Can a second battery be charged via a cigarette lighter socket?

Hi,

I would like to have some extra power available when needed, especially separate from the main electrical system. (The multimedia port hums when I use my laptop as a DVD player and power it with the inverter).

The idea was to have a corrosion-resistant box that would house the battery and a disconnecting relay, allowing the battery to be charged via the socket in the trunk without being connected to the ignition system.

Can this power outlet in the trunk handle the charging current of a conventional car battery?

"Thank you."
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hi,

How is it protected? Usually, a cigarette lighter typically has a fuse of no more than 10 amps. Therefore, I consider it risky to use it without additional measures. It would probably be best to add a charge regulator or build a small electronic circuit for current limiting.

Best regards,

Jan.

Regarding the multimedia port:
Perhaps it would be beneficial to connect the external devices using an isolation transformer.
My multimedia hub is also making a whistling noise.
I haven't looked into it in detail yet.

Best regards.
Maxx.

Hi,

If you only connect the battery via the ignition (relay), it will also participate in the preheating and starting process. This would overload the socket and the wiring.

A large diode in the power line would prevent that; however, it would also reduce the charging voltage to an unacceptable level . Perhaps there are ready-made solutions from the RV world (?)

WoMo World is latching onto the D+ of Lima.
http://www.kerschhofer.net/t3/2batterie.htm

I would also need that information (or guidance).

I've noticed that the 3C already comes with a 2.0 battery, so there must be something original available for it.


Regarding the maternity benefit (MuBu):
Under normal operation, the sound is clean – although it's quite insensitive to radio and CD sources. You really have to crank up the volume. My first test was with my Nokia 6680 using an AD-15 line-out adapter, followed by a laptop.

Only it seems that the laptop is also sending the AC voltage from the inverter to the audio output , causing it to "saw."

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hello Martin,

Powering the auxiliary battery through the cigarette lighter socket will only work well as long as the auxiliary battery is not significantly discharged.

If you connect these batteries directly, a very large equalization current will flow immediately after they are connected due to the significant voltage difference between them. This will likely damage the wiring of the cigarette lighter socket or cause the fuse to blow.

My tried-and-tested suggestion:
'At least 16mm² wiring should be run into the trunk, and a charging circuit should be implemented using a 75A relay connected to terminal 61.'
It works flawlessly in all measurement vehicles with an auxiliary battery, even if those batteries are occasionally completely drained.

(is the camper van wiring).

Best regards, Jochen.

I had suspected that.

I think I'll take a look at how VW solved it with the original second battery. Maybe I've already installed the most important components.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Ach echt, ist der Passat schon in die Stromversorgungsknappheit aufgestiegen das eine zweite Batterie her muss? Wo ist die dann eingebaut? In the trunk?

"Hmm, we probably won't need them in ours. Besides heated seats, there's nothing else that isn't standard equipment... let's see when the body control module (which will probably be a Passat one too?) cuts power to the heated seats."

The 3C is located in the left rear of the trunk.

It's easy to identify: if the compartment on the left isn't as deep as the cargo area, but rather a "platform," then that's it.
Hast du Standheizung, hast du 2. Batt.

The instructions also state that the main battery is located "in the back, with the larger motors."
What about "large" engines with a pre-heating system?
Is my 170 horsepower engine then a "small" one ?


Sure, he has a car network interface that you can wonderfully and extensively program.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

dieselmartin wrote:

So, is my 170 horsepower engine then considered a "small" engine?

Hehe... bought it too small . Well, what can I say? Don't code too much or for too long!

[Assumption]
In the original design, the second battery is directly connected in parallel to increase the overall capacity. A separation is not implemented due to cost-saving measures.
[End of speculation]

"How thick are the wires leading to the rear cigarette lighter socket, and what kind of fuse does it use? The wire resistance can cause a significant voltage drop at these current levels, which means that the actual current flowing may not be as high as expected."

R = specificResistance * length / area, where specificResistance ≈ 0.0175 Ohm*mm²/m.

Hypothetical example: 30A fuse, 1.5mm² wire gauge, 7 meters cable length (plus and minus, so effectively 14 meters) --> R=0.16 ohms. At 30A, this results in a voltage drop of approximately 5V.

"In that case, the fuse would hold even when starting. Just try it out; you're unlikely to damage anything more than the fuse itself. As long as the wires are long and thin, it should work. Although my example is already quite extreme in terms of values."

I suspect that your cigarette lighter adapter might not be able to handle the power draw.

Regards,
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

dieselmartin wrote:

Hi, I would like to have some extra power available when needed, especially separate from the main electrical system. (The multimedia port hums when I use my laptop as a DVD player and power it with the inverter). The idea was to have a corrosion-resistant box that housed the battery and a disconnecting relay, allowing the battery to be charged via the socket in the trunk without being connected to the ignition system. Can this power outlet in the trunk handle the charging current of a conventional car battery? "Thank you." m;

Warum säurefest ? Nimm doch eine Gel-Batterie - was anderes wird im Innenraum AFAIK ab Werk sowieso nicht verbaut. Die Begrenzung des Ladestroms ist zur Not auch mit einem Vorwiderstand zu lösen. Allerdings schauert es mich ohnehin bei dem Gedanken an einen das Bordnetz mit Oberwellen überschwemmenden Wechselrichters. Dass der stört, hast Du ja schon akustisch feststellen können. Un...in a vehicle where, for electromagnetic compatibility (EMC) reasons, not even a mobile phone with an external antenna is allowed to be operated.

You are connecting a switching regulator (inverter) in series with a switch-mode power supply.
I'm surprised that it even works. Why don't you use a universal AC adapter for the laptop?
I can provide you with a cost-effective source for such a device if needed. It is adjustable over a wide range and delivers up to 120W.
And it doesn't interfere with the vehicle's electrical system and remains cool even during continuous operation. Perhaps this makes the entire conversion unnecessary...

@guste100:

Quote:

[Guessing] In the original design, the second battery is directly connected in parallel to increase the overall capacity. A separation is not implemented due to cost-saving measures. [/End of speculation]

Two lead-acid batteries connected in parallel will discharge each other due to equalization currents until they are both empty. Therefore, I actually assume that they should be disconnected.

It's likely that due to the inverters and switching power supply, the vehicle chassis and the laptop chassis have different potentials. Consequently, a balancing current flows through the ground wire of the multimedia port...
I would also recommend using a car power adapter.
If that doesn't satisfy your crafting enthusiasm, you can build your own step-up regulator .

Hello, I installed a second battery in the trunk of my car during my final year of high school due to my auxiliary heater.
It is very important to use a non-sealed battery if it will be located inside the vehicle; otherwise, you could risk being exposed to harmful gases!

The second battery is powered by the positive terminal of the starter battery, and is connected via a relay that is switched by the D+ terminal of the alternator.
The mass is located at the rear of the body.
That is to say, both batteries only operate in parallel and are charged simultaneously when a charging current is actually being generated.

When the ignition is off or the engine has not yet started, the batteries are disconnected.
I installed 10mm² cables as the main supply lines because, as already correctly stated, the problem isn't the charging current itself, but rather the current that flows when both batteries try to equalize their state of charge.

It's been working perfectly for about 8 months now with a 45Ah gel battery in the trunk.


I'm not a fan of using the cigarette lighter to charge the battery; I prefer to remove it instead.

http://www.passatforum.com/forum/viewtopic.php?t=8102&highlight=batterie+laden



You can find good information here about charging technology and disconnecting batteries. However, it works perfectly fine for me with just a single isolating relay.

http://www.microcharge.de/trenndioden.html


Calculating the required capacity is quite simple: multiply the power consumption of the connected devices by the operating time and then factor in a value between 1.3 and 1.8 (depending on the battery type).

Example: 2 hours of auxiliary heating (power consumption 10A) = 20Ah x e.g., a factor of 1.8 = A battery capacity of 36Ah is sufficient.






Sven.