resistor?

[Paulus]

Our refrigeration unit stopped working on the way home from the North Channel.  Back to ice blocks for the trip home.  After trouble shooting the system, I discovered that the thermostat was not functioning. The manual was very helpful in and practical in trouble shooting the problem.  Simply bypassed the thermostat.   I ordered a new one from Nova Kool and also the resistor for pre setting speed for the compressor.  They are sending me 2 new resistors, the resistor was not bad.
My question is:  Why would there be different resistors for the compressor speed?  I am installing the same one as the unit came with(black one).  I have a very limited knowledge of electronics and would appreciate a little feedback.
Thanks,
Paul
PS:  They did not charge me for the resistors.

[KWKloeber]

Is the unit 12v or possibly dual 12v/24v?
Sounds like a question for the mfgr?

[Paulus]

It is only a 12 volt, not dual.
Paul

[DaveBMusik]

from: http://www.kollmann-marine.com/tip6.aspx

When changing the thermostat on Danfoss BD 35 and BD50 compressor systems the amperage in that circuit is very small, from 2 to 5 milliamps, depending on the size of the compressor's speed resistor, installed in the thermostat's wiring. With no resistance in this circuit, 5 milliamps will cause the control module to operate the compressor at a minimum speed of 2000 rpm. By adding a 1500 ohm resistor the compressor will run at its maximum Rpm of 3500. Other compressor speeds between 2000 and 3500 rpm are achieved by using resistors smaller than 1500 ohms.

[Paulus]

Thanks Dave,  Just getting back home.  Had a email from Sure Marine with the same info.  This is were I bought the new thermostat.  Did not answer the question whether or not the fan would run faster depending on the resistor.  When I install later this week, I will try the the two different resistors and see if the fan speed changes. 
Thanks,
Paul

[KWKloeber]

Paul, does this info help at all w/ your issue?

If trying to slow down the fan, these seem to work fine on a fan hooked to DC, but unsure if it would affect a fan powered through the Danfoss module, or cause potential RF interference.

https://www.allelectronics.com/item/msc-35/3-amp-dc-motor-speed-controller/1.html

The inline resistors are installed to vary the speed of the compressor, not the fan.
If trying to quiet a noisy fan, the resistors is not how to do that.

Depending on whether your unit has the DC or AC/DC controller, the physical configuration of the resistor cards is slightly different, but basically, there are 3 common resistor values, and 4 common speeds.

No resistor - the compressor runs @ 2000RPM,
277 Ohm resistor @ 2500 RPM
692 Ohms resistor @ 3000 RPM
1523 Ohm resistor @ 3500 RPM.

Note it will also run at all speeds between 2000 & 3500, so one could put a 0-1500 Ohm potentiometer in series and (continuously) tune it up or down.

-ken

[Noah]

I am confused.. what brand reefer does Paulus have? He said he ordered a new thermostat and resistors from Nova Cool...?? Is his system same as usual C34 OEM Dometic Cold Machine system?

[Paulus]

Noah, I have a Nova Kool.  I do not know if the compressors are the same or not.  The info Ken provided does not pertain to my reefer.  SureMarine  send me the thermostat and resistors with an explanation.  I will be installing it tomorrow with the same resistor that was in the thermostat line but the  new one.  The old one was tested and was OK.  I will check to see if the fan runs faster if you change to a higher resistor.  Just for my own interest.  Dave's earlier post was similar to Suremarine's info. 
Thanks,
Paul

[KWKloeber]

I am confused.. what brand reefer does Paulus have? He said he ordered a new thermostat and resistors from Nova Cool...?? Is his system same as usual C34 OEM Dometic Cold Machine system?

Noah,
I am confused also, The info came from my tech contact, and is for a Nova Kool, which is what I thought Paul had?

Paul,

<< I will check to see if the fan runs faster if you change to a higher resistor. >>  Did I miss something along the way?

If you are wondering if which resistor you use affects the fan, the techies say that it has NO effect on the fan speed, but you can control it other ways.   Maybe they are mistaken - could be, I'm not a HVAC guy; just repeating the "expert(s)" info. 

[J_Sail]

Just to be clear; the resistor does NOT in any way affect the speed of the fan. Its purpose is to vary the speed of the compressor in the Danfoss BD35 models that support it.  With a variable speed compressor you can run it at the slowest speed that will cool your box.  The benefit is that the compressor is more efficient at slower speeds; running the compressor slowly for a longer period of time takes less total electricity than running it faster for a shorter time. 

Skipping the resistor won't hurt anything; the compressor may run for a shorter period each day without it, but since it draws proportionally more power than the increased cooling the speed provides, in the end you spend a bit more energy when it runs faster than optimal.

http://files.danfoss.com/TechnicalInfo/Dila/06/bd_compressors_04-2007_pk100c802.pdf
http://www.suremarineservice.com/LT201-UNIT-ACDC.html

[Paulus]

Thank you!! J_Sail.  This is the info I received from Suremarine.  Hopefully this clears it up for others that participated in this post.  A clear concise explanation does not muddy up the waters.
Thanks,
Paul

[KWKloeber]

Just to be clear; the resistor does NOT in any way affect the speed of the fan. Its purpose is to vary the speed of the compressor in the Danfoss

J,

YES!  Thanks for corroborating the info I received/passed on.  I was ready to slap the techie up side the head for fibbing (after Paul said the info didn't apply to his Nova)!
It wasn't clear whether changing the fan speed is a desire or just an "inquiring minds wonder," but have you ever used or know anything about that controller (in the link that I passed on)?
i.e., https://www.allelectronics.com/item/msc-35/3-amp-dc-motor-speed-controller/1.html

-ken

[Paulus]

Installed the new thermostat, ran new wire, relocated the location of the thermostat  and used the black 500ohm resistor.   All is good.
Thanks for the help.
Paul

[KWKloeber]

Doncha like a plan that all comes together. Especially when at least some of the parts are no cost!