Running a fridge on a leisure battery

maddp

Guest
Hi there,

I am a newbie here, and already this forum has been a great source of excellent information, many thanks to the knowledgeable people who contribute!!!

I have a question about what to do for a fridge in my campervan. I know this type of question does pop up frequently on here, but, excuse my un-mechanical/electrical knowledge, I am still not too sure what to do. My partner and I have recently bought a VW LT35 conversion, which we are really excited about. We are going to be travelling around mainly Spain and Portugal for 2 1/2 months from late August. We will be doing a mixture of wild camping and camp grounds to stock up on supplies/charge battery etc... we would probably be doing no more than 2 wild camping days in a row. The van seems to have pretty much everything we need for this trip except a fridge.

We have been researching into the best fridge option for us, I understand a lot of people recommend a 3 way for wild camping, but due to the cost and logistics of instalation we are a lot keener to stay away from gas. Our leisure battery is a Platinum leisure plus, 6110L, 110Ah. We were looking at running a 35 watt compressor fridge off this (about 2.9 Amps by calculations). Can anyone please tell me how I work out how long the leisure battery might power the fridge for? we will only be running a few small lights and occassionally a water pump off the battery while the fridge is running, and will also most likely be doing a couple hours of driving a day between free camping.

Any advice would be greatly appreciated.

Thanks in advance!
Matt
 
compressor fridge is the way to go. but you will i think need more batteries and i would invest in a couple of 80wt solar panels from ebay. you can try to work it all out but in practice keeping a fridge just on battery is very difficult with out regular hook up to mains. i mean like every second day. i use solar and only in the shortest days of winter dec /jan does it really let me down.just had a week of it mind here. been very dark. if you look at some of the battery discusions we have had lately and threads on solar you should get all you need to know. have fun been miles in an lt used one to tow my trailer for along time. best go away in winter .when you come back most of us are preparing for our summer holidays from oct-may. come home for winter here may -sept. ha ha .cheers alan.
 
When battery is fully charged roughly %80 of rated value equals 88 amps in your case.
If you run battery down to %50 of rated value (should never go lower than this) this would give you 55amps, take 55 from 88 gives you 33 amps of usable power in theory.
This means you could run you fridge for 11 hours without anything else running.
Take vwalan good advice or maybe yourself being in a smaller unit would actually be better off with a three way fridge. We have solar panels and a bank of batteries but when parked we use the gas and conserve our battery power for other things (sat, tv, laptop, phone charging etc), the choice is yours.
 
trouble with 3 way is they atre only absorbtion fridges and when the ambient temp gets hot they stop worling. about 32 c i believe. i used to have a 3 way ran it on gas all the time but just when you really need it it stops working . thats why i went compressor fridge.
i am mean .when i built the truck originally i used gas even for the lights as its so cheap in maroc to fill up. but every year the fridge stopped working. also sometimes in uk when it got very hot.
i also have gas water heater, gas lights, gas thermex catalitic heater. never had an expensive electric system but in the end had to give in as i like a home made lolly pop when its hot in the desert. also have an addiction to ice cream. cheers alan.
 
Try googling for a `cool box`. If you can find one big enough for your needs, it might be more power efficient.

2 hours driving will not put a great deal back into your battery and that leaves 22 hours of drain on your battery. A solar panel of 80 watts would be very beneficial to you.

They are sold on ebay but I bought mine from a Britsh company.It cost a bit more but is lightweight and supplies a lot of power into my battery bank. It is 90 watts capacity. I have a solar panel thread going at the moment if you want to check it out.
 
When carrying out any battery calcs on a compressor fridge don't forget that they run on a duty cycle regime eg 30% to 40% of time.
 
becarefull with cool boxes most work on thr peltier system and are more useless than the absorbtion system. compressor is off about 40 mins in an hour. have tried it believe me.
 
as a rough guide an absorption fridge 80litr consumes about 2300watts in 24 hours .while a compressor fridge uses about360 watts in 24 hours. some even have an energy accumulator that takes a small amount of energy to store a liquid that solifies and as a button you can press to stop the fridge working at night and this liquid keeps it cool .in the morning when you let thr fridge come back on it starts the process all over again.
 
vwalan said:
as a rough guide an absorption fridge 80litr consumes about 2300watts in 24 hours .while a compressor fridge uses about360 watts in 24 hours. some even have an energy accumulator that takes a small amount of energy to store a liquid that solifies and as a button you can press to stop the fridge working at night and this liquid keeps it cool .in the morning when you let thr fridge come back on it starts the process all over again.
Click to expand...

Well you learn something new every day, but at the moment we will march on with our absorption fridge. However vwalan when these new compression fridges come out Refrigeration
using only a 1/4amp per hour we will be getting one.:rolleyes:
 
interstingly enough thats my mates shop if you look at the address its st austell.was going to see him today. they do have lots of intersting stuff.roger is building his own camper at the moment. i,ll tell him you have read his bits . nice chap he his. we talk solar andall this sort of thing continually. ha ha ,
 
Many thanks for advice vwalan. So do you think if I did hook at a campsite every 2nd day I should be ok to run the fridge? We were looking at something small, about 20 litres or a little less...
 
Thanks a lot paulhag. Does that calculation of 11 hours take into account the 40 minutes an hour that a compressor fridge is off, as vwalan suggested?
 
if it was me i,d be sending off tomorrow for a panel why pay for camp sites could wel cost you up to 50 quid a night at this time of year. even at 20 quid it soon mounts up .a panel is almost for life .tru one but go for at least an 80 wt. you could turn it off at night to save abit. may be fit another battery aswell.keep the engine battery just for engine leisure can go flat then but at least you can drive on.
 
maddp said:
Thanks a lot paulhag. Does that calculation of 11 hours take into account the 40 minutes an hour that a compressor fridge is off, as vwalan suggested?
Click to expand...

No this calculation was done for an absorbtion fridge (my mistake) but really I think you should take a look at this link Refrigeration it clearly explains even compressor fridges use a lot more power when outside temp increases.
To be honest vwalan is spot on if you are in the hotter climates then the compression fridge is right for you, but has vwalan says get a solar panel and definately another battery, its your cheapest option.
PS If I were travelling for extended periods and using a compression fridge I would invest in a battery to battery charger.
BTW are you using a 12v compression fridge or 240v if the latter then an inverter will eat up the power.
 
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you can rule of thumb say a absorption fridge use 6 times more energy than an equivalent size compressor fridge.

years ago we used to say a colour tv used 7 times more power than a black n white tv. cant say today as now we need freeview my blackn white tv,s are useless . the french one works in some area,s abroad still.
when travelling if you link the batteries it will charge them all but you will need a big red key switch to turn the connection off when you park .i prefer manual switch to auto .as the relays do go wrong. use the big red isolation switches . works a treat . should the engine bat go down if you use big cable you can jump off the leisure side if they are up. i always use truck batteries dont find gel or leisure bats any better than normal wet batteries.
 
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maddp said:
I have a question about what to do for a fridge in my campervan. I know this type of question does pop up frequently on here, but, excuse my un-mechanical/electrical knowledge, I am still not too sure what to do. My partner and I have recently bought a VW LT35 conversion, which we are really excited about. We are going to be travelling around mainly Spain and Portugal for 2 1/2 months from late August. We will be doing a mixture of wild camping and camp grounds to stock up on supplies/charge battery etc... we would probably be doing no more than 2 wild camping days in a row. The van seems to have pretty much everything we need for this trip except a fridge.

We have been researching into the best fridge option for us, I understand a lot of people recommend a 3 way for wild camping, but due to the cost and logistics of instalation we are a lot keener to stay away from gas. Our leisure battery is a Platinum leisure plus, 6110L, 110Ah. We were looking at running a 35 watt compressor fridge off this (about 2.9 Amps by calculations). Can anyone please tell me how I work out how long the leisure battery might power the fridge for? we will only be running a few small lights and occassionally a water pump off the battery while the fridge is running, and will also most likely be doing a couple hours of driving a day between free camping.
Matt
Click to expand...

The practicalities --

Refrigerator drawing 3 amps, running for say 8 hours a day - will draw a total of 24 Amp-hours (Ah) from the battery.

A 110Ah battery being charged from the engine alternator for two hours per day will not ever be consistently 100% charged, so say it gets to 85%. That translates to the battery storing say 90Ah. Depending on the type of battery, it is best to only discharge them to 40 or 50% capacity, although if you are recharging them straight away, 30% is OK but will result in reduced life.
This means you can draw 90 - 35 = 55Ah each day - assuming the engine can recharge the battery to 85% each time.

So it means that provided you do drive every day and provided you don't lean on the fridge door for hours choosing what to get out and provided you don't use too much power to run lights, water pump, TV and computer (the last two using lots more power than you think) you will be OK.

Hot weather requiring more fridge running time will cut your margin finer, while installing a battery - to - battery charger (does a better job than the alternator provided it has at least a 25 amp charge rate. Expensive though) will add margin depending on how long you drive. For short drives - say up to an hour - direct charging from the alternator will likely do better than a battery-to-battery charger. Hooking up to mains every 2nd or third night provided you have a good three stage mains charger will get your battery closer to 100% which adds to your margin and helps maintain the battery in good condition.

Other considerations - Adding a second battery, provided you can charge it (and the first one) up from a mains charger will add a couple of extra nights.

Having two batteries is only of much use if you have the means to charge them properly at least once every three or four days.

Running the engine for much less that 2 hours a day is not going to be enough to get them back up close to charged and the danger is that they get more and more discharged as the days pass and their longevity will suffer.

If you are not going to be on the road permanently and you are happy to stay in campgrounds every two or three nights and you do have a decent mains charger, then the cost of doing anything useful with solar may not be worth it. Doesn't matter how much solar you have, if the weather is bad, you won't get much charge from the panel.

Some smart people - who just make the one trip a year - buy a couple of the cheapest starting batteries they can find and hammer them to death and hope they last long enough to end the trip. Then they throw them out when they fail and buy a couple more. Can be more cost-effective than spending a thousand pounds on solar or generator, weighs less and saves a lot of messing around.

Another thing you can do is get the second battery, but reserve it exclusively for the refrigerator. This requires a bit of messing around and the installation of a split charge relay, but it will ensure your fridge is looked after and would allow an extra days wilding without taking the chance of food spoilage.

If you are happy to shop every couple of days, then there is also the option of winding the thermostat up a degree or two. Nothing magic about the "safe" limit of 4C and a couple of degrees higher is not going to make the milk go off much quicker and it will reduce the running hours.

Make sure you use decent size wiring for any battery interconnections, put fuses in the appropriate places and also use heavy (ish) wiring to the fridge.


Buy a cheap digital multimeter and get into the habit of measuring the battery voltage at the same time every day - say first thing in the morning but when the fridge is not running. The voltage can be translated into a rough idea of how charged the battery is and you will then be able to gauge how soon you will need to move on.

Have fun and despite what I and others have warned about, don't worry about the batteries too much. You will soon "know" how things are going and once you get a bit of experience, you will just about be able to ignore the batter and enjoy your travels
 
The three way fridge is only intended to be run on 12v whilst on the move.

They can use up to 10 amps and have no thermostat in the that mode.

The 12v compressor fridge is the only real answer.
 
Tony Lee,

If there are newcomers to motorhoming reading your reply, they should print it off and keep it in their van (or frame it and put it on the wall)

I wish I could be as concise and accurate as yourself.

BTW Solar Panels have come down a bit in price if you shop around (sorry to nitpick):D
 
IMHO a 3 way fridge is the only viable option if you intend to spend any time wilding or off hookup.

Plenty of people manage to fit them into campers. Alternativly look for a 3 way cool box which can be placed outside at night and run from a gas bottle plugged into the cigar lighter when travelling. You will have Gas I expect for your cooking.

IMHO its just not worth the agro and worry to run a fridge from a battery 24/7. Imagine finding a really nice place you want to stay parked for a few days and then having to find a way to constantly charge up the batterys so the beer stays cold :( :(
 
Hi Tonylee, good advice, but if I were doing longer spells of wilding the battery to battery charger would be a must. It doesn't do marginally better it actually pulls 3-4 times more charge from your alternator and charges your leisure battery in stages getting closer to the 100% full charge. I read on here or another forum that after 30 minutes of leaving van on tickover batteries were fully charged, pretty impresssive if you ask me.
It is true as maingate says solar panels have come down in price and in perfect conditions they work great, if you intend to spend more time in sunnier climates eg spain/france then solar panels will help.
 
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