Turn on a fan automatically when a heater is activated?

pro3d

I have a drybox that acts as a chamber in DWC. As a safety feature I would like to turn on the fan when activating the heater in the chamber (drybox). Is this possible and how? I know I can set the fan to be always on but that is not what I am looking for. I want something like "If Hx=1 then Fx=1"

This is why I need this function:

dc42

@pro3d can you connect the fan in parallel with the heater, if they accept the same voltage?

pro3d

@dc42 said in Turn on a fan automatically when a heater is activated?:

@pro3d can you connect the fan in parallel with the heater, if they accept the same voltage?

I would have to check but we want the fan to stay on after the heater is turned off. At least for a while to cool down the heater. Is it possible to make a conditional relation?

jay_s_uk

@pro3d you can use the object model to get the heater status and daemon.g to control the fan

pro3d

@jay_s_uk said in Turn on a fan automatically when a heater is activated?:

@pro3d you can use the object model to get the heater status and daemon.g to control the fan

I am not familiar with daemon.g

jay_s_uk

@pro3d https://docs.duet3d.com/en/User_manual/Tuning/Macros#daemong

deckingman

@pro3d Or how about wire a small relay in parallel with the heater, connect the contacts to a spare io pin and use that to run a trigger macro which will turn on the fan. https://docs.duet3d.com/User_manual/Reference/Gcodes#m581-configure-external-trigger and https://docs.duet3d.com/en/User_manual/Tuning/Triggers

pro3d

@deckingman said in Turn on a fan automatically when a heater is activated?:

@pro3d Or how about wire a small relay in parallel with the heater, connect the contacts to a spare io pin and use that to run a trigger macro which will turn on the fan.

Yeah I was hoping to solve this by firmware without to much workarounds. It would be nice to trigger the fan just by activating the heater by firmware. But maybe it's not straight forward as I thought

deckingman

@pro3d Unfortunately triggers are only external via io pins. I agree that it would be good if any event could be a trigger. A kind of "If This Then That" approach.

fcwilt

@pro3d

Does it have to come on immediately or could it be tied to temperature?

You could have a temp sensor placed where appropriate and set up the fan to be tied to a threshold temp, like you would with a extruder fan.

Frederick

pro3d

@fcwilt said in Turn on a fan automatically when a heater is activated?:

@pro3d

Does it have to come on immediately or could it be tied to temperature?

You could have a temp sensor placed where appropriate and set up the fan to be tied to a threshold temp, like you would with a extruder fan.

Frederick

It has to come immediately yes. As the Temp sensor is in the box, not on the heater

fcwilt

@pro3d

I was thinking of putting the temp sensor in the box.

So what bad things would happen if it didn't come on until the temp sensor read some threshold temp?

Thanks.

Frederick

pro3d

@fcwilt said in Turn on a fan automatically when a heater is activated?:

@pro3d

I was thinking of putting the temp sensor in the box.

So what bad things would happen if it didn't come on until the temp sensor read some threshold temp?

Thanks.

Frederick

The sensor will not read more than ambient for a while and the heater will go wild and the fan shroud will creep/melt

fcwilt

@pro3d

Well if you put the sensor where the heat is an issue and set the threshold to 30 it should turn on quite soon after the heat turns on.

Frederick

jens55

I have a similar issue that is still waiting for me to implement a solution. What I will be doing is to set up a time delay relay of some kind. Either a commercial relay or a standard relay with a simple 555 timer circuit (ie home-brew).
The fan turns on with the heater. The heater turning on sets/activates a relay that also provides power to the fan (so the fan is powered by the heater as well as through this relay). When the heater turns off, a timer starts while the secondary relay stays activated (and thus provides power to the fan). After a given time period (say 30 seconds) the timer drops out, the secondary relay releases and the cooling fan has no more power and stops.
Depending on how the fan is powered (high side switched or low side switched), the relay might be in the high side circuit or the low side circuit.
I have not yet looked to see if an off-the-shelf time delay relay can be had for cheap or if I should implement the timer function myself .... I would expect a commercial solution would be available from AliExpress at a reasonable cost.

pro3d

@fcwilt said in Turn on a fan automatically when a heater is activated?:

@pro3d

Well if you put the sensor where the heat is an issue and set the threshold to 30 it should turn on quite soon after the heat turns on.

Frederick

This would not report box temp as being close to the heater temperature would be higher than chamber temp

fcwilt

@pro3d said in Turn on a fan automatically when a heater is activated?:

This would not report box temp as being close to the heater temperature would be higher than chamber temp

I've gotten confused.

I thought the goal was to turn on the fan to protect the fan shroud.

So if the sensor is near the shroud would it not serve to protect the shroud by turning on the fan before the temp was high enough to be a problem?

Frederick

pro3d

@fcwilt said in Turn on a fan automatically when a heater is activated?:

@pro3d said in Turn on a fan automatically when a heater is activated?:

This would not report box temp as being close to the heater temperature would be higher than chamber temp

I've gotten confused.

I thought the goal was to turn on the fan to protect the fan shroud.

So if the sensor is near the shroud would it not serve to protect the shroud by turning on the fan before the temp was high enough to be a problem?

Frederick

Yes but the sensor is supposed to monitor the chamber/box temp. Not the heater temperature, so the sensor need to be away from the heater....

engikeneer

@pro3d he's meaning add a second sensor. The advantage of this method is that you actively know if the shroud is getting too hot, and you could even set up over temperature warning if it still got too hot with the fan on (or the fan fails!). It also gives you the delayed turn off in on, as itll stay on til the heater has cooled (which may be differentlengths depending on how longs its been on). To me, this is the 'safe' way to monitor this issue, though generally I prefer to avoid designing in potential thermal runaway events where possible.

The Daemon.g option is the firmware only approach you want. It is a script that repeatedly runs in the background, so you can use metacommands (I.e. the RRF built in programming language) to put whatever if/else/while/whatever blocks in to control your fan based off accessing machine data in the object model. You'll need to be on RRF3 and do some reading up on the meta commands which is all on the wiki.

pro3d

@moth4017 managed to get this sorted out with the daemon.g file and some if, elif commands

Now the fan activate when heater turns on, and off when temp is below 35c