Thread: Traxide vs. Redarc

Hi Scott and most batteries, regardless of the type of isolator, will be at different voltage levels, when driving around town.


With conventional isolators, the auxiliary battery can be fully charged and sitting at 12.7v, but because of say lots of short drives, the cranking battery can be at 12.2v, a common found voltage level when doing short drives.


With my isolators, it is still common to have the Auxiliary settle at a higher voltage than the Cranking battery, after lots of short drive.


In this type of situation, because the auxiliary battery is in a higher state of charge, it will VERY slowly back discharge and eventually equalise with the cranking battery and this will take anything up to 24 hours.


But if the vehicle is doing a lot of long drive times, after starting the motor, the as you say, they are both likely to be at the same charge level and voltage.


I am currently using my RR for some tests. My RR is not used very much, and when I went to install a new version of the DT90 in my RR, after sitting for 3 days, the cranking battery was at 11.84v when I opened the door.


Opening the door on a D3, D4, RRS and an RR, usually causes a voltage drop in the cranking battery and the amount of voltage drop depends on the charge state and condition of the cranking battery


I fitted the new isolator and did a bit of driving of about 90 minutes and then didn’t use it again for 3 days, but this time it was at 12.25v when I opened the door.


It was driven for about 2 hours, 6 days ago, and I am waiting to see what the voltage will be tomorrow, after leaving it unused for 7 days.


I am actually testing both the new DT90 and a new 65Ah Lead Crystal battery.


See how it goes in the morning!

Originally Posted by roverrescue

Tim
Add another one to your list of "four" or whatever isolaters out of 4000 that were replaced
I put an SC80 into a friends 80 series a few years ago
All good initially but after a bit of hard starting (likely insufficient driving) and me on leave
she went to an auto elec who hacked your sc80 out and put a redarc in - which fixed her low start voltage after not driving issue????

Anyway I never got the unit back to send back to you to check if it was faulty.

Anyways add it to your list????

To be honest if I was installing a VSR I would choose one with terminal lugs on the unit for
Wiring purposes.

But Me I'm happy with manual switches a voltmeter and a brain.

S

given the lack of troubleshooting/information, i'm not sure how you can say its faulty.

Originally Posted by LRD414

I must admit I don't understand how the reverse charging from aux to cranking battery works with the SC80 when the voltage is above cutoff and isolator open. Aren't the batteries sitting at a single voltage in that case, so no flow of current?

Scott

Hmmm same.
Assuming sat idle, engine not running, connected together above isolation voltage, they should be equal. That's just how it works - voltage will flow to level itself.
Now when I start it, does the isolator split them? Maybe? Even so, how much current is used to start the engine that would be consumed by the starter?
850CCA max, say 3 seconds cranking?
3/60/60 * 850 = 0.71amp hour capacity used? Seems really low I admit but I can't see the issue with this calc.

So I've used under an amp capacity starting it?
Charging should direct equal flow to both once running as I understand the isolator is capable of more than enough current flow to the secondary.

So I can't understand how there can be a great disparity. Yes if they were heavily discharged then I can see how they could take a while to stabilise.

If the starting and auxiliary batteries are different types - maybe a starting battery and a secondary AGM - they will also charge and discharge at different rates. AGMs discharge slowly, which is why they are good for running a fridge. Starting batteries operate faster, to give a big burst to start an engine. So it's not surprising if they show different states.

Hi Jeffster and there is a lot more to it than that.


There is not only the energy used to crank the motor, but in the case of a D3 and 2.7L D4, the alternator does not start charging for exactly 30 seconds after the motor is started, every thing is running off the cranking battery ( and the auxiliary when one of my isolators is in use ).


On D4s, this can be up to a few minutes before the alternator starts charging.


Then there is the energy lost at the last time you turned the motor off because it takes approximately 3 minutes for the computers to shut down. This one can be timed by watching the PARK BRAKE light on the dash.


This remains on until the Shut-Down sequence is finished, and is done so so that you do not disconnect the battery before the Shut-Down sequence is finished.


All this used energy has to be replaced and it does not happen in an instant. It takes at least 10 minutes driving just to replace the energy used by the starter motor and starter solenoid.


BTW, my isolators rarely shutdown during starting, because they are designed to tolerate a voltage drop below the cutout level for 16 seconds.

Originally Posted by DiscoMick

If the starting and auxiliary batteries are different types - maybe a starting battery and a secondary AGM - they will also charge and discharge at different rates. AGMs discharge slowly, which is why they are good for running a fridge. Starting batteries operate faster, to give a big burst to start an engine. So it's not surprising if they show different states.

I would argue this is not correct sorry. An AGM is a more stable design and tolerates heavy discharging, plus can accept higher inrush charging currents and discharge currents. After all, they can deliver 850CCA and more so they are more than capable of high output.
Any battery will discharge in line with its capacity. Two different type 90ah batteries outputting the same current will discharge at the same rate. An AGM will tolerate going to a lower voltage without damage and thus can deliver effectively more 'juice' without being damaged. This is why you're right, AGM is great for a fridge. They're also great for cranking, just come at a price premium which on most cars is not good value or necessary.

My understand is that cranking batteries are actually slower to charge than an AGM as AGMs are capable of higher amperage. Yes if you have different types of batteries, there could be times when you have disparity, but that should still only really be when they've been isolated from each other.

Originally Posted by DiscoJeffster

Yes if you have different types of batteries, there could be times when you have disparity, but that should still only really be when they've been isolated from each other.

Hi again Jeffster and there is more to it than that.


For example, in a D4, the auxiliary battery is nearly twice the cable distance from the starter motor and because of the voltage drop high currents cause, the cranking battery will still supply far more of the energy for starting than the auxiliary battery will.


In a D3 the cable distance is much greater again so the auxiliary battery will supply even less.


Then you get the flip side.


Because an Optima is a rapid charge battery, it will charge at a much faster rate than the cranking battery will, even when the cranking battery is another AGM.


This is because the currents used to charge batteries is a fraction of the high current used to start the motor. As above, during starting, these high current cause a huge voltage drop.


While charging, even with the high current alternators in a D4, the current while charging is much lower and this leads to a much small voltage drop. Hence the higher charge capability of the Optima is exploited.


So after a start and a short drive, the Optima is most likely going to be in a higher state of charge and this occurs without the batteries ever being isolated.

Ok, but do we agree that two batteries linked together will not stay with a voltage disparity and will level each other by one discharging to the other until they are at the same voltage? If not my faith in science is lost. For example, when parked after a drive.