Thread: Discovery 4 "smart" charging system.

Originally Posted by GIL

Hi Tim,
Thanks for your input.



So to summarise.
If by disconnecting my brake controller I have achieved a normal behaviour of the system, should I change the brake controllers power supply source to an ignition switched relay?

Regards
GIL

If you do, and you don't have a cubby cool box, you can use Central Junction Box fuse 16P as it is ignition powered. See attached extracted page from the D4 Electrical Wiring Diagrams Manual. My preferred method of tapping into an unused powered feed (i.e. one that is powered - by the ignition in this case - but does not have a fuse in place) is to use a piggy back dual fuse holder with the original circuit's fuse removed, so that only the new circuit that you need is powered.

Brake controllers need a lot of amperage to drive the electric brakes (assuming it’s an electric brake controller) which is why the instructions will state to connect it with decent cable and individually fused to the battery. Also if it’s like mine (Redarc tow pro) it calibrates itself each time it loses power and won’t work correctly until recalibrated, which can be annoying, albeit briefly.

Connect an ammeter in-line with the brake controller and measure it’s actual draw at different times, or alternatively reconnect the brake controller and redo the experiment.
—-
What is the model of brake controller and have you checked to see if it’s wired up correctly? I bet it’s got an ignition trigger wire to help put it to sleep that’s connected to battery permanently that’s causing your issue. Installer couldn’t find a trigger so wired it permanently on.

To do this I need access to a tong (also called clamp) tester which will reliably measure down to a resolution of 1mA. I found this on fleabay:

That should work ok, I have a similar unit. An old trick if you are chasing very low currents, providing there is enough slack in the wiring, is to pass the conductor through the jaws of the clamp meter TWICE. Then just halve what ever reading that you observe.

Reading your results and the testing you are carrying out, I’m arriving at the result that you are chasing a non-existent issue.

The BMS will not discharge to 80% whilst the vehicle is off.
The vehicle slowly lowering voltage is a result of door opening and closing whilst parked up - normal, as it wakes up expecting to be started shortly after opening. The BMS will protect the vehicle to a certain extent, warning you when you’re getting close to low.

These vehicles will start down to around 11.8v.
When camping for extended periods use a solar panel either into the vehicle or by keeping the van linked to share its charge (depends on your system and how connected).

I think you may be chasing ghosts.

I'm not quite understanding something here,

Why does the battery management system "try to discharge the batteries"?

This doesn't make any sense to me at all. What software commands are doing this and for what reason?

These are the kinds of things in modern systems that concern me and turn me away from purchasing latest products.

I don't want to have to be concerned about this type of stuff when I'm doing my bush pilgrimages each year where I just cannot afford a purposely flattened battery.

This is why I'm thinking of "downgrading" to something like a perentie. Sensibility says do it.

Originally Posted by ramblingboy42

This is why I'm thinking of "downgrading" to something like a perentie. Sensibility says do it.

I wouldn't discount a horse and cart....

Originally Posted by ramblingboy42

I'm not quite understanding something here,

Why does the battery management system "try to discharge the batteries"?

This doesn't make any sense to me at all. What software commands are doing this and for what reason?

These are the kinds of things in modern systems that concern me and turn me away from purchasing latest products.

I don't want to have to be concerned about this type of stuff when I'm doing my bush pilgrimages each year where I just cannot afford a purposely flattened battery.

This is why I'm thinking of "downgrading" to something like a perentie. Sensibility says do it.

Basically, it is a means of testing as to whether the battery is in a good condition, or needs replacing.

But, I am yet to see a post or report, where this test deemed the battery needed replacing, and indicated in some way that this was needed.

Hi Folks,
Thanks all for your insights and input. Hopefully we are all learning about our amazing vehicle.

DieselLSE
Thank you for the info about fuse 16P in CJB. This could work well as the thermal circuit breaker for the brake controller is mounted internally on the front wall of the start battery box.

DiscoJeffster
My brake controller is a Tekonsha Prodigy. I moved it from my old D2 onto the previously installed wiring for the controller (Redarc with the RED knob) the car had when I acquired it, which by the way was mounted INSIDE the cubby box. I checked the wiring install and it seemed to follow the recommended pattern. +12v direct from battery via thermal circuit breaker, ground, brake sense (from rear LHS light IIRC) and output to van brakes. This was also the installation I had in the D2 and which I ran for 10 odd years.

Old Farang
The cable I thought would be the easiest to measure the quiescent current drain on is the big battery to CJB one. As such there is neither the room or the flexibility to allow multiple wraps in the tester tong.
However this multiple wrap trick is good.

Tombie
The reason I started this investigation is that I was concerned at the (compared to my old D2) short time it took for the start battery to drop to the stage the car prompted for a start. I have 2 mates with D4's and both see similar behaviour so initially I thought this was normal. Both also tow vans. Anyway I started checking and also this post to canvas the knowledge and wisdom of the brains trust of AULRO.
I think the discussion in this thread proves the point of how good and sharing are the members.

Now that my brake controller seems to be a contributor my cars behaviour, I will see if I can mitigate its influence. eg relay fed power.
As to the other thoughts eg CCF yes I think it is chasing ghosts. The car does what I want it to do and I do not want to change for changes sake.
Your insights are always welcome and worthwhile. Thanks.


To all, thank you for the discussion.

I have a solo 100km round trip, maybe tomorrow, so I will get a chance to leave the brake controller disconnected and start the monitoring time again. I will report results.

Best Regards
GIL