Safely repair an arcing coffee maker? - Page 1
Forum section: electronics / repair

author: cigmas
author_rank: Regular Contributor
timestamp: April 22, 2021, 01:45:32 am
content: I was alarmed to hear arcing while the coffee maker was turned on. With it disassembled, I could see arcing at the discolored and charred spade connector that is disconnected in the image above. The short wire connected to it also feels stiff and crunchy. Tightening the connector stopped the arcing at that terminal, but it sound like there might now be arcing inside the wire. I'm guessing the wire is damaged.Can this be safely repaired, considering it's a relatively high current appliance?Note that I previously repaired this coffee maker by replacing one of the thermal fuses which had blown. That's why parts of one of the braided insulation wires look a bit frayed, since I had to move the insulating sleeve over to one side, replace the thermal fuse, then slide it back.While repairing, I had also noticed the browning of some plastics and wires near the power switch. The two brown wires from the mains were hardened near the spade connectors. I cut and re-terminated one (bottom) that was more brittle, which now has a red insulation segment, though part of it is discolored browned now. I would not expect that area to heat up much, so I wonder if there's a problem that needs to be identified for this to be safe.I realize it's an inexpensive decades-old machine, but if practical I'd like to repair it, both because I hate waste, and because it makes better coffee than newer and more expensive units.

author: amyk
author_rank: Super Contributor
timestamp: April 22, 2021, 01:57:29 am
content: Spade connectors should be very,verytight. I'm surprised it got loose enough to arc. I'd polish the terminals, then crush the connector slightly with pliers to make it tighter. Check the others too while you're at it.

author: cigmas
author_rank: Regular Contributor
timestamp: April 22, 2021, 02:13:23 am
content: The first thing I did was to try to clean it a bit and tighten the spade connector with pliers. It stopped arcing at the connector. It was lose enough to wiggle a bit beforehand. But I'm concerned that there is now arcing inside the wire connected to that connector, as it now feels stiff and has crunchy/crackling sounds when moved.I'm not sure how to replace that wire since it looks spot welded to the thermostat terminal. I'm thinking that soldering is not a good idea in this application, due to the current and heat involved.Good idea, I will check all the spade connectors. They were very tight and difficult to remove the first time, so perhaps some got loosened when reattached.

author: andy3055
author_rank: Super Contributor
timestamp: April 22, 2021, 05:26:04 am
content: That top connection to the switch with 2 wires should be turned around so that it is away from the metal where it has touched - the brown wire can come towards the bottom.

author: Ian.M
author_rank: Super Contributor
timestamp: April 22, 2021, 07:10:47 am
content: If the wire and female spade connector have overheated like that, I'd regard the switch as suspect. Take a really close look at it with the connector removed, for any signs of distortion or other damage around the terminal and check the terminal is still rigidly attached to the switch body.

author: cigmas
author_rank: Regular Contributor
timestamp: April 22, 2021, 10:38:30 pm
content: Quote from: andy3055 on April 22, 2021, 05:26:04 amI could do that, though note that other than the screw there is no metal nearby, just a plastic liner, and it doesn't touch. I'm not sure why it has heated so much to brown the plastic and make the wire insulation more brittle, and I find that a bit concerning.Quote from: Ian.M on April 22, 2021, 07:10:47 amWhy do you suspect the switch? I forgot to mention that with the previous repair I also replaced the switch. On the original one, the rocker switch plastic had cracked and one terminal's contact was broken inside the switch, so that the switch was always in the ON position and would not click to the OFF position. The machine had to be unplugged to turn it off. I can certainly check the new switch, but the connectors are on really tight and they will be difficult to remove, as they were difficult to insert.My concern is that it sounds like something is still arcing, perhaps the wire with the overheated spade connector, due to degradation from heat. I'm not sure how to replace it though.

author: james_s
author_rank: Super Contributor
timestamp: April 22, 2021, 11:36:51 pm
content: I wouldn't be surprised if it was arcing at the crimp where the wire goes into the connector. They make special heavy duty crimp spade connectors for appliance use, they fit tightly and are thicker than the standard ones. You can buy high temperature appliance wire too.

author: sean0118
author_rank: Frequent Contributor
timestamp: April 23, 2021, 01:26:29 am
content: One problem with spade crimps is that they can go into thermal run away. A slightly poor connection causes the crimp to heat up and expand, which increases the resistance which then increases the heat more...Quote from: cigmas on April 22, 2021, 02:13:23 amIf you are sure the wire is the only issue and you have the correct crimping tool you can splice in a new wire. Cut off the section of wire with the brittle insulation, splice on a new one with a new spade crimp. These are the styles of butt splice crimps to use (just cover in heatshrink for extra protection):https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/35115/255834https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/55824-1/659774

author: andy3055
author_rank: Super Contributor
timestamp: April 23, 2021, 04:27:14 am
content: I would use this type of fiberglass covered wire designed for appliances:https://www.mcmaster.com/high-temperature-wire/Then, put in a new switch and use good quality heavy duty spade lugs of the correct size depending on the spades on the new switch. I am sure you can find the wire from a local electrical supply store.

author: cigmas
author_rank: Regular Contributor
timestamp: April 23, 2021, 11:56:27 pm
content: How should the replacement wire be attached? Yes, I want to use that fiberglass insulated high-temperature wire, and luckily have have some left over from a range repair. But I'm not sure how to connect it to the thermostat's post since it looks welded. I could leave some of the old wire and crimp to it, but that doesn't seem ideal.As for the switch, it was already replaced, and the burn marks were from before. Though the discoloration of red plastic insulation on a new spade connector at the switch is unexpected and of some concern.In case it wasn't clear, I've updated the image and circled in orange the spade connector that was definitely arcing (confirmed visually), and the "crunchy" high-temperature wire connected to it which sounds like it might be arcing internally.

author: andy3055
author_rank: Super Contributor
timestamp: April 24, 2021, 12:47:05 am
content: From what I can see, The lead going to the thermostat is welded on to a spade terminal. Is it possible to find a spade connector of the correct size and renew that wire completely? If you can find the correct size connector, you can remove the weld and file off to make it smooth and clean first. I must warn you that it might break beyond repair if it has become weak due to the heating. You will have to judge it for yourself. Other thing is to find out the ratings of the thermostat and put in a new one there. It should not be that hard to find the info.The other alternative is (since you seem to have enough length on that lead) to just renew the spade connector only. If you go that route, make sure to slip in a new piece of fiberglass sleeving before you crimp it back.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: April 24, 2021, 03:13:14 am
content: looking at the mains switch, is that live connected to one side (the wire you repaired) and neutral connected to the other (where the stacked spaded connector is)? if so, is the switch one with a neon light in it, or a changeover switch (and no neon light)?cheers,rob :-)

author: cigmas
author_rank: Regular Contributor
timestamp: April 24, 2021, 07:43:08 pm
content: Quote from: andy3055 on April 24, 2021, 12:47:05 amOh!!! I did not realize that the thermostat contacts are actually spade terminals! It is slightly different (4.75mm wide, 0.6mm thick) than the heating element's spade terminal (4.5mm wide, 0.6mm thick). Could the same connector size be used on both?How would the weld be removed? What about cutting the welded tab flush with the terminal instead? The terminal thickness would increase and possibly the contact area would decrease.Quote from: robert.rozee on April 24, 2021, 03:13:14 amThe plug is not polarized, so the live and neutral could be at either of the mains switch outer terminals. The switch does have a light (probably a bulb or maybe LED, kinda doubt it would be a neon light). I'm not familiar with changeover switches, but I take it this probably isn't one.

author: andy3055
author_rank: Super Contributor
timestamp: April 25, 2021, 12:10:15 am
content: The terminals on the thermostat looks the same size as the rest of them. However, as mentioned in my earlier post-last paragraph, you can avoid a few steps and just renew the connector on that lead only and give it a try.Whatever you do, make sure to clean the spade terminals nicely and make the connectors real tight on them.

author: cigmas
author_rank: Regular Contributor
timestamp: April 25, 2021, 01:28:07 am
content: Quote from: andy3055 on April 25, 2021, 12:10:15 amI didn't quite understand what you meant. Do you mean cutting off the connector and just crimping a new one on the same wire? Because the issue is that the wire feels brittle and it sounds like there might be arcing internally. This is after I squeezed the connector more firmly onto the terminal so that there is no more visible arcing at that location.Quote from: andy3055 on April 25, 2021, 12:10:15 amThey look similar, but I measured a 0.25mm difference in width with calipers. 4.75mm is apparently a standard size while I did not find 4.5mm listed anywhere, so I'm hoping they are intended to be the same.

author: sean0118
author_rank: Frequent Contributor
timestamp: April 25, 2021, 02:13:02 am
content: Ops, just realised I was looking at the wrong wire earlier, I thought the issue was with the brown wire going into the switch. Are you sure that one is okay? What caused the heat damage around it?I wonder if there is some underlying issue here like the heater coil is shorted?

author: andy3055
author_rank: Super Contributor
timestamp: April 25, 2021, 06:15:06 am
content: Quote from: cigmas on April 25, 2021, 01:28:07 am

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2021, 06:17:15 am
content: if the wire is crunchy sounding, I ran into this before. Get rid of all of it. It sounds like celohpane candy.I have a thread about it, something happens where the outside stays OK (in this case fiberglass) but the inside literarly turns into brittle plastic. I expect when you cut it open, the insulation willpourout like sand.It happens with double insulated wire, I found it on a rubber outer sheath, so like the outer sheeth was holding the disintegrated insulation together enough not to short the cable out.This happened in a 3 conductor cable to me. I thought there was paper in there, and I ever turned it on remotely to check.. it was fine in the state it was in. However when I started to strip the insulation to check, the wire insulation stated to pour out like tiny macaroni! It's very confusing because you sometimes find brown paper inside of cables, and naturally if you hear crinkling you think its something with the paper being old or dry.. but the fucked up insulation can make the same noise as dry paper or celphane.The only way to repair that connector is to braze on a crimp terminal of the correct gender so you can connect the wire through an adapter. Not recommend! You need to make sure it does not get hot enough to melt silver braze either. 55% silver usually works for weird shit.I would toss it, a coffee maker is low cost. Sounds like the repair is going to take alot.

author: Ian.M
author_rank: Super Contributor
timestamp: April 25, 2021, 09:34:53 am
content: It would be no big deal to get replacement high temperature fiberglass insulated wire, appropriate uninsulated crimp connectors, and a new thermal switch of the same temperature rating and mounting and replace *ALL* the white wires in the photo. They are all the same age, connected by the same batch of failing connectors, so IMHO they should all be replaced. Its possible the existing thermal switch could be reused, but it will have to be removed to grind or file off the spot-welded wire terminations, and that's a PITA to do with a risk of damage to it, and old thermal switches aren't particularly trustworthy anyway.

author: cigmas
author_rank: Regular Contributor
timestamp: April 27, 2021, 05:23:54 pm
content: Quote from: sean0118 on April 25, 2021, 02:13:02 amNo I'm not sure of anything, but since the thermal fuse to blew a months ago (due to old age or something else?), I figured there could have been a poor contact somewhere. This time with the arcing there was definitely a bad contact. The heater coil works to heat well and makes coffee, so I doubt it's shorted.Quote from: andy3055 on April 25, 2021, 06:15:06 amBut are the wires ok? That is the million dollar question. I don't have spare fiberglass sleeving, and I'm not sure why I would replace just the connector.Quote from: coppercone2 on April 25, 2021, 06:17:15 amOh my! This wire isn't that bad, though I saw a bit of the white plastic-like insulation crumble like chalk under the fiberglass sleeve. The crunchy sound was there at first, but after moving it around a bit it is quiet now. I'm not sure how this wire is supposed to feel, and I'm worried that it has weakened either due to metal fatigue or heating, etc. Definitely won't be trying exotic things like brazing..Quote from: Ian.M on April 25, 2021, 09:34:53 amYes, replacing the wire would be best for peace of mind. I wouldn't mind replacing the rest of the wires too if I can source the supplies. Would it be ok to just cut the welded tab flush with the thermal switch's terminal? It would be thicker but avoid the strain and difficulty of removing a weld, which I'm not sure how to do anyway.And the "failing connector" was probably my fault for not putting it on tight enough, since I had previously removed it to diagnose the blown fuse.

author: andy3055
author_rank: Super Contributor
timestamp: April 27, 2021, 05:34:20 pm
content: Not knowing where you are located (good if you can edit your profile so we know that), it is difficult to suggest where to buy stuff. Here is an eBay link for the wires you need:https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=appliance+wire&_sacat=0I think you have sufficient info/ideas from so many members to carry out the repair. It will be advisable for you to do some research on the thermostat and see where you can get one as we cannot see all the markings on it (may be there is info if you lift it off from the two screws holding it down. Once you have everything, just replace one thing at a time unless you feel brave enough to draw a diagram yourself (or take a photo) and go with that.Good luck.

author: Ian.M
author_rank: Super Contributor
timestamp: April 27, 2021, 05:38:35 pm
content: No, you can't just cut off the welded connection, leaving its tab welded to the thermal switch lug. If the lug is thicker in the middle than normal you cant use push-on spade connectors with it, so unless you have a spot welder, would have to drill it for a bolted connection using a ring terminal and a Belville washer to keep it tight.