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Elements stopped midfire


moonzie

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Howdy y'all!
 
I replaced the quad elements on my L&L e18s-3 earlier this year and they've seen about 50 firings so far - all with no issue. I usually do medium fires and they take 7-8 hours. Last night I was doing a fast glaze fire and noticed a big difference between upper and lower zones - about 300 degrees hotter in the lower zone - over 1300*f below and just barely over 1000*f above @ 7 hours into the fire. Checked again at 7:45 into the fire and the lower zone was 1600 with the upper around 1200. Noticable color difference between the upper and lower zones looking at peep holes.
 
I ran some diagnostics and with my digital ammeter I found the upper zone was only drawing .2 amps while the lower was drawing 11. My outlet voltage was 245. I had voltage present at the upper elements when the relay was engaged. I started a cool down program to run the vent fan.
 
 
I checked this morning. All appears normal. ??? Amp draw is around 11-12 amps on both elements. Voltage still good. No signs of arcing or burning. Elements read around 10.2 between upper/lower halfs and 19.8 across the entire element (quad).
 
What gives? Help!
 
Jason
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You either have a thermocouple wire that's loose, or a sticky relay. Check, all the thermocouple connections, especially the wire where it connects to the ceramic block holding the TC. The wire can break under the screw and be loose. If it's the relay, it'll probably die in the next couple of firings.

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I suspect the relays may have around 350-400k cycles on them. What's the lifespan of mechanical relays?

I went to Indy and picked up some Skutt relays that are the equivalant. Going to install later when i get home.

Can partially failing relays cause extended fire times? 

I feel like when i tested for voltage at the element block last night i was getting 60v across the two posts and the lower one had 80v but i cant quite remember...

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Checked all around for any loose wires and found none.

Replacing the relays solved the issue. I completed a fast fire last night in just over 5 hours.

I'm still curious about this tho. I've always assumed mechanical relays will usually fail on or off - not in between. But if they half-fail like mine did, then aging mechanical relays it would seem can impact fire times. As they wear, would carbon buildup on the relay pads substantially increase resistance to the circuit? 

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13 hours ago, moonzie said:

Checked all around for any loose wires and found none.

Replacing the relays solved the issue. I completed a fast fire last night in just over 5 hours.

I'm still curious about this tho. I've always assumed mechanical relays will usually fail on or off - not in between. But if they half-fail like mine did, then aging mechanical relays it would seem can impact fire times. As they wear, would carbon buildup on the relay pads substantially increase resistance to the circuit? 

Relays can fail on, off, or even one leg can fail. It's not uncommon for them to stick a few times before failing, and it often happens at high temps when they're running hot.

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