Overheated Terminals On 18Kw Immersion - Suggestions Welcomed

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kme

kme

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The brewery has a large vessel with a pair of 18KW TP immersions in - they`re on for about 2 hrs every hay; at the same time, to vigorously boil the mixture.....

When they were originally installed ( by others), they were wired in 6491x, through flexi conduit.

But - the junction temperatures are baking the connections - two of the lugs have come detached on one unit.

I`m going to be rewiring the units in the morning, with glass mica insulated cable - 250 degree operating temp - but the connection to the pins of the immersion is going to be an issue.

They will not sign off on replacing the immersions (>£300 each), as they`re working.....but I`ve got , effectively, rigid copper bar sticking out into the terminal box.

Any suggestions as to re-attachment? I don`t think solder will work, leaves compression ( iffy on solid bar) or something else, like a miniature CV spring??

 
I had to replace a standard 230V single phase immersion due to overheating terminals. I concluded it was faulty and the replacement fixed the ongoing problem with overheating terminals.

 
First thought is, is there a much larger version of the ceramic connector blocks used for high temperature lighting available.

As to the soldering, I'd have thought that if the tanks were empty it might be possible to solder a lug to to the brass bar, and then bolt to to a lug crimped on the cabling, You'd obviously need a plumbers torch rather than a soldering gun though! Treat it as if you were soldering a pipe fitting. Bear in mind that soft soldering is probably no good beyond 120degrees, but assuming this is heating the liquid rather than boiling it dry, this might be sufficient. If soldering will not cut it, perhaps you could look into having someone braze the lug on?

Last resort... find an old neutral block from a DB and saw it down into sections with two terminals in each. Some makes of DB have the link between neutral blocks made with solid rod. Temperature cycling might have an adverse effect on the screwed connections though?

 
kme said:
The brewery has a large vessel with a pair of 18KW TP immersions in - they`re on for about 2 hrs every hay; at the same time, to vigorously boil the mixture.....

When they were originally installed ( by others), they were wired in 6491x, through flexi conduit.

But - the junction temperatures are baking the connections - two of the lugs have come detached on one unit.

I`m going to be rewiring the units in the morning, with glass mica insulated cable - 250 degree operating temp - but the connection to the pins of the immersion is going to be an issue.

They will not sign off on replacing the immersions (>£300 each), as they`re working.....but I`ve got , effectively, rigid copper bar sticking out into the terminal box.

Any suggestions as to re-attachment? I don`t think solder will work, leaves compression ( iffy on solid bar) or something else, like a miniature CV spring??
Click to expand...
Martyn, is that a round bar or flat .?  

Any chance of a piccy ?

As I'm sure you know, a high resitive heating load like that will often melt the final connections and sometimes have to treated as sacrifical .

 
Last edited by a moderator:
What size were the 6491x cables ,were the lugs insulated or uninsulated.Think i would try soldering the lugs onto the intemp 250 cable

 
Thanks all.

The bar is round mate, the lugs were insulated with 4mm singles.

They don't boil dry.....that would destroy the immersion.

I reckon they're too thin to thread...but nice thinking.

N block is a Damn good idea...sweating lugs on May be a good one to try first, though.

Thank you gents

 
Don't sweat lugs on with soft solder though, you would need to use silver solder or braze to get a reliable connection at elevated temperatures.

You would not need a N block a "normal" "chock block" would do as long as you have sufficient air space between the connections so that you are no relying on the polymer encapsulation.

You could thus just split down a "chock block"...

Oh, and it's 18kW not 18Kw!

The other issue that you could have had is the lack of sufficient flexibility in the 6491 for the vibration caused during the boiling process, high frequency, small amplitude, regular exposure, and almost of a true chaotic nature.

Inadequate design thought I would say!...

 
I like the threading solution, it's elegant if they're a decent diameter and can withstand the reduction in diameter the threading would cause. I've used just the brass inside of choc blocks before on elements, never on anything above 20A but it generally works well if you meticulously dress the element posts with a file or emery cloth or even a Dremmel tool first. If you're thinking about solder or silver solder then rather go with spotwelding a threaded terminal onto the terminal post, that's how we manufacture or elements in our workshop and it's much more reliable and robust than solder. If the terminal post is damaged then take a pipecutter and cut 15mm of the outer tube off to expose more of the post. The cold zone of the element is usually long enough to allow this assuming there's sufficient tube protruding from the mounting boss, if you're in doubt you can define the length of the cold zone using a magnet first. Just re-seal the element outer incoloy/hastelloy tube to the inner steel terminal post with silicone because the internal mica filling is very hygroscopic and can cause low IR if it's left open to the air.

 
standard solder melts at 270oC, avoid silver solder , solader paste as this is designed to melt at lower temperatures of around 130oC. Failing that Brazing  i around 600oC. Think the suggestion for a good mechanical join though is probably better in that it makes future works a lot easier, and it sounds like it will need repairing again sometime soon.

 
I would use uninsulated lugs  much better fit on 4mm ,insulated lugs (yellow) will fit 4mm & 6mm never thought that was a good idea

 
what type of insulated lug was fitted was it a push-on spade type or bolt type

 
binky said:
standard solder melts at 270oC, avoid silver solder , solader paste as this is designed to melt at lower temperatures of around 130oC. Failing that Brazing  i around 600oC. Think the suggestion for a good mechanical join though is probably better in that it makes future works a lot easier, and it sounds like it will need repairing again sometime soon.
Click to expand...
Why avoid silver solder?

I would avoid soft solder yes, but not silver solder, and as far as I can remember it has better conductivity than brass based brazing materials.

The silver solder I have melts at around 600 deg C.

It would easily see service up to 300 deg C.

It's Johnson Matthey stuff.

 
600 deg C, sounds more like silver braze. In my experience silver is added to lower the melting point, so tends to be very popular with surface mount devices on printed circuit boards, never come across a high temp version.

 
Binky,

I think we are cross purposes, I refer to silver braze as silver solder, so as to distinguish it from brass based brazing alloys.

600 is a lower melting point, the silver solder alloys I have used are all above 500 melting point.

Brass based tend to be around 700, well the ones I have used anyway.

I also know them as hard soldering alloys, rather than soft soldering alloys.

 
I run my iron @ 450 most of the time, regardless of melting temp of the solder, offers a thermal cushion to heat the joints up quicker, in and out as quick as possible and all that! ;)

 

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