Is the alternator up to it

Went for our first camp trip in the D40 and come across a problem.

We have:
Second battery in the tray
Connected directly to the first battery via a battery world controller and a huge thick double core cable (negative returns to battery)
Between the controller and second battery we have an accessories fuse box
Waeco 45l fridge which is connected to the accessories fuse box
No other accessories connected or running

The setup performed wonderfully with cold fridge and freezer for four days and nights, however driving home yesterday we found a problem. When driving along with the fridge on, if we plugged the phone into the cigarette lighter or the iPod into the socket in the arm rest neither would charge. The IPod would play through the stereo but wouldn't charge.

When we turned the fridge off the phone and iPod immediately started charging fine. I'm no auto electrician (installed the second battery and controller entirely by following the instructions in the box) but this don't seem quite right.

Is this because the alternator is not producing enough power to run the fridge pls phones or is there some other issue here? Both batteries were fully charged (second battery fully charged on the bench at home before left and engine running for about six hours each day while we toured around)

Any ideas? any fixes for this?

I would suggest there is another problem. The alternator should handle that much while the engine is running, even my old Subbie could handle a 40l fridge, a music player, phone chargers 2 CB's and the usually car stuff and that didn't have a second battery.

My 09 is set up fairly similar in that all cabin stuff comes off the feed line to the secondary battery before the battery and I can run the fridge in either the cabin off the feed line or in the tub after the battery (electronically it makes no difference where it's plugged in) and mine's only ever faltered once when the aux battery dropped a cell. When that happened the battery still tested relatively well across the terminals (14.3 charging 12.5 standing), I had to do a cell test to prove a cell failed.

I'm sure there is alteast one thread around that talks about newer model D40's having some system that limits the output of the alternator or some such thing. It's not something that's ever bothered me so I don't read them, or atleast don't remember them but someone might be able to shed more light on that and whether it may be your issue. But i wouldn't be blaming the alternator yet.

Your accessories fuse box should be coming off the second battery not off the cabling in between the two batteries. It seems to me you are getting voltage drop to your accessories. Hopefully someone like Tony will be along soon who can explain things a whole lot better than I can.

Cheers Brad

Or Krafty!

I'll suggest his current configuration will work and is not the issue he's chasing but don't listen to my explanations, although they work and are electronically sound I don't agree with the majority of dual battery experts out there and I prefer to do things the easy way.

Krafty - easy is always good.

Nevyn - the issue isn't the accessories (in my case only the fridge) as the fridge is still running fine. It's the aux in the arm rest and cigarette lighter on the dash that loose the power

What voltage drop are you getting from the battery to the fridge along the wires?

If I recall, the lack of power in the console is due to a dodgy earth. Try something: connect something to the centre console that would not normally charge, check that it's not charging then connect a wire between the outer rim of the socket to the negative of the battery.

The aux system should be independent of the console inside - completely separate wiring. I'd be concerned about voltage drop over the distance, and I'd be making sure that both ends of the cable were fused:

main batt -> fuse ----------------------------------------- fuse <- aux batt -> fuse -> aux items

To answer the thread question: the D40's alternator should manage nicely under normal conditions.

Is that the voltage with the engine and/or fridge running or just sat with everything turned off? I'll measure tomorrow

Old tony, I'll give it a try tomorrow as well

I don't know what your fridge consumption is however with the fridge turned on there may be voltage drop down the line but you should be getting 14.4 at the main with the engine running and the same at the back (real world figures may vary slightly).

As stated above my system is similar to yours in that I stem off all in cabin power between the self resetting fuse and the rear battery and I have no issues running anything in the cabin and little voltage drop. But as Tony said the two points in the console are independent of your aux battery (unless it's been rewired) and if you are only showing problems on those points I would suggest you need to look between the console and the main battery not the rear battery.

YBOD said:

Is that the voltage with the engine and/or fridge running or just sat with everything turned off? I'll measure tomorrow

Old tony, I'll give it a try tomorrow as well

Click to expand...

Voltages will vary. With the engine running, the alternator will pump out somewhere between 14.1V and 14.7V - supposed to be 14.4V but within the ballpark is okay (and 14.1V is what mine does just after starting, then settles at about 14.3 after a while). At the other end of the cable you'll see 14.x volts MINUS the drop induced by the cable. Don't bother trying to measure it with the engine running, it's too dynamic.

Turn everything off and let the main battery sit for an hour quiet (disconnect the aux battery). Measure the main battery, then measure the voltage at the other end of the cable - this will give you an idea of how much voltage drop you have over the length of cable. Any more than about a volt and your cable is too small. Ideally you want no more than about half a volt drop - and at 14.4V of alternator output less 0.5V of line drop you get 13.9V which is JUST over the absolute minimum charge voltage.

Hope that helps.