In car Battery monitor's

Hi guys was wondering if any one has fitted an incar battry monitor, I'm heading down south for easter and I'll be running two fridges plus other bits and pieces i was thinking of running a third battery of the aux wired in series temporarily (Just for thr trip) and was toying with the idea of a monitor, Ive seen them in 4wd mags somewere and was wondering if any one has any reports on them thanks
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Reply By: Member - John and Val W (ACT) - Tuesday, Mar 31, 2009 at 09:21

Tuesday, Mar 31, 2009 at 09:21
Hi,
If you do add another auxilliary battery, wire it in PARALLEL with the present auxilliary battery, NOT IN SERIES!

Only the better (more expensive) battery monitors are useful.

HTH

John
J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
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AnswerID: 357207

Reply By: Member - Phil G (SA) - Tuesday, Mar 31, 2009 at 09:38

Tuesday, Mar 31, 2009 at 09:38
What info do you need from a monitor? I use a digital voltmeter with an on/off/on switch to measure the 2nd and 3rd batteries. The meter is inside the cab, and measures to 2 decimal points.

This will tell you:
- That your alternator and regulator are working (voltage goes up)
- the isolator is working and has kicked in (voltage rises after starting battery hits 13.5)
- voltage drop to the 3rd battery - this is proportional to how much current is going into it. The voltage drop is reduced as the 3rd battery recharges, so you have a more accurate idea of how well recharged it is.
- resting voltages of each when you're camped as a rough idea of what's left.

I no longer use a low voltage cutout because they consume some power and I don't let batteries drop to a level where the cutout would be necessary.

Cheers
Phil
AnswerID: 357212

Reply By: Rangiephil - Tuesday, Mar 31, 2009 at 10:05

Tuesday, Mar 31, 2009 at 10:05
I have used a $29 Jaycar digital temp/clock/battery monitor for about 9 years with no problems. One of the camper trailer makers include these in their spec.

I have a two way switch.

It has been useful in monitoring the level of charge in the second battery to predict whether the battery has enough for overnight for instance. It has also alerted me to a regulator problem by confirming that there was no charge when the red light flickered or came on.

It also is good in determining the % charge of the second battery when driving, as the voltage varies with state of charge eg it will run 13.7 for 1 hour then slowly increase to 14.2 as the battery gets to 100% after a couple more hours. I have two separate alternators so I charge quite quickly.

I believe it is within 0.2 volts accurate which is IMHO plenty good enough.

Regards Philip A
AnswerID: 357219

Follow Up By: Rangiephil - Tuesday, Mar 31, 2009 at 10:10

Tuesday, Mar 31, 2009 at 10:10
PS I have a Projecta low voltage cut out on the fridge input line near the fridge itself.

I believe they are important to protect the second battery seeing my non electronic engel has no low voltage cutout. If you have a modern fridge with a low voltage cut out they are redundant.

I have had a Chinese "Absorbed Power " 90 AH AGM for over 4 years now and it still goes strong.
Regards Philip A
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FollowupID: 625312

Follow Up By: troopy 2005 - Sunday, Apr 05, 2009 at 12:39

Sunday, Apr 05, 2009 at 12:39
this is all you need exactly .it is after all a very simple cuircut.these are a digital meter that cost $29 buy 3 ,if had one for at least 15 year and works perfectly.KISS IS BEST.
I have a commander second battery that will run a 40l engel for about 3 days without any recharge.
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FollowupID: 626283

Reply By: Member - Mick O (VIC) - Tuesday, Mar 31, 2009 at 14:06

Tuesday, Mar 31, 2009 at 14:06
I've done exactly as you want to do. I have two 90AH AGM's in the Patrol, the 2nd being in the middle of the vehicle where the passengers seats would normally be. I run a major wire out of the second battery through an ammeter gauge to a 6 gang fused switch panel. This allows me to see just how much is being drained out of batteries by the fridges (I run a 40 litre Engel as a freezer and a waeco 50 litre as a fridge) and other accessories. There is an in line voltmeter to keep an eye on the 2nd battery but this is largely superfluous as I monitor both batteries with an Autron digital dual battery gauge mounted on the 'A' pillar. I'll post a couple of photo's when I get home tonight.

Cheers Mick
''We knew from the experience of well-known travelers that the
trip would doubtless be attended with much hardship.''
Richard Maurice - 1903

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AnswerID: 357256

Follow Up By: Inkbandit79 - Tuesday, Mar 31, 2009 at 21:46

Tuesday, Mar 31, 2009 at 21:46
Thanks mick was looking at the national luna model it can be hard wired to the batteries i run my fridge on 12 volt for at least 8 hours every day then chuck it on 240 if and when i get home so the monitor is a valuble piece of tech for me let me know how ur photos go as im keen to see ur setup
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FollowupID: 625457

Reply By: Member - Norm C (QLD) - Tuesday, Mar 31, 2009 at 15:14

Tuesday, Mar 31, 2009 at 15:14
In the vehicle, I use a Voltminder from Derek Bester at ABR Sidewinder (ExplorOz advertiser). It is a simple digital voltmeter that can be set up to monitor two batteries separately (starter and aux), whichis how I have it set up. Also an alarm (flashing light) to help alert you to preset low voltage.

Of course, voltmeters only give a guide to state of charge, but with experience, they are helpful. The only reliable way (other than measuring SG) is with an expensive controller that measures current in and out. I have one of these in the van, but the expense is not warranted in the vehicle IMO.

Voltminder Details

AnswerID: 357265

Follow Up By: Lex M (Brisbane) - Tuesday, Mar 31, 2009 at 15:32

Tuesday, Mar 31, 2009 at 15:32
Unfortunately current in /out may not be as accurate as you might think.

see reference
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FollowupID: 625351

Follow Up By: Member - Norm C (QLD) - Tuesday, Mar 31, 2009 at 17:01

Tuesday, Mar 31, 2009 at 17:01
Lex, perhaps I should have used the term 'the most reliable way' rather than 'the only reliable way'. Of the readily available solutions, the 'smart' controllers like Plasmatronics give excellent battery management information. Like most things to do with 12 volt systems, nothing is perfect or absolute.

A bit like democracy - flawed, inefficient and with very patchy outcomes depending on who and what is involved at the time. But easily the best system so far devised by man.

Norm C
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FollowupID: 625372

Follow Up By: Lex M (Brisbane) - Tuesday, Mar 31, 2009 at 17:24

Tuesday, Mar 31, 2009 at 17:24
Quite so. It's interesting that the SG is not as accurate as normally believed either.

seereference.

Some very interesting stuff on that site.
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FollowupID: 625380

Follow Up By: Boobook2 - Wednesday, Apr 01, 2009 at 07:09

Wednesday, Apr 01, 2009 at 07:09
Ditto re Derek's Voltminder.
You can set it to been at any voltage and you don't have to keep an eye on it.
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FollowupID: 625496

Reply By: desert legend - Wednesday, Apr 01, 2009 at 00:28

Wednesday, Apr 01, 2009 at 00:28
Hi, I have had various dual battery systems in 4WD's over the last 35yrs and am now using a WA built unit called a dual mate to manage and keep track of my batteries.
It allows me to test/ isolate and bring on charge the batteries as I need and has a constant in vehicle display of voltage on both batteries as well as audible and led warnings of low voltage etc.
I looked at all the latest options and this unit is the best by far. Easy to fit and have had it for nearly 2 yrs now and its reliable.
Not cheap but you get what you pay for so to speak.
Cheers
dave
AnswerID: 357347

Reply By: Member - Mick O (VIC) - Wednesday, Apr 01, 2009 at 06:22

Wednesday, Apr 01, 2009 at 06:22
The photos as promised

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Hope these are of help.

Mick
''We knew from the experience of well-known travelers that the
trip would doubtless be attended with much hardship.''
Richard Maurice - 1903

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AnswerID: 357356

Follow Up By: Inkbandit79 - Wednesday, Apr 01, 2009 at 07:39

Wednesday, Apr 01, 2009 at 07:39
Mick, what type of battery are you running in the back, I was told not to install one inside the cabin for saftey reasons, is your battery box a sealed unit, out of curiosity how long would your fridges run for on ur setup?
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FollowupID: 625502

Follow Up By: Member - Mick O (VIC) - Thursday, Apr 02, 2009 at 10:22

Thursday, Apr 02, 2009 at 10:22
Batteries are sealed AGM so safe for intedrior of vehicle as they have internal gas recombination and no vent. Fridges will run up to 3 days unsuplemented. With solar supplement and management (like wrapping and turning the freezer of at night) they'll go longer.

Cheers Mick
''We knew from the experience of well-known travelers that the
trip would doubtless be attended with much hardship.''
Richard Maurice - 1903

Lifetime Member
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