Lower cost fridging

[MtB]

Given that 12v fridges are stupidly expensive compered to 240v fridges, I'm wondering about fitting a 240v fridge (e.g. this one ) and powering it from an inverter. Total cost seems to be way lower than a 12v fridge.

 

Has anyone done this? Is there a terminal flaw in my stunning plan?

[Robbo]

Given that 12v fridges are stupidly expensive compered to 240v fridges, I'm wondering about fitting a 240v fridge (e.g. this one ) and powering it from an inverter. Total cost seems to be way lower than a 12v fridge.

 

Has anyone done this? Is there a terminal flaw in my stunning plan?

 

I think Inverter choice and battery charging methods, etc will need to be looked at... If your getting a cheap inverter it will be so inefficient, you more than likely spend more on diesel charging your battery over the lifespan of the fridge.

[Mick_B]

Really like the look of that fridge I must say.

 

But.... I never could do this math. Maybe Chris Pink / Whatnot etc..

 

Energy Consumption: 0.38 kWh/24hr???

[pistnbroke]

cheap inverter or not your biggest problem is getting the compressor to start ..if its been off for a while and the pressure has dropped it may start but if its on off on off no chance ..I had a 90w fridge needed a 1kw inverter to start it . My domestic fridge freezer would stall a 2 kw generator ..I eventually built a timer that only allowed the inverter to output every 60 min so in essence the fridge came on for 20 min then off for 40 whilst the pressure dropped ..worked fine in that mode..

Edited February 27, 2012 by pistnbroke

[Keeping Up]

The consumption of 0.38kwh per 24h equates to 15.8 watts average. Add approximately 10% for the inverter - as said above, a cheaper inverter will be less efficient, but the more expensive ones can nowadays be more efficient. All the same 10% is a fairly average figure, although see the next paragraph. That makes 17.4 watts

 

The inverter will have to be a surprisingly high wattage rating, because fridges take a very high surge current every time the thermostat switches them on and off. Apart from the extra cost of the larger inverter, there is the problem that large inverters tend to take a large standby current; in other words, even when the fridge motor is switched off the inverter will draw some current. Unless you were going to be leaving the inverter running 24x7 anyway, you will be wasting this standing current which is typically 10 watts, increasing the effective draw by the fridge to 27.4 watts.

 

The equivalent 12v Shoreline fridge is stated to consume 0.8 Amps average, which is 9.6 watts. So the 240v fridge will consume almost 3 times as much power as the 12v one, which will have to be repaid in diesel, oil, engine wear, etc - not to mention the fact that the battery will go flat quicker.which means the batteries will have a shorter life unless you charge them more frequently.

 

I am not saying you can't go down the 240v route, but be aware that it is not necessarily cheaper than the 12v option.

 

(Edited to clarify and correct some of the numbers)

Edited February 27, 2012 by Keeping Up

[Jim Batty]

cheap inverter or not your biggest problem is getting the compressor to start ..if its been off for a while and the pressure has dropped it may start but if its on off on off no chance ..I had a 90w fridge needed a 1kw inverter to start it . My domestic fridge freezer would stall a 2 kw generator

 

We had a Hinari 240v - 100w fridge and 1.5Kw inverter on board when we bought our boat. There was no way we could keep the inverter on all the time to drive the fridge and keep the batteries charged anything like normally. We replaced it last year (giving the Hinari to a local guy on the towpath to keep his beer cool in his basement) with a same-size 12v Shoreline. Because the 12v fridge draws about a third of what the 240v one did it is always on and works a dream. (Uses about 30Ah/day, although the spec sheet says 22Ah/day).

 

The saving we made in not having to chuck out spoiled food over a year's period paid for about half the Shoreline's cost.

 

If you have access to shore power, or CC every two or three days (and have a reasonably sized battery bank) you could get away with the cheaper 240 volter.

[smileypete]

Given that 12v fridges are stupidly expensive compered to 240v fridges, I'm wondering about fitting a 240v fridge (e.g. this one ) and powering it from an inverter. Total cost seems to be way lower than a 12v fridge.

 

Has anyone done this? Is there a terminal flaw in my stunning plan?

If you want to get round the inverter quiescent current for about £25, see this post by using one of these:

 

 

Though this would be a more suitable delay relay.

 

If the startup surge of the fridge is a problem it could be reduced a bit with an inrush limiter.

 

Nice thing is the kit can easily be swapped over to a different mains fridge.

 

cheers,

Pete.

[MtB]

Ok, this is a hobby boat not a liveaboard so I'm not especially bothered about slightly higher diesel consumption. And it looks as though it will work provided I have a big enough inverter to deliver the start-up current for the compressor. 1kW seems likely to be about right.

 

So this looks a likely candidate. Does anyone know the quiescent current an inverter like this probably draws while the fridge compressor is OFF? The spec does not say.

[bottle]

Standby input current: <0.7A, from the specifications.

[Robbo]

Ok, this is a hobby boat not a liveaboard so I'm not especially bothered about slightly higher diesel consumption. And it looks as though it will work provided I have a big enough inverter to deliver the start-up current for the compressor. 1kW seems likely to be about right.

 

Makes sense to use a cheaper 240v then, as your using it for leisure your engine is more than likely be in use when your on the boat so less electric generation concerns. A good tip is when on the move, turn the fridge up so it cools the fridge more, then turn it down to normal when the engine is not running.

[Chalky]

We've got exactly the set up you're asking about. We're not live aboard. As a holiday boat we can cruise for a day and get about 1 to 2 days standing (depending how often the kids open the fridge). We tend to turn the fridge on at 8:00 ish and off at about 21:00.

The inverter is a sterling modified sine 600W and will start our indesit fridge (no freezer compartment). The quiescent is about 400ma. Although the inverter will start the fridge a bigger one will give you a better safety margin.

When the engine is running the fridge thermostat is turned up to max and down to low when its not. The idea is to use the fridge contents as a thermal mass to help reduce thermal losses when the fridge is off.

I'm looking at other ways of reducing load including a pic based temperature controller with adaptive set points and solar powered fans to blow air over the condenser and reduce the system pressure in the fridge cooling circuit and thus the power used.

I've got 400Ah of batteries and will start a charge when they get to 12.6V - from 12.8/12.9 (AGMS). Bulk charge is usually completed in about 1/2 hr.

[smileypete]

I'm looking at other ways of reducing load including a pic based temperature controller with adaptive set points and solar powered fans to blow air over the condenser and reduce the system pressure in the fridge cooling circuit and thus the power used.

These days the A rated fridges seem to use bigger condensers, if it only gets lukewarm as it is, there might not be much improvement from adding some fan cooling.

 

If using a temperature controller, the fridge thermostat could be set higher and used when the engine is running/sun is out, by over-riding the controller.

 

cheers,

Pete.

[ditchcrawler]

Here are the actual readings I took with out 240 volt Lec Fridge running via an inverter but from 24 volts not 12 so the Amps will be half of what you should expect.

 

see below

 

 

 

I have been running another set of tests on our 240 volt fridge.

The fridge runs via a Mastervolt Mass Sine 24/1500 and all current

readings are take from a Sterling Battery Management unit.

 

The inverter + Fridge + fans =3.5 amps

The Inverter + Fridge = 3.4 amps

The Inverter = 0.4 amps

 

I have connected a RS hour meter across the refrigerator compressor to

record compressor run hours.

The refrigerator is a LEC Elan and sits under a work top with 25mm air

gap each side and 50mm between the top of the refrigerator and the

underside of the work top. The air space behind the refrigerator is

well over the recommended space as the hull side slopes from the floor to

the gunwale.

There are ventilation holes drilled in the floor behind and below the

fridge. Also there are 4 computer fans mounted in the floor connected in

series parallel that when running blow cool air from under the floor up

the condenser. All readings were taken with the fridge in normal use.

 

The fridge thermostat was set at 3 and had been running for a couple of

days to allow things to stabilise before readings were taken at 1700 hrs

each day. The thermometer inside the fridge was reading at the top of

the acceptable range.

 

At the end of the first day with the fans off and the fridge running as

normal the hour meter recorded 7.6 hrs in 24 hrs.

On the second day the fans were switch on and the reading at the end of

24 hrs was 7 hrs.

The next day the fans were switched off and the hours run were 7.1

This indicates to me that the fridge was adequately ventilated as

installed. That night I insulated the fridge on both sides and the top

with sheets of 25mm close cell insulation foam covered on both sides

with aluminium foil as used in the building trade. At this point things

got interesting which I can't explain. The running hours were slightly

less but the internal temperature of the fridge fell. Over the next 2

days I adjusted the thermostat setting to bring the internal temperature

back to its original level. This resulted on it now being set at 1.5 as

opposed to the original 3. I don't know why this happened as in my book

the thermostat should keep the inside of the fridge at a constant

temperature. I suspect it is a timer and not a stat.

 

Once this had settled down I started recording readings again which run

between 6.3 and 5.7 hours per day

11/8/06 1700hrs 1170.2

12/8/06 1700 hrs 1177.8 7.6

Fan on

13/8/06 1700hrs 1184.7 6.9

Fan off

14/8/06 1700hrs 1191.8 7.1

Insulation added and fans on

15/8/06 1700hrs 1198.5 6.7

reduced stat setting

16/8/06 1700hrs 1205.0 6.5

17/8/06 1700 hrs 1211.3 6.7

18/8/06 1700hrs 1217.0 5.7

19/8/06 1700hrs 1223.6 6.6

20/8/06 1700hrs 1230.0 6.4

21/8/06 1700hrs 1235.5 5.5

22/8/06 1700hrs 1241.2 5.7

--

[Phil Ambrose]

The consumption of 0.38kwh per 24h equates to 15.8 watts average. Add approximately 10% for the inverter - as said above, a cheaper inverter will be less efficient, but the more expensive ones can nowadays be more efficient. All the same 10% is a fairly average figure, although see the next paragraph. That makes 17.4 watts

 

The inverter will have to be a surprisingly high wattage rating, because fridges take a very high surge current every time the thermostat switches them on and off. Apart from the extra cost of the larger inverter, there is the problem that large inverters tend to take a large standby current; in other words, even when the fridge motor is switched off the inverter will draw some current. Unless you were going to be leaving the inverter running 24x7 anyway, you will be wasting this standing current which is typically 10 watts, increasing the effective draw by the fridge to 27.4 watts.

 

The equivalent 12v Shoreline fridge is stated to consume 0.8 Amps average, which is 9.6 watts. So the 240v fridge will consume almost 3 times as much power as the 12v one, which will have to be repaid in diesel, oil, engine wear, etc - not to mention the fact that the battery will go flat quicker.which means the batteries will have a shorter life unless you charge them more frequently.

 

I am not saying you can't go down the 240v route, but be aware that it is not necessarily cheaper than the 12v option.

 

(Edited to clarify and correct some of the numbers)

 

I agree with this, I have both an under counter fridge and a under counter freezer, we live aboard so need them. We have never had to turn either of them off at night our 5 X 110A/H domestic bank copes OK and for the life of me I can never understand why anybody would want to take perfectly good 12volt leccy and turn it into 240.

 

Phil

[mrsmelly]

Given that 12v fridges are stupidly expensive compered to 240v fridges, I'm wondering about fitting a 240v fridge (e.g. this one ) and powering it from an inverter. Total cost seems to be way lower than a 12v fridge.

 

Has anyone done this? Is there a terminal flaw in my stunning plan?

 

It will depend greatly on the inverter choice. My last boat had mains appliances including fridge. My inverter was on the entire time running off 3 110 a/h batteries and I had no problems whatsoever. However I did run it all from a 2kw Mastervolt inverter which are expensive but well worth the money. This sterling unit I have on this boat would flatten the batteries due to its inferior capability.

[pistnbroke]

have not read all of above but what you need to do is to bring the wires for the thremostat out from the fridge and connect them to the on/off switch on the inverter ..then when the thermostat clicks in the inverter comes on and so does the fridge and it all then goes off with the stat ..no standby current ..... You could fit another thhermostat and leave the original on MAX or just short it out ...worked for me

 

The inverter switch does not carry the full DC load just asks the electronics to turn on ...EPLS most frigdes have a wiring diagram stuck on the back .....

[davidb]

Hello,

 

for 12 years we have run a normal Electrolux domestic under couter fridge from a 24 volt heart interface ( crude ) invertor. 2500 kva left on 18 hours a day, but off 6 hours at night, spare space inside taken up with water bottles and beer, and ice packs in the freezer compartment.

 

No problem at all, but must say that the fridge is extremely well ventilated - it is suspended with a 12" gap under it open to the bilge and it is sited next to the wheelhouse door and also has a 6" gap behind,

 

In a good summer, a 3' x 2' solar panel used keep up with it during the day.

 

cheers, David

[dor]

. At this point things

got interesting which I can't explain. The running hours were slightly

less but the internal temperature of the fridge fell. Over the next 2

days I adjusted the thermostat setting to bring the internal temperature

back to its original level. This resulted on it now being set at 1.5 as

opposed to the original 3.

 

I have suspected for a while that basic fridges use a timer rather than a thermostat. This does make me wonder how effective the idea of turning the fridge up whilst running the engine, then turning it down is.

 

I would be interested to know if anyone has information on fridges using thermostats or timers to control temperature.

[alan_fincher]

So this looks a likely candidate. Does anyone know the quiescent current an inverter like this probably draws while the fridge compressor is OFF? The spec does not say.

 

Please be aware that the last time I checked over one of those 1000 watt Maplin inverters with a multi-meter, the 230 volt output was not earth-neutral bonded.

 

The recommendation for any permanently installed inverter on a boat is that there is an earth-neutral bond, otherwise an on-board RCD may not trip in fault conditions.

 

The inverter is probably suitable for modification to have the bond, (I have done this on 300 watt Maplin inverters in the same range), but you need to check out the threads on that topic, as not all inverters can be modified. Gibbo did a long explanation of this once.....

 

Note that if the quiescent current is as much as the quoted 0.7A you will be using nearly 17 Ah a day to keep the inverter ticking over when not in use. Probably not a problem if regularly moving, but less than ideal if you want to stop at the same place for a day or two, and not be running the engine to replenish losses, particular if the fridge itself isn't particularly efficient too.

 

With your background, I'd consider an LPG fridge, and forget all the need to keep batteries charged!

[WotEver]

I have suspected for a while that basic fridges use a timer rather than a thermostat.

This link chosen at random from a Google for Fridge Thermostat would suggest otherwise.

 

Of course this doesn't mean that maybe some of the lower end fridges do indeed only use a timer.

 

Tony

[Ally]

we use a 230v and inverter, as we originally wanted an inverter anyway, and as you say the cost of 12v fridges...... however, we have now switched everything to 12v that we possibly can, even our laptops. We were reading up about low running cost fridges last night, and found a forum that suggested the cheapest way of running a 230v fridge is to actually use a 230v chest freezer. You then add a thermostatic probe which cuts off the freezer at..say 5 degrees. As a freezer it takes little time to get to 5 degrees, and will hold it well, especially as a top opener. A bit faffy for use, you'd really need to box everything in it, but it apparently cuts the power useage dramatically.

[pistnbroke]

the standby current of the inverter is not relavent if the thermostat controls the On/OFF of the inverter rather than the fridge itself

 

I just realized I have exactly that fridge in the garage with little use ..you can have it for £30 about 100m from the canal at Rugby 01788 310500

Edited March 1, 2012 by pistnbroke

[ditchcrawler]

I have suspected for a while that basic fridges use a timer rather than a thermostat. This does make me wonder how effective the idea of turning the fridge up whilst running the engine, then turning it down is.

 

I would be interested to know if anyone has information on fridges using thermostats or timers to control temperature.

Well I am glad I am not the only one. I have considered turn it up to maximum and then use an electronic plug in mains time switch to turn it on and off so I can chose a different mark/space ratio for the time the engine normally runs.

[smileypete]

Over the next 2

days I adjusted the thermostat setting to bring the internal temperature

back to its original level. This resulted on it now being set at 1.5 as

opposed to the original 3. I don't know why this happened as in my book

the thermostat should keep the inside of the fridge at a constant

temperature. I suspect it is a timer and not a stat.

The stat is often right next to the evaporator, often under the icebox if present, and it has a surprisingly large hysteresis (on-off difference) to prevent short cycling.

 

The duty cycle is quite stable when the contents are down to temperature and the door is kept shut.

 

If the condenser gets quite hot, adding some forced cooling to the condenser can make a surprising difference to the duty cycle.

 

cheers,

Pete.

Edited March 1, 2012 by smileypete