MikP

Thanks for all the suggestions. I sealed up the lid gap and did another run, max temp did increase to 1141C (up from 1080C with the gap) but still well shy of the 1250 target, results graphed below. Had a range of cones from 03 to 8 in there to check accuracy and they more or less lined up with thermocouple readings. @Bill KielbYou're right about this being a low voltage issue. The Nominal voltage down under is 230V with a -6%, +4% tolerance which already puts me under the 240V rating of the kiln. Wiring to kiln is adequately sized IAW Aussie standards (they allow for a 5% drop). Not much I can do about the voltage supply, could upsize the feeder cable from the mains but I doubt cost of doing so would justify the increase in wattage I'd get from reduced voltage drop. I'm thinking my best option to increase wattage would be to play with the resistance values for the heating elements. The replacement elements I got were 14 AWG Kanthal A1, figure I could go to 13AWG and size for a current draw of 30A @ 240V. I'm working on a small DIY kiln for glaze testing to see if my element design math checks out, if that goes well I'll have a go at some custom elements for this project. @jbruce thanks for the offer for tech support, haven't focused on tuning yet as I wanted to verify max temps first, will have a go at tuning before the next bisque fire.

I've caused a bit of confusion as the controller UI doesn't display the schedule shifting well, it 'squishes' the measured temperature onto the target profile so it appears as though it climbs and stops abruptly. I've pulled the raw data from the controller and plotted it below to clarify: Target profile in red, measured temp from thermocouple in blue. Schedule shifting takes the target profile and shifts it right until the measured kiln temperature catches up. Kiln can't meet the ramp rate (approx 200c / hour) at around the 800c mark and maxes out at 1080c, SRR is on continuously at this stage. Kiln sitter timer switched the kiln off at 17h (a bit excessive but I wanted to confirm the temperature plateau). Voltage drop across SRR is 1V, voltage supply to SRR drops to 228V (down from 236V) when elements are firing. Element and section resistances match up to values given in the service manual (820-1/820-2 for 240V supplies): Based on this, I'm inclined to think its a shell loss issue. Am I barking up the wrong tree?

Hi Bill, Green line is the target firing schedule, white line on top is is progress against firing schedule. Controller has built in schedule shifting if kiln temp lags behind setpoint to allow temperature to catch up (thus why the 2 hours @ 1080c I mentioned doesn't show up in the graph, it basically waits at the 7:20ish hour mark indefinitely). Don't believe its a controller issue/SRR issue as it works fine for bisque firings and tracks well up to 1080c. Link for the controller I'm using below if anyone is interested. As you say I think the issue is to do with shell losses @ 1080 exceeding heating ability of coils. At first I also thought it was a worn coil issue so I replaced all 8 elements so I'm confident its not a power issue. Measured voltage at the supply is 236.3V, measured Amps were 25.6A with the new elements which is approx. 6050W (I'm thinking the higher than nameplate current draw is a result of the new elements and supply voltage being lower than 240V). Intent is to use the kiln up to cone 6 firings but I figured I'd shoot for cone 8 as a test with the elements newly replaced. Sanding down the lid to minimise the gap will be my next step but I wanted to sanity the idea that the gap could cause that much drop in max temp while I wait for the kiln to cool

Hi everyone, I'm refurbishing a Duncan EA820 and I'm having trouble getting it up to temperature. The kiln is a Duncan EA820, Single Phase, 240V, 24A, 5760W, 1260°C Max temp (Cone 8). I've added a digital controller (kept the kiln sitter wired in but replaced the timing circuit and mechanical relays with an zero crossing SRR driven by a raspberry Pi), replaced the lid and replaced all 8 elements with new ones. I've measured the supply voltage to the kiln and the current draw and confirmed its IAW with specs. I've tried firing a cone 8 schedule but the kiln temperate maxes out at around 1080°C (approx. cone 03?) according to the thermocouple. It has been hovering around this temperature for about 2 hours now with all elements on continuously and there's been no increase in temperature. I noticed while firing the lid has some high spots resulting in a gaps between 3mm - 5mm around the kiln which I have yet to sand down. Gap exists when the kiln is cool but I never considered sanding the high spots down as I had previously only used the kiln for bisque firing with no issues. Is this kiln lid gap significant enough to be the most likely cause for not reaching cone 8? Other things I've considered are: Inaccurate Thermocouple - I'm waiting for the kiln to cool down and i'll have a look at the witness cones. I've previously ran a 06 bisque fire with no issues. Kiln too loosely packed - didn't fully pack for this initial test run, would this have a significant effect on the max temp? Any advice from the kiln gurus would be much appreciated. Cheers, Mik

Hi there, I'm looking for replacement bricks (specifically KB 002 820 Grooved Brick, see below) for a Duncan EA820 but am having trouble sourcing them where I am (Australia). I was wondering if anyone has experience using bricks from other 8-sided top loaders (paragon, Skutt etc) models, are any brands "close enough" to the Duncan bricks such that I could make it work with some minor shaping/finagling? Cheers, Mik