Current sensing Variable Voltage alternators in NW...

[Dion]

I wonder what it is for on my NW too. If the auxiliary battery is earthed straight to the chassis it may negate the action of the inductive loop and whatever it is meant to do.
Peter

Nah current still flows through it. Easier to put the loop over the negative than the positive I suspect. They both read the same

[likatiger]

Thanks again Paul for the updated info.

Seems that these smart alternators have opened a can of electrical worms when it comes to dual batt systems for the later models.

My plan is to proceed with the install, try some monitoring and see how it pans out, not very scientific I know.

Cheers
Larry

Oh! you are so right about the info and knowledge gained from the forum, it's awsome.

[pauld]

I agree with your plan

[cyclopsoz]

I have an NW and switching between batteries with my sidewinder meters shows no difference between the aux and main whether accelerating or idle??

more humbug from ARB

pete

[pauld]

Correct no difference between them, but is your voltage dropping when accelerating?

[cyclopsoz]

No drop

[pauld]

would appear you do not have a 'smart alternator' then............................. are we looking at something that has come into the NW but was not there at the start...... Sounds like your lucky.

[pauld]

so what is your voltage?

[Morville]

My point was if the inductive loop on the earth terminal of the main battery is in some way part of the variable voltage "smart alternator" system and current to and from an auxiliary does not go through the inductive loop it may affect charging of the auxiliary battery. Should the auxiliary battery be earthed to the main battery earth terminal so all the current to and from both batteries goes through the inductive loop?
These are just my thoughts and someone more expert than me may be able to provide an answer.
Peter

[pauld]

Definitely a good question Peter fairly complex to answer, lots of factors, I am intrigued by cyclopsoz who has consistent voltage...

[Dion]

My point was if the inductive loop on the earth terminal of the main battery is in some way part of the variable voltage "smart alternator" system and current to and from an auxiliary does not go through the inductive loop it may affect charging of the auxiliary battery. Should the auxiliary battery be earthed to the main battery earth terminal so all the current to and from both batteries goes through the inductive loop?
These are just my thoughts and someone more expert than me may be able to provide an answer.
Peter

Oh sorry gotcha Peter, see what you're saying. Would be a good idea.
You could also just run the second cable through the loop too (i.e. from second battery to earth point, but run it through the loop) which would achieve the same effect as the loop will "add" the current flows in each cable. Just make sure both cables are pointing the same way, so to speak (that is, they are both earthed on the same 'side' of the loop).

[NWGLX]

would appear you do not have a 'smart alternator' then............................. are we looking at something that has come into the NW but was not there at the start...... Sounds like your lucky.

I have an NW and put the battery system that I took out of my NS into this new one. I use a Redarc isolator and a 100 amp AGM mounted in the well where I removed the foldown rear seats. I had it located here in the NS as well. After reading the posts I got concerned that it might not charge properly and I am about to embark on 3 month trip around Oz. I asked the question of of a large Mitsubishi dealer here and was told that as far as they are concerned the alternator has not changed since the NM model. I havent measured voltages anywhere but am interested if anyone has any other information. I was told however that a lot of cars have smart alternators and at the dealership, if they have flat batteries they wont charge if they leave them idling so turn the lights on. Suppose if I have any problem I can just drive with the lights on.

[gaudough]

Voltage Test Results

Hi all, being an Electrical Engineer with a new NW and about to install an aux battery I got my voltmeter out and have done some testing. It is a little odd how it all works but this is what I have found.

Started the car 14.2V, drove 5kms with Air con on and the volts would drop to 13.5 under any acceleration or cruising and go back up to 14 or so on deceleration.

Stopped for 15mins at Bunnings and when I got back in and started driving I turned the Air con off, the volts slowly dropped to 12.1 where it would then cycle up to 12.9 for a few kms then back to 12.1. If I put the parkers on it went back to 13.5, air con on back to 13.5.

I think the Alternator knows via the other ECU's if the Air con or parkers are on but when I selected the rear window demister the volts just dropped a further 0.1 to 12.0, the alternator did not pick up the load so I assume the alternator ECU is told of the Air con or parkers being used and its not just sensing a lower voltage to start charging at a higher rate.
Drove 100kms to Brisbane yesterday without a restart and the voltage seemed to stay at 14.2 the whole way. However today I did the same trip to Brisbane but stopped for fuel 2kms from home in the morning and it did the up down cycling bit.

I don't think its temp related, its definately throttle related and if you are using cruise control and you overrun downhills it does not come up to 14V but cancelling the cruise does it straight away. So its not really that smart, over run or no throttle is the same thing as far as engine load is concerned but the Jap engineers havent taken this into account.

So the problem I see is this.
I was going to use the Redarc SBI12 solenoid but it energises at 13.2 and drops out at 12.7. If my aux batt is a bit low or I have a load on it, I hope it will be enough for the alternator to sense this and keep the volts at 13.5 or some other value. Once its charged I dont really care if it drops a little but if it drops below 12.7 the Redarc will drop out and wont re engage unless I have the Air con on or parkers on etc.

I will definatley have to connect the aux battery earth to the main battery terminal to ensure the current shunt on the negative lead sees the load from the second battery. This could also be why after 2 days of ownership and a few short trips with no air con running the battery was almost too flat to start the car.

I would love to know what the alternator ECU algorithm is so we can work out how to trick it to do what I want.

The workshop manual for my previous 4WD (2003 Discovery) went into great detail to explain how each input and output of each ECU was used and what to expect under normal and abnormal conditions. I Would love to hear from a MMC auto electrician that has the workshop manual that could explain all of this to us.

[pauld]

It is perplexing how the voltage could drop as low as 12V, the battery should be keeping it up above that.... Where was the voltage being measured? The Aux battery should help to keep that up once installed.
My redarc isolator cuts out at 12.5, I am almost certain that was the spec a few years ago when I bought it but Redarc now say 12.7 as you say, I did find 1 reference to 12.5 on their site do would seem they have changed it....
If your battery seems to be cranking the car slowly maybe you should take it back

[securegsm]

Low beam lights on should keep alternator at a higher voltage, 13.5v at least is my guess. It would be silly otherwise. Would you be able to confirm when/if possible?

...If I put the parkers on it went back to 13.5, air con on back to 13.5...