Concern about changes in your 12/24 volt refrigeration’s performance.

[Richard Kollmann]

I get more email questions on determining 12/24 refrigeration performance as it relates to; refrigerant volume, compressor speed, condenser efficiency, and how to determine what is the normal amperage for a one of a kind system. Yes, ice box conversion refrigeration in every boat installation will be different.
All of the above conditions can be evaluated with one Non Destructive Test (NDT) tool known as a magnetic field tester or the more common in line ammeter, as long as it has accuracy in the 1 to 15 amp range. Digital AC/DC clamp on amp meters are now available from $30 to $50. To get a refrigerator current amp reading just clamp meter on either the refrigerator power or ground wire. Remember the rule, put your hand around a DC wire the magnetic field goes in direction of your fingers do no get confused if it reads Minus instead of plus Amps either way it is reading units amperage draw that second.
Before these Clamp on meters can define changes in a refrigeration unit’s performance a stable base line of normal performance is required for that unit only. To use any type ammeter to test refrigeration stable or changing performance you need a base line of normal amperage required for that specific unit. Coming up with approximent base line figures for fixed speed compressor like a BD2, or 2.5 or 3 can be found on manufacturers design data sheet. Also there is good manufacturers information an amperage draw for variable speed compressors. Manufactures current draw is based on condenser temperatures so on your one of a kind unit when you establish and record amperage the temperature of condensers cooling medium should also be recorded. Yes there will be minor changes but rarely will they be greater than ¼ of an amp.

The base line system amperage record should be recorded when evaporator is at system desired temperature. Future testing with clamp on meter reading adjusted for ambient temperature changes. Major amperage up or down will identify system electrical current changes, as a result of one of the following conditions has changed since your system’s base line amperage was developed :
1. Variable compressor speed change. If you want to verify actual compressor speed a milliamp meter in series with one of the thermostat wires will identify compressor speed at that time. One milliamp is slow speed five milliamps is maximum design speed on Danfoss/Seacop BD compressors with standard visaible speed control modules. When using their AEO module your clamp on meter the continuing up and down 300 Rpm changes looking for low energy Sweet Energy Spot will be visible.
2. Poor condenser cooling results in a higher system current draw or too much refrigerant.
3. Normal evaporator thermostat temperature changes from what it was when base line was set till increase or decrease base line current figure. Changing evaporator temperature can change system’s daily SCOP up or dowm.
4. The big advantage of your base line amperage is in confirming the refrigerant’s correct volume on a capillary tube refrigerant flow control system. When installing one of these ice box conversion pre charged kits some refrigerant could be lost or there has been a loss of refrigerant do to a leak how do you or a service man know when to stop adding refrigerant. If a base line has not been established use the compressor manufactures energy tables to prevent over charging. If this cap tube system already had a base line amperage figure very slowly add refrigerant carefully and wait till evaporator is at normal temperature before final adjustment. Confirmation of correct refrigerant charge by frost line comes 24 hrs later.
5. When a cap tube system has the correct amount of refrigerant and cooling stops it is generally blamed on low volume of refrigerant. What follows is Tech person add refrigerant and later compressor will not start and run so they let out refrigerant and tech goes away again. Later someone checks amp draw of system they now know it has a full refrigerant charge and amperage drops from 5.5 amps to 3 amps and cooling stops. Now the decision is open up system and install a new filter even when it is not advisable installed in boat. Finally when they look for experienced help and listening for refrigerant flowing sounds in evaporator to see is flow is interrupted and restarting flow several minutes later as it would if their were moisture in system. The clamp on meter makes it easy to identify between moisture restricting flow verses solid cap tube blockage or coagulated thick over heated oil. Blockage shows up on a drop in amperage. Amperage returns to normal when flow is back to your base line.
6. The best thing about a clamp on ammeter is you do not need a technician confirm your unit is in good operating condition which also avoids contaminating the refrigerant cycle by connecting a pressure gauge to it.

[OzeLouie]

Originally Posted by Richard Kollmann

I get more email questions on determining 12/24 refrigeration performance as it relates to; refrigerant volume, compressor speed, condenser efficiency, and how to determine what is the normal amperage for a one of a kind system. Yes, ice box conversion refrigeration in every boat installation will be different.
All of the above conditions can be evaluated with one Non Destructive Test (NDT) tool known as a magnetic field tester or the more common in line ammeter, as long as it has accuracy in the 1 to 15 amp range. Digital AC/DC clamp on amp meters are now available from $30 to $50. To get a refrigerator current amp reading just clamp meter on either the refrigerator power or ground wire. Remember the rule, put your hand around a DC wire the magnetic field goes in direction of your fingers do no get confused if it reads Minus instead of plus Amps either way it is reading units amperage draw that second.
Before these Clamp on meters can define changes in a refrigeration unit’s performance a stable base line of normal performance is required for that unit only. To use any type ammeter to test refrigeration stable or changing performance you need a base line of normal amperage required for that specific unit. Coming up with approximent base line figures for fixed speed compressor like a BD2, or 2.5 or 3 can be found on manufacturers design data sheet. Also there is good manufacturers information an amperage draw for variable speed compressors. Manufactures current draw is based on condenser temperatures so on your one of a kind unit when you establish and record amperage the temperature of condensers cooling medium should also be recorded. Yes there will be minor changes but rarely will they be greater than ¼ of an amp.

The base line system amperage record should be recorded when evaporator is at system desired temperature. Future testing with clamp on meter reading adjusted for ambient temperature changes. Major amperage up or down will identify system electrical current changes, as a result of one of the following conditions has changed since your system’s base line amperage was developed :
1. Variable compressor speed change. If you want to verify actual compressor speed a milliamp meter in series with one of the thermostat wires will identify compressor speed at that time. One milliamp is slow speed five milliamps is maximum design speed on Danfoss/Seacop BD compressors with standard visaible speed control modules. When using their AEO module your clamp on meter the continuing up and down 300 Rpm changes looking for low energy Sweet Energy Spot will be visible.
2. Poor condenser cooling results in a higher system current draw or too much refrigerant.
3. Normal evaporator thermostat temperature changes from what it was when base line was set till increase or decrease base line current figure. Changing evaporator temperature can change system’s daily SCOP up or dowm.
4. The big advantage of your base line amperage is in confirming the refrigerant’s correct volume on a capillary tube refrigerant flow control system. When installing one of these ice box conversion pre charged kits some refrigerant could be lost or there has been a loss of refrigerant do to a leak how do you or a service man know when to stop adding refrigerant. If a base line has not been established use the compressor manufactures energy tables to prevent over charging. If this cap tube system already had a base line amperage figure very slowly add refrigerant carefully and wait till evaporator is at normal temperature before final adjustment. Confirmation of correct refrigerant charge by frost line comes 24 hrs later.
5. When a cap tube system has the correct amount of refrigerant and cooling stops it is generally blamed on low volume of refrigerant. What follows is Tech person add refrigerant and later compressor will not start and run so they let out refrigerant and tech goes away again. Later someone checks amp draw of system they now know it has a full refrigerant charge and amperage drops from 5.5 amps to 3 amps and cooling stops. Now the decision is open up system and install a new filter even when it is not advisable installed in boat. Finally when they look for experienced help and listening for refrigerant flowing sounds in evaporator to see is flow is interrupted and restarting flow several minutes later as it would if their were moisture in system. The clamp on meter makes it easy to identify between moisture restricting flow verses solid cap tube blockage or coagulated thick over heated oil. Blockage shows up on a drop in amperage. Amperage returns to normal when flow is back to your base line.
6. The best thing about a clamp on ammeter is you do not need a technician confirm your unit is in good operating condition which also avoids contaminating the refrigerant cycle by connecting a pressure gauge to it.

Sorry Richard but I have to disagree with the core issue you raised here: Determining condition of a DC refrigeration system based upon amp reading at unit is likely to provide a wrong outcome. I have noticed also in the past that you traditionally quote this method and it is incorrect unless voltage is similar / stable each test and it seldom is.. I agree that your method and comments otherwise are very good but you need to establish watts not just amps and here is why:

Energy is measured as watts (amps X volts) and amps is the current flow. It is energy rate that you need to monitor not amps. To establish the watts simply multiply the amps by the voltage to provide the watt rate. (energy)

For example when first tested, lets say system is running fine at 100 watts but the voltage is down to 11.1VDC, the amp reading would be 9.0 amps. and say this is considered the reference value .
Now later while the batteries are charging to their max at 14.7 VDC., the reading from the tong tester now reads 6.8 amps.. In both situations the system is working similarly with both reading the same energy rate of 100 watts albeit vastly different amp readings due to variations of voltage.

Relying on the amp reading from the tong tester could cause the user to arrange or start a totally un-needed repair job. So follow the OP's suggested method but also read the voltage each test and do the simple calculation to establish watts for a more accurate comparison check.

Also there are many other simpler observations that can indicate if the system is operating properly or not.

[Richard Kollmann]

I believe the average boater has sufficient mechanical aptitude to read and record amp meter flow as many have used it in replacing refrigerant on cap tube pulse driven compressors. Danfoss BD compressor modules void any concerns over electrical power in getting accurate amp flow readings. There must be a more efficient way to analyze our small 12 volt refrigeration so I offer one.

If someone has better plan than my system amp flow measurement method for pinpointing and correcting a trouble area, like simply adding the correct refrigerant charge to within 25 grams when amount of refrigerant to be added is unknown, please post it..