Flat battery - dual battery system?

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Originally Posted by nw393y

Do you have a multi-meter? If so, leave both the batteries in and disconnect one of terminals from the auxillary battery and put your mm in line to test if there's any current draw when the vehicle is not running. You may have some sort of current leak...

Nathan

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Yep, got that sort of stuff - I'm an electronics tech. I've done that. The P38A draws quite a bit of current until the BECM goes to sleep, then drops back to about 50 mA. It is going to sleep as I've monitored it. Of course, it is possible that local RF interference is waking the BECM.

If needs be, I'll connect a data recorder across a current shunt and monitor the current draw over a 24 hour period. I've got both paper chart recorders and electronic data loggers that could do that.

I've also disconnected electrical ancillaries from the main battery to be sure they aren't causing the problem.

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Originally Posted by 81stubee

hmmmmm.... interesting.

Mine is all melted and sides have split, from the heat in the engine bay i guess, thats why i don't think it will be going back in. I don't have one here, but could you not put it on a variable power supply and see when the changeover occurs? This is how you were meant to test the dual battery kit from Jaycar that I built once upon a time. I was under the impression that they are a oneway flow (charging only).

Stu

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If needs be, I will. I have a variable power supply. I also built the Electronics Australia dual battery charger (the Jaycar kit to which you refer). It's on the shelf in my electronics workshop.

Hi Ron and thanks for not trying dump the SC40 it the #### but I don’t mind if people mention that they have my gear installed as it makes it easier to sort out the problem.

Because of where you are driving, I don’t think you are charging your batteries enough while driving.

That area is all 80kph between your place and Springwood so you may not be running at high enough revs, long enough to fully charge the batteries and slowly, over time, you are gradually discharging the batteries.

That’s my excuse and I’m sticking to it.

Seriously, I think your problem is the short drives. Try putting your battery charger on as much as possible, for a week and see if this solves the problem.

Also, see if your alternator is working properly, it just seems strange that everything worked well for a year and then you get a problem.

The SC40 is not going to cause the sort of problem you have and I would like to get your problem solved so keep me informed of any findings.

Cheers, Tim.

PS. your 100 amp Alternator is heaps big enough to run everything and charge your batteries.

battery split and leaking? did it smell like seaweed? sounds like overcharging

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Originally Posted by drivesafe

Hi Ron and thanks for not trying dump the SC40 it the #### but I don’t mind if people mention that they have my gear installed as it makes it easier to sort out the problem.

Because of where you are driving, I don’t think you are charging your batteries enough while driving.

That area is all 80kph between your place and Springwood so you may not be running at high enough revs, long enough to fully charge the batteries and slowly, over time, you are gradually discharging the batteries.

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I think that was the problem I was having recently, just not driving enough (no SC40 involved) to fully charge the auxillary batteries. I've since got a CTEK charger and whack it on charge once a month overnight and it's never missed a beat.

Nathan

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Originally Posted by Mudsloth

battery split and leaking? did it smell like seaweed? sounds like overcharging

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No, the battery is fine in that respect.

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Originally Posted by drivesafe

Hi Ron and thanks for not trying dump the SC40 it the #### but I don’t mind if people mention that they have my gear installed as it makes it easier to sort out the problem.

Because of where you are driving, I don’t think you are charging your batteries enough while driving.

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Tim, I was thinking along the lines of the second battery not charging sufficiently owing to the long cable run and consequent voltage drop resulting in lower charge voltage at the battery terminals.

My thoughts are that with a lower terminal voltage on the second battery, perhaps it is draining the main battery. The second battery is an AGM and the main battery is a lead-calcium.

On one occasion about two weeks ago, I went out to the car 4 hours after driving home from Springwood (at 7am so the lights weren't on). When I turned the ignition on, there wasn't even enough power to operate the radio - it kept muting. It didn't dawn on me what the problem was until I turned the ignition to start the car. I thought it was the RDS system blanking the radio.

I think I'll double up on the supply cable. Also, I haven't done your other recommendation of running a separate negative cable. I've been slack and it might have now returned to bite me! I've been relying on the body to provide the return path. I think I had better run the negative cable at the same time.

It would be interesting to get a set of long leads for my DVM and check the potential difference between the negative terminals on each battery when the system is charging - and, in fact, the PD between the positive terminals.

These are the other reasons I haven't blamed the SC40. There are two many variables that need to be checked first. What are the voltages at which the SC40 connects and isolates the two batteries?

I assume that, when charging, there is a certain voltage that must be reached by the main battery before the second battery is connected. Equally, I assume that the second battery will be isolated once it falls below a certain terminal voltage. However, if the main battery falls below a certain voltage, are the batteries isolated?

Regards

Hi Ron, cut-in voltage is 13.2, so pretty well straight after you start the motor, the SC40 will cut in.

Cut-out is at 12.0 volts and in a normal situation, with two fully charged batteries, it will take anything up to a month or more before the batteries get down to 12.0 volts.

Although having a low Auxiliary battery will drain the cranking battery but this will take hours to days to pull the cranking battery down to the auxiliary battery’s voltage and if the auxiliary battery is below 12.0 volts, the SC40 will cut out when the cranking battery gets to 12.0 volts and at 12.0 volts, you should still have heaps of power left in the cranking battery to easily start the motor, even on the coldest morning.

I still suspect the continual short drives are the problem, this is what I call the Shopping Trolley Syndrome and is a common problem and one of the long term effects of Shopping Trolley Syndrome is that your cranking battery eventually holds less and less charge, which may explain why everything seemed to be working fine for a year and now the system is starting to show the results of Shopping Trolley Syndrome.

Again, try putting a battery charger on your batteries every opportunity you get for a week and see if this fixes the problem.

If your battery charger is big enough, ( 4 amps or more ) connect it to your cranking battery and it will eventually charge up both batteries, via the SC40.

Cheers and keep us informed, Tim.

Thanks Tim.

My charger is a 16A 4-stage unit.

I've been thinking of adding an expanded scale voltmeter. Maybe I had better.

I'll keep you posted.

Interesting tale Ron.

I've run an SC40 in the Disco for about 3 years now - for weeks at a time the the wife just drives it about 5km to her work and back.
Never had a problem with a flat starting battery. Both batteries are Exide Extreme N55s - nothing flash.

The fact that the problem goes away when you disconnect the SC40 "circuit" seems to point to a problem on that side of things.

Have you tried leaving the SC40 connected to your main battery, but just disconnecting the second battery from the SC40 output ?
That would isolate it to being a problem with the SC40 itself or something with the second battery, or circuits running off it.

Mind you the SC40 seems pretty bulletproof so wouldn't expect an issue there.

Hi again Ron, I just read waynep’s post and that reminded me to ask you to check your voltage at the cranking battery after you have driven the RR for at least 15 minutes.

Say, next time you go to work, pull up and leave the motor running.

Pop the bonnet and see what voltage you have at the battery.

Measure at the battery terminals, not off an earth point in the engine bay.

Some of the Discos run at 14.7 volts and this really makes a difference at keeping the battery in a better state of charge.

Your RR may be running at a much lower voltage and this can easily cause the sort of problem you are having.

Just another suggestion.