Sunday, Sep 17, 2023 at 12:06
Hello William
The Engel people call their compressor a SWING MOTOR for some strange reason, as nothing
swings at all inside. The piston and solenoid slide back and
forth, ie, a normal petrol motor has reciprocating piston parts too and they are called reciprocating, not SWING.
It is purely a short stroke sliding reciprocating solenoid with a little piston at one end to pump gas.
The internal resistance is around 2.7 ohms to 3 ohms and the unit, as other have said, runs on around 20vAC. 17 V AC will make it less effective while 22V AC gives more grunt to the solenoid. I had one running on a 18V AC transformer output for a couple of weeks.
Forget the 12V actions as it is DC and only causing a shorted/stalled situation inside the solenoid, which is flicked in it's sliding action by the AC current reversal acting on the internal magnet. I have one cut apart in my shed at the moment.
The only way you can see if compressor is active, is to apply around 20V AC direct to the compressor, without it's lead attached to the inverter unit, of course. Maybe give it a hit as has been mentioned if applying the current/voltage and it doesn't run.
I added two 12v DC computer fans in series, to my 40L long before Engel ever began fitting them and they ran off the AC compressor feed and was rectified to dc for those fans.
Mine ran at 18V AC but the specs say 20V AC or so.
Mine has never had a fast cool down or good performance because the voltage is low from the inverter.
Placing one fan to directly blow airflow over the compressor is a good idea as they get HOT, especially if using as a freezer.
If AC to the compressor makes it run and then reconnecting the normal lead and tested whilst also reading the applied AC voltage, may mean the inverter is faulty and not the compressor, if there is an absence of AC from the inverter.
EDIT
Sometimes on older gear the electrolytic capacitors in the inverter may become out of spec and stop the inverter from oscillating, ie, cycling it's switching and therefore NO AC is produced. If you are electronic minded and solder ok, then maybe, that is a maybe, changing the electrolytic capacitors in the inverter with the same spec capacitors may make it work again. Just a chance. The
inverters are costly! Not easy to get them apart though.
AnswerID:
644430
Follow Up By: Allan B (Sunshine Coast) - Sunday, Sep 17, 2023 at 16:10
Sunday, Sep 17, 2023 at 16:10
Hi RMD,
There can be an issue when expressing voltages present in an Engel fridge as the compressor solenoid is driven by a square wave but your digital meter actually responds to the peak value but is calibrated to read as though it is a regular sine wave which will be 0.707 of the peak value. So the question arises….. what value are the "specs" referring to?
To resurrect a phrase…. "Oils 'aint oils Sol"
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Follow Up By: RMD - Sunday, Sep 17, 2023 at 17:56
Sunday, Sep 17, 2023 at 17:56
G'day Allan.
I have a 15 litre Engel, donated by my local Engel dealer, ie scrapped it. Old one though with plastic case which had been used as a football. It didn't work.
The circuit board for the temp Pot had been butchered. After soldering wires to replace missing board sections, it still didn't work. Then I found the indicator LED was stuffed and when replaced, all worked ok. However, I put a digital scope on it and the waveform is mostly hash and nothing like a square wave or even a sine wave. Hard to read the voltage value. Somehow it must have the majority of the output as a square wave or close to and the rest must be spurious rubbish.
"Not sure if it is Castrol in the compressor".
FollowupID:
924512
Follow Up By: Allan B (Sunshine Coast) - Sunday, Sep 17, 2023 at 19:58
Sunday, Sep 17, 2023 at 19:58
Well RMD, I have never put a scope on an Engel but as all the power supply has to operate is a simple solenoid coil I don't think the manufacturers would trouble to make a noise-free inverter. So yes, I expect the waveform to be shrouded in hash. A few picofarads of capacitance across the cro probes would possibly dampen the hash enough to see and measure the basic waveform. But why bother..... an analog voltmeter will respond to the waveform and not be much affected by some hash so it will read the 'average' voltage. Good enough for servicing. But a digital voltmeter may read very badly when confronted with a noisy signal.
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Follow Up By: qldcamper - Monday, Sep 18, 2023 at 07:41
Monday, Sep 18, 2023 at 07:41
Purely out of curiosity, has anyone measured the frequency the inverter runs the compressor at?
I imagine it would be close to 50 Hz to make AC operation simpler.
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Follow Up By: RMD - Monday, Sep 18, 2023 at 08:04
Monday, Sep 18, 2023 at 08:04
G'day QLD
From memory, earlier ones used to run the compressor off a 240V AC transformer tapping to get the approx 20V AC.
The 12v electronics just switched a section of that transformer to make the 20V AC, All selected/decided by the slide blanker/inhibitor at the power entry connections. So, I believe it to be 50 Hertz according to the diagram I saw.
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Follow Up By: Allan B (Sunshine Coast) - Monday, Sep 18, 2023 at 09:11
Monday, Sep 18, 2023 at 09:11
I have located a screen-grab of a Sawafuji compressor.
Unlike what RMD saw with a screen full of hash it appears quite regular with the small return overshoots probably being the induction back-EMF from the solenoid coil. Related text indicated a frequency of "about 50Hz". Another Engel document nominated the voltage as "14 to 18 volts" which I should think was peak-to-peak.
Sawafiji waveform
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Follow Up By: Nomadic Navara - Monday, Sep 18, 2023 at 09:17
Monday, Sep 18, 2023 at 09:17
"I imagine it would be close to 50 Hz to make AC operation simpler."
Where do Engel refrigerators originate from? If they are a USA company then the natural frequency will be 60 Hz.
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Follow Up By: Stephen L (Clare) SA - Monday, Sep 18, 2023 at 10:17
Monday, Sep 18, 2023 at 10:17
Peter, Engel is a Japanese company, and like many manufacturers, the fridges are now made in Thailand and are the longest portable fridge manufacturers in the world, having produced their great fridges for just over 60 years, a feat that no other car fridge manufacturer can claim.
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Follow Up By: RMD - Monday, Sep 18, 2023 at 11:46
Monday, Sep 18, 2023 at 11:46
Nomadic Navara
I was surprised to see you asking about the Engel origin, I though everyone who knew of those fridges knew Japan are the makers. Japanese symbols and look etc. The boxes they arrive in are a dead giveaway.
While the USA does use 60Hz and the small 120V AC
grid, a solenoid wouldn't really matter if it was 50 or 60. I guess the mass of the siding/reciprocating piston and magnet assembly dictates how fast it can effectively change direction and still effectively pump refrig gas. Faster may not be so good. You don't want it to sit in the middle and just jiggle a bit
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Follow Up By: Allan B (Sunshine Coast) - Monday, Sep 18, 2023 at 13:30
Monday, Sep 18, 2023 at 13:30
.
The Sawafuji compressor in the Engel fridge will have a natural resonant frequency determined as a function of the armature/piston mass and the spring rating. For efficient operation, the applied electrical frequency needs to be very close to that resonant frequency and it would appear that is approximately 50Hz. I doubt that the mains frequency plays any part in what is applied to the reciprocating piston assembly. I expect that the ac mains is rectified and applied as a nominal 12vdc supply to the inverter and control system. All technical information that I have seen points to that.
Incidentally, it is that reciprocating compressor that turned me against the Engel fridge. I put one in my camper 40 years ago and the whole camper responded to its vibration. I found it necessary to mount the fridge on rubber vibration isolation devices to make it bearable. When I parted with that camper so I did with the fridge and turned to Waeco forever since.
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Follow Up By: Allan B (Sunshine Coast) - Monday, Sep 18, 2023 at 14:08
Monday, Sep 18, 2023 at 14:08
.
Ah yes, I thought that I had it somewhere……. the Engel circuit diagram.
You can see that it has a switch-mode power supply to convert the mains ac to dc and feed directly to the inverter to power the oscillating motor coil. Mains frequency does not play a part in the compressor frequency. The frequency is determined by the inverter.
Engel schematic
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Follow Up By: Nomadic Navara - Monday, Sep 18, 2023 at 20:11
Monday, Sep 18, 2023 at 20:11
Thanks Stephen and RMD for the source of Engel fridges. I did a quick search this morning and did not locate a head office for the manufacturer. The reason I was concerned about the mains frequency country of origin is my experience back in the days of steam radio. We had a lot of problems with equipment designed for countries where 60 Hz mains frequency was used. When this equipment was used in Oz on our 50 Hz mains a large percentage of that equipment was subject to overheating problems. The reason was that the mains transformers designed for 60 Hz mains did not have enough steel in them to cope with the lower mains frequency. This would be more problematic in something like the swing motor that relied on a natural harmonic frequency as Alan pointed out.
If someone attempted to use the fridge via mains power through a step down transformer as was attempted by some on this thread and the mains frequency did not suit a 60 Hz natural resonant frequency of the motor then there is a large probability of the motor life would be somewhat shortened. However, as pointed out above the operating frequency of the motors is 50 Hz then there is no problem here. Forget this problem in Engel fridges, the mains frequency if of no consequence.
On the other hand, if you come across any equipment that has mains transformers and designed to operate on 60 Hz, that is the time to remember my warning.
FollowupID:
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