Frigomatic AV35F Compressor Problem

[Slow Graffiti]

Hello all. I’ve been lurking for a while and have gathered a lot of useful information in that time. I’m hoping that someone can help me out with a refrigeration problem I’ve been having:

I have a Frigoboat Frigomatic AV35F refrigeration unit, and in the past few days it has stopped cooling and the Frigomatic Master (E51600) controller keeps saying that I have a low battery problem. However, I’ve checked the voltage at the breaker panel, the Master itself, and the secondary control unit that comes with the AV35F (Danfoss 101N0210) and the voltage is well within the limits of the system. After checking all of these voltages and cleaning all the connectors on the Master controller, I’m beginning to suspect that the problem is with the controller itself.

That being said, I can get the compressor to work if I connect the power from the breaker panel directly to the Danfoss 101N0210 and take the Master controller out of the loop completely. Is anyone aware if this is a safe option to keep the compressor functional? Or do I have to look into getting a replacement Master controller?

Thanks for any help you can give.

[Scott Berg]

While a functioning controller will make the unit more efficient, you can indeed power the frequency controller directly assuming you have the thermostat connected there and not to the external "smart" controller. FYI Frigoboat now sells a small card based "Merlin" Controller that fits directly on the pins of the Danfoss Freq Controller

[GordMay]

Greetings and welcome aboard the CF, Slow Graffiti.

Richard Kollmann would know.
http://www.cruisersforum.com/forums/...lmann-831.html

[Richard Kollmann]

Gadgets like the Frigomatic Master E51600 are not necessary on Danfoss BD compressors in marine environments in most cases. After removing E51600 compressor will operate on standard thermostat. Without this speed controller compressor will operate at 2000 rpm its most energy efficient speed as long as it runs less than 50% of the time. If compressor should run more than 50% of the time in a hot climate a $1 resistor can be added to thermostat wire to increase speed and reduce running time to just under 50% running time.

[foggysail]

Originally Posted by Richard Kollmann

If compressor should run more than 50% of the time in a hot climate a $1 resistor can be added to thermostat wire to increase speed and reduce running time to just under 50% running time.[/FONT]

Would you explain how adding a resistor to the thermostat wire impacts the duty cycle? The thermostats I am familiar with are simple on/off controls that operate between temperature limits.

Even if the compressor is capable of operating at a higher frequency thereby chilling the cooling volume faster is that going to significantly reduce the operating duty cycle?

[Richard Kollmann]

In the First place these Icebox conversion refrigeration units are not always sold as a balanced system for each size intended box. These units fall into the mobile refrigeration category were temperature conditions wary from season to season. Now with variable speed compressors like Danfoss’s BD35 and BD50 each system can be more closely balanced to produce best System Coefficient Of Performance. (SCOP). This overall system performance begins with selection of compressor/condensing unit large enough to cope with daily box heat load for planed and future boat cruising area. Next selection of evaporator it must be capable of removing as many Btu of daily heat from box to satisfy thermostat without unbalancing system and wasting energy.

In the past one size compressor would unbalance system energy consumption in small boxes by cycling too often or in large boxes because evaporator was not large enough. The Variable speed compressors today permits operator to control compressors speed to not only better balance of all components of a system but also run compressor at its best COP. I can not explain why this compressor at low speed uses less energy but it my be better Volumetric Efficiency or just less process heat to dispose of. I can give you actual 80 degree test room controlled 24 hour tests I ran., BD50 compressor at 2000 Rpm 41.5 amp-hrs 2500 rpm 46.4 amp-hrs, 3000 rpm 52.6 amp-hrs, 3500 rpm 60.6 amp-hrs. Daily compressor running time at 2000 Rpm 12.7 hours, when running at 3500 rpm compressor ran 9.3 hours. In these examples energy reduction of 40% in a small box was achieved by running compressor at slowest speed over highest speed. As box size increases system will be less efficient and in a 10 cu ft box right now in Georgia there is no benefit to reduced speed.

Foggysail Thermostat on these systems is designed to control evaporator temperature so heat transfer in evaporator can remain as near to a balance as possible with the rest of system. No one is able to provide the best compressor running time for each system installation 50% is a ballpark figure actual amp-hrs consumed per day comparing different speeds may be a better way but most boats are not equipped with a amp-hr meter.

Danfoss BD 50, 35, and BD80 Compressor Speeds are controlled by changing the milliamps of current in thermostats wiring. With no resistance in this circuit it draws 5 milliamp and compressor runs at 2000 rpm increase resistance of thermostat wiring anywhere up to 1500 ohms will increase compressor speed. A 1500 ohm resistor added will produce 3500 Rpm. For more info on this see the slide show on my web site.

[foggysail]

Thanks Richard

[Oceanride007]

So instead of cycling is Richard saying that it works like a inverter drive on a AC machine. Interesting! In that case I'd say its overkill and your probably better off without it. I would argue that the COP is best at higher speed. You may have to measure the Amps until you figure which resistor.

Qualification Iwhen I was a Marine Engineer and would always listen to what the refrig mechanic says.

[Slow Graffiti]

Thank you very much for all the replies.

Been busy with off the boat stuff the last couple of days, but I shall be tackling the fridge again today, as it seems that the Danfoss unit is giving me some sort of problem. Hopefully it will be something simple.