Engel MT45F Fan Replacement / Upgrade

Hi Allan B, very much appreciate your advice. You do make a great point I had not considered the degree of improvement however for a small investment it is worth the experiment. I had considered mounting both fans at the bottom to draw the cooler air and angle them slightly (very shallow triangle) in an attempt to hit different areas. I think leaving one at the bottom (original position) and mounting the second above the power supply (only other space for it) will only draw warm air from the condenser and power supply.

So now for the dumb question, if the original 24V DC fan was rated at 150 milli-amps, should I be looking for 2 x 12V fans with draw of 75 milli amps each or 150 milli-amps each?

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You are right Papa, it is "worth the experiment". I added an extra fan to my old Waeco years ago. Never sure if it improved the fridge but I felt happier about it. lol

Your original fan at 24V x 0.15A = 3.6W.
Two 12V fans of 150mA in series is (12v x 0.12A) = 1.8W each so 3.6W in total so no increase in wattage or airflow.
So if you put two 12V fans in series to run on 24V then they each need to be rated at 300mA which will provide approx double the original airflow.

I went through the same excersize with a Waeco unit, I found upgrading the existing fan made little difference to the airflow or cycle times. Contary to Allans belief I found adding an additional fan to the exit side of the case made a significant difference to the airflow and the cycling rate of the fridge. I use mine as a freezer and the additional fan resulted in a significant reduction in A/H drawn though at the expensive of a significant increase in fan noise but as the unit is mounted in the rear of the car doesn't matter in my case.

One thing to consider though is with the Waeco units is the fan controller circuit can't handle much current. Two fans will cause a fan error, I made up a simple transistor switch to turn on the additional fan. This may not apply to your unit.

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Hey Leigh, what "Allans belief"? …. What am I blamed for now?

Placing two fans in line will move the same amount of air as one fan will. With no obstruction that might be the case but with small portable fridges I would suggest obstructions hinder the airmovement the motor housing section. Adding a fan to the exit side helps drag the air through.

I found uprgading the original fan did little, ie could just fell airmovement through the exit grill. After adding a fan to the exist side there is now a stong airflow out. Result was it lowered the motor run time from around 3 minutes and 40 seconds down to around 3 minutes. May not be the case with an Engel though.

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Ah yes, well it wasn't actually the "same column of air", was it?

Suppose it depends how you look at it, a fan at each end of a pipe is moving the same columb of air, putting a fan at one side of the motor compartment and another at the other side is moving the the same same columb of air assing they are the only entry exit points. Advantage is you have one pushing one pulling, so if we put a ristricton between the entry exit and have one fan pushing only then we pressure one side and have atmosphere pressure the other. If we add another fan pulling to the otherside of the restriction then we create a low pressure which helps move air through the restriction and in creases airflow.

Could achieve the same with a bigger fan on one side or two fans etc but space to mount will be the problem.

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Leigh, I very advisedly said "column" in my expression to Papa.
In aerodynamics a column is defined as body of air travelling in laminar format. That is, without turbulence. Putting a second fan in that column cannot accelerate what is already flowing at the fan's speed. I have actually seen someone from this EO community place one fan directly on top of the other expecting an improvement to the airflow. Even worse, he actually. had them blowing in opposite directions!!!
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What you describe is a volume of air in a turbulent condition, not flowing in a regular direct format which is quite another matter where a second fan may well have a beneficial effect on moving the air.
Thank you for muddying the water with your incomprehension. You could have asked me what I meant before smearing me.

Thanks Kazza055

Thanks for the heads up, I have ordered a replacement fan so if my experiment fails I can revert to the factory setup. I am happy to risk failure of both fans in series as (for me in my thinking) it carries the same risk as running one fan. ( I am sure the mathematicians will disagree) :-)

The current one is caked in dust, after air dusting it and a liberal dose of electrical cleaner it was a less than 50% it would spin up by itself, a little push with the finger fixed that. Hence the timing to replace and experiment while it is apart....appreciate the advice Thank you.

Many Thanks Bigfish

Thx Bobsabobsa

I will only be using the feed going to the existing fan. Am trying to avoid a complicated mod & blowing up the fridge & setting fire to something :-)

Thanks Phil G, good to know about the thermal control. I only stumbled on the buggered fan when I was testing the freezer. After having it run in the shed for a few hrs I noticed more heat than I would expect. After pulling off the back, the fan was not spinning. A gentle poke with the finger the fan spins to life.

The fan blades were caked with dust/mud :-) ...............................

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Good one Kgarn. Mind you, it may make some peoples head hurt trying to apply it to an Engel. lol

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Hi Rod, that is wise advice from you about directing the airflow to where needed with baffles. The manufacturer's norm seems to be to position the fan wherever convenient and the cooling air does not necessarily travel where needed. When I added as second fan to my Waeco I drilled a pattern of holes in the plastic casing to allow effective egress of the air and installed some fibre-board baffles internally to direct it better.

The Vitrifrigo upright fridge in my motorhome has a fan mounted directly onto the condenser but some air discharging from the other side was circling back to the fan inlet (revealed by strips of thin paper) so I placed a baffle to prevent this. I also have a pair of additional fans that feed air through a plenum to the fridge intake and exhaust hot air out so that it does not just circulate around the cabinet.

EDIT:
Rod, I have now read your report on the Super Cheap fridge. The positioning of the original fan is far from optimal…. it certainly will blow air directly through the condenser but then it would recirculate to the fan inlet which is nowhere near the outside air.
Your observation about the fairly constant off-times is to be expected. The 'off-time' is of course the time it takes an unpowered fridge to rise in temperature to the setting at which the motor restarts. This is totally a function of the insulation quality of the cabinet and ambient temperature. Modifications to the refrigerating components will have no bearing on it. They will only affect the run-time as your test results reveal.

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Hi Ken,
That is much as I have done. Although a different model fridge, it has a similar arrangement in the compressor compartment. You would think that a company so convinced of their product superiority, would arrange things better. A simple baffle is all.
Because of the poor thermal conductivity of air, it is more important to focus on the temperature of the incoming air rather than the velocity of its passage over the heat exchanger.

The rear of my fridge is not open directly to the outside as is yours, so it sits on a plenum chamber beneath, divided into incoming and outgoing sections with a fan on each. Seems to do the job.
The other modification was to add insulation on all sides of the cabinet. Easily achieved as it is contained within cupboards. Although not so convenient for those with chest type fridges.

When I changed to a compressor fridge on the caravan, I sealed off the two vents to prevent dust getting in.
For airflow, I installed a quiet 5" fan high up on the wall between the fridge and ensuite - air is drawn in under the fridge then past the compressor unit and up to the top where the 5" fan extracts the warm air into the ensuite.
I monitor temperature in the airspace behind the fridge and it sits at anything up to 6 degrees warmer than ambient inside the caravan.
I also monitor duty cycle simply by looking at the history on my Victron smart shunt (via a bluetooth app) - the graph showing amp draw shows a jump of 4 amps whenever the compressor cycles on. On the cooler nights, it was only cycling 2-3 times overnight - will see what happens on warm days shortly.