12v Fridge

Repolho

Hi All,

I have a 1976 VW westfalia. There is a small 12v fridge in it runs which currently runs off the leisure battery only. This is practically useless as it drains the battery in about 3 hours. There is a split charge relay which charges the leisure battery when driving once the engine battery is charged up but I have no other way of keeping the battery topped up.I have an electrical hookup on the outside of the van which is just connected to a single socket inside the van. I'd like to be able to run my fridge while hooked up on a site for a few days or even to run it at home to get it nice and cold before we set off!

Would anyone around these parts be able to describe to me what I would need to fit to work this?

Thanks.

You need a mains charger that'll compensate for running loads, so 15 amp min. (10A for fridge (assuming a 125W fridge) and 5A for battery charging). Really 20A or 25A would be better.

Maybe a few more internal mains sockets too. 1 or 2 for appliances and one beside the batteries for a charger.

The alternator won't keep the battery topped up. At best it'll charge it to 80% maybe 70% depending on the regulator, wire guage and distance to batteries.
It'll look charged on a voltmeter but not on a hydrometer or discharge testing.

These are good chargers hence the price tags. Load compensation is rare on cheapies. I wouldn't bother with a non temperature compensating one.

I've a very low opinion of coach build charging units but someone may say different, and have more options to offer.

Sealed Batteries Only

• CTEK
• Newmar
• Mastervolt

Open Lead Acids and Sealed.

• Victron
• Sterling
• Ring (cheap re-branded Chinese).
  
  

I'd be interested in other suggestions myself in the 20A+ range.

Repolho

Oh and the bad news is you probably need a new battery too. I imagine you gave your current a hard life by the sound of things...

Repolho wrote: »

as it drains the battery in about 3 hours.

...what you have left is a 40Ah sulphated battery (if that's a 125W fridge).

The other option is to run your fridge off a suitable 12V PSU. 150Watts should do it.
Example here.
Careful to isolate the batteries from the transformer though the transformer might kill them. A changeover switch or relay or simple cross-plugging would suffice.

I'd still recommend a decent battery charger though at the very least a little 3 stage 3.5A (and not a bargain basement one they're lethal left to their own devices).
Alternators are old, inefficient and stoopid chargers. Good for bulk charge and running loads, that is all (without modification ).

Repolho

Sir Liamalot wrote: »

You need a mains charger that'll compensate for running loads, so 15 amp min. (10A for fridge (assuming a 125W fridge) and 5A for battery charging). Really 20A or 25A would be better.

Hi Sir Liamalot,

Thanks for all the information; looks like I have a bit of reading to do .

Can I just clarify, your solution is not to "install" any sort of system, just get a (decent) charger which I can plug into to socket already in my van (or add more sockets) whenever I am hooked up?

Thanks again for your help.

I'd add more sockets anyway.
I've 8 x mains sockets, 8 x 12v sockets, 3 x inverter sockets, 5 x USB sockets, 1 x 9V, 1 x 4.5v, 2 sets of croc. clips, 3 extension cables and 4 mains converters. :pac:

Screw the charger/traffo to a wall and hard wire it with a switch or relay would be the neatest. But you can plug and play if you prefer until you get comfortable with your set-up.

You might also want to check your fridge manual an see that the 12V element has a thermostat. I'm convinced Dometic signed off early on the 12V side of refrigeration and instead of making a working solution decided to write "12V is for driving only" in the manual. Working under the presumption that everybody starts a journey with a warm fridge and then switches to another power source after a few hours, they're so impractically inefficient to run in 12v nobody would want to. The upshot of this is that if you run them in 12V for >5 hours your food will start to freeze. In which case you may have to retrofit a thermostat (>10ADC Normal Closed thermostatic switches are hard to find) or turn it off every so often or design some temperature compensating on-off timer tomfoolery...or periodically open the door for a chin-wag...females are generally quite good at the latter...maybe bring one along. :pac:

vincent coffey

Hi. I put a ctek mxs 10 into my vw. It will recondition flat leisure batteries, it maintains over winter by dropping to 90 percent and then recharging on a regular basis and it has a float setting that you can run your 12v circuit on while charging when attached to mains.

Drawback was it was not cheap but it has not missed a beat in 2 years and brought my leisure back from the dead and kept it alive ever since.

The float charge will allow you run the 12 v fridge in the van indefinitely as long as you have mains hookup.

Regards vinny

Ctek make a fine charger (but only for sealed batteries which are not the may west imho). The problem with the MXS10 and a 10A fridge is it'll only power the (125W) fridge (and very little else) after it's done charging....otherwise it'll over-current.

vincent coffey

Sir Liamalot wrote: »

Ctek make a fine charger. The problem with the MX10 and a 10A fridge is it'll only power the (125W) fridge after it's done charging....otherwise it'll over-current.

Good to know. Thanks for the heads up.

You can set that model to cold for OLA, but I don't understand why it would have a cold setting and a temp sensor. My batteries would easily hit 15.1V in a Irish Winter, with the heating on (heating me not the batteries).

pete4130

Time for a new battery for sure. I've got a 40L Waeco Fridge Freezer and depending on outside temps I run it anywhere from -4C to -18C and I get days from the 2nd battery. It's a 100ah battery. I check it every day when I'm not moving with a multi meter to keep an eye on the voltage and top it up when needed by running the ending for a while.

Waeco compressor fridge?
If Repolho is running a compressor fridge it bodes worse for the battery; 5Ah battery then assuming a 35Ah p/d compressor.
Absorption fridges take about 6.5 times the juice in 12V or about 1.5 times if run off the inverter.

Good news is a compressor fridge will have a stat though.

Find out what type and energy cosumption your fridge is Repolho and you might be able to get away with a smaller charger. I'm just guessing absorption because they seem to be most common these days. Probably a different story in 1976.

Do you have to empty the condensation outtov fridge compressors, anyone know?

moodrater

Sir Liamalot wrote: »

Good news is a compressor fridge will have a stat though.

Though struck me when we were out last, why not disconnect the mains, rewire the 12v element to the stat and run it from a 12v switchmode when on mains. A scrap computer supply would do the job or a 15 euro chinese special with a fan added. Repurpose the 12v switch for an circulation fan. Should save a few ah. And much cheaper than replacing with a compressor fridge.

I believe it's just a 12v only fridge in question and we don't know if it's a compressor or absorption model yet.

I think switch-mode is the best solution though if the fridge is designed to operate 24/7.

moodrater

moodrater wrote: »

....rewire the 12v element to the stat..

I've been thinking about doing this (sorry, minor thread hi-jacking abound). Where is the stat sensor?
What is the switching mechanism? Bi-metallic? Wax filled and spring loaded thingy?
Is it measuring internal fridge temp or condenser or element?
Is it in series with the element?

I'd be concerned that stat is rated for ~0.5A AC.
I really don't think it'll last very long load breaking 10A DC.

I have two notions how to get an exponential efficiency increase from my fridge. If the thing runs off a thermostat then it's roughly 50Ah p/d not 150Ah p/d.
The knock on effect is any chargers have a fighting chance of sustaining the demand.

Notion A;

Hard-wiring the AC side of the fridge to a dedicated inverter.
Relay's or cross-plug for mains changeover.

You could take that further with a relays to turn the inverter on and off and save the self-consumption.

Notion B;

Three relays two C/O and one make and break.
2 x mains C/O relays back to back either side of the thermostat; first one backwards second traditional this keeps 12v and mains isolated but they can share the stat (until one of them fails :eek::eek:...maybe the first ought to be a switch).
The M&B relay is just to load break the DC element and save the T-stat the carbonisation.


I reckon I could convert an absorption fridge to close compressor efficiency (maybe double) like this and still have the option of gas. :cool:
Since my new thermostatic 4 fan upgrade it hasn't needed to be set above 60% all Summer.

Ps these numbers are pretty rough, p/d means not at night ....I have yet to test the night-time tolls.

John T Carroll

Repolho wrote: »

Hi All,

I have a 1976 VW westfalia. There is a small 12v fridge in it runs which currently runs off the leisure battery only. This is practically useless as it drains the battery in about 3 hours. There is a split charge relay which charges the leisure battery when driving once the engine battery is charged up but I have no other way of keeping the battery topped up.I have an electrical hookup on the outside of the van which is just connected to a single socket inside the van. I'd like to be able to run my fridge while hooked up on a site for a few days or even to run it at home to get it nice and cold before we set off!

Would anyone around these parts be able to describe to me what I would need to fit to work this?

Thanks.

I have helped a friend with some small jobs on his Fiat Ducato "type" motor home. If he has the house mains plugged into the side of the van then this will supply everything (including the fridge) AND charges his leisure battery as well, it only seems to maintain 12.95 Volts to the battery but this may be a characteristic (or a fault) of the charger. His fridge is an absorbtion type which runs on bottled gas, or mains (230V). It will only run on 12 Volts once the engine is running, I dont know if this is then off the vehicle battery or in conjunction with the leisure battery. I know yours is a VW but one would think that the leisure battery(s) should be charged from the mains, once plugged in,?
Should have added that the leisure battery will also be charged from the engine alternator once the mains is disconnected.

*Kol*

John T Carroll wrote: »

I have helped a friend with some small jobs on his Fiat Ducato "type" motor home. If he has the house mains plugged into the side of the van then this will supply everything (including the fridge) AND charges his leisure battery as well, it only seems to maintain 12.95 Volts to the battery but this may be a characteristic (or a fault) of the charger. His fridge is an absorbtion type which runs on bottled gas, or mains (230V). It will only run on 12 Volts once the engine is running, I dont know if this is then off the vehicle battery or in conjunction with the leisure battery. I know yours is a VW but one would think that the leisure battery(s) should be charged from the mains, once plugged in,?
Should have added that the leisure battery will also be charged from the engine alternator once the mains is disconnected.

The OP has said that his 220v hook up is only connected to a single socket in the van. however what you have said above is true for most MH in relation to 220v and charging the leisure batteries etc