Battery issues

G’day Nutta.

What sort/type of fridge is in the van? If a 3way fridge on 12v it will use a significant amount of AH over 5 to 6 hours.
The fridge will use around 15 amps if 3 way on 12v. That is nearing the total full output of the panel system if in good sunlight.
A few questions to investigate the issue.

How do you know the batteries are in good condition?
Are they actually being fully charged by the regulated solar panel system?
Are the panels clean so they can develop near full output?
Is the cable size from panels to regulator of decent cross sectional size so to minimize any voltage drop.

If the vehicle alternator is also connected to the 3 batteries, then it should provide sufficient charge flow of amps to maintain more than 12.5v, at the fridge input leads right at the fridge back. If not, then the alternator may not be delivering high enough charge voltage, or the cables to the battery system are too small and they are restricting current flow and therefore voltage under load to the fridge.

If the cabling to all components and especially the condition of any Anderson plugs in the charge lines is faulty, dirty, loose or corroded, then that will reduce or prevent a good alt flow to the van batteries.

From what you have said you have as equipment it should all perform quite well.

If your system has some common eart points and or uses the frame of the van or vehicle as a return negative line to all the batteries, then one of the earth/negative connections may be loose and not effective at returning the necessary current flows for battery charging. If so all systems will be less than full effectiveness.

With the genny running, is it run to provide 240vac to a decent output amperage charger which delivers to battery? A 30 or 40 amp charger would be needed for a charge in a reasonable time. 30 amps into 3 x 100ah batteries from 50% charge will take around 5 hours of genny run time.
OR
Is the genny only running it's small 12v output of around 8 amps which requires the genny to run at full speed and does very little to restore a large amount of charge to 3 batteries. A 1 hour run would only provide around 3ah to the 3 batteries, so not much at all, hardly worth starting for although the voltage of the batteries may seem to be better.


If using or relying on the alternator it may have a blown diode and that will reduce the alt output by 66% even though it may still be able to get to it's full regulated voltage under a relatively light load. Under load it will not keep the batteries charged even with everything else all good and correct.

Sorry for the many possibles, but there is a fault somewhere. At low 12 or high 11, the flow of amps is not reaching the batteries it seems.
With along piece of auto wire and a multimeter set to read 12v, you can read from each end of a cable while it is being used to see if there is significant voltage drop over that distance. Both pos and neg lines need to be checked. Because of the charging voltage and the battery voltage not being a large difference, any voltage drop in cables over 1volt (preferrably less) will reduce current and charge flows from solar and alt systems quite significantly, result, batteries can't get charged fully or fridge use can't be compensated for, = van batteries become discharged.

Hope you find the fault/cause.

Are you using a 12 volt DC to DC charger or are you feeding straight from battery to battery.

A 3 way fridge running on 12 volts will use at least 12 amps so unless you're putting that into the battery you will flatten your house batteries fairly quickly.

Most of us run our 12 volt fridge power direct from the Car , not from the house batteries.

You need to find out why the alternator isn't charging the van batteries while driving.
I assume you have a 3 way fridge in the van, which will draw around 10 to 15 amps, and if the van batts are fairly full before driving, will only draw around 10 to 15 amps as well, so not a big drain on the alternator.
If the alternator isn't charging the van batts while driving, the 120W solar panel will not keep up with the fridge on it's own.

What size cabling are you using between the truck's alternator and the van? Is there a DC-DC charger in there?

Can you post a sketch of your system and include cable sizes? That would help.

The old small absorption fridges drew 12 A on 12 V if you ran heavy enough cable. The 2 door fridges draw over 20 A. This requires serious size cable. If you are trying to charge a battery and run an absorption fridge on the one feed then the supply cable should be around the size of your little finger. You should be using 2 gauge cable for preference, particularly as you have a long tug and require longer cables than those with smaller vehicles.

I suggest you should be using separate cables. Run a new 4 gauge cable for the battery charging. Use the existing cable for the fridge alone.

People think that if they use cable that is 2 or 3 times the current rating then that should be sufficient. It may be if you have very short runs like just around the engine compartment. On long runs like from a tugs battery to the vans battery you are running a lot of wire.

You can get the big alternator upgrade from f series mods at Mt cotter al, hoopers crossing..
I run 3 batteries in truck plus another in canopy,

Nutta
If testing/inspecting yourself, with the alt and or solar running, with the multimeter on 12v reading and that long wire, you can progressively test at points starting at the batt +ve and read the voltage along the various points as you move rearward.
There will be some small reading which gets more as the length of cable increases, but a sudden increase in reading should identify a faulty connection etc. That may avoid having an auto elec do tests.

Same test for the return/negative line as it is aso part of the whole circuit.
You may look at all the positive cables and they are ok, but the negative side, often bolted to chassis etc, must be good for it all to work properly.

I know it is a few $$'s, but a clamp type amp meter is good to have for any circuit as they are able to be placed around the cabl, while operating, and a reasonably accurate amp flow reading can be taken to confirm what is happening and or deficiencies in flow, be it cable size related or faults. Just another way of doing checks.

Yes it would seem to be lack of voltage from tug ,the other thing to check ,is your F250 fitted with a "smart alternator " , if so your batteries are not getting enough charge when it goes into eco mode

HI
Nutta
Simple really ,
Good bet u are only running 6B&S cable 13mmsq thru 50A ando plugs
STd type Altenator charging
Current draw 3 way 15amps upto 20amps+ depending model

13mmsq// 6b&s 9mtrs volt drop carries 18amps at .4volt drop
25mmsq // 3 b&s 9mtrs volt drop 35amps at .4 volt drop

Charging at 14.2v or greater is upto 3 times faster than lower voltages
14.00v and above charging happens
below 13.8v charging is slow

Either run 1 large cable or 2 smaller ones