RD3 Blower Output over Set Temp

I have been doing an 11lb brisket for a family gathering today with folks in from California to watch the Bears-49ers game. I put it on yesterday at about 4:30pm with temps set at 225. As an aside, I immediately had to leave for a dinner party and was able to use the HeaterMeter web service for great conversation with some strangers, many thanks again to the HM community!

So, I've noticed I have had a couple of temp overshoots where my RD3 blower is not kicking off soon enough. At about 11pm last night, I got home and probed the brisket. It read 161F, which I thought was pretty fast. With my setpoint at 225, the blower showed output until 242F. Temps wound up peaking around 290F and came back in line and held pretty close to 225 the rest of the night. However, I woke up to find my meat dropped 20 degrees. This morning, with my fuel running low, as evident by the high output, I wrapped the brisket and loaded my kamado bowl up again. So, as I am worried it won't finish in time, I cranked her to 270 and the blower was outputting until the temp reached 283F.

I think based on this, I want to decrease my D setting to reduce this overshoot, right? How much would you suggest?

Good news is that the meat has gone up about 10 degrees in the last 40 minutes, just hope it rises steadily in time for half-time.

HM Graph
http://imgur.com/9sQLVdh

PID Settings
http://imgur.com/AieCGeI

Maybe I'm just not understanding it because mine's a 4.1 and uses pulse mode, but it looks like you've got your fan set to never shut off (5% min) and to run at full-blast when maxed out (100% max).

For a kamado, 100% output is way overkill with the RD3's fan. I'm on a 22" WSM and I cooked chicken yesterday at 300F, and 40% max was enough to hold it perfectly steady. I know when I first started off with the HeaterMeter (no RD3 at that time), that I had issues because I had my fan speed way overcranked.

Again, maybe voltage mode is set differently, but my first suggestion would be to check those fan speeds.

I thought the On Above setting at 99% is saying that the fan only comes on when the damper is fully open. And then, the 5% min is saying that it comes on at 5% and up to 100% as needed?

Ah you're right, my bad. So yeah, your fan only comes on when the damper is all the way open. But look at your fan settings.

If I'm understanding the documentation correctly, your current setup only allows the fan to come on at full blast, and furthermore, your fan is config'd to max out at true full blast. I'm curious where you got the settings from ---- other Kamado users?

You're showing:
On Above: 99%
Min: 5%
Max: 100%
Startup: 100%

Here's the documentation:
On Above:
Do not run the blower at or below this PID output. The blower output is linearly increased from this value to 100%, where the blower output will be MAX. Setting to 50% means that the fan won't turn on until the PID output is above 50%. To replicate the old "only on at MAX" setting, set "on above" to 99%. (LinkMeter v13)


Note the following statement -- "the blower output is linearly increased from this value to 100%". If you set the value to 99%, then it can ramp from 99% to 100%, that's it. So it's either practically-full-blast or true-full-blast, unless the wording in the documentation is ambiguous (which it totally could be).

Have you tried running it in a standard config where the servo and fan output are equal, but with a fan max of like 40, 50%?

There used to be a setting in a previous configuration that was a check box to basically only have the fan come on as needed only after the damper was fully open. It was then explained to me that the On Above set to 99% would do the same thing. I may be misusing the Min/Max/Startup %s though, I'm honestly not sure. My goal is to have the damper maintain the temp in my Vision Kamado, which holds temps great via the dampers alone, so fan should really only come on when ramping up to temps, and later on in my cooks when fuel is low. For the most part, I am seeing that. But the overshoots suggest something is amiss in either my PID settings or the Min/Max/Startups as you pointed out.

100% Max is probably way to high, try around 30% for MAX (you can leave Startup Max at 100%). Also, I would put the MIN back to 0 if you are using the stock blower, having the min a 5% will cause the HM to bank up time when the blower should be running slow and release it in bursts of air instead. There is no need to set the Min about 0 with the stock blower.
The overshoot spike there is kinda large, that seems to indicate that either the damper was not moving to where it should be or there was an event like a grease flare-up or a chunk of wood that ignited and burned sending the pit temp too high. Top vent setting could also play a role in this...

Ralph - I'm with you on the Min back to 0%, but if I'm noticing my blower in the later stages of a long cook needing to go up to at least 80% in the last couple of hours to maintain the temp, I gotta think 30% Max would fail me, right?

I still don't think I'm clear on my original question. I'll keep an eye on the damper next time as it approaches my setpoint. To clarify, the blower shouldn't come on until the damper is wide open if the On above Setting is at 99%, right?

I was seeing 0-5% blower output up to 17 degrees above my setpoint. I would think this would be more due to the PID settings vs a flareup which could happen independently of the blower operation, unless it was purely coincidental, but both overshoots I noted the output above the setpoint. So, in reading the PID tuner article, I was wondering if the the D setting was causing this and if so, how much should it be cut to correct?

All that aside, the HM and the RD3 performed extremely well on my cook this past weekend, much better than what it would take from me manually. The brisket came out at the same temp as my last non-HM cook, covering the same time. Other than these overshoots, I didn't have to even THINK about checking my cooker! It was well enjoyed at my party too

There is a bit of skill associated with building a proper fire to sustain a long low and slow cook in addition to having your HM dialed in. So you have to make sure the fire is right, that it has enough fuel to get through, that is it breathing properly (not piled tight or choked with coal dust) and that ash is not clogging up your pathway for air delivery.
On your PID questions, yes, if the put is way into overshoot and the HM is still above 0% output that is a PID setting issue. You will have to experiment with it and learn how the PID settings effect the cook, and work with your top vent settings etc. The thing that I find most odd about your graph is the overshoot is in a rather steep spike, not a gradual ramp. This tends to happen after a lid opening when the fire is over stoked or after a grease or wood flare up in the pit.

You're absolutely right. The spikes you see are shortly after the lid was opened in both cases.

My initial fire build on Saturday wasn't my best effort, was rushed, so I think I may have overburned out of the gate causing less fuel than I should have had yesterday morning as you can see with the high blower output, but I know what you mean. I didn't do a clean sweep of my bowl before lighting either.

I have another big brisket scheduled to go on for Christmas, but I may try a small flat in the next week or so and play with my settings again. Thanks Ralph!