Outer Limits 4x4 Board

Want to run a Engel 80 litre as a fridge and a waeco 18litre as a freezer.

I have a dual battery system.

Don't think it will be up to the job, but not sure

How much driving would i need to keep the batteries charged.

How fast does an alternator charge your battery.

Any ideas and info appreciated.
thanks
steve.

I think your question is a bit too generalised for anyone to be able to help out?

Info like what sort of isolator you've got fitted, battery capacity (and type), alternator capacity, vehicle, wire sizes used, ambient temperatures the fridges will experience, how long they will be left on without the engine running etc. etc...... will all play a part in the answer.

Okie. cheers
Landcruiser 80 series.
not sure on battery monitor system,
second battery is a deep cycle 75 amp hour
80 litre engle on fridge mode
18 litre on freezer,
Don't know how much driving I would be doing, thats one of a few things I'm trying to work out,

Hi Bruiser

murcod is right - your question is a little like "how long is a piece of string". There are a significant number of variables which determine how long you need to drive, and without detailed testing of the configuration in your vehicle it's impossible to give a good answer.

The biggest issue is that a standard vehicle alternator can fully charge both your batteries, but the charge rate drops as the charge level rises.

Some (very) rough numbers (and yes, I'm making this up as I go ):

Your second battery will get to around 70% quickly (hour or two), but the last 30% can take significantly longer.

If you run your fridge sensibly (well shaded, kept full, don't open & close a lot) it could consume about 24Ah each day (this is a figure I've read in a few places, but I don't know how accurate it is.)

A freezer typically draws more (harder to maintain lower temperatures), but again, it depends on how it's used. Let's guess it uses almost as much as the fridge, and guesstimate 40-45Ah total consumption each day.

So, fridge & freezer together will draw down over half of your second battery's capacity every day. Not good.

It's generally accepted that recreational deep cycle batteries shouldn't be discharged below half - to do this will shorten the life of the battery. (Some expensive commercial batteries are designed to use 80% of their capacity every cycle - but few people buy them for recreational use.)

Even touring (driving 6 - 8 hours each day) you're unlikely to return your second battery to 100% every day. On a good day, you might get it back to 70Ah stored energy, but you're likely to discharge it back to 25-30Ah (remaining capacity) the next day.

If you then take a short drive (1 - 2 hours), you may only get back to 50 - 55Ah stored (70% of 75Ah), so the next day you're potentially draining your battery down to 20Ah/30% or less. That's when most batteries start to really shorten their life.

So, what's all this mean?

Your system isn't ideal.

You'll need to aim to drive for 2 hours every day to avoid having your second battery drain completely, but you'll probably need to replace your battery every year or two.

If you drive 4-6 hours each day the situation is a little better, but you still won't get lots of years from each battery.

Ideally, I would say you need a second battery of 100Ah or larger, or a third battery - but you'll still need to drive pretty much every day.[/list]

Good post Scott... what happens if you feed a bit of solar topping up into this? Just wondering.

Thanks for the reply scott.
Think you summed it up well, probably not going to work they way I initially thought without thinking about it,

My option I am now considering is:

Engel 75 combi at camp site run off large deep cycle batery and 80 watt sollar panel and my waeco 60 litre in car as it always has been.

so
meet, bait in freezer, veges and drinks at site on solar and battery

beers and food for the day in 60l fridge in car

My uses are.
Camping up beach for up to a week, Sometimes heaps of driving, fo example Fraser, (about 4 times a year) other times almost non driving, maybe an hour.

chimpboy wrote:Good post Scott...

Thanks.

chimpboy wrote:what happens if you feed a bit of solar topping up into this? Just wondering.

Well, any extra power into the battery will help. It all comes down to how significant the help is.

bruiser wrote:80 watt sollar panel

80W would be the maximum rated output under ideal conditions. In reality, you'll get less.

Generally, people figure on 5 effective hours per day from a solar array. 80W (in the real world, after losses) is probably going to produce around 5A max (in round figures, 14V is required to charge a battery, so 14V at 5A = 70W useable). So, 5A x 5 hours = 25Ah, which should effectively cover one of your fridges, but not both.

If you strike some overcast days solar output will decrease, but chances are good that the fridge(s) won't need to work as hard, so the reduced solar output will be offset (to some extent) by reduced power consumption.

So, you'll still be draining your battery over time, and will need to go for a drive on a regular basis. Let's say 6 - 8 hours of driving every 2 - 3 days to keep your second battery above 50%.

At the end of the day, you'll need some trial and error, but I think your "system with solar" will be a good workable system.

Hi bruiser and what I’m about to do is a NO NO but this will be the cheapest way to both increase your available stored battery
capacity and reduce the amount of driving time needed to replace the used capacity.

Bruiser check out my web site, the link is bellow.

If you plan on sticking with only one auxiliary battery the my SC40 DBS will do the job, if you think you might get another auxiliary battery later, the my SC80 DBS would be better.

Now for the reason for such a blatant bit of spamming.

nearly all other dual battery controllers cut-in once the alternator is running ( motor running ) and so do mine, but while all other controllers cut-out once the motor is stopped, or soon there after, my controllers remain on and the cranking battery and auxiliary battery(s) remain connected.

My controllers keep the batteries connected until the common voltage of all batteries is at 12v ( 50% SoC ) when the cranking battery is then isolated.

At 50% SoC, your cranking battery has heaps of power remaining and can easily start your motor on the coldest of mornings.

Now there are a number of advantages for doing what my controllers do.

The obvious is that you have at least 50% more power available for operating your accessories.

This in itself means you can either go longer between charges or you don’t have to take your auxiliary battery anywhere near as low as you would have to do with an ordinary DBS set up.

Next, because you can charge two batteries at once, in nearly the same amount of driving time as it takes to charge one battery, you have a huge saving in driving time and also means you will have two batteries at a much higher state of charge at the end of your drive than can be done when only using your auxiliary battery by itself.

All this also goes to extending the operating life span of your auxiliary battery and has no effect on the operating life span of your cranking battery.

There is more to it but this will give you some idea of what my controllers do for you and the info above is based on 20 years of making these controllers.

Cheers and sorry for the spamming.

My stie is at :-

www.traxide.com.au