Little update.... I seemed the last couple days to be having trouble keeping fire with the coal. Temps would be down in the 140s in the morning, with just a little fire burning. Still had some wood, but the coal just couldn't get going. So yesterday evening I raked everything down, and decided to load a little more wood than I had been doing. Also put in some split stuff on the bottom. I added my bucket of coal first, then the wood. Also tossed in a couple big lumps on top of the wood when I finished. I didn't add a full load of wood, but more than I had been. Also set my differential to 10.
Big Difference!!! Bigger, hotter fire, that would have probably given me a 30+ hour burn. Loaded it back similar this evening. Saw a 1 ft flame shooting out a bit ago, so i think it's rolling!!
It ran a cycle in ~10 minutes
I believe when I started earlier in the week, I had a good bed of wood coals to keep the coal burning. After a couple days,my wood coals had burnt up, and the big heavy locust rounds just weren't coaling up good enough to keep a good mix of wood and coal "coal bed". I think it is similar to the problem I had early in the year when I was under loading my stove, and couldn't keep it burning.
Not sure how much a bucket of coal saves me in wood per day, but it seems substantial.