[Gwagensteve]

And people think I'm a hater when I say I don't like dual battery systems.

[henno]

I don't like them either.

Almost as much as I don't like other people's work. It's a running joke in my household that a two hour job always becomes a 20 hour job once I dig in and find the skeletons in the closet of previous owners.

Back to the drawing board.

[Kor3y101]

Why not just get a redtop Exide that has 60ish A/H and 660CCA and get a solar panel/small solar charger to top it off if it's needed? A normal fridge uses roughly 1a/h once at temp and such so that will last you 2 days with some power to start the old girl.

[henno]

I probably should have mentioned this from the outset, but I am not looking at a solution that I used for a day and then toss it back in the shed; ideally I want a setup that can just run all the time.

Besides, 60/AH and 660CCA is far less than what I have already anyway: I have a dedicated N70 with 720CCA and 95AH which doesn't need to start anything as there's an entirely separate battery in the car as a starter.

[THE_DICTATOR]

Are you sure that the isolator hasn't failed? All mine still work fine

[henno]

THE_DICTATOR wrote:

Are you sure that the isolator hasn't failed? All mine still work fine

It hasn't failed in the two most obvious ways: being stuck open or closed. The starter battery is definitely not losing charge and the AUX battery is definitely getting charge after a short drive.

There is a possibility that it is not allowing enough amps through it I guess, but I just think my maths might be out with regards to size of battery and the amount of energy I am using versus the amount of driving I am doing. As in, I am not even close by the looks of things.

24 hours would be a nice figure to go off. If I could drive the car 40 minutes every 24 hours to keep everything happy that would keep me happy. One or two big drives thrown in every week. But as it stands, voltages are dropping well into the low 11's overnight, so if that is not a result of the battery being cactus then it soon will be if I keep cycling that deep.

[henno]

I recharged the battery overnight using a proper 240 charger. It got the battery back up to 12.7v which was about 12.5v once the compressor kicked in under load. By midday (five hours later) the battery was 12.2 and after a quick drive to get lunch (20 mins max) it was back up to 12.55v under load. All of that seems healthy and fine. I'll do another test after work and see how it's hovering, but I am still not loving the rate of discharge.

[henno]

Left work four hours after my last measurement and the battery was at 12.17v by that stage (bearing in mind that the car is parked in the sun). After my quick drive home (only 5kms) it was back at 12.67v which was 12.52v once under load when I kicked the compressor in.

So everything seems fine, but the rate of discharge might just be a little too fast and a little too deep for it to be healthy for the battery long term. Or, this battery is just a dud.

[henno]

henno wrote:

So everything seems fine.

Scratch that. Three hours later (in the cool of night, no less) and the battery is 11.95v at the poles and 12.05v with the fridge turned off. That is deep into screwing up your battery territory, so I am turning it off again. It's only 7:30pm so by the time I wake up at 6am what's left of this battery will be nothing but sulphate and fail.

I am half inclined to sell the lot and go back to using my Evakool fibreglass esky, which has kicked all kinds of ass for over decade. It's good for 3 days sitting in the sun and 5 days in the shade, all for ten bucks of wet ice.

[pete_79]

So what else is running off this battery?

I'm a complete retard when it comes to anything electrical, so won't waste any time with advise. I can only offerer an uneducated opinion.

Due to my complete incompetence with electrical systems I did the most basic set up possible to run the fridge in my dual cab.

50amp fuse on the cranking battery.
Positive wire from fuse at battery, run along chassis to Anderson plug in tray.
Negative wire from Anderson plug in tray and bolted to chassis.

The only thing plugged into the Anderson plug is the CF40 fridge.

Just did a 15 day trip to Cairns and back with fridge plugged in and running the whole time.
Parked in full sun and not starting the vehicle for 48 hours, voltage dropped to 12.65.

Same fridge locked in a baking hot trailer running straight off a 100ah battery will only take a full battery from 12.7 down to 12.3 in a 24hour period with no top up from the solar.

If there is nothing else running off your battery and you're getting that much drop, perhaps you have some leakage there???

[fordem]

You're only looking at the charge side of the equation - you also need to consider the discharge side - is the fridge drawing more power than it should be - is the compressor running continuously or is it stopping & starting as it should? Also - as pete_79 has mentioned - the environment in which the fridge is operating affects the frequency with which the compressor cycles on & off and that in turn affects the total power draw.

One more thing - I went back through the thread, I don't see the type of fridge mentioned anywhere - is it a compressor or a thermoelectric (peltier) type - thermoelectric will draw 4A continuously and flatten just about any battery overnight.

[henno]

I am looking at the discharge side of things also. Aside from hooking up an ammeter and physically logging current use over time, there's not much more I can do aside from measure the drop in voltage at the battery poles over time.

Voltage loss across the cable to the back is more than respectable (0.08v under fridge load) so it can't be that. The fridge could be cycling more frequently than normal but even 4amps constant should still see it do 10 hours straight before needing a charge (40ah out of the 95ah battery).

To answer your last question fordem, it's a 60L compressor type fridge, not thermoelectric.

pete_79 wrote:

If there is nothing else running off your battery and you're getting that much drop, perhaps you have some leakage there???

That's quite possible and should be easy to diagnose with the fridge removed. The only thing connected to that battery at all is the winch, which is easy to disconnect.

[pete_79]

Chuck one of these directly off the terminals on the battery and all will be revealed.

Watt meter

[henno]

pete_79 wrote:

Chuck one of these directly off the terminals on the battery and all will be revealed.

Watt meter

They look pretty nifty for ten bucks. Although rather than wait I might just toss my multimeter inline and see what spits out. The fridge is currently (pun intended) off, so initial startup should show current draw at its absolute worst.

[pete_79]

They're good for logging your consumption over a period of time. And the peak draw is handy to know, my trailer setup registered a spike of over 8amps which 'on paper' should never happen.

The only downside is they only log outgoing and don't take into consideration anything you feed back into the battery. But considering your loosing so much power when parked up it will give you a bit of insite into the rate of discharge (big spikes or just higher then expected over a period of time).

I just found using a volt meter at random intervals didn't give me an accurate picture of what was really happening.

[henno]

Well, at least one half of my calculation is out of whack. These are supposed to be the specs for the fridge I have:



Now, I realise that real world current expectations are never what they say in the manual but it is consuming way more energy than I hoped for. Starting from an ambient temp of 23 degrees, and going on a drive for the past two hours I figured I would see what sort of current it would use. By the time I got home (just a few minutes ago) they fridge was at 4 degrees (it's set at 5) and still drawing a solid 5.6-5.8 amps. (EDIT: I worded this poorly. I am aware that the compressor will draw this amount when on, it all depends on how often it cycles.)

Turning the car off, the voltage at the rear is 12.44 and at the poles of the battery is 12.48 under load, so that is an entirely acceptable (if not excellent) voltage drop along the cable so that is still not it.

Honestly, I think I have undershot in my calculations of average amp draw and overshot in my expectations of a 95ah 'dual purpose' battery, which when combined have lead to a situation I am less than impressed with.

EDIT #2: 10ah used in four hours, peak of 6.73amps draw. I might reset now that log now it's at temp and see how it holds cycling under best case conditions: in the cold of night without being opened once.

[henno]

Sorry for continually bumping this thread, but I might as well update as I gather more information.

So from 8pm until 8am this morning the fridge used 16ah of power while set at 5 degrees, so 1.3amps per hour which is actually right smack bang in the middle of the quoted range in the table above and actually less than I had accounted for in my own expected 'real world' calculations (sorry for doubting you, Evakool).

That said, their stated usage is for a 24 hour period at 32 degrees, and last night was a lot less than that so I reset the log at 8am this morning and will see how it goes during the day today - I expect sitting in the sun, the current draw will be a LOT more. At least this will give me something to work with and tackle the rest from there.

[jdk81]

Out of curiosity whats currently in the fridge?

[henno]

About 20 beer cans and a couple of bottles of water. Best thing I could think of that could handle getting hot and cold as I tested things out.

[cairns27]

I'd prefer that the temperature of the beer didn't go up and down to many time if you're serving it to me.

[henno]

It's shit beer in a can loaded with preservatives. It'll be fine if it goes between 4 and 16 degrees. It was sitting in a carton in a random bottle shop at temps higher than that.