PDA

View Full Version : Charging third battery via starter battery



Aidan
10th September 2012, 09:39 AM
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
10th September 2012, 05:40 PM
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
10th September 2012, 07:18 PM
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
10th September 2012, 10:56 PM
What's the problem with using inverters on the move? I've never heard that before:o

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
11th September 2012, 09:14 AM
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
11th September 2012, 09:48 AM
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
13th September 2012, 08:23 PM
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
14th September 2012, 02:20 PM
Thanks for the reply drivesafe. It was not something I had thought about, so good to at least know the risks.

Aidan
14th September 2012, 02:25 PM
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. :oops2:

drivesafe
14th September 2012, 05:15 PM
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.php?p=1759808#post1759808

Aidan
29th October 2012, 12:11 PM
CPR for an old thread ...

I've measured the voltage drop at the 50A Anderson plugs on my father-in-laws D4. He has one at the rear coming from his auxiliary battery in the engine bay, which is protected by a breaker, and one inside in the rear which comes from the starter, for powering a boat winch. This has no breaker, and is designed to be used with the engine running.

I induced the voltage drop by running 12V/50W halogen downlights (in parallel) from the anderson plug, and measuring the voltage at the plug with 0, 1, 2 and 3 lights connected.

Each light pulls about 4A. I also measured the zero amp (OC) voltage, but this changes a fair bit, and the battery voltage sags as soon as load is applied, so I didn't take too much notice of this figure. I did a few rounds of measuring, some on different days, here are the results for the rear anderson:

0A,12.72V
4A,12.69V
8A,12.38V
12A,12.23V

0A,12.59V
4A,12.30V
8A,12.15V
12A,12.00V

0A,12.97V
4A,12.70V
8A,12.45V
12A,12.24V

They are nothing if not inconsistent! Clearly I should be measuring the current to one of the lights (I did this once, and it was about 4A, but it will vary somewhat with voltage).

Is this too random to be useful? I don't know how I got such variation.

If I plug some of these numbers into the formula for calculating voltage drop (http://www.campertrailers.org/collyns_page.htm):

Voltage drop equals (cable length (in metres) X current (in amps) X 0.017) divided by cable cross-section in mm.sq.

in symbols:

V = L x I x 0.017 / Ax

I get some strange numbers for the cable cross-section.

Worse case scenario:

V = 0.6V, I = 8A, L = 8m (estimated, +ve & -ve cables)

implies

Ax = 1.81 mm2

That can't be right. The cables themselves are quite thick, even with insulation I'm pretty sure they can't be that puny.

Best case scenario:

V = 0.3V, I = 8A, L = 10m

implies

Ax = 4.53 mm2

I'm guessing this is closer to the truth. Without removing a cable and stripping it I can't tell for sure. With this sort of voltage drop, by the time we ran more cables out to the camper trailer it is getting close to the range a DC-DC charger with auto-cutout would cease to function.

The anderson inside the rear cabin is similar to the best case scenario above:

0A,12.54V
4A,12.30V
8A,12.10V
12A,11.98V

He should be able to do a lot better than this, no?

We've measured the alternator output with a cheap cigarette voltmeter in the cabin. We've checked and it agrees with the voltage measured directly across the terminals. Apart from the first few minutes after starting the alternator keeps a steady 14v, and drops to 13.8V when the lights are on.

rufusking
29th October 2012, 03:02 PM
With each of these measurements did you measure the voltage at the battery? As soon as a load is applied the batteries voltage will also drop.

Aidan
30th October 2012, 01:29 PM
With each of these measurements did you measure the voltage at the battery? As soon as a load is applied the batteries voltage will also drop.

The voltages you can see there are measured at the Anderson plug. What I'm interested in is the relative voltage drop as the current is increased. So for example in the best case scenario, going from 4A to 12A the voltage dropped from 12.30 to 12.00. So I've used V=0.3 and I=8 in the above formula.

I can see your point though -- if the voltage from the battery sags badly under load I am over-estimating the voltage drop in the cable. I would be surprised if the voltage from the battery sagged that badly under load, these aren't terribly high currents after all.

I can see some more testing in my future.

drivesafe
30th October 2012, 06:30 PM
Hi Aidan and as rufusking posted.

While you are partially correct, a 12 amp load is not that much but lead acid batteries are finicky things and a small load may have no major effect on one battery but could easily cause a considerable voltage drop on an identical battery.

One more point, when you measure the voltages at the battery and the Anderson plug, if you happen to have access to a second multi meter, DO NOT use it.

Take all your measurements with the same meter. There can be a small difference in readings from one meter to another, and while this is not that important normally, when trying to measure voltage drop, accuracy is imperative.

Aidan
2nd November 2012, 11:45 AM
While you are partially correct, a 12 amp load is not that much but lead acid batteries are finicky things and a small load may have no major effect on one battery but could easily cause a considerable voltage drop on an identical battery.

Granted, but the rear anderson is coming off an Optima Yellow Top. Those things can supply (and take) massive currents. Internal resistance should not be a factor.


One more point, when you measure the voltages at the battery and the Anderson plug, if you happen to have access to a second multi meter, DO NOT use it.

Take all your measurements with the same meter. There can be a small difference in readings from one meter to another, and while this is not that important normally, when trying to measure voltage drop, accuracy is imperative.

Thanks for the heads up. I won't have a chance to re-do the measurements for a while, but when I do I'll post the results.

drivesafe
2nd November 2012, 04:44 PM
While you are partially correct, a 12 amp load is not that much but lead acid batteries are finicky things and a small load may have no major effect on one battery but could easily cause a considerable voltage drop on an identical battery.


Granted, but the rear anderson is coming off an Optima Yellow Top. Those things can supply (and take) massive currents. Internal resistance should not be a factor.

Hi again Aidan, it does not matter what type of lead acid battery it is, the potential of different voltage readings, caused by the current draw will still be the same.

All lead acid batteries react in a similar manor.

Aidan
12th November 2012, 01:59 PM
Ok, back again!

This time with much more carefully measured results. Voltages were measured at the Anderson plug and the battery (with the same meter) and another multimeter was inline with one of the 50W halogen bulbs to give an accurate measure of current.

All measurements were repeated with the car running

I = current draw
Va = Voltage measured at read Anderson plug
Vb = Voltage measured at battery


Engine off:

I Va Vb

4.00 12.34 12.42
7.86 12.18 12.34
11.61 12.03 12.27


Engine on:

I Va Vb

4.22 13.86 13.93
9.60 13.76 13.91
12.48 13.65 13.90


As drivesafe said, the battery voltage did sag under these relatively modesty loads. The sag making up for half the voltage drop.

As before, the formula for voltage drop is:

V = L x I x 0.017 / Ax

If I use the "engine on" numbers,

V = 0.19V (correct for slight sag on alternator), I = 8.26A, L = 10m (estimated, +ve & -ve cables)

implies

Ax = 7.80 mm2

Engine off:

V = 0.16V (correct for sag on alternator), I = 7.61A, L = 10m (estimated, +ve & -ve cables)

implies

Ax = 8.09 mm2

8 AWG (B&S) is 8.36 mm2, so that looks about right.

Thanks for the tips on measuring that correctly.

Now the question: is it possible to successfully charge a 120 Ah AGM (Fullriver) in a camper trailer with this sort of voltage drop? Even if we use 6 AWG/B&S from the rear anderson to the battery we're looking at another 6m of cable (+ve and -ve). Given that 6 AWG cable is 0.65 of the resistance of 8 AWG, but we running more than half the cable run of the car wiring -- roughly speaking it will drop at least half the same voltage again as the car wiring.

(As noted previously, the D4 never seems to put out more than 14V from the alternator)

So at 8A it's down to 13.7V, probably lower. The float voltage on my Projecta charger is 13.7V.

I'm thinking a DC-DC charger is required.

drivesafe
12th November 2012, 06:21 PM
Hi Aidan and some good feedback plus it demonstrate why the correct size cable is imperative.

As far as the operating voltages go, they are at idle. Once out on the road you will find you will get both lower and higher voltage readings.

It would be a lot cheaper to fit the correct size cable before worrying about a DC/DC device, which will still need decent cable, depending on the size of the device.

Next, does your father-in-law have a 3 way fridge is his set up?

Aidan
12th November 2012, 09:17 PM
Hi Aidan and some good feedback plus it demonstrate why the correct size cable is imperative.

You're not kidding! It is doing my head in trying to think about the design "envelope" after the constraints of voltage drop.


As far as the operating voltages go, they are at idle. Once out on the road you will find you will get both lower and higher voltage readings.

I bought him a cheap (and I'm not joking it is very cheap) cigarette lighter voltmeter to measure the output of the alternator. We confirmed it is reading the same as the voltage at the starter battery, and during driving the alternator never exceeds 14V, and often drops to 13.8V on a long drive.


It would be a lot cheaper to fit the correct size cable before worrying about a DC/DC device, which will still need decent cable, depending on the size of the device.

You're suggesting we replace the cable with heavier duty stuff? I know it depends on what I'm planning to install, but in general would 6 AWG suffice? An auto-electrician installed it in the first place. I guess we could trace the route and replace it, but to be honest I'm not all that keen.

In any case, if it is the case that the alternator puts out a maximum of 14V, and often 13.8v, there is very little wriggle room for voltage drop.


Next, does your father-in-law have a 3 way fridge is his set up?

He has a Trailblaza, which, as you probably know, is a very efficient 12v/240V fridge which draws a maximum of 5A, and uses 1A on average.

drivesafe
12th November 2012, 09:42 PM
Hi again Aidan and cigarette volt maters can have up to a 1 volt error, caused by other devices being connected to the same loom.

Things like your sound system, will cause voltage drop and you should see voltage readings in the high 14v, 14.8v is common place, particularly when you first start your drive.

OK the fridge is a low current draw, which makes your set up easier ( and cheaper ) to set up.

As you posted, by the sounds of it, you have some 8B&S cabling.

6B&S is the best size for voltage drop reduction verses cost.

Aidan
13th November 2012, 01:49 PM
Hi again Aidan and cigarette volt maters can have up to a 1 volt error, caused by other devices being connected to the same loom.

That is interesting. We did check that it was reading the same as the voltage at the starter battery. Obviously this was at idle, when the car was first started.

I've had a thought -- he has the Anderson in the rear load bay that is directly connected to the starter battery. I'll get him to wire up the voltmeter to that to check the voltages.


Things like your sound system, will cause voltage drop and you should see voltage readings in the high 14v, 14.8v is common place, particularly when you first start your drive.

It doesn't seem to matter what is "on", the voltage at the cigarette outlet never exceeds 14V. It will be interesting to see how the voltage at the battery differs from the cigarette outlet.


6B&S is the best size for voltage drop reduction verses cost.

Ta.

Aidan
19th November 2012, 09:42 AM
Hi again Aidan and cigarette volt maters can have up to a 1 volt error, caused by other devices being connected to the same loom.

Things like your sound system, will cause voltage drop and you should see voltage readings in the high 14v, 14.8v is common place, particularly when you first start your drive.

We've now measured the starter battery voltage when the car is running, and confirmed that it is the same as that measured by the cigarette volt meter (within error -- the cigarette one is out by 0.1V sometimes). We measured the starter voltage from the anderson plug in the rear load bay -- it is connected directly to the starter battery. It had no load, so the voltage was the same as the battery.

So to recap, the Disco 4 alternator appears to output 14V only when first started, and then not always that high, and quickly drops to 13.7-13.8V.

gghaggis
19th November 2012, 11:52 AM
[QUOTE=Aidan;1799784
So to recap, the Disco 4 alternator appears to output 14V only when first started, and then not always that high, and quickly drops to 13.7-13.8V.[/QUOTE]

Mine will run at around 14.5V if the battery is a little low, but you won't generally see the higher voltages at idle - only when driving and on overrun. The alternator output is reduced at idle and when under power to improve economy, unless really needed.

Cheers,

Gordon

Aidan
19th November 2012, 01:49 PM
Mine will run at around 14.5V if the battery is a little low, but you won't generally see the higher voltages at idle - only when driving and on overrun. The alternator output is reduced at idle and when under power to improve economy, unless really needed

These voltages were measued on a 35 minute trip with variable driving conditions - some stop/start city driving and including up and down some reasonable grades.

This was done to check if the cheap cigarette lighter voltmeter was giving a true indication of alternator voltage. It was confirmed that it was.

According to a months worth of driving with the cigarette lighter voltmeter the alternator NEVER produces more than 14v, and typically it is 13.7-13.8. Admittedly I don't think the starter battery has been heavily depleted during this time.

gghaggis
19th November 2012, 03:22 PM
According to a months worth of driving with the cigarette lighter voltmeter the alternator NEVER produces more than 14v, and typically it is 13.7-13.8. Admittedly I don't think the starter battery has been heavily depleted during this time.

That's probably the difference. Mine and most of the cars I've installed dual battery systems into generally run quite a few accessories, often permanently wired. I can confirm that under those situations, the charging regime will easily see over 14V

Cheers,

Gordon

Aidan
5th December 2012, 02:31 PM
Back again again!

Now we're trying to figure out what the voltage drop will be in the camper trailer. I got 4m of 6 B&S cable (will probably only need 3m), attached a 50A Anderson plug to one end, stripped 50mm of insulation back on the other end and measured the voltage drop with the engine running.

I = current draw
Va = Voltage measured at cable attached to rear Anderson plug
Vb = Voltage measured at battery

I Va Vb

4.07 13.59 13.68
8.06 13.44 13.64
11.97 13.30 13.60

First up, that is a low alternator voltage! Turns out the air-con was on the whole time (only noticed after we'd packed up), but this is still relevant. He wants to be able to use the air-con. Additionally, the alternator dropped 0.08V when the load increased by 8A. In the previous trial (with air-con off) it only dropped 0.03V. Does that mean the alternator will struggle when under load?

Secondly, the additional voltage drop wasn't too bad, only 0.21V for 7.9A extra draw, compared to 0.18V ** for 8.24A when we measured at the rear Anderson plug. This translates to a 0.027V drop per amp, compared to 0.022V / A, so approximately a 20% increase in voltage drop.

If I want to run a 20A Ctek DC-DC charger, it will pull at least 24A to make up for the voltage drop. If the alternator output was similar to that measured above I'd be down to 12.81V at the charger. This is just marginally above the voltage where the CTEK D250S dual starts to throttle the current (I emailed CTEK -- apparently the charger will drop to a 10A max current, and if the voltage is still below 12.8 it will shut off). It is unlikely the CTEK would shut off completely, but it would also mean a low charge current, and therefore an unreliable SOC.

If the alternator output was closer to that observed in my previous post (13.93V @ 4A, 0.03V sag @ 12A at the alternator), the voltage at the CTEK would be closer to 13.19. This would be ok -- the CTEK powers on at 13.1V, but this is with no current flowing.

I'm going to advise my father-in-law to keep an eye on the alternator voltage -- to see if 13.7 is typical now that he is using the air-con more.
If it is, then we're going to have to go for a switched DC-DC charger which doesn't shut off with this extra voltage drop.

Cheers

Aidan



** I made a simple error in the other post and said this was 0.19V, but

DiscoMick
5th December 2012, 03:04 PM
A very intereesting discussion and I've learnt a lot - thanks.
A question: What is the effect of the D3/4 having a 'smart' alternator regulated by the ECU? Does that mean the voltage will be adjusted to demand, and does that reduce the effect of voltage drop? How would that affect the situation being discussed here, and how would it be different to that of vehicles with normal alternators?
Just trying to get my head around this electronic stuff...

Aidan
5th December 2012, 03:43 PM
A question: What is the effect of the D3/4 having a 'smart' alternator regulated by the ECU? Does that mean the voltage will be adjusted to demand, and does that reduce the effect of voltage drop? How would that affect the situation being discussed here, and how would it be different to that of vehicles with normal alternators?
Just trying to get my head around this electronic stuff...

Not sure I can help alot with specifics, but I'm trying to reconcile my father-in-law's experience with what gghaggis reported about seeing over 14V from the alternator.

I'm guessing (and this is pure speculation) that the "smart" alternator is only different from traditional ones in that it won't always boost the voltage when there is a load -- it will boost, but other criteria come into play.

When we did this latest test the air-con was on, but the car was idle. The alternator didn't boost output, and in fact the output sagged worse when we loaded it more. If the car had been doing 100km/hr downhill the alternator output may well have been much higher.

Plus this car has never had seriously depleted batteries -- the starter and auxiliary have yet to be "used in anger".

We're going to do some more testing and observing -- going on a camping trip this weekend -- to see how the alternator behaves. He's going to turn the air-con on and off, under different circumstances to see what effect that has on the alternator output. Plus the auxiliary will be drawn down somewhat as it will have powered the fridge overnight.

drivesafe
5th December 2012, 04:02 PM
Hi again Aidan and you have done a lot of work there but it’s not going to give you the info you need.

The only way to get the relevant info is while the vehicle is on the move.

You need some form of data logger, to monitor both the voltage and current at the house battery.

Measuring voltage anywhere, while the motor is idling is not going to give you the operating info you need to make a decision about what will work the best.

The D4 has a 180 amp alternator and you are not getting anywhere near the potential while the motor is idling because the D4’s own electrical requirements are anything up to 50 amps and at idle, you will have very little left for any accessories.

I have a system that is capable of producing 60 amps battery to battery and works from as low as 11.0v but it’s of no use if there is nothing available from the alternator and at idle, thats what you have, or more correctly, don’t have.

Aidan, you need operating info while on the move because the info achieved at idle does not reflect to true ability of any vehicle’s charging capability.

rufusking
5th December 2012, 04:30 PM
Interesting discussion. So it seems there's little benefit in running the vehicle at idle when out camping to recharge the batteries (main & aux). Seeing that the days are gone when you could just wind up the hand throttle so there's little option to increase RPM with some reliable control.
I'm considering one of those alternators coupled to a small petrol motor plugged in to the rear Anderson to recharge the Aux. Probably isolate the main to reduce the risk of any damage to the vehicle electronics.
Is there any implications running current reverse through the circuit breaker?

drivesafe
5th December 2012, 04:55 PM
Hi rufusking, and you can run current in both directions through a circuit breaker.

Next, the newer the vehicle, the more power the vehicle’s house keeping requires, and this not only applies to LRs, all new vehicles have this “problem”.

If you do a lot of free camping, there are a number of options available for keeping batteries charged.

As for your alternator/motor idea, they are already on the market but getting a small to medium sized inverter generator is a simpler way to go and offers additional uses.

rufusking
5th December 2012, 05:16 PM
I'm well aware of the unit. The reason I was leaning towards it was the availability of 55A and an option of 14.6V or 14.0, this coupled with the Optima's ability to accept a high charge rate.
I have yet to find an inverter generator that puts out double digit current on "12 Volt" plus I like to keep things simple without a separate charger. I'm more likely to find someone who can fix a stationary engine or alternator than an inverter. Less things to take, less things to go wrong. Bit of a contradiction having a D4.

drivesafe
5th December 2012, 07:09 PM
Hi again rufusking, generator 12v outputs are no good for charging batteries, they are a 12v power supply and as such are not high enough to charge any battery properly.

Although you don’t seem to like the idea, but a small generator and a 60 amp battery charger would do what you wanted and, as mentioned above, be useful for other applications.

Aidan
6th December 2012, 03:47 PM
Hi again Aidan and you have done a lot of work there but it’s not going to give you the info you need.

The only way to get the relevant info is while the vehicle is on the move.

You need some form of data logger, to monitor both the voltage and current at the house battery.

Measuring voltage anywhere, while the motor is idling is not going to give you the operating info you need to make a decision about what will work the best.

I know what you're saying, but for our purposes I think it will be enough to keep an eye on the voltage at the cigarette outlet (I know I know, not too accurate etc -- but we've established to our satisfaction that it appears to track the alternator voltage "near enough") under typical conditions.

Clearly charging the battery corresponds to another, sometimes significant, load. But in the end, a load is a load, and how it responds to one load should be roughly the same as another. The biggest problem -- we have no idea what the loads are! :thumbsup:

As long as the voltage is never much below 13.8 we should be sweet.

I'll report back after this weekend.


The D4 has a 180 amp alternator and you are not getting anywhere near the potential while the motor is idling because the D4’s own electrical requirements are anything up to 50 amps and at idle, you will have very little left for any accessories.

Thanks for the explanation.


Aidan, you need operating info while on the move because the info achieved at idle does not reflect to true ability of any vehicle’s charging capability.

I can see it now -- screaming down the Hume with me in the load bay taking alligator clips on and off halogen light bulbs! :eek:

(I'm not going to do that by the way)

Like I said, we'll see how far some sloppy observation gets us.

Thanks again for the help

drivesafe
6th December 2012, 08:05 PM
Like I said, we'll see how far some sloppy observation gets us.

Hi Aidan, and they were not “sloppy” observations, nor did I intend to infer that they were.

The info you got will be a good starting point but as I posted earlier, sourcing the relevant info is not easy and most people are unaware of what is needed to see what is really happening with a charging system.

Your own observations showed that you were causing a voltage drop, while idling, just by having the A/C on, and this is the problem with taking measurements while the vehicle is idling. You are not seeing what the vehicle can really do.

There is a simple device, that I use regularly, to get basic info, to help evaluate a system, without the need to spend loads of time setting up gear to get more accurate data.

I have a string of Doc wattson Meters. Have a look at the link below.

Doc Wattson Meter - DC Inline (http://www.powerwerx.com/digital-meters/doc-wattson-meter-dc-inline.html)

These store enough info for me to be able evaluate a systems potential without too much work.

This will give you an idea of how simple it is to set up to take some On-The-Move measurements using these devices and a few basic purpose made connectors.

I have about a dozen or so of these and while the manufacturer claims they can measure up to 100 amps, 25 amps is about as much as I like to put through them because the thin cable used on them induces a voltage drop in the set up.

If I need to measure higher currents I use two meters connected in parallel.

https://www.aulro.com/afvb/images/imported/2012/12/927.jpg

https://www.aulro.com/afvb/images/imported/2016/01/346.jpg

bcl
8th December 2012, 10:02 PM
Sorry may seem silly, I have had a few drinks and may be missing the point here. Why not just get the father inlaw to increase revs to 2000rpm while in neutral. Wouldn't this be the same as driving up the Hume.

drivesafe
9th December 2012, 12:46 AM
Hi bcl and you have not missed anything.

With just about any other vehicle, increasing the rpms will increase both the voltage and current output of the alternator.

The problem with increasing the D4’s rpms while the motor is NOT under load, is that the D4’s BMS may increase the current output but may not increase the voltage level.

Increasing the current available but not the voltage will give the wrong info as to whether you need to artificially step the voltage up to get a decent charge voltage for auxiliary/house batteries.

You will only get the actual operating voltage and current level available while the vehicle is on the move.

There are large numbers of people with my isolators in their D4s and they have no problems with charging and maintaining any number of auxiliary and house batteries, with out the need for any additional assistance.

This post form gghaggis gives you an idea of what it takes to get the higher voltage readings.


Mine and most of the cars I've installed dual battery systems into generally run quite a few accessories, often permanently wired. I can confirm that under those situations, the charging regime will easily see over 14V

Aidan
13th December 2012, 12:33 PM
Hi Aidan, and they were not “sloppy” observations, nor did I intend to infer that they were.

I was referring to the "so what is the voltage now" observations we were planning to do on the camping trip.


There is a simple device, that I use regularly, to get basic info, to help evaluate a system, without the need to spend loads of time setting up gear to get more accurate data.

I have a string of Doc wattson Meters. Have a look at the link below.

Doc Wattson Meter - DC Inline (http://www.powerwerx.com/digital-meters/doc-wattson-meter-dc-inline.html)

These store enough info for me to be able evaluate a systems potential without too much work.

Thanks for the link. I see it can be used as a "fuel gague" for the battery too, which is nice.

Well first off, the sloppy observations from the weekend. On a 300K drive, including some fairly hilly sections the D4 alternator voltage never went above 13.8V, and more commonly showed 13.7V. Good news is that is also didn't sag when the aircon was turned on. We've decided we need not worry about alternator voltage sag as far as calculating voltage drop goes.

During the camping weekend the aux battery (optima yellow top 55Ah) got as low as 11.9V. When going for a drive at this SOC the alternator never went above 13.8V. That optima must have been pulling some current, but the alternator didn't increase the voltage beyond 13.8V, but did seem to be on the slightly higher value for most of the 4 hour drive home.

Get this. The next morning, pulling out of his driveway, alternator is at 14.1V! He has never seen it that high before.

I give up.

rufusking
13th December 2012, 01:47 PM
Could it be that the starting battery slowly discharged into the optima after you switched off (considering the low SOC ). On restarting the system sees the part discharged starting battery and increases voltage in response?

drivesafe
14th December 2012, 05:00 AM
During the camping weekend the aux battery (optima yellow top 55Ah) got as low as 11.9V. When going for a drive at this SOC the alternator never went above 13.8V. That optima must have been pulling some current, but the alternator didn't increase the voltage beyond 13.8V, but did seem to be on the slightly higher value for most of the 4 hour drive home.

Get this. The next morning, pulling out of his driveway, alternator is at 14.1V! He has never seen it that high before.

I give up.

Hi Aidan, and I’m taking a guess here but when your father-in-law got home, he probably took a while to unpack the D4 and as such, had doors open and there would have been a fair bit of cranking battery capacity used while the doors were open.

As a result, the next morning the D4’s BMS, after monitoring the battery once the motor was stated, set the voltage at a higher level, that the BMS deemed would replace the used capacity as required.

If your father-in-law wants to continue his experiments and get even higher voltage readings, put a small load on the cranking battery while the motor is off, like a compressor fridge.

Leave the load on the battery till the voltage is around 12.2v and then go for a drive.

Don’t be surprised if the readings go up over 15v.

As Gordon posted, this lower cranking battery voltage when the D4’s motor is first started and the way the BMS works to fix the lower voltage by increasing the operating voltage, is the very reason my isolators get the best results for charging auxiliary/house batteries, without the need for any assistance from other devices.

Aidan
14th December 2012, 09:14 AM
Could it be that the starting battery slowly discharged into the optima after you switched off (considering the low SOC ). On restarting the system sees the part discharged starting battery and increases voltage in response?

They are separated by a Redarc VSR, and the Optima was well charged after the run home. So probably not.

Aidan
14th December 2012, 09:25 AM
Hi Aidan, and I’m taking a guess here but when your father-in-law got home, he probably took a while to unpack the D4 and as such, had doors open and there would have been a fair bit of cranking battery capacity used while the doors were open.

As a result, the next morning the D4’s BMS, after monitoring the battery once the motor was stated, set the voltage at a higher level, that the BMS deemed would replace the used capacity as required.

First off, thanks for sticking with me on this journey! I do appreciate it.

That could be the case, that the starter was drained, I'd have to ask him. However when we were camping he had the back open a lot (the fridge was in the back of the car) and I even commented that the cabin lights seemed to be on a fair bit. This didn't seem to make the alternator voltage increase.

One thing I guess he could keep an eye on is the battery voltage before he starts the car, to see if a low initial charge on the starter leads to a high alternator voltage once the car is started.


If your father-in-law wants to continue his experiments and get even higher voltage readings, put a small load on the cranking battery while the motor is off, like a compressor fridge.

Leave the load on the battery till the voltage is around 12.2v and then go for a drive.

Don’t be surprised if the readings go up over 15v.

Good idea. I'll see if he wants to experiment more!

He just got the D4 serviced, and asked about the low(ish) alternator output. Their only response was that as long as it was 13.5V or above there was no problem.

Thanks again

rufusking
14th December 2012, 10:29 AM
In the early days I was courious about the starting battery voltage especially when I was getting the "Low Battery .." message on the radio.

Measuring via the tow socket I could get a "Sleep" reading and another once I unlocked the vehicle. Waking the vehicle up would generally drop the measured battery voltage by 0.2V. This might give a better understanding of the batteries state of charge.