current sensing 220v kitchen exhaust fan for adding automatic shutoff valve - Page 1
Forum section: electronics / beginners

author: thisisagoodusername
author_rank: Newbie
timestamp: December 29, 2021, 01:42:26 pm
content: (new here), been a fan of eevblogs youtube shenanigans for years - also inspired me to look at the same solar charging system for my upcoming full electric car.But I'm at a loss, I have a fairly simple problem, and I'm finding it dificult to find a existing product for my need, or maybe it just doesn't exist?.. well in that case i would have to build it myself, it shouldn't even be needed with arduino.I really hope to get some ideas from you guys, be it existing products or some inputs for a little hobby project.preamble/problem:We installed a heat recovery ventilation system in our house - doing all the ducting ourselves, but getting an authorized dealer to install the aggregate and ensure our system is balanced - why would we want this ?- for 2 reasons:- better indoor climate- reducing of radon in our house (>5Pci/l)by doing best practice for radon elimination we can get to <0.5pci/L, which is good enough for australia (and denmark in this case), but this entails sealing off our kitchen exhaust fan. - we purposefully didn't connect the kitchen exhaust to the ventilation system due to recommendation of possible grease vapors getting into the pipes, even with filters etc..by doing this we can establish a overpressure in our house, that basically makes a "barrier" for radon seeping into the house, get great indoor climate, basically no moisture and great temperatures.solution 1:get rid of the kitchen fan entirely..solution 2:put a manual shutoff valve on the kitchen exhaust fan. - would be cheap and would work - but would suck, also my wife would kill me if i presented this solution to hersolution 3:put a automated shutoff valve on the kitchen exhaust fan, its a 100mm pipe - and theres several 100mm motorized shutoff valves on the market. - personally looking athttp://www.lindab.com/global/pro/products/pages/dtbu_2533.aspxorhttp://www.lindab.com/global/pro/products/pages/dtbcu_1991.aspxit will be a fairly simply thing to install it - yet i need to drive it with something.solution 3ajust a pushbutton that i stick to the kitchen fan control panel = my wife will say.. nope... :Sbut it would be super simple to do.solution 3bsome motor control that can sense the kitchen fan is drawing power from the wall socket, and then open itself and stay open when the fan is running, and shut itself when the fan is turned off.. should be simple no ?so something like:(current clamp/probe on the kitchen fans 220v plug) <-> (if amp > some level then send 24v to the motor else do nothing)I've never played around with detecting / current sensing before, and never been playing with 220v either - only done 5-12-24volt analog stuff + arduino projects.is it me is this just a futile project?, shouldn't there be a simple over-the-counter product for this ?or... am i over thinking it... and should i just get a completely new kitchen exhaust fan with something like this built-in ?i don't know if its the right place to ask a question like this, but it should be such a simple little thing to do and really hoping to get some ideas/feedback on how to approach this.

author: madires
author_rank: Super Contributor
timestamp: December 29, 2021, 02:55:24 pm
content: How is the kitchen fan controlled? That could be the starting point for a solution.

author: rstofer
author_rank: Super Contributor
timestamp: December 29, 2021, 04:07:28 pm
content: Sometimes the damper just works against gravity (a weight on a lever closes the damper). Other times a vane style flow switch will work. The turbulence of a running fan and a closed damper might still be enough to trip the vane.https://www.amazon.com/Dwyer-Vane-Operated-Flow-Switch/dp/B009PARWYS

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 29, 2021, 09:31:23 pm
content: How much the current the fan draws? I because of what I know I would do have a solution although may be expensive but completely with off the shelf components. I use a current transformer suitable for the fan current that output a DC voltage or current (0-10V or 4-20mA). Feed this signal into a PLC with analog input.But you can simply put a relay with 220VAC coil where you connect power to the fan. When the fan is on there must be power there and you can use the contact of the relay to activate something.

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2021, 11:06:15 pm
content: How much current does the fan use?Current transformers are normally used for large currents. An exhaust fan is most likely going to use around 1A. You could use an ordinary 12V 1A transformer wired in reverse, with the mains on the 12V side and the burden resistor on the 240V side. The secondary current would be1/20of the primary, so roughly 50mA. A 30R resistor would give 1.5VAC out, which is 4.24V peak to peak out and is within the range of an MCU's ADC, when run of 5V.

author: thisisagoodusername
author_rank: Newbie
timestamp: December 30, 2021, 03:54:28 pm
content: So many ideas and questions- love itI was hoping to do a setup that could even work if we change the fan to a fancy siemens one at some point, but thinking about it - the characteristics would be different with another model - different wattage and so on :/ - so that might not be possible.I was looking at a ACS712 kit with a clamp/sensor, the idea would be that it wouldn't be that intrusive, but - i would need to make something intrusive anyway to get the line out for measurement.perhaps i should just open up the fan control circuit - and see if i could break into a on/off switch directly on the fan instead :/ - however that also breaks the re-usability slightlyI've been looking at some PLC components as well, since these "building" blocks would basically be able to do what i want, but yeah when i look at the modules i would need, it just seems crazy over engineered (not that i'm against that)but enough about my ramblings, heres some answers:- I haven't done the measurements yet - but i'm guessing its max 1.5amps ~ being a 200-300watt motor. Can't really find the modelnr anywhere, ill have to take the whole thing down - which ill most likely need to do anyway when i do the actual project.- the fan is controlled by a touch interface, basically 7 "hidden" buttons : lights on/off, fan on/off (low speed), speed1, speed2, speed3, turbo, timer (basically just shuts it off after 10minutes if you hit this button)- i havent even considered a gravity based valve/damper - this guyhttp://www.lindab.com/global/pro/products/pages/caru.aspx- with some weights on the blades - should honestly do it, i cant believe i haven't thought about this, will require some careful balancing thoughI think i'm going to try out the air stream operated damper with some glued on weights. brazing or welding onto the blades might warp them due to the heat - just need some strong glue for it i reckon.Ill write back here in a few weeks after i've tried it out, if its a success or not. I would love to just keep it simple.otherwise its back to the electronics project

author: tooki
author_rank: Super Contributor
timestamp: December 30, 2021, 04:08:41 pm
content: Is the exhaust fan hard-wired, or does it actually just plug into an outlet hidden somewhere? If it's the latter, you could try one of those power strips that have one sensed "master" outlet which, when a load is detected on it, then turns on all of the "slave" outlets. (Typical application for those were e.g. on a 1990s computer before power saving modes: you'd plug the PC into the master outlet, and the display, speakers, external drives, modem, etc. into the slave outlets. Then, when you turned on the PC, everything else turned on, too, and turned off when you turned off the PC.)Here's an example of a typical off-the-shelf product:https://www.brennenstuhl.com/en-SI/products/extension-leads/secure-tec-19.500a-automatic-extension-socket-with-surge-protection-8-way-anthracite-3m-h05vv-f-3g1-5-1xmaster-5xslave-2xpermanentand example circuits for building one yourself:-https://www.electroschematics.com/building-smart-masterslave-switch/-https://studylib.net/doc/18079246/982063-uk-master-slave-switch

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 30, 2021, 04:28:28 pm
content: Quote from: Zero999 on December 29, 2021, 11:06:15 pmAlthough I don't think I would need to measure the current because I simply connect a relay coil across the power for the fan. When the fan run the relay would be pulled in. However to measure low current I can use something like thishttps://www.cdiweb.com/products/detail/atp001024usp-nk-technologies/415389/?pid=2225%3futm_source%3dgoogle-search%2c2225

author: vu2nan
author_rank: Contributor
timestamp: December 30, 2021, 05:30:36 pm
content: A standard 230 V / 6V transformer and a 230 V relay could be used to drive the automatic shut-off valve.The current available to drive the relay would be = (X * 6 * 1000) / 230 mA.

author: themadhippy
author_rank: Super Contributor
timestamp: December 30, 2021, 06:05:25 pm
content: As usual i'll come at it from the opposite end,forget about current measurement and detect whether the fans rotating or not.Added advantage if the fans stuck the damper will remain closed

author: John B
author_rank: Frequent Contributor
timestamp: December 30, 2021, 11:53:30 pm
content: I've done something similar, a current transformer with an amplifier then rectified into a low pass filtered DC measurement. It doesn't need to very accurate or have high bandwidth as you're basically looking for a threshold voltage. It's also safe as the mains is well isolated from your project. I use the toroidal types where you run the wire through the middle.

author: fordem
author_rank: Regular Contributor
timestamp: December 31, 2021, 02:32:09 am
content: A simple relay wired in parallel with the fan motor will energize when the fan is switched on, wire the contacts to whatever controls the damper - fan turns on, damper opens - fan turns off, damper closes - no need for any fancy current sensing.

author: madires
author_rank: Super Contributor
timestamp: December 31, 2021, 12:30:02 pm
content: I agree, too much over-engineering. What about a cloud based solution?

author: themadhippy
author_rank: Super Contributor
timestamp: December 31, 2021, 12:51:24 pm
content: QuoteOr a solenoid that pushes the vent open

author: Ian.M
author_rank: Super Contributor
timestamp: December 31, 2021, 01:06:26 pm
content: Adjustable threshold current-sensing relays are commercially available, so worst case, if switched AC when fan is running isn't available on one of the controller terminals, a few minutes with a clamp meter to get the minimum operating current of the fan, and also its lights on their own to see if there's enough difference for reliable discrimination, then some digging through distributors websites for a CSR with a suitable sensing range should solve the problem.Another possible technology you may encounter for the shutter actuator is an electrically heated'wax motor'.

author: Ian.M
author_rank: Super Contributor
timestamp: December 31, 2021, 01:38:38 pm
content: Yep, you've found one:https://www.lazada.com.ph/products/02-30a-nonc-adjustable-ac-current-sensor-switch-self-powered-flameproof-i1804808160.htmlHowever as this is going to be a permanent electrical installation, presumably in the O.P's flagged country: Denmark, it would be advisable to source a CSR from an EU based supplier, to get one that's legitimately CE marked (and probably TuV approved) so as *NOT* to give his local electrical code inspector fits!

author: Gregg
author_rank: Super Contributor
timestamp: December 31, 2021, 08:33:36 pm
content: Here is a simple solution:Fire dampers are used extensively in the US. They consist of a shaded pole motor that opens the damper (valve) against a spring. The shaded pole motor basically sits stalled and creating some heat when fully open. A fire alarm circuit removes power (somewhat fail safe) and it closes. These are quite well sealed when closed and come in a huge number of sizes and voltages.You could wire such a device in parallel with the stove fan and it would work with any fan of the same voltage.

author: wizard69
author_rank: Super Contributor
timestamp: December 31, 2021, 09:21:56 pm
content: If you are thinking current sensing, I'm thinking you are on the wrong path. Assuming the fan gets turn on in some manner you are applying a voltage to that fan motor. That same voltage can drive a solenoid, a fire damper or other device that responds to the applied voltage.It is probably more important to make sure everything is UL rated and for the purpose, to preserve your insurance coverage. This especially when it comes to kitchen/stove vents which are known fire risks. I'd be reluctant to install a DIY solution in there due to the problem of insurance coverage. It seems like there is a fire every year around here that involves this area of a house.

author: Ian.M
author_rank: Super Contributor
timestamp: December 31, 2021, 09:33:54 pm
content: The O.P's fan has five speeds so is certainly not a simple fixed speed 230V AC motor you can wire a relay coil in parallel with. <DEITY> only knows how its wired without knowing the make and model number. It could be a PSC motor with a switched capacitor dropper for speed control, it could use phase angle control or it could be an electronically commutated DC motor. No doubt there are other weirder possibilities as well.The advantage of current sensing is running one of the supply wires through the core of a current sensing relay approved in the EU in an appropriate enclosure will not violate local code, whereas tapping into the controller would be an unauthorized modification unless the manufacturer's installation manual indicates that's permissible.

author: not1xor1
author_rank: Frequent Contributor
timestamp: January 02, 2022, 08:36:03 am
content: usually a non-return valve would do the jobI couldn't find that on amazon.com so here is the link to amazon.ithttps://www.amazon.it/Raccordo-Ventilazione-Estrazione-Impedisce-Circolante/dp/B0943T1P7B

author: mikerj
author_rank: Super Contributor
timestamp: January 02, 2022, 10:11:12 am
content: Quote from: thisisagoodusername on December 29, 2021, 01:42:26 pmI'm likely missing something here, but why can't you simply connect one of those valves to the switched side of the exhaust fan supply?

author: mikerj
author_rank: Super Contributor
timestamp: January 02, 2022, 04:01:53 pm
content: Quote from: Ian.M on December 31, 2021, 09:33:54 pmPresumably it has a 6 way switch (including off) that switch in various capacitor combinations. A bunch of 1N4007s to tap off each switch position to drive a relay (with half wave rectified DC) may be possible. Assuming a relay across the motor would not reliably trigger at all speeds.