Dual Battery Charging Behaviour

Quote:

---

Originally Posted by drivesafe

If you have not driven your D4 yet, leave it for another day or two if you can.

I would like to see what happens when the isolator turns off.

---

Thanks Tim,

I’ve had it on charge for another 24 hours, both batteries settling to about 12.8V resting this morning after a couple of hours off. I don’t need the car for another week, so can leave it till the SC80 isolates below 12V, which will probably be in about 5 days. I’ll come back to you after then how they behave independently.

Just a few notes on my configuration and potential power draw from stock, I have Llams (set to neutral), Tow-Pro Elite (but no trailer connected), a UHF unit (turned off), linear electronic design LED adaptor module (turned off), Traxide SC80 and ABG25, a BM2 on each battery, and an iPod in the glovebox USB. Nothing in any of the 12V points for the moment (normally a 45l fridge in the rear Traxide outlet but currently unplugged for this test).

Driving habits a 20 min commute, avoiding the local shopping run. A monthly CTEK charge at the rear Anderson.

I still don’t understand why the batteries show different voltages while linked.

Cheers, Chris

Quote:

---

Originally Posted by winglen

Thanks Tim,

I’ve had it on charge for another 24 hours, both batteries settling to about 12.8V resting this morning after a couple of hours off. I don’t need the car for another week, so can leave it till the SC80 isolates below 12V, which will probably be in about 5 days. I’ll come back to you after then how they behave independently.

Just a few notes on my configuration and potential power draw from stock, I have Llams (set to neutral), Tow-Pro Elite (but no trailer connected), a UHF unit (turned off), linear electronic design LED adaptor module (turned off), Traxide SC80 and ABG25, a BM2 on each battery, and an iPod in the glovebox USB. Nothing in any of the 12V points for the moment (normally a 45l fridge in the rear Traxide outlet but currently unplugged for this test).

Driving habits a 20 min commute, avoiding the local shopping run. A monthly CTEK charge at the rear Anderson.

I still don’t understand why the batteries show different voltages while linked.

Cheers, Chris

---

When linked they should be the same, the more current (amps) that flows through a bad connection the worse it'll be.

If you have a aux battery needing a charge. It'll pull amps. If you have an issue in your circuit. You'll have voltage drop, which is the difference between the two points.

I've got the usi160 system and I can run the aux down to 11.v but as soon as I start the car they equalise. Because the wiring and isolator are a match to the current.

A loose terminal or battery terminal could be all your issue is. Voltage drop also means the aux charging time will be longer

I agree Josh. These are simple parallel batteries in circuit. They can’t show a different voltage potential when they’re connected together when the flow of current is so low as when the vehicle is off.

If the aux discharges faster than the starter, assuming the Traxide is connecting them together, then the starter will flow to the aux to compensate. It’s simple electron flow and potential difference won’t be maintained.

I’d be inclined to suggest the BMS monitors aren’t as accurate as they could be. The only time I’d expect significantly different voltages is if they’re not connected to each other or the current draw is so large that they can’t stabilise between each other. Otherwise, the voltage eg potential should be the same, even if their actual capacities aren’t equivalent. That’s my understanding of electronics over time. Eg you can have a dud aux but when it’s connected in parallel to a good starter, it’ll show good voltage measured in circuit, but will not provide any actual amperage capacity to the circuit - where the starter provides it all. The only way to determine that is isolation of each battery to measure health and capacity.

Quote:

---

Originally Posted by josh.huber

A loose terminal or battery terminal could be all your issue is. Voltage drop also means the aux charging time will be longer

---

Quote:

---

Originally Posted by DiscoJeffster

I agree Josh. These are simple parallel batteries in circuit. They can’t show a different voltage potential when they’re connected together when the flow of current is so low as when the vehicle is off.

---

Thanks Josh and Jeff, right on the money. I knew the terminals were fine a couple of months ago when I put in the BM2s. Double checked again just now and found the chassis earth only finger tight. Nipped up and now voltages match!

I love this forum and was a significant factor in buying the brand when compared to the macho and fractious competition. Proven again.

https://uploads.tapatalk-cdn.com/202...d86c5abaad.jpg
https://uploads.tapatalk-cdn.com/202...42cda935c9.png

That’s awesome buddy. That makes so much sense. Good on you you continuing to investigate!

Quote:

---

Originally Posted by winglen

Thanks Josh and Jeff, right on the money. I knew the terminals were fine a couple of months ago when I put in the BM2s. Double checked again just now and found the chassis earth only finger tight. Nipped up and now voltages match!

I love this forum and was a significant factor in buying the brand when compared to the macho and fractious competition. Proven again.

https://uploads.tapatalk-cdn.com/202...d86c5abaad.jpg

---

Good find and those nuts are crap.

They are good till you undo them and then no matter how tightly you secure them, they tend to do exactly what you have found, them become loose.

I found these were a problem many years ago and supply Nylock locknuts with my kits to replace those things.

It would pay you to get some 6M Nylock locknuts and replace any of those you have reused.

Quote:

---

Originally Posted by drivesafe

Good find and those nuts are crap.

It would pay you to get some 6M Nylock locknuts and replace any of those you have reused.

---

Will do! Certainly before I traverse most of the corrugations that WA and NT have to offer next year in my imagined post-COVID touring nirvana…

And thanks for your constant sage advice Tim. Legend how you give on here. [emoji122]

A bit off topic,but may help others, question for Tim,with DT-90,if for whatever reason i need to isolate the two batteries,but dont want to start the engine and change the toggle switch,etc,and go into storage mode,will a switch in the thin earth wire do this,same as it does for the SC80?

Will it also drop off the auxillary power to the accessories,while the switch in the thin earth wire is in the off position?

TIA.

Quote:

---

Originally Posted by scarry

A bit off topic,but may help others, question for Tim,with DT-90,if for whatever reason i need to isolate the two batteries,but dont want to start the engine and change the toggle switch,etc,and go into storage mode,will a switch in the thin earth wire do this,same as it does for the SC80?

Will it also drop off the auxillary power to the accessories,while the switch in the thin earth wire is in the off position?

TIA.

---

Hi Paul and yes, a switch in the earth lead will totally shut the DT90 down.

Note, after turning the switch back on, just like the SC80, you will need to start your motor to get the DT90 to turn on again.

Quote:

---

Originally Posted by drivesafe

If you have not driven your D4 yet, leave it for another day or two if you can.

I suspect your batteries need a few more charge cycles as they seem to be discharging a bit quickly.

The isolator will draw power and is likely the cause of the voltage drop, but yours is dropping too quickly for supposedly full charged batteries.

---

Tim,

Since sorting the loose aux earth point so the batteries are linked and both BM2s giving identical readings, I’ve been doing a reconditioning charge for the last week, 12 hours on and off each day. Settled SOC after a couple of hours is about 12.8V.

Have also done the cranking battery load test (aux disconnected, ignition and headlights on) for 5 minutes. Dips below 12 for a few seconds then settles unmoving on 12.13V, screenshot below. I assume from this the cranking battery health is ok.

My last question relates to the whether I have a problem with rate of discharge, about 0.10V per day. My configuration is at #11 of this thread, and after a full charge, the batteries isolate after a week.

https://uploads.tapatalk-cdn.com/202...21be30ae6e.jpg

https://uploads.tapatalk-cdn.com/202...a66c5abfbf.jpg