1: This video indicates that you can check for voltage drop with a Multi-meter!
Recently a marine forum self appointed refrigeration guru claimed that you can’t check for system’s DC supply voltage drop with a multi-meter. Totally incorrect.
This test is presented in an attempt to expose that ‘Fake News!
(This is the same refrigeration expert who constantly claims that the high side pressure on an air cooled system should not exceed 120 PSIG Can you believe it! To say this indicates this guy does not understand the basic fundamentals of refrigeration.. period. )
The test cabinet used for this test has a Danfoss BD50 12VDC compressor. This video shows how voltage can easily be read before and as the compressor starts / tries to start, so as to indicate if the power supply and/ or supply chain is adequate.
Question being: Is the supply voltage dropping sufficiently to cause the Motor Driver Module to default into either low voltage or over current mode.
A multi meter used this way will not determine if the Motor Driver Module (Black box on side of the compressor) is faulty or not, but it will indicate if there is the possibility of a bad power supply. (Battery or supply lines) Bad power supply or a defective battery is the most common cause of a compressor failure to run, yet so easy to check.
This simple test may prevent a Motor Driver Module being replaced unnecessarily.
To check voltage simply put the your Multi-meter to DC volts and the two test lead prongs onto where the DC power connects to the compressor. Usually the top two terminals on the Motor Driver Module.
Take note of voltage before and while starting / attempting start. If the difference is more than one and a half volts or it dips below 10.50 volts then I suggest upgrading the power supply / battery.
Note: A high voltage reading with no load is irrelevant, it is what is available when the load is applied. (motor starting etc.,)
Voltage spikes or Transient voltages are a completely different issue. They are NOT related to the lack of supply voltage issue, but they can use the supply voltage circuit to travel upon.. Transient voltages or Spikes are not ‘Low voltage spikes’ as some incorrectly quote, they are HIGH voltage often extremely high but with very little current.
Unlike using a multi meter to easily test the power supply voltage that is related to motor drive / start, it is near impossible to detect spikes this way, in fact spikes are near impossible to identify and can occur any time therefore it is best to have protection against them.
High voltage spikes can originate from various sources and are usually very short lived. Protection is the best and only way to prevent spike damage. Use a ‘Voltage clamp’ (AKA ‘Zorb’ AKA ‘Transient voltage arrestor,) able to clamp >36V. These devices cost less than $2.00 and simply are applied across the power input positive and negative.
Standard on Ozefridge systems, don’t know why all others don’t!