Burned up a contactor - identifying problems

[morbster]

This was my fourth brew session on my 220V, 5500W eBIAB setup, and halfway through my mash I noticed smoke coming from my panel. After shutting everything down and opening it up, it looks like one of my contactors has been scorched.

View attachment ImageUploadedByHome Brew1497198883.968998.jpg

I will order another on Amazon today, and I was wondering if anyone had some advice on identifying the underlying issue. I've read that loose wiring is a common problem.

I would love to say it's just bad Chinese equipment; but it is just as likely that it was something I did incorrectly.

 

[BrunDog]

That black wire and associated terminal look overheated so that would lead me to believe you had an inadequate connection there. Even the slightest resistance will generate significant heat. The damage extends from the distal end of the wire and into the contractor, looking at the peeling label.

Obviously replace the contractor. Replace the entire section of wire as well. Make sure to terminate the wires properly for those screw terminals. It might be better to use crimped sleeves.

Oh and a quick "thanks" to the spirit(s) you serve - this happened without a fire. Electrical fires are dangerous and sometimes catastrophic.

 

[morbster]

That black wire and associated terminal look overheated so that would lead me to believe you had an inadequate connection there. Even the slightest resistance will generate significant heat. The damage extends from the distal end of the wire and into the contractor, looking at the peeling label.

Obviously replace the contractor. Replace the entire section of wire as well. Make sure to terminate the wires properly for those screw terminals. It might be better to use crimped sleeves.

Oh and a quick "thanks" to the spirit(s) you serve - this happened without a fire. Electrical fires are dangerous and sometimes catastrophic.

Thank you for the input, and I certainly agree that I was fortunate that this didn't turn out worse.

I'll replace the contactor, as well as all connected wires. All of them (except the burned black one) are showing some discoloration from heat exposure, and I want to keep everything in good shape.

 

[LarMoeCur]

I'm crazy paranoid about electrocuting myself or burning down my house. So every fourth or fifth batch, I go in re-tighten every screw in my panel and inspect the wires for signs of heat.

 

[morbster]

Yeah, this will prompt some changes in my brewing checklist.

I also purchased a proper crimping tool so I can install crimped sleeves that should have better contact with the screw.

 

[golfindia]

I've had twist lock connectors melt and fail (open, thankfully). It's always been from weak contact between the tines of the two plugs. Some may think this opinion is bologna, but in my experience buying the cheapest part on amazon/ebay is not always the best route for electronic parts installed in potentially hazardous gizmos. I.E. there is a huge internal design/engineering difference between the $14 L6-30 plugs that have melted on me, and the $30 ones which have not melted. If you need to retighten stuff routinely, it may be a good idea to look and see if you can get another part that is designed better.

 

[LarMoeCur]

I've had twist lock connectors melt and fail (open, thankfully). It's always been from weak contact between the tines of the two plugs. Some may think this opinion is bologna, but in my experience buying the cheapest part on amazon/ebay is not always the best route for electronic parts installed in potentially hazardous gizmos. I.E. there is a huge internal design/engineering difference between the $14 L6-30 plugs that have melted on me, and the $30 ones which have not melted. If you need to retighten stuff routinely, it may be a good idea to look and see if you can get another part that is designed better.

In the case of electronic components you get what you pay for! I had a cheap ebay fuse block melt. Lucky on two accounts! One it was at the end of the boil and two it didn't take any more expensive parts with it. The fuse never blew but the block melted like wax. Ponied up the green and got some BussManns no worries now.

 

[kal]

Cheap parts often have poorly mating connection points which can exacerbate the issue. You want parts that have parts that hold on to the wire firmly all around, not just in some spots.

The heat is created when current flows through an area that is too small to handle the amount of current that wants to pass. This can happen:

(a) with a loose connection where only a few strands are making contact because the wire is not properly tightened/fastened, and/or
(b) a wire that is too small to handle the current is used, and/or
(c) when a properly sized wire is used but some of the copper strands were cut/trimmed to get it to fit (this should never be done).

Most likely (a) - it's the most common case.

All of these cases effectively reduce the contact area meaning that more current flows through a smaller area which in turns creates more heat which can melt the insulation on wires and damage nearby components.

A last option that can cause issues is if you’re pulling too much current by using oversized heating elements.

I may also be a bad part, but that's rarer.

Cheers!

Kal

 

[processhead]

Just to add to Kal's excellent points. When a terminal begins to heat up, you often will see a discoloration due to oxidation of the metal.

Once the metal contacts of the terminal, or the wire itself, heat to the point where they begin to oxidize, the surface will no longer be a low resistance conductor of current.

Even if you are able to re-tighten the connection, they will often overheat again because of this. At that point you either have to replace terminals and/or strip back wire conductors till you find bright unoxidized surfaces.

Another gotcha, when a loose electrical terminal begins to heat up, the metal components expand which just compounds the loosening and heating of the terminal. Its a common failure mode in electrical equipment that is improperly assembled and maintained.

 

[kal]

Good points processhead! Yep - it's often a slippery slope!

Kal

 

[morbster]

Thanks for all the input!

I'm going to swap out the contactor and all of the wiring that shows heat discoloration. At this point, I'm pretty sure the issue was a bad connection at the terminal. That was one of the final wires I installed, and I remember it being a real pain to get the wire properly into position.

 

[BrunDog]

I think the lesson from this is to measure the resistance of all your connections post build. Maybe worth doing it a few months later once some aging and cycling has occurred. I think some of these evolve from dissimilar metals contact but all should be identifiable by measurement. One half ohm across a junction would be enough on a 25A circuit to generate over 300W... that will get it toasty right quick!

 

[processhead]

I think the lesson from this is to measure the resistance of all your connections post build. Maybe worth doing it a few months later once some aging and cycling has occurred. I think some of these evolve from dissimilar metals contact but all should be identifiable by measurement. One half ohm across a junction would be enough on a 25A circuit to generate over 300W... that will get it toasty right quick!

Another panel wiring QC practice, that is very low-tech but highly effective, is to physically pull on every wire that is connected to a terminal. This includes crimped lug connections. (note, always shut off power while doing this.)

I have located many bad connections over the years with this method during initial assembly and also when troubleshooting problems on existing equipment.

 

[kal]

Another panel wiring QC practice, that is very low-tech but highly effective, is to physically pull on every wire that is connected to a terminal. This includes crimped lug connections. (note, always shut off power while doing this.)

I have located many bad connections over the years with this method during initial assembly and also when troubleshooting problems on existing equipment.

+1

I do this when tightening: Screw down the nut to tighten, then pull and jiggle the wire (but not enough to pull it out of course even if it wants to), then screw down again. Repeat 2-3 times and you'll often find you can go tighter or it seems slightly loose after the jiggle. This helps get a good firm seating/mating of the parts.

Kal

 

[BrunDog]

Guys, if a terminal/wire is loose at all - it's a complete failure. Do you know the force it takes to pull a properly crimped terminal off a wire? MIL specs are about 150 lbs and UL are about half of that. That's required withstand, not failure. You think your "jiggle" test can impart even 20 pounds of tensile force? Heck no. If you are relying on this test, you are not using proper terminals or a crimper.

 

[kal]

Yup! Which is why if you can pull it out at all, there's a big issue!

Kal

 

[processhead]

Guys, if a terminal/wire is loose at all - it's a complete failure. Do you know the force it takes to pull a properly crimped terminal off a wire? MIL specs are about 150 lbs and UL are about half of that. That's required withstand, not failure. You think your "jiggle" test can impart even 20 pounds of tensile force? Heck no. If you are relying on this test, you are not using proper terminals or a crimper.

That is for AWG 10. Smaller wire sizes need to hold up to proportionally less force.
https://www.checkline.com/res/products/125799/wire_pull_test_standards.pdf

Granted, there are a lot of loose crimp connections out there, and crimp connectors used where they shouldn't be used

 

[BrunDog]

That is for AWG 10. Smaller wire sizes need to hold up to proportionally less force.

Of course. I picked 10 because that is the most common AWG used here for element power.

 

[morbster]

So I got around to replacing the contactor today, here's what the burned up one looked like inside.

View attachment ImageUploadedByHome Brew1499043539.416733.jpg

Anybody want to guess which terminal had the bad connection?

 

[processhead]

Always fun doing a post-mortem on dead gear components.

 

[BrunDog]

Looks like the connection. Oxidation from heat prevalent at screw, block, and contacts nearby.

 

[doug293cz]

Looks like the connection. Oxidation from heat prevalent at screw, block, and contacts nearby.

I agree.

Brew on

 

[The_Bishop]

When I built my panel, I did the belt-and-suspenders routine.

All the heavy power leads that were going on screw terminals got rings installed that were crimped on with a roll-over crimper, then soldered. The joint was covered with the type of shrink wrap that seals. Anything that was going into a screw-tight connection was tinned in a slightly flat configuration, then tightened to the appropriate torque. I have since checked these roughly every-other brew, and none of them have loosened up.

Yeah, it took a while done that way, but it was worth it to me.

 

[BrunDog]

Tight connections are important - no doubt. But I feel the need to reiterate that the electrical connection quality is what matters. Electrical resistance creates heat. So while a tight connection will likely reduce the probability of a poor electrical connection, it's no guarantee. Clean metal-metal contact is the name of the game. I suspect we see failures from corrosion and galvanization as often and loose connections alone.

 

[itsnotrequired]

i didn't go the crimp route on my build, just one more potential source of a failure. manufacturer's publish torque values for their compression terminals so if you really want to get it right, get a torque screwdriver and follow the instructions.

 

[golfindia]

Personally i would also avoid solder on any AC connections, including tinning. Solder always seems to makes things corrode faster, specially in wet/humid environments.

 

[processhead]

Personally i would also avoid solder on any AC connections, including tinning. Solder always seems to makes things corrode faster, specially in wet/humid environments.

There are applications where soldering a.c. connections is appropriate. If soldered connections are corroding, it may have more to do with technique or materials. Always use rosin flux for electrical soldering.
Acid flux will likely cause corrosion in electrical connections and should never be used.

Tinned wires in compression screw terminal can loosen over time.

 

[The_Bishop]

That's why when I tinned mine, I 'flattened' the wire package out so it was more in the form of a flat tab and not a round bundle. They're tight, and haven't loosened at all in several checks since build.

If you're getting corrosion in your soldered joints, you're likely using an acid based flux. Use rosin flux. Don't overheat the wire. Not sure what AC/DC's got to do with it.