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Old 07-05-2024, 12:45 PM   #1
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Fixing Fridge performance issues and changing from DC to DC/AC

New Secop 101N0510 Controller
I had been looking at my refrigerator’s performance, and some anomalies that I wanted to understand. During that period, I came across a good deal on a Secop 101N0510 controller on Ebay. It peaked my interest, so I pulled the trigger and purchased it. This would replace the existing Secop 101N0212 controller.




I had concluded that no matter how much I wished it was the other way around my Van still spends most of its time in the driveway and I usually have it plugged in. This will allow me to have the refrigerator running off of 120 volts when hook up is available. If 120 volts is available it runs off of that, if not it runs off of 12 volts. It should also be noted that I have a couple of addons that run directly off of 12 volts.

First when it showed up it was actually labeled a Dometic unit, not a Secop, but I assume the same thing. In any event I decided to move forward with the installation. The first issue was it is bigger, actually quite a bit bigger. I disconnected the wires and undid the mounting screw, while the unit came off, I didn’t have room to get the unit out. I found three screws that allowed you move the compressor unit back. This gave me the room to remove the older unit, but more importantly install the new bigger unit. After a couple of tries I had the unit mounted and was ready to move on to hooking it up.

My plan was to do this in stages, first hookup and run in 12-volt mode, after I am satisfied with that, I will add the 120-volt addition. That of course is just two wires. You can see the top two tabs are for the 120-AC connection. The remaining connections are pretty much the same, but there are additional tabs A and C for lighting. This causes some issues as distance between tabs is tighter, this makes direct hook up of my Merlin II unit impossible. No problem, I have a plan to remote mount the unit on the back of the unit.

My Victron Multiplus II 3000 120x3 has two separate outputs. The main output I run to my 30-amp main breaker panel. This output is available via charger and inverter mode. The secondary out is only available when the unit is plugged into shore power. I am hooking the refrigerator up to this output. This will eliminate me from having to make sure the AC input is turned off when running on the inverter.

Merlin II speed Controller

The Merlin II unit is an automated speed controller for the unit. Instead of hard setting the compressor speed with a resister, you can instead set the speed based on temperature, the objective being running at the lowest speed. It will increase the speed if needed, like when the door is opened. There had been a reported error with the Merlin II shutting down unexpectedly during operation. I have possible seen this issue multiple times, so I returned my older unit for a newer updated one. This was not an overall difficult process, so thumbs up for Coastalclimate. This was not an easy issue to replicate. In any event I have run the unit for years and only seen the failure maybe three times. So of course I will monitor for that condition.



The above diagram shows the higher current usage (speed) when starting as the temperature is high. After a period of time, you can see the current comes down and settles into a low setting.

In any event to swap to the AC/DC module I would need to mount the Merlin II remotely, not right on the Secop controller. This would also in my mind provide better airflow for the Merlin II. I decided it was the time for better power distribution, as the connectors on the controller were getting kind of janky. I decided to use a small 4 circuit ST Blade fuse holder and some DIN Rail Terminal Blocks for the ground and other connections. The kit comes with terminal strips to connect multiple Wago type connectors together. I created a ground bus and a couple of dual connectors for the T and C terminal connections and single for the D (Diagnostic) connector.

Digital Thermostat

The other previous upgrade I had made was installing a Coastal MK3 12v Digital Thermostat/Thermometer. While this was a nice unit, the cost was high. I decided to replicate using an Inkbird INT 1000 controller. It actually fits in the same size whole and is much cheaper. This allows you to set the refrigerator temperature with direct input and display the temp of the refrigerator. If you run the D terminal to an LED, you can get a get fault codes if something goes wrong. Obviously the Inkbird doesn’t come with a wiring harness and LED, but from cost perspective make this an attractive solution. The final thing added was an outside control for the controlling C & T terminals. I have an Ethernet relay controlled by my Stick Computer and RV control program. This mainly will be for testing fun but being that I also have a Ruuvi Temp sensor inside the refrigerator I have temperature feedback for the program.



Fans

It looked like a good time to look at upgrading the fans. The current fan is a 3000-rpm fan pulling 0.19 amps. While relatively quiet, I decided I would try upgrading. The controller can handle 6 watts of power. I decided to try double fans, I ended up trying two Noctua NF-A12x25 PWM fans. Each of these will pull 0.14 amps, for a total of 0.28 amps or 3.36 watts. Noctua fans come with a variety of connectors, including a single to dual connector. This will make it easy to implement and test the single to dual fan configuration.

Fan direction

The factory installed position of the fan blows air from the back over the compressor. This ends up with limited airflow as really isn’t and room for air to exit. At the moment I have kept with the factory fan configuration, I will try turning the van around to pull air over the compressor and coils towards the back.

Internal Fan

I added a small internal fan: Noctua NF-A4x10 FLX, Premium Quiet Fan to move air inside the fridge. I mounted the fan on the upper rack, in the little cubby between freezer and side of unit.

Venting

I have a couple of inches of room behind the fridge and have multiple vent holes in the cabinet. The 130 is notoriously bad on compressor placement. I originally installed a 4” round vent on the side of cabinet.



I decided to go with a larger 3” x 10” rectangular vent.



120 Volt Hook-up

While this may seem to be relatively simple, it does require some thought. I want the fridge to run off of 120 volts when I am plugged in, I don’t want it on 120 volts when I am running the inverter. Obviously, this can be done in multiple ways; to initially test I will probably plug it into the same plug I use for my Start Battery Charger, it has its own breaker. For long term, I will hook this up to the AC-Out-2 of my Victron Multiplus -2X120V. This AC output is only active when the inverter/charger is plugged in. In this configuration I won’t have worry about switching anything off when the inverter is active, because “I want to spend my time camping, not managing my van's electrical system.”

Monitoring System

I run a Victron Cerbo in my van and it allows me to communicate with various Victron and Non-Victron devices. Being that the refrigerator is one of our larger DC consumers, I dedicated a Victron Smart Shunt for monitoring power used by the fridge. This is grossly overkill (current wise) but unfortunately Victron doesn’t really have smaller current shunt solutions. It can be set up as a DC Meter, allowing me to capture current, power and voltage data for the refrigerator. The Cerbo GX also reads and stores temperature data, I use a Bluetooth Temp Sensor (Ruuvi). Here is a quick sample of the data from my Victron VRM portal.






Computer Control

The Victron Cerbo monitoring system gives me direct access to all the sensors it reads, I have an external program running on my Stick Computer that that will monitor various devices throughout the day. I generally can display this data real-time but also keep daily consumption usage. n my program I also compare the time the compressor is on and off to get the duty cycle of the unit. You can see those in the Refrigerator display in my program.

While this is set up to mostly monitor data, I have the capability to add control. If I turn the Inkbird temperature controller off, I can control the combining of the T and C terminals with a connected relay. This overall gives me greater accuracy, as my setpoint and differential can be measured to 1 decimal. It will also give me control of changing these values based on other variables captured via the computer program
Many will think data collection is overkill, but I spent most of my career as a Test or Validation Engineer. Instrumenting up products is just second nature. We used data like this to nor only prove something was working, but when you’re telling an engineer their design isn’t working you need data to back that up. So, I will admit I may have more of an obsession with data collection than most.

The issue

This is how I got to this upgrade. I noticed some odd behavior with my initial setup (Secop 101N0212 controller, CoastalClimateControl MK3 12v Digital Thermostat/Thermometer, and CoastalClimateControl Merlin II, mini smart speed board)





The above data just never seemed to correlate with what I thought it should be doing. In this 24-hour period it was not overly hot or cold. We do see the Duty Cycle track with temperatures, the hotter it gets the duty cycle increases, and decreases as the temperature gets colder. What doesn’t track is the temperature of the refrigerator. Why does the refrigerator temp go up when the ambient temps are lower, and actually colder when the temperature is hotter. When the temperature gets warm, I would expect the inside temp to track a little higher. It would hit the setpoint and turn off. The outside temp would make sure there was little undershoot before the temp started to rise. I originally suspected the actual Thermostat Controller; this is why I tried the Inkbird unit. The Inkbird unit ran about as well as the more expensive Controller, so that didn’t appear to be the issue. I ran directly to the Secop controller and bypassed the Merlin II and saw pretty much the same issue.
When I changed to the Inkbird controller I had to change the temperature sensors. The coastal sensor was a little bigger and much thicker cable, the Inkbird was smaller and thinner cable.

When comparing the temperature readings from the controllers to the Ruuvi temperature sensors they were always off, and the amount of being off depended on temperature. I tried some extra insulation on the entrance hole for the sensor, no change.

In any event I remembered when installing an Isotherm Smart Energy Controller that it said to make sure 20 -27 inches of cable were inside.






I actually wrapped about 15 inches of sensor cable around sensor grill, this would not have been possible with the Coastal Climate sensor. This I believe was the primary reason for some improvement in my issue. It is reasonable to believe that the sensor was off, and that the was a mismatch between temperatures.

Testing

Of course, testing should be easy. I have a good platform, and data collection system. The bigger issue will be the outside environment, that I won’t have any control over. The van will be outside and be at the mercy of my seasonal temperatures. I am quickly losing my cold weather platform. The temperature inside of the van can also be altered by window shades, fans, or driving the van. I will do my best to keep the setup of the van inside the same as much as I can. I will note the changes that may come into play while posting results

First Run
  • Compressor cabinet fan – set to 60°
  • Compressor Fan - Stock Single
  • Compressor Fan Direction – Default
  • Power Source – 12 volts
  • Fridge – empty

First 24 hour run





The first run went pretty much as expected, with the lower temperatures we can see the duty cycle is around 25%. As we move through the day it warms up and we see the duty cycle start get higher. Eventually we see the benefit of the Merlin II speed controller, as the on cycle gets larger the compressor speed rate (current) increases. The speed increase keeps the refrigerator temps within are expected range. As the temperature decreases, we again see the compressor speed reduce. Overall, for the day the duty cycle is 44% with a total of 35.03 Ah (0.46kWh) for the day.


Second 24 hour run
  • Compressor cabinet fan – set to 60°
  • Compressor Fan - Stock Single
  • Compressor Fan Direction – Default
  • Power Source – 12 volts
  • Fridge – empty



The second captured 24hrs pretty sows much of the same, we do see a shift on the low and high side move when the temperature is increasing refrigerator


When I wrapped the cord of the sensor inside of the fridge I had it around 17” I increased it to 27”
Warmer day
  • Compressor cabinet fan – set to 60°
  • Compressor Fan - Stock Single
  • Compressor Fan Direction – Default
  • Power Source – 12 volts
  • Fridge – empty




Outside temp peaked around 80, I don’t have any window shades on the van, no windows open, or roof vent fans active. In this case I am trying to get the inside temp warmer. The results look good on this point. Refrigerator temp is pretty much tracking, even when temps were high, refrigerator temp held steady even during a three hour on cycle.
Fan Direction
I did not see any significant data changes when changing the fan direction.
Two Fans
I did end up doubling the fans, but I replaced my cabinet temperature-controlled fan with the secondary fan. This allows the use of a secondary fan when needed.
This was the final solution I came up with.
  • Compressor cabinet fan dual – set to 70°
  • Compressor Fan – Single/dual, see above
  • Compressor Fan Direction – Default
  • Power Source – 12 volts
  • Fridge – empty



This was a pretty warm day, the Inkbird is set to 39 ° with a 2 ° differential. The fridge held the temp control very well with a swing between 39 ° and 41.4 °. In the warmer temperatures you can see that the overshoot is larger, as it takes a bit to change the temp direction, and the undershoot is less.

It appears to be a benefit in having the secondary fan compressor fan. This runs whenever the fridge cabinet is above 70 °. I also in this run had the MaxxFans running in exhaust to control inside temps.

The power usage for the fridge was 52.70 Ahs (0.7Kwhs), this had a duty cycle of 60.8%. Because of the control of the Merlin II, I can see current draws from 2.4, 3.6 and 5.4 amps depending on the temperature.

The MaxxFans and Temperature controlled Compressor fan came in wit a current usage of 13.57 Ahs (0.18Kwhs)

I have tested the computer control inputs. If I turn off the Inkbird I can run the refrigerator with my existing computer hook up. This would allow me to change the set point and differential with greater definition and could be changed based on other environmental inputs. I will probably look into that more during the off season, but I am getting the performance I want without it.

I have tried out running the fridge off of AC, it works and runs fine. I want to add some stuff to monitor just the refrigerator power usage, and also hook it up to my secondary output of my inverter, which only works as passthrough. It unfortunately is a little hot this weekend to be making those changes.

Summary
  • What fixed the problem? Unfortunately, I changed pretty much everything, but I suspect that the biggest problem was caused by the temperature probe. Being that my refrigerator cabinet would see some pretty high temperatures this, I think that wrapping 20 inches of the Temp Sensor was most likely the big fix. The Coastal climate sensor was thicker in diameter, I didn’t suspect it would have the same issue, but I believe it did. I really don’t know how much cable I would put into the unit with it.
  • The Merlin II was replaced because of a different issue, I have not seen that issue with the replacement, so I don’t think it had anything to do with the issue.
  • The thermostat was replaced with the Inkbird unit, again I don’t think it has anything to do with the problem. I for this time keeping the Inkbird unit, it is performing well. It is a far cheaper option.
  • The Secop controller was replaced, this again had had nothing to do with the issue I was having, but now works on DC/AC.
  • The new fan change appears to work well showing better performance. Switching to a dual fan was even better. Switching the secondary fan to be temperature controlled gave me the benefit with a little less current usage.
  • The increased vent size also I believe showed performance improvement.

Having the Victron Cerbo GX report out the inside temperature of the refrigerator was a big aid in finding this issue. My original thought was the compressor couldn’t hold the temps; the sensor was reporting incorrect temperature data back to the thermostat.

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Old 07-06-2024, 11:17 AM   #2
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Interesting data. Ive added a fan to my setup too and casual observation tells me it helps reduce the duty cycle a bit. A better set up might allow exhausting hot air directly outside through the vans wall, rather than the current setup that pushes the hot air out into the interior. Even better would be reversing the fan in winter, bringing in colder air rather than recycling interior air warmed by the diesel heater. This would also help reduce the duty cycle when less solar charging is available due to shorter days and more cloud cover. Now to find an acceptable through wall vent of some sort that wont allow large amounts of dust ingress.
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Old 07-07-2024, 09:31 AM   #3
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Totally agree on the exhaust vent directly outside. Location of the fridge did not make that all that feasible in my current build. You can see the difference between that last two charts, on the very last one I turned on the MaxxFan, you can probably tell it was where you see the temp decrease on the Rear Van Sensor. Having that exhaust fan on kept both the fridge cabinet and rear van temps tracking very close to outside temp.

I have thought of adding an 4" intake vent via the floor, the hope being it would take in shaded cooler air in the summer. I could control it with a wood working dust blast gate. At the moment I'm not sure I need to do that, but agree the cooler air improves the duty cycle. We had some cooler weather in June outside temp was between 45° and 64° and look at the result 25.3% duty cycle or 18.05 Ahs compared to 50.6° to 82.3° I had 59.9% duty cycle and 53 Ahs.



My main concern when digging into this was the accuracy and control of the fridge temps. My wife is a professional chef, and is kind of a stickler about fridge temps. This was one of the primary reasons I went with external digital thermostat. The bad thing is the temperature that the digital thermostat was displaying and working off was wrong. This become more evident when starting using and trusting the Ruuvi sensor I put in the unit. So getting that sorted out was the big thing. The good news is the $20.00 Inkbird thermostat works as good as the coastal climate one.

I am also still happy with the Merlin II compressor speed board, uses the slowest speed (pwr) for default, but increases when needed. Also very happy with the support provided for the board.
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Old 07-07-2024, 11:54 AM   #4
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Ive thought about a vent through the floor. Im less concerned in the summer because the max air fan seems to keep interior temps close to ambient and there is plenty of solar, but in winter when there is a 30 or 40 degree delta, the heater is running and little solar input, reducing the duty cycle would go a long ways to preserving the battery state of charge for keeping the heater running. I like the idea of using a blast gate and only opening it as needed.
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