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Pegasus Ultimate v2 and dew heater "ringing" noise

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#1 jeffcrilly2

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Posted 15 April 2021 - 02:21 AM

I just got a Pegasus Ultimate Power Box v2.

 

I'm powering it with a 30amp Astron power supply.   A very clean linear power supply.

 

I'm using the UPBv2 (at the moment) to power, and supply USB, for a QHY camera, and run a single dew heater strap.

 

One thing I noticed was a lot of audio noise coming from the dew heater strap.   (I'm using a DewBuster  heater strap which I've had for quite a while.)

 

My understanding is the powerbox uses pulse modulation on the Dew heater output.   It sounds like it is pulsing at something like 1000hz.

 

I previously used a DewBuster manual dial controller, and it also "pulsed", but the DewBuster ran at like 1 hz... I never heard any sound.

 

This thing is so noisy I don't think I can use it at a public party.. I find it annoying when I am out with the telescope.

 

Can I work around this problem?    

Will some ferrite chokes help?   (I wouldn't think so.)

Does this happen with other Dew Straps?

 

Btw The Ultimate PB v2 is currently running firmware version 2.4, in case that matters.

 

thx for any suggestions.

 

-Jeff



#2 LuscombeFlyer

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Posted 15 April 2021 - 05:54 AM

You could try soldering a capacitor (say... 16v 470pf) across the output jack. That should smooth out the DC enough to quiet it down.

Edited by LuscombeFlyer, 15 April 2021 - 05:54 AM.


#3 dayglow

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Posted 15 April 2021 - 05:32 PM

Do the dew strip controllers have internal series inductors on their outputs ?

 

Unless they do, I think getting significant filtering results at that switching frequency (1 KHz) would require a small external series inductor ("L") with a much larger capacitor ("C") parallel to the dew strap.

 

An effective combination might be 2.5 mH inductor with a 1000 uF electrolytic capacitor.  This combination sets the low-pass cut-off frequency at 100 Hz and will smooth out the 1KHz nicely.  Exact values are not critical but sizing the components for the load means the inductor should be rated for at least 0.5 amps and the capacitor for 20 Volts.

 

Unless I've made an error in my calculations, for a small capacitor like 470 pf to have much effect at 1 KHz, there would need to be quite a large inductor (perhaps 200 Henry) between it and the controller.

 

Please let me know if I've made an error here.

 

-- David F.



#4 jeffcrilly2

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Posted 16 April 2021 - 01:18 AM

Good point about the capacitor.

 

It turns out I have three Dew heater straps.. They are Kendrick "Dew Remover" heater straps.

 

The long one (which is for a 12" SCT), has the ringing noise.   If I vary the power the ringing frequency and volume varies a bit, but doesn't go away.

 

The other two heaters do not have the ringing.

One is about the size for 5" refactor OTA, the other is super short - like for a small guidescope.

 

So.. problem kinda solved as I'll just use the shorter Dew heater strap.   (I normally just use the long strap on the smaller OTAs and just wrap it around a couple times.)

 

I'll probably need to seek out some long dew straps as the noisy one is just too noisy.

 

-jeff




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