Is this normal for fridge to drain batteries so much/

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tim_ber

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If I hook up to shore power and turn fridge on (sorry, just left boat and forgot watts of fridge and amp hours of my 2 domestic batteries; but they are big suckers), then my voltage panel soon goes from a green LED showing batteries well charged to red showing batteries are loosing charge.

Before I start investigating shore power connections, voltage regulators etc, and ideas for where I should start looking. Or do you think this could be normal if my fridge is an old sucking a lot of juice job?

Thanks
 
I assume that your fridge has a compressor and is not a thermoelectric one.

When I am on shore power an 8 Amp charger easily charges the battery bank (3 x 110 Ah) when the 80Ltr fridge is running. The off /on ratio of my compressor fridge is about 5 to 1 so it is not very greedy on power.
 
A Danfoss 35 fridge compressor typically consumes 3-4 amps when it is running. Cycling on and off is dependent upon ambient temperature. A combined gas/240v/12v adsorption fridge can consume 10 amps on 12 volts, the power is used to heat an element. A thermo electric Peltier fridge consumes around 5-7 amps. Either of the latter will flatten a bank of two batteries in short order.
 
vyv_cox said:
A Danfoss 35 fridge compressor typically consumes 3-4 amps when it is running. Cycling on and off is dependent upon ambient temperature. A combined gas/240v/12v adsorption fridge can consume 10 amps on 12 volts, the power is used to heat an element. A thermo electric Peltier fridge consumes around 5-7 amps. Either of the latter will flatten a bank of two batteries in short order.
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Thanks all,

I should have said with the battery charger on, of course.

So does that still apply? Adsorption fridge will still flatten two domestic batteries whilst they are on charge?

I am not saying fridge does flatten them because I'd never allow batteries to become flat; I mean the charger does not input as much as fridge is taking out. I know this because volts of two batteries does not stay the same or increase whilst on charge and whilst fridge is on, but diminishes from 12.7 to 12.2 and lower if I kept fridge on and I thought a shore powered charger would keep up?
 
On motorhomes I have owned with adsorption fridges it was not possible to run them on 12 volts unless the engine alternator was charging. Some sort of switching device prevents it from happening to preserve the batteries, even if the battery charger was on, in which case the fridge ran on 240 volts.
 
vyv_cox said:
On motorhomes I have owned with adsorption fridges it was not possible to run them on 12 volts unless the engine alternator was charging. Some sort of switching device prevents it from happening to preserve the batteries, even if the battery charger was on, in which case the fridge ran on 240 volts.
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That makes sense, although conflicts with MoodySabre and Strathglass.
I forget specs of battery charger, but will look into it and the wiring / switching and battery capacities.
Thanks all
 
It doesn't conflict, it's just the way motorhomes are built to save the batteries, with the options of gas or mains instead. Some people, especially catamaran owners, have adsorption fridges but they cannot cope with heeling so are not that common in other yachts.

You have not said what type of fridge you have. If it's a compressor type then a battery charger should cope with it. Mine runs on solar panels for six months of the year.
 
Some thoughts

Generally our fridge, a compressor version, draws about 5 amps and runs about 20% of the time. We do turn it off at night if the ambient is not too high and have a cheap computer fan to blow air over the coils when the ambient is a higher than normal.

Had a very similar problem

We have an old fridge installed and found from the instructions that it could be wired into the boat's mains supply. This meant that it would detect if the mains was available and use that as the primary supply.

Then the charger would charge the domestic batteries without them being loaded by the fridge demand.
Also found a 'black box' in the battery compartment that was intended to prevent the fridge driving the battery voltage too low. This was also not connected.

Both of these options, when connected, made a huge difference.

We have since gone over to a dedicated fridge battery with its own charger and output from a diode on the alternator supply.
 
tim_ber said:
Thanks all,

I should have said with the battery charger on, of course.

So does that still apply? Adsorption fridge will still flatten two domestic batteries whilst they are on charge?

I am not saying fridge does flatten them because I'd never allow batteries to become flat; I mean the charger does not input as much as fridge is taking out. I know this because volts of two batteries does not stay the same or increase whilst on charge and whilst fridge is on, but diminishes from 12.7 to 12.2 and lower if I kept fridge on and I thought a shore powered charger would keep up?
Click to expand...

Probably a bit of a 'girlie' charger, not able to cope when the fridge is running and then having to work very hard and not quite catch up when the fridge is not running.
So, probably depends on what the capacity of the charger is relative to the demands of the fridge.

See my other recent post regarding 'improving' on the situation. You could just use a relay to switch to mains supply when it is available and switch back to the batteries when mains is not available.
 
Our BD50F compressor draws 7 amps when running with a duty cycle of 75% in summer. Solar panels or battery charger have no problem keeping up. Maybe your batteries or charger are knackered but you need to use a proper volt and ammeter rather than led display to see accurately what's happening.
 
I'm puzzled! I didn't think people in the UK needed refrigeration?

Seriously, we wouldn't dream of installing absorption type fridges in our Australian climate AND our freezers would have a minimum of 4 in insulation. I suppose it takes a lot more energy to reduce the temperature from 35C to 3c (Aus) than it does to reduce the temperature from (say) 22C to 3C (UK)
 
coopec said:
I'm puzzled! I didn't think people in the UK needed refrigeration?

Seriously, we wouldn't dream of installing absorption type fridges in our Australian climate AND our freezers would have a minimum of 4 in insulation. I suppose it takes a lot more energy to reduce the temperature from 35C to 3c (Aus) than it does to reduce the temperature from (say) 22C to 3C (UK)
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My boat, and fridge, is in Greece where temperatures are similar or even higher than yours. I agree that 100 mm of insulation is highly beneficial but I run a bog standard Waeco front loading fridge with a small freezer compartment. I doubt that some of the insulation is more than 10 mm but it does OK with a water cooled heat exchanger.
 
vyv_cox said:
My boat, and fridge, is in Greece where temperatures are similar or even higher than yours. I agree that 100 mm of insulation is highly beneficial but I run a bog standard Waeco front loading fridge with a small freezer compartment. I doubt that some of the insulation is more than 10 mm but it does OK with a water cooled heat exchanger.
Click to expand...

Of course Australia is an large place compared to Greece so I can easily quote statistics which would make Greek temperatures seem mild. If you accept the graphs as being accurate (below) then Perth temperatures would be quite a bit warmer than Greece.

You probably get away with your fridge working OK because it is water cooled (but water temperature get high in Greece - see below)

Marble Bar, Western Australia - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Marble_Bar,_Western_Australia‎
Marble Bar is a town and rock formation in the Pilbara region of ... The town set a world record of most consecutive days of 100 °F (37.8 °C) or ... average maximum temperature exceeds normal human body temperature for 6 months each year.


View attachment 40720
 
+1 Battery charger should be able to cope with the fridge load. Big batteries (100ah+) should be able to run 10amps for an absorption fridge for two or three hours before showing 'battery low' voltages.

Motorhome 3 way fridges are wired so that they can only work on 12v if the alternator is running, which is a standard wiring practice in motorhomes, not of the fridge. Its perfectly possible to over-ride that feature but is done to avoid flattening (usually) the starter battery.
 
vyv_cox said:
I cannot see much sense in arguing about relative temperatures in Greece and Australia. we experience out there are at least as high as the ones shown in Temperatures your graph.
Click to expand...

They are graphs of temperatures in Greece. If you accept the (Wikipedas?) graphs as being correct temperatures even in Perth are appreciably warmer than Greece.
 
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