Danfoss compressor and thermostat

[borvaprops]

Hello everyone, I'm running a isotherm watercooled fridge/freezer and a BD50 compressor. The unit was working flawless and it's now constantly drawing 6amps hike running. If I bypass the thermostat the unit runs first at around 6amps and slowly makes its way down to 3.4amps which is what I was seeing before. The thermostat is a isotherm version and it has a 600ohm resistor in the T connector of the electronic unit which is contradictory to any other BD literature that tells me resistor should be on the C connector of the control unit.
Any advice would be greatly appreciated.


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[Zanshin]

Just to confirm, the controller for a BD35 looks like this:



A 600 Ohm resistor between the "T" connector and the "C" connector will give a speed of about 2800RPM.
The other resistor between the "C" and "P" connector controls the cut-in and cut-out voltages.

See this link if you need more information: http://www.vfamerica.com/pdfmanuali/bd35-50f-manual.pdf

[borvaprops]

Yes the controller is similar to the one you posted p/n101N0210 I'm wondering if this is a controller issue or thermostat issue


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[Richard Kollmann]

C terminal is the normal location for speed resistor if the P terminal has a wire connected to it if no it does not matter if resistor is on the T terminal. Isotherm units with their start up speed controller piggybacking Danfoss module will not have an external speed resistor. The thermostat wiring loop between C and T terminals only carries from one to six milliamps of current. Six milliamps no resistance produces 2000 rpm one milliamp caused by a 1500 ohm resistor will increase compressor speed to 3500 rpm.

The higher the speed of compressor the poorer it’s Coefficient Of Performance. Refrigerant volume, Condenser cooling and volume of heat removed from evaporator will determine amperage needed. A BD 50 compressor at 2500 rpm will draw around 6 amps and as box cools amps will drop to a low of 4 amps. These amperages will be lower as seawater gets cooler and higher as seawater warms on your water cooled unit. These power consumptions figures will also be reduced if a small amount of refrigerant has leaked out. In the case of refrigerant loss if the system has a standard flat plate evaporator its surface will no longer be completely covered with frost.

[Reefer.]

Hi,

anyone know what the little black box attached to the thermostat is?

Danfoss compressor.

[Reefer.]

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[HappyMdRSailor]

Originally Posted by Reefer.

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Haha... tried to fix the link twice with the same result as you! Dunno what the problem was, but the fallback is to attach a saved image... Ah well... it's there...

And...

No... no idea what your mystery box is... "turbo mode" just like the old PC's had?

[Reefer.]

Hehe, 'turbo' on the old 386. A screaming 33MHz processor...becomes 66MHz. The fridge box though, funny thing is, the two positions give two different compressor speeds.

[captjcook]

I would think we could figure out the black box if we knew where the black wire went....


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[HappyMdRSailor]

Originally Posted by Reefer.

Hehe, 'turbo' on the old 386. A screaming 33MHz processor...becomes 66MHz. The fridge box though, funny thing is, the two positions give two different compressor speeds.

Faster than your 128MB of RAM and 80MB HDD could communicate... Look out! I'm pushin' it! Wooo Hoo!

[Richard Kollmann]

The BD35 compressor is a variable speed compressor. The two wires attached to thermostat are what switches compressor off and on. The amperage in this wire loop will determine speed of compressor, if amperage is 6 milliamps compressor will run at 2,000 rpm. If amperage in this wire loop is 1 milliamp compressor will run at 3,500 rpm.

My guess is that inside the black box there is one or two speed resistors connected to the exterior switch allowing manual compressor speed changes.

[Reefer.]

Thanks Richard, what is point of having two speeds? Power saving?

[SV THIRD DAY]

Originally Posted by Reefer.

Thanks Richard, what is point of having two speeds? Power saving?

For efficiency you want to match the BTU removal rate of the compressor (IE the RPM) with the heat uptake ability of the evaporation plate in the box. Running the compressor faster than the evaporator can pull absorb the heat doesn't get you colder beer...it uses/waster power. Some systems control the compressor speed automatically while some use a resister to set the speed.

For all the tech data you never really wanted to know.
The data table on Page 15 shows the Resister Ohms, Miliamps, and compressor RPM.
http://kontes.gr/pdf/compressors_BD.pdf

Cheers

[Richard Kollmann]

Originally Posted by Reefer.

Thanks Richard, what is point of having two speeds? Power saving?

Variable speed is becoming the answer to daily energy consumption in refrigeration. The major improvement pleasure boat icebox conversion refrigeration compressor is the ability to balance a system based on ambient heat load conditions. Daily System Coefficient Of Performance (SCOP) is best when all components in a system are balanced together. The compressor has a major effect on efficient performance the faster it runs the more energy is wasted do to loss of volume metric inefficiency and excess heat generation. Slowing down compressor can cut daily power consumption in half in some cases even though compressor runs much longer. As a general rule a Danfoss BD compressor should run less than 50% of the time at its slowest speed.

If there is no resistance in thermostat wiring circuit connected to C and T module terminals and thermostat maintains desired box temperature and compressor runs much less than 50% of the time you have a very energy efficient system.

If your boat has an amp-hr meter run unit 24 hours and record total amp-hrs. Now without changing thermostat setting change position of switch on black box and record 24 hours usage. As long as box temperature remains at desired temperature amperage consumed will tell you what position to leave the switch in.

Another method of selecting the correct size resistor is make up four sizes of resistors as shown on my web site slide show. First set thermostat to desired box temperature and leave it set there for a day or two. Now with no resistors in thermostat wiring see if box temperature is satisfied by unchanged temperature. If box temperature is too low change resistor to the next size higher ohms until box temperature is satisfied without tampering with thermostat.