Controlling 12-volt heaters with a power relay

Tagged: apogee, power, relay

This topic has 6 replies, 2 voices, and was last updated 2024-08-19 at 2:54 PM by Braedon.

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- 2024-05-01 at 4:45 PM #18453
  Braedon
  Participant
  I have some apogee pyranometers and pyrgeometers for my monitoring stations, and each of these sensors has an internal heater that helps to clean off snow, rain, and frost. The heaters operate at 12 volts, so I have them connected directly to my 12-volt battery which powers my entire setup. Having the heaters connected 24/7 draws a lot of power relative to the other sensors and instrumentation I am using, which quickly drains my batteries. I would like to move to a less frequent logging interval (going from every 15 minutes to every 60 minutes), and I would like to potentially power the heaters on my sensors for less time, for example for the 15 minutes leading up to my new logging time (on the hour). Because these heaters need a 12-volt supply, my understanding is that using a power relay could be an appropriate tool for controlling these heaters with a signal from the Mayfly while still having their power source come directly from the battery.
  
  There are quite a few relays out there, and I’ve seen some previous discussion posts with references to Seeed’s website (https://wiki.seeedstudio.com/Seeed_Relay_Page/). I’ve also seen lots of relays on Adafruit, such as the following which seems like a good option from my limited knowledge in this area: https://www.adafruit.com/product/2923. I wanted to run this by the EnviroDIY community to get some input or suggestions. Also, from what I’ve read, it seems like a latched relay will help me save on power, which is really important for this implementation, and the Adafruit example has that option as well.
- 2024-05-02 at 1:17 PM #18456
  Shannon Hicks
  Moderator
  What’s the current draw of your heaters? There’s a variety of relays you could use, but I know several people have had good luck with various Grove-compatible relay boards, like the ones from Seeed. But your options are going to depend on how many amps of current the heater draws from the battery.
- 2024-05-02 at 3:59 PM #18457
  Braedon
  Participant
  I have four sensors with heaters, and combined they draw 61.6 mA.
  - 2024-05-04 at 2:16 PM #18458
    Shannon Hicks
    Moderator
    That’s not much current, so most relay boards should be able to handle that with no problem. I think that latching Grove board (https://www.seeedstudio.com/Grove-2-Coil-Latching-Relay.html) would probably work good for your situation so your Mayfly board could activate the relay 15 minutes before you want to sample, and then go back to sleep and it won’t have to hold a pin high to keep the relay closed. You can connect the relay board to the Mayfly via one of the unused Grove jacks (but make sure you set the voltage selection jumper next to that Grove jack to 5v since the relay board operates at 5v). I’m sure there are other latching relay boards out there that would work as well, but the Grove jack makes wiring it up convenient.
- 2024-05-06 at 1:51 PM #18459
  Braedon
  Participant
  This looks like a great option. Thanks Shannon for your help!
- 2024-08-01 at 5:22 PM #18607
  Braedon
  Participant
  @shicks I wanted to run by what my thought process is with these relays and some of the questions I have now that I have purchased a few. I think my questions are general enough that you should be able to help me with them. I am looking to connect the Seeed relay to the D10-D11 grove terminal on the Mayfly. This would connect the relay’s SIG pin to D10 and the NC pin to D11 and supply it with switched 5V power.
  
  There is a Wiki page made by seeed studio (https://wiki.seeedstudio.com/Grove-2-Coil_Latching_Relay/#with-arduino), but I am having a hard time following it because in the sections where they talk about the rising and falling edge of the SIG pin, they mention both the NC and NO states, and it isn’t really clear which state (NC/NO) is associated with edge (rising/falling). When I mess with it on my own, it seems that the NO state occurs when I drive the SIG pin low, and the NC state occurs when I drive the SIG pin high. Is that correct?
  
  I’m not entirely sure how to use the six screw terminals, but my thought is that I would connect the positive terminal of my battery to one of the NO relay terminals (such as 1NO), and then I would connect all of the heater positive leads to the other NO relay terminal (such as 2NO). I would also take all the negative leads of the heaters and connect them straight to the battery ground. I would then turn on the switched power on the Mayfly when my 15-minute mark came up, drive D10 low, and then turn the switched power off. This would turn on the heaters by making the connection between the battery and the heaters’ positive leads. When my data logging was complete for that interval, I would want to turn of the heaters, so I would turn the switched power back on and drive D10 high to close the relay. I could then turn the switched power off until the next 15-minute marker came.
  
  Is this a sound approach to this problem?
- 2024-08-19 at 2:54 PM #18633
  Braedon
  Participant
  @shicks I’m also going to be adding an air temperature sensor that has a 12-volt fan in the radiation shield. The fan can run at lower power by using pulse width modulation. I’m wondering if there might be a way to accomplish this with the power relay, since the fan will have to be connected directly to the battery like the heaters on my other sensors. Is that something that can be done using the Mayfly and the Seeed Studio power relay we’ve discussed here? PWM is new for me, so I’m not exactly sure how that would look trying to control the power consumption of a fan that is not drawing its power from the Mayfly.
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