Roasting
Fan assist
On a fluid bed, the fan takes over part of the temperature control when the heater runs out of headroom late in the roast.
On a fluid-bed roaster the fan carries the heat, and late in the roast it can carry it away faster than the heater puts it in: the heater sits at 100 % and bean temperature stops climbing. A roaster then lowers the fan by hand. Fan assist does it for you: while the heater is pinned it takes a little air away, and once the heater has room again it gives the air back.
It needs a roaster with both a heater and a fan output, with temperature control on (the roaster's own PID in auto, or a profile driving the bean temperature).
Using it
- Switch it on on the Roast page's Control tab ("Fan assist", next to the fan slider), or for a roaster by default under Roasters → the roaster → Control → Fan assist.
- The fan you set is the most it uses. The slider becomes the ceiling; the assist only
ever takes air away from it, and the readout shows the trim next to the fan
(
assist −8 %). While a profile drives the fan, the profile's fan is the ceiling. - Moving the fan yourself sets a new ceiling with no trim. Switching the roaster to manual or turning the heater off stops the assist and hands the fan back.
- It waits for the beans to dry. Right after CHARGE the heater is pinned on purpose, so the assist only starts once bean temperature passes 150 °C.
Settings
Roasters → the roaster → Control → Fan assist:
| Setting | Default | What it does |
|---|---|---|
| Minimum fan | 70 % | Never below this. It cannot go under the roaster's fan floor while heating (roaster setup). Keep it where the beans still move. |
| Start above BT | 150 °C | Below this the assist waits; 10 °C under it, it lets go. |
| Lower fan when heater above | 92 % | The heater (smoothed over 10 s) above this takes air away. |
| Give fan back when heater below | 80 % | Below this the trim is returned. Between the two, nothing moves. |
| Lower at most / give back at most | 15 / 6 %/min | How fast the fan may change. |
| Faster per °C behind | 2 %/min | Extra speed for each °C the bean temperature is behind its target. 0 = heater only. |
If the fan and the heater hunt, widen the gap between the two heater thresholds or slow the rates. With gain scheduling the PID gains follow the fan the assist sets, the same as for a fan you move yourself.
From the command line, roast roaster show <id> includes the fan assist's settings and state.