Boil Coil plug overheating

[rudylyon57]

Fellow brewers- Has anyone using a Blichmann boil coil ever had issues with plug overheating & melting housing? I've had two 55 gallon size plugs overheat and melt plastic plug housing. Running on 208V so less current than rated 240V. Blichmann has replaced one under warranty but I'm doubtful the root cause problem has been addressed. Wire to terminal screws were loose on both burned legs but I don't know if that was the cause or effect from high resistance on posts. My plan is to open plugs and insure wire to terminal screws are tight and use electrically conductive grease on posts.

 

[doug293cz]

Fellow brewers- Has anyone using a Blichmann boil coil ever had issues with plug overheating & melting housing? I've had two 55 gallon size plugs overheat and melt plastic plug housing. Running on 208V so less current than rated 240V. Blichmann has replaced one under warranty but I'm doubtful the root cause problem has been addressed. Wire to terminal screws were loose on both burned legs but I don't know if that was the cause or effect from high resistance on posts. My plan is to open plugs and insure wire to terminal screws are tight and use electrically conductive grease on posts.

Loose connections cause high resistance, and are the most common cause of connections of any type overheating. This is a quality control problem at Blichmann. They apparently do not insure that screws are torqued correctly in order to prevent loosening with thermal cycling.

Something you can do is periodically check, and tighten, screw connections. But, you shouldn't have to.

Brew on

 

[Bobby_M]

It wouldn't hurt to put some lock washers between the screw and the ring terminals.

 

[rudylyon57]

Thanks for inputs guys. Blichmann is insinuating that heat is coming from boil coil pins and you can't tell good from bad with simple resistance check. That is root cause is the coil itself. I'm speculating but it seems like a problem where heating element joins pin and that heating softens copper, loosens screws and melts plastic housing. Yikes.
Seems like a serious issue to me if you are listening Blichmann Engineering.

 

[doug293cz]

Thanks for inputs guys. Blichmann is insinuating that heat is coming from boil coil pins and you can't tell good from bad with simple resistance check. That is root cause is the coil itself. I'm speculating but it seems like a problem where heating element joins pin and that heating softens copper, loosens screws and melts plastic housing. Yikes.
Seems like a serious issue to me if you are listening Blichmann Engineering.

A loose pin to socket connection will create excess resistance and generate excess heat in the connector. Look to see where the plastic melting is most severe - that's where the heat is being generated. It's always hottest where the heat is being generated. If it's at the screw terminal, then the screw connection is loose. If it's along the socket barrel, then the pin is loose in the socket.

Brew on

 

[Bobby_M]

Definitely get some 220 grit sandpaper going on the pins and inside the sleeves. Also evaluate the fit between the sleeves and pins to ensure it's snug. It's possible from overheating that the sleeves expanded and didn't quite contract back to original fit. You can check the resistance through the coil to ensure that it's within spec and not actually pulling more current than designed. I doubt that would be the case with only 208V applied though. Conductive assembly paste is a good idea.

 

[rudylyon57]

All your points are spot on Bobby. Once pins were cleaned off resistance checked at 10.4 ohms-which meets spec. The copper sleeves lost strength (tempered) and contact pressure from overheating. The split sleeve over pin design only allows for three "lines" of contact vs a flat plug design. That's just how an expanded hoop works. Over heating also caused pitting on the already compromised contact.
All plugs and coils have been replaced with new parts, screws checked for tightness and pins covered with conductive grease so we'll see how things go from here.