Cable size to run Waeco 80L fridge/freezer?

Hi,

just wondering what size and sort of cable I should use to run from my aux battery to my Waeco CF80 in the tray? It draws 2.9 amps/hr in normal conditions.....

Cheers!

Matt

Waeco's use a Danfoss compressor that can draw over 5amps when running, any cable with a 15amp rating will work OK, dont forget to use the same rated cable for the earth too. If the fridge is a long way from the battery you could use something heavier. Buy the cable from DickSmiths/Jaycar etc, buy by the meter.

Cheers mate! Any recommendations on a deep cycle battery for it too? I was thinking at least 100 ah?

Most people go for a 100aH, check the physical size will fit in your spot, then get on the phone and start ringing around for best prices.

The cable size really does depend on the distance as well as the amps being drawn. The heavier the cable, the less loss in the cable too - that doesn't mean you should use #0 cable, but a decent size that can safely carry 30A from the front of your car to the rear is 6 sq.mm stuff, and it comes in a double-insulated package so running positive and negative is a simple thing. Get it from any good auto electrician.

If you're putting the battery in the tub, then the size of the battery depends on how you are dealing with the whole process. I have a 60L Engel in my tub, and a 50Ah deep cycle to run it. Because I am constantly driving, I have my 6mm cable running into the tub, where I power an inverter, which drives a battery charger and the fridge (so the fridge is not drawing on the battery while the battery is being charged). This means while the car is running (I have a relay up front providing power only when the ignition is on) I am charging the battery.

If you want to just take the battery fully charged and run off somewhere for 3 days, we can calculate how large the battery has to be. The fridge should draw 5A, but only about 50% of the time, so in a 24 hour period it will draw 60A. For 3 days, that's 180A and since you should only ever use about 50% of your battery's capacity, you will need to get a 360Ah battery.

Cheers for the info Tony. I plan on running the fridge from a deep cycle aux battery in the engine bay which will be isolated from the main using a 140 amp voltage sensitive relay. I reckon the most amount of time the battery would need to run the fridge without getting a charge from the alternator would be 24 hours so I was thinking a 100 ah battery would be sufficient? What do you think?

Cheers,

Matt

At worst that fridge will draw 60A in that time and I really can't see that killing a true deep cycle battery.

I should have amended those figures with an observation I made of my Engel. It is supposed to draw 4.5A max, but I put a datalogging multimeter in to measure current and hooked it up to my pc. I let it run a full 24 hours in summer.

What I noticed was that it only used max current while it was initially cooling, after that it drew about 1.5A. Let's say yours would do similar, and draw about 2A. Over the 24 hour period, you'd only use 24Ah.

Sounds to me like you're putting a good setup together, don't forget that BOTH batteries should have fuses hanging off them, in case the cable between gets damaged, so it goes like this:

Main battery -> fuse -> isolator -> cable to tub -> fuse -> aux battery

i ran 25amp cable to my tub socket which is a 20amp socket and running a 20amp fuse near battery.

While I realise the amperage involved in just the Engel fridge is much lower, in your case Al I have to recount a situation that occurred with some electric brakes on a Subaru Forester hauling a trailer and using 4mm (40A) cable.

Each brake will draw up to 6.5A (give or take a little) and this Forester was pulling a double axle, so the draw was about 26A. Should have been ok?

The electrician thought so. Common sense would make you think 40A cabling for 26A max is ok too, but what happened proved otherwise and it's because of the cable lengths involved.

A modest drive with a modest amount of braking caused the 40A wire to heat up so much the insulation became soft, the bitumen-like compound on the inner guard then softened and the wire melted into it, shorted out and blew the fuse.

The wire was rated just fine, but remember that low voltage DC can only really travel short distances on the cable at the rating stated. If you want to run in excess of (say) about 2m, even 5sqmm cable (50A) is going to get warm. 6sqmm (60A) cable has enough inner conductors to be fairly safe.

If you're running a 20A outlet and intend to get close to that, that 25A cable could get really warm.

only running at most 1 thing from that socket tony, and the biggest thing i use from it is a cf80 waeco. won't go anywhere near 20 amp.

Some light reading...

Auto Cable by Collyn Rivers

I run a 120a/h agm(12v 120AH 1150cca DEEP CYCLE/MARINE/RV AGM BATTERY (eBay item 300346454084 end time 02-Feb-11 09:14:23 AEDST) : Cars, Bikes, Boats) in the tub and a 60l engel fridge (uses around 25-35amps per day). Its joined with 8 Gauge cable on the positive and earthed to the chassis. It gets about 14.4V when the ute is running (not much voltage drop at all)

Is there any reason why your going with a 140a/h solenoid? (STD alt on puts out 60amps max, less what ever your using)

120a/h lasts about 2 days/3 nights 'til it gets down to 12.0V (when you should charge 'em). In the near future, will probably go for a solar panel over another battery (versitility and weight saving)

Nah, no reason for the 140, it's just the size that came in the kit I bought:

MATSON 140 A 12V DUAL BATTERY KIT WITH OVERRIDE SWITCH (eBay item 300497037767 end time 24-Jan-11 19:17:40 AEDST) : Cars, Bikes, Boats

Tony, as far as those fuses go in between the two batteries, what size do you recommend?

I would use a fuse that covers the power requirement that you're likely to use. Since you're charging that battery down in the tub with the battery up front, you could see a large amount of power heading down - and really, if you've dropped a deep cycle battery in the tub, you don't want to be dumping power in there.

I would use about 30A, and use a thermal-reset breaker type so that you don't have to keep replacing the thing. If there's an overload/short, the breaker heats up and trips. When it cools, it automatically re-establishes the connection and continues this cycle until you rectify the problem. This means if there's a momentary "oops" down the back, you only need to wait a short time (I believe no more than a couple of minutes) and the breaker sets itself again.

If you use higher, you run the risk of dumping power too fast to the aux battery and that will destroy it.

Old.Tony said:

The fridge should draw 5A, but only about 50% of the time, so in a 24 hour period it will draw 60A.

Click to expand...

Are you sure that's right, not worried about the actual current draw but drawing that current 50% of the time?

Last time I measured my Liemack once it was maintaining a temperature between -2 and +2 the current draw only happened for a period of about 3 minutes every 20 minutes, (that would be dropped to about 15 mins if the fridge was being used as a beer fridge). Even at 3 mins running every 15 thats only 12 minutes an hour, where as 3 minutes every 20 in traveling situations or over night where the fridge isn't being constantly opened is only 9 minutes every hour.

My fridge is only 60l but from memory I'm also looking at a current draw in the 2-3 amp region once the fridge is maintaining temps too, but like I say my question was more about the running time than power requirements.

It's a worst-case estimate. In the heat of the day my Engel does indeed cycle 50% of the time, although its current draw isn't as high as it's supposed to be.

Glad I kept with my old Liemack then, it's hard to get parts for but it's obviously more efficient that the new fridges, even in 45 degree heat in SA last year the thing wasn't cycling more than once every 15 minutes according to the battery meter.

Old.Tony said:

I would use a fuse that covers the power requirement that you're likely to use. Since you're charging that battery down in the tub with the battery up front, you could see a large amount of power heading down - and really, if you've dropped a deep cycle battery in the tub, you don't want to be dumping power in there.

I would use about 30A, and use a thermal-reset breaker type so that you don't have to keep replacing the thing. If there's an overload/short, the breaker heats up and trips. When it cools, it automatically re-establishes the connection and continues this cycle until you rectify the problem. This means if there's a momentary "oops" down the back, you only need to wait a short time (I believe no more than a couple of minutes) and the breaker sets itself again.

If you use higher, you run the risk of dumping power too fast to the aux battery and that will destroy it.

Click to expand...

Problem with the breakers are:

1. They can cycle on/off quickly over and over again. (like a little kid flicking a light switch)

2. have greater voltage drop compared to fuses (usually)

3. more expensive.

If you go for a std wet sell deep cycle, they aren't really suited to being charged directly from the alternator (you'll really need something like Old Tony's" inverter/240V charger setup.

Prob the best is an AGM deep cycle. Can accept large current charging (what you want in a alternator situation) but still provides the deep cycle capabilities. And although more expensive you'll get more capacity from the same rated battery (amp/hours)

AGM Batteries (same site as before, but info can be found elsewhere, if you want to do your own research)

I am running a CF80 with an extended lead.
Simply got leads and joined and soldered them - no worries.

I have a 110aH battery and my Waeco will drain that easily in 24 hours, especially in hot weather.