I am powering a 24VAC thermostat from an output on a bulldog Heatpump. Heatpump board is picking up extra noise from its board and pushing noise to our thermostat. I am looking for a 24VAC noise cleaner.
Can someone recommend a model?
Hello aleks1,
Welcome to the DigiKey TechForum! We have many different options for filters in our catalog, however to recommend one we’ll need to know a little more about your application. Are you looking for a cable ferrite to clamp around the wires going to the heat pump? Perhaps you need a common mode choke with wire leads that sits between the heat pump and thermostat? Do you have the opportunity to put a snubber on the board itself?
If you’d like to know about which filter might work best for your application and how you wish to apply it, I highly recommend checking out the “Filters” section of the Product Selection Guide.
Regards,
Klint
hi Klint_12443
We have used some ferrite chokes with limited success.
I have attached the Heat pump board spec sheet to give you some more insight…
if you can recommend a common mode choke and a snubber that would be greatly appreciated.
IKV-HKV-ERV-IOM-July-2020.pdf (4.2 MB)
Heat Pumps.pdf (4.4 MB)
Hi aleks1,
Without knowing more about the nature and source of your noise it is going to be very difficult to identify the best solution for you. Generally speaking, I didn’t think that additional filtering was typically required on such systems, so it may be an indication of a problem somewhere in your overall system.
If you could isolate the source of the noise, that might help to both evaluate whether there is a problem which needs to be corrected or, at least, help you figure out where to most effectively apply filtering or shielding to mitigate its effects. Perhaps the noise is being picked up in the cabling because it is passing too close to a noise source. If so, just rerouting of the cable might be sufficient to fix the problem. Using a shielded cable may also help if the noise is being transmitted (though the air) rather than conducted (from a connected circuit board).
A valuable experiment might be to try connecting the thermostat via a very short cable and see if the noise problem persists. If not, then the noise may not be coming from your control board.
I also presume that you don’t have a means of adding filtering components to the circuit board(s) itself, so you are limited to inline off-board options. I further assume you don’t have a means of characterizing the noise, such as its frequency and amplitude.
Going with these assumptions, this limits us to clamp-on type ferrite devices or inline integrated power line filters. Sounds like you’ve tried a few clamp-on units with limited success. If possible, running multiple turns through those devices can increase attenuation. Each pass adds almost as much additional attenuation as the initial pass (so 3 loops will attenuate almost 3x).
Snap-on hinged ferrite cable filter:
Power Line Filter Module:
Placement of the filter may also be important. There may be a significant difference between placing it near the controller board vs. near the thermostat, depending on the source of the noise. Placing one at each end of the line may also improve results, depending on the source of the noise and which devices are being affected by the noise.
We do offer some ferrite kits which might be of interest to you. With one of these kits, you could experiment with various parts and see if one does a better job than the others. If you then needed more of a particular ferrite part, you could likely order additional pieces of that one part from us rather than having to buy additional kits.
If you try a ferrite kit or two and do not get the results you need, then going to the in-line integrated power line filters would be the next step. These parts would require cutting the power cord and splicing in-line. For your application, you shouldn’t need much current, so the link I provided is just for the lower current options from 1A to 3A.
Among the integrated power line filters, one would first select based on preferred form-factor and connection method. Connection options include quick-connect terminals, terminal block, stud mount, or flying leads. Once on has filtered to that point, the task gets a bit harder, as most of the remaining means of comparing parts comes down to examining and comparing attenuation curves in datasheets.
We do specify whether the filters are single-stage or two-stage, with two-stage generally being more effective, but with a typically a higher price tag. If you are not needing filters for multiple systems, then I might suggest going with a two-stage filter right away, as it has a better chance of working right off the bat. However, if this is going to be needed for multiple systems, then trying some lower-cost filters to see if they are effective enough might save you some money.