How to power 12v fridge from 240v shore power

[Bugsworth Tippler]

I have a 12v fridge/freezer which serves its purpose well when travelling the system. However, during the winter months I may be staying on the boat at its home moorings which has a 240v supply. I would want to run the fridge/freezer without running the batteries down.

Is there any reason why I can't use a 240v/12v transformer wired as shown in the diagram?

Would a 12v-10 amp transformer be suitable?

It is possible to switch off the 12v supply to the fridge/freezer independently of all other 12v circuits. I imagine it is important to do so before switching to the transformer supply. Could any damage be done if I forgot to switch off the 12v supply?

Any comments and suggestions welcome.

Thanks
Ian

 

[rusty69]

Battery charger? 

[Robbo]

Use a multi stage battery charger when on shore power.   Keeps LA batteries in good condition and powers ya 12v stuff.

[Alan de Enfield]

Rusty is correct - but from your question and proposal I guess your electrical knowledge is limited.

 

1) Leave the fridge running off the batteries.

2) Switch on battery charger *

3) Turn off all other 12v appliances at their switches, or leave them switched on - it doesn't matter.

 

* If you don't have a battery charger, 'shout' now for suggestions - you need the correct type.

Edited August 8, 2018 by Alan de Enfield

[OldGoat]

10 minutes ago, Bugsworth Tippler said:

I have a 12v fridge/freezer which serves its purpose well when travelling the system. However, during the winter months I may be staying on the boat at its home moorings which has a 240v supply. I would want to run the fridge/freezer without running the batteries down.

Is there any reason why I can't use a 240v/12v transformer wired as shown in the diagram?

Would a 12v-10 amp transformer be suitable?

It is possible to switch off the 12v supply to the fridge/freezer independently of all other 12v circuits. I imagine it is important to do so before switching to the transformer supply. Could any damage be done if I forgot to switch off the 12v supply?

Any comments and suggestions welcome.

Thanks
Ian

 

Nothing's that simple...

 

A transformer is just that - converts A/C mains to 12v BUT it's still A/C - so it needs converting to DC. You need to 'rectify' it to DC.

However a straight transformer / rectifier will not have enough power to cope with t6he startup surge from the fridge.

 

What you need is a battery charger.  That can have a relatively low power output as it can be charging your batteries all the time which replenishes whatever power your fridge takes from the batteries - and keeps them topped up as well.

You can get inexpensive chargers from Aldi and Lidl from time to time or Halfords... at more expensive prices.

BUT I don't know if they're safe enough to be left on all the time.

Now let's see what two other have said. 

[Robbo]

If you don't have a multi stage battery charger then a small charger from the likes of Victron doesn't cost the earth.    You don't need to go high amps (and it's best not too) if only using via shore power.

[Neil2]

The Waeco 12v/240v two way adapter is about £40 from memory.  You plug it into the 12v supply but when you connect to mains electric it switches off the 12v circuit.  

[Alan de Enfield]

5 minutes ago, Neil2 said:

The Waeco 12v/240v two way adapter is about £40 from memory.  You plug it into the 12v supply but when you connect to mains electric it switches off the 12v circuit.  

But he does say he has a 12v fridge (not a dual-voltage fridge) which is why he wanted a "transformer" thinking that would take 230v AC to 12v DC.

[Neil2]

3 minutes ago, Alan de Enfield said:

But he does say he has a 12v fridge (not a dual-voltage fridge) which is why he wanted a "transformer" thinking that would take 230v AC to 12v DC.

The Waeco adapter is for 12v fridges ie it is a transformer.  

[Bugsworth Tippler]

I thought I maybe had made a fundamental misteak (ac/dc).

 

I do have a battery charger (Paco 20A) as below and have had it connected whilst on shore power.

 

https://www.alpha-batteries.co.uk/12v-20a-connect-forget-automatic-leisure-battery-charger/?gclid=CjwKCAjwqarbBRBtEiwArlfEINB8K9EC4MUwePG0vYP7XTyTrEXNlceZeP6jJLWiJJYoQqfIFeCBKhoCDFgQAvD_BwE

 

However, I recently read the instructions and they state that there should be no load on the batteries while it is in use.

[Alan de Enfield]

8 minutes ago, Neil2 said:

The Waeco adapter is for 12v fridges ie it is a transformer.  

I stand corrected - but plead 'misinformation' having read :

 

21 minutes ago, Neil2 said:

......….but when you connect to mains electric it switches off the 12v circuit.  

 

Having now done a search. the manual explains it better and yes it is basically the innards of a battery charger changing 230v AC to 12v DC.

I would still suggest that he would be better spending the £86 + P&P on a battery charger (if he doesn't already have one) as any use of lights, water pump, TV etc etc will deplete the batteries and they will need charging.

[Higgs]

 

If you're prepared to do a bit of soldering, you can use a computer supply unit. I've been using one for I think more than 4 years, non stop. The unit is a Tesla 650 TE-BR . You can find videos on YouTube that can instruct you. You then need a suitably high inline fuse. I've got a 30amp fuse inline. The unit can deliver about 35amps. Think the unit cost about £26.00. The make of unit doesn't matter. The one I use isn't particularly high output, hence the price.

 

I have a Shoreline RR47. The small freezer compartment can freeze small bottles of water in this hot weather at a setting of no more than 2.

 

 

Edited August 8, 2018 by Higgs

[Neil2]

41 minutes ago, Bugsworth Tippler said:

I thought I maybe had made a fundamental misteak (ac/dc).

 

I do have a battery charger (Paco 20A) as below and have had it connected whilst on shore power.

 

https://www.alpha-batteries.co.uk/12v-20a-connect-forget-automatic-leisure-battery-charger/?gclid=CjwKCAjwqarbBRBtEiwArlfEINB8K9EC4MUwePG0vYP7XTyTrEXNlceZeP6jJLWiJJYoQqfIFeCBKhoCDFgQAvD_BwE

 

However, I recently read the instructions and they state that there should be no load on the batteries while it is in use.

I suspect that is because the charger (obviously) won't perform its proper function whilst you are still drawing a current from the batteries.  

 

I see where you're coming from though.  Given that on most boats the fridge is the chief power hungry appliance, maybe there is an argument for having a transformer device powering the fridge on shore power to reduce the load on the batteries, which then allows the charger to bring the batteries up to charge quicker.    I use a waeco transformer but until recently I never had need of a charger anyway as the solar power took care of the battery bank when we were at rest.   That was a previous boat, I do now have an onboard charger but I still use the waeco when we are connected to shore power.  Those with better knowledge of electrics may have an opinion on whether lightening the load on the batteries in this way makes a significant difference. 

[cuthound]

The battery charger will not know whether it is supplying the fridge, the battery or both, providing you get one large enough to supply the running load of the fridge and more than meet the self discharge current of the battery, say one with an output of at least 10 amps.

Edited August 8, 2018 by cuthound
To remove a spurious word

[Boater Sam]

I have used a Halfords automatic battery charger just to keep the batteries at float when tied to the landline for 18 years, never been a problem. It has kept up with all our 12v demands, holding the battery bank at 13.6 v before going into maintenance mode.

When the sun is shining it knocks off and the solar keeps the voltage up.

[Alan de Enfield]

4 minutes ago, Boater Sam said:

I have used a Halfords automatic battery charger just to keep the batteries at float when tied to the landline for 18 years, never been a problem. It has kept up with all our 12v demands, holding the battery bank at 13.6 v before going into maintenance mode.

When the sun is shining it knocks off and the solar keeps the voltage up.

But you do need to be careful - I have a Halfords battery charger that just doesn't stop.

The current will drop as the battery becomes charged but the voltage continues to rise - ideal if you are trying to give the batteries an equalisation charge, but when it has got to 16v and still rising its time to switch it off.

The one I have is certainly not one that can be left unattended.

[Boater Sam]

Not like mine, it drops off, the lights change over, and it goes into a pulse mode. It has worked fine.

[cuthound]

54 minutes ago, Boater Sam said:

Not like mine, it drops off, the lights change over, and it goes into a pulse mode. It has worked fine.

 

It gives the battery some beans then? ?

[Boater Sam]

Beans are good for you.

 

The mark space of the pulse mode is variable, eventually it stops altogether until there is a load on the batteries. I get 4 to 6 years out of a set of 4 not expensive  135Ah sealed batteries, and considering that they sit neglected over 4 months in winter with only an 80W panel I reckon is good.

[cuthound]

6 minutes ago, Boater Sam said:

Beans are good for you.

 

The mark space of the pulse mode is variable, eventually it stops altogether until there is a load on the batteries. I get 4 to 6 years out of a set of 4 not expensive  135Ah sealed batteries, and considering that they sit neglected over 4 months in winter with only an 80W panel I reckon is good.

 

I hate having to explain jokes. Perhaps this link will help.

 

https://www.nhs.uk/live-well/eat-well/beans-and-pulses-nutrition/

[philjw]

30 minutes ago, Boater Sam said:

Beans are good for you.

But too many lead to excess gassing