12V compressor fridge not starting/staying on. Thoughts?

[e9999]

I picked up this older little compressor fridge. It's a Coolmatic (by Waeco) CCF18 12/24V.
I didn't have an OEM cord but another fridge (a Peltier type) cord I have miraculously does fit, although I'm not sure if it's the correct polarity (this may be important).

So I said to myself, bleep it, let's just try and see if it blows up.

I did and what happened is that the compressor will try to start for a fraction of a second, like a blip, I can feel it vibrating but them immediately stops. Then maybe 5 secs later it does it again. and so on. I put a Wattmeter on and I see the background level at 4W (there is a LED on) and when it tries to start it goes to 16W or so.

Thoughts before I contemplate taking this thing apart? Anything obvious?

 

[cruiserpilot]

Before you take it apart, the interweb should be able to find you the proper cord easily enough.
I'd try that first.

 

[e9999]

yes, well, not easily enough, this is quite old, which is why I took a gamble. I do have to say, though, that I don't know what would happen if the polarity were reversed. Would the compressor simply go the wrong way?

I'm hoping that since the LED was working that it's OK.

 

[Rebus Knebus]

I had a similar problem with my dometic recently. Turned out to be a dirty connection at the cigarette lighter. There was enough power to turn on the display, but when the compressor would try to start it would draw more current and the resistance of the dirty contact would make the voltage drop low enough that the fridge would shut the compressor off. I’d recommend making sure you have good connections to your power source and that your power cord is a sufficient gauge.

Don’t know anything about that particular model, but generally equipment like that has reverse polarity protection and just won’t run. YMMV

 

[e9999]

yes, could be something like that, especially since I'm using a funky old 12V power supply from 120V. I should try it on the main receptacle in the truck, maybe that might make a difference and it's easy enough to try. I kinda doubt that this old fridge would have some sophisticated low voltage protection, though.

 

[ducktapeguy]

What kind of power supply are you using? Sounds like it doesn't have enough power to handle the startup load of the fridge.

 

[e9999]

^ Possible. I'll try the fridge on some batteries and see what happens. Should probably have started with that TBH but I was in a hurry and the power supply was right there and it is beefy. It is an old transformer-based unit, though, so I don't know if the voltage control is very good actually, that could be part of the problem. With a bit of luck it's only that.

 

[80t0ylc]

Another thought, being that it's an older fridge, does it have a 12v-24v voltage switch that might be in the wrong position?

 

[e9999]

^ that is a very good thought. So I went to check and no, it does say 12-24V but does not have a voltage switch that I can see.

However, upon closer inspection, thanks for the incentive, I realized I had misunderstood one of the controls. One switch says "High" and "Low" and I had wrongly assumed that was a reference to the temperatures. But now I see it says in tiny print that this is the "battery monitor". Not sure what that means but I assume it's 2 different settings for a low voltage cutoff. Don't know which way. Should have looked more carefully. This may have been part of the issue, together with the power supply, but I don't recall which way I had it. This thing may be more sophisticated than I thought at first.
Anybody with a Waeco knows what this "Battery monitor" High and Low refers to, exactly?

added: I just saw that for both the Waeco and Dometic CF-18 which look a lot like mine, High is 11.5V cutoff and Low is 10.4V , so I'll assume for now that it is the same for mine.

 

[80t0ylc]

 

[e9999]

well, good news. I got it to work fine (I think) with a better power supply and a LiFeP battery as a buffer. Must have been, as suggested above, that the first power supply gave too low a voltage, or too messed up a one (almost surely a pulsed half rectification), then I also lost almost 1V over the skimpy 18ga cord I managed to find; and I probably had the voltage cutoff on high; or some combination of all that. Or who knows, possibly the comp just loosened up finally after some years of disuse (unlikely).

But, temporary conclusion: input power issue leading to hiccupping compressor. And batteries are your friends. I have to admit that I did not expect that from that apparently beefy power supply. Goes to show you...

Got it to go down to 8F with 75F ambience using about 36W. Not bad for an antique. And sure beats that little thermoelectric cooler I have (not saying much, these things are so grossly misrepresented in ads, really annoying).

 

[e9999]

Ouch! There is something weird going on.

As I said, I got it to work just fine with another Power supply feeding into a LiFeP battery and then to fridge. But, weirdly, if I connect the fridge directly to that good benchtop adjustable Power supply without the battery, and set the PS to the same voltage as the battery was, the fridge will NOT start. Even if I set the PS to a good volt above the otherwise battery voltage, still won't start.

No idea why the fridge needs a battery. This is a good PS that maintains voltage very well up to 10A. But it's not that the fridge will try to start and then stops like earlier, here it won't even attempt to run the compressor. I have a voltmeter right at the connector to the fridge so I know there is enough voltage there to at least otherwise start the compressor so I don't think it's a voltage cutoff problem (if that cutoff circuit is OK). I can't imagine the fridge would know the difference between a given voltage off a battery vs the same voltage off a PS, without even trying to start. But that could have been the cause of the problems with the first power supply as well. Yet, I can't believe that this much newer solid state benchtop PS would also give a bad waveform, can't be that. Weird! Thoughts?

 

[80t0ylc]

Might need an O-scope to see what the output of your PS is. I would bet that the obviously sensitive DC fridge and your PS are just not compatible, without a filter. Sounds like the battery is acting like a filter, somehow. Makes me wonder how the performance would be in a vehicle where your alternator is charging the battery. A fridge needs to be reliable when you rely on it to keep your food from spoiling.

 

[e9999]

I still have to try in the vehicle but I'm hoping that a battery there will help too.

The odd thing is that 2 very different power supplies now gave me trouble and it's unlikely they both have the same type of output. It would be pretty strange if the Waeco would be that sensitive to any non-perfectly constant DC input. It must have some sort of built-in power processing since it can apparently handle 12 to 24V, I would hope that would clean up things a bit already. I have several other DC supplies I could try but that's going down a rabbit hole. Reality is that I will always have a battery in the vehicle so can take advantage of that. But puzzling, I got to figure this out.

 

[80t0ylc]

Maybe you do have a component out in the Waeco circuitry. I'm not sure if starting up a compressor is the same as starting an electrical motor, but if it is, you may have a capacitor or diode that is failing. Been a long time since I've troubleshot circuits, but caps and diodes are easy to test, unless they're part of an IC board. And a schematic would be nice to keep you on track.

 

[e9999]

well, it just goes to show you...

tried the fridge in the back of a newer (2019) SUV with the OEM lighter plug there. And was surprised at what I saw. It's running fine with engine on, BUT with the engine off but circuits on, it will NOT start properly, even in the Low setting. From looking at an inline voltmeter, it seems that the voltage in the back when various circuits are on is only about 12.4V and much less than that when the compressor is starting. So it's doing the blip start thing. I guess they skimped on the wires from battery to the back of the vehicle and there is too much voltage drop. Dang.

And the bad thing is that if I use a LiFeP in the back as a buffer, which will start the fridge fine, the battery will charge OK with the alternator going at about 14.3 which is great BUT if the engine is off, the starting battery will be less than the standard 13.3V of the LiFeP, so the latter will get discharged by draining to the starting battery as well as running the fridge, which is NOT great.

yup, wiring and voltage drops are critical for this kind of stuff... Don't assume that because there is a lighter plug it will for sure support a fridge.

 

[e9999]

and more:

Tried yet another power supply without battery as a buffer. No go. Would not start. Even seemed to have zapped the PS a bit cuz it behaved weirdly afterward.

Then tried on the 100. Both in the back and in the front it started fine with engine on. I saw that there is about 1V lost over the cab wiring with fridge on.

But with engine off (and key on) it would NOT start on either low or high battery setting, whether front or back.

Interesting: if the fridge is running with engine on and I turn the engine off, the fridge will KEEP running. But if it turns off it won't start again. This suggests yet again that the inrush current makes the voltage drop too low for the compressor to start. I tried to measure the inrush current with a Fluke max min feature but it was too fast to be captured. Just casual observation with a meter inline suggests it is at least 5A and likely much more, whereas the normal running current is 3A.

So, the battery buffer is essential with the built-in 100 wiring as well. (But of course, this may not be a problem if the wiring to the back were to be very thick dedicated wires, maybe then the fridge would start. Need to check that still.)

Anybody else saw something like this with their fridge or is it just a quirk of this antique Waeco?

 

[87warrior]

Interesting: if the fridge is running with engine on and I turn the engine off, the fridge will KEEP running. But if it turns off it won't start again.

This was my experience when trying to run a 54quart Costway fridge from the rear 12v power port in my 100. I've since ran a dedicated 8awg line to an ARB style plug in the back and the fridge purrs along without any issue.

 

[e9999]

^ Yep, bigger wires will do it.

I'm thinking that there are 2 separate issues at play here with my fridge:

- fridge won't start if the inrush current is such that the voltage at the fridge is too low because of overly small wires. That's not surprising.

- something else funky going on with direct connection to a power supply. That is less obvious. In fact, I saw something weird: I tried running the fridge running off a power supply at 15, 16 and 18V and it would NOT start. However, when I lowered the voltage in real time from 18V, it did start up while I was actually reducing the voltage.

 

[e9999]

I have not yet put a scope on those power supplies, so no progress there, but checked in the 80 which has a custom dedicated 10ga wire to a rear cig lighter receptacle I put in, and no surprise there, all was well, fridge starts OK with engine off and I only see a drop of 0.5V from battery to fridge, so no issue with a charged battery, even on High. I am just surprised that the other 2 vehicles I tried have such skimpy wires to the back outlets that the fridge which draws 36W when running can not be supported there with engine off, even though the circuits should be able to handle 120W. What were they thinking? I guess in 2003 there were few fridges out there, fine (although I would expect better from a LC), but a 2019 SUV...?