated 1/4” females at an appliance parts store, they are used on clothes dryers, for the heating element connections as james_s pointed out. I’ve never seen 3/16” but then I haven’t asked. Good luck.
scootley:
--- Quote from: WattsThat on March 01, 2021, 05:31:12 am ---Those faston lugs need to be steel and then nickel plated. Anything less will fail at those temperatures. If they are the usual tinned brass lugs, it’s no wonder they failed. Tinned brass or bronze has two problems. The tin plating burns off and the surface oxidizes, causing an increase in contact resistance and the brass expands due to the temperature, causing a loss in contact pressure. Again, more high contact resistance which becomes a thermal run-away. It’s a double whammy failure mode.
The problem may be the size. You can usually source crimp on nickel plated 1/4” females at an appliance parts store, they are used on clothes dryers, for the heating element connections as james_s pointed out. I’ve never seen 3/16” but then I haven’t asked. Good luck.
--- End quote ---
Thanks. Yes I noticed the factory 3/16 ones did seem to oxidize. I am going with new TCOs that have 1/4 spades and so will of course use 1/4 connectors on them.
I didn't see any insulated steel ones that can do higher temps than the insulated brass ones; clearly the issue seems to be the insulation temperature rating and not the metal.
If I do the insulation myself, I wasn't sure what the easiest and least expensive way to insulate them would be in a way that can handle 160C. Maybe capton tape?
Side point: I have no idea what causes heat in these wires/TCOs during healthy operation vs failure scenarios. Clearly the oven is generating heat. But maybe there is some non-insignificant heat from the current too given the small gauge wires. I would imagine they will be nowhere near 160C (or even 110C) during normal operation, so maybe trying to insulate for 160C is going overboard.
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