Charging third battery via starter battery

[Aidan]

For a Cape York trip my father-in-law is planning on taking the
battery (120 Ah AGM) out of the camper trailer and mounting it in
the back of his Disco 4 so he has some extra capacity (he isn't
taking the camper on that leg of the trip).

He already has a dual battery setup under the hood, an Optima
Yellow Top with a Redarc VSR system. He has an Anderson at the
tailgate that is fed from his secondary battery, but the Anderson
inside the back of the Disco is designed to power the winch with
the car running, so comes off the starter battery.

He would like to charge the 3rd battery in the back of the car off
the Anderson.

There are 3 issues with this that I can see straight up

1. No VSR, so the AGM could drain the starter battery or prevent
it from being full charged

2. The AGM will be subjected to "high inrush currents" which some
believe can be harmful to normal (not hybrid) deep-cycle batteries

3. Variable voltage D4 regulator dropping back the voltage and so
not charging the third battery.

The first issue is not a big deal as long as he disconnects when he stops
for long periods?

If he doesn't have a VSR will that prevent the starter battery from being
correctly recharged?

The second issue I am less sure about. Is it true that most AGMs can,
roughly speaking, handle a charging current of equal magnitude to
their max discharge current? That inrush current will depend on how
depleted the battery is.

The third issue seems not to be such a problem as long as the loads
on the starter battery are terminated at the body of the vehicle and not
directly to the negative terminal of the battery. I believe this allows the
ECU to detect the load and so keep the alternator chugging along.

This is a temporary setup, for a short period of time. As long as no
lasting damage is done he is happy to just disconnect manually when
stopped.

I guess a DC DC charger would fix the first two problems, but as it is
likely to be a cheap 10A calibre, this would come at the expense of
recharge time.

If the biggest problem is high inrush currents, a self-resetting breaker
set to 30A might also do the trick?

Edit: Another option I forgot to canvas was using an inverter from
that Anderson outlet to power a Projecta 2100 charger that I already
own. This overcomes most of the problems above, typically inverters
have a low voltage cut out, and the current would be controlled by the
charger.

If I went this route what size inverter would I need (the Projecta is
listed as consuming 600W)? I guess I don't need a pure-sine wave inverter,
for this application, but it might be useful for other sensitive loads?

[alien]

Welcome to AULRO.
2 quick thoughts..
1/
How easy is it to swap the power feed for the existing anderson plug to the second battery instead of the starting one?
2/
As an option could you make a lead up?
Tempory mount a new anderson plug in the rear and run the cable out/under to the rear.
When the battery comes out of the camper plug the above lead to the exisiting anderson plug and the battery to the plug inside.
It's all charging as it does in the camper then and easily removed at home afterwards.

Cheers, Kyle.

[drivesafe]

Hi Aidan and welcome to AULRO.

First off, if the D4 was wired up correctly, you should be picking up power for your rear Anderson plug as alien suggested, from your auxiliary battery.

Has the rear Anderson plug been wired independently or is it simply connected to the D4’s rear tow plug wiring.

If it’s simply connected to the existing D4 tow plug wiring, you really need to wire the rear Anderson plug with some decent cable, such as 6B&S twin ( 13.5mm2 x 2 ) or 16mm2 twin, as the D4's wiring is too thin.

Now as far as the operating voltage of D4 goes, ignore everything you have read or heard about how other vehicles operating voltages work, your D4 is in a world of it’s own and while the D4’s voltage will drop, unlike all other vehicle, reduce the load on the D4's motor by lifting your foot on accelerator and the voltage will go up again, depending on driving conditions.

BTW, look through the threads on here and you will come across the access code for bringing up your vehicle operating data, and amongst the info is a voltage readout.

The readout is accurate to an error of 0.1v so it works very well at giving you a exact indication of what the alternator is doing at all times.

Now to your battery charging.

The Optima will safely take everything your alternator can produce.

As for the AGM in the rear, if it is in a very low state of charge when you start off, the battery will try to draw a high current but the high current draw will cause a considerable voltage drop in the long cable length so the battery is actually self protecting.

As far as using the inverter while drive, this is an absolute No-No because there is only one system available that can make inverters safe to operate while on the move, plus with the high current and voltages available from the D4’s alternator, you can easily charge banks of batteries and there is a large number of D4s doing just that without any need for anything else in the system.

BTW Aidan, have you set up your own D4's dual battery system yet?

[kenl]

What's the problem with using inverters on the move? I've never heard that before

I often use a small can sized inverter to run my tool battery chargers (drills and the like) whilst driving from job to job, but didn't khow it could dangerous.

[Aidan]

Welcome to AULRO.

Thanks.

2 quick thoughts..
1/How easy is it to swap the power feed for the existing anderson plug to the second battery instead of the starting one?
2/As an option could you make a lead up?
Tempory mount a new anderson plug in the rear and run the cable out/under to the rear.
When the battery comes out of the camper plug the above lead to the exisiting anderson plug and the battery to the plug inside.
It's all charging as it does in the camper then and easily removed at home afterwards.

*slaps head*

Of course, swap the leads in the engine bay. Great idea, kicking myself I didn't think of it. The Disco is in Tasmania currently, but when it gets back I'll take a look and see if that is possible. Even if they aren't easily swappable, at least one of them goes to a breaker, so a new lead could be used if required.

The second idea is also a good one, though the first one results in far less voltage drop (fewer plugs), so is definitely perferable.

Thanks

Aidan

[Aidan]

Hi Aidan and welcome to AULRO.

Thanks. A helpful bloke tipped me off that this is the place to ask about D4s ...

First off, if the D4 was wired up correctly, you should be picking up power for your rear Anderson plug as alien suggested, from your auxiliary battery.

Has the rear Anderson plug been wired independently or is it simply connected to the D4’s rear tow plug wiring.

Both Anderson plugs are properly wired with nice thick cables directly from the battery. The rear Anderson comes off the auxiliary battery, the back compartment Anderson off the starter.

Now as far as the operating voltage of D4 goes, ignore everything you have read or heard about how other vehicles operating voltages work, your D4 is in a world of it’s own and while the D4’s voltage will drop, unlike all other vehicle, reduce the load on the D4's motor by lifting your foot on accelerator and the voltage will go up again, depending on driving conditions.

I have read a number of posts, and apart from some possible problems with earlier models, it seemed to me that the Disco should keep up a decent voltage as long as there is a load connected, and that load is "earthed" to the body of the vehicle and not the negative terminal of the battery.

Is this correct? If it is, I'm assuming a charging battery would be sensed as a load. Is that assumption correct?

BTW, look through the threads on here and you will come across the access code for bringing up your vehicle operating data, and amongst the info is a voltage readout.The readout is accurate to an error of 0.1v so it works very well at giving you a exact indication of what the alternator is doing at all times.

This is on the models with a SatNav panel, no?

As for the AGM in the rear, if it is in a very low state of charge when you start off, the battery will try to draw a high current but the high current draw will cause a considerable voltage drop in the long cable length so the battery is actually self protecting.

The high current draw heats the cable causing an increase in resistance, so increasing voltage drop, which slows the rate the battery is charging dropping the current? Is that the theory?

As far as using the inverter while drive, this is an absolute No-No because there is only one system available that can make inverters safe to operate while on the move, plus with the high current and voltages available from the D4’s alternator, you can easily charge banks of batteries and there is a large number of D4s doing just that without any need for anything else in the system.

I am also interested to know why this isn't safe.

BTW Aidan, have you set up your own D4's dual battery system yet?

As I said initially, this is my father-in-laws Disco, but we're sharing a camper trailer, so I'm researching how to set up the electrics for this so they are compatible with the Disco. It just so happens he is doing a Cape York trip and thought it would be useful to have extra power in the back of the car, hence using the camper battery in the back.

In answer to your question, he has already had a RedArc VSR system installed.

[drivesafe]

Hi kenl and Aidan, first off, I want to make it very clear so there is no misunderstanding, I am NOT an electrician and I normally do my best to avoid getting involved in 240vac threads.

BUT, the problem with using 12v to 240vac inverters while on the move is that up until now there has been no way to make them safe if an accident should occurred and these devices remain powered.

If it is a SINGLE non earthed type appliance ( Live and Neutral pins and no earth pin ) connected to the inverter, then the chance of getting electrocuted is VERY low, as long as there is only one device connected to the inverter.

If the appliance is earthed and/or there is more than one appliance connected to the inverter, then there is a real potential risk of someone getting electrocuted if you have an inverter running and your vehicle is involved in an accident.

The likely hood of someone getting electrocuted is low but it exists and for many years I and others have campaigned vigourously on many forums, condemning the use of inverters in vehicles while the vehicle is on the move.

There have been a couple of deaths on work sites in Qld and Vic and there was ( is ) an enquiry into their safety.

This danger has not diminished with newer type inverters and is actually worse because of the huge increase in the use of inverters and the fact that most people using them are unaware of the danger they pose if not treated with the same respected you use when you handle normal 240vac appliances at home.

But there are additional safety issues with using inverters that most people are also unaware of, like plugging a power board into an inverter.

This dramatically increases the risk potential of electrocution, and this doesn’t just apply while driving, it applies to inverters ( and generators ) being used at camp sites or the likes.

Be aware, most inverters do not have protection built in and you need to add something like an RCBO fitted to EACH output of an inverter to make them safer.

There are no plug-n-play versions of RCBOs and installations are required to be carried out by an electrician.

There is a new device now available that is installed inside the inverter and makes the inverter safer than the protection given by your power points at home and makes inverters safe to use in vehicles while on the move and allows the safe use of power boards with these inverters.

The new technology also makes generator use safer.

[Aidan]

Thanks for the reply drivesafe. It was not something I had thought about, so good to at least know the risks.

[Aidan]

The high current draw heats the cable causing an increase in resistance, so increasing voltage drop, which slows the rate the battery is charging dropping the current? Is that the theory?

Please disregard this nonsense. It was me having a brainfade and forgetting about the current dependence of voltage drop.

[drivesafe]

The high current draw heats the cable causing an increase in resistance, so increasing voltage drop, which slows the rate the battery is charging dropping the current? Is that the theory?

Hi again Aidan and I’m not sure which part of that is nonsense, It's right on the money.

BTW this thread may be of some interest to you Aidan.

http://www.aulro.com/afvb/showthread...08#post1759808