My heatstick

[Garak]

After weeks of waiting for parts my heat stick is finally done. I assembled and tested it the night before last. I wish I could say it was uneventful, but shorting out 30A is always interesting.

The heating element has two terminals sticking out about 1 1/4" and the element is going into a 90 degree swagelok fitting... so it took alittle bending to get it into place. In the process of doing so I damaged the insulation without noticing. I checked for shorts with a multimeter after assembling it, I think I only checked up to 20k ohm isolation between each hot and ground. When I hit the breaker I seen a very bright flash coming from one of the inline fuses. Which left me pretty puzzled as I was sure I had tested everything. Just as I was about to hit the breaker and turn it off I noticed there were bubbles forming on the element, so I took my clamp on meter and checked for current in each of the wires. Hot 1 had 10A, hot 2 had 0A and ground had around 7A. So short ground, disconnected everything checked resistance between ground and each hot and everything measured as it should, 12.4 ohms between the hots and over 200k ohms to ground. This left me even more puzzled, so I hauled the full thing a part to find scorch marks on the insulation in the elbow. All I can figure is that the slightest bit of heating expanded the terminals so that they made contact with the wall of the elbow.

After repairing the damaged insulation reassembled it and tested it again. Clamped the meter on, only 17.6 amps on each hot. So only then did I check the voltage, only 208v as I'm in a large apartment building running on 3 phase power. That drops the element from 4700watts at 240v down to 3606watts. I think I'll be doing most of my brewing down at my buddies house which should have normal residential 240v.

I had around 6 gallons of water in the pot, it took around 45min to go from tap water cold to rolling boil. I also took advantage of this to test my 25' 3/8" immersion chiller which took only about 10 min to get down to pitching temps with lots of stirring. Stop stirring for 10 seconds and the water coming out of the chiller would drop in temperature showing that it isn't picking up much heat. It seemed the more I stirred the hotter it got. So my plans to make a wort stirrer from an old cordless drill motor assembly must go ahead.

Its been a good week for me, I'm that much closer to doing full sized all grain batches and I just got news that my new job is official. I'll be joining the Discovery Centre full time in about month. I'll be working in the exhibits department developing, building and maintaining the exhibits. In a lot of ways its my dream job, a great mix of engineering and fabrication while not making anyone else rich(its a not for profit).

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[LiverDance]

Looks sweet! Nice job

[BBrianBoogie]

Looks like a good setup. You're right, you likely damaged the insulation. A megger would have picked it up, but an ohmmeter sometimes won't depending on the degree of damage. The problem being that the ohmmeter only puts a very small potential on the wire, whereas a full voltage will exploit the tiny problem and make it worse very quickly. That'd be my guess based on what you said.

[mr x]

Looking good. Fun popping big fuses ain't it.

[Garak]

Yea the high voltage could be just enough to ionize the air to bridge the gap. There was noticeable damage from arcing inside the elbow. My cellphone was dead at the time so I couldn't take any pictures. All my multi-meters are very cheap, the most reliable one I own is one I built from a kit in college.

There was about 4" of high temperature insulation covering the the terminals, so I just slid it back and cut away the 1" damaged part and pushed it back over the terminals. The insulation is kinda like a finger trap, push to together and it slides off easily. No signs of any leakage current after the repair.

Good grounding is everything with something like this. That fault could of been lethal if everything wasn't properly grounded. I had the stainless pipe grounded and the pot was sitting on the grounded range. Interestingly about 70% of the current during the fault went through the ground wire attached the the pipe. The other 30% I can only assume when through the range the pot was sitting on. Conducting from the pipe to the wall of the pot. Its unlikely that any significant current went through the water. I think my next bit of work is adding a grounding lug to the pot, just for added piece of mind.

I think I'm going to include two split core transformers in my controller when I build it. They will allow the electronics to monitor the current and detect any faults, it will operate sort of as a poor mans GFIC, shutting down the SSR and sound an alarm. Because SSR's can fail on it won't be a replacement for a GFIC. Now that I finally will have a steady income for the first time in a year, it won't be long before I'll be picking up a real GFIC breaker to power it all.

I forgot to thank Mr. X for linking me the forum post that inspired this design and to the ebay listing of the heating element. He also helped me out sourcing the pipe used.

[mr x]

I'm shocked you are only getting 208 vac. That would be one scenario where the variac would fix things (mine will output 15% over line voltage). But if you can go your friends house with 230/235, that's great. It's a nice design for a number of reasons.

[moxie]

I like that design a lot. Very clean. Congrats on the new job.