Thread: Aux battery running down too quickly

Your dash cam does actually use a fair bit of power. When u had my BlackVue permanently wired in to the aux battery of the D2 that I sold, I had to wire in a permanently mount a solar panel to the roof rack. I was never able to keep my aux battery charged. I don’t know how much the BlackVue used, but from what you’ve mentioned it seems about right

Hi Redtail, going on the first graph, it looks like you have the USI-160 In-Cab module set to STORAGE mode ( toggle switch set towards the LED ) and this will dramatically reduce your runtime before ABG-25 shuts down.

Try running the USI-160 in SHEARED mode ( toggle switch set AWAY from the LED ).

This should near double your runtime.

Originally Posted by drivesafe

Hi Redtail, going on the first graph, it looks like you have the USI-160 In-Cab module set to STORAGE mode ( toggle switch set towards the LED ) and this will dramatically reduce your runtime before ABG-25 shuts down.

Try running the USI-160 in SHEARED mode ( toggle switch set AWAY from the LED ).

This should near double your runtime.

Won’t that flatten his starting battery?

Originally Posted by John_D4

Won’t that flatten his starting battery?

Hi John and NO.

My SC80, DT90 and USI.160 isolators, when operated in SHARED Mode, separate and isolate the CRANKING battery when the voltage at all the batteries is at 12.0v.

At 12.0v, your cranking battery still has 50% of its capacity available to start your motor.

Your CCA rating is based on a battery at 40% of its capacity, a 0 degrees, and you can start most modern vehicle motors with a cranking battery as low as 20%, thats 11.6v.

So at 12.0v or 50% SoC, there is still plenty in reserve, to be able to start your motor.

But there is more to it than just starting your motor.

While my isolators have been operating in this manor for over 30 years, since the introduction of SMART alternators in 2004 ( the D3 was one of the first vehicles to have a SMART alternator function ), my isolators have proven to be far better suited to these new SMART alternator operations, than any other form of auxiliary charging.

When the cranking battery is NOT used, with any system, not just one of mine, once the vehicle’s BMS decides the cranking battery is fully charged, the alternator’s operating voltage is lowered.
In this situation, because the BMS does not monitor the auxiliary battery ( or house batteries if they are connected to the system ), if the cranking battery is in a high state of charge, the alternator voltage drops shortly after the motor is started.

This means if the auxiliary battery ( or house battery ) is low, you will need to do some very long driving times to get the auxiliary battery back anywhere near to a fully charged state.
This is a common result when using one of my isolators when set to STORAGE Mode and the same result when using a standard VSR type isolators.

When you go camping and have my isolators set to SHEAED Mode, you not have more additional battery capacity available to run your accessories, allowing up to twice the operating time that any other system can provide.

But you are also setting up the cranking battery so that when you start your motor, the BMS will see the cranking battery is in need of a charge, and as such, the BMS will now run the alternator at a higher voltage for a longer time, to try to fully recharge the cranking battery as quickly as possible.

This higher operating voltage is also applied to the auxiliary battery and because these vehicles have such large alternators, not only is the cranking battery charged at a very fast rate, but so is the auxiliary battery.

So I hope this helps to explain why my isolators should be set to SHARED Mode, especially when on a trip.

There is heaps more info relating to this operation and its benefits and I can cover more if required.

Originally Posted by John_D4

Your dash cam does actually use a fair bit of power. When u had my BlackVue permanently wired in to the aux battery of the D2 that I sold, I had to wire in a permanently mount a solar panel to the roof rack. I was never able to keep my aux battery charged. I don’t know how much the BlackVue used, but from what you’ve mentioned it seems about right

They are thirsty.

I have one on my primary battery, and a LVC on it. It runs about 2 days before cutting out dragging a fully charged battery down to 12.2v in that time.

Currently it sits on the charger awaiting reassembly next week

Okay, more data and observations.


In-cab module is definitely in SHARED mode. Confirmed by switch position and LED fading in and out as described.


Fridge removed, dashcam seems fine.
The fridge is a 40L Engel Combo, working as a fridge only, no freezer and the divider removed, set to 3 degrees.
Fridge seems to be the cuplrit!


Here's the next few days graphs from the battery monitoring app:
The rest of Sunday.
Drive about an hour home, back on charge overnight.
Fridge removed. Dashcam on.
Graph 210314.png
Monday
On charge overnight
Parked all day at home
Graph 210315.png
Tuesday 16/3
On charge overnight
Up early, pool, home, work (parked all day) home
Graph 210316.png
Wednesday 17/3
Parked all day at home
Drop at around 5pm when I open the door to check batteries.
No charge overnight
Graph 210317.png
Thursday 18/3
Same routine as Tuesday
Pool, home, work, home
No charge overnight
Graph 210318.png
Friday 19/3
Home all day
Dropped a Projecta 12V/5W solar panel on the dashboard around 7.15am to see what it would do.
Looks like the panel had a very minor lift in the Crank battery.
Graph 210319.png

Anyway, it looks like the fridge is the issue, unless the D34 battery is on its way out?

Hi RedTail, and there is something not right about your operation.

The batteries are being separated at about 12.6v.

In SHARED Mode, the batteries should not separate ( the USI-160 should not turn off ) till the batteries are at 12.0v.

Can you tell me where the thin GREY earth wire is connected to?

Sorted!


A quick call to Tim on Saturday morning confirmed that it was the GREEN earth wire I was after, my USI-160 being an older model.
I extended it and bolted it to the earth plate near the battery.

Threw the fridge in the back with a couple of bottles of vino just to give it something to cool, starting from an ambient temp of about 27 degrees, setting it to 3 degrees. (I like my whites chilled!)
Left it in the car all weekend in pretty much full sun. Temps in Perth were in the high 30's.

The graph tells the story …
Sunday:
Graph 20210321.png
Both CRANK and AUX running down nice and slow.
Power meter showed the fridge drawing a solid 2.8A most of the day, dropping to 0.15A when the sun went down.

Finally, about 1.30 this morning, it all shut off as it should.

Graph 20210322.png

So, instead of getting maybe a day out of it, that was more like 3 days with very little driving on Sat morning and the one short trip on Sunday.

Thanks, Tim, for your excellent and patient advice!