My A level physics days were too long ago to work this lot out, and I’m a car electrics eejit.

I’ve got a Mazda Bongo with a 110ah battery. It must have a split charger, as it’s obviously charging from the alternator.

This runs a small underseat fridge, the stereo, water pump and led lights. To be honest, it’s never run flat (I know that would be a bad thing though), but I’ve usually had a AC hook up and used a charger to trickle charge it through the 12v cig socket.

We’re planning on camping for 4 nights without a hook up, and I’m guessing this will drain the battery if I leave the frige on during the day? So to charge the battery, without AC, I either need:

1. solar charger – but I assume this will be virtually useless

2. Start up the engine to use the alternator, but how quickly does this charge up a battery? eg: will running the engine for 15 minutes really help things much (or just annoy other campers…). Will the alternator even charge the battery quicker than the fridge is discharging it?

Are there any other options, short of carrying a spare leisure battery?

cheers

What power do each of the loads pull? The fridge will have it printed on it somewhere.

Depending on what type of fridge, most three way units seem to run at about 7 amps, and ideally would only run on 12 v through a relay so that it only runs on 12v whilst vehicle running. It would soon drain a battery. Although specific leisure batteries are designed to be charged and run flat more so than standard car batteries. Can you run it on camping gas? Normally a twin relay is best fitted to charge battery and fridge separately.

I find I generally only turn the fridge on when driving anyway.

It will keep cool enough when it’s off that you only really need to turn it on occasionally. Especially if you have some thermal mass in there like 4 pint pins of milk etc. Just dont open it up too often, or leave it open when ferreting – i.e. you want the butter out, dont let the wife do it 🙄

As for draw, I too have a 110Ah leisure battery and wouldnt try and charge it from the alternator whilst camped (antisocial-r-solitis), would take ages to charge, and dont forget the split charge relay wouldnt send any juice to the leisure battery until the car battery was 100% either.

An alternator output could be somewhere between 55 and 90 amp in most appllications I’ve seen in campervans.

at tickover or at hamster-bashing revs Shmikuk?

A relay wired in as a split charge relay could charge a leisure battery even if vehicle battery wasn’t 100%. (I know some “smart” systems do have a delay or level before switching in). So long as alternator is putting out the required voltage, it would also charge the secondary battery.
Just to add, what Stoner said is pretty bang on ref the usage etc.

I’ve got a camper with a 110aH leisure battery and no hook up. We lived in it all through Europe in the summer.

The fridge will be the main draw, and obviously it depends on the make, weather conditions etc but we used to get about three days out of the battery when camped. That was with occasional use of the water pump and LED lights. Didn’t use the stereo (also hooked up to the leisure battery) as they draw a surprising amount of juice.

You can get a bit of juice back into the battery by running the engine, but you’ll need to run it for at least an hour to make it worthwhile. Ours would get a full charge on the five-ish hour drives (and the charge needed that long) we did between sites every three or four days.

If it’s cool, obviously the fridge will work less and the battery last longer. And, even when its out of juice, it still acts like a big insulated coolbox. Won’t chill beer, but will keep milk from going off.

We’re away in it agin in the summer and will be buying a hefty solar charger so we can stay in one place for longer, you can get them from caravan places for exactly this function. Not cheap mind, few hundred quid.

I have toyed with fitting another leisure battery, but whilst that would double the amount of time you could run the fridge for, it would also double the length of time needed to fully charge the batteries…

IHN have you done the maths on the size of solar charger you’d need?

blummin big and expensive.

ok here goes
I lived on a boat and depended on 12 volt so trust me on this – i wont do the maths

Dont bother is the simple version
Long version

boat fridges draw about 1 amp or 22 amps per 24/hr at 5 amps for your fridge [ i am being kind] it will flatten the battery in circa 5-7 hours [ flat at 50% charge and more amps as the charge drops]
OIf you have a three way gas fridge it will be terrible on 12 volt I would not even bother tbh] If a boat type one [ shoreline iirc then you may get three days if you are really lucky]

Charging form your alternator is ineffective beacuse an alternator is designed to respond to load and not to charge a battery – it assumes the battery is charged and increases output when you say put on the lights for example

It will charge at circa 50% its rated watts at circa 2000 rpm for about 10 minutes then the surface temp and other stuff will make th ealternator thingk the battery is fully charged and oit will trickle at about 5 amps [ this is irrespective of the size of the alternator or the battery bank .

SO dont bother
Get electric hook up or buy one of these
http://www.sterling-power.com/products-altreg.htm
which will trick the alternator into producing full power

The amps of the fridge are so high I would not even bother trying to be honest it will be terribly inefficient

Stoner is correct i would guestimate at a minimum of 50 watt panel

Usin little solar chargers for AA batteries and the like and use them to power stereo is a good way of reducing power as well]
Lights use a fair amount as well so swap to LED if possible

Normally a twin relay is best fitted to charge battery and fridge separately.

…now that’s confused me, I dont really get the concept of “charging the fridge”?

I had been told that the alternator would only output about 5 amps or so, once all the inefficiencies in the charging process were taken into account. The fridge probably draws more than that I would guess, but need to check.

Not looked into runnig off case, dont know what sort of modification would be required. I think the answer is to fill up with cold cider and frozen milk and keep the think closed.

But, I’m sure I’ve got 20 hours of fridge use in the past without topping up the battery with a charger, which doesnt seem right.

Also, would you expect the fridge to automatically protect the leisure battery by turning itself off when the voltage dropped too low?

it will probably charge the battery at 5 amp buit will be power the fridge as a load

yes most have an alarm and stop at roughly 10 volts but yu can buy something to do this to be certain if required

My van has a compressor fridge (economical on power) and 170ahr of leisure batteries, and 4 days without a drive would be a real stretch.

Its likely that your fridge/coolbox will draw a lot more than mine, 2 and 3 way fridges and the Peltier type coolboxes draw a lot of amps and will run a battery flat in less than 24hrs. We used to have a 12v coolbox and it would flatten the 110ahr battery in our car if left on overnight.

If the current draw on your fridge is manageable, you could use a solar panel but you are probably talking £200 plus for a panel that will make a noticeable difference (a maplins dashboard job isn’t going to cut it) plus you will need a controller as larger panels will overcharge a battery in good weather.

Your options are: go for a scenic drive in the middle of the holiday, buy a 2 or 3 way chest type fridge that can run from a campingaz cylinder (but they MUST be outside when using gas), or you could get another battery, but if you are thinking of spending more on batterys, solar panels are probably a better investment. Problem with a Bongo is the solar panels on the roof will be obvious, at least on a larger motorhome they are usually hidden from view.

(Edit after reading Junkyards post: My compressor fridge is probably the same technology that is in his boat…mine is a Waeco though. Most motorhomes and campers are fitted with the cheaper 2/3 way fridges/peltier coolboxes which are much more power hungry)

^this. It’s not charging the fridge, it is providing a power source for the fridge, via the battery. The relay is used so that the live feed is provided only whilst the vehicle is running, due to it’s draw. The relay is switched by the charge warning light wire or similar .

My fridge will cut out when the battery is low, but it does it at about 10.5v which means the battery is completely knackered anyway. Your fridge will just keep running down.

You say you’ve never flattened the battery, but I suspect you have. I flatted mine regularly without realising, it was only when I got an expensive battery monitor that I realised how quickly it drained. If you ever see the lights start to dim, the battery probably ‘went flat’ several hours earlier!

Also, would you expect the fridge to automatically protect the leisure battery by turning itself off when the voltage dropped too low?

Mine does, it’s a Waeco compressor super economic type as mentioned above. It’s also a top loader, so the cold air stays in when you open it.

Stoner – yeah, I realise I’m looking at three hundred quid ish. Just don’t want to go down the hook-up route, I like being self sufficient.

Oh, and we flattened the battery any number of times while we were away, didn’t seem to affect it’s performance hugely. It did get a good ‘soak charge’ every three or four days though with the long drives between sites.

A three way could be used on gas in the vehicle subject to the correct ventilation and exhaust fittings etc (standard and readily available).

My compressor fridge

yes that is the part iirc they did all the compressors and all low drain systems.

flattening them is not a good idea to tbh unless you have traction batteries [ and you dont].

they will hold charge for a few days but not really for months as a new one would – it is never good to flatten a abttery and it is considered flat at 50%

gas is a better option for in a camper van tbh jsut vent the exhaust to th eoutside – the flame is the same size as a night light so I assume having a suitable vent on the roof and at low level would allow enough free movement of air to be safe but not actually legal

IHN – spunk some proper cash on one of these:

Plug into you hook up to charge the battery. Rated 900W
about £750, but only 53dB. I can fart louder than that.

posh mans version Stoner. Pah, get the chavs,paupers clone @ £300

dB of 64 = over 10 times louder.
Cheap junk, junky 😉

OK, thanks. Few more questions!

Junkyard – how do you arrive at 5 to 7 hours, when the battery is 110ah? I realise I wouldnt get 110 / 5 = 22 hours for a 5amp fridge, but surely you’re not being very generous? I know I’ve got more than 7 hours out of it (but then it isnt on continuously, as there’s a thermostat on the fridge obviously – but dont know what % of the time it is on).

I’m about to buy a new 110ah battery to replace the old one, I dont want to trash it by running it too low, but not sure how to avoid this? I have no idea if the fridge turns itself off at a certain voltage, but have never noticed lights going dim (but they are led). It did die once, I realised because I couldnt power the stereo, even when driving. Came back to life with a top up of water (it’s an old battery) and an AC charge. But it isnt right!

Where’s a good place to get help on this and have someone check out the electrics? The garage I use doesnt really specialise in this.

cheers

if you get a “deep discharge” battery youre far less likely to trash it than a cranking/starting battery.

Most leisure batteries are specified as deep discharge.

Its a marketing trick.

A leisure battery is marginally better at bigger discharges, but only because the plates are fewer in number, and thicker, to offset the faster erosion of the plates caused by repeated discharge/charge cycles. They are essentially still a starter battery, just with a different sticker. An instant give away is when a leisure battery includes a half decent cranking amps rating, to achieve high cranking amps the battery will have thinner plates to increase surface area (at the expense of discharge ability) This is why most places will recommend you treat your leisure battery in the same way you would treat a starter battery – don’t discharge past 50%. 50% charge is 12.2v (without a load), fully charged is 12.6-7v.

A deep discharge battery is a traction battery, you will know if its a proper deep discharge battery as it will be substantially more expensive!

Stoner – I don’t have a hook up, and a generator feels like cheating…

substantailly and some I had them in 2 volt cells superb they were heavy and very dear lasted a few years though before performance dipped 😯

Junkyard – how do you arrive at 5 to 7 hours, when the battery is 110ah? I realise I wouldnt get 110 / 5 = 22 hours for a 5amp fridge, but surely you’re not being very generous? I know I’ve got more than 7 hours out of it (but then it isnt on continuously, as there’s a thermostat on the fridge obviously – but dont know what % of the time it is on).

1. It is flat at 50 % charge so that gives us 55 amps [ which would be 11 hours – not really see below]
2. As you use it the amps increase [ watts stay the same so the lower voltage has to run faster [ go on you want the maths dont you 😉
3. personal expereince teaches me that what they claim about a battery and what it actually does is a world of difference.
4. its not new so you wont get new performance from it
You may have a fair point about my time if you riun the battery till it wont work /cuts out. However 5 hours is what I would do with a new battery and a 5 amp fridge to preserve the battery

A cheapo leisure battery is a bit of a con IME and itis ok if you dont really discharge it much but rubbish if you really do

Stoner

How do you go about calculating the size of solar charger you’d need for a given system?

I am planning on getting a solar Panel for my shed to power a few LED lights and an car stereo via a old car batery.

Rusty – have a look here:

http://www.selectsolar.co.uk/cat/167/ready-reckoner-for-solar-kits

I reckon you’d get away with 30 or 40W. I’d be going for a 60W for my van.

http://www.greenweld.co.uk/data/How%20to%20calculate%20your%20solar%20power%20requirements.pdf

50 watt left me self sufficient on 12 volt for most of the summer running a fridge and TV every day – it is a lot if you dont plan to live in your shed/van tbh – they want yuo to but big panels for sure on that site. It doesdepend though as I could cope if i got less one day as I had a huge battery bank
20-30 watts van??? – depends whow long you want to be free and how often you run the engine/move tbh

10 watt for the shed assuming you use it once per week and swap the stereo out for sya an Ipod with active [ computer speakers for example] that run of 12 v or less

Buy another leisure battery or buy a gas cool box
Or fill your fridge to the max and keep it off during the night when it’s cooler and on during the day when you are less likely to be using other stuff like lights etc

Me, I would get a small genny FWIW

Most UK campsites specifically prohibit use of generators – they tend to only be used by people who will pull up in any field where the gates aren’t secured.

Cheers for the links guys, will look at them when i get home. Previously i’d been looking at much larger pannels.

How do you figure out the power useage of a car stereo?

The stereo says 45W O/P however in my old car it came out of i could and did run it for 2hrs on the car battery with no charging from the engine whilst waiting for my girlfiend to sit an exam. Car also started and ran fine after so it didn’t take all the juice out of it either.
Te car battery was not massive @ 41Ah so it must not have been drawing 45W.

Amps = Watts/Volts

so 45w @ 12v is only 3.5 amp draw.

Hang on I’m being an idiot looking at point 4 on the greenweld site explains it. and if it does draw 45w i’d get 10hrs + of useage I think? It has been a long day.

Are you camping without a hook-up because the site doesn’t have them or because your van doesn’t have one? If the latter: http://www.gooutdoors.co.uk/mobile-mains-kit-p155317 🙂

I went away in my van before I finished the electrics, and once I got home I decided to not install the 240v hookup.

The reasons are:

We are completely self-sufficient; we can wide camp overnight and at places like twentyfour12 we are not left wanting a hookup.
We can use grass/tent pitches, which are usually more secluded with better views than the serviced pitches.
Seems to be a common theme for sites to move towards ‘fully serviced/premium pitches’ which means if you want electric, you get a water tap, drain, TV hookup and a hard standing, all of which commands a silly price.
People pay for hookup ‘to save their gas’ but my LPG costs next to nothing, and throughout a year, I reckon its considerably cheaper to use your own gas than pay a flat rate for ‘all-you-can-use’ electric.

If I struggle for power, I will buy a big solar panel. Not been too much of an issue yet 🙂

We have a hookup but don’t use it for short stays for mostly the same reasons 🙂 Even Camping Gaz works out cheaper than a couple of quid a night for electricity.

A VSR across the leisure battery? saves it being drained too far.

We have a hook up, the campsite doesnt. I agree that booking pitches with hook ups often means you are on hard standing pitches surrounded by monstrous RVs and poor views.

To be honest, it’s a bit of a novelty, since buying a Bongo as an alternative to tent camping. To be honest, the electricity is only used for the water pump (avoidable), LED lights (will run for hours off the battery) and AC mains for a kettle, laptop, battery chargers etc.

Other than the kettle, where gas is an option, I can do without AC and either charge up before hand most of the time, or take plenty of AA batteries.

I’m tempted to test some of the estimates in this thread by seeing how long the fridge, lights or stereo will run off a 110ah battery before it dies, as I need to buy a new battery anyway.

Out of interest, what current is a small LED light likely to draw?