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Old 22-07-2019, 00:57   #16
Marine Service Provider

Join Date: Aug 2004
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Re: Fridge cycling frequently for very short periods

Danfoss believed that everyone would use there compressors within their design specification, so yes control modules fail when exposed to overloaded conditions. I have only found two compressor field coils shorted on air cooled BD compressors, water cooled are another story. The two air cooled field coil failures were the result of owners connecting 12 volts direct to compressor. If you check Danfoss specification application sheets after the BD2.5 you will find the field coil tests seem to disappear. For a voltmeter to be of value in testing voltage drop the duration of the voltage spike must be long enough to see on your meter, unfortunately the module sees low voltage spikes you do not see and prevents compressor from starting.

Of the maybe 300 modules I tested over the last 20 years 60% were mailed back. Owner was advised to follow my five step test that also deleted field coil resistance test. The 200 modules I sold at 1/2 the going rate boosted my retirement income.
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Old 07-08-2019, 18:57   #17
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Re: Fridge cycling frequently for very short periods

Quote:
Originally Posted by CF32907 View Post
Perhaps you should look up Danfoss site. They specifically say that low voltage is a major problem, did not give a reason for low voltage. And sport, the only way to check it is with a quality VOM. They also will give you resistant loads for the three wires going to the compressor. Again you need a VOM, Do a little checking before you make quotes to what is correct diagnostics. You have two items, check your voltage, both static and running, if you got 12v then your controller is probably bad. There compressors are damn close to bullet proof, not so with the compressors controllers.
Absolutely correct CF. The most common issue that causes these tiny 3 phase alternating current output motor drivers (MDM) to shut down is low voltage. (voltage collapse under load due to bad power supply.)

The industry accepted method of checking for poor power supply input causing the Motor Driver Module to shut off is with a good multi-meter as you described and you, we and almost all know that is correct.

Talk about 'low voltage spikes' is nonsense. Spikes are usually 'transient high voltage erratic charges and nothing to do with voltage collapse caused by a faulty battery or defective battery to MDM wiring etc.

High voltage spikes: High voltage spikes can damage the MDM, fans and digital controllers. The voltage of these erratic transients can be sufficient to cause arcing and therefore damage electronics, but easily prevented.

We fit a Voltage Clamp, (AKA Zorb, AKA Spike arrestor), to all systems as
standard and highly recommend all users fit one of these very inexpensive devises to help protect all electronics coupled to the DC power supply.
We use a type P6KE33CA - TVS Diode, P6KE3 Series, Bidirectional, 28.2 V, 45.7 V, DO-204AC, 2 Pins.

Here is a simple supply voltage test as described on our Ozefridge web site Tech page (Fridge assist):

Click on pic to expand..

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Cheers OzePete
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Old 08-08-2019, 05:46   #18
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Re: Fridge cycling frequently for very short periods

Volt meter tests for voltage drop may be good business if you are selling replacement systems but it will not detect a short duration voltage drop that occurs on compressor start. The common cause for this fast very short low voltage drop is always a result of momentary resistance somewhere in boat's refrigerator wiring, weak circuit breaker, old switch contacts, any wire terminal connection or aged undersized wiring. If you want to save time and money leave the voltmeter in the tool box and bypass probable causes till a fix can be made. The troubleshooting LED has already pointed you to the low voltage error code.You would not use a voltmeter to locate a boot up problem on your computer so why would you think it would produce results on the similar circuits in a Danfoss control module. What else would a short low voltage short duration drop that could not be seen called other than a low voltage spike.
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Old 08-08-2019, 05:53   #19
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Re: Fridge cycling frequently for very short periods

The Danfoss BD compressor system supports adding a diagnostic LED to understand the detected faults, as-shown in this topic.

My refrigerator was modified by me to add a "hidden" diagnostic LED that may be observed by opening the freezer door.


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Old 08-08-2019, 07:01   #20
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Re: Fridge cycling frequently for very short periods

Anyone not having a trouble LED on their BD35 or BD50 Danfoss module Email me and I will send a complete Pdf file with pictures on installing one.
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