5 ms·

I've wanted to do this sort of thing for a while, but I am a bit concerned about using many of the smart plugs on the market with large motors, and I assume mos

by jchw 3y ago

I've wanted to do this sort of thing for a while, but I am a bit concerned about using many of the smart plugs on the market with large motors, and I assume most dryers contain a fairly large electric motor (not sure how large.) I'm in the midwest U.S., so my dryer is a gas dryer; so presumably, the only real thing being driven off the electricity is indeed a micro-controller and a fairly large motor of some kind. I can find very few smart plugs that specifically advertise the ability to handle inductive loads, which makes a ton of sense of course, since I think that winds up needing relatively expensive MOSFETs and circuit design more advanced than I can really understand to be robust. I think the best recommendation I've seen is to simply not use smart plugs for inductive loads at all, and instead use other methods to either measure current or implement switching. I'm a bit afraid to use most any of these smart plugs. I have a couple Zigbee ones that seem to work fine but I am only trusting them with relatively small resistive loads for now since it feels dicey to put anything serious on them.

yjftsjthsd-h 3y ago
> and instead use other methods to either measure current or implement switching. Yeah, I keep meaning to look at clamp style measurement. That doesn't give you control, of course, but I'm mostly interested in finding out how much power larger appliances are actually using (my dryer is pure electric).
- chongli 3y ago
  A current clamp meter will not tell you anything unless you break out the individual wires you want to measure. Having both live and neutral running through the clamp will cause the electric field of the neutral to cancel out the field of the live whenever the device draws current, so the meter will be unable to read anything.
  - jchw 3y ago
    This isn't too big of a deal since at least around here, appliances tend to be wired with screw terminals. So, in a lot of cases there actually is a separate place to measure hot and neutral without any terrible hacks. (Not sure if that applies to my dryer, though: I should check.)
    - chongli 3y ago
      My dryer (I live in Canada) has a 240V plug with a heavy-duty cable, no exposed wires. My dishwasher is wired directly into the mains (I installed it myself) but neither the laundry washer nor the dryer are hard-wired.
      - wtallis 3y ago
        Your dryer may have screw terminals at the other end of the power cable: those are often sold separately and installed when you take delivery of the dryer, because there are multiple types of outlets your home could have for an electric dryer.
        chongli 3y ago
        If there are screw terminals they are internal to the machine. The power cable goes directly into the machine with no exposed terminals.
        pixl97 3y ago
        I mean, no not really. Take off the plate where the wire goes into the machine and there is a terminal block at that point. Unless you have some very odd machine I have never (and I've installed quite a few machines) seen one that comes with the wire.
        chongli 3y ago
        I watched the delivery guys install the machine. They brought it into the laundry room, took the packaging off, hooked up the flexible ventilation duct, and plugged it in. They didn’t do any wiring. I’m in Canada (as I said at the top of this thread). Are you in the US? Perhaps it’s different there.
      - Scoundreller 3y ago
        > My dishwasher is wired directly into the mains (I installed it myself) but neither the laundry washer nor the dryer are hard-wired. You probably have an “American” dishwasher like a GE or Whirlpool. If you upgrade to a “European” one like a Bosch or Miele, you’ll need to wire up a socket in an adjacent cabinet and plug it in, or buy their ~$50 junction box. The Europeans like to move with their appliances instead of leave them in place. It’s another reason for their big kitchen appliances like fridges being smaller: so it’s easier to move and it will fit wherever you move next.
kabouseng 3y ago
You can either wire a relay yourself, your smart plug just switches the relay, and you can size the relay according to your needs. Or use smart switches made for geysers. Something like the sonoff pow3 can handle up to 5.5kW. Since it is just a relay inside I am pretty sure it can handle inductive loads fine. https://sonoff.tech/product/diy-smart-switches/powr3/ https://sonoff.tech/product/diy-smart-switches/powr3/
MisterBiggs 3y ago
I tried automating a portable A/C unit using a smart plug and I can confirm that the large power draw will eventually burn them out. The post does mention Shelly which is a brand I would trust for this sort of thing assuming they have a product with the right rating.
js2 3y ago
Some folks have success with vibration sensors: https://community.home-assistant.io/t/blue-print-to-work-with-aqara-vibration-sensor-for-automation-to-trigger-notification-or-other-action-when-dishwasher-or-washing-machine-is-done/ https://community.home-assistant.io/t/blue-print-to-work-wit...
chongli 3y ago
I don't think it's an issue for this application with a dryer because it's not cutting power to a running motor. The problem with switching an inductive load using a small relay (like the ones in smart plugs) is that the magnetic field collapses in the motor as soon as the relay contacts open. This causes a very large flyback voltage to build across the contacts as the relay is still in the process of opening (mechanically driven by a spring) and so you get arcing which damages the contacts and results in carbon deposits (with higher resistance than clean metal). In this application the smart plug is already switched on (contacts closed) when the dryer is started and the smart plug doesn't switch off while the dryer is running. Instead, the smart plug's only job is to monitor the power usage of the dryer and send a notification when it drops below 10W.
- jchw 3y ago
  Hmmm.... That's a valid point that I didn't consider. I guess if the relay remains closed all the time, inductive loads shouldn't really be any trouble. It still does seem a little sketchy, though.
hinkley 3y ago
Gas dryers often run 120V because they’re only running a small blower and a motor to spin the drum. You’re probably in much better shape to find an inline unit that can handle that amperage. First gas dryer I could find at best buy: LG 7.4 cu ft (beefy boy) needs 11.5 amps. I’d be shocked if you can’t find a 15A smart plug.
jtriangle 3y ago
Temperature sensor, tape it to the exhaust duct, when temp falls below X for Y minutes, send an alert, sleep until temp rises above Z. Super simple, cannot be fooled if your values for XYZ are set appropriately.

by jchw 3y ago

yjftsjthsd-h 3y ago

> and instead use other methods to either measure current or implement switching. Yeah, I keep meaning to look at clamp style measurement. That doesn't give you control, of course, but I'm mostly interested in finding out how much power larger appliances are actually using (my dryer is pure electric).

chongli 3y ago
A current clamp meter will not tell you anything unless you break out the individual wires you want to measure. Having both live and neutral running through the clamp will cause the electric field of the neutral to cancel out the field of the live whenever the device draws current, so the meter will be unable to read anything.
- jchw 3y ago
  This isn't too big of a deal since at least around here, appliances tend to be wired with screw terminals. So, in a lot of cases there actually is a separate place to measure hot and neutral without any terrible hacks. (Not sure if that applies to my dryer, though: I should check.)
  - chongli 3y ago
    My dryer (I live in Canada) has a 240V plug with a heavy-duty cable, no exposed wires. My dishwasher is wired directly into the mains (I installed it myself) but neither the laundry washer nor the dryer are hard-wired.
    - wtallis 3y ago
      Your dryer may have screw terminals at the other end of the power cable: those are often sold separately and installed when you take delivery of the dryer, because there are multiple types of outlets your home could have for an electric dryer.
      - chongli 3y ago
        If there are screw terminals they are internal to the machine. The power cable goes directly into the machine with no exposed terminals.
        pixl97 3y ago
        I mean, no not really. Take off the plate where the wire goes into the machine and there is a terminal block at that point. Unless you have some very odd machine I have never (and I've installed quite a few machines) seen one that comes with the wire.
        chongli 3y ago
        I watched the delivery guys install the machine. They brought it into the laundry room, took the packaging off, hooked up the flexible ventilation duct, and plugged it in. They didn’t do any wiring. I’m in Canada (as I said at the top of this thread). Are you in the US? Perhaps it’s different there.
    - Scoundreller 3y ago
      > My dishwasher is wired directly into the mains (I installed it myself) but neither the laundry washer nor the dryer are hard-wired. You probably have an “American” dishwasher like a GE or Whirlpool. If you upgrade to a “European” one like a Bosch or Miele, you’ll need to wire up a socket in an adjacent cabinet and plug it in, or buy their ~$50 junction box. The Europeans like to move with their appliances instead of leave them in place. It’s another reason for their big kitchen appliances like fridges being smaller: so it’s easier to move and it will fit wherever you move next.

kabouseng 3y ago

You can either wire a relay yourself, your smart plug just switches the relay, and you can size the relay according to your needs. Or use smart switches made for geysers. Something like the sonoff pow3 can handle up to 5.5kW. Since it is just a relay inside I am pretty sure it can handle inductive loads fine. https://sonoff.tech/product/diy-smart-switches/powr3/ https://sonoff.tech/product/diy-smart-switches/powr3/

MisterBiggs 3y ago

I tried automating a portable A/C unit using a smart plug and I can confirm that the large power draw will eventually burn them out. The post does mention Shelly which is a brand I would trust for this sort of thing assuming they have a product with the right rating.

js2 3y ago

Some folks have success with vibration sensors: https://community.home-assistant.io/t/blue-print-to-work-with-aqara-vibration-sensor-for-automation-to-trigger-notification-or-other-action-when-dishwasher-or-washing-machine-is-done/ https://community.home-assistant.io/t/blue-print-to-work-wit...

chongli 3y ago

I don't think it's an issue for this application with a dryer because it's not cutting power to a running motor. The problem with switching an inductive load using a small relay (like the ones in smart plugs) is that the magnetic field collapses in the motor as soon as the relay contacts open. This causes a very large flyback voltage to build across the contacts as the relay is still in the process of opening (mechanically driven by a spring) and so you get arcing which damages the contacts and results in carbon deposits (with higher resistance than clean metal). In this application the smart plug is already switched on (contacts closed) when the dryer is started and the smart plug doesn't switch off while the dryer is running. Instead, the smart plug's only job is to monitor the power usage of the dryer and send a notification when it drops below 10W.

jchw 3y ago
Hmmm.... That's a valid point that I didn't consider. I guess if the relay remains closed all the time, inductive loads shouldn't really be any trouble. It still does seem a little sketchy, though.

hinkley 3y ago

Gas dryers often run 120V because they’re only running a small blower and a motor to spin the drum. You’re probably in much better shape to find an inline unit that can handle that amperage. First gas dryer I could find at best buy: LG 7.4 cu ft (beefy boy) needs 11.5 amps. I’d be shocked if you can’t find a 15A smart plug.

jtriangle 3y ago

Temperature sensor, tape it to the exhaust duct, when temp falls below X for Y minutes, send an alert, sleep until temp rises above Z. Super simple, cannot be fooled if your values for XYZ are set appropriately.