How do I know if my battery is charging when towing

Submitted: Saturday, Jan 18, 2014 at 17:00
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Hello people, we have towing our caravan with jeep grand cherokee 2012 CRD diesel. I have heard these new vehicles maybe fitted with an ECU Alternator which may prevent the battery from charging properly, do how can I know if the battery is indeed charging when towing? Fidge is running off battery when towing. Which then poses another question, how do can I then be sure the caravan battery is isolated when the car is turned off. Thanks in advance.
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Reply By: Member - Rosco from way back - Saturday, Jan 18, 2014 at 17:34

Saturday, Jan 18, 2014 at 17:34
G'day Toby

Q1. Probably the easiest way is to check across the terminals of the 2nd battery with the engine running at fast idle or up to say 2000 RPM (you may need to get the boss to hold the throttle). Should read well above 13V probably >14V. If so, it means the alternator is supplying charge to the 2nd batt. Use a multimeter for this.

Q2. As a general rule you should always use a battery management unit when running an aux batt (even the one in the van). That will take care of isolating the 2nd batt from the cranking batt when necessary.

Of course you will need to consider very heavy wiring if the batt is in the van + a suitable plug.

May I suggest an auto sparky if you feel you're getting out of your depth.
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Follow Up By: Member - Rod N (QLD) - Saturday, Jan 18, 2014 at 18:19

Saturday, Jan 18, 2014 at 18:19
You can/should fit a motion activated 'Fridge Switch'. This will switch off the 12v to the fridge when you are stopped.
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Follow Up By: Ross M - Saturday, Jan 18, 2014 at 18:40

Saturday, Jan 18, 2014 at 18:40
I would imagine most people who have a fridge will want it to be running ie connected to the 12v battery when stopped so the fridge will continue to be cool inside.

Usually, that is the reason for the second battery.
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Follow Up By: Member - Rod N (QLD) - Saturday, Jan 18, 2014 at 20:46

Saturday, Jan 18, 2014 at 20:46
No Ross most most people who have a 3way fridge will not want it to be running ie connected to the 12v battery when stopped so the fridge will not flatten the battery. They draw around 15 amps and it doesn't take long to flatten a battery. In any case if the stop is only a couple of hours the fridge will not heat up appreciably.
A 12v compressor fridge is a different kettle of fish.
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Follow Up By: Ross M - Saturday, Jan 18, 2014 at 21:39

Saturday, Jan 18, 2014 at 21:39
G'day Rod

Exactly where did he mention anything about a 3 way fridge?
If present the rules do change.
At present, we don't think it is because he wants the battery charged for a fridge, therefore it is unlikely to be a 3 way amp sucker. Could be, and the wrong application of a few things.
Unfortunately OP's often don't give enough info or don't know what to mention.
Cheers
Ross M
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Follow Up By: Member - Rod N (QLD) - Saturday, Jan 18, 2014 at 21:46

Saturday, Jan 18, 2014 at 21:46
Yes, he did not say what type of fridge so we just have to guess until he clarifies.
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Follow Up By: Slow one - Saturday, Jan 18, 2014 at 22:00

Saturday, Jan 18, 2014 at 22:00
The only thing it can be is a 3 way fridge. 12 volt fridges won't flatten the battery in a days travel, and I can't think of anything else that will.

One way to check, is have a voltage sensitive light on the front of the van so you can see it in the mirror. Green light all good. Same principle as you would watch the temp and status of a fridge pan in the mirror of a prime mover.

That way you don't have to run wires to monitor the state of your battery from the cab.

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Reply By: Ross M - Saturday, Jan 18, 2014 at 18:45

Saturday, Jan 18, 2014 at 18:45
By using an additional two wire plug the wires can run from the van battery to a digital voltmeter on the dash and it will indicate the voltage when the charging system, whatever it is, is delivering charge to the aux battery.

Because of the sensitivity you should also be able to see when the fridge is ON or OFF.
Some learning of the charging and voltages happening will need to be observed to do that though.

If charge not happening then volts will go down and then rise when charging is occurring.
Cheers
Ross M
AnswerID: 524726

Reply By: steved58 - Saturday, Jan 18, 2014 at 18:53

Saturday, Jan 18, 2014 at 18:53
Hi Toby I am asuming because of the type of questions you are asking that you are new to towing a caravan if you read electricity for camping do a search for it on this site it will answer many of your questionsand some you dont even know you want to ask yet After reading that you will find you will have most of your questions answered and can come back and ask us some that may be more particular to your circumstaces
Have fun Steve

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Follow Up By: Toby T1 - Sunday, Jan 19, 2014 at 00:30

Sunday, Jan 19, 2014 at 00:30
Hi Steve, not new to towing, just brought a new car with an ECU Alternator. Now that is new to me. bTW it is a 3 way fridge :)
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Follow Up By: steved58 - Sunday, Jan 19, 2014 at 00:49

Sunday, Jan 19, 2014 at 00:49
Toby check out abr sidewinders web site he has a fuse with a diode installed that bumps up the voltage half a volt to compensate for ecu controlled alternators The three way fridge should be isolated when the engine is turned off a fridge switch is a cheap and very easy way to do this Camec sell them I have an isolator between the start battery and the battery in the rear of vehicle running a compressor fridge there and a fridge switch on the caravan fridge 3 way to isolate that fridge from the battery in the rear of the vehicle the battery in the caravan has a diode in the setec unit to prevent it from discharging back to the vehicle and I monitor this with a plug in volt amp meter from abr it can record how many amp hours have gone into the battery and max and min voltages Not the best way to achieve what I need but it was achieved at a reasonable price and works for me The most important component is heavy wiring I hope some of this answers your questions
All the best
Steve
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Follow Up By: Member - Frank P (NSW) - Sunday, Jan 19, 2014 at 09:43

Sunday, Jan 19, 2014 at 09:43
"Toby check out abr sidewinders web site he has a fuse with a diode installed that bumps up the voltage half a volt to compensate for ecu controlled alternators"

Before you do that check with your dealer. You have a new car. Dicking around with the electrical system taking it outside manufacturer's design specs will no doubt affect your warranty, and not for the better.

Cheers
FrankP

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Follow Up By: gbc - Sunday, Jan 19, 2014 at 10:11

Sunday, Jan 19, 2014 at 10:11
My dear strange Ford ranger with its electrical foibles also has a 'smart' alternator which Ford has tried on various occasions to disable.
My own dicking around fix was to remove the fuse marked 'BMS' (battery management system) from under the bonnet.
We are well out of manufacturer's spec and warranty, I drive around with a little red battery light on the dash constantly, but the beer most certainly is cold and it cost me nothing to do.
Check your jeep for a similar electrical setup, or get on a jeep specific forum with guys who have circumvented this stuff already.
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Reply By: Member - Frank P (NSW) - Monday, Jan 20, 2014 at 12:31

Monday, Jan 20, 2014 at 12:31
Toby,

You wrote in a follow-up:
" just brought a new car with an ECU Alternator. Now that is new to me. bTW it is a 3 way fridge :)"

At the risk of starting another 12 volt war ....

If you are now sure that your new vehicle has an ECU-controlled alternator and you want to properly charge your caravan batteries while driving, then I think you need a DC-DC charger located in the van, near the battery, with a 6 gauge supply from the car all the way to the charger via Anderson at the back of the car.

Your 3-way fridge running on 12V draws relatively high current, probably in the range 10 to 15 amps. I don't know what your present wiring arrangements are, but it would be better not to have that sort of load connected to the van battery while you're trying to charge it. Instead, have it powered directly by the supply from the car. Reason for this is that the fridge will absorb a large part of the output from the charger instead of that output going toward charging the batteries. You will need an isolator in the car to ensure that the 6 gauge supply from the car is energised only when the engine is running.

In my Avan when I had it, I had the 6 gauge cabling all the way from car battery via isolator and Anderson to a fused terminal block in the van. The supply to the charger was connected to that.

I had a relay so that when the supply to the charger was live (car engine running), the 3-way fridge ran directly off the supply from the car, and when it was dead (engine off) the fridge ran off the van batteries until I switched it over to gas or 240. Reason for that was to keep the fridge going if stopped for an hour or so .

That system worked very, very well for me.

If you don't like the idea of running your fridge off the van batteries at all then you'd supply the fridge directly from the terminal block and forget the relay. The isolator in the car would ensure that your fridge will not flatten your car battery when the engine is not running. You could do without the isolator, but then you'd have to remember to unplug your Anderson every time you stop for lunch, shops etc or risk flattening your car battery. Not worth it, IMO.

A simpler, and in my opinion NOT recommended, way is to not have the isolator in the car and connect the fridge direct to the van battery (still need the dc-dc charger). Much of the output from the dc-dc charger will be taken by the fridge so you won't get the full benefit of the charger and you may need a longer drive time to charge the battery. When the tug's engine is off the dc-dc charger will act as an isolator to isolate the fridge and the rest of the van electrics from the car.

Are you contemplating a second battery for the tug?

Cheers
FrankP

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Follow Up By: Member - Frank P (NSW) - Monday, Jan 20, 2014 at 13:42

Monday, Jan 20, 2014 at 13:42
"Not worth it, IMO", 2 paragraphs above

To clarify, should read "Not worth the risk, IMO."
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Follow Up By: Brian 01 - Monday, Jan 20, 2014 at 15:33

Monday, Jan 20, 2014 at 15:33
As a follow up to the good info that Frank has posted, also be aware that with ECU controlled alternators it is generally recommended that accessory (read as "any electricals that you add") earths should go to the chassis, not to the main battery negative terminal.
This includes charge lines to caravans, fridges in the back etc. etc.
You can run a wire all the way up to the front if you are so inclined, but it should still be connected to the chassis, not the battery.
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Follow Up By: Member - Frank P (NSW) - Monday, Jan 20, 2014 at 19:00

Monday, Jan 20, 2014 at 19:00
Why is that, Brian?

As it turns out I have wired the Anderson neg forward to a chassis earth in the engine bay, which is then connected directly to the battery neg.

What gives?

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Follow Up By: Brian 01 - Monday, Jan 20, 2014 at 20:07

Monday, Jan 20, 2014 at 20:07
It has to do with the voltage sensing requirements for the ECU.
The ECU needs to know load levels on the system in order to control alternator output (contrary to what has been said elsewhere, it is not simply temperature control).
It does this by a variety of sensors and gets its info. via the CAN Bus in most cases.
If you bypass the main earth wire from the chassis to the battery, then you will, in many instances, bypass the current sensing facility which will leave the ECU with a lack of info. on real load conditions.

A case in point is the later model Ford Rangers which have the sensor on the negative cable adjacent to the battery terminal.
For that sensor to give accurate load indications, all currents in both directions need to be accounted for, and that won't happen if your extra neg. cable goes straight to the battery.

The list of vehicles with ECU controlled variable voltage alternators is extensive.
Holden Commodore range from 2006 VE up, Mazdas - 6, BT50, Nissans - Patrol V8, Navara, Pathfinder, Hyundai Santa fe, Range rover, Landy Disco, Subaru Forester, BMW X5, Pajero, Ford Ranger, etc.
Voltage outputs from these can vary from 15v down to 12.3 and sometimes a complete shut off.

As an aside, provided a chassis connection is made correctly (operative words, clean, tight, and sealed against moisture ingress) you will get far less circuit voltage drop using the chassis as the return path than you will using a dedicated cable.

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Follow Up By: oldtrack123 - Monday, Jan 20, 2014 at 22:23

Monday, Jan 20, 2014 at 22:23
Hi Brian
Thanks for that info on the battery neg to frame
Re'[quote}As an aside, provided a chassis connection is made correctly (operative words, clean, tight, and sealed against moisture ingress) you will get far less circuit voltage drop using the chassis as the return path than you will using a dedicated cable.'[end quote]
Perhaps ONE little point
Do NOT RELY ON the coupling connection for a frame return
Bond the neg terminals of the plug & socket to the ADJACENT frames
[Bright metal surfaces]
Make surethere are NO BOLTED FRAME /chassis joints between THOSE points & the batteries

PeterQ
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Follow Up By: Member - Frank P (NSW) - Tuesday, Jan 21, 2014 at 08:32

Tuesday, Jan 21, 2014 at 08:32
Brian,

Thanks x 2

Cheers
FrankP

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