Compressor coolboxes - test results

[AngusMcDoon]

Last week I asked about compressor coolboxes, and after some good reports, I bought a small one. I said I would experiment on the power consumption, and report back...

I bought the smallest that Waeco sell. It's only 18 litres capacity, but that's enough for me on my own.

I measured power used with an outside temperature of about 20c and the temperature control set to an inside temperature of 4c, i.e. typical fridge temperature.

The cool box was reasonably full, and was loaded with already cooled content. The box was also brought down to operating temperature on mains power before being tested on battery power. I opened the box once an hour during the day and not at all during the night. I monitored current consumption over a 24 hour period using a PC logging kit. The power was supplied from a fully charged 12V battery, which was producing about 12.5V at the start.

Here are the results...

Standby current consumption (cool box on, but compressor not running) is 44mA.

Compressor running consumption is 2.55A.

Duty cycle approximately 15%.

So averaged power consumption over the day was 420mA, or 5.2 Watts.

It will of course use more if required to cool down warm content.

I also measured the minimum temperature it would cool to, and it got down to -16c, so can be used as a freezer.

Seems like it does what was expected.

 

[Talbot]

Had to be something good for the price!

 

[Plum]

Many thanks for useful feedback. How noisy is it? Did it keep you awake at night?

 

[AngusMcDoon]

It is almost silent. You have to put your ear near it to hear it at all. It doesn't make any fridge-like click when the compressor switches on and off either.

The sound it makes is like that from a quiet computer's power supply fan, which is not surprising, as it has a very similar fan inside it.

 

[brownsox]

HWMBO is busy and I'm afraid electricity is a foreign language for me (sorry about the stereotype). But this is very interesting as we have the same little Waeco fridge. We have a single 95 ampere hour battery, an alternator from a 9.8 hp outboard, and a 60w solar panel, which means that the battery is well charged. If we leave the fridge on when the engine is not running we get the red error light and it sounds unhappy. I'd love to be able to leave it on all the time, of course - any advice?

 

[AngusMcDoon]

It could be...

Battery past its best and not holding charge very well. Sounds like you have ample supply, certainly for the short term.

Poor or dirty connections or switch contacts somewhere between the battery terminals and the coolbox.

Cable somewhere between the battery and the coolbox too thin. The connecting cable supplied is pretty chunky. Are your boat's cables used by the coolbox circuit similar or bigger?

You may be taking too high a total load from your electrical system from the cool box and all other electrical equipment, but I would have thought this unlikely, especially during daylight with no lights on. (Lights are electrical big hitters on small sail boat systems.)


There is a switch on mine where you can choose either a high or a low cut-out voltage. The low setting cut-out voltage really is low, at approx 10.5 volts. If you are only getting this at the coolbox you have one of the electrical problems above. 2.5A on its own should not pull down the voltage of a fully charged 95Ah battery to this level for a considerable time if everything is else healthy if the compressor is running only 15-20% of the time.

Try connecting your coolbox directly to the battery as an experiment, without the engine running. Measure the battery terminal voltage as well. It may give you a clue as to the problem.

 

[Petercatterall]

Angus,
Thanks for the report!
This sounds like ideal size of unit for us to use in our camper and on the boat. We have one of those cheapo non compressor ones which is the right size but uses about 5amps all the time (and not too cool either).
What is the aprox size of yours? has it a model name? and where should I look for prices?
Thanks again.

 

[Mirelle]

One of these?

US test report found on Google

I would also like to know prices and where to buy in UK, as SWMBO has shown definite interest!

 

[brownsox]

Angus many thanks for that - we'll check all that out.
Peter - we got ours from Compass where it was significantly cheaper than anywhere else I found - and especially a lot cheaper than at last year's Soton Boat Show Waeco stand!
It's the only 18 litre one they do.

 

[AngusMcDoon]

Compass Watersports advertised in their Spring catalogue the 18 litre model as £300 which included a mains adaptor as well. This price was only available until April. Although well past the end date of the offer I rang them and asked whether the could still do the offer last week. With a bit of haggling they agreed.

Compass Watersports home page

Click On Line Shop on the left in red
Choose Comfort on Board from the list
Choose Cool boxes from the next list

Scroll down, you will see Coolmatic CF-18, and then below a link to the other sizes (CF 25, 35, 40 and 50) that they now sell.

For sizes and specs, go to this web page on the Waeco site. It shows the whole model range. Click on an image of a coolbox, and then click on Download Tech Details. This gives physical dimensions.

I am not, of course, a salesman for either Waeco or Compass. Other places sell them too, but Compass was the cheapest I could find.

One disadvantage to these coolboxes - they are a bit of a lump. You wouldn't want to carry them far. Check the weights on the Waeco site.

 

[Mirelle]

Ta, muchly. SWMBO won't have to drink UHT milk in her tea.

 

[Phoenix of Hamble]

I've just fitted the Isotherm compressor based unit that refridgerates the existing coolbox..... be interesting to see how it compares with the portable version in power consumption..... i'll don't have an ammeter, so difficult to track.... but its about the same price for a unit that will cool and freeze a 100L box without too much trouble.... I am told that it uses 0.74A on average.....

 

[gjgm]

not the same league perhaps
but bought a halfords electric coolbox other week 35-40 litres,£80 including mains adapter (12v otherwise). all stayed very cold, and with a freezer pack, which stayed frozen for 3 days, even the milk froze.
may meet the price conscious bill for some...

 

[AngusMcDoon]

Cheap digital multimeter from Maplin only £5. Sometimes they sell 2 for that price. Measures upto 10 Amps at 0.5% accuracy. Good enough for fridge investigations.

Someone will now post how Lidl sell a crate of 24 for 18p. /forums/images/graemlins/smile.gif

 

[Phoenix of Hamble]

So what do you do?.... stick it in series?...

I'll have to have a look at mine tommorrow evening (its on the boat), and see if it measures amps as well..... never used it for that purpose before....

 

[AngusMcDoon]

Yes, I do it with the multimeter in series with the battery, on the meter's highest current setting (normally via a separate + socket on the meter).

I switch off all other circuits, take a no load reading (usually not quite zero because of unswitched circuits like the switch panel voltmeter), and then take another reading with the equipment being investigated switched on.

It doesn't matter which side of the battery you use, and with digital multimeters which can display negative values, the polarity of the leads doesn't matter either. Just ignore the negative sign if you get one.

There's always a chance that you could blow a fuse in the multimeter if the equipment you are testing takes more than the meter can cope with, but two-dozen meters at Lidl for 18p, who cares?

The current you measure this way will be very slightly lower than the unmeasured current, because the meter will have a low value shunt resistor in it that you are putting in the circuit, but not enough inaccuracy to make a difference.

 

[roger]

I put in a Waeco DIY system with compressor and evaporator separate and joined up during installation. USed fair amount of insulation. My duty cycle is about 20%. However the about 4 inch diameter computer fan disturbs my wifes sleep so we switch the fridge off at night. It works well and will freeze food if placed next to the evaporator plate.
The duty percentage does go up on very hot days but no data I'm afraid.

 

[AngusMcDoon]

I did some more experimenting last night which may be able to help you.

Using my battery that was giving a no load reading of 12.5 Volts at the terminals, I tried connecting up my coolbox through 4m of typical mains lamp flex, where each core was about 1.5mm diameter. With this connection, the coolbox would not run when the switch was set to the up position (high voltage threshold cut-out at 11.5 Volt). It would still run in the low voltage threshold position (10.4 Volt cutout). Measuring the voltage at the coolbox when the compressor was running (it runs briefly before cutting out and displaying the red light) it was not surprising. The cable and the plug/socket were dropping the received voltage at the coolbox by 1.5 Volts, below the high cut-out threshold level.

There is a graph in the manual which says that for a 4m cable I need cable with 7 square mm cross section, rather than the 1.8 square mm I was experimenting with, so no surprises there.

So it seems that the advice in the manual must be followed closely in order to keep your coolbox running off a battery only (i.e. engine not running)...

Minimize the cable run between the battery and coolbox
Minimize the number of connectors, switches and fuses
Use a 15 Amp fuse (this will be lower resistance than a 5 Amp one)
Use a sufficiently big diameter cable, using the graph in the manual
Ensure all connecting equipment is in good condition and clean

If you still have a significant voltage drop, use the low cutout switch position (down) rather than the high one (up).

 

[brownsox]

Angus that's really good of you. We're going to the boat on Sunday night so will try these things. We've only ever tried it on the low setting, and we had the plug put in by supposedly professionals specifically for the coolbox ... but clearly something is wrong and we will now find out what.
As I saw someone else comment recently - what would we beginners do without this forum?! Thanks very much indeed.