Dual Battery problems

G'day Peter

Wouldn't the fact that he ran the waeco on 240v of an inverter have caused his batteries to run flat??....Personally i would have run the fridge on 12 volt...correct me if i'm wrong mate...

Cheers.......Borgy

Peter,

Not many people understand that you cant fully charge a battery to its maxium capacity from a car alternater.

Col

Ok so I am a total newbie s far as car electrics goes. Obviously...

but how do I run my fridge directly of the battery.
to be clear. it is a Mobicool 35 litre 3-way fridge. so it has a normal plug and a 12 volt plug.

I ran it off the normal plug now. but the other guy said I would not be able to run it of a cigarette plug neither. how do I hook it up?

You buy some 6mm twin cable and a fuse and some 8mm ring connectors and run the wires from your aux battery into the car through the firewall and hook it up to a ciggy socket or a Hella socket ( for the Purists)

Then you plug the 12 volt cord from the fridge into that.

As I said above the normal ciggy socket wiring IS NOT HEAVY ENOUGH TO RUN A FRIDGE

@ Dave,

running the fridge via the inverter increases the power drain on the battery by an estimated 30%, so you're right there are some unnecessary losses.

@ Col,

if they only would listen to us hey...

@ Aukedb,

I'm guessing your fridge doesn't have a compressor?
If so, it could be quite power hungry, up to 12~15 amps which would flatten your AGM battery within 8 hrs if it was fully charged and if it had retained its specced capacity.

@ snoopyone,

quite true, I'd even add that the ciga lighter socket itself acts as a bottleneck for currents above 8~10A.
If it's got to be a 'purist's' setup, you could treat yourself to adding another socket in parallel and also double up the plugs on the fridge wire, to keep things cool ;)

cheers, Peter

they call it an Absorption cooler. So I guess it's not a compressor. On the manual it says it should have a current consumption of 6.1 A.

Is that the power hungry fridge you are talking about or should that do fine?

Thanks for all your help!!

Hi Aukedb,

6.1A is power hungry sort of....compared to a compressor fridge of similar size, which draws about 1~1.5A in average.
But that's the nature of absorption type fridges, can't change the laws of thermodynamics.

So looking at this 6.1A consumption figure, your 100Ah battery should last for 16 hrs on a single full charge, so I'm afraid your battery's either pretty much toast if it's only lasted for five hours or so (taking into account the additional run time reduction incurred by the inverter), or it only was partially charged, or both.

BTW, this current is suitable for ciga lighter connections.
You can double check this by putting your finger on the plug/socket, which shouldn't get hot to the touch after some tens of minutes of fridge operation.

I hope this small avalanche of replies to your original query contains enough information to make up your mind on how to proceed.

cheers, Peter

Where did the ....."weaco 40 L fridge which should only draw 0.3 ah".... dissapear to?
Sheesh!!

Hi all

I have just been reading up a bit about fridges and seems there are now 3 types - thermo electric, 3way (absorption), and compressor.

I read in amongst it all that 3way on 12V will draw significantly more than a compressor fridge as per what Battery Value is saying.

But the Waeco compressor fridges I was just looking at seemed to indicate a requirement of about 4 Amps - Battery Value mentions about 1.5Amps which I like a lot better.

I got the 4 Amps by the specification I saw of an average of .85A per hour and run time of about 20% of the time at 32 degrees ambient temp - so I multiplied .85A by 5 to get 4 Amps when actually running - have I got this wrong??

I figured 20% run time (1/5 of an hour) woudl have to draw about 4A while running to come up with .85A average per hour??

Ken

Yes Ken, I believe your considerations are correct.

A typical 40 litre 12v compressor fridge draws about 4 amps and runs maybe 25% of the time when set to 4c in an ambient of 30c. So its averaged consumption is about 1 amp.

The fridge manufacturer's published specifications can be somewhat unclear (they confuse amps and ampere-hours) and are usually optimistic.

So in 24 hours such a fridge will consume 24ah and the nominal 100ah battery will be able to support it for a couple of days without discharge below 50%.

All this is very notional and does not account for such things as extra fridge load like adding warm cans of beer or a battery which is less-than-perfect. There are so many variables involved that it can only be considered a starting point and the individual needs to assess their own situation by experience.

As you say there are just so many variables - like how cold do you like your beer and how many you drink per hour. Now maybe that should be a new rating for the fridges??

Just for extra info to others on what I have just been reading, what you say seems to apply to "Fridge Only" operations from what I have just seen - and this can also be in "economy" run mode.

When you add in Fridge / Freezer mode they were getting up to around 4A average per hour so we could be talking as high as 20ah (480ah in 24 hours) - that will kill your battery.

I think I was looking at the Evakool specs which might be a bit higher than some others but I would imagine the same principles would apply - don't expect to run Fridge / freezer mode and get long run times unless you have a boot full of batteries.

Ken

Ken, the Evakool is an excellent fridge and I think their expression of specifications is more comprehensive and honest than some others.

Running the fridge in freezer or part-freezer mode certainly raises the power consumption. I run my 35 litre Waeco at 4c measured halfway down which will just maintain some food frozen on the bottom. We vacuum pack our meat to avoid the need for maintaining it frozen. Works for us.

Hi Al - good advice as usual.

So would I be right in saying that in a "good set" up you would have a battery isolator between starter and house battery, but should also have a low voltage cut out on the house system to protect the house battery from being over discharged??

I know recently I saw a fairly low cost unit for this purpose that switched about 20A - the break point could be set between 10.4V and 13.3V and of course you could use it to switch a higher current relay as necessary. Used standard 6mm spade terminals.



Ken

Hi Ken, Thanks but rather wasted on the OP methinks!

Certainly you could have a low-voltage cutout on the house system to protect the auxiliary battery from over-discharge although it would be of doubtful value if set much below 12.0 volt. Regular discharge below 12v is what ruins batteries.

However I think most, if not all, current 12v compressor fridges already incorporate a low voltage cutout feature. This will of course not disconnect loads other than the fridge but that would probably be the only unattended load.

The question arises - what is your priority? The food and beer, or the health of your battery? In a "good setup" it is probably better to invest in adequate auxiliary battery capacity, good charging arrangements and minimal load to ensure maintaining your batteries properly.
The specs and design of the 12v system depend in part on the individual camping style, and of course the budget. If staying in one spot for more than several days you will need battery charging other than the vehicle alternator such as solar. But if, as with me, you tend to drive the vehicle for at least a couple of hours each day then supplementary charging would probably not be needed.

Al

As you do you have put it all in perspective.

I am looking around at fridges at the moment and what I am seeing is low voltage "protection" specifications of 10.2V and even lower - so that is way under what is good for the battery.

Anyway this is "off topic" and all for another discussion.

I like your rationalisation of "what is more important - the cold beer or the battery" - I bet most would say the beer - and the battery is just an associated cost of a good cold beer.

Ken

I'd think that the battery system is working just fine, and that 5 hours running a three way off an inverter is a stellar effort for a 100 a.h. battery.
It sounds like the o.p. has been duped by the advertising guff. As others have said, either switch it immediately to gas every time you stop for more than a couple of hours, or ditch it for a compressor fridge.

Aukedb posted:
Ok so I am a total newbie s far as car electrics goes. Obviously...

but how do I run my fridge directly of the battery.
to be clear. it is a Mobicool 35 litre 3-way fridge. so it has a normal plug and a 12 volt plug.

I ran it off the normal plug now. but the other guy said I would not be able to run it of a cigarette plug neither. how do I hook it up?


About 5 posts down from the first clarifies what type of fridge. Nil clarification on the inverter, but I'm fairly confident a 300w inverter would not cope with a 3 way fridge for very long if at all?

gbc,

The whole issue remains very confused. There have been a lot of replies which provide valuable factual material, but are they relevant to the original poster's problem? The problem has not been stated well enough to be certain what we are all talking about! A compressor driven Waeco that's in fact a Mobicool absorption fridge? (or is it?) A 1500W - 300W inverter - what's that? And why is it being used on a 12V fridge anyway?

There's lots of help available on this forum, and willingly offered by a lot of experienced and knowledgeable people, but first, the problem itself must be adequately defined.

IF the fridge is an absorption type, the simple answer is that it cannot be satisfactorily run from a 100Ah battery, with or without inverter.

I think the op would gain a lot be reading the Electricity for Camping article.

Cheers

John

Aukedb

There are far more experienced people on this forum than me but for what it is worth I would suggest the following and hope it helps somewhat.

What they are all trying to tell you in a nutshell is that

1. to run it off 12V in the vehicle you need a properly wired up 12V outlet somewhere - be it a Cigar socket, Hella/Merit socket, or any other kind of 12V outlet you can plug the fridge into. This will involve cable with the right current ratings and various other crimp fittings and fuses.

2. the current requirement of the 3way (absorption) fridge on 12V is quite high compared to a compressor fridge so you will require bigger battery capacity to run it for any length of time when the vehicle is not running.

3. depending on your requirements maybe you should have bought a compressor fridge.

4. forget using the inverter for the fridge as suggested - it is inefficient and except for small appliances you would generally not run much off an inverter. Also be aware that (as most advertising does) advertised ratings are often far removed from reality - a 1500W inverter may in reality only be a 300W continuous rating and the 1500W a "surge" rating for a few seconds if that. Also note that some are rated in VA and some in Watts and you need to match equipment in the right units - Watts usually being lower than VA ratings. But enough of that. Read the fine print on the inverter for true ratings.

5. to wire up a couple of sockets from the one battery or dual battery system does require some knowledge and with respect you do not seem too "savvy" on electrics which is completely understandable if you are not in that line of work. It can lead to catastrophic issues if not done properly - the comments about not being able to run it from your Cig lighter are absolutely correct based on power requirements to run a fridge - and it seems especially a 3 way on 12V.

6. Either you need to get it wired by someone that does know how to do it properly or come up with some other way of connecting the fridge to the battery without the internal wiring.


None of us would want to see anyone "hurt" or a vehicle damaged by trying to advise you how to do something that does need some proper knowledge.

Ken

Good advice Ken.
Your last line is why I got out of the conversation!

When using your 3 way fridge when the vehicle is not running, run it on gas, then your not using any form of power, thats what they are designed for.

Cheers Col