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Old 03-15-2011, 07:53 PM   #21
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RE: RFI Nois

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skipperdude wrote:



It does keep the beer cold.

Trading one buzz for another



Clearly you have your answer.* Drink enough beer so that you can't tell where the hum is coming from - your brain, or the radio.

You said that the unit will run on both 120 vac and 12 vdc.* Is that through the ship's inverter, or are you saying there is a separate inverter on the Norcold?



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Old 03-17-2011, 11:50 AM   #22
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RE: RFI Nois

The older Norcold have a two transistor inverter, relay and a multistep transformer to run from either AC or DC. I have one but it does not , that I'm aware of, cause any noise detectable by my VHF.
My VHF though has its own power supply from one battery set, the fridge has its own power supply from a different battery set and the wiring run is separated to a good degree.
That may be part of the reason I don't have a noise problem from the fridge.
Take a look at the wiring and if they are fed from the same terminal strip somewhere try separating them , including the ground side, even temporarily as a test.

These old fridges can be tuned up a bit. Do you run it on AC periodically? Try plugging it onto AC when it is running on DC. If you hear a change in the motor noise, such as a speed up, then there is a adjustable resistor that needs to be twiddled to get the frequency up again. Be carefull. If the frequency has fallen off it may increase the noise or the ability to hear it. The freq. fall off will also affect the cooling of the fridge and not for the good.
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Old 03-18-2011, 06:47 AM   #23
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RE: RFI Nois

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C lectric wrote:

The older Norcold have a two transistor inverter, relay and a multistep transformer to run from either AC or DC. .................

These old fridges can be tuned up a bit. Do you run it on AC periodically? Try plugging it onto AC when it is running on DC. If you hear a change in the motor noise, such as a speed up, then there is a adjustable resistor that needs to be twiddled to get the frequency up again. Be carefull. If the frequency has fallen off it may increase the noise or the ability to hear it. The freq. fall off will also affect the cooling of the fridge and not for the good.

And how old is that technology?* Something Fred Flintstone designed?

Seriously, I've read a lot of stories on how the dual voltage refrigerators operate and I'm not sure who or what to believe.* I'm assuming they are doing something different now, but what and starting when?
*
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Old 03-20-2011, 09:50 PM   #24
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RE: RFI Nois

MOre like Barney.

My version is a 1977/78. Norcold used that power design for a long time. I don't know if or when they quit. I found the schematic on the back of my fridge many years ago and using it have managed to keep it tuned up.

It is slated for replacement and darn near was done this year. The fridge works well still BUT its replacement will be much bigger and use the Danfoss system along with better insulation.

I don't know what other mfgrs. of the period used so can't comment although for the period I don't think they were any better/worse untill the Danfoss came along.

My DE-490 is still made, looked online, although I can't tell if the same power module is used, likely not. At some point I'll check as I downloaded the parts list. Thetford seems to have put manuals and parts list online, nice change from before.
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Old 03-27-2011, 08:07 AM   #25
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RFI Nois

Using a Ferrite choke right at the source (the switching supply for the old Norcold) and grounding the frig should take care of the problem. I use a newer Norcold DE0061 dual voltage unit. I always run the unit off it's DC power it does not induce common mode RF noise into any of my systems. As far as chartplotters they are probably MFD's so by design emit some RF from the microprocessor. I use a receiver like device from a telco toner kit (you can get them from Home Depot or Lowes) I find this to be a great way to find common mode noise sources.
At least you found the problem another thing you could try is if you don't use the frig on AC disconnect the plug and see if the interference goes away. The switching supply in these units can backfeed (on the DC side) I have seen it in the past when helping another slip neighbor track down the same issue you had.
Bill


-- Edited by Billylll on Sunday 27th of March 2011 08:08:39 AM
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Old 03-28-2011, 12:53 PM   #26
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RE: RFI Nois

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Billylll wrote:
*I use a receiver like device from a telco toner kit (you can get them from Home Depot or Lowes) I find this to be a great way to find common mode noise sources.
*Great idea, I already have one but have never thought of this use.* I wonder if it could help me find how R.F. is getting into my autopilot.* My VHF, and my SSB both will cause the autopilot to go hard over.* I've tried chokes in several places, but it still does it.* I've also carefully checked my ssb grounding foil and both connections are clean and tight.* Any ideas?...................Arctic Traveller

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Old 03-28-2011, 02:54 PM   #27
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RFI Nois

With my SSB I ended up going with two of the largest DynaPlates and doing their connection to the auto tuners ground using 3" wide copper foil. In addition I had to move the HF SSB antenna and tuner away from my electronics locker and install multiple chokes on the affected devices as well as the power supply leads at the back of the HF transciever. I swapped my large VHF primary antenna location with the SSB 23' Marine grade antenna. It was a real pain in the you know what but now I dont interfere with any of the electronics on the boat and the radio performs better because it has less noise.

Bill


-- Edited by Billylll on Monday 28th of March 2011 02:55:11 PM
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