Charging/maintaining the battery via the vehicle's permanent power connection?

Hi.

Thanks to the 13-pin trailer hitch socket and the 15A-fused, 2.5 sq mm permanent power cable, I have the following idea:

If you want to work on a car for an extended period with the ignition on, without further stressing the battery that's already struggling with short trips, you could "feed it power from the back."
It would definitely be practical, as the trekking bike can be locked, it's waterproof, and it's very quick to get ready to ride.

Will the auxiliary battery box explode within a short period of time, or do I need to reduce the voltage/current to a level where it's no longer useful?

I don't want to apply the 14.4 volts that the alternator produces there.
But anything above 12.3 (my current battery's low-voltage threshold) is already being used.

m;

dieselmartin wrote:

Thanks to the 13-pin trailer socket and the 15A-fused 2.5 mm² permanent power cable, I have the following idea: Bitte gib den Text an, den du übersetzt haben möchtest. I don't want to apply the 14.4 volts that the alternator provides there.

Why not? If it's a constant positive voltage, there will also be 14.4V at the trailer hitch connector when the engine is running.

Choose a charger that is small enough to ensure that the fuse remains intact. Otherwise, there is no electrical difference between charging directly from the battery.

Okay, you definitely need to install a blocking diode so that the two batteries don't charge each other. I suspect that the two batteries don't have exactly the same voltage. Unless you ensure that the rear battery always has a higher voltage, and then install the diode... but then the diode will cause a voltage drop of 0.7V. Without electronics, it probably won't work to regulate this.

Sure.

Okay, so the engine is definitely not running during that process.

However, when I try to apply 14.4 volts to the rear, the car (since all control units are active) draws significantly more than 15 amps.
Because everything is powered, and the battery is also being charged.

It's no coincidence that the Lima has a three-digit current rating mentioned on its label.

My "30A" charger isn't even reaching 14 volts, even when connected directly to the battery.

Before anyone asks any clever questions: I have an aftermarket AHK (trailer hitch), so the constant power doesn't go through the AHK control unit (as it would from the factory) but bypasses it. I've connected it directly to terminal 30 with a 15A fuse, located on the left side of the fuse box (A-board), using a standard SC38 fuse holder.

m;

Hello Martin,

With 2.5mm², it won't be much. For a car, it's already 5 meters of cable length, and the caravan usually requires a similar length. So, 10 meters (or more) of 2.5mm² cable, fused at 15A... that's quite daring. I would recommend at least 4mm².

To charge it, you'll need a booster with a blocking diode that further increases the voltage. However, this also results in a higher current being available.
And it's absolutely essential to have a disconnecting relay that shuts off in case of undervoltage, otherwise your CAN bus attacker will be rendered useless .

Hmm?

Everyone seems to misunderstand me.

(1) 15A und 2,5 qmm sind original Westfaliateile, und die werden wiederum als org. VW verkauft. Therefore, these values.

(2) The car is broken, the engine is not working, and all of this happened right here in my driveway.
Behind it, there's a 230V socket, a car battery charger, or alternatively, the 88Ah battery from a T4. There are also some cables lying around.

The reason for this action is that I recently wanted to test the behavior of an engine control unit, which required me to leave the ignition on for a few hours.
The battery is dead. Also, the hood is open, the battery cover is off, I have to somehow place the charger on the engine... it's all too much.

Therefore, the question is, can I simply "plug it in at the back," and what do you think about that?

If someone has already "grilled" their AHK can with this action, that would be a clue for me .

m;

....
Therefore, the question is, can I simply 'plug it in' at the back?


I wouldn't do that with a CAN Bus bomber...

goettmann wrote:

dieselmartin wrote: .... Therefore, the question is, can I simply "plug it in" at the back? Bei einem CAN Bus Bomber würde ich das nicht machen ....

Hello Göttmann,

Could you elaborate on the reasons a bit more, without revealing any confidential information?

Thank you.
m;

"So, the cable/wire with a cross-sectional area of 2.5 sq mm can easily handle 15 amps. I wouldn't worry about that."
The amperage that the AHK socket allows should be specified somewhere, indicating the capacity of the connectors. However, based on my feeling, it's likely around 20A.
If there's no transition resistance, nothing happens (oxidized contacts), because only where there's a voltage drop will there be any heating.
In my opinion, the only solution is to recharge the device using a charger.
But this charger should not have a rated current of 15A.
Since the charger doesn't provide a stabilized, regulated DC voltage, I'll leave it up to you to risk charging a battery with the ignition on. In the past, people used to blow out diodes on the alternator's voltage regulator because of this.
Option 2, connecting the second battery to the rear, is probably not feasible due to excessively high balancing currents. Alternatively, you could use two identical batteries, which is practically impossible.

The idea is sound, and it should work without too much fuss. However, if the current exceeds 15A, the fuse will blow. I don't believe that all control units draw more than 15A with the ignition on, but even when you turn on the ignition, it starts to glow, and you already have an excessive leakage current in the circuit (whether using a battery or a charger). If you only connect it when the ignition is already on, it should work. In that case, you need to pay attention to two things: as mentioned above, the diodes will be damaged if you have a cheap charger that doesn't properly rectify the voltage (from AC to DC). Secondly, no consumers that draw additional current should be turned on.Ventilation, radio, etc.

See you later.

Hi dieselmartin,

1.) Yes, that works.
Depending on the "quality" of your charger, you will eventually damage the battery if you charge it with it, regardless of whether you charge it from the front or the back.
Most "cheap" chargers output up to 28V (use an oscilloscope to measure this, as most standard multimeters won't register it), especially when lightly loaded. This means your battery will be charging at a much higher voltage than intended.
If you have one, use a power supply to "feed" it. Then, set the current limit to 10A and the voltage to 13.8V. You can leave the power supply connected for 1 minute or 1 year without having to worry about anything.

Regards,
Sure, here is the translation of the text from German to English:

"Micha"

Hello Martin,

15A über die AHK Steckdose und 2,5mm² Leitungen sind überhaupt kein Problem. Die AHK Dose und auch 2,5mm² Kabel sind für 25A freigegeben. (siehe http://www.erich-jaeger.de/detail_prod_sub_asv_13p.asp?nid=124&lid=3) Nicht ohne Grund: Kühlschränke im WoWa ziehen auch um 10A über Dauerplus und in den besseren Ausstattungen kommt häufig noch ein ~8A Booster zum Laden der WoWa Batterie verbaut der häufig ebenfalls über die Dauerplus läuft (Ladeplus wird dann nur zum Aktivieren des Boosters verwendet). Somit laufen dann auch dauerhaft knapp 20A über diese Leitung. Das The towing vehicle must therefore be able to handle this continuous load.

If you are using a charger with a current limit of <=25A, you can leave it connected and start the motor. (Or 15A if you don't want to change your fuse.)

Berücksichtige grundsätzlich die Spannungsabfälle: Bei 20A und 5m Dauerplus + 2m Masseleitung fällt an einem 2,5mm² Kabel ziemlich genau 1V ab (0,0178V/(A*mm²*m)). Zuzüglich dem Teil, der bereits auf den Leitungen vom Ladegerät zur AHK-Dose abfällt. D.h. Dein Ladegerät sollte je nach Last also deutlich über der Batterieruhespannung eingestellt sein, wenn du eine Batterieentladung vermeiden möchtest. Ich I would choose 13.8V, if there's anything adjustable. (You're not getting any extra charge anyway.)

Best regards,
Guste.