Is it the Leisure battery Or the fridge that’s playing up?

[AMcQ46]

First time away in the van for a while and the leisure battery only lasted 36hrs before dropping below the 10.4v low voltage limit for the fridge to trip out (some time on the 2nd night)

the only load was the dometic fridge, not much solar as it was pretty overcast Through the day.
but in the past it has lasted Over 3 days, so something is failing, is it the battery or the fridge?
I throw the fridge into The equation as It is making a lot more noise than it used to and goes through rapid and short compressor cycles with the pump frequency speeding up Then tripping out in 30 seconds.
So Is it pulling more current than it should?

so my question to the experts is ... what checks should I make to start the diagnosis?

The set up is in a Ford transit dayvan as follows

115Ah leisure bat. I hadn’t put it on ehu to charge, but had driven the van a fair bit in the week.
100w solar
Dometic fridge 12V , book rated at 31Ah/24hr Power consumption And also 5.9A current rating.

any way I can measure the fridge power consumption? Or check the battery health?

 

[Fazerloz]

What you can hear more than likely is the fan cycling due to low battery. As the voltage comes back up a little the fan kicks in which in turn causes the voltage to drop in the battery and the low voltage limit on the fridge opperates. Then the voltage comes back up a little etc,etc . Even though you have a 115ah battery you only really have a 50/60 usable ah. Run your engine for a while to get your voltage back up and get your battery on a charger as soon as pos .
More than likely not the fridge thats faulty.

 

[AMcQ46]

Thanks fazerloz. Just to clarify, the fast cycling of the fridge happens even when the battery is at full charge, so defiantly not the pull in surge dropping the voltage below the min limit.
The worry is that I could get double the life a year ago, so something is changed.

Am I correct to think that I can use the EHU to fully charge the leisure battery?

 

[molly 2]

It could be that your battery was under charged before you set off , to fully charge a healthy battery charge for about 24 hours

 

[trevskoda]

Thats some suck from fridge,my 230v with a niakki smart inverter is using .45 ah and can easy run 2 days on 180ah battery,plus 200w solar can get ahead with battery charging.

 

[wildebus]

First time away in the van for a while and the leisure battery only lasted 36hrs before dropping below the 10.4v low voltage limit for the fridge to trip out (some time on the 2nd night)

the only load was the dometic fridge, not much solar as it was pretty overcast Through the day.
but in the past it has lasted Over 3 days, so something is failing, is it the battery or the fridge?
I throw the fridge into The equation as It is making a lot more noise than it used to and goes through rapid and short compressor cycles with the pump frequency speeding up Then tripping out in 30 seconds.
So Is it pulling more current than it should?

so my question to the experts is ... what checks should I make to start the diagnosis?

The set up is in a Ford transit dayvan as follows

115Ah leisure bat. I hadn’t put it on ehu to charge, but had driven the van a fair bit in the week.
100w solar
Dometic fridge 12V , book rated at 31Ah/24hr Power consumption And also 5.9A current rating.

any way I can measure the fridge power consumption? Or check the battery health?

Firstly, getting 36 hours from a 115Ah Leisure Battery with poor solar is not actually that bad, especially if you haven't got a fully charged battery to start with. You are not just using the battery for the Fridge I would imagine but all kinds of other uses.

Second, what is the size (gauge) and length of the cable going to the Fridge? The most common cause (maybe 50%?) I see of 12V compressor fridges not starting due to apparent low battery issues is not the battery at all, but poor cabling. You may think the fridge draws 5.9A when it is running, but it actually pulls way more than that when it tries to start the compressor. The big current draw results in a high voltage drop on the cable going to the fridge if it is inadequate and so the voltage delivered to the fridge is below the 10.4V threshold even if the battery is much higher.
Have you check the battery voltage after the fridge has failed to start up due to voltage being under 10.4V? What is it?
Depending on the length of cable to the fridge, you need a absolute minimum of 4mm2, quite likely 6mm2 and possibly even 10mm2 if you have a long and convoluted cable run to the fridge.

 

[kevbuzz]

I have a crx50,110ah battery and without solar mine only last two days and needs charging on the 3rd I also have thick cables going straight to the fridge terminals so 36-42hours sounds about right.

 

[AMcQ46]

Thanks for the suggestions everybody, looks like there is a good chance that the battery wasn't on a full charge to start with, as I was just relying on the alternator to do it all.

And regarding the cable losses from Wildebus, I will look into that, I can only see the last section of cable from the 12v accessory socket to the kitchen unit, and it is fairly low gauge. But I will have to find out what gauge wire is used to run from the battery to the socket.

Thanks all

 

[molly 2]

Depending on the age of your van it could have a smart alternator fitted , if so the charge into your leisure can be very poor to almost nothing ,you would benefit from having a battery to battery charger , for info try youtube sterling power products battery to baatery charger , allso consider fitting a solar panel not expensive but will transform your of grid camping,

 

[r4dent]

Simple calculations
Your fridge uses 31ah per 24 hours. So 46 ah in 36 hours. However, if the fridge wasn't cold at the start then usage will be more than 46ah.
Your 115 ah battery will give around 56 ah(50%) before it is flat. Less if not fully charged to start with.

So if you started with a non cold fridge an a battery no fully charged everything seems to be functioning as they should.
Don't forget that lights; gas igniters and water pumps use electricity, and depending on the technology level of your van there can other hidden 12v demands.

First check is to start with a fully charged battery and a cold fridge.

Your "3 days in the past" could be solar assisted.

 

[AMcQ46]

Thanks all, some good info in all posts.

Van is 2 year old transit custom so might have the smart alternator, I will check with the company who did the conversion as to what is in there to charge the leisure bat.

So I looked at the voltage drop in the wiring to the fridge. With the fridge running Continuously in the cool down stage (and drawing 5.4A), the battery was at 12.8v and the fridge terminals were at 12.3V.
so V/I=resistance, says I have a 0.1 ohm wiring.

the current draw looks to be in line with the manual, so fridge is ok.
the voltage drop / resistance is a bit high, so wire gauge is a bit low. But I did find the positive wire insulation was under the screw on the terminal block, so that wouldn’t have helped, and I didn’t recheck the voltage drop after fixing

final conclusion is that I should have put the van on ehu to charge batteries and get the fridge down to temp rather than rely on the alternator doing the work in the 3 hr drive.

thanks to all for the hints and tips.

 

[wildebus]

Thanks all, some good info in all posts.

Van is 2 year old transit custom so might have the smart alternator, I will check with the company who did the conversion as to what is in there to charge the leisure bat.

So I looked at the voltage drop in the wiring to the fridge. With the fridge running Continuously in the cool down stage (and drawing 5.4A), the battery was at 12.8v and the fridge terminals were at 12.3V.
so V/I=resistance, says I have a 0.1 ohm wiring.

the current draw looks to be in line with the manual, so fridge is ok.
the voltage drop / resistance is a bit high, so wire gauge is a bit low. But I did find the positive wire insulation was under the screw on the terminal block, so that wouldn’t have helped, and I didn’t recheck the voltage drop after fixing

final conclusion is that I should have put the van on ehu to charge batteries and get the fridge down to temp rather than rely on the alternator doing the work in the 3 hr drive.

thanks to all for the hints and tips.

You miss the point about the volt drop.

Redo the calculations but instead of using 5.4A, put in 60A instead and see what the result is.

This graph is for an AC mains Compressor Fridge, but the same happens on a DC Compressor Fridge. And the graph spike is actually conservative (the peak isn't captured here) - my fridge in-rush current is 20 x the running current. I'm only suggesting a 10x running for your calculations.

EnergySnapshot - AC System by David, on Flickr

 

[Harryw]

Not sure you’ll ever fully recover the battery from being 10.4v I.e absolute 0 charge remaining.
My limited understanding was permanent damage (whatever that is) can occur below 12v which is around 50% For a AGM?

 

[wildebus]

it is the Fridge that is seeing below 10.4V. The actual battery won't be close to that.

 

[Harryw]

it is the Fridge that is seeing below 10.4V. The actual battery won't be close to that.

Be interesting to see though.
If the fridge is not running, ergo not drawing current, then the battery potential will be very similar If not the same as that seen at the fridge Terminals.
Whether the fridge low Voltage sensor/monitor is very accurate is another question.

 

[AMcQ46]

Checking the book for the fridge, the low voltage cut in threshold is 11.7V to try and prevent it cutting in then dropping out as soon as the current flows.

wildebus,
I will need to sample a lot faster than my multimeter to capture that type of inrush peak.
watching the Current on the meter, from switching on, it starts at 3A (Fan?) for a few seconds and then the compressor feeds in and it ramps Up Fairly slowly to 5.3A

I assume the Inrush is very short otherwise it would take out fuses. the feed to the fridge is on a 15A fuse and my multi meter has a 10A fuse.

I will see if I can rig up a heavy duty lead to a new accessory socket.

 

[wildebus]

The In-rush lasts for around a second.
If you watch this video you will see what happens in terms of power surge when the fridge compressor kicks on (watch video from 0:45 seconds if restarting).
You don't see much of a voltage drop here as I have 380Ah of Battery and 16mm2 cable going to the inverter (plus the monitor is at the battery end anyway).

If you don't think your fridge has an in-rush current and so doesn't need a suitably heavy gauge to avoid the inevitable voltage drop, that is fine. However if you want a properly setup supply to avoid this problem, refer to my previous note.