I am trying to detect a woodstove's fan and it's effects on the temp around the house. The question is how to I detect whether the fan is off or on. I can't destruct the stove in anyway, like tapping wires to the fan motor etc, it has to remain original. I know the temp of the stove triggers the fan, but I can't use a temp sensor to "guess" that the fan is on, plus there are cats in the house so using long wires are out of the question.
I was thinking of using sound/light detection to determine if the fan is on, but I don't think it will work. Any suggestions?
robfmcc:
I can't destruct the stove in anyway, like tapping wires to the fan motor etc, it has to remain original.
Usually, devices like this would have wiring terminals which are accessible for maintenance rather than being a completely sealed unit. So it ought to be possible to connect to it without compromising the existing wiring.
If you really can't manage anything like that then given that you are already planning to measure temperatures I would put one temp sensor upstream and one downstream of the heater and look for a temperature differential between them. It would take a bit of care to work out when the fan is on, but I'd expect to find a substantial difference when the fan and heater were on, which gradually faded away after the fan was turned off. Sensing the fan state directly would be a far simpler approach, though. Depending on the physical characteristics of the far you might also consider designing a sensitive flap/switch system so that the airflow triggered a switch. That would need more design work but would give you a more reliable solution than looking at the temperatures, I would have though. Simply connecting to the fan circuit would be the best approach though, IMO.
Could you shine a light at the fan (an LED?) and detect its reflection from the blades. When the fan is turning the reflected light will be intermittent. Otherwise it will the constant on or off.
Took a clue from peterH...I might buy a cheap wind meter and try to hack it. It should spin while the fan is on and then stop or at least slow when the fan is off. Access to wires not allowed, it would be the easiest way...
I'm trying to understand why not: I mean, anything is "hackable" if you have the right tools (like a nice angle grinder with a cut-off wheel - or a cutting torch, perhaps).
I mean, it's one thing if you're not the owner, or it's still under warantee or something - but beyond those kinds of situations, there shouldn't be anything to stop you from modifying it at will - provided you understand what you are doing (or are willing to learn).
If the fan is inside the stove what exactly is its role? Do you have a link to the stove specifications or a photo of it?
I had assumed the fan was external to cause air to circulate within the room.
Presumably a fan inside the stove is intended to regulate combustion and its effect should be detectable in the external temperature of the stove - using a thermocouple, perhaps. If so it may not be necessary to know anything about the fan.
I would NOT make holes in the stove even if I owned it in case carbon monoxide escaped. Holes would quite likely also adversely affect the combustion of the fuel and the efficiency of the stove.