Refrigeration questions

[rascacio]

Hi all, I have a bit of a problem with my fridge. It goes like this, it's a Waeco Coolmatic RSA-110 with an accumulator plate and the TEC control unit, however with the TEC unit I find that within an hour or so of running off fully charged batteries the unit shuts down and the yellow voltage light flashes.

The battery voltage measured at the unit is still showing 12.5v but the unit will not run unless the engine or shore power is back on.

The blurb on site says the switch off voltage is 10.4v and the switch on is 11.7v. My batteries are well above this but it just doesn't work.

Has anyone experience with this TEC unit and also can I simply get rid of it and use a normal type of thermostat, which I had with my old system ?

Maybe the TEC unit is knackered but any info from anyone who has or has had one of these would be much appreciated.

By the way this is a used unit that was not very old when I got it, it was being changed for a watercooled system., and works flawlessly on shore power and a fixed voltage of 13.5 volts.

 

[duncan99210]

Is the 12.5 measured under load (ie when the unit is running) or not under load? It is possible that there's a bad connection that is dropping under load voltage intermittently and causing the problem.

 

[rascacio]

Hi there, if I remember correctly it is about 12.2 when under load. The cable is the same cable that ran my previous built in fridge and I have just disconnected it and reconnected to the new unit, no change in length cable size. This set up, with a standard thermostat would run no problem and right down to 11.5 volts if I let it, which I only did once a few years ago to test the set up.

It seems that the TEC unit is too sensitive and I think a standard stat or different electronic controller may be better as getting info from Waeco/Domotec is more or less impossible.

 

[rivonia]

We had the same unit. When the fridge is on "ON IT'S OWN" with nothing else on you will probably find that it works OK. However with orther electrical items on then the voltage supply to the TEC unit is impaired / dropped and so it goes into safe mode Yellow. What we did was to fit an inverter fitted to the mains in supply, it dropped the 240V down to 12V and that load was fed directly to the fridge. It worked fine. Also if you take the TEC apart and give it a really good clean.

 

[charles_reed]

They all have a voltage drop problem if you wire them into the standard bus-bar.
I'm afraid they need a big fat input direct from the battery bank. Starting up the solid state inverter on the Danfoss AC unit might only take a recorded 5.4amps but the transient pull is quite a lot larger.

Great units - I've had two of the Italian Isotherm units since 1990 and only got rid of the 1st because it was Freon 12. Internally Waeco and Isotherm use exactly the same gubbins with slightly different contol systems.

 

[rascacio]

Thanks for the input, not sure what I'll do yet, have to wait till I'm back on board again and have a tinker.

 

[MBullock]

If you can measure the voltage at the compressor, and the batteries. You may just have a large voltage drop which heavier duty cabling or as suggested direct cabling from the battery will sort. You could always fit a relay to your existing fridge switch if you use a direct power from the batteries allowing you to keep an on/off switch on your panel. One final option other than inverting up to 240v is to use a doc/doc convertor, I think you can get 12/12 and that will hold a static output voltage for you.

 

[rivonia]

When I converted the electric on mine I got a fellow yachtie to do it for me as he is an electrician wizzo. Cost me a few beers. Plus the cost of materiel.

 

[charles_reed]

If you can measure the voltage at the compressor, and the batteries. You may just have a large voltage drop which heavier duty cabling or as suggested direct cabling from the battery will sort. You could always fit a relay to your existing fridge switch if you use a direct power from the batteries allowing you to keep an on/off switch on your panel. One final option other than inverting up to 240v is to use a doc/doc convertor, I think you can get 12/12 and that will hold a static output voltage for you.

The Danfoss compressor unit, fitted to both Waeco and Isotherm units, has a plug&play built-in inverter, which clips onto the compressor control unit and handles either 12/24 volts. It's a very reliable unit (until flooded) and extremely efficient. I'd advise against doing anything but supplying it with ample clean power @ 12v.
The Isotherm unit has an override which speeds up compressor and brings in a fan to cool the holding plate to -14C when system volts exceed 13.8. On start-up it does need 6 amps @ 12.2v or better - inadequate wiring inevitably leads to the OP's reported problems.
It is possible that his domestic battery has got one duff cell - (hence the drop to 10.6v and the warning). However it's impossible to start diagnosing the problem unless you have a good 12v supply.
In fact the supercool light and fan starting up have proved, for me over the last 24 years, the most reliable check on alternator charge.

 

[rascacio]

Hi Charles, thanks for your comments. I think I will bring a new (fused) supply direct from my batteries, I have a feeling that the original wiring through the main switchboard is what is causing the problem. It may have been adequate for the old (20 years ? R12) original compressor but it is probably not quite delivering the volts for the TEC unit, which seems to be pretty sensitive to voltage.

On another related issue, perhaps you know of somewhere to buy a voltage stabiliser to even out the supply to the unit when the engine is running. I have a Sterling smart alternator to battery charger which pushes out 15+ volts on part of its charging cycle, this appears to shut down the unit temporarily (yellow led flashing) with the over voltage protection so I would like to stabilise the voltage for the compressor to maximise refrigeration time when using the engine. Any ideas ?

 

[MBullock]

I'm never owned that make of compressor therefore I wasn't aware of the voltage sensing trick Charles mentions. Even more reason to suspect voltage drop then. Boat wiring is usually woeful in my experience, both in quality and gauge. So, based upon the max draw I'd put in one thicker than the 3% drop chart suggests or work out the actual drop and go for something very low. Then use good quality, preferably tinned, preferably marine cable. I read recently someone advocating "high quality hifi cable" - each to their own! Obviously fuse it, and you'll probably want to switch it, hence my suggestion of a relay from the original Cable/panel.

Ideally, an amp meter wired in via a shunt will tell you what you need to know. If not source and buy a clip on amp meter. The later was suggested to me when I lost all my batteries overnight one night! Helps troubleshooting no end! With that tool you can measure volts and amperage whilst the compressor is running.

Who am I to question sterling, but your voltage under charge seems too high to me. It would fry my agm's anyhow. Other than for an equalising charge are you sure it's working correctly, or how/where are you measuring that output voltage from. If a 12v controller is shutting down due to over voltage surely that's not right?

Cheers.

 

[rascacio]

I think I may have overstated the high voltage on the charger, I've checked my note book and on max it is 14.8 volts on its equalising phase but usually not for long. I do monitor my batteries whether on shore power or engine charging fairly closely, the way you do when you're on board and everything else on board is OK, even my old compressor system that is still in situ just in case it needs resurrecting ! Unfortunately the TEC instructions are a bit random and can be confusing as to what each light is supposed to do and when but I do think that a new supply direct to the compressor, suitably switched and fused will be the best/simplest option to try first. I'll take some cable out with me in spring. Give me something to tinker with anyway !
The relay sounds like an idea I may try but I am probably going to change my main board in the not too distant future so will probably leave it until then.

Thanks for your input it is much appreciated as is everyone elses. I like to be prepared when I get out there.