Well I discovered a problem.
Fixed a shortwave receiver and fired it up. I got some nasty RFI whenever the power supply was putting out voltage when the motors are connected through a 20' extension cord.
Would a small value of capacitor across the power outlet eliminate the RFI or do I need one of those Corcom EMI filters?
Fixed a shortwave receiver and fired it up. I got some nasty RFI whenever the power supply was putting out voltage when the motors are connected through a 20' extension cord.
Would a small value of capacitor across the power outlet eliminate the RFI or do I need one of those Corcom EMI filters?
Class D amp has filters? If not you shouldn't be using long wires at all because its a radio transmitter as you have found the wires become an antenna....
Look up drive output reactors. They help both the motor from reflected wavefronts and keep RFI under control. Required as the distance from drive to motor increases. Shorter will be better therefore.
Things to check/observe:
Measue the current/voltage along all the frequencies you will need at the class D output so as to estimate the minimum impedance seen by the amp to see if it will be able to handle it.
Keep in mind that at DC or very lower frequencies (1, 2, 3Hz) the transformer will behave like a shortcircuit. So any frequency pop during turn on either from the class D or from the signal generator may trigger the class short circuit protection. You may have to think about a "soft start" of your system.
Normally well design class D is quite at start, but the signal generator in general charges some capacitor producing low frequencies during turn on.
You may think about sequencing the power at each stage. Maybe following the steps:
1) turn on power supply
2) turn on signal generator
3) turn on class D without the load
4) apply the load maybe with a resistor in series to soft start and then short it to deliver full power
I had this problem when I designed a similar thing to control the speed of an old turntable that had a syncrhonous motor and was out of correct RPM.
It only consumed 11W. I chose a 25W class-D but had to make the sequence I described to turn all parts on, otherwise the class D would shutdown right after powering it up.
Measue the current/voltage along all the frequencies you will need at the class D output so as to estimate the minimum impedance seen by the amp to see if it will be able to handle it.
Keep in mind that at DC or very lower frequencies (1, 2, 3Hz) the transformer will behave like a shortcircuit. So any frequency pop during turn on either from the class D or from the signal generator may trigger the class short circuit protection. You may have to think about a "soft start" of your system.
Normally well design class D is quite at start, but the signal generator in general charges some capacitor producing low frequencies during turn on.
You may think about sequencing the power at each stage. Maybe following the steps:
1) turn on power supply
2) turn on signal generator
3) turn on class D without the load
4) apply the load maybe with a resistor in series to soft start and then short it to deliver full power
I had this problem when I designed a similar thing to control the speed of an old turntable that had a syncrhonous motor and was out of correct RPM.
It only consumed 11W. I chose a 25W class-D but had to make the sequence I described to turn all parts on, otherwise the class D would shutdown right after powering it up.
Most likely the record player consumed more than 25 watts upon startup.
I'm sure they do, but the filters were likely designed with a speaker load in mind and not intended for the load I have.
When initially testing the amp, I had the load connected and had a scope on the output of the transformer so that I could see any anomalies with the sinewave. The sinewave looked clean.
I did a test and I can unplug the motors from the extension cord and the interference goes away.
So I may try to find an RFI filter from a defunct piece of equipment and try that.
Try the capacitors used in electric drills, small toffee size, they are suppressors.
I might try one.
I wonder if the common mode choke used in some switch mode power supplies would work?
Also maybe one of those Corcom EMI filters would do the job.
What I don't get is the output waveform is a sinewave and I see no other waveform shown on the scope. Also the signal passes through a toroidal transformer. So unless the scope cannot see the signal and/or the transformer passes the frequency the class D amp uses, I should be picking up no interference at all.
I wonder if the common mode choke used in some switch mode power supplies would work?
Also maybe one of those Corcom EMI filters would do the job.
What I don't get is the output waveform is a sinewave and I see no other waveform shown on the scope. Also the signal passes through a toroidal transformer. So unless the scope cannot see the signal and/or the transformer passes the frequency the class D amp uses, I should be picking up no interference at all.
Did you try to apply an equivalent motor load very close to the toroidal transformer? The idea is to load the system without the cord extension+motors - you can use a bulb or any other equivalente load in terms of voltage/current.
This way, you can check if the interference is being radiated by the cord extension+motors, if it is being radiated by your system (power supply, class-D, transformer etc) or if your system is injecting high frequency in the mains.
Knowing that, it will be easier to select and apply a filter or even shield parts of the system if it is the case.
This way, you can check if the interference is being radiated by the cord extension+motors, if it is being radiated by your system (power supply, class-D, transformer etc) or if your system is injecting high frequency in the mains.
Knowing that, it will be easier to select and apply a filter or even shield parts of the system if it is the case.
Class D is basically a last stage modulation of AC from digital, and discussing that will get very long.
Suffice it to say that your motors are emitting EMI, which should be controlled at the source.
Another thing, use a 3 core wire connected to body and physical earth at the ends, the emitted radiation will go to Earth.
That is for the motors and the amp.
And we use a 40 or 100W filament lamp th check Earth, it must glow brightly...there could be a weak link in your house wiring as well.
Suffice it to say that your motors are emitting EMI, which should be controlled at the source.
Another thing, use a 3 core wire connected to body and physical earth at the ends, the emitted radiation will go to Earth.
That is for the motors and the amp.
And we use a 40 or 100W filament lamp th check Earth, it must glow brightly...there could be a weak link in your house wiring as well.
I can unplug the motors from the extension cord and the RFI stops.
I also tried grounding the center tap of the transformer and that didn't work.
I also tried grounding the center tap of the transformer and that didn't work.
But when you unplug the motors, there is no load on the system.
I'd load the system (right at the toroidal transformer output) to see if the RFI stops or continues to make sure the interference comes from the extension cord + motors.
I'd load the system (right at the toroidal transformer output) to see if the RFI stops or continues to make sure the interference comes from the extension cord + motors.
It is likely interference being sent along the cord coming from the amp and somehow getting through the toroidal transformer.
I cannot connect the motors directly to it without the cord, but I might be able to use a 100 watt lightbulb, although that will be nowhere near the same type of load.
I cannot connect the motors directly to it without the cord, but I might be able to use a 100 watt lightbulb, although that will be nowhere near the same type of load.
Well I found quite by accident a filter that eliminates the RFI.
A string of nearly 50 incandescent C9 Christmas lights I have strung up in my 12' X 12' building.
Plugged them in and the interference went away.
Incidentally the supply for the motors is right under the outlet where the Christmas lights and it plugs in so I moved my hand near the power brick for the AC supply and the interference came back. So the issue is the power brick. It generates RFI.
Now I need to find a 24 volt 6 amp power brick that doesn't generate RFI so that I do not need the Christmas lights plugged in the whole time I want to use the receiver unless there's a way to shield the power brick so that it doesn't emit RFI.
Thing is I don't know why the Christmas light string eliminates the RFI unless the RFI is being put on the power wiring through the power cord and the load of the lamps is enough to stop the interference and maybe putting my hand near the power brick is causing the interference to be able to be received.
Would something like this work?
https://theelectronicgoldmine.com/products/g26992?_pos=18&_sid=7e3bf721b&_ss=r
https://www.digikey.com/en/htmldatasheets/production/16511/0/0/1/5vb3
A string of nearly 50 incandescent C9 Christmas lights I have strung up in my 12' X 12' building.
Plugged them in and the interference went away.
Incidentally the supply for the motors is right under the outlet where the Christmas lights and it plugs in so I moved my hand near the power brick for the AC supply and the interference came back. So the issue is the power brick. It generates RFI.
Now I need to find a 24 volt 6 amp power brick that doesn't generate RFI so that I do not need the Christmas lights plugged in the whole time I want to use the receiver unless there's a way to shield the power brick so that it doesn't emit RFI.
Thing is I don't know why the Christmas light string eliminates the RFI unless the RFI is being put on the power wiring through the power cord and the load of the lamps is enough to stop the interference and maybe putting my hand near the power brick is causing the interference to be able to be received.
Would something like this work?
https://theelectronicgoldmine.com/products/g26992?_pos=18&_sid=7e3bf721b&_ss=r
https://www.digikey.com/en/htmldatasheets/production/16511/0/0/1/5vb3
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So I found a linear power supply.
I can use the 24 volt version of this power suppl which is rated at 4.2A.
https://www.antekinc.com/100w-linear-power-supply/
Or the 24 volt version of this power supply which is rated at 8A.
https://www.antekinc.com/200w-linear-power-supply/
I would put one of the supplies in a box.
I had wanted a regulated supply, but with a good stiff power supply, the B+ will not drop very much under load.
I can use the 24 volt version of this power suppl which is rated at 4.2A.
https://www.antekinc.com/100w-linear-power-supply/
Or the 24 volt version of this power supply which is rated at 8A.
https://www.antekinc.com/200w-linear-power-supply/
I would put one of the supplies in a box.
I had wanted a regulated supply, but with a good stiff power supply, the B+ will not drop very much under load.
Radiated EMI is usually common mode, so paralleling caps is useless. The best solution is a common mode choke, including clamp-on ferrites, placed near the source.
Ok I tried a variable voltage linear supply I have that can do 24Vdc.
With the motors running I get absolutely no RFI whatsoever. So it is indeed that switch mode power supply.
I may find another use for it unless there's some sort of filter I can use to eliminate the RFI.
With the motors running I get absolutely no RFI whatsoever. So it is indeed that switch mode power supply.
I may find another use for it unless there's some sort of filter I can use to eliminate the RFI.
I found something interesting.
While testing my 6-9.1MHz receiver I discovered I only have RFI on 7.15MHz and 8.35MHz.
I might can live with that since there's no normal broadcast on those two frequencies.
While testing my 6-9.1MHz receiver I discovered I only have RFI on 7.15MHz and 8.35MHz.
I might can live with that since there's no normal broadcast on those two frequencies.
Just put a wire mesh cage over the supply, connect to Earth, and use a grounded supply cord to the SMPS, should work.
I found this regulator.
https://www.amazon.com/Converter-9V-40V-24V-Waterproof-Transformer/dp/B089ZSKQLY
Would that be good to use with a linear power supply?
https://www.amazon.com/Converter-9V-40V-24V-Waterproof-Transformer/dp/B089ZSKQLY
Would that be good to use with a linear power supply?