FAULTY FOG MACHINE THERMOCOUPLE

[partyanimallighting]

Hi wizards! It's been sometime since I last sought advice in this forum but I'm looking for a solution to a problem I've encountered. I have a perfectly good heater block for a Hurricane 1301 Fog Machine that has a broken thermocouple wire. These newer blocks have the thermocouple cast into the block itself during manufacture so they can't be replaced if something goes wrong (a broken wire in this case). My questions are 1, can this broken thermocouple be replaced with another type? And if so, what type and what value? I see that there is ring types and also  threaded K types which screw into a hole in other types of blocks (Antari 1200 II, M5). Question 2, if I can replace the broken thermocouple with say a ring type or screw type, do I take a guess as to where to drill the hole that will be used to fasten the new thermocouple to the block? I wouldn't like to accidentally drill into the capillary fluid tube cast into the block. Question 3, if the new thermocouple does not trigger the pump, is it simply a matter of adjusting the pot at the thermocouple terminals on the fog machine motherboard? I've done this before when replacing substitute heater blocks in other units in the past with no issues operationally.

Hoping for a positive response!!

[Jivemaster]

I have no idea whether that is a thermostat (bimetallic) or a resistance thermal sensor of which type.

Can you locate the point where the sensor wire leaves the block (where the broken wire should be) then dig some resin out and refix a wire.

If a fog machine is essential, I wouldn't want to go out with a bodged one. How much will a replacement machine cost in your market?

[richardash1981]

That doesn't look like the thermocouple is "cast in" - I'm not sure it's even possible, because the thermocouple relies upon joining two different metals (neither of them the same as the block, and has to be electrically insulated from them).

With thermocouples, it is vital that the combination of metals used is the same as the original, and connected the same way round! The metal combination is what the letter code means - for instance a K Type Thermocouple positive leg is composed of 90% nickel, 10%chromium and a negative leg is composed of 95% nickel, 2% aluminum, 2% manganese and 1% silicon. Any replacement has to be the same letter type to work.

There are standard colour codes for the lettered types (all right, three standards, but still). The fact that yours seems to have both leads white makes me suspect it isn't a thermocouple. It could be a Platinum Resistance Thermometer (PRT) - which is platinum wire which changes resistance, rather than generates a voltage. These are reversible (hence two white wires), but come in a number of nominal resistances - 100 and 1000 ohms are common. Again, you need to know which.

Digging enough of the broken end out to get a connection and meter it might at least answer this question - PRT would measure about 100 or 1000 ohms, thermocouple will be nearly short circuit (but might measure differently if the polarity is reversed).

[Jivemaster]

Does the pcb that uses the signal offer any help? Does it say what sensor it needs in lettering on the board?

[partyanimallighting]

Hey guys! Firstly thanks for all the responses. So here goes. This heater came off a Chauvet fog machine and I don't want to poke around I.e: drill into where the wire leads exit the block because I don't want to drill through the capillary fluid tubing accidentally and ruin the block. Jivemaster, there seems to be no type of resin or filler where the wires enter the block so I was assuming (maybe wrongly) that the sensor/thermocouple/PRT (???) is cast into the block itself. I have encountered ring type 6MM thermocouples bolted onto the block itself on other brands and I know for a fact that the Antari models use a K type 6MM threaded thermocouple screwed into the rear of the block where the heating element terminals exit the block. Replacing the block with an original block for Chauvet units runs between USD110.00 to USD185.00 and this is before inland shipping and US sales taxes. Then there's overseas shipping to me plus Customs duties and taxes. Not worth it hence me posting here looking for a solution. richardash1981, I also would assume that the thermocouple can't be cast in because it has to "expand/flex" if it's a bi-metal type. Regarding the color coding, the wires themselves both carry white insulation but the terminals that connect to the PCB are color coded (RED+ and BLACK-) and the PCB itself is marked + and -.

Moving on.........I decided to take a gamble and I drilled a 6MM hole in the back of the block in the same general area where these screw type thermocouples are connected on the Antari heater blocks. Strangely enough, the block seems to be hollow inside but I didn't investigate that further. I then tapped out the hole with a 6MM tap and screwed in a K type thermocouple. I then reconnected everything and powered up and the block heated up and I checked the temperature, which climbed steadily. The thermocouple did not trigger the PCB at all to activate the pump but I adjusted the potentiometer that controls the thermocouple ever so slightly and VIOLA!! The Green FOG LED comes on! The fog output was exactly like the original output and the machine cycles on and off as it should during use, no spitting, no sputtering, no liquid residue when the output dies down and no burning fluid smell so the output seems to be fine. The block itself reaches a temperature of around 165 ~180 degrees (taken at the front of the block with a laser temperature gun) before the thermocouple triggers the fog output and everything seems to be fine. Just to be safe I put a 185 degree N/C thermostat across the LIVE AC lead feeding the block. This is where I expect to hear you guys SCREAM at me and warn me that I've just created a fire hazard...........or am I OK here?

[timsabre]

All fog machines I have seen have a thermal fuse or resettable thermal trip on the AC feed to the block, for safety overheat protection. Does this machine not have that as standard (I realise you say you've added one)?

I have experienced an aluminium block melting when the AC feed triac shorted on and the thermal fuse had been bypassed, so it is definitely a safety issue that something like this should be fitted.

Clearly there's all sorts of potential legal/insurance issues with modifying a machine like this but you're presumably aware of that.

[kerry davies]

How much time (money!) have you spent so far on this machine, bits of which look quite aged?

Does that amount exceed the cost of a second hand one from Fleabay?

Does it not make sense to purchase a cheap like for like replacement and strip the current one for spares? 

As usual I claim old age and ignorance for these thoughts but ..... ????

[KevinE]

The original thermocouple is spot-welded to the capilliary tube. You can see the spiral tube poking through the aluminium alloy casting in the first picture. So to do it properly you'd have to uncover a little bit of the tube and re-weld it. Those cheap spot welders from Amazon meant for battery packs will work.

Of course many smoke machines as you know do mount a simple normally closed stat somewhere on the casting.

 

The thermocouple does not act like a switch as I'm sure you know but produces a variable voltage for the circuit. The pump will be enabled some time before the heater begins proportional energy control (switching on-off at a mark-space ratio proportional to the setpoint-process variable error).

 

Hopefully when you said the aluminium block seemed hollow, you didn't hit the tube with the drill, but you'll find out in time! Probably just an air pocket. 

 

[partyanimallighting]

Hi all!! timsabre, yes. The unit does normally carry a bi-metal thermostat mounted on the heater housing or a plate mounted to the block but this machine has been sitting around waiting to be repaired and that thermostat appears to have wandered off somewhere so I simply installed another where the original one was fitted. And also yes, I was also amazed to encounter that melting heater block scenario in the past. Right through the vents on the bottom of the machine's housing. Thankfully before any major damage happened and it was an incident that I was no way involved in. Blocks on cheaper machines are normally wrapped only in fiberglass insulation and this could happen but the larger (better quality) machines have their blocks fitted into a sheet metal enclosure and in case of melting, I would think that this enclosure will trap the melting aluminum.

kerry davies, I have wayyyy too much spare time on my hands!! 🤪Money wise, just the cost of the thermostat actually......it's aged yes, but these Hurricane models take "lots of licking and keep on ticking" as they say. Even if I source a used one, there's still the additional cost of shipping a used unit overseas to me, and that's just not cost effective.

KevinE, to date I've haven't had the idle need to take a blow torch to a heater block and melt away all the aluminum but to be honest, I've been dying to see the internal makeup. I'm assuming there's the capillary tube coil exiting front and back and the heating element fitted inside this coil inside a mold and the molten aluminum is poured into the mold and that's that. I have seen (just yesterday actually) the thermocouple spot-welded to a capillary tube in a Froggy's Fog H4 Hazer (first time seeing this)  Also, thank you for pointing out the spiral tube poking through the aluminum block in my picture. I DID NOT notice this at all and I now have an idea as to how close the spirals run to the edge of the block.You're saying that I can just scrape away a bit of the aluminum and spot-wend on a new thermocouple and this sounds like a new project that peaks my interest for sure. What type and value of thermocouple should be used for this? I know that the ring type and screw type K is normally used in fog machines but is there a particular type that can handle the spot-welding? Or do I use the standard ring type?

As for the drilling of the hole into a supposed pocket, I've run the machine and there's no leaking of fog fluid or smoke anywhere near where I drilled the hole so it seems that I missed the capillary tube........hopefully. I would have assumed that the entire block was solid but I suppose the formation of an air pocket is quite possible during casting.

Thanks all!!!!