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Old 11-16-2019, 11:00 AM   #1
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Angry AC ripple in DC line

I recently replaced my refrigerator with a Dometic 2+2. There is a very small ac ripple in the dc power supply to the unit. The electronic controls are unable to cope with this ripple and continually malfunction. Any suggestions as how to remove/filter out the ripple?

I just found a 1990 thread that provided my answer... thanks to those who responded. Jim
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Old 11-16-2019, 11:30 AM   #2
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How small? How did you measure it?

If it were mine, I'd just design a capacitance multiplier and attach that to the incoming supply. But only after 'scoping it and seeing what I would be dealing with.

Where is the ripple coming from?
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Old 11-16-2019, 11:37 AM   #3
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What is supplying the DC Voltage to the fridge?\


Sounds like a 'converter'.
Converter uses AC IN and produces DC Out.
Converters produce 'dirty' DC and 'Clean' DC
Dirty is direct unfiltered
Clean is Filtered using capacitors............that source should be used for fridge/water heater/furnace/AC controls due to the 'electronics' (circuit boards)


AC Ripple can be easily tested fof when on AC Shore Power

Voltmeter set to low scale AC Voltage
Measure DC Voltage going to the Fridge Circuit Board at the Terminal Block
Voltage you will be reading is the AC Ripple



2001 .....old converter -----time to upgrade




No Converter...........
Then it is the Charging Section of your Inverter causing the AC Ripple.
Same problem......Bad Capacitor in Inverter Charger


2001...time to upgrade Inverter
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Old 11-16-2019, 11:45 AM   #4
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Originally Posted by JTFreeman View Post
I recently replaced my refrigerator with a Dometic 2+2. There is a very small ac ripple in the dc power supply to the unit. The electronic controls are unable to cope with this ripple and continually malfunction. Any suggestions as how to remove/filter out the ripple?
Make sure your battery disconnect switch is on. The older converter needs the batteries to "smooth" out that dirty ripple.
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Old 11-16-2019, 11:53 AM   #5
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What is supplying the DC Voltage to the fridge?\


Sounds like a 'converter'.
Converter uses AC IN and produces DC Out.
Converters produce 'dirty' DC and 'Clean' DC
Dirty is direct unfiltered
Clean is Filtered using capacitors............that source should be used for fridge/water heater/furnace/AC controls due to the 'electronics' (circuit boards)


AC Ripple can be easily tested fof when on AC Shore Power

Voltmeter set to low scale AC Voltage
Measure DC Voltage going to the Fridge Circuit Board at the Terminal Block
Voltage you will be reading is the AC Ripple



2001 .....old converter -----time to upgrade




No Converter...........
Then it is the Charging Section of your Inverter causing the AC Ripple.
Same problem......Bad Capacitor in Inverter Charger


2001...time to upgrade Inverter
I'm sure you are correct on upgrading my inverter/charger however i found an old thread that provided another solution. Thank you for responding. Jim
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Old 11-16-2019, 11:57 AM   #6
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How small? How did you measure it?

If it were mine, I'd just design a capacitance multiplier and attach that to the incoming supply. But only after 'scoping it and seeing what I would be dealing with.

Where is the ripple coming from?
Inverter/charger. Just found my answer in an old thread (1990). Thanks for responding. Jim
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Old 11-16-2019, 01:14 PM   #7
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I'm sure you are correct on upgrading my inverter/charger however i found an old thread that provided another solution. Thank you for responding. Jim
Quote:
Originally Posted by JTFreeman View Post
Inverter/charger. Just found my answer in an old thread (1990). Thanks for responding. Jim



So how about sharing that info .....others might find it as a solution for them also
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Old 11-16-2019, 01:23 PM   #8
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Inverter/charger. Just found my answer in an old thread (1990). Thanks for responding. Jim



And the answer was?
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Old 11-17-2019, 07:51 AM   #9
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And the answer was?
Hi Greg, i just found this thread in one of my RV Forums. It reads like the "fix" I'm looking for on my refrigerator problem. Is ths something you can help with while you are in Pensacola?


I have had similar problems with the board issues from AC ripple on the DC line. I have installed 12 volt noise filters in line with the 12 volt power circuit (like those for CB radios) and have had great results. Noise generally is caused by a noisey converter or a fluorescent light ballast board failure. Generally the 110 Volt fuse blowing is caused by a defective 110V heating element. If your unit is a 50 amp shore power a loose nuetral (white wire) will cause excessive AC voltage into your unit causing failures.
‐------------------------
The noise filter contains a capacitor and coil internally. It has a negative and positive DC input and output. The negative and positive wires at the rear of the fridge control board are to be connected to the input of the noise filter and the output filter wires connect to the fridge. It is a inline device that can be purchased from most car stereo installation facilities. It should be rated for a minimum of 10 amps DC.
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Old 11-17-2019, 09:19 AM   #10
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Yeah, I'm curious too what the converter is and how the ripple was measured. I can't imagine a 2001 36' rig having a basic transformer/rectifier converter that requires batteries for filtering. I also can't see a switching converter putting out line frequency ripple, even the old ones switched at kHz frequencies. So there's a few moving parts to the problem I'd be wanting to know about before I just put a band-aid filter on it. I had to rebuild the converter in my 2005, the capacitors in it were bulging and leaking. Just making the point that if a 2005 converter was giving up, a 2001 probably isn't better.

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Old 11-17-2019, 09:53 AM   #11
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Many older converters back in the day specifically warned against operating the converter without a 'load' battery for anything other then short periods. I remember reading it for my '94 Bounder and I wouldn't be surprised it if wasn't the rule of the day for other brands. I assumed that doing so would increase both the DC output voltage and AC ripple to potentially destructive levels. This could affect many of the control boards in the RV designed for no more than 15 volt which I found had little in the way of protective circuitry. Even some incandescent light bulbs don't care for overvoltage.

Reverse engineered several RV control boards, and often found that there was poor overvoltage protection, much less then I would have designed in.

There's many economical converter/charger designs that use the battery as a filter, saves on parts. It is just a big capacitor after all. I still follow the 'don't use the converter without a battery' rule on my newer '02 rig and when helping friends with their RVs. But I've never tested for ripple either. Someday...
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Old 11-17-2019, 11:25 AM   #12
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Back in the 80's and early 90's, AC ripple was a common problem. It's conceivable a 2001 Discovery still has a inverter/converter/charger that is a bit sloppy with the DC power output, but most by then were pretty decent. As I recall, the Discovery used a Heart inverter and they were never known to have a ripple problem. Nor was AC interference a known and common problem on Discoveries. I'd be looking for other sources of the ripple, maybe fluorescent lighting or some add-on gadget.


On the other hand, if the noise filter works, it may not be worth hunting down the source.
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Old 11-18-2019, 03:08 PM   #13
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I don't know where the ripple originates but we came up with a temporary solution. We simply disconnected the Dometic from the originsl 12 vdc power supply and installed a simple 12 vdc power supply from an auto parts store. This has worked fine for the past 11 months however when unplugged from shore power there is no eady way to get 110 to power the the unit. I am noe looking to reconnect the on board 12vdc power supply and use a Powerwerk DC Line Filter to clean 12vdc.
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Old 11-18-2019, 11:38 PM   #14
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I don't know where the ripple originates but we came up with a temporary solution. We simply disconnected the Dometic from the originsl 12 vdc power supply and installed a simple 12 vdc power supply from an auto parts store. This has worked fine for the past 11 months however when unplugged from shore power there is no eady way to get 110 to power the the unit. I am noe looking to reconnect the on board 12vdc power supply and use a Powerwerk DC Line Filter to clean 12vdc.
Do you get noise on the batteries alone / not plugged in?
If no noise unplugged-you could use a double pole double throw 120v relay in a little different manner than usual . Both commons on relay to fridge wires , both NC to battery lines and both PS wires to NO . Goes without saying. get the neg and pos right on all 6 connections . Connect the coil to same 120v source as PS is plugged into.. Tiny 12v ATS.
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