Thread: BATTERY CHARGING in 4WDs–How to get it right - What do people reckon of?

For those who care, there is a really good response in the comments section. He pretty well picks the whole segment apart, pointing out the anomalies and inconsistencies. The writer has researched the subject really well, and includes links to his research. He also (right at the end) states that he is, in fact, an electrical engineer.
He also, (like many of us), has large reservations concerning the widespread use of DC-DC chargers, particularly when marketed as necessary items for dual battery systems.
As soon as I saw the headline for the video, my first thought was that Andrew may just shoot himself in the foot on this subject.

Originally Posted by donh54

For those who care, there is a really good response in the comments section. He pretty well picks the whole segment apart, pointing out the anomalies and inconsistencies. The writer has researched the subject really well, and includes links to his research. He also (right at the end) states that he is, in fact, an electrical engineer.
He also, (like many of us), has large reservations concerning the widespread use of DC-DC chargers, particularly when marketed as necessary items for dual battery systems.
As soon as I saw the headline for the video, my first thought was that Andrew may just shoot himself in the foot on this subject.

And shoot him self in the foot once again
Wait for Johntins to come out in his defence

Originally Posted by drivesafe

Hi DAMINK, I was not having a go at you, just at that idiot in the video.

Next, there is no charging system or isolator that first charges the cranking battery, then charges the auxiliary battery.

All batteries ar charged at the same time.

My isolator does infact charge one first then the other mate.
Here is a quote from a supplier of a similar product to mine.

"When the engine is started, the starting and auxiliary batteries are separated allowing only the starting battery to be charged. When the charge voltage reaches 13.3 volts the VSR engages allowing both starting and auxiliary batteries to be charged. "

Originally Posted by DAMINK

My isolator does infact charge one first then the other mate.
Here is a quote from a supplier of a similar product to mine.

"When the engine is started, the starting and auxiliary batteries are separated allowing only the starting battery to be charged. When the charge voltage reaches 13.3 volts the VSR engages allowing both starting and auxiliary batteries to be charged. "

generally. as soon as you start the car the alternator should be putting out 14.0-14.4volts, so the relay should engage/close straight away.

Originally Posted by Eevo

generally. as soon as you start the car the alternator should be putting out 14.0-14.4volts, so the relay should engage/close straight away.

Yes true. But the isolator reads the batteries charge not the alternators. The starting batteries charge and if that is below the threshold then it will take all the charge until the charge battery is full.
Then when the charge battery gets low again it will take all the charge and leave the second battery out of the loop.

Thats my understanding of the units and i thought that was why they call them isolators. Isolating your charging battery from the aux so that your charge battery will always be full regardless of your aux.

Originally Posted by DAMINK

My isolator does infact charge one first then the other mate.
Here is a quote from a supplier of a similar product to mine.

"When the engine is started, the starting and auxiliary batteries are separated allowing only the starting battery to be charged. When the charge voltage reaches 13.3 volts the VSR engages allowing both starting and auxiliary batteries to be charged. "

Hi again DAMINK, 20 to 25 years ago, if you had an old vehicle with a 45 amp alternator, and you had a near dead flat cranking battery, that only just got your motor running, then in this situation, the SMALL alternator would take a few minutes to get some charge back into the cranking battery.

But even in an extreme situation like this, within minutes of starting the motor, the voltage at the cranking battery would rise above 13.3v and your VSR would turn on.

The deliberately misleading ADVERTISING put out by your VSR's manufacturer, is nothing more than a play on words, to try to make out that their isolator does something special.

All isolators work this way and as all vehicles these days have alternators of 80+ amps, within SECONDS of the alternator spinning up, the voltage at your VSR ( and all others ) will be way in excess of what is needed to turn your isolator on.

Some isolators have a turn on delay, like mine. Mine have a 15 second turn on delay, to prevent oscillation as the alternator spins up.

Once again, that statement is nothing more than a deliberately misleading ADVERTISING STUNT.

BTW as to trickle charging. A few years back, a guy in the UK accidentally flattened his Optima D34 while on a long weekend camp in Scotland.

His D3 has a lot of monitoring gear installed and he posted up that when he was driving back to his home in England, he noted that his Optima was drawing as much as 97 amps. Thats some trickle charging.

The guy in the video is a moron and should be treated as such.

Originally Posted by drivesafe

But even in an extreme situation like this, within minutes of starting the motor, the voltage at the cranking battery would rise above 13.3v and your VSR would turn on.

So in the above example there was minutes where the isolator was doing its job.

Thats all i was trying to say mate. That they isolate the cranking battery to protect it from discharge. During start if the cranking battery is low it will charge first. Or if the battery is below a threshold the isolator will separate them.
I own a DISCO and up until yesterday had a bad starter motor. Dealt with it for years. Took often a couple of minutes to start the car as the starter would jump out. Draining the primary battery all the time.
I never tested this but assume the isolator stays off while my car is in this state. Only when charged does it charge the aux.

Also i was under the impression an alternator charge rate was determined by the engines revs? So at idle your alt will not put out as much? I could be wrong here but just something i recall.

For the record again i dont like the guy in this video nor subscribe to what he says generally.


As for it all being marketing... Im not so sure. I mean one could install an idiot switch to do the job and not bother with the isolator, but we all know how that will potentially work out.
So an isolator does its job to some extent as claimed.

Originally Posted by DAMINK

Also i was under the impression an alternator charge rate was determined by the engines revs? So at idle your alt will not put out as much? I could be wrong here but just something i recall.

Even at idle, modern alternators will easily charge both batteries.

For example, my isolators allow the use of up to 50% of the cranking battery and many people, while free camping, will idle their motors to put some charge back into BOTH batteries at the same time.

If your theory was correct, they could not charge both batteries, but would just simply put some charge into the cranking battery.

Even when starting a motor and letting it idle, because alternators are so big these days, the isolator will turn on within seconds of the motor being started.