Home Technical Discussions Volkswagen EuroVan: 1992-2003 (T4)

Volkswagen EuroVan: 1992-2003 (T4) '03 Eurovan Aux Battery


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Last Post: May 17, 2019 3:28 AM Last Post By: RandyBonnette
Gerry

Posts: 2
Registered: 12/09/03
'03 Eurovan Aux Battery
Posted: Aug 7, 2003 12:54 PM
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I heavily upgraded the stock stereo in my new Eurovan. I asked them to run the power off the auxiliary battery under the drivers seat rather than the main battery.

My thought was that if i was running the stereo without the engine on without paying attention I'd drain the auxiliary battery rather than the main battery and still be able to start the car and drive away. Smart? Stupid? Please clue me in.

2 questions 1.) If i run the stereo too long and drain down the aux battery will it then start sucking down the main battery as well? and 2.) if the stereo draws 11 amps an hour, how long can i run it before I find myself either without the aux battery or, worse- stranded without power?
Art

Posts: 2,743
Registered: 09/08/00
Re: '03 Eurovan Aux Battery
Posted: Aug 11, 2003 8:39 AM   in response to: Gerry in response to: Gerry
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Good Morning, Gerry,

I spent a considerable amount of time on Friday researching information on the auxiliary battery system on the EuroVan, but alas, there is essentially nothing available in the service information system except for a wiring diagram.

After studying the wiring diagram (#9), the auxiliary battery system seems to be a simple system with the only other components being the second battery (A1), a battery cut-out relay (J7), and a bit of extra wiring. The aux. battery is completely isolated from the entire system when the engine off. This is accomplished through the open contacts of J7. When the engine is started, J7 is energized through the exciter wiring of the generator and starter solenoid windings. A diode in J7 prevents reverse current flow in the pull-in circuit. So, when the engine is running, the auxiliary battery is paralleled with the regular battery in the charging circuit. When you shut the engine off, the relay opens and disconnects the fully charged aux. battery.

So, the answer to your first question, then, is no; running the stereo with the aux. battery will have absolutely no effect on the the starting of the vehicle even if you run the aux. battery completely flat.

The answer to the second question has only vague solutions based on the limited information available and in fact, generates more questions. Does your stereo draw 11 amps continuously? What is the amp-hour rating of the auxiliary battery? Is the auxiliary battery a standard automotive type or is a deep cycle?

The parts information lists batteries with 44, 60, 70, 80, and 95 amp hour ratings as being used by your EuroVan. You can probably eliminate the three smallest batteries, so assuming a continuous 11 amp draw, you should be able to get around 7 hours or around 8 hours depending on the battery rating.

Deep cycle batteries are designed to be run completely flat and you'll get substantially more time with this type; standard battery types are not and can be damaged if they are.

Your thought to run your stereo from the auxiliary battery seems like a "six of one, half-dozen of another" type of decision. However, if you often play the rig with the engine off, then I'd say you made a good choice. Don't forget that if you run the aux. battery below the security threshold of the radio, you'll have to re-activate the security coding every time. Hope this helps you.

Arthur LeBrun
Bentley Publishers

As a postscript, our Eurovan CD has this wiring diagram and a ton of other useful information. Check it out at:
http://www.bentleypublishers.com/product.htm?code=VET4&subject=20
Ari

Posts: 1
Registered: 08/11/03
Re: '03 Eurovan Aux Battery
Posted: Aug 11, 2003 3:49 PM   in response to: Gerry in response to: Gerry
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Gerry,

I have posted a picture of the wiring diagram that Art makes reference to at this address. Please check it out.

http://www.bentleypublishers.com/tech/vw/vw.eurovan.bat.2003-08-11.htm

Thank you,

Ari
Gerry

Posts: 2
Registered: 12/09/03
Re: '03 Eurovan Aux Battery
Posted: Oct 24, 2003 7:36 PM   in response to: Gerry in response to: Gerry
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Thanks so much for the very useful analysis and pointers on how to dig deeper. I really appreciate your quick response to my post and I apologize for not expressing my appreciation sooner. You guys are the best.

-Gerry
chendermi

Posts: 17
Registered: 12/09/03
Re: '03 Eurovan Aux Battery
Posted: Oct 30, 2003 3:25 PM   in response to: Art in response to: Art
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The auxiliary battery in my '03 Weekender is rated at 60Ah, but doesn't run the underseat refrigerator (rated at 4A continuous) for more than 4-5 hours.

There is a security device in the refrigerator that cuts out the power to the Peltier device and fan when the battery voltage drops below about 11.73V to avoid damage to the battery.

Carl
LAJohn

Posts: 2
Registered: 07/12/05
Re: '03 Eurovan Aux Battery
Posted: Jul 12, 2005 3:12 PM   in response to: Art in response to: Art
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Hi Art,

I noted the discussion about the auxiliary battery and I think my problem sounds like a faulty Battery Cutout Relay. Let me know what you think.
I note that the Relay is supposed to be under the driver's seat but I don't see any sign if it under the seat. Do you know where it is located?

Problem:
I recently put a new auxiliary battery in and it worked fine for a while but a recently when I parked it for a while and then started it up the voltage quickly ran down from about 11 volts to below 10.5 volts at which time the fridge cut out. Once the fridge is turns off the voltage seems to climb again but not above 11.1 volts. The fridge was turned off and the voltage stayed at 11.1 volts. Once I got it home and plugged it into the mains the voltage went up to 12.7 volts.

The other odd thing is that the status screen shows the battery flashing when the voltage is at 11.1v but it's not supposed to flash until it goes down to 10.5 volts.

Thanks for any help.
John Towndrow
LAJohn

Posts: 2
Registered: 07/12/05
Re: '03 Eurovan Aux Battery
Posted: Jul 12, 2005 3:55 PM   in response to: Art in response to: Art
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A follow up to my question. I realize now they mean in the fuse box but there are lots of "Modules" in the fuse box so I wonder if you ahve any idea what number it might be?
Thanks,
John Towndrow
Art

Posts: 2,743
Registered: 09/08/00
Re: '03 Eurovan Aux Battery
Posted: Jul 12, 2005 4:28 PM   in response to: LAJohn in response to: LAJohn
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Good Afternoon, John,

Are you also working with an '03 Eurovan? I must admit that I am not familiar with these specific systems, but there are some things that they all have in common.

If you suspect that the Battery Cutout Relay is bad, simply test it! While you are probably correct in your assessment, wouldn't you rather be sure? Try the following:

Before starting the engine, use a voltmeter and measure the voltage of the vehicle battery. Then measure the voltage of the auxiliary battery. Note the two readings.

Start the engine and repeat the test. If both readings are within about 0.1 V, then the Battery Cutout Relay is OK. If not, then the relay could be bad, or the trigger circuit, or transfer circuit.

For example; with the engine off, say you measure 12.6 Volts on the vehicle battery and 12.4 Volts on the auxiliary. When you start the engine the Voltage at the vehicle battery is no longer battery Voltage, but rather, it is charging system voltage. For the sake of argument, let's say that the reading at the vehicle battery now shows 14.5 Volts. If you measure Voltage at the auxiliary and still get 12.4, it is obvious that the charging system voltage is not getting there, so the relay or some connecting wiring is at fault. If the auxiliary battery reading IS around 14.5 (in this example), then that relay and the related circuitry is OK and the problem lies elsewhere. Perhaps a series draw or a defective battery.

Use a voltmeter as I've described and don't depend on the status panels. I trust my test equipment; even Wal-Mart sells a digital Voltmeter for small money and Harbor Freight practically gives them away every now and again for a buck or two.

I believe that the on-board charging system is a separate circuit and that is why you show 12.7 Volts when connected to the "mains". The voltage climbs with the fridge off due to the battery "recovering" slightly.

By the way, please update your profile to show where you are (Los Angeles, CA?). Your reference to the "mains" sounds UK-ish.

Arthur LeBrun
Bentley Publishers
volksnut

Posts: 80
Registered: 05/24/04
Re: '03 Eurovan Aux Battery
Posted: Jul 20, 2005 1:58 PM   in response to: Gerry in response to: Gerry
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Art,
Recently had alternator go out on my 02 weekender while on vacation and had to run on battery to get to a town w/auto parts store. I assumed the auxilary battery would supplement the primary battery while driving. You mentioned a diode in the charging circuit. Does this prevent the auxilary battery from providing power to the primary system?
Art

Posts: 2,743
Registered: 09/08/00
Re: '03 Eurovan Aux Battery
Posted: Jul 20, 2005 4:10 PM   in response to: volksnut in response to: volksnut
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Good Afternoon,

The Auxiliary Battery (A1) does not get switched into the system unless the relay J7 is energized. J7 receives the signal to switch in the auxiliary battery when there is positive voltage on the blue wire at terminal 85; a signal that is ONLY present if the alternator is charging. No charging, no auxiliary battery in the system.

You could make a manual bypass circuit with another relay so that you could use the coach battery to power the vehicle in an emergency.....

Arthur LeBrun
Bentley Publishers
volksnut

Posts: 80
Registered: 05/24/04
Re: '03 Eurovan Aux Battery
Posted: Jul 20, 2005 4:34 PM   in response to: Art in response to: Art
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Art,
Thanks for the reply. That explains why I was on the side of the road in the Chihuauan desert in west Texas sooner than expected. By the way, Eurovan alternators can't shed the heat generated under full load w/112 deg F ambient temperatures.

Mark
Art

Posts: 2,743
Registered: 09/08/00
Re: '03 Eurovan Aux Battery
Posted: Jul 20, 2005 4:44 PM   in response to: volksnut in response to: volksnut
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Mark,

That's one reason why the industry is moving towards liquid cooled versions.

Art LeBrun
Frog_eugene

Posts: 1
Registered: 09/13/13
Re: '03 Eurovan Aux Battery
Posted: Sep 13, 2013 10:02 AM   in response to: Gerry in response to: Gerry
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Based on the Aux Battery wiring diagram presented for the 03 Eurovan, can I charge another deep cycle battery i use for my canoe as i am driving down the road?
thank you
RandyBonnette

Posts: 1
Registered: 05/17/19
Re: '03 Eurovan Aux Battery
Posted: May 17, 2019 3:27 AM   in response to: Gerry in response to: Gerry
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How to wire an auxiliary battery? Is there any tutorial? Which cables are better? I'm working on an engineering project (my case study - anyway, need to write this and do my essay fast).

Edited by: RandyBonnette on May 17, 2019 3:27 AM

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